J. D. Kilkenny et al- Hohlraum Drive and Implosion Experiments on Nova

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UCRLJC-118255Re v. 1PREPRINT

Hohlraum Drive and Implosion Experiments on NovaJ. D. Kilkenny, L. J. Suter, M. D. Cable, C. B. Darrow, T. R Dittrich,S.W. Haan, B. A. Hammel, S. P. Hatchett, R. L. Kauffman,C. J. Keane, H. N. Kornblum, 0.L. Landen, S . M. Lane,R. A. Lerche, T. J. Murphy, D. W. Phillion , . J. Powers, D. B. Ress,

M. D. Rosen, R. Thiessen, R. E. Turner, R WallaceLawrence Livermore National LaboratoryA. A. Hauer and W. W. Hsing

Los Alamos National Laboratory

This paper was prepared for submittal to the15th International Conference on Plasma Physics andControlled Nuclear Fusion ResearchMadrid, SpainSeptember26- October 1,1994

September 8,1994


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This document was prepared as an account uf work sponsored hy an agency ofthe t'n ited States Government. Neither the thit ed States


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DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.


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INTERNATIONAL ATOMIC ENERGY AGENCYFIFTEENTH INTERNATlONAL CONFERENCE ON PLASMA PHYSlCSAND CONTROLLED NUCLEAR FUSION RESEARCHSeville, Spai n, 26 September - 1 October 1994

IAEA-CN-60/

Hohlraum Drive and Im plosion Experiments on Nova*J. D. Kilkenny, L. J. Suter, M. D. Cable, C. B. Danow, T. R. Dittrich, S . W. Haan,B. A. Hammel, S. P. Hatchett, R. L. Kauffman,C . J. Keane, H. N. Kornblum, 0.L. Landen, S . M. Lane,R. A. Lerche, T. J. Murphy, D. W. Phillion, L. J. Powers, D. B. Ress, M. D.Rosen, A. R. Thiessen, R. E. Turner, R. WallaceLawrence Livermore National Laboratory, University of California Livermore,California 9455 1A. A. Hauer, W. W. HsingLos Alamos National Laboratory, University of CaliforniaLQS lamos, New Mexico 87545

This is a preprint of a paper intended fo r presentation at a scientific meeting. Be rx st : of the provisioiial nature of i t sconte nt and since changes of substance or detail may have to be made before publication, the Fjteprint is made available o n thunderstanding tha t it wi l l not be cited in the l iterature or in any way be reproduced in its present form The views expressedthe statements made remain the responsibility of the named author(sl; til e views do not necessarily reflec r those of the govement o f the designating Member State k) or of the designating organiza tion(s). In particular, neither the W A nor any otherorganizationor body sponsoring this meeting can be held responsible for any materia; reproduced in :his preprint.


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IAEA-CH-GO/BII-3Hohlraum Drive and Implosion E xperiments on Nova*AbstractExperiments on Nova have dem onstrated hohlraum radiation temperatures up to 300 eVand in lower temperature experiments reproducible time integrated sy mm etry to 1-296.Detailed 2-D LASN EX simulations satisfactorily reproduce Novas drive and symmetryscaling data bases. Hohlraums has been used for implosion experimen ts achievingconvergence ratios (initial capsule radius/final fuel radius) up to 24 with high densityglass surrounding a hot g as fill(1).Radiation drive measu rements and calculations o n NovaThe radiation temperature in a hohlraum is determined by a balance of sources and sink sexpressed byThe x-ray sou rce is ~ P Lhere9,s the laser power, the hole loss is om4Ah, and thewall loss is (1-a)O T R ~ A ~ ,here Ah and Aw a re the areas of th e holes and wallrespectively, TR is the effective brightness temperature of th e hohlraum and a s th e wallalbedo(2). For Nova hohlraums, a 0.8 and the x-ray conversion efficiencyq can berelated to open geometry experiments.The targets for Nova experim ents are right circular cylinder s 1.6mm diam eter and2.5-2.8 mm long made of high Z material. Five beams per side, with up to 30 TW of0.35 pm light in a 1ns square laser pulse, are focused through the two laser entranceholes (LEH) in the ends of the cylinders onto the inside cylinde r walls. Scaling is alsoinvestigated using 1.2 mm and 1.0 mm diam eter targets.

rlL = (Aw (1- a) + A h)a4

Th e radiation temperature in the cavities is determined by obse rving the velocity us of ashock wave generated when radiation is absorbed in AI wedged and step ed witnessplates. For th e temperature range of these experiments, TR = 0.0126 U S 8.63 where TR isin units of eV and us is in units of c d s . The shock velocity is measured with an errorcorresponding tok e V in TR , by time resolving the op tical emission from an A1 wedgedor stepped w itness plate.TR is also measured(3) from the reradiated flux, Sr, from the x-ray heated wall using anarray of x-ray diode s with a tim e resolution of 150ps.Using 1 ns constant power (square) laser pulses, TR measured from the shock breakout asa function of average laser power is shown in Fig. 1. In smaller cylindrica l cavities, wemeasure temperatures of 290 eV and 300 eV for a 1.2 mm and 1O mm diameter cavity,respectively. Th e present experim ents significantly extend the range of radiationtemperatures attained in the laboratory(4) to temperatures of interest for high gainimplosions. Results of the fit from the pow er balance equation are the lines shown in Fig.1 with q being 0.75,0 .65, and 0.50 for the 1.6 mm, 1.2 mm and 1.0 mm diametercavities, respectively. Th e 1.6mm cavities have also been modeled using 2-D LASNEXand are also shown a s open circles in Fig. 1.

