Working Group 6:

Laser-Plasma Acceleration of Ions

Leader: Sergei Tochitsky, UCLA

Co-leader: Manuel Hegelich, LANL

Abstract Index Buffechoux Bulanov d'Humières Fernandez Fluza Flippo Gaillard Helle Hur Jaekel Khudik Kiefer Maksimchuk Nishiuchi Pogorelsky Pomerantz Rossi Roth Schaumann Sentoku Sheng Steinke Wu Yan Zeil

Name of submitting author Sébastien Buffechoux Institution École Polytechnique, CEA, CNRS Email sebastien.buffechoux@polytechnique.edu Abstract Title Recent experimental results on laser driven proton

acceleration and concepts toward higher beams energies

Author/Affiliation listing S. Buffechoux1,2, M. Nakatsutsumi1, S. Fourmaux2, L. Romagnani1, M. Geissel3, L. Hurd1, H. Ieuji4, A. Kon4, P. Rambo3, M. Schollmeier3, Y. Sentoku5, R. Kodama4, P. Audebert1, J.C Kieffer2, H. Pépin2, G. Mourou6, J. Fuchs1 1LULI, École Polytechnique, CNRS, CEA, UPMC, route de Saclay, 91128 Palaiseau, France. 2INRS-EMT, 1650 Bd Lionel Boulet, Varennes, QC J3X 1P7, Québec, Canada. 3Sandia National Laboratory, Albuquerque, NM 87123, USA 4CREST, Japan Science and Technology Agency, 5-Sanbancho, Chiyoda-ku, Tokyo, Japan. 5Nevada Terawatt Facility, MS-372, University of Nevada, Reno, Nevada 89557, USA. 6IZEST, Ecole Polytechnique, Palaiseau, France Abstract The behavior of proton acceleration according to the pulse

duration was studied so as to clarify the relevance of ultra-short laser pulse facilities. Micro-focusing of ultra-intense laser light using plasma re-focusing mirrors was studied. We will present the newly launched IZEST project aimed at pushing forward a new laser technology.

Summary Currently the proton energy improvement is achieved by increasing the laser pulse energy, i.e. the laser facility size. The significant cost increase of these more powerful lasers reduces the relevance of this technology compared to conventional accelerators. Therefore, it is relevant to study approaches using Ti:sapphire technology which permit reaching comparable laser intensity (I = 1.1020 W.cm-2), thank to a short pulse duration, at a lower price while allowing a high repetition rate. This approach has been studied at the 200 TW laser Advanced Laser Light Source (ALLS) facility at INRS-EMT in Québec (Canada). We studied the behavior of proton acceleration according to the pulse duration so as to understand the optimum parameters for proton acceleration and clarify the relevance of ultra-short laser pulse facilities. Another approach that we studied was micro-focusing of ultra-intense laser light using plasma re-focusing mirrors [1]. It is observed that the resulting laser intensity increase allows pushing up the maximum energy of protons as well as the conversion efficiency from laser to protons. 2D-PIC simulations however reveal that in these conditions strong magnetic fields appear at the target rear-surface. Induced by pronounced electron sheath gradients, these fields affect detrimentally proton acceleration as the charged particles are bent during acceleration, and thus could represent a fundamental limitation when trying to push the proton energy. Finally, to push forward laser-driven ion beams for societal applications, laser development has also to be a strong research element. In this respect, we will present the newly launched IZEST project [2] aimed at pushing forward a new laser technology and demonstrating experimentally that very high-energy beams, of the order of what can be obtained with conventional accelerators, can be accessed with lasers. A pillar of the technology that will be pushed by IZEST will be plasma optics since to amplify, compress, or extreme light power, plasmas appear as a natural solution, being not limited, as conventional solid-state optics, by damage threshold issue, and being also extremely compact. [1] M. Nakatsutsumi et al. Opt. Lett.35, 2314 (2010). [2] www.izest.polytechnique.edu.

Name of submitting author Sébastien Buffechoux Institution École polytechnique, CEA, CNRS Email sebastien.buffechoux@polytechnique.edu Abstract Title Recent experimental results on focusing of high-

energy density proton beams and their interaction with solid targets

Author/Affiliation listing S. Buffechoux1,2, S. N. Chen1, M. Nakatsutsumi1, L. Romagnani1, P. Antici1, E. Brambrink1, C. A. Cecchetti3, E. d’Humières4, T. Kudyakov6, E. Lefebvre7, A. Pipahl6, Y. Sentoku8, T. Toncian6, M. Borghesi3, O. Willi6, R. Kodama5, P. Audebert1,H. Pépin2, J. Fuchs1. 1LULI, École Polytechnique, CNRS, CEA, UPMC, route de Saclay, 91128 Palaiseau, France. 2INRS-EMT, 1650 Bd Lionel Boulet, Varennes, QC J3X 1P7, Québec, Canada. 3School of Mathematics and Physics, The Queen’s University Belfast, Belfast BT7 1NN, U.K. 4Université de Bordeaux, CNRS, CEA, Centre Lasers Intenses et Applications, 33400, Talence, France ; 5CREST, Japan Science and Technology Agency, 5-Sanbancho, Chiyoda-ku, Tokyo, Japan. 6Heinrich Heine Universität Düsseldorf, D-40225 Düsseldorf, Germany 7CEA, DAM, DIF, 91297 Arpajon, France 8Nevada Terawatt Facility, MS-372, University of Nevada, Reno, Nevada 89557, USA. Abstract We will present recent results on the topic of the use

of proton beams for fast ignition of fusion targets. In particular, we studied the dynamics of laser-driven ion beams focusing using concave solid targets.

Summary We will present recent results on the topic of the use of proton beams for fast ignition of fusion targets. In particular, we studied the dynamics of laser-driven ion beams focusing using concave solid targets [1]. Using transverse proton radiography, most of the ion beam energy is observed to converge at the center of the cylindrical targets with a spot diameter of 30 µm, which can be very beneficial for applications requiring high beam energy densities. Also, unbalanced laser irradiation does not compromise the focusability of the beam. However, significant filamentation occurs during the focusing, potentially limiting the localization of the energy deposition region by these beams at focus. We also studied the issue of the interaction between the proton beam launched from the source foil and a wall, as will take place at the tip of the re-entrant cone in a proton-driven fast ignition target. We found there that by adjusting the distance between the wall and the source foil, we could tune the proton distribution that would cross the wall. [1] S.N. Chen et al., Phys. Rev. Letter. 108, 055001 (2012)

Name of submitting author Stepan Bulanov Institution University of California, Berkeley Email sbulanov@lbl.gov Abstract Title Optimized laser pulse profile for efficient

radiation pressure acceleration of ions Author/Affiliation listing S. S. Bulanov/University of California, Berkeley,

California 94720, USA C. B. Schroeder/Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA E. Esarey/Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA W. P. Leemans/Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA; Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

Abstract The RPA regime of ion acceleration requires high intensity laser. The requirement for the foil to be opaque leads to large acceleration distances in the ultrarelativistic regime. Proper profiling of the laser pulse can significantly reduce the acceleration distance, leading to a compact laser ion accelerator.

Summary We study the optimization of the RPA regime of ion acceleration, based on the analysis of the electromagnetic wave reflection by the thin foil. In order to ensure high efficiency of acceleration the foil should be opaque for radiation. The most efficient acceleration should happen at the threshold of the foil transparency/opacity. At this threshold the foil is opaque for radiation, but this opaqueness is ensured by the minimum possible number of ions. For relativistic energies of the foil the effect of relativistic opacity increases the effectiveness of acceleration. As the foil is accelerated to relativistic energies it becomes less transparent to radiation. We show that by utilizing a laser pulse with proper intensity profile it is possible to maintain the optimal acceleration conditions during all the interaction, i. e. the accelerated foil will be at the threshold of opacity/transparency for the incident laser pulse at each instant in time. This would lead to a significant reduction of the acceleration time, which will reduce the requirements on the laser pulse, providing a way to a more compact laser ion accelerator. In the conventional RPA scheme, the acceleration distance will pose a technological challenge, since it would be extremely difficult to have a very high intensity laser system that would provide a Raleigh length of the order of several millimeters. Another way of maintaining high intensity during the acceleration of the foil over the distance of several millimeters would be the utilization of some external guiding structure. In this case the group velocity of the laser pulse will be limited to the values smaller than the speed of light, and thus the ion energy will be limited to the value, corresponding to this group velocity. The profiling of the incident laser pulse offers a way to compact laser ion accelerator with relaxed requirements on the total laser pulse energy needed to achieve certain accelerated ion energy. Work supported by the NSF under Grant No. PHY-0935197 and the Office of Science of the US DOE under Contract No. DE-AC02-05CH11231.

