A 2013-2020 roadmap towards Inertial Fusion Energy based on a 2007-2012 watching brief

Table of content

Executive Summary A. Overall evolution of the IFE Research B. Scientific and technological FP7 highlights 1. Laser developments 2. Alternative ignition schemes a. Shock ignition b. Fast ignition α. Electron-driven fast ignition β. Ion-driven fast ignition c. Impact ignition d. Heavy-ion fusion 3. Laser-plasma interaction 4. IFE-relevant basic science 5. Diagnostics 6. Fusion technologies: from targets to materials and power plant systems a. Targets b. Materials c. IFE technologies: reactor chambers and blankets, safety and radio-protection

d. Consequences of Different Meteorological Scenarios in the Environmental Impact Assessment of Tritium Release

C. FP7 transverse activities 1. Community developments 2. Knowledge diffusion 3. Mobility 4. IFE-MFE synergy D. The IFE roadmap beyond 2013 Mission 1.1 - Acquiring new insights into the basics of ignition physics 1. Atomic Physics 2. Laser-Plasma Interaction 3. Hydrodynamics Mission 1.2 - Demonstrating Shock Ignition on the LMJ Mission 2 - Developing key elements for IFE technologies

1. Laser driver technology 2. Materials 3. IFE technologies: reactor chambers and blankets, safety and radio-protection E. Concluding remarks – Case for continuation of the EURATOM IFE KiT activities and funding

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Executive summary The Consultative Committee for the EURATOM specific research and training programme in the field of Nuclear Energy (CCE-FU) endorsed in 2007 continuation of the keep-in-touch (KiT) activity over civilian research activities in inertial confinement fusion for energy (IFE), as part of the Annual Work Programmes of the involved Associations. To monitor this KiT activity, the CCE-FU set up the Inertial Fusion Energy Working Group (IFEWG) from whom annual Watching Briefs, as well as in-depth proposals, are requested. IFE is currently not mentioned in the “EFDA roadmap to the realization of fusion energy” motivating the drawing up of the present document. The IFE missions that are described in this document fit naturally into the “Training and education” and “Breaking new frontiers – the need for basic research” sub-programmes. They include acquiring new insights into the basics of ignition physics, demonstrating shock ignition (one of the most credible scheme for fusion energy) on the LMJ as well as exploring other alternative approaches, and keeping watch over scientific and technological developments conducted within other international IFE programs, while ensuring synergies with MFE activities (in material research, radiation protection issues, computational developments, for instance) and efficiently strengthening the overall fusion community,. The FP7 EURATOM KiT activities have resulted in a steadily increasing number of collaborations throughout the participating laboratories in Europe and enabled a strong and fruitful research program across national approaches. It has attracted a significant number of PhD students and excellent young researchers who continue to actively contribute to fusion-relevant scientific developments. Based on its expertise, the IFE working group is convinced that it is mandatory that IFE-oriented research be conducted at a trans-national level to be visible and credible as an alternative road towards sustainable and secure energy source.

The following report is first summarizing the work performed under the 7th European Framework Programme from 2007 to 2012 within the EURATOM IFE KiT activities (section B). It takes into account the recommendations issued in January 2010 by the CCE-FU following compulsory adaptation of the fusion programme beyond 2011. It also presents (section D) a European roadmap to the realization of laser fusion energy which completes the EFDA MFE roadmap.

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A. Overall evolution of the IFE Research

Inertial Fusion Energy research is currently enjoying significant developments. The National Ignition Facility (NIF) at LLNL (USA) (figure right) was completed in April 2009. Shortly after its dedication in May 2009, the National Ignition Campaign (NIC) began, conducting shots to first fine-tune the performance of the NIF's lasers (up to 1.85MJ of ultraviolet light), then calibrate the diagnostic equipment (more than 50), and finally implode cryo-layered targets, making steady progress toward achieving indirectly-driven ignition. Ignition-level radiation temperatures, up to 330eV, were reported, shock timing was optimized close to specs but hotspot densities and pressures were kept lower than predicted. 90 % of the predicted implosion velocity was reached but the achieved pressure was insufficient for achieving ignition. Evidence suggested that 3D hydrodynamics is a significant factor affecting performances of current DT implosions through large P4 asymmetry and ablator/fuel mix. The NIC formally ended in September 2012 but the effort to achieve ignition (i.e. α-particle heating of the fuel and burn) on the NIF is further pursued. The proposed strategy is based on (i) focused experiments to improve basic understanding - with the help of improved simulation capabilities - of the complex physics phenomena occurring in a laser-driven implosion (including fundamental physics, i.e. opacities, equations of state, etc) and (ii) integrated implosions to test new understanding, designs and models. A recent review by the National Academy of Sciences strengthens this strategy by concluding that there is no indication that ignition would not be achievable on NIF, that high priority shall continue to be put to target physics programmes on NIF and other facilities and that “so far as target physics is concerned, it is a modest step from NIF scale to IFE scale.” The United States are thus examining the viability of IFE as a clean source of energy and LLNL is developing a Laser Inertial Fusion Energy (LIFE – figure right) baseline design and examining various technology choices for developing a power plant prototype for the next decade. Anticipating a successful demonstration of ignition and gain on NIF and on the Laser MégaJoule (LMJ, which is close to completion, with first light expected end of 2014 – figure right), scientists and engineers from across Europe are developing the case for the next generation laser fusion facility: HiPER (High Power Laser Energy Research Facility). Coordinated by the UK Science and Technology Facilities Council (STFC), the project is a fully-civilian European one, included in the ESFRI Roadmap; it gathers 26 partners from 10 European countries, including almost all the EURATOM IFE keep-in-touch (KiT) partners, with international links to Russia, Japan, South Korea, China and Canada. The HiPER objective is then to address separately (thanks to IFE modularity) all the technological challenges still faced (in terms of target injection, materials, blanket design, heat extraction…) in order to advance on the route to a real laser fusion reactor

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device and, through a “single-facility build” strategy, demonstrate the potential of Laser Energy (including reliability and availability).

After a 2-year conceptual design, the project entered in 2008 a 5-year Preparatory Phase (PP), partly funded by the European Commission, which shaped many aspects of the IFE-relevant research within Europe, and beyond. Numerous studies were conducted to scientifically and technologically support it; they led to reference designs for the laser beam lines, for the target and finally for the facility itself (figure above left), including the fusion chamber (figure above right) and the target injection system. Three operation modes were defined: (i) a burst mode (with bunches of 100 shots including, at max., only 5 DT shots) without any blanket, (ii) a low-power prototype mode and (iii) a full-power reactor demo mode. They led to different chamber designs and allow identifying bottlenecks for a realistic roadmap towards IFE. It has been shown that, to be commercially attractive, (i) the fusion cycle must run at a repetition rate of at least 10 Hz and that a “target gain” (Elaser/Efusion) close to 100 is required, (ii) diode-pumped solid-state laser (DPSSL) technology and alternative ignition schemes may fulfil such requirements. These so-called alternative schemes rely on decoupling direct drive target compression from fuel heating - and thus ignition – using an “external” match, a laser-launched strong shock (for the shock ignition scheme which will be programmatically studied in the following years), or a laser-accelerated ultra-fast particle beam (for the fast ignition scheme which has been extensively studied in the past but still requires validation). It is worth noticing that these scientific studies were financed at the national level or through European initiatives, such as the LASERLAB-Europe I3 and the EURATOM IFE KiT programme, but not on PP funds which were devoted to “integration” activities. Europe is highly advanced in the strongly competitive ICF/IFE research and shall not lose its expertise (evidenced for instance by the highlights reported in section B). The HiPER PP ending on April 2013, and the EURATOM FP7+2 programme at the end of this year, it will now enter a new phase, complying with a shared roadmap (presented in section D) within the Horizon2020 programme, and mainly based on national initiatives. Actually, there will be - for the moment - no research and development program that will integrate the whole range of technologies and sciences required to demonstrate the viability of IFE, which undoubtedly represents a lack of coordination at the European level. B. Scientific and technological FP7 highlights In order to improve the added value of the currently low EURATOM funding, the IFE Working Group has agreed to focus its effort during FP7 (following the 2010 recommendations) on coordinated high-impact energy-relevant topics (fast and shock ignition, laser-plasma interaction, IFE materials, reactor physics and target fabrication processes, reactor pre-designs) whilst maintaining an active keep-in-touch on solid-state or KrF laser technology, Heavy-Ion Fusion, etc. Experimental, as well as theoretical/numerical, tasks have been supported. They contributed to keep a community of

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knowledgeable experts healthy which may be considered as one of the main achievements of the EURATOM IFE KiT programme. 1. Laser developments Allowing IFE to transition from a physics demonstration to viable applications requires establishing a step-change in laser capability, which implies innovation (through a dedicated DPSSL R&D program), but also continuous improvements of the operating facilities. The laboratories participating in this IFE KiT activity operate thirteen laser facilities, open to the IFE community, which constitute the skeleton of the collaboration activities, in addition to specific facilities devoted to material sciences. Due to their moderate laser energy, these facilities are of course only suited to IFE-relevant fundamental physics studies.

Country Association & laboratories (if any) Facilities

Czech Republic IPP.CR PALS

France CEA LULI, CELIA, CPhT, IRAMIS and LPGP

LULI2000 & ELFIE UHI100

Germany IPP GSI Darmstadt MPQ Garching

PHELIX LWS & ATLAS

United Kingdom UKAEA STFC/RAL/CLF VULCAN Hungary HAS Wigner Research Center for Physics (WRC) KrF laser Italy ENEA 1 ABC Poland IPPLM 10TW Ti:sapph. laser Portugal IPFN/IST L2I Spain CIEMAT DENIM, GIFI CLPU, HIPIMS

The whole continuum of inertial fusion drivers is encompassed, from the “nominal” nanosecond-picosecond Nd-glass lasers to “alternative” KrF lasers or heavy ion (HI) beams. Ti:sapphire lasers are also accessible for studies devoted to optimization of ultra-short radiation and particle secondary sources. These “small” human-scale facilities are continuously upgraded to improve access to users, train students and ensure competitiveness, thanks in particular to a great versatility. A summary of the laser developments performed since 2007, and mainly funded on a national basis, is listed below: • completion of the LULI2000 facility with (i) commissioning

of the pico2000 laser beam line - to allow combining on target high-energy (1kJ / 1ns) and high-power (up to 200J / 1ps) laser pulses – and of its experimental radio-protected environment, (ii) implementation of the first 100J / 1ns auxiliary laser beam, (iv) completion of a second experimental area (figure right) and (v) development of a new ns all-fiber diode-pumped Nd:YLF front-end with improved pulse shaping capabilities;

• upgrade of the ELFIE facility with up to 200J in 4 fully-synchronized beams (including 2 at the 100TW/0.3ps level);

1 University of Roma, CNR-INO, University of Pisa and University of Milano Bicocca

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• production – in collaboration with the Laserayin Tekhnika Armenian company – of YAG crystals with tailored gradients of Yb dopant; 1st “10J” milestone reached for the LUCIA active mirror DPSSL, with 14J delivered at 2Hz (figure right); development of a 2nd cryogenic amplifying stage based on an innovative, patented, cooling architecture 2;

• completion of a major upgrade of the VULCAN Target Area West (figure below, left) to allow the facility delivering 6 long pulse beams (for implosion) and 2 short pulse CPA beams (for heating and probing) to address a wide range of studies where the interaction of short pulses with compressed, heated plasmas is required with flexible short pulse probing capability;