Name of submitting author Prof. Emmanuel d'Humières Institution Univ. Bordeaux / CNRS / CEA - CELIA, Talence,

France. Email dhumieres@celia.u-bordeaux1.fr Abstract Title Laser ion acceleration in the ultra-high laser

intensity regime Author/Affiliation listing R. Capdessus - Univ. Bordeaux / CNRS / CEA -

CELIA, Talence, France. V. T. Tikhonchuk - Univ. Bordeaux / CNRS / CEA - CELIA, Talence, France.

Abstract Radiation losses of electrons in ultra-intense laser fields constitute a process of major importance when considering laser-matter interaction at ultra-high intensities. A study of the effect of radiation friction on the electron and ion dynamics in various regimes of ion acceleration is presented.

Summary Radiation losses of electrons in ultra-intense laser fields constitute a process of major importance when considering laser-matter interaction at ultra-high intensities. Radiation losses can strongly modify the electron (and in turns ion) dynamics, and are associated with intense and directional emission of high energy photons. Accounting for such effects is therefore necessary to obtain a correct modeling of electron and ion acceleration and creation of secondary photon sources at the forthcoming ultra-high power laser facilities. To account for radiation losses in the particle-in-cell code PICLS, we have introduced the radiation friction force obtained by Sokolov [1] using a renormalized Lorentz-Abraham-Dirac model. The associated angular and energy spectra of the radiated high-energy photons are also computed. A study of the effect of radiation friction on the electron and ion dynamics in various regimes of ion acceleration is presented [2]. A wide range of laser intensity, target thickness and target density is explored, allowing for the study of directed-Coulomb-explosion (DCE) of nanometric targets, radiation pressure acceleration (RPA) of thin foils, and hole-boring (HB) of semi-infinite targets. We will discuss the effect of radiation losses on the electron heating and accelerated ion energy spectrum. In particular, we will show that the piston velocity in the HB regime is reduced, and that its correct modeling requires to account for the high-energy photon momentum flux in the pressure balance [3]. The regime of low density targets has also been investigated. Finally, the angular and energy spectra of high-energy photons for all three overdense interaction regimes (DCE, RPA and HB) will also be discussed. 1. V. Sokolov et al, Phys. Rev. E 81, 036412. 2. R. Capdessus, et al., submitted to Phys. Rev. E, Modeling of radiation losses in ultra-high power laser matter interaction. E. d'Humières, et al., proceding IFSA 2011, Laser ion acceleration in the high laser energy and high laser intensity regimes. 3. R. Capdessus, et al., proceding IFSA 2011, Modeling of radiation losses for ion acceleration at ultra-high laser intensities.

Name of submitting author Prof. Emmanuel d'Humières Institution Univ. Bordeaux / CNRS / CEA - CELIA, Talence,

France. Email dhumieres@celia.u-bordeaux1.fr Abstract Title Laser ion acceleration scaling laws with low

density targets Author/Affiliation listing S. G. Bochkarev Physics Institute, Russian Academy

of Sciences, Moscow, Russia. V. T. Tikhonchuk Univ. Bordeaux / CNRS / CEA - CELIA, Talence, France.

Abstract Laser driven sources of high energy ions have many promising applications. Using PIC simulations and Vlasov-Poisson simulations, we have studied in detail laser ion acceleration using low density plasmas and obtained scaling laws. Very efficient ion acceleration can be achieved in this regime.

Summary Laser driven sources of high energy ions have applications in plasma and fusion science as an electromagnetic field probe and may find other applications in medical science and laboratory astrophysics. These sources commonly use thin solid foils, and ions are accelerated at their rear side in the electrostatic field created by hot electrons. Gaseous targets can also produce ion beams with characteristics comparable to those obtained with solid targets. By adjusting the laser and plasma parameters, a two-step acceleration process can be triggered using low density plasmas: first, ions are accelerated in volume by electric fields generated by hot electrons, second, the ion energy is boosted in a strong electrostatic shock propagating along the descending density profile [1]. Very efficient ion acceleration can be achieved and this regime constitutes a promising alternative to schemes involving high density targets. The obtained proton spectra ar e broad due as the acceleration mechanism relies on electron heating by the laser. Large amplitude magnetic field affect the first step of the process and the directionality of the beam. Using Particle-In-Cell simulations and Vlasov-Poisson simulations, we have studied in detail ion acceleration with high intensity laser pulses interacting with low density plasmas [2]. Scaling laws for the maximum proton energy, maximum number of accelerated protons and beam divergence in this regime were obtained and are used to discuss the possibility to highlight this regime experimentally using nowadays laser setups. Recent experimental results obtained at LULI will be discussed. The influence of the laser wavelength has also been investigated and the possibility to use CO2 lasers to study this regime is discussed. The strong electrostatic shock launched during this process is easy to control and can be applied to study low velocity astrophysical shocks relevant to supernovae explosions and gamma ray bursts. 1. E. d'Humières et al., J. Phys.: Conf. Ser. 244, 042023 (2010). E. d’Humières et al., MOP153, PAC11 proceedings 2011. 2. E. d'Humières et al., Eur. Conf. Abstracts 35G, P5.005 (2011).

Name of submitting author Dr. Juan C. Fernandez Institution Los Alamos National Laboratory Email juanc@lanl.gov Abstract Title TOWARDS ISOCHORIC HEATING WITH

IONS: FROM SOLID-PLASMA INTERACTIONS TO FAST IGNITION

Author/Affiliation listing J. C. Fernández1, B. J. Albright1, J. F. Benage1, D. C. Gautier1, B. M. Hegelich1, J. J. Honrubia2, C.-K. Huang1, D. Jung1, S. A. Letzring1, S. Palaniyappan1, R. C. Shah1, L. Yin1, H.-C. Wu1 1. Los Alamos National Laboratory, Los Alamos, New Mexico, USA 87545 2. ETSI Aeronáuticos, Universidad Politécnica de Madrid, 28040-Madrid, Spain

Abstract Isochoric heating of matter with laser-driven ion beams is emerging as a key experimental capability for a broad range of for research at Los Alamos. We highlight two general unsolved problems that can be addressed with this technique, at two vastly temperatures and densities: particulates in plasmas, and Fast Ignition.

Summary Isochoric heating of matter and plasmas is emerging as a key experimental capability under development for a broad range of for research at Los Alamos. Specifically, there are experiments and applications where a high-very high power density must be delivered to create a configuration, much quicker than it can disassemble either hydrodynamically, or by transport of the heat away from the volume being heated. Depending on the size and the temperatures, the disassembly time can range from tens of ps to sub-ns. At Los Alamos, we build on progress in developing laser-driven ion beams, which are created in ps timescales with high currents, thus providing arguably the best tool for depositing the largest power densities. In this presentation, we highlight two general unsolved problems that can be addressed with this technique, at two vastly different points in temperature and density. One is the evolution of solid particulates in a low-temperature ( ~ eV) plasma, and the other is the creation of the hot spot in a compressed DT capsule for Fast Ignition (FI). The evolution of solid particles in plasmas is germane to situations as diverse as comet tails and the plasma-wall interface of a magnetized-target fusion implosion. There are several theories for the evolution of such particulates, which lead to very different predictions. The other problem, FI, is very challenging, requiring the creation of a ~ 5keV, ~ (40 µm)^3 hot spot near the core of DT fuel previously compressed to a density of ~ 500 g/cm^3 and an areal density of ~ 3 g/cm^2, in order to ignite. We propose to ignite with a laser-driven, quasi-monoenergetic C-ion beam at ~ 450 MeV. In this paper, we summarize the scientific unknowns that arise in these respective regimes. We present experimental concepts to study these problems, and discuss the requirements for success of the experiment/application, especially for the isochoric ion driver. We summarize our progress with various laser-driven ion acceleration schemes. This work motivates our recent for the High Intensity Laser Laboratory (HILL) facility to NNSA. We will briefly describe the requirements for HILL and the resulting concept for the facility.

Name of submitting author Frederico Fiuza Institution GoLP/Instituto de Plasmas e Fusão Nuclear – LA,

Instituto Superior Técnico Email frederico.fiuza@ist.utl.pt Abstract Title 200 MeV monoenergetic protons produced by a

laser-driven collisionless shock Author/Affiliation listing F. Fiuza / GoLP, Instituto de Plasmas e Fusão

Nuclear - LA, Instituto Superior Técnico (Portugal) A. Stockem / GoLP, Instituto de Plasmas e Fusão Nuclear - LA, Instituto Superior Técnico (Portugal) E. Boella / GoLP, Instituto de Plasmas e Fusão Nuclear - LA, Instituto Superior Técnico (Portugal) R. A. Fonseca / GoLP, Instituto de Plasmas e Fusão Nuclear - LA, Instituto Superior Técnico (Portugal) L. O. Silva / GoLP, Instituto de Plasmas e Fusão Nuclear - LA, Instituto Superior Técnico (Portugal) D. Haberberger / UCLA S. Tochitsky / UCLA C. Gong / UCLA W. B. Mori / UCLA C. Joshi / UCLA

Abstract We derive the optimal conditions for electrostatic shock formation and ion acceleration in laser heated plasmas. Our results show the possibility of generating monoenergetic 200 MeV proton beams for medical applications with 100 TW class lasers.

Summary The study of electrostatic shock formation and ion acceleration is relevant not only to understand the physical processes associated with these nonlinear structures in space, but also to explore the potential generation of high energy and high quality shock accelerated ions for applications such as tumor therapy or radiography. We have extended previous theoretical work on electrostatic shocks from the interaction of plasmas with different densities and temperatures [1], to derive optimal conditions for ion reflection. Moderate Mach number shocks are shown to be formed and to accelerate ions to high energies and with high quality in the interaction of strongly heated plasmas with significantly different densities. Multi-dimensional particle-in-cell simulations were used to explore the possibility of creating these optimal conditions for ion acceleration in laboratory from the interaction of lasers with plasmas. We show that critical density plasmas allow on-the-one-hand for the strong electron heating required to accelerate ions to high energies and on-the-other-hand to generate sharp density variations, from the laser-induced density steepening at the critical density surface, that trigger shock formation and ion acceleration. Moreover, we show that in order to preserve the high quality of the shock accelerated ions it is essential to control the TNSA fields at the back of the target, and that this control can be achieved by using a tailored plasma with an exponentially falling density profile. Our results demonstrate the possibility of using this scheme to generate 200 MeV proton beams with an energy spread of 10% with 100 TW class lasers [2].

Name of submitting author Dr. Kirk Flippo Institution Los Alamos National Laboratory Email kflippo@lanl.gov Abstract Title High Energy Density Science and Laser Particle

Acceleration: From Isotopes to Fusion Author/Affiliation listing J. A. Cobble, D. S. Montgomery, D. T. Offermann, J.

Ren, T. J. Kwan, M. J. Schmitt Los Alamos National Laboratory; S. A. Gaillard; T. Kluge, M. Bussmann, T. E. Cowan HelmhotzZentrum Dresden-Rossendorf,GERMANY; B. Gall, S. Kovaleski University of Missouri, Columbia; D. Rose, D. Welch Voss Scientific, Albuquerque, NM

Abstract High energy density science and the creation and applications of intense ion, electron, and neutron beams an sources from short-pulse laser systems will be discussed in the context of work at Los Alamos, Sandia, and the Texas PW, as well as our efforts to understanding the focusing of these beams.

Summary In the realm of high energy density science, laser-plasma accelerated ion and electron beam sources is a developing field with vast prospects and the promise of enabling many superior applications in a variety of fields such as hadron cancer therapy, compact radioisotope generation, table-top nuclear physics, laboratory astrophysics, nuclear forensics, waste transmutation, special nuclear material (SNM) detection, and inertial fusion energy. The European Union is currently spending almost a billion €’s as part of its Extreme Light Infrastructure (ELI). The US has yet to commit any such resources to develop large facilities like these, but does support the basic science behind those same pillars, having adopted a wait and see attitude, likely to follow suit with facilities in the future. LANL has been at the forefront of this science effort, engaged for many years now in several projects seeking to develop compact high current and high energy laser ion and electron sources. We have been especially active in three specific applications: ion fast ignition using deuterons, neutrons for SNM detection for homeland security, and radiation oncology/nuclear medicine in conjunction with our partners. Laser-to-beam conversion efficiencies of over 10% are needed for practical applications, and we have already shown inherent efficiencies of >5% from flat foils using our 200TW Trident laser with only a 5th of the intensity and energy of the Nova Petawatt. With clever target designs, like structured curved cone targets and diamond hemi targets, we have been able to improve ion energies and show the non-ballistic nature of the focusing. The significant ion yields of these beams will pave the way toward our intended applications. In addition to cone targets and hemispherical diamond focusing targets, we are developing in partnerships a new near-critical density and solid density cluster deuterium targets for ion and electron acceleration to tailor the ion energy and lead to staging of acceleration for further increases in energy, efficiency and improved beam characteristics.

Name of submitting author Dr. Sandrine Gaillard Institution Private Contractor Email sandrine.gaillard@gmail.com Abstract Title HIGH PROTON ENERGIES FROM LASER

INTERACTION WITH MICRO-CONE AND REDUCED MASS TARGETS

Author/Affiliation listing K. A. Flippo, D. Offermann, J. Ren, F. Archuleta, R. Gonzales, T. Hurry, R. P. Johnson, S-.M. Reid, T. Shimada ; Los Alamos National Laboratory M. Schollmeier, A. Sefkow, M. Geissel Sandia National Laboratories B. B. Gall ; University of Missouri, Columbia M. Bussmann, T. Kluge, T. Burris-Mog, T. E. Cowan HelmholtzZentrum Dresden-Rossendorf

Abstract Laser-accelerated protons with energies >75 MeV were obtained using specialized targets at the LANL 200 TW Trident short-pulse (1 µm wavelength, 80-100 J, ~600 fs, ~10^20 W/cm2) high contrast (>10^10) laser. The ion beams were diagnosed with various detectors, the caveats of which will also be discussed.

Summary We have conducted laser-ion acceleration experiments using the Trident short-pulse laser at ~10^20 W/cm^2 and high contrast to elucidate the production of hot electrons and ions from a variety of targets, and link proton performance to laser pre-pulse interaction. For regular size flat foils (~2 mm by 2 mm), energies of 50 MeV were obtained, while for reduced mass targets (50 µm to 500 µm diameter) we obtained proton energies in excess of ~75 MeV and for micro-cone targets [1,2], in excess of ~67 MeV. 2D PIC simulations have identified a mechanism [3] in the cone distinct from optical collection and electron guiding predicted for conical targets from previous work [1,4]. That mechanism, which increases the hot electron population by Direct Laser Light Pressure Acceleration of electrons along the cone wall surface when the laser interacts at grazing incidence, will be discussed in the context of the ion beam performance. In addition, the laser pre-pulse and pre-plasma characteristics and effects will be presented from a 3D point of view. During experiments, to diagnose the ion beam, we use a Thomson parabola, an electron spectrometer with image plates, and a RadioChromic Film stack. General use and characteristics of the diagnostics will be discussed, and the proton spectra and beams recorded in RCF will be shown. [1] Increased Efficiency and Energy of Laser-Accelerated Protons Using Novel Cone Targets, K. A. Flippo, E. d’Humières, S. A. Gaillard et al., Physics of Plasmas, 15, 5 (2008). [2] Increased Laser-Accelerated Proton Energies via Direct Laser-Light-Pressure Acceleration of Electrons in Micro-Cone Targets, S. A. Gaillard, T. Kluge, K. A. Flippo et al., Physics of Plasmas, 18, 056710 (2011). [3] High Proton Energies from Cone Targets: Electron Acceleration Mechanisms, T. Kluge, S. A. Gaillard, K. A. Flippo et al., New J. Physics 14 023038 (2012). [4] Laser light and hot electron micro focusing using a

conical target, Y. Sentoku, K. Mima, H. Ruhl et al., Physics of Plasmas 11, 3083 (2004).

Name of submitting author Dr. Michael Helle Institution U.S. Naval Research Laboratory Email mike.helle@nrl.navy.mil Abstract Title Laser Ion Acceleration from Sub-Critical Density

Gas Foil Author/Affiliation listing Michael Helle, Daniel Gordon, Dmitri Kaganovich,

and Antonio Ting U.S. Naval Research Laboratory

Abstract Laser acceleration of ions is typically achieved using an optically thin, over-dense layer of plasma. At optical wavelengths this has meant the use of solid targets that limit repeatability. We will present the development of a “gas foil” target that operates at high rep rates, high gradients, and sub-critical densities.