• completion of the 1st phase (front-end) of the 10PW OPCPA VULCAN laser upgrade, of direct

relevance for fast ignition whilst offering a basic science capability of very broad applicability; • development of a new technology platform, called DiPOLE (figure above right), for pioneering

and exciting new applications of DPSSL technology; • construction of table-top laser systems at MPQ, delivering extremely short (few-cycle phase-

stabilized) pulses and high intensities on target (LWS-20 180mJ/4fs as well as DPSSL-based and PFS 2J/5fs) for single attosecond pulse radiation production and relativistic laser particle acceleration for the generation of brilliant radiation to probe IFE-relevant dense plasmas;

• upgrade of the ATLAS laser (currently ~1.5 J / ~25fs) to ~6J and ultimately to 3PW (thus approaching 1023 W/cm2) to become the major IFE facility in Garching;

• completion of the PHELIX facility with the possibility to combine - on target - ns and ps laser pulses as well as ion beams; development of a diode-pumped ultra-fast OPA front-end in collaboration with GoLP and the Friedrich Schiller University (Jena, Germany) that allows boosting the temporal contrast of the PHELIX short-pulse front-end (figure below); upgrade of the target area to allow intensities above 1021 W/cm2;

• increase of energy of the L2I Yb-doped diode-pumped regenerative amplifier from the mJ level

to 100 mJ; installation of a permanent suite of diagnostics to monitor the TW output beam in terms of energy, wavefront and spatial and temporal profiles; implementation of a novel patented deformable mirror to reach intensities close to 1019 W/cm2; start of a R&D program on diode-pumped ultra-broadband OPCPA;

• completion of the Czech TW-class nanosecond iodine laser by a synchronized Ti:Sapph. femtosecond laser designed for pump-probe interaction experiments and fast plasma probing;

2 M. Arzakantsyan et al., J . Crystal Growth 329, 39 (2011) & Opt. Mat. Express 2, 20 (2012) ; T. Goçalvès-Novo et al., Opt. Express 21, 855 (2013)

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• increase of energy of the Hungarian short-pulse KrF laser from 15 to 60mJ, either in a single shot regime or at 1Hz, with improvements of the beam quality and of the contrast for intensities above 1018W/cm2 in 620fs; implementation of a pulse cleaning technique using a plasma mirror 3.

In parallel, work is ongoing at ENEA (optimization of the diode assembly and of the cooling system, spectral and spatial characterization of the diode emission at 800nm) and at IST (development of a numerical code to simulate Yb-doped amplifiers at 1053nm, experimental characterization of Yb:KYW and Yb:CaF2 gain media, study of super-continuum generation to create an ultra-broadband optical source, investigation of the high-energy diode-pumped optical parametric amplification scheme) and contributes to the European technological effort to demonstrate the feasibility of an efficient multi-kJ DPSSL. Clear benefits in different fields (not only IFE) and return on investments could be expected. Major upgrades of ICF-relevant facilities were also achieved worldwide. They mostly aim at adding kJ/ps PW capabilities to kJ/ns ones [for instance OMEGA-EP at LLE, USA, FIREX-I at ILE, Japan, PETAL on LMJ, France, ORION in UK] to investigate the IFE-relevant fast ignition scheme or benefit from the potentialities of such ultra-short energetic laser pulses in terms of plasma diagnostics. High-energy PW beam lines are also appearing at Chinese (SG-III) and Russian (LUCH) facilities. 2. Alternative ignition schemes Progress in the understanding of alternative ignition schemes is playing an important role for reducing driver energy and efficiency requirements, with the specific aim of Laser Energy, as they should lead to high gains and to simple target designs (especially for shock ignition). a. Shock Ignition Nominal central hot spot ignition requires high implosion velocities (350 - 400 km/s) and thus is prone to hydrodynamic instabilities; furthermore, the target must be driven on high adiabats and non-optimal hydrodynamic efficiencies. The shock ignition scheme (SI) has been recently proposed to overcome these difficulties; it relies on decoupling target compression from ignition by launching in a nominally imploded target a strong convergent shock (produced by means of an intense - ~1016W/cm2 - laser pulse, or spike) precisely timed to reach fuel at stagnation. Ignition is then obtained with lower implosion velocities (240-300km/s), thus reducing risks of shell break-up during acceleration and allowing compression of larger masses for the same laser energy, thus achieving high target gains, of strong interest for Inertial Fusion Energy. However, due to the high intensity of spike, the SI scheme is prone to parametric instabilities. Detailed studies – both numerical and experimental – are required to assess its viability. A series of numerical simulations were first performed at CELIA with the help of the CHIC code (and at the University of Roma La Sapienza with the DUED code) to demonstrate the attractiveness of the scheme in terms of performances (gain, ignition threshold, …) and robustness (for instance in terms of delivery time for the ignition shock) 4. Susceptibility to the Rayleigh-Taylor instability (RTI) was also studied 5. Two planar experiments were then conducted on LULI2000 and at PALS to answer the two key questions of the SI physics: (i) is it possible to launch a high pressure shock through a large coronal plasma? and (ii) are the parametric instabilities efficient enough to backscatter a large amount of

3 I.B. Földes et al., J. Phys. Conf. Ser. 244, 032004 (2010) 4 M. Lafon et al., Phys. Plasmas 20, 022708 (2013); S. Atzeni et al., New J. Phys. 15, 045004 (2013) 5 X. Ribeyre et al., Plasma Phys. Control. Fusion 51, 015013 & 124030 (2009); S. Atzeni et al., Plasma Phys. Control. Fusion 53, 035010 (2011)

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incident laser light and produce a hot electron population? The basic idea was to create - with the help of a “compression” pulse at moderate intensity (1013-1014 W/cm2) - a long-scale hot plasma into which is focused an intense pulse (at intensity up to a few 1015 W/cm2) to mimic the spike.

VISAR and SOP images (figure above left) clearly showed on the LULI2000 experiment the coalescence of the strong shock launched by the latter pulse with the shock due to the initial ablation process. A good agreement between these observations and 2D hydro-simulations was found. Low backscattering level (no more than 15% in the focalization cone) was additionally measured (figure above right). Similarly, the backscattered energy in the PALS experiment was found to be in the range of 3 to 15%, mainly due to 438nm light, increasing with the delay between the two laser beams. In addition, fast electrons below 50 keV were measured; they were found to contribute to less than 1% of the laser energy. The values of peak shock pressures inferred from shock breakout times were somewhat lower than expected from 2D numerical simulations. These simulations also revealed that 2D effects play a major role in these experiments for which the laser spot size was comparable to the distance between the critical and ablation layers. Laser-plasma interaction simulations were, in parallel, performed in collaboration with the Czech Technical University in Prague and CELIA 6. The parameters for the laser pulse and the plasma conditions were derived from an experimental campaign conducted on the OMEGA laser in June 2010. The computed absorption features were found in agreement with the observations and it was found that the ratio between the energy of the fast electrons, produced by the two-plasmon-decay instability, and the shell areal density is the key parameter affecting the neutron production. A second series of experiments was thus conducted on OMEGA by researchers from various laboratories, including CELIA 7. It used a novel beam configuration (figure right – illumination pattern in 1015W/cm2), with 40 spherically-arranged repointed beams (top) to compress a 430µm-outer-radius plastic-shell target (with an irradiation uniformity as good as 3%) and 20 beams arranged according to a dodecahedron illumination geometry (bottom) to launch the spike (figure right). No significant dependence of the neutron yield on the spike onset time was observed either in the experiments or in 1D CHIC simulations (figure below right) while the areal density was shown to vary (with observation direction) similarly in the experiments and in 2D CHIC simulations at stagnation. A low hot-electron temperature was measured during the experiment, independently of the spike intensity and onset time. At the highest intensity, the two-plasmon decay instability was suppressed and hot-electron production was dominated by stimulated Raman scattering. A laser energy backscattering of up to 36% was measured on a laser shot at 8 1015 W/cm2 but the hot electron temperature was kept relatively low (~30 keV) and a good coupling of spike energy into the imploding capsule was observed, which is encouraging for the shock ignition scheme.

6 O. Klimo et al., Plasma Phys. Control. Fusion 52, 055013 (2010) & Phys. Plasmas 18, 082709 (2011) ; S. Weber et al., Phys. Rev. E 85, 016403 (2012)

7 W. Theobald et al., Phys. Plasmas 19, 102706 (2012)

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b. Fast Ignition α. Electron-driven fast ignition As for the SI scheme, fast ignition (FI) relies on decoupling fuel compression to hot spot heating (and thus ignition). The spark is however in that case quite different. The current electron-driven FI design relies on production of an energetic electron beam by interaction of a high-energy multi-PW (~70 kJ / 10-20 ps) laser pulse with the tip of a re-entrant double gold cone (used to keep a path free of plasma and allow efficient particle generation and guiding close to the compressed core). The FI physics was in fact a rather unexplored area at the beginning of FP7. The scheme was thus widely studied as one of the targeted IFE KiT topics and several issues were rapidly identified. Among them, electron transport in a solid and in a cold and dense (pre-compressed) plasma received particular attention, the divergence of the electron beam being identified as a key parameter in minimizing the required laser energy. Dedicated experiments were then conducted on the LULI and CLF laser facilities thanks to the availability of the unique coupling of high-energy ns and ps pulses and of innovative time-resolved diagnostics techniques. A study of the laser-to-electrons energy conversion efficiency has for instance been undertaken by a LULI-CELIA-RAL-GoLP consortium, in collaboration with Italian researchers, on LULI2000 at FI-relevant intensities; a reduction in the electron beam spread, which could be associated with a decrease in the divergence, was clearly observed when the plasma gradients steepened 8. Electron energy losses over a rather inhomogeneous propagation volume (from the critical density - nc - where laser absorption is maximal to the compressed fuel - at ~50nc) should also be accurately predicted in order to properly design the nominal FI target.

Experiments were performed on LULI2000 and on Titan (LLNL, US) to characterize fast electron stopping power in shock-compressed aluminum, in under-scaled FI experimental conditions, and benchmark transport models thanks to discrimination of resistive and collisional effects for high electron current densities (above ~1011 A/cm2 – figure left) 9. Controlling the divergence of the electron beam thanks to magnetic fields generated at resistivity interfaces was proposed 10 and experimentally confirmed at RAL, first in one dimension

(using a planar “sandwich” target) 11 and then in two dimensions (using a core/cladding cylindrical structure). In that last configuration, the electron beam was observed to be restricted to ~60µm FWHM, which opens the design space for FI 12. Other methods to control the divergence of MeV fast electrons entering a target were also proposed and confirmed experimentally: use of a dual laser pulse 13, etc.

8 P.A. Norreys et al., Plasma Phys. Control. Fusion 52, 124046 (2010) 9 B. Vauzour et al., Phys. Rev. Lett. 109, 255002 (2012) 10 A.P.L. Robinson et al., Phys. Rev. Lett. 100, 01503 (2008) 11 S. Kar et al., Phys. Rev. Lett. 102, 055001 (2009) 12 B. Ramakrishna et al., Phys. Rev. Lett. 105, 135001 (2010) 13 A.P.L. Robinson et al., Phys. Rev. Lett. 100, 025002 (2008); R.H.H. Scott et al., Phys. Rev. Lett. 109, 015001 (2012)

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Other issues that were identified are directly linked to the use of cone-in-shell targets. • Recent experiments showed that a sizeable underdense plasma may be created in the cone by an

intense prepulse, or ASE pedestal, which leads to a significant reduction of the laser-to-electrons conversion efficiency, as probably observed in recent integrated experiments at LFEX - ILE, Osaka Japan - and OMEGA - LLE, Rochester USA.

• The cone-in-shell target geometry prevents from symmetrical laser compression, as required in high gain designs, and may lead to plasma jet propagating along the cone axis.

• The re-entrant cone may not survive the high pressure put on the cone wall during the compression phase.

A series of experiments was proposed on LULI2000 to systematically study such shock-driven cone perturbations. After characterization of the shock collision/sliding along the cone walls and breakout inside the cone, fast electron generation and transport in shock-perturbed cone-embedded targets were studied. Analysis is ongoing. Other ideas to transport the FI ultra-intense laser light directly through the surrounding plasma to the compressed core were also considered: channel boring at RAL 14 or super-penetration. They both exploit a combination of several nonlinear processes to achieve laser penetration above the critical density: relativistic self-focusing, relativistic transparency and hole boring. An experiment, conducted on LULI2000 in collaboration with CEA, the Graduate School of Engineering (Osaka, Japan) and the Universities of St Andrews (UK) and Roma Tor Vergata (Italy), aimed at studying laser penetration in well-characterized slightly over-critical (1- 2×1021 cm-3) plasmas with steep density gradients, thanks to a novel target design (figure right). In parallel with these above-mentioned “integrated” experiments, generation of quasi-monoenergetic electron beams with energies in the 100MeV range (suitable for FI) was studied at MPQ on ATLAS and the electron bunch parameters stabilized thanks to a new “shock front injection” technique 15. Improvements in terms of divergence and pointing stability were observed with wave guiding in capillaries at MPQ and in a simmer discharge at GoLP. For the first time, laser-plasma interaction experiments approach maturity and accuracy to challenge the predictability and reliability of PIC numerical simulations. A series of hybrid PIC simulations of fast electron transport and energy deposition in pre-compressed fusion targets were performed by the GIFI and MPQ groups, assuming “ideal” initial fast electron distribution and taking full account of collective magnetic effects and the hydrodynamic response of the background plasma 16. It was shown that self-generated magnetic fields substantially improve electron beam collimation (as suggested by the above-mentioned experiments). But, for more realistic electron distributions (as given by 2D PIC simulations), this collimation is attenuated and the required ignition energy increased 17. The influence on the FI laser requirements of the fast electron stopping and scattering modeling was also clarified and a new realistic Monte-Carlo energy deposition routine implemented in the DUED code 18.

14 G. Sarri et al., Phys. Plasmas 17, 113303 (2010) 15 A. Buck et al., Phys. Rev. Lett. 110, 185006 (2013) 16 J. Honrubia and J. Meyer-ter-Vehn, Plasma Phys. Control. Fusion 51, 014008 (2009) 17 A. Debayle et al., Plasma Phys. Control. Fusion 52, 124024 (2010) 18 S. Atzeni, A. Schiavi and J. Davies, Plasma Phys. Control. Fusion 51, 015016 (2009)

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Laser channeling and fast electron generation were numerically studied at GoLP with the help of the OSIRIS code; a novel hybrid algorithm was implemented and allowed for the first time full-scale ab initio simulations of the FI scenario 19. Experiments have been conducted at RAL to investigate this physics. Hole boring was also investigated at CELIA 20. The DENIM ARWEN rad-hydro-code capabilities were enhanced using newly developed routines: laser ray-tracing, multi-group radiation transport, time-dependent ionization, multi-materials, non-LTE radiation physics, etc. It was successfully used to analyze cone preheating in Japanese FI experiments, an important issue that could be partly solved with CH coating: a half-sphere target was thus designed. The use of ultra-short (1ps) KrF lasers for FI was also investigated at WRC as the shorter laser wavelength holds promise for lower electron energies and better coupling to the dense core, without re-entrant cone 21. Finally, a scheme based on ultra-relativistic electrons (above 140 MeV) to drive FI was proposed. It allows pion-catalyzed DT fusion, assuming that negative π- pions could be in situ produced through electro-disintegration reactions and that πDT molecules could be formed. Calculations of the π-

stopping power in a binary ionic mixture in FI-relevant conditions were then performed 22. β. Ion-driven fast ignition Laser-driven ion beams (more especially protons and carbon ions) were considered as an alternative for fast ignition 23. Experiments dedicated to optimization of their production mechanism and then of the laser-to-ion energy conversion efficiency were conducted on various facilities:

• at LULI, proton beams of MA currents and TA/cm2 current densities were produced at

interaction conditions approaching the skin-layer ponderomotive acceleration requirements studied at IPPLM 24;

• the influence on proton acceleration of the laser parameters (wavelength, energy, duration), target thickness and pre-plasma density scale length was also numerically investigated by IPPLM 25: it was shown that shortening the laser wavelength leads to a prevalence of the ponderomotive acceleration mechanism and, at a fixed Iλ2 ~(0.5-1)x1020 Wcm-2µm2, to an increase of the ion energy and current density; the use of multi-ps circularly polarized laser pulses was also examined 26;

• mass-limited targets (ultra-thin - nm - diamond-like carbon foils) were studied at MPQ (and subsequently on TRIDENT at LANL, USA) and their efficiency in terms of proton generation - for the first time through the radiation pressure mechanism – confirmed 27, followed by demonstration of particle energy, conversion efficiency and spectral shape required for ion-based fast ignition 28;

• acceleration of 1.5 1013 protons with an exponentially decaying energy spectrum up to 30MeV was achieved on PHELIX with only 170TW;

19 F. Fiuza et al., Plasma Phys.Control. Fusion 53, 074004 (2011) 20 V. Mironov et al., Plasma Phys.Control. Fusion 54, 095008 (2012) 21 I.B. Földes and S. Szatmári, Laser Part. Beams 26, 575 (2008) 22 P. Fromy et al., EPL 92, 15002 (2010) ; Cl. Deutsch and P. Fromy, J. Plasma Phys. online (12/02/2013) 23 M. Roth et al., Phys. Rev. Lett. 86, 436 (2001) 24 J. Badziak et al., Laser Part. Beams 28, 575 (2010) 25 J. Badziak and S. Jabłoński, Phys. Plasmas 17, 073106 (2010) 26 J. Badziak et al., Phys. Plasmas 18, 053108 (2011) 27 A. Henig et al., Phys. Rev. Lett. 102, 095002 (2009) ; A. Henig et al., Phys. Rev. Lett. 103, 245003 (2009) 28 B.M. Hegelich et al., Nucl. Fusion 51, 083011 (2011)

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• the Fast Ion Generation Experiment, conducted by ENEA at RAL, and theoretical modeling allowed proving that efficient generation of well-collimated high-energy (20÷150MeV/nucleon) ions could be achieved 29.

The minimum ignition energies for ion-driven FI were finally determined by a GSI-CELIA collaboration, thanks to 2D hydro-simulations: more than 100kJ appears to be required to ignite a pre-compressed DT pellet, of the same order of magnitude as for the electron-driven FI scheme 30. Further studies of cone-guided carbon-driven FI offer higher efficiency 31.

Recently achieved high intensity laser pulses open new prospects in their application to hole boring in inhomogeneous overdense plasmas and to ion-driven FI. An analytical model and numerical simulations demonstrate that pulses with intensities exceeding 1022W/cm2 may penetrate deeply into the plasma as a result of efficient ponderomotive ion acceleration in the forward direction. The penetration depth ~ 100-200μm can be achieved for laser fluences exceeding a few tens of GJ/cm2. The fast ions, accelerated at the bottom of the channel with an efficiency of more than 20%, show a high directionality and may heat the pre-compressed target core to fusion conditions. This work was done in collaboration between French groups and GSI 32. c. Impact Ignition The impact ignition scheme aims at impacting an accelerated high-velocity macroparticle onto a highly compressed DT target. A crucial milestone is then to demonstrate impact-compressed densities of ~100 g/cm3 in addition to high implosion velocities of ~108 cm/s. Several advanced cavity pressure acceleration (CPA) schemes proposed by IPPLM were validated at PALS: the Reversed Acceleration Scheme (RAS – figure a) below) and the Laser-Induced Cavity Pressure Acceleration (LICPA – figure b) below). They both proved to efficiently accelerate macro-particles to very high energies for moderate incident laser energies (of the order of hundreds of Joules) 33.

The alternative concept of jet impact ignition was numerically studied at DENIM 34 with the help of 2D and 3D rad-hydro-simulations while jet experiments were conducted at PALS in collaboration with IPPLM. Laser generation of highly supersonic plasma jets on different high-Z targets (to study radiation cooling) was for instance systematically investigated at the PALS facility, in collaboration with CELIA, as well as their transport through a low-density low-Z plasma and their mutual interaction 35. The use of conical (figure below middle) or cylindrical channels (figure below left) was

29 C. Strangio et al., Laser Part. Beams 25, 85 (2007) 30 J. Honrubia et al., Phys. Plasmas 16, 102701 (2009) 31 C. Regan et al., Plasma Phys. Control. Fusion 53, 045014 (2011) 32 N. Naumova et al., Phys. Rev. Lett. 102, 025002 (2009) 33 S. Borodziuk et al., Appl. Phys. Lett. 93, 101502 (2008); J. Badziak et al., Appl. Phys. Lett. 96, 251502 (2010) 34 P. Velarde et al., J. Phys.: Conf. Ser. 112, 042010 (2008) 35 Ph. Nicolaï et al., Phys. Plasmas 15, 082701 (2008) ; A. Kasperczuk et al., Phys. Plasmas 17, 1 (2010)

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also proposed for efficient jet guiding and collimation. Finally, a combination of a conical target and the CPA technique (figure below right) allowed reaching jet velocities above 107 cm/s.

d. Heavy Ion Fusion HIF is not directly studied within the EURATOM IFE KiT programme but related studies (as ion stopping power studies) allow keeping expertise. Such motivation justifies involvement of the LPGP and GSI teams in the HEDgeHOB international collaboration. 2D hydrodynamic simulations of the implosion of some LAPLAS targets were performed; they indicated that the LAPLAS scheme should be rather robust against the Richtmyer-Meshkov instabilities and that a high-energy-density regime could be reached, opening the possibility to create yet unexplored states, such as, for instance for water, the very interesting superionic phase 36. Modeling of generation and propagation of thermal shock waves launched in solid matter by the Super Proton Synchrotron was also carried out; simulations showed that a W target is severely damaged and that the target material, in the beam–heated region, is converted into a strongly coupled (non-ideal) plasma 37. 3. Laser-plasma interaction In the context of laser interaction with under-dense fusion-relevant plasmas, the understanding of the mechanisms responsible for the nonlinear saturation of parametric instabilities - especially the three scattering instabilities: “stimulated Raman scattering” (SRS), “stimulated Brillouin scattering” (SBS) and filamentation - is an important goal. These instabilities involve excitation of longitudinal plasma waves, the electron plasma (or Langmuir) waves - for SRS - and the ion acoustic waves - for SBS -, which can be easily excited to high amplitudes, up to nonlinear saturation, at laser and plasma parameters corresponding to fusion-relevant conditions. In recent ‘ignition’ experimental campaigns conducted on the US National Ignition Facility, SRS was identified as one of the main mechanisms responsible for rather poor (at least insufficient) laser-plasma coupling, unexplained and unexpectedly high (up to 50%) backscatter levels being observed. The filamentation instability has been observed in large scale-length plasma experiments at RAL when the intensity on target is above 1014 Wcm-2µm2. Methods to mitigate its growth include focusing the SI pulses at the original target surface and using channeling to the critical density surface to prevent beam break-up. These require experimental verification 38. While SRS growth is usually spatially limited in inhomogeneous plasmas (as the one encountered close to the hohlraum walls in the indirect drive laser fusion scheme) by phase detuning of the required 3-wave resonance, kinetic effects due to trapped particles in plasma waves can compensate such a dephasing and eventually lead to much higher scattering levels than expected, thus motivating sustained understanding efforts. The criteria for the onset of these effects were worked