Summary For over a decade, high-energy ions have been accelerated by means of laser-solid target interactions and more recently by means of a CO2 laser interacting with gas jets that yield critical density plasmas. The advantages of gas targets are that they are relatively simple and can be operated at high repetition rates. However, they typically operate at densities far below those required for optical wavelengths, where most of the world’s terawatt lasers operate, and have long gradients that complicate laser propagation and ion acceleration. To get around these issues, a new type of target, a “gas foil,” is being developed at the Naval Research Laboratory. The target is created using a gas jet and introducing an optically driven hydrodynamic shock into the supersonic gas flow. Experiments have shown that a laser-ignited shock in hydrogen is capable of producing 4 times ambient. The SPARC module of turboWAVE has been used to model the shock dynamics and has shown that even higher peak densities can be reached using a colliding shock scheme. These results have been incorporated into 3D PIC simulations. Results for a moderate power of 20 TW yielded protons with energies in excess of ~2 MeV. The hydrodynamic and PIC simulations as well as the preliminary experimental results will be discussed. *This work is supported by the Naval Research Laboratory Base Program, the Department of Energy, and by NERSC

Name of submitting author Dr. Min Sup Hur Institution UNIST Email mshur@unist.ac.kr Abstract Title Pulse shaping by relativistic transparency in an

overdense plasma and its applications in particle accelerations

Author/Affiliation listing Min Sup Hur/UNIST Youngkuk Kim/UNIST Inhyuk Nam/GIST V.V. Kulagin/Moscow State University Hyyong Suk/GIST

Abstract By two-dimensional simulations, we studied laser pulse shaping by relativistic transparency in an overdense plasma. From properly tapered plasma slab, the transverse shape of the pulse could be controlled. We discuss the usage of the shaped pulse in ion acceleration and electron mirror generation.

Summary From a series of one-dimensional simulations and a few two-dimensional simulations, we obtained a semi-phenomenological formula for the channel-digging speed of the relativistic transparency in an overdense plasma. The one-dimensional formula was found to be well applied even for the two-dimensional cases, from which the transverse shape of the laser pulse could be predicted. By using an overdense plasma slab tapered transversely in its density of thickness, it was possible to generate a sharp-cut and concave laser pulse front. Such a specially shaped pulse can possibly used in ion beam focusing, and generating concave electron mirror for X-ray focusing. We present diverse PIC simulations with some preliminary results of the effects of the shaped pulse in ion acceleration and concave mirror.

Name of submitting author Oliver Jäckel Institution Helmholtz-Institut Jena Email address oliver.jaeckel2@uni-jena.de Abstract Title Foil thickness scans at JETI and POLARIS – from

TNSA to radiation pressure assisted ion acceleration Author/Affiliation listing Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena,

Germany

Abstract An extensive study explores the influence of the target thickness and material in laser-driven ion acceleration from 50µm down to 0.4µm ranging from Aluminium to Tantalum at Polaris. With the high contrast JETI system even 2nm DLC foils have been used and for 15nm hydrocarbon foils signatures of radiation pressure assisted acceleration were detected.

Summary Two regimes of laser-based ion acceleration are currently investigated in the community. These are on the one hand the well established target normal sheath acceleration (TNSA) and on the other hand the encouraging radiation pressure (assisted) acceleration (RPA). For further improvements the first mainly relies on the enhancement of the laser pulse’s energy while the latter requires sufficient laser contrast at enhanced laser intensities. In Jena, two high intensity lasers are available: JETI and POLARIS which are high contrast and high power lasers, respectively. Both were used to perform material and thickness scans for the entire target foils deployed in ion acceleration experiments ranging from 50...0.4 µm (10 steps) and from Aluminium to Tantalum (5 steps). At the POLARIS system an extensive material and thickness study was carried out to characterise the TNSA process in a more general manner and to provide a data set for precise comparisons to theoretical descriptions. With the JETI laser a pulse contrast in the 10^12 range was reached using a plasma mirror. Here, it was possible to extend the thickness scan for diamond like carbon foils down to 2 nm. Using 15 nm multi species hydrocarbon foils RPA signatures became visible but not for comparable DLC or different hydrocarbon thicknesses. These results will be discussed in the focus of stability studies for radiation pressure assisted acceleration from multi species foils.

Name of submitting author Vladimir Khudik Institution University of Texas at Austin Email vkhudik@physics.utexas.edu Abstract Title Rayleigh-Taylor instability in RPA regime of the

monoenergetic ion acceleration by the laser pulse. Author/Affiliation listing V. Khudik, Univ Texas Austin, Dept Phys, Austin,

TX 78712 USA, S.A. YI, G. SHVETS.

Abstract A self-consistent kinetic model of the target with distributed electron and ion densities irradiated by the circular polarized chirped laser beam is developed for the case of constant target acceleration. It is shown in the fluid approximation that the irradiated target with distributed density is still susceptible to Rayleigh-Taylor instability.

Summary Dynamics of acceleration of the ion target irradiated by a circularly polarized chirped laser pulse is studied analytically and via particle-in-cell (PIC) simulations. A self-consistent analytical model of the target with finite thickness is developed. In this 1-D kinetic model, target parameters are stationary in the center of mass of the system, and electrons are bouncing in the potential well formed by the laser ponderomotive and electrostatic potentials. They are distributed in the direction of acceleration by the Boltzmann law and over velocities by the Maxwell-Juttner law. The laser pulse interacts directly only with electrons in a thin sheath layer, and these electrons transfer the laser pressure to the target ions. In the fluid approximation it is shown that despite the distribution of the density in space, the target is still susceptible to the Rayleigh-Taylor instability [1]. Using PIC simulations we found the growth rate of initially seeded perturbations as a function of their wavenumber for different target parameters and compare it with analytical results. Useful scaling laws between this rate and laser pulse pressure and target parameters are discussed. Also, specially designed numerical experiments are performed to reveal difference between instabilities of the accelerated target and Rayleigh-Taylor instability. [1] T.P. Yu, A. Pukhov, G. Shvets, M. Chen, T. H. Ratliff, S. A. Yi, and V. Khudik, Phys. Plasmas, 18, 043110 (2011).

Name of submitting author Daniel Kiefer Institution Ludwig-Maximilians-University Munich (LMU) / Max Planck

Institute of Quantum Optics (MPQ) Email daniel.kiefer@mpq.mpg.de Abstract Title Laser-Ion Acceleration and Biomedical Application with

Shortest Pulses Author/Affiliation listing Jianhui Bin 1,2, Klaus Allinger 1,2, Walter Assmann1, Günther

Dollinger3, Guido A. Drexler4, Anna A. Friedl4, Dieter Habs1, Peter Hilz1, Rainer Hoerlein2, Nicole Humble5, Stefan Karsch 1,2, Konstantin Khrennikov2, Daniel Kiefer2, Ferenc Krausz 1,2, Wenjun Ma1, Dörte Michalski5, Michael Molls5, Sebastian Raith1, Sabine Reinhardt1, Barbara Röper5, Thomas E. Schmid5, Toshiki Tajima1, Johannes Wenz2, Olga Zlobinskaya5, Joerg Schreiber 1,2 and Jan J. Wilkens5 1.Faculty of Physics, Ludwig-Maximilians-Universität München 2. Max Planck Institute of Quantum Optics, Garching b. München 3. Institut für Angewandte Physik und Messtechnik (LRT2), Universität der Bundeswehr München 4. Department of Radiation Oncology, Ludwig-Maximilians-Universität München 5. Department of Radiation Oncology, Technische Universität München, Klinikum rechts der Isar

Abstract The application of nanometer thin foils constitutes a quantum leap for laser-ion acceleration. A 100-fold enhanced proton flux as compared to TNSA enabled exposure of tumor cells to single 1ns proton bunches with up to 8 Gy on the verge of entering a new era for laser-based radiobiological studies.

Summary After more than one decade of successful operation at the Max Planck Institute for Quantum Optics, the Advanced Titanium-Sapphire Laser (ATLAS) system has been dismantled and is currently transferred to its new, temporary home, the Laboratory for Extreme Photonics (LEX). This move will allow us to upgrade the peak power from currently 60 TW to 300 TW before it can take on its final upgrade to 3 PW at the Centre for Advanced Laser Applications (CALA), possibly constituting one of the world’s most powerful laser systems. The opportunities are manifold. GeV-electron bunches with a few femtoseconds pulse duration will be available routinely and in turn enable for the generation of even shorter light, UV, X- and Gamma-ray pulses. The high laser pulse energy (60J) paired with the short duration (20fs) will allow to access light intensities of up to 1023W/cm2 and address fundamental questions of modern physics. One major prospect, however, is t he generation of ion bunches with energies beyond 100 MeV/u, sufficiently high to approach and investigate their applicability in tumor therapy. I will explain various concepts of laser-driven ion acceleration that have been employed and studied over the past years. At present, the application of nanometer thin foils seems to be most promising both in terms of achieving highest energy and conversion efficiency. The demands on the quality and control of the laser pulses, mainly in terms of the suppression of pre-pulses, are enormous. Despite of these difficulties, we could demonstrate first biological studies with tumor cells irradiated by laser accelerated proton bunches with single shot doses of several Gray in 2011. This demonstration has been a major milestone of our research. Moreover, the combined efforts in laser, target and detector development disclosed a number of new and partially surprising insights that constitute my excitement for this field of physics and motivate for the future challenges and possibilities that await us.