36 N.A. Tahir et al., New J. Phys. 12, 073022 (2010) 37 N.A. Tahir et al., Phys. Plasmas 16, 082703 (2009) 38 E. Higson et al., New J. Phys. 15, 015027 (2013)

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out with the help of only two key parameters: the laser intensity and the plasma mode wavelength. The scenario of “auto-resonance” was also carefully studied thanks to 1D and 2D PIC simulations with the CPhT EMI code 39. A new statistical model for forward SBS of spatially incoherent monochromatic laser beams propagating in plasma has been developed by French groups. A threshold for the average speckle power, well below the self-focusing one, has been found in agreement with recent experimental data. The origin of the low SBS reflectivity, observed in LULI experiments carried out with a mono-speckle laser beam, was explained by SBS inhibition due to strong self-focusing and resonant filament instability. It demonstrated the important progress achieved in the last few years and the current code capacity to simulate mm-size plasma volumes. An experiment was designed and performed on the LIL facility 40 to study the propagation of a high-intensity laser beam in a hot 1D mm-long under-dense plasma, observe modifications of its coherence properties and measure their consequences. Irradiation of low-density Cl-doped foam cylinders allowed demonstrating supersonic propagation of an ionization wave through the underdense medium, modification of the laser beam spatial coherence, imprint reduction and SBS reduction, in accordance with Harmony2D simulations. Two continuation campaigns on the GEKKOXII laser facility (Osaka, Japan) were then conducted in 2011 and 2012; they provided some indications of instability inhibition and on the effect of the foam structure on the laser propagation (namely the slowdown of the ionization process due to porosity) which required a new module of the CHIC code to be developed 41. It is important to underline that parametric instabilities are still important issues for achieving ignition on NIF as they induce energy transfer between laser beams and thus symmetry loss. Effort towards a better understanding of their intrinsic nature shall be pursued. 4. IFE-relevant basic science The hydrodynamic simulations of the Inertial Confinement Fusion targets require very accurate basic data, i.e. equations of state (EOS), radiative transfer (opacities, emissivities) and transport coefficients. Theoretical models providing these data have still to be improved (especially at high density, close to the solid density) and validated (mainly in the XUV and X-ray range) thanks to well-diagnosed radiatively-driven (to reach plasma conditions close to Local Thermodynamic Equilibrium - LTE) absorption spectroscopy experiments. A set of numerical codes (ABAKO/RAPCAL) was developed by DENIM 42 to reproduce population kinetics and detailed radiative properties of low-Z plasmas; it was modified to take into account mixtures, external radiation fields and non-Maxwellian free electron distributions. Thanks to inclusion of adequately selected configurations, the SCRIC code was in parallel used to compute higher-Z (Fe, Ge, Mo and Xe) emission spectra. Finally, he relativistic screened hydrogenic model in the ATMED code was improved to be able to compute optical and thermodynamic properties of plasmas in both LTE and non-LTE regimes. A new variational code (VAAQP) was also developed at CEA/IRAMIS to solve the problem of atoms

39 Th. Chapman et al., Phys. Plasmas 17, 122317 (2010) & Phys. Rev. Lett. 108, 145003 (2012) 40 S. Depierreux et al., Phys. Rev. Lett. 102, 195005 (2009) 41 Ph. Nicolaï et al., Phys. Plasmas 19, N11 (2012) 42 R. Florido et al., J. Phys.: Conf. Ser. 112, 042008 (2008) ; R. Rodriguez et al., Commun. Comput. Phys. 8, 185 (2010)

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immersed in a quantum plasma 43. It allows ab initio calculations of the free electron density, the equation of state of mid-Z warm plasmas as well as their opacities and conductivities. From the experimental point of view, opacity measurements at close-to-LTE conditions (i.e. in radiatively-heated matter) were conducted on LULI2000 in collaboration with MPQ 44. Various atomic physics and thermodynamical aspects were investigated for mid-Z pure or mixed elements: thermal (configurational) broadening of 2p-3d and 3d-4f transition structures, spin-orbit splitting, etc 45. Different theoretical approaches (detailed configuration accounting, configuration averaging, average atom, …) were then compared. A novel double hohlraum design (consisting in two cavities - each of them being irradiated by one kJ ns laser - placed on both sides of the sample to ensure better symmetry of its radiative heating and planar expansion) was validated. Combined with the use of a short duration radiography source, temporal and spatial variations of the sample temperature and density are dramatically reduced, which allows fruitful comparisons between codes, from fully detailed (FAC or HULLAC) to statistical (SCO). A hybrid approach (SCORCG) has been developed by CEA/IRAMIS to account for relativistic configuration interaction through detailed calculation of some well-chosen levels. Understanding the early stages of inertial fusion also requires a good knowledge of the Warm Dense Matter (WDM) state; experimental evidences have to be collected to validate underlying hypothesis and models currently used in simulations. Laser-accelerated particle (especially proton) sources can be used to isochorically heat a solid target and thus produce WDM. A first demonstration experiment was carried out at LULI in collaboration with researchers from Italy and Serbia; various diagnostic techniques (TASRI, proton deflectometry, x-ray absorption spectroscopy and XANES) 46 helped constraining hydro-simulations and then characterizing the produced medium. It opened the route towards accurate measurements of ion stopping powers in plasmas and validation of numerical tools (using, for instance, a variational Hermite-Gaussian Wave Packet Molecular Dynamics approach) developed at LPGP. In parallel, exploiting the unique combination of laser and heavy-ion beams, experiments on swift ion energy deposition in hot fully-ionized plasmas have been conducted at GSI. Experiments on ion energy loss in indirectly-driven plasmas have achieved first results. A 3.6 MeV/u Ca17+ beam from the UNILAC was found to yield an approximately 70% higher energy loss in a 1022 cm-3 / 15 eV plasma generated by a laser beam impinging on the interior of a hohlraum (see figure below).

A study of laser absorption in porous materials was conducted by ENEA in collaboration with the

43 R. Piron and T. Blenski, Phys. Rev. E 83, 026403 (2011) & HEDP 7, 346 (2011) 44 C. Reverdin et al., Rev. Sci. Instrum. 83, 10E134 (2012) 45 T. Blenski et al., Phys. Rev. E 84, 036407 (2011) & HEDP 7, 320 (2011) 46 A. Mančić et al., Rev. Sci. Intrum. 79, 073301 (2008) ; A. Mančić et al., HEDP 6, 21 (2010) ; A. Mančić et al., Phys. Rev. Lett. 104, 035002

(2010)

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Lebedev Institute. Efficiency of energy transmission of the ABC laser beam in polystyrene foams was determined. Finally, an experimental programme aiming at determining fusion cross-sections was launched on ABC. Measurement of the laser-accelerated proton energy distribution function and of the α particle emission will allow p-B11 reaction rates to be evaluated. 5. Diagnostics Fusion-relevant plasmas, proven to be opaque to visible light, are then rather difficult to characterize in situ. One of the possibilities to gain access to the hydrodynamic parameters (i.e. to the “density-temperature” couple) is to probe them at shorter wavelength (below a few hundreds of nm). Therefore, one of the IFE KiT tasks is devoted to the development of appropriate secondary radiation sources. A new experimental set up for high-order harmonics generation (HHG) from argon pulsed gas jet was designed, implemented and successfully operated at CEA/IRAMIS. It was used to probe a metallic plasma and assess the temporal evolution of its density and temperature from its XUV reflectivity. For a probed medium in the plasma state, the experimental data were successfully reproduced, but, at close-to-solid density, the model failed to correctly handle the solid-plasma transition. IST has initiated a programme to use HHG as an above-critical density probe for warm dense plasmas. Refraction by thin plasma slabs is measured with a wavefront sensor. A campaign to probe solid density plasmas produced by the LCLS, an US x-ray free electron laser, and measure opacity in the 40-70 eV region has begun. Extension of HHG to harder x-rays would enable probing macroscopic plasmas. Solid density plasmas were employed to demonstrate substantially increased efficiency in the XUV range at MPQ, RAL and CEA/IRAMIS, in collaboration with WRC 47 et al, at very high laser contrasts. HHG with laser pulses as short as 8fs was successfully demonstrated as well as focusing down to the diffraction limit (to intensities higher than the incident laser intensity) 48 and mutual coherence of several harmonic sources. Two production mechanisms (the Coherent Wake Emission for low-order harmonics, and the Relativistic Oscillating Mirror, for the high-energy harmonics) were identified and the role of the CEP phase variation identified. Effect of the target roughness on HHG was assessed and proof-of-principle experiments of plasma probing realized. Plasma-based x-ray lasers are investigated too. The only operational x-ray laser is the PALS quasi-stationary-state collisional one, emitting at 21.2nm. It is currently used for various applications, as an XUV probe. During a GoLP-PALS experiment, filamentary structures were observed in a cylindrical plasma at under-critical densities, their vanishing at higher densities suggesting the presence of magnetic fields. New experimental set-ups (involving larger plasma widths) were proposed using simulations performed with the ARWEN rad-hydro-code in order to increase the x-ray laser output energy 49. DENIM also contributed to the design of a high-power x-ray laser 50. Following the ATLAS upgrade and implementation of a new variable-length gas cell, an increase in electron energy and beam charge was achieved, which allowed generating multi-10keV betatron radiation and tunable, monochromatic X-ray pulses via Thomson scattering, thus offering a new hard x-ray probe source for IFE applications. The upgrade also allowed acceleration and transport of

47 P. Heissler et al., Appl. Phys. B 101, 511 (2010); P. Heissler et al., Phys. Rev. Lett. 108, 235003 (2012) 48 B. Dromey et al., Nat. Phys. 5, 146 (2009) 49 E. Oliva et al., Phys. Rev. E 82, 056408 (2010) 50 E. Oliva et al., Nature Photonics 6, 764 (2012)

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mono-energetic 5.3 MeV proton bunches over one meter, enabling first studies with 1 ns resolution 51. In addition to the development of secondary sources, innovative diagnostic apparatus were designed and operated. Among them, it is worth to notice the phase-amplitude imager (combining interferometry and polarimetry) and the solar blind VUV diamond detectors developed in Poland and Italy and tested at WRC, the three-frame laser interferometer/shadowgraph and the ion collector developed at IPPLM, the four-frame x-ray CCD camera built in the Czech Republic as well as the new diagnostic installed on ABC to measure the laser-accelerated ion energy distribution functions. The LIGHT experiment at GSI uses laser-accelerated protons (accelerated up to 10 MeV by the TNSA mechanism) and demonstrates their focusing and re-compression in time (spiral resonator), which has a potential as compact, short-pulse imaging device for dense plasmas.

The pulsed iodine photo-dissociation laser facility at the PALS Research Center in Prague has been successfully synchronized with an auxiliary Ti:sapph. laser system. By increasing the EMI shielding and precise timing of distribution of trigger pulses the shot-to-shot jitter in the delay of pulses of both lasers was reduced to +/- 100 ps. This made it possible to use the Ti:sapph. laser beam as an ultrafast probe in the femtosecond interferometry and shadowgraphy of the plasma produced by a nanosecond laser pulse (figure right) 52. 6. Fusion technologies: from targets to materials and power plant systems a. Targets Effort within FP7 was mainly devoted to understanding the route to producing and characterizing IFE-relevant targets. Important progress was made in

• mass production of IFE target components (implementation of novel micromachining techniques for FI cone mandrels, robotic micro-assembly, harnessing of the MEMS-based lithographic growth technology, etc),

• coating technologies, for production of gradually-doped ablators or polychromatic backlighters (using “cocktail” targets),

• high-speed sphere mapping, • levitating targets, …

In addition, sophisticated targets were produced for the KiT collaborative experiments, such as embedded wire or dot targets, sinusoidally structured surfaces or DLC foils.