Name of submitting author Dr. Anatoly Maksimchuk Institution University of Michigan Email tolya@umich.edu Abstract Title PARAMOUNT DEUTERON ACCELERATION

AND GENERATION OF NEUTRON BEAMS USING HIGH-INTENSITY SHORT LASER PULSES

Author/Affiliation listing A. Maksimchuk1, F. Dollar1, G. M. Petrov2, A. Raymond1, L. Willingale1, F. Yu1, C. Zulick1, J. Davis2, and K. Krushelnick1 1.Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109 2.Naval Research Laboratory, Plasma Physics Division, Washington, DC 20375

Abstract The results of the experiments on preferential deuteron acceleration from a heavy water ice covered copper target and subsequent experiments on neutron generation from d-d and d-Li reactions in a pitcher-catcher geometry will be presented.

Summary Neutron production using high energy protons or deuterons from p-Li or d-Li reactions are superior in terms of the number and directionality compared to that from d-d reactions [1]. These schemes require a pitcher-catcher target geometry instead of using laser-driven fusion neutron production d (d,n)3He from bulk deuterated plastic targets. The experiments performed with the 400 fs, 10 TW T-cubed laser focused to a maximum intensity of up to 3.10^19 Wcm-2 onto bulk, deuterated plastic targets which produced neutrons beamed preferentially in the laser propagation direction with a flux of 2.10^4 neutrons/J/steradian [2]. In recent experiments, we cryogenically cooled a 10 micron thick Cu target down to -165ºC and sprayed the vicinity of the target with heavy water that resulted in formation of thin heavy water ice layer which overcoats the H-containing contaminants on the surface of the Cu. We found a regime when the pulsed spraying increas ed the deuteron signal by more than 10 times compared to deuterated plastic coated targets and allowed deuterons to be the paramount acceleration species with maximum energy up to ~ 8 MeV. We carried out the following experiments on neutron generation in which the results of neutron production from pitcher-catcher d-Li reaction were compared to that of the bulk d-Li target. The performed PIC simulations provided insight into the deuteron acceleration process and confirmed the importance of the front side deuteron acceleration from heavy water ice coated targets. This work was supported by DTRA and the NRL. [1] J. Davis et al., Plasma Phys. Controlled Fusion 52, 045015 (2010) [2] L Willingale et al., Phys. Plasmas 18, 083106 (2011).

Name of submitting author Dr. Mamiko Nishiuchi Institution Japan Atomic Energy Agency Email nishiuchi.mamiko@jaea.go.jp Abstract Title Proton acceleration up to 40 MeV with Ultra-High

Intensity High-Contrast Ti;Sappire Compact Laser System

Author/Affiliation listing Mamiko Nishiuchi, Koichi Ogura, Alexander S. Pirozhkov, Tsuyoshi Tanimoto, Akito Sagisaka, Timur Zh Esirkepov, Masaki Kando, Hiromitsu Kiriyama, Takuya Shimomura, Shyuji Kondo, Shuhei Kanazawa, Yoshiki Nakai, Hajime Sasao, Fumitaka Sasao, Yuji Fukuda, Hironao Sakaki, Masato Kanasaki, Akifumi Yogo, and Kiminori Kondo Japan Atomic Energy Agency, Kansai Institute, 8-1, Umemidai, Kizugawa, Kyoto 619-0215, Japan

Abstract Protons are accelerated up to 40MeV from the interaction between the laser pulses from compact laser system and the mm-thick tape target. The laser parameters are 800 nm in wavelength, 40 fs of pulse width, 7 J of energy, 1010 contrast and > 1021Wcm-2 of peak intensity.

Summary Since the first observation of the energetic ion beam from the interaction between the Ultra-high intensity short pulse and solid density target [1], many experimental efforts have been extensively made in all over the world in order to extend the maximum energy of ions. In the past decade, the highest ion energy recorded is 120 MeV for the sub-ps laser pulse from relatively large laser system [2] and 25 MeV for the compact Ti:Sapphire laser system which can deliver repetitive ≾ 100fs laser pulses [3]. Here in this paper we present the extension of the maximum energy of protons from the interaction between the short-pulse compact laser system and soild thin-foil target. The laser pulses with parameters of 800 nm in wavelength, 40 fs of pulse width, 7 J of energy, 1010 contrast are focused onto the target with the peak intensity of more than 1021Wcm-2, which is also well confirmed by the measured electron temperature of 16 MeV. The Al-0.8 mm-thick or SUS-2.5mm-thick targets are irradiated from 45 degrees incidence angle. The observation of the proton beam is conducted with CR-39 stack detector set at the rear side of the target 55 mm downstream. The direction of the higher energy protons are deflected away from the target normal direction for Al-0.8mm-thick target. The most probable explanation of this is due to the deformation of the target shape caused by the ASE pedestal pulse component [4]. This achieved 40MeV energy with the efficiency of 0.1 % (>15MeV) of the proton beam obtained by the combination with relatively compact repetitive laser pulses and the simple foil target indicates the potential for future laser-driven ion accelerator systems. [1] R.A. Snaverly et al., “Intense High-Energy Proton Beams from Petawatt-Laser Irradiation of Solids” Phys. Rev. Lett., vol. 85, 2945-2948 (2000). [2] Physics Flash September 2011 [3] A.J. Mackinnon et al., “Enhancement of Proton Acceleration by Hot-Electron Recirculation in Thin Foils Irradiated by Ultraintense Laser Pulses”, Phys. Rev. Lett., vol. 88, 215001-1-4 (2002). [4] O. Lundh et al., “Influence of shock waves on laser-driven proton acceleration”, Phys. Rev. E., vol 76, 026404-1-8 (2007).

Name of submitting author Dr. Igor Pogorelsky Institution Brookhaven National Laboratory Email igor@bnl.gov Abstract Title Optical probing of shocks driven into over-critical

plasmas by laser hole-boring Author/Affiliation listing N. P. Dover1, C. A. J. Palmer1, M. Babzien2, A. R. Bell3,

A. E. Dangor1, T. Horbury1, M. N. Polyanskiy2, J. Schreiber1, S. Schwartz1, P. Shkolnikov4, V. Yakimenko2, I. Pogorelsky2, and Z. Najmudin1 1 Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom 2 Accelerator Test Facility, Brookhaven National Laboratory, NY 11973, USA 3 Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom, and 4 Stony Brook University, Stony Brook, NY 11794, USA

Abstract We present our observations of the interaction of an intense CO2-laser pulse with near-critical overdense plasmas. Using transverse optical probing, we observed the recession of the front surface driven by hole-boring by the laser pulse, and the resulting radiation pressure driven collisionless shocks. The observations are supported by PIC simulations.

Summary This paper details our study of a shock driven into minimally over-critical plasma by laser hole-boring. The experiment was undertaken at the Accelerator Test Facility at Brookhaven National Laboratory using a circularly polarized infrared (CO2) laser, for which nc =1019cm-3, i.e., > 100 times lower than that for optical wavelengths. This selection allowed us to use gas jets as a target, as well as supporting the direct optical probing of the plasma. The probe, a frequency-doubled (532 nm) Nd:YAG laser, passed orthogonally through the plasma before being split; we imaged one part directly onto a CCD for shadowgraphy to reveal non-uniformities; the other went to a Mach-Zender interferometer, for diagnosing the plasma’s density. By varying the timing of the probe relative to the drive pulse, we explored the evolution of the shock, identifying three separate phases. Initially (the 1st stage), hole-boring creates an electrostatic double layer that accelerates background ions. Once the laser stops, reflection of particles from the propagating double layer decelerates it rapidly. The structural transitions into a solitary ion acoustic-wave, continues to slow in the cooling plasma (2nd stage). As the speed of the shock declines (3rd stage), the ion mean-free-path also decreases and the shock eventually becomes collisional. In considering the interaction as a source for a laser plasma\ ion accelerator, there is a tradeoff between the higher maximum energies attained from a hotter plasma, wherein a small fraction of the particles are accelerated up to higher energies, and the higher efficiency from a colder plasma where all the particles are accelerated to a smaller maximum energy. This reciprocation explains the larger flux of accelerated protons observed with a short, circularly polarized laser pulse [1], compared to a longer, linearly polarized driver where heating is stronger [2]. These findings are supported by our particle-in-cell (PIC) simulations.