51 J. Bin et al., Appl. Phys. Lett. 101, 243701 (2012). 52 J.Huynh et al., ECLIM 2012, P-37, to be published

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A new target laboratory was established in the Technical University of Darmstadt thanks to a collaboration between various German institutes and to a long-term secondment to the RAL to allow training in key target fabrication techniques. The fabrication of tiny sub-mm sized spheres, cylinders, cones, etc, as well as free-standing cryogenic targets was successfully realized. A novel way to levitate and position solid (spherical) targets of various material and size with micrometer accuracy has been developed and implemented in first laser plasma experiments at LMU/MPQ Garching. The design of a robotic target inserter at high repetition rate was finalized in collaboration with General Atomics (USA) and successfully implemented on the GEMINI laser facility. It can place 3D targets to a precision of 2 µm, with over 1000 targets per carousel, and has transformed the RAL ability to undertake experiments at high repetition rate with complex solid targets. b. Materials An ENEA-led review of the best materials to be used for fusion technology was conducted. Silicon-carbide composites, ferritic/martensic steels and austenitic stainless steels were identified as suitable for an IFE reactor. At DENIM, a program was established for study performances of first wall, optics and structural materials for IFE applications, with clear synergies with some MFE research. The lack of irradiation facilities able to reproduce IFE ion and x-ray beam characteristics for the validation of plasma facing components was evidenced. In 2011, ultra-intense lasers were proposed as a powerful tool to generate ion and x-ray bursts which, to date, best fit the IFE plasma conditions. Preliminary shots at the Central Laser Facility in UK have demonstrated the viability of such a proposal. Applications to LASERLAB-Europe facilities are currently submitted. So far, an important effort was placed on the generation and characterization of laser-driven protons beams in terms of optimization of the process and detection tools. In parallel, a review of the state of the art of laser-driven neutron sources was elaborated. At present, they might not reach the fluxes necessary to test fusion materials but this should change in the near future, opening a more cost-effective way of validating nuclear radiation damages 53. α. First wall materials Irradiation of first wall materials by ion and x-rays has been studied to quantify temporal and spatial energy deposition and identify their operating conditions for a dry wall chamber 54. Tungsten was retained as a first option but other solutions, such as carbon foams or 3D engineered materials, could be adopted later on. However, works carried out up to now have identified some limitations that have to be defeated in order to fulfill specifications. Ultrafine grain and nano-structured materials are thus being investigated. Nano-structured tungsten coatings with a thickness up to 5mm have been deposited by using DC magnetron sputtering and the influence of the deposition conditions (gas pressure and cathode voltage) on the coating microstructures studied. Their morphology (in particular the grain size), stress state and mechanical properties (harness and Young´s modulus) were also studied as a function of the coating thickness.

53 J. Alvarez et al., Plasma Phys. Control. Fusion 54, 124051 (2012); S. Nakai et al.,J. Phys. Conf. Ser. 244, 042027 (2010) 54 J. Alvarez et al., Nuclear Fusion 51, 053019 (2011); J. Alvarez et al., FST 60, 565 (2011)

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For optimized parameters, scanning and transmission electron microscope images showed that the deposited material is formed by nano-columns (figure right) with an average diameter of around 100nm and a cylindrical shape that grows perpendicular to the substrate, while x-ray diffraction studies indicated that the coatings are pure α-phase and polycrystalline. Moreover, when optimized, they exhibit good adhesion to the substrate and hardness as high as ~14 GPa 55. In the case of W, the retention of light species may be a cause for concern. Light species, mainly H, D, T and He, which are produced by IFE implosions, impact at high velocity the nearest surface on the first wall, leading there to the formation of bubbles and thus notably degrading W mechanical properties and heat load performances. The role of grain boundaries in the light species behavior is however still under debate. Experiments were carried out in collaboration with the Helmholtz Zentrum Dresden-Rossendorf (Germany) to compare nano-structured W (NW) films and coarse-grained W (CGW) by measuring 1H(15N,αγ)12C nuclear reaction rates. The samples were implanted either with H at an energy of 170 keV or with C (665 keV) and H (170 keV) sequentially, at a fluence of 5 1016 cm-2 and at two different temperatures (room temperature and 400ºC). Data evidenced that the H concentration, for samples implanted only with H, is higher for NW than for MW but it tends to be of the same order of magnitude for samples sequentially implanted with C and H. Increasing the temperature during irradiation up to 400ºC led H to completely diffuse in both samples 56. The microstructure, morphology and mechanical properties of implanted samples are currently under investigation. Interaction of helium with W, in particular helium retention, has been identified as a serious problem. The DENIM group has contributed to the development of a sophisticated new Monte-Carlo code allowing comparing He pulsed irradiation with continuous. The results 57 clearly indicated that pulsed irradiation (e.g. in a laser fusion reactor) is much more detrimental than continuous irradiation (e.g. in a conventional ion accelerator). This explains previous experimental results reporting much lower threshold damage in the former case. Dislocation mobility calculations are computationally intensive and highly parametric. Different techniques were study to accelerate convergence of stress-controlled simulations of dislocation motion. Simple short 'ramps' were shown to be sufficient to dampen stress oscillations that require nearly one order or magnitude more to reach when stress is applied as a sudden step 58. The assessment of interatomic potentials for atomistic analysis of static and dynamic properties of screw dislocation in W were completed; a modified embedded-atom potential was shown to achieve the best compromise in terms of static and dynamic screw dislocation properties, although at an

55 presented at the “Trends in Nanotechnology” conference (Madrid SP September 2012) by N. Gordillo et al. and at the 14th international conference on “Plasma Facing Materials and Components for Fusion Applications” (Jülich DE May 2013) by R. Gonzalez-Arrabal et al.

56 presented at the “Trends in Nanotechnology” conference (Madrid SP September 2012) by R. Gonzalez-Arrabal et al. 57 A. Rivera et al., Nucl. Instrum. Meth. Phys. Res. B 303, 81 (2013) 58 D. Cereceda et. al., Comput. Mat. Sci. 62, 272 (2012)

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expense of about ten-fold compared to central potentials 59. β. Optical materials A large effort has been developed to study silica and quartz samples (and for comparison other dielectric materials) under irradiation with swift ions. To some extent, it is a fundamental work but of important application as swift ions will be ubiquitous in laser fusion plants and will certainly affect the final optics materials, especially for the final lenses. The kinetics of quartz amorphization, the changes in refractive index and iono-luminescence were studied. As an important by-product,the knowledge acquired was applied to waveguide fabrication 60. Thermo-mechanical simulations of IFE final optics were carried on by means of finite elements under the three HiPER scenarios. For continuous prototype and demo modes, neutron irradiation heats the optics (here a lens) and generates color defects that absorb laser energy. The lens temperature must then be kept constant (by auxiliary systems) during start-up and operation to avoid focal length variations. In addition, the final lenses for the demo scenario must be moved away from target chamber (beyond the current 8 meters) 61. The mechanical response and crack damages in ceramics due to ion irradiation were also studied. Simulations with finite elements in LiNbO3 evidenced the stress field generated by nano-tracks near the surface that led to a swelling of the material and crack fractures at a given fluence. γ. Structural materials The influence of Cr concentration in FeCr alloys (from 0 to 15%) on formation and binding energies of vacancy clusters up to 5 defects was studied. The calculations were performed with two empirical potentials specially developed to study radiation damage in FeCr alloys: the modified version of the concentration dependent model (CDM), used in previous works, and the two-band model (2BM). Both potentials predict an increase of the defect stability with the cluster size and no real dependence on Cr concentration for the binding energy 62. The elemental distribution for as-received, H implanted and post-implanted annealed Eurofer and ODS-Eurofer steels was characterized by means of various techniques. Micro-particle-induced x-ray emission measurements pointed out the presence of inhomogeneities in the Y distribution for ODS-Eurofer samples which might notably influence their mechanical properties. Moreover, a small percentage of hydrogen was found along the whole investigated depth for as-received samples, which indicates that H incorporates into the steel during its manufacturing in a H2-rich atmosphere. Resonance nuclear reaction analysis and secondary ion mass spectrometry evidenced that hydrogen easily diffuses in these steels even at room temperature. This diffusion is responsible for the strong decrease of the hydrogen concentration with time. The H depth profiles suggested that the sample surface might play an important role in the hydrogen release. Indeed, a higher hydrogen concentration was detected in the near surface layers, which may indicate that the surface strongly reduces hydrogen releasing. Finally, micro-elastic recoil detection data showed that annealing at temperatures as low as 300 ºC strongly accelerates the hydrogen diffusion process, driving out up to the 90% of the initial hydrogen to diffuse 63.

59 D. Cereceda et. al., J. Phys. Condens. Matter 25, 085702 (2013) 60 A. Rivera et al., Proc. SPIE 7916, 79160S (2011); O. Peña-Rodríguez et al., Appl. Phys. Express 5, 011101 (2012) & Nanoscale 5, 209 (2013);

O. Peña-Rodríguez et al., “Optical waveguides fabricated by ion implantation/irradiation: A review” in Ion implantation (In Tech) 267 (2012)

61 D. Garoz et al., Nuclear Fusion 53, 013010 (2013) 62 E. Martínez et al., J. Mech.Phys. Solids 56, 869 (2008); E. del Rio et al., J. Nucl. Mat. 408, 18 (2011); J.M Sampedro et al., Nucl. Instrum.

Meth. Phys. Res. B 303, 46 (2013) 63 R. Gonzalez-Arrabal et al., Nucl. Instrum. Meth. Phys. Res. B 271, 27 (2013)

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ε. Target materials DENIM studied phase changes occurring in the DT layer during compression thanks to electronic structure simulations of solid hydrogen and isotopes with the SIESTA code. Discontinuities in the sound speed, not fully addressed in the macroscopic equations of state, were evidenced 64. c. IFE technologies: reactor chambers and blankets, safety and radio-protection Programmes on “Safety, Environment and Fusion Technology of interest for IFE” are ongoing in Spain and in Italy. A review of the 2007 HiPER conceptual design was performed at ENEA in terms of safety and identified no serious obstacle to licensing. A wide study including all technology aspects was also performed by an European-Japanese collaboration 65. Extensive studies were carried out computationally for defining the HiPER chamber and blanket, covering all aspects from neutronics and activation of the LiPb eutectic to helium Brayton power cycle and maintenance. A self-cooled lead lithium blanket-based chamber, with a dry first wall, was assumed 66. To perform all these calculations, a series of 3D codes was developed. It includes a CAD description of the reactor, the MCNP neutronics code, the ACAB activation code, the FLUENT thermo-fluid dynamics code and the ANSYS thermo-mechanics code, as well as the TMAP code to get the tritium response in the coolant. The neutronics and activation studies allowed choosing the thickness of the LiPb breeder, for a given TBR (of 1.1) and thus an adjusted 6Li enrichment, taking into account in the decision process criteria related to radiobiological threatening inventory (T, 203Hg and 210Po) or to reweldability. A thin (~50 cm) blanket showed a better performance in terms of radiobiological threatening inventory and a thick (~75 cm) blanket offers better shielding of the vacuum vessel. But, to guarantee reweldability after 40 years of operation, thicknesses well above the specified 20cm one are required in both cases. Thus, a thin blanket was selected but an additional shielding of the vacuum vessel will be required. A 20cm-thick neutron reflector in graphite is under study; it also allows reducing the 6Li enrichment from 75% to 20%, with evident economical advantages. In activation calculations, several approaches allow quantifying uncertainties, either deterministic by means of sensitivity analysis or stochastic by means of Monte Carlo simulations. Two different Monte Carlo approaches were studied: the Total Monte Carlo (TMC) approach and the Covariance Uncertainty Propagation approach, a Monte Carlo sampling of the covariance information included in the nuclear data libraries to propagate these uncertainties throughout activation calculations. The JEFF-3.1.2 cross-section data are used into MCNP/ACE libraries for different temperatures depending on the application needs. The library at 300K was verified and compared to other available libraries. A Quality Assurance procedure allowed pointing out any error/mistake found during the analyses. The impact of potential uncertainties was analyzed with the ACAB activation code 67. It was decided to separate the first wall and blanket cooling systems. While the LiPb blanket is self-cooled, the first wall is cooled through a helium loop operating a Brayton cycle. The temperature range for the blanket is 350 ºC – 450 ºC while, for the first wall, it is >350ºC – 650ºC. To finalize the