1. C. A. J. Palmer et al., Phys. Rev. Lett., 106, 014801 (2011). 2. D. Haberberger et al., Nat. Phys., 8, 1 (2012).

Name of submitting author Dr. Ishay Pomerantz Institution The University of Texas at Austin Email ipom@ph.utexas.edu Abstract Title Laser Acceleration of Protons Using Nano

Structured Plasma Author/Affiliation listing E. Schleifer

Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel I. Pomerantz Department of Physics, University of Texas at Austin, Texas 78712, USA E. Nahum, S. Eisenmann, M. Botton, A. Zigler Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel

Abstract We report on the first generation of 5.5–7.5 MeV protons by a moderate-intensity short-pulse laser (~5 10^17 W/cm^2, 40 fsec) interacting with frozen H2O nanometer-size structure droplets deposited on a sapphire substrate. In this setup, the laser intensity is locally enhanced by the snow nanowire, leading to high spatial gradients.

Summary The ability to generate fast protons from small and relatively inexpensive systems is of great importance to many applications such as medical radiation treatment and others. Target structuring is considered as one of the possible ways towards this goal. Nano-structured solid or quasi-solid targets attract significant attention. The presented scheme of using H2O “snow” nano-wires can relieve the demand for very high laser intensities, thus reducing the size and the cost of laser systems [1-4]. Usually ultra high intensity laser beams produce protons above the MeV energy level when the multi-terawatt scale laser facility provides intensity on the target which is at least 10^18 − 10^19W/cm^2 and the beam irradiates targets such as thin-foils or gas jets. In this study, we examined the ability to achieve the same proton energy range with use of relatively modest laser intensity (10^17W/cm^2) and a nano-structured H2O target. In this present experiment, we used frozen H2O deposited on Sapphire.In this setup, the plasma near the tip of the nano-wire is subject to locally enhanced laser intensity with high spatial gradients, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced, and protons are accelerated to MeV-level energies. Nano-wire engineered targets will relax the demand of peak energy from laser based sources. [1] A. Zigler, T. Palchan, N. Bruner, E. Schleifer et al., Phys. Rev. Lett. 106, 134801 (2011). [2] N. Bruner, E. Schleifer et al., Nucl. Instr. and Meth. A (2010). [3] T. Palchan, S. Pecker, Z. Henis, S. Eisenmann, and A. Zigler, Appl. Phys. Lett. 90 041501 (2007). [4] T. Palchan, et al., Appl. Phys. Lett. 91 251501 (2007)

Name of submitting author Mr. Francesco Rossi Institution Dipartimento di Fisica, Università di Bologna and

INFN Sezione di Bologna Email mail.francesco.rossi@gmail.com Abstract Title Transport of laser generated protons and post-

acceleration by a compact linac Author/Affiliation listing S. Sinigardi, P. Londrillo, F. Rossi, M. Sumini, G.

Turchetti Dipartimento di Fisica, Università di Bologna and INFN Sezione di Bologna D. Giove, C. De Martinis Dipartimento di Fisica, Università di Milano and INFN Sezione di Milano

Abstract We propose a hybrid acceleration scheme of laser interaction with a near-critical density layer on a metal foil, a solenoid to focus and select 30MeV protons with 1MeV spread and a high-field linac for post-acceleration up to 60MeV. Start-to-end 3D simulations give 10^7 protons per shot, an intensity adequate for medical use.

Summary We propose a hybrid acceleration scheme based on laser target interaction, a transport line and a compact linac. Our results are based on a start to end 3D simulation of the process. A laser beam of intensity 2 10^21 W/cm2 interacting with a near critical density layer deposited on a metal foil on the illuminated side allows to accelerate, in the TNSA regime, a proton beam with average energy above 7 MeV . A transport line based on a high field pulsed solenoid is used to focus a beam of 30 MeV protons with a 1 MeV spread and adequate intensity by selecting them with a collimator placed on the their focus. As a result over 10^7 protons are available for injection and post acceleration on a 3GHz compact linac which rises their energy up to 60 MeV. Supposing a 10 Hz frequency can be reached the dose deposited in a couple of minutes would be adequate for irradiation of small superficial tumors. * K. Zeil, S. D. Kraft, S. Bock, M. Bussmann, T. E. Cowan, T. Kluge, J. Metzkes, T. Richter, R. Sauerbrey, and U. Schramm, New Journal of Physics 12 (2010). * I. Hofmann, J. M. ter Vehn, X. Yan, A. Orzhekhovskaya, and S. Yaramyshev, Phys. Rev. Spec. Top. Acc. and Beams 14 (2011). * I. Hofmann, A. Orzhekhovskaya, S. Yaramyshev, M. Roth, and M. Droba, in Proceedings of HIAT09, Venice ITALY (2009). * M. Schollmeier, S. Becker, M. Gei?el, K. A. Flippo, A. Bla?zevi?c, S. A. Gaillard, D. C. Gautier, F. Gr ���uner, K. Harres, M. Kimmel, et al., Phys. Rev. Lett. 101 (2008) * V. G. Vaccaro, M. R. Masullo, C. DeMartinis, L. Gini, D.Giove, A. Rain?o, V. Variale, L. Calabretta, A. Rovelli, S. Barone, et al., in Proceedings of Linear Accelerator Conference LINAC2010, Tsukuba, Japan (2010).

Name of submitting author Dr. Markus Roth Institution Technische Universität Darmstadt / Los Alamos

National Laboratory Email markus.roth@physik.tu-darmstadt.de Abstract Title Laser-driven ion accelerators as an advanced

source for medical applications Author/Affiliation listing Markus Roth

Technische Universität Darmstadt / Los Alamos National Laboratory

Abstract Ion acceleration by lasers is linking physics only found in stellar objects to application as next generation ion sources and in medicine. Lasers have accelerated ions over short distances with excellent beam parameter. I will show the status of research, requirements and ongoing experiments.

Summary Ion acceleration by ultra intense lasers has become an exciting field of research linking physics otherwise only found in stellar objects to the potential application as next generation ion sources and in medicine. The laser acceleration of ions provides a many orders of magnitude larger acceleration gradient than conventional acceleration, of the order of 1 TeV/m. Thus, lasers have demonstrated ion acceleration to tens of MeV over distances of only µm and with excellent ion beam parameter, like particle number or beam quality. The advantage of ion beams in particle therapy lies in their Bragg peak property, which allows predominant and peaked irradiation in depth at the position of the tumor. This unique radiobiological advantage of protons and even more with carbon beams is evidenced by the success of ion beam therapy in the more than 30 facilities worldwide (in Europe, USA and Asia). Numerous proton facilities are successfully in operation worldwide. Conventional accelerator technology for medical applications has been developed to extremely high efficiency due to 3D scanning techniques in irradiation and proven high reliability (up to 98%). One of the drawbacks of synchrotrons is their large size and cost, which qualifies this approach for larger hospitals with multiple treatment rooms. The potential for laser acceleration replacing cyclotrons or linacs & synchrotron for medical applications could be a significantly reduced system size and cost combined with possibly further advantages (potentially facilitating gantry design for example). While the most established acceleration mechanism, the TNSA mechanism so far suffers from a rather wide energy spectrum and insufficient particle energy for the treatment of deep-seated tumors new mechanisms have been proposed and first experimental results have been obtained that could satisfy the required beam characteristics. In Europe, the coupling of these high intensity, low emittance ion beams to conventional ion optical systems has been explored in first experiments within the LIGHT collaboration, and high repetition rate system development has been the focus of the LIBRA collaboration.

Name of submitting author Dr. Gabriel Schaumann Institution University of Darmstadt Email GSchaumann@ikp.tu-darmstadt.de Abstract Title Target fabrication for high power laser

experiments Author/Affiliation listing Gabriel Schaumann / University of Darmstadt

Oliver Deppert / University of Darmstadt Dennis Schumacher / University of Darmstadt Alex Ortner / University of Darmstadt Markus Roth / University of Darmstadt

Abstract The target laboratory at the University of Darmstadt is a small-scale facility with its focus on the development of manufacturing techniques for complex micro-targets used in high energy density experiments. I will present on target fabrication techniques and show targets used for shaping laser generated particle beams

Summary The Detector- & Target Laboratory at the TUD-Institute for Nuclear Physics is a small- scale university facility with its focus on the development of manufacturing techniques for targets used in particle and laser beam experiments. Complex three dimensional micro-targets are often used in the realm of high energy density experiments and for applications such as X-Ray back lighting & Thomson scattering, shock-wave generation, equation of state studies, to generate strong electromagnetic fields or as converter targets to produce an intense neutron or proton beam for diagnostic purposes from an intense high energy laser pulse. I will show fabrication techniques, which are amenable to the production of 3D micro-targets and give examples of experiments they were used in. A focus will be on targets for laser accelerating particles, such as a thin free standing cryogenic hydrogen target and specifically formed micro-targets designed to shape the transvers beam properties of a laser generated particle pulse, e.g. to foster refocusing into a conventional accelerator structure.

Name of submitting author Yasuhiko Sentoku Institution Department of Physics, University of Nevada, Reno Email sentoku@unr.edu Abstract Title Numerical modeling of proton acceleration by

micro-focusing ultra-intense laser pulses Author/Affiliation listing Y. Sentoku1, M. Nakatsutsumi2, J. Fuchs2

1) Department of Physics, University of Nevada, Reno, Nevada 89557, USA 2) LULI, École Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau Cedex, France

Abstract Micro-focusing of ultra-intense laser light has been demonstrated by using plasma re-focusing mirrors. It is observed that the resulting laser intensity increase allows pushing up the maximum energy of protons accelerated to multi-MeV energies from solid targets, as well as the conversion efficiency from laser to protons.

Summary With the advent of high-powered, short pulse lasers, it becomes possible to extend laser intensities to 10^21 W/cm^2. By applying a micro-focusing device such as the recently developed elliptical plasma mirror, it is possible to focus the beam to a micron-scale spot, thus enhancing the intensity more than an order of magnitude [1]. Boosting proton acceleration by such micro-focusing ultra-intense laser pulses has been demonstrated by M. Nakatsutsumi, et al. [2] with the LULI 100 TW laser system. Also we had been working on numerical modeling of the ultra-intense laser matter interaction to study absorption, transport and particle acceleration. Our modeling is based on Particle-in-Cell scheme (PICLS), which includes atomic physics such as the Coulomb collision, ionizations, and radiation. Especially when the laser pulse interacts with a high Z target such as a gold, the atomic physics becomes important to determine the plasma condition in the interaction region and also the energy transport inside the target. Two-dimensional PICLS simulation explains well the proton energy observed in the micro-focusing experiment. The experimental results, modeling details and also the speculation for the future parameters are discussed in this talk. [1] M. Nakatsutsumi, A. Kon, S. Buffechoux et al., Opt. Lett. 35, 2314 (2010). [2] “Boosting proton acceleration by micro-focusing ultra-intense laser pulses”, M. Nakatsutsumi, S. Buffechoux, Y. Sentoku et al., submitted to PRL.

Name of submitting author Professor Zheng-Ming Sheng Institution Shanghai Jiao Tong University Email zmsheng@sjtu.edu.cn Abstract Title Two-stage acceleration of protons from relativistic

laser-solid interaction Author/Affiliation listing Jin-Lu Liu, Z.M. Sheng, J. Zheng, J. Zhang

Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China W.M. Wang Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190, China M. Y. Yu Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, China C.S. Liu East-West Space Science Center, University of Maryland, College Park, MD, USA

Abstract We propose a new target design that can lead to two-stage acceleration of protons. Two-dimensional (2D) particle-in-cell (PIC) simulation shows that it can result in a well-collimated nearly mono-energetic proton bunch with peak energy over 200MeV by a readily available laser pulse at focused intensity less than 10^21W/cm^2.

Summary Generation of high energy well-collimated proton beams by relativistic intense lasers has attracted much interest in the past decade because its wide potential applications. Several schemes for generating energetic protons/ions from laser-solid interaction have been proposed, e.g., target normal sheath acceleration (TNSA), radiation pressure acceleration (RPA), laser break-out afterburner (BOA), Coulomb explosion acceleration (CEA)], collision-less shock wave acceleration, hole boring acceleration, acceleration with mass-limited target], as well as combination of two or more of these schemes. So far, TNSA is the most experimentally investigated, with which one is still not able to produce proton beams with energy over 100MeV. Theoretically the RPA scheme can produce high-energy protons. However, extremely thin targets are used, which bring significant challenges for laser technologies, particularly on high contrast ratio at extremely high laser intensity. In this paper, a two-stage proton acceleration scheme using present-day intense lasers and a unique target design is proposed. The target system consists of a hollow cylinder, inside which is a hollow cone, which is followed by the main target with a flat front and dish-like flared rear surface. At the center of the latter is a tapered proton layer, which is surrounded by outer proton layers at an angle to it. In the first acceleration stage, protons in both layers are accelerated by target normal sheath acceleration. The center-layer protons are accelerated forward along the axis and the side protons are accelerated and focused towards them. As a result, the side-layer protons radially compress as well as axially further accelerate the front part of the accelerating center-layer protons in the second stage, which are also radially confined and guided by the field of the cylinder electrons (also laser accelerated to the back) surrounding them. Two-dimensional particle-in-cell simulation show that a laser pulse with focused intensity 8.5x1020W/cm2 and pulse duration of 80fs can produce a proton bunch with ~ 267MeV maximum energy and ~ 9.5% energy spread, which is suitable for many applications, including cancer therapy.

Name of submitting author Dr. Sven Steinke Institution Max Born Institute Berlin Email steinke@mbi-berlin.de Abstract Title Stable Laser Ion Acceleration in the Light Sail

Regime Author/Affiliation listing S. Steinke1, P. Hilz 2, M. Schnuerer1, G. Priebe1, J.

Braenzel1, F. Abicht1, D. Kiefer 2,3 ,C. Kreuzer2 ,J. Schreiber 2,3 ,A. A. Andreev 1,4, T. P. Yu 5,6, A. Pukhov5, and W. Sandner1 1. Max-Born-Institut, D-12489 Berlin, Germany 2. Fakultaet f. Physik, LMU Muenchen, D-85748, Garching, Germany 3. Max-Planck-Institut f. Quantenoptik, D-85748 Garching, Germany 4. Vavilov State Optical Institute, Sankt Petersburg 199034, Russia 5. Institut f. Theoretische Physik I, Heinrich-Heine-Universitaet Duesseldorf, Duesseldorf D-40225, Germany 6. Department of Physics, National University of Defense Technology, Changsha 410073, China

Abstract We present experimental results on ion acceleration with ultrahigh contrast laser pulses focused onto ultrathin two-species targets. We observed spatially and energetically separated protons and carbon ions that accumulate to pronounced peaks around 2 MeV containing as much as 6.5 % of the laser energy.

Summary We present the first experimental investigation of stable radiation pressure regime utilizing carbon foils with a high proton content, irradiated by a circularly polarized laser pulse. Freestanding polyvinyl formal (Formvar ) films with thicknesses down to 20 nm have been illuminated at normal incidence and ultrahigh temporal laser pulse contrast. In the experiments, the early separation of heavier carbon ions and lighter protons is expressed by the observation of isolated energy distributions of the two species. At an optimum target thickness that depends on laser intensity, the fastest carbon ions coincide with the slowest protons, while both accumulate to a distinct maximum. These spectral characteristics are observed for a variety of target thicknesses and laser pulse durations. The measured velocity of the ion interface is in excellent agreement with the analytical 1D light sail model. Our interpretation is supported by both 2D and 3D par ticle-in-cell (PIC) simulations. The experiments were performed at the 35 TW laser facility at the Max Born Institute in Berlin. The Ti:sapphire laser delivers pulses with an energy of 1.2 J in 34 fs FWHM at a central wavelength of \_lambda = 810 nm. The intrinsic amplified spontaneous emission (ASE) contrast ratio of the laser equipped with a frontend based on cross polarized wave (XPW) generation was characterized to be smaller than 10^−11 on a few picosecond scale. This contrast was further enhanced by a recollimating double plasma mirror (DPM) to an estimated value of _ 10^−15. Taking into account the 60 % energy throughput of the DPM system, laser pulses with an energy of EL = 0.7 J were focussed to a focal spot of 3.6 µm diameter (FWHM) using a f/2.5 off-axis parabolic mirror resulting in a peak intensity for circular polarization of Ipeak = 5 × 10^19 Wcm^−2.