64 presented at the 7th IFSA (Bordeaux FR September 2011) by C. Guerrero et al., 65 K.Mima, V. Tikhonchuk and M. Perlado. Nucl. Fusion 51, 094004 (2011) 66 J.M. Perlado, Proc. SPIE 8080, 80801Z (2011) 67 O. Cabellos et al., J. Nucl. Mat. 386, 908 (2009)

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study, several layouts of the helium Brayton power cycle were analyzed to optimize the thermal efficiency. Efficiencies up to 37% were obtained, even when real performances of the cycle components and pressure drops in the heat exchangers were considered. Regarding fluid-dynamics studies, severe issues were first identified. In order not to reach a local maximum temperature of 550ºC (allowed by EUROFER) the mass flow must be so high that the outlet average temperature must be very low (390ºC instead of 450ºC). Despite this high mass flow, cooling may be locally insufficient and very high corrosion rates reached (up to 600 mm/yr, while the limit was fixed to 200 mm/yr). These problems arose from recirculation occurring in the simulations after first beam penetration in the inner duct. Further simulations were then launched to understand this phenomenon. It was shown that it was a pure numerical artifact, without any physical reality, as using a more detailed LESS model to describe the fluid turbulence led to disappearance of the recirculation. The previously used RANS model, which speeds up computations by spatially averaging quantities, was then inadequate and the blanket performances shall be re-evaluated. The LiPb circuit will also be modified to avoid any appearance of recirculation. Apart from structural and constructability difficulties for the first proposed Φ16m spherical chamber, the shape was found to be not suitable enough for easy maintenance of the blanket, first wall or vessel itself. A cylindrical vacuum vessel, together with some final optics modifications, was thus proposed to allow optimization of the maintenance tasks. The following figures present the preliminary design for an IFE reactor and some ideas for the blanket systems 68.

Finally, in the framework of the Singular Spanish Facility of Science and Technology TECHNOFUSION, the construction of an R&D laboratory to study the behavior of liquid lithium on fusion-relevant environments was proposed. The development of liquid metal technology is indeed of paramount importance as liquid metals, such as lithium and lead-lithium eutectic, could be the coolants and the breeding materials of the future fusion reactors 69. d. Consequences of Different Meteorological Scenarios in the Environmental Impact Assessment of Tritium Release Refined environmental tritium dose impact assessment schemes are overwhelming. Detailed assessments can be procured from the knowledge of the real boundary conditions of the primary tritium discharge phase into atmosphere (low levels) and into soils. Lagrangian dispersion models using real-time meteorological and topographic data provide a strong refinement. Advance

68 R. Juárez et al., Fusion Engineering & Design 86, 694 (2011), 87, 336 (2012) & online (24 June 2013); J. Sanz et al., FST 60, 579 (2011); C. Sánchez et al., Fusion Engineering & Design online (4 January 2013)

69 A. Ibarra et al., Fusion Engineering & Design 85, 1659 (2010); A. Abánades et al., Fusion Engineering & Design 87, 161 (2012)

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simulation tools are being developed in this sense. The tool integrates a numerical model output records from European Centre for Medium range Weather Forecast (ECMWF) with a lagrangian atmospheric dispersion model (FLEXPART). The composite model ECMWF/FLEXTRA results can be coupled with tritium dose secondary phase pathway assessment tools. The aim of the performed work is to consider different short-term releases of tritium fluxes to the atmosphere from a potential ITER-like fusion reactor located in the Mediterranean Basin. Values of the tritium oxide (HTO) / hybride (HT) ratio were explored and influence of the meteorological conditions examined 70. C. FP7 transverse activities The IFEWG also agreed, following the 2010 recommendations, to better focus the IFE KiT activities on knowledge integration, to organize a workshop to bring together the magnetic and inertial fusion communities and to examine ways of enhancing co-ordination. Various measures were thus taken or reinforced. 1. Community development Fusion energy being currently envisaged in more than two decades, it is urgent to attract and train young scientists (researchers and engineers). Actions were initiated to develop the laser-plasma community at RAL (through a training programme for new students), MPQ (lectures at the LMU university). Participation of new users to IFE-relevant collaborative experiments, conducted on LULI2000, VULCAN, ASTRA and PALS, was also encouraged. Finally, scientific workshops and conferences were organized in this framework. Heavy Ion Stopping, October 2007 (Germany) 1st conference on Ultra-Intense Laser Interaction Science (ULIS), October 2007 (France) 2nd European Target Fabrication workshop, October 2008 (UK) 30th ECLIM, August 2008 (Germany) Annual Hirschegg workshop on High Energy Density Plasmas (Germany) Direct Drive Fast Ignition workshop, May 2009 (Portugal) and following editions in Czech

Republic and UK, France 2nd ULIS, May 2009 (Italy) 14th International Conference on Emerging Nuclear Energy Systems, June 2009 (Portugal) 31st ECLIM, September 2010 (Hungary) PALS10, September 2010 (Czech Republic) 1st Technology in Inertial Fusion workshop, September 2010 (Portugal) 14th RPHDM, October 2010 (Spain) AOP2011, May 2011 (Portugal) 50th International School on Quantum Electronics, July 2011 (Italy) 68th Scottish Universities School in Physics, August 2011 (UK) 7th IFSA, September 2011 (France) Alternative Ignition workshop, September 2011 (France) Workshop on High contrast, intense laser pulses, September 2011 (France) 3rd ULIS, October 2011 (Portugal) 32nd ECLIM, September 2012 (Poland) 2. Knowledge diffusion A web site www.ife-kit.eu was set up to provide useful information to the public and to facilitate

70 P. Castro et al., Fusion Engineering & Design 87, 1471 (2012)

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coordination (and data exchange) within the partners through an internal password-protected section. The site is maintained and updated by her webmaster, S. Jacquemot (LULI, France). It was also proposed that the IFE KiT activity be represented in major fusion events. An overview paper was then given at the 23rd IAEA Fusion Energy Conference in October 2010 (Daejeon, Korea) and an article, duly acknowledging the EURATOM contribution to the highlighted studies, was subsequently published in Nuclear Fusion 71. The European keynote speaker at the 7th international conference on Inertial Fusion Sciences and Applications (IFSA2011, 12-16 September 2011, Bordeaux, France) also emphasized the structuring effect of the activity. 3. Mobility The following graph summarizes the intra-European visits - representing more than 30 weeks per year - that were supported through the IFE KiT programme.

CZ FR DE UK HU IT PL PT SP CZ FR DE UK HU IT PL PT SP

4. IFE-MFE synergy As required, an IFE-KiT Technology Watch Workshop was organized at UPM in March 2010; it gathered ~50 participants, with the aim to identify areas where the magnetic and inertial communities have knowledge to share. The discussions led to a critical evaluation of the recent achievements in IFE research in an energy perspective, an analysis of ways to achieve better coordination and focus within IFE-KiT activities and proposals to promote coordination in those areas. It followed increased participation of the laser-plasma community to fusion conferences (as the EPS Plasma Physics annual conference, thanks to sustained efforts of J. Meyer-ter-Vehn, member of the EPS-PP Board and of the EURATOM IFE KiT programme, et al.) and then enhanced opportunities for the two communities to meet, discuss, discover common interests, etc. Note that, as maybe a consequence, the EPS Plasma Physics Division is for the first time chaired by someone from the Inertial Fusion community. Three key IFE-MFE Synergies were identified and actions initiated. Fusion physics currently relies on simulations; massively parallel codes are developed and run in both IFE and MFE communities and access to HPC is essential. The possibility for the IFE researchers to benefit from the EFDA-HPC project was explored. However, extensive use of Tier-1 and Tier-0 machines through national federative structures (as GENCI in France) or through PRACE is currently privileged by the IFE community,

71 S. Jacquemot et al., Nucl. Fusion 51, 094025 (2011)

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but also, to a great extent, by the MFE one. One of the IFE proposals on JUGENE was highlighted in the 9th volume of the PRACE newsletter (October 2012). Collaborations on the IFMIF-EVEDA accelerator prototype started: radioprotection studies were conducted at DENIM; at GSI, expertise on ultra-high linear accelerator currents and collective beam stability issues got involved in TRACEWIN code development to predict beam loss effects. Simulations of the thermo-mechanical effects on W first wall under IFE and MFE irradiation conditions were performed at DENIM. It was shown that, except during MFE disruptions, the plasma facing materials are subject to comparable thermal loads and, therefore, present similar thermo-mechanical response; however, radiation-induced atomistic effects appear to be different due to ion energies in the eV range for MFE and in the keV-MeV range for IFE. D. The IFE roadmap beyond 2013 Considering the state of the art in research and developments and the ambition of its long-term goal of demonstrating the viability of clean energy production by laser-driven fusion, as demonstrated by the HiPER roadmap, the European community has established a roadmap towards IFE for the near future. This roadmap aims at:

• mission 1a: conducting a programme of experiments and numerical simulations culminating in the demonstration of shock ignition on the LMJ circa 2021-2023, followed by a 5-year period of optimisation to achieve gain values required for IFE; this mission will rely on access on programmatic access to the LMJ from 2016 and to existing mid-scale European (and possibly US) laser facilities for underpinning sub-ignition experiments (and associated numerical modelling) to give confidence in the IFE underlying physics;

• mission 1b: conducting a programme of experiments and numerical simulations to understand underlying obstacles to central hot-spot ignition on NIF and LMJ, particularly x-ray / optical drive asymmetry and hydrodynamic mix, to reduce uncertainties that input into all inertial fusion ignition schemes; this mission will rely on academic access to the VULCAN, ORION and US laser facilities and involve active collaboration with inertial fusion scientists worldwide;

• mission 1c: conducting a programme of numerical simulations and experiments to test the viability alternative schemes such as electron- and ion-driven fast ignition or impact ignition;

o development of laser-driven electron and ion sources, as well as of laser-based acceleration methods for plasma macro-particles, using advanced numerical simulations and experiments on the existing and future laser facilities;

o development of computer codes and capabilities for unified simulation of the fast ignition scheme, from compression to ignition and burn;

o investigation of the potential of alternative schemes for high-gain fusion with reactor-scaled targets by performing massive numerical simulations;

2012 2014 2016 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040

2012 2014 2016 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040

Technology Devt. & Risk Redn.

Laser: 10kJ / 10Hz beamline prototype; Target mass prod.; Chamber concept

HiPER construction & commissioning

NIF Ignition

LMJ Ignition

LMJ available

Robust ignition; physics optimisation

Invest. decision

Exploitation

HiPER B. C.

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• mission 2: developing (including prototyping) key IFE technologies such as laser driver, advanced materials for fusion chambers, target injector and position sensor; this mission will also look for mass production of fuel capsules and will include works on engineering concepts for an IFE reactor; it will provide unique opportunities of innovation and transfer to industry.

To these programmatic missions must be added:

• mission 3: building a stronger Fusion community and enhancing IFE visibility;

• mission 4: keeping watch over scientific and technological developments conducted within other IFE programmes, especially on alternatives to DPSSL-driven shock ignition (KrF or Z-pinch drivers, etc) or on new reactor technologies;

• mission 5: developing IFE-MFE synergies in areas of common interest, such as computational physics or developments relevant to the IFMIF-EVEDA project.

Considering the current expertise of the EURATOM partners, this roadmap has been distributed into various tasks. Some of them are explained in the following paragraphs. Mission 1.1 - Acquiring new insights into the basics of ignition physics 1. Atomic physics Plasma atomic physics is of first importance for diagnosing and modeling all the experiments (especially those directly related to IFE) that will be conducted on high-energy laser facilities. As the laser energy will be increased from a few kJ to hundreds of kJ on the LMJ, new states of matter will be reached and matter models (based on many-body theories to take into account electrons and ions simultaneously) shall be able to describe them accurately. Three axes of research have been identified and will be followed. a. development of innovative diagnostic methods based either on time- and frequency-resolved x-ray emission spectroscopy of doped capsule cores (which implies accurate knowledge and control of the radiative properties of the emitting plasmas, including line broadening and opacity effects) or on Thomson scattering (which requires, especially in the XUV range, theoretical and numerical developments to take into account ion structure effects in the modeling of the electronic properties of the probed plasmas and to touch some of their condensed matter aspects)

1st step (2013-2015): implementation of density effects (as for instance plasma potential lowering) in detailed opacity modeling 2nd step (2015-2020): emission spectroscopy studies of various “tracers” on the LMJ; exploration of the PETAL potentialities (i.e. of the secondary radiation and particle sources this multi-PW beam can produce) in terms of plasma diagnostics; development of a new quantum theory to model Thomson scattering (depending on efficiency of the developed algorithms)

b. improvement of the statistical or hybrid methods used to model unresolved emission and absorption x-ray and XUV spectra (emitted by the doped capsule ablator or by the irradiated first wall) and thus energy transfer mechanisms, in conditions close to or far from local thermodynamic equilibrium, taking into account plasma thermodynamics (such as density effects)

1st step: near-LTE XUV absorption measurements in mid-Z plasmas at densities between 0.001

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and 0.01 g/cm3 and a few tens of eV on LULI2000 thanks to the innovative double hohlraum arrangement validated under the FP7 EURATOM KiT programme; implementation of a new temperature diagnostic method (based on the well-known x-ray absorption – in the same conditions – of low-Z plasmas); participation to UK-led experiments on ORION (at higher radiative temperatures); investigation of the role of configuration interaction (CI) effects on opacity and radiative transfer calculations; investigation of time-resolved XUV opacity and refractive index at fs timescales using HHG on several LASERLAB infrastructures; extension of coherent backlighter emission to shorter (x-ray) wavelengths using HHG generated in solids or long wavelength-gas interaction 2nd step: design of a multi-purpose (opacity, hydro instabilities …) indirectly-driven experiment on the LMJ; development of a hybrid opacity code (coupling STA formalism and detailed calculations) fully taking into account CI note that the experiments planned under this task will contribute to maintain European expertise on indirectly-driven ICF (mission 4)

c. theoretical exploration of the validity at over-critical densities of plasma models currently neglecting correlations between electrons bound to different ion centers, with impact on equations of state and energy transfer to fuel core (step 1); exploration of the use of XFELs and high-energy UHI laser facilities to reach IFE-relevant high-energy-density-matter regimes and validate the developed models (step 2) 2. Laser-Plasma Interaction Analysis of the state of art of IFE-relevant LPI physics clearly shows that energy transfer from laser to plasma still remains a major challenge, for theoretical modeling and for experimental demonstration of ignition. One of the most crucial issues is in fact the control of the deleterious parametric instabilities due to the scattering of the incident laser light off plasma waves (namely Stimulated Raman Scattering - SRS - and Stimulated Brillouin Scattering - SBS). In recent NIC campaigns, onset of these instabilities, backscattering of a significant fraction of the incident laser energy and energy transfer between crossed laser beams have actually been evidenced. For the SI scheme, the role of these instabilities has to be carefully revisited, in particular with respect to the potentially inhomogeneous character, at relatively high temperature, of a directly-driven fusion plasma, and considering the required intensities, up to 1016 W/cm2. Furthermore, the present MJ laser facilities (the NIF and the LMJ) were designed to meet requirements dictated by indirectly-driven ICF. It is thus necessary to adjust the spatial distribution of the laser beams for direct drive by redirecting and smoothing them. The focusing systems need also to be re-designed and re-configured to allow defocusing (the so-called polar direct drive - PDD). Even though, irradiation symmetry may be insufficient. In such a PDD configuration, overlap of laser beams and oblique incidence are unavoidable. Coupling between multiple laser beams and absorption in such a geometry remaining partly unresolved, further studies are required. Beam crossing can give rise to energy exchange between them (a process which is highly complex and may involve simultaneously resonant coupling and collective non-resonant exchange, both of high relevance) which can lead to non-uniformities in the laser illumination of the target. The main objective for the next years of this task will be to continue modeling the complex non-linear multi-scale underlying processes that may affect laser-plasma coupling efficiency and improving capacities to describe SRS and SBS, and their mutual coupling, in realistic plasma conditions, taking into account crossing laser beam configurations. The difficulty lies then in the different spatial (from sub-µm to mm) and temporal (from fs to ns) scales that are involved.

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Experimental investigation of LPI issues will be conducted within the following mission. In the past years, within the FP7 EURATOM IFE KiT programme, models for laser self-focusing and SBS have been developed and integrated into large-scale numerical codes based on a fluid-type plasma description and paraxial laser propagation algorithms, taking into account statistical (speckle) properties of optically smoothed laser beams (as those used on the NIF or, in the near future, on the LMJ). These predictive capabilities allow computing laser coupling to mm-size plasmas but are currently severely limited to the description of a small number (2-3) of interacting laser beams and by their extreme computational cost. Theoretical models for SRS still need to be improved and validated (using PIC simulations) prior to their integration. Particularly attention has to be paid to the multi-dimensional aspect of the SRS instability (steps 1 & 2) and multi-speckle aspects (step 3) which were neglected in already performed studies. Finally, the role of the hot electrons that are generated by LPI will be clarified (steps 2 & 4). A few years (5-6) shall be needed to complete this mission. 3. Hydrodynamics Stability of the shell implosion is the major preoccupation of all ICF schemes. By imploding thicker targets at lower velocity, SI is naturally less prone to hydro instabilities. However, the growth of target perturbations needs to be appropriately modeled. In particular, sensitivities of the fusion yield with respect to low- and high-mode non-uniformities need to be studied. This includes analysis and control of the target perturbations (at the outer and inner surfaces) as well as control and reduction of the laser intensity fluctuations (including spatial and temporal smoothing, temporal profiling of the laser intensity, thermal smoothing using foams, …). The main objective of this long-term task will be to determine technical requirements on the target surface roughness, target positioning, laser imprint, laser pointing, beam-to-beam imbalance, pulse shape tolerances, etc (step 2). These theoretical and numerical studies need to be confronted to experiments, in planar and converging geometries (see mission 1.2). Ignition target design requires numerous parametric studies with a robust and reliable hydrodynamic code, such as the 2D Lagrangian rad-hydro code CHIC and DUED. A reliable database has been built and several modules accounting for major physical effects developed and validated thanks to a series of experiments during these last 5 years. However, improvements of the code performance and of some specific modules (in particular laser beam propagation and energy deposition, electron energy transport, magnetic field generation, plasma turbulence, nuclear reactions and transport of the reaction products) have still to be done (step 1). The development of a 3D version is also planned (step 3). The code, which will be continuously upgraded and validated against experimental results, must be made fully available for the scientific community; this goal will require establishment of a proper institutional utilization framework, as well sustained human and economical efforts over a rather long period (step 4). Mission 1.2 - Demonstrating Shock Ignition on the LMJ Shock ignition is - according to our current level of knowledge - the ignition scheme that has the strongest potential for being tested in the next few years on MJ laser facilities and that can demonstrate a high gain performance, with only minor facility adjustments. In contrast to the conventional central ignition scheme, as tested on the NIF, where the compressed fuel is self-consistently ignited at the very end of the shell implosion, SI separates the implosion and ignition phases; it relies on ignition of the compressed fuel by a strong shock wave launched at the end of the compression phase thanks to adequate temporal profiling of the laser pulses. Lower in-flight

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aspect ratio and implosion velocity may in that case improve the shell hydrodynamic stability and the energy required for compression is reduced, which leads to a higher net energy gain. However not all the physical aspects of the SI scheme and not all the technological limitations are for the moment properly addressed. One of the main challenges will be to demonstrate the possibility to achieve required central pressures at the level of a few hundreds of Gbars (starting from a initial shock amplitude of ~300 Mbar). Although theoretical scaling laws indicate that it’s possible to reach such a pressure at laser intensities of the order of 1016 W/cm2, ablation pressures obtained to date do not exceed 100 Mbar. Another challenge will be to experimentally verify on available intermediate-scale facilities that the PDD arrangement (required to demonstrate SI on the existing MJ facilities) will produce a sufficient drive uniformity to achieve the required level of compression, as predicted in simulations. The growth of the filamentation instability is a particular concern. Proposed methods to control this instability require experimental verification. This task aims then at addressing and experimentally demonstrating all the key SI physical issues, before full-scale demonstration on the LMJ.

1st step (2013-2018): (i) development of SI-relevant diagnostics and of dedicated numerical post-processors; (ii) development of a LMJ inserter, dedicated to SI cryogenic targets; (iii) build a proper case for funding a target lab in Aquitaine in order to reduce, in the long run, transportation time and costs; (iv) perform planar experiments on: o laser-plasma interaction under SI-relevant conditions (at up to 1016 W/cm2, 2ω and 3ω) to

learn how to control parametric instabilities and energy exchange due to beam crossing, in close coupling with code developments (task 1.1.2),

o hot electron generation and transport in dense plasmas, o control of the filamentation instability in large scale-length plasmas, o laser imprint reduction, thanks to thermal smoothing techniques, to guarantee the best

possible irradiation uniformity and validate pre-defined laser requirements (task 1.1.3, step 2),

o hydro (Rayleigh-Taylor and Richtmyer-Meshkov) instabilities, to study competition between them and validate pre-defined target requirements (task 1.1.3, step 2),

o shock formation (scaling of the shock pressure with the laser intensity and wavelength) and propagation in inhomogeneous long-scale-length plasmas,

o self-generated magnetic fields in directly-driven quasi-symmetric fusion plasmas and delocalization effects on laser absorption and energy transport (in relation with implementation of the corresponding modules in the CHIC code: task 1.1.3, step 3);

2nd step (2018-2020): perform experiments in spherical geometry on: o optimization of the PDD configuration, including beam zooming and/or dynamical pointing, o absorption at oblique incidence and beam crossing effects, o strong shock formation, timing and stability, o convergence and shock effects on the growth of the hydro instabilities, o influence of the LPI-generated hot electrons on a cryo implosion.

Dedicated targets will be used for these campaigns, restricting the use of cryogenic ones to the very last experiment or when neutron diagnostics can’t be overlooked (for instance to validate the symmetry of the implosion at stagnation), preferably after 2019.