Name of submitting author Dr. Hui-Chun Wu Institution Los Alamos National Laboratory Email hcwu@lanl.gov Abstract Title Review of multi-dimensional large-scale kinetic

simulation and physics validation of ion acceleration in relativistic laser-matter interaction

Author/Affiliation listing L. Yin, B. J. Albright, K. J. Bowers, C.-K. Huang, T. J. T. Kwan ;XCP-6, Los Alamos National Laboratory, Los Alamos, NM 87544, USA H.C. Wu, B. M. Hegelich, J. C. Fernández, R. Shah, S. Palaniyappan, D. Jung ;P-24, Los Alamos National Laboratory, Los Alamos, NM 87544, USA

Abstract High-energy ions (>100MeV/u) have been observed in intense laser nano-foil interaction by Trident laser at LANL. Here, we review the updated multi-dimensional large-scale modeling and simulations on physics of the acceleration mechanism, called break-out-afterburner. Simulations related to direct temporal observation on relativistic self-induced transparency and pre-pulse effects are also discussed.

Summary Laser-driven ion beams have shown promise for a range of applications, including ion-driven fast ignition, nuclear detection and medical applications. Ultra-intense laser interaction with nm- to µm-thick targets has been examined in 2D and 3D particle-in-cell simulations using the VPIC code [1]. A linearly polarized laser pulse at intensity I > 1020 W/cm2 can turn a solid density, nm-scale carbon target up to 1 µm thickness relativistically transparent, and then a period of dramatic acceleration of carbon ions and protons starts. Called break-out-afterburner (BOA) [2], this acceleration phase lasts until the electron density in the expanding target reduces to the critical density in the non-relativistic limit. The maximum ion energy is obtained when the time interval of the acceleration phase overlaps with the peak intensity of the laser pulse. Recently, 3D PIC shows that the ion beam symmetry is broken, with the production of lobes in the direction orthogonal to the laser polarization and propagation directions [3]. The physics of the BOA is consistent with recent Trident experiments [4] and analytic theory. Experimental and simulation study of light propagation through initially over-dense plasma and ultra-fast optical switching at the onset of relativistic transparency and the associated femtosecond-scale plasma dynamics [5] provide further understanding and validation of the physics in relativistic laser-matter interaction. We also consider the possible pre-pulse effect on ion acceleration in the laser nano-foil interactions and find its effect is small, which reinforces our earlier understanding and simulation in disregard of the pre-pulse. [1] K. J. Bowers, J., B. J. Albright, L. Yin, B. Bergen, and T. J. T. Kwan, Phys. Plasmas 15 055703 (2008). [2] L. Yin, B. J. Albright, B. M. Hegelich, K. J. Bowers, K. A. Flippo, T. J. T. Kwan, and J. C. Fernández, Phys. Plasmas 14, 056706 (2007). [3] L. Yin, B. J. Albright, K. J. Bowers, D. Jung, J. C. Fernández, and B. M. Hegelich, Phys. Rev Lett. 107, 045003 (2011). [4] B. M. Hegelich, et al., Nucl. Fusion 51, 083011 (2011). [5] R. Shah, et al., “Dynamics of relativistic transparency and optical shuttering in expanding over-dense plasmas”, Nature Physics, submitted (2011).

Name of submitting author Prof. Xueqing Yan Institution Institute of Heavy Ion Physics, Peking University Email x.yan@pku.edu.cn Abstract Title Laser driven plasma lens for pulse

shaping/cleaning and ion acceleration Author/Affiliation listing X.Q.Yan, C.Lin, H.Y.Wang, J.E.Chen, X.T.He Abstract In order to improve the laser energy transmission

efficiency, an ultra-high intensity, high contrast laser pulse with steep front is required. A plasma lens with near critical density is proposed. When the laser passes through the plasma lens, the transverse self-focusing, self-steepening and pre-pulse absorption can be synchronously happened.

Summary By both 3D particle-in-cell (PIC) simulation and analysis, a plasma lens with near critical density is proposed. When the laser passes through the plasma lens, the transverse self-focusing, longitudinal self-modulation and pre-pulse absorption can be synchronously happened. If the plasma skin length is properly chosen and kept fixed, the plasma lens can be used for varied laser intensity above 1019W/cm2. The plasma lens can be implemented by a micron-scale glass cone irradiated by the pre-pulse with precisely controlled timing before the main pulse. Simulation shows by combining the cone target and DLC target, both acceleration efficiency and proton energy can be about 3 times higher than in RPA regime and 6 times higher than in TNSA regime. It shows 180 MeV proton beam can be generated at laser intensity of 10^20W/cm^2. References： 1.H.Y.Wang, X.Q.Yan, Phys. Rev. Lett. 107, 265002 (2011) 2.X. Q. Yan*, H. C. Wu, Z. M. Sheng, J. E. Chen and J. Meyer-ter-Vehn, Phys. Rev. Lett. 103, 135001 (2009) 3.A. Henig*, S. Steinke, M.Schnuerer, T. Sokollik, P.V. Nickles,D. Jung, D. Kiefer,J. Schreiber, T. Tajima, X. Q. Yan*, M. Hegelich, W. Sandner, and D. Habs, , Phys. Rev. Lett. 103, 245003 (2009) 4.T. Tajima*, D. Habs* and X. Q. Yan*, Review of Accelerator Science and Technology (RAST), 2: 201-228 (2009). 5.X. Q. Yan*, C. Lin, Z. M. Sheng, Z. Y. Guo, B. C. Liu,Y. R. Lu, J. X. Fang, and J. E. Chen，, Phys. Rev. Lett. 100, 135003 (2008) 6.X. Q. Yan*, T. Tajima, M. Hegelich, L. Yin and D. Habs, Appl. Phys. B, 98：711-721, (2010)

Name of submitting author Karl Zeil Institution Helmholtz-Zentrum Dresden-Rossendorf, Germany Email k.zeil@hzdr.de Abstract Title High-power laser development projects for laser

particle acceleration at HZDR Author/Affiliation listing K Zeil 1, M Baumann 1,2,3, E Beyreuther 1, S Bock 1,

T Burris-Mog 1, T E Cowan 1, W Enghardt 1,2,3, U Helbig 1, L Karsch 2, S D Kraft 1, L Laschinsky 2, M Loeser 1, J Metzkes 1, D Naumburger 2, M Oppelt 1,2, J Pawelke 1,2, C Richter 1,2, F Roeser 1, R Sauerbrey 1, M Schürer 2, U Schramm 1, M Siebold 1 1. Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany 2. OncoRay - National Center for Radiation Research in Oncology, TU Dresden, Germany 3. Clinic for Radiation-therapy und Radio-oncology, TU Dresden, Germany

Abstract We report on the development status of our high-power laser projects for the generation of laser accelerated protons for the radiobiology program at OncoRay and HZDR.

Summary Recent developments in the field of laser particle acceleration enable potential applications as, e.g., radiotherapy with laser driven proton beams. Laser driven proton therapy, not only requires sufficiently high proton energies but also a reasonable repetition rate for appropriate control of the dose delivery. In Dresden, this ambitious vision is addressed by close collaborative work at OncoRay (represented by Technical University Dresden and Helmhotz-Zentrum Dresden-Rossendorf (HZDR)) combining expertise in laser plasma physics, accelerator physics, and medicine. A dedicated research building later housing both, a laser driven proton beam delivery system and a conventional proton therapy accelerator for direct comparison in clinical trials is presently under construction. For the development of a medical high intensity laser prototype to be installed at OncoRay we focus on two major projects in parallel. The first project uses a commercialized Ti:Sapphire based laser concept providing ultra short pulses of tens of femtoseconds at a repetition rate of 10 Hz. With the 150 TW Draco laser the proton acceleration process was investigated in the last three years [1], and a long-term stable and reliable mode of operation was established which has enabled first in vitro cell irradiation studies [2]. The laser system is presently upgraded by an additional amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. By use of the increased pulse energy and the multiple beam option the proton energy scaling will be investigated and the radiobiological program will be extended to the irradiation of tumors in animals. Complementary to the ultra short pulse laser approach, the direct diode pumped solid state laser PENELOPE is under development. The status of this energetically more efficient technology providing longer pulse durations at comparable beam power and therefore favoring potentially higher proton acceleration performance than ultra short pulses will be presented. [1] Zeil, K. et al. New J Phys, 12, 045015, 2010. [2] Kraft, S. et al. New J Phys 12, 085003, 2010.