3rd step (after 2020): demonstration of SI on the LMJ

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The figure on the right summarizes the above-mentioned experimental roadmap. Note that the series of experiments required to fulfill this mission will be performed by an international collaboration, including mostly European partners. Access to the intermediate-scale facilities in France, UK and the Czech Republic will be mainly programmatic and the campaigns will be led by nationals under their own roadmap; access to US facilities (mainly OMEGA at LLE) or Japanese ones (if necessary) will be obtained through already or to-be-build collaborative agreements. Access to the LMJ will be gained through the French Institut Laser-Plasma, which is also in charge of establishing an access policy. A fraction of laser beamtime (~20%) will be allocated from 2016 by CEA to this institute and thus to the academic community. A scientific programme, with 4 pilars (High Energy Density Physics, Laboratory Astrophysics, High Energy & Acceleration and IFE), is currently under construction; it will allow prioritizing the various experiments that will be proposed and the diagnostics to be built. From 2016, the LMJ will be coupled to the multi-PW PETAL facility; funded by the Région Aquitaine and the European Union, it’s a fully academic facility which will allow, thanks to the generation of bright secondary radiation and particle sources, advanced backlighting techniques (mission 1.1.1.a, step 1). The PETAL+ project, funded by the French Research Agency (ANR), as well as the CALA project funded by the German Research Foundation, will, in parallel, allow the community building the first set of PW-oriented diagnostics. IFE-relevant experiments requiring years of preparation (~1-2 on LULI2000 to 2-3 on the LMJ), some of them have already been scheduled in the framework of this roadmap.

On LULI2000, two relevant campaigns are scheduled in 2013: “Diagnostics development for shock ignition studies” led by M. Richetta (University of Rome) (mission 1.2, step 1) and “Laser plasma interaction physics for ICF and Shock Ignition: development of numerical modelling and experimental assessment of the LPI risk” led by S. Depierreux (CEA/DIF) (mission 1.2, step 1). On the LIL, at CEA/CESTA, a campaign, led by S. Baton (LULI), is planned in 2014; it will address laser-plasma interaction and shock generation with LMJ-like laser beams; a new (hemi-spherical) target design will also be tested to try to obtain a spherical plasma corona in planar geometry and to study shock uniformization. On OMEGA, the CELIA team is co-leading an integrated SI experiment to be performed in 2013; this experiment will use sub-scale spherical targets imploded with 60 laser beams to increase the focal spot intensity, while maintaining a highly uniform target illumination. The target design aims on assessing the max shock strength achievable at SI relevant intensities. With the beams focused to a 300 μm spot size, the target will be irradiated at an averaged intensity of 5 1015 W/cm2 (25 kJ, 1 ns). A pressure above 200 Mbar is expected.

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The figure on the rigth indicates how all the mentioned infrastructures will be used.

Mission 2 – Developing key elements for IFE technologies 1. Laser driver technology Laser-driven IFE commercial viability requires an overall efficiency of ~10% and a laser pulse repetition rate of 10-15 Hz, which implies a new laser architecture. Revolutionary developments of the laser technology are expected to continue in the forthcoming years, giving a hope to great steps forwards. The most cost effective solution identified for IFE is based on advanced solid-state laser gain materials pumped by diode lasers (DPSSLs). The present HiPER conceptual design is based upon such ~10kJ beamline units, replicated to deliver the required total laser energy uniformly to the target. Each of these beamlines will in fact consist of a matrix of 9 to 16 ~1kJ beamlets, arranged in three-by-three or four-by-four arrays, with overlapped output beams, to meet the “single spot” energy requirements on target. The development path for HiPER is based on continual risk reduction. A series of prototypes are proposed at energy levels increasing from a few Joules to the kJ at 10Hz, each prototype de-risking the next one. Prototype energies were selected appropriate to the performance testing required for confidence in gain media thermal properties and heat extraction technology, diode pumping arrangements and amplified spontaneous emissions (ASE). Clear benefits in different fields (not only IFE) and return on investments could be expected as these laser developments are also linked to other European projects, such as ELI and its pillars in Czech Republic, Hungary and Romania, the CALA facility in Germany or the APOLLON laser facility in France. R&D programs have been launched through the whole Europe, in Germany (at MPQ), in Portugal (at IST) or in Italy (at ENEA). For instance, a small-scale system is currently under development at LULI, Ecole Polytechnique, Palaiseau. A first energetic milestone set at 10J has been recently reached thanks to large efforts dedicated to the study of the deleterious consequences of Amplified Spontaneous Emission (ASE) and thermal load on the amplifier gain medium. While ASE can lead to parasitic oscillations leading to gain depletion, inadequately managed heat load in the gain medium affects the spatial quality of the amplified beam. A comprehensive experimental cross-evaluation of both ceramic and crystalline YAG disks was performed to identify advantages and limitations of both materials with respect to ASE and thermal management. This work was supported by detailed theoretical analysis allowing an in depth understanding of the underlying physics. Adequate thermal and ASE management solutions were implemented to mitigate the above-mentioned related negative consequences. After successive improvements, a 2 Hz train carrying 8 ns, 1030 nm pulses of 13.7 and 13.9 joules was ultimately obtained for respectively crystalline and ceramic Yb:YAG disks used on the amplifier. The next step will then be to reach the “30J” milestone within the next 3 years, with adjunction of a second, cryogenic, amplifier head; in parallel, an experimental study on tailored gain media will continue.

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The WRC sub-picosecond KrF laser will also be upgraded from 60 mJ to hundreds of mJ energy closely connected to the Hungarian ELI facility.

1st step: build a high-repetition-rate (above the Hz) facility at high enough energy (above 30 J) to 2nd step: test other IFE technologies (target injection for instance); 3rd step: contribute to the down-selection of the HiPER laser technology according to the HiPER roadmap.

The innovative technological developments that will be done under this task may lead to transfer to industry, thus fulfilling one of the key objectives of the Horizon2020 programme. 2. Materials One of the key inputs when designing an IFE reactor is not only the burn time duration but the time-dependent energy distribution of all the output products - neutrons, x-rays and ions - to correctly treat their interaction with a potential filling gas, the first wall and the blanket. The need to protect the chamber and the pulsed nature of the radiation and particle energy deposition shall be carefully considered, while they have little influence in MFE. The bursts of very energetic ions, coming from the ablation of the capsule and the fusion reaction itself, are known to severely damage the materials of the first wall. In order to properly evaluate their thermo-mechanical and atomistic effects, the spectral energy distribution (particles/MeV) of each species must be precisely known. The problem is that, before impacting the wall, those ions cross the remaining target plasma and the low pressure, but highly ionized background gas of the chamber, which may substantially modify their final energy spectrum.

1st step: develop modeling capabilities which include time- and space-resolved interaction physics of the capsule burn products in the high-energy-density regime 2nd step: investigate, numerically and experimentally (potentially on high-energy laser facilities) the influence of different background gases/plasmas, at varying densities and temperatures, on the energy distribution of ions and x-ray radiation impacting the first wall or final optics

The first wall materials for an IFE reactor will be quite different from the MFE components as already performed calculations indicate that ion energy spectra and expected flux are not identical. The choice of the strategy to protect the first wall is thus critical. For a non-protected wall (as considered for the HiPER project), the development of new nano-structured or 3D-tailored materials may be unavoidable. Nano-tungsten is being developed but other materials need to be explored.

1st step: follow progress in development of W nanostructures and in the demonstration of their thermal stability in the adequate range of temperatures 2nd step: irradiate nano-structured W samples under IFE-relevant ion fluxes and energies 3rd step: evaluate performances of alternative materials, such as foams or engineered 3D structures

Final optics materials have also to be carefully chosen. The damages that ions, x-Rays and neutrons can produce on them shall be more deeply defined and understood.

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1st step: study the various possibilities for the final optics allocation, knowing the irradiation and reactor parameters (in an iterative process) 2nd step: model and test silica under pulsed operation 3rd step: evaluate alternative materials

The structural materials for an IFE blanket are identical to those considered for a MFE blanket. A clear IFE-MFE synergy is then identified. The use of FeCr alloys (EUROFER et al.), ODS steels or SiC composites is considered in both approaches. However, in IFE systems, the pulsed nature of the neutron irradiation may be further assessed.

1st step: follow MFE developments of advanced materials 2nd step: initiate a programme to experimentally and numerically evaluate the influence of pulsed irradiation

3. IFE technologies: reactor chambers and blankets, safety and radio-protection The design of the reactor chamber and blanket has already started on the basis of existing ideas derived from various projects (HIBALL, HYLIFE, SOMBRERO, KOYO and more recently from LIFE, LiFT, KOYO-FI and of course HiPER). These reactor designs propose different blanket allocation concepts (due to sometimes different ignition schemes). Liquid coolant and breeder were proposed but solid breeder with liquid gas coolant may also be considered. During the next years, within this Roadmap, these different possibilities will be studied for the three envisaged facility modes (see section A). The analysis will be based on the Virtual Reactor Model – developed by a CEA-RAL-DENIM collaboration - connecting the various sub-systems of an IFE Power Plant. This model, for the moment based on the HiPER preliminary design, will support evolutions.

After reviewing the HiPER concept, in comparison with other approaches, a series of questions will be successfully addressed.

1st step: identification of the key issues under repetitive operation 2nd step: comparative study of LiPb and Li breeders, making use of the experimental capabilities at TECHNOFUSION (Spain)

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2nd step: study of the tritium cycle (exhaust from the chamber materials, conduction through the liquid coolant, separation, purification and final target manufacturing) assuming a minimum inventory 3rd step: study of the reactor fluidynamics under different options for coolant and structural materials, taking into consideration heat extraction and tritium breeding 4th step (from 2018): study of the economics of an IFE reactor (cost of electricity, cost of construction, etc) including an analysis of the role of laser energy in the future energy mix, of the possible investment and funding scenarios or of the impact on industry (including development of spin-off technologies)

E. Concluding remarks – Case for continuation of the EURATOM IFE KiT activities and funding IFE is going through a unique and very exciting period, with the 5 last years of considerable progress in Europe, the continuous effort to demonstrate ignition on NIF and a realistic program of scientific and technological R&D for risk reduction towards IFE. Focusing EURATOM KiT activities on dedicated IFE-relevant scientific topics has resulted in increasing collaborations throughout the participating laboratories in Europe, enabling a research programme to be fruitfully developed across national approaches, and thus enhancing the strength of the European fusion community as a whole. The selected topics being highly competitive, it has also played an important role – together with the top quality of the offered intellectual environment and facilities - in attracting a very healthy cohort of motivated PhD students and young researchers from the whole Europe into the fusion field. Many achievements, not only scientific or technological results, but also strong connections among the partners, were actually key inputs for the HiPER project. To be visible and credible, IFE-oriented research must be conducted at a trans-national level; however, the currently operational large-scale laser facilities and the on-going (or planned) technological developments are (or will be) mainly funded on a national basis. To ensure complementarity and completeness, it is thus important that a European programme can provide mechanisms to support mobility, to foster collaborations, especially towards countries without nationally-funded initiatives, as well as information and staff exchanges. The EURATOM IFE KiT programme, funded at a reasonable level, is an adequate tool to achieve this goal. As IFE today combines science and engineering, such a programme will allow scientists to continue to go beyond the frontiers and contribute to improve our understanding of the ignition physics, as well as of the technologies required to build an IFE reactor; even if HiPER has already selected some of them, it will keep authorizing monitoring of alternatives, as critical scientific and engineering challenges still remain. Helping then assessing the fast-evolving IFE field and maintaining a good understanding of the scientific and technological issues by establishing a minimum viable level of capabilities and capacities (not below the current funding level, 25% lower than at the beginning of the FP7 programme), it will reinforce the European attractiveness and provide opportunities to broaden the Fusion community.

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