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In g eneral, x-ray drive becom es easier for larger facilities, because the temp erature isdetermined by the w all loss 1-a- @.5 t 0.5. For longer times, or for highertemperatures, the wall loss drops(2). For 1.6 mm cavities on N ova, t - 1 nsec, T -260eV and 1 - a = 0.2: in contrast the NIF will have t - 10nsec and T - 300 eV and1 -a-0.11.Radiation symm etry experiments and calculationsIn sep arate experiments, we have prod uced nine different symm etry scaling data basesusing pulse shapes from 1 nsec flat top to 3.2ns shaped pulses, and pure go ld and linedhohlraums. In some cases, we varied the length of the hohlraum with the pointing so thatthe beams always cross in the plane of the laser entrance hole (LEH).For the l500A of nickel lined series for example, the hohlraums were 1.6mm diameterwith 1.2mm diameter laser entrance holes. In this series the hohlraum length was variedwith pointing such that the beams always crossed in the plane of the LEH. Drivesymm etry was m easured by imploding a capsule with a convergence of -8 and measuringthe shape of the imploded capsule(5,6). Figure 2displays the results of this experimentand compares it to our modeling. The solid circles are "distortions' (ratios of theFWHM's of the x-ray images) from our experiments as a function of beam pointing. Themodeling's distortions are the open circles, Clearly we can control Nova sym metry byvarying the beam pointing. For this series, the pointing of best symmetry is -1200 pm inexperiment and - 150 pm in simulation.Figure 3summarizes our ability to simulate with LASNEX(7) the pointing of bestsymm etry over this wide range of experiments.The fundamental asymm etry in a Nov a-like hohlraum is a long wavelength, pole to waistflux variation which varies like the P2 legendre polynomial. In a sp herical hohlraum, theP2 compon ent of capsule flux vanishes when the P2 compon ent of the source flux is zeroat the polar angle where P2 is zero, 54.7O. A laser entrance hole modifies this and thecenter of emissivity in a spherical hohlraum m ust be at about 44" nd in our moredetailed LASNEX simulations, which include higher 1-mode compo nents, volumeemission and mode-coup ling due to having a sphere inside a cylinder, we find thepo1e:waist fluxes are balanced when the ce nter of emissivity is at -48'.Spo t motion, the migration of the radiation production region to smaller polar angles,causes a simulated Nova-type hohlraum to have an equator-high to pole-high asymm etryswing as the pulse becomes longer. For all three pulse shapes we find that near thepointing of best symmetry the center of emissivity sweeps through the "op timal angle"(where pole pressure = equator pressure; -48' fo r these hohlraums) when -50% of ashape's useful energy has been delivered.Ho t sp ot implosion exDerimentsOur best implosion targets were x-ray driven, 180 pm o.d., 5 p m thick gas filled glassmicroballoons overcoated w ith 37 p m of plastic. Fill pressures varied from 25-200 atmof deuterium. Ten Nova beams (21 kJ) produced a uniform x-ray flux o n the capsulesu'dace. Th e radiation brightness temperature had a 100 eV foot, rising to 210 eV peak in1.6 nsec, chosen to optimize the pressure-density trajectory of the capsule compression,

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giving 8 Mbar ablation pressure at the foot of the pulse and 110Mbar at the peak of th epulse.Convergenceof these capsules is limited by the x-ray d rive symmetry both inherent to thehohlraum and due to random variations from imprecise laser beam-to-beam powerbalance and pointing. We maintain tolerances of 8% (RMS) beam-to-beam powerbalance during the foot of the laser pulse and 4% power balance during the peak, g ivingan x-ray power balance on the capsule uniform to 2%(RMS) at peak power and 4% inthe foot.Burn averaged fuel densi ty and capsule convergence were determined frommeasurements of fuel areal density, giving densities up to 19 k 1.5 gm/cm3, withconvergences up to 24, in agreement with simulations. Primary neutron yield, pusherareal density, burn duration, bum time, and fuel ion temperature were also measured.Primary neutron yields for these implosions were in agreement with simulations using theHaan mix mode@). Measured fuel ion temperatures were 0.9 k .4 keV correspondingto a final fuel pressure of 16 Gbar. Glass shell densities were measured at 160 k 20g/cm3. Th e bum d uration for the 100atm capsules was measured to be 50k 15ps givingmeasured values of nz = 1.9 x 1014 s/cm3.In conclusion, the x-ray temperature and deg ree of symmetry in Nova implosions areaccurately mod eled. X-ray d riven implosion have demon strated radial convergen ces at alevel close to the convergences required for a ignition capsules.*This work was performed under the auspices of the U.S. Department of Energy byLaw rence Livermore National Laboratory under contract No. W -7405-ENG-48.

References[11 K. A. Brueckner and S . Jorna, Rev. Mod. Phys. &, 325 (1974).[2]131

R. Sigel, et. ala,Phys. Rev. A By779 (1988).H. N. Komblum, R. L. Kauffman, and J. A. Smith, Rev. Sci. Instrum. 57 ,2 17 9(1986).

[4][5]

H. Nishimu ra et. al., Phys. Rev.,My323 (1991).J. D.Kilkenny et. al., Plasma Ph ysics and Controlled Thermo nuclear FusionResearch 19 88 ,3, p29, IAEA Vienna 1989.J. D, Kilkenny, Rev. S ci. Instrumen., 6;2,4688 (19 92).G .Zimmerman and W. Kruer, Comm ents Plasma Phys. Con trolled Fus ion 2 , 8 5(1975).

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[8] S. W. Haan, Phys. Rev. 5812 (1989).

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Figure CaDtion sFigure 1 Radiation temperature as a function of laser power f or 1 ns laser pulses. Th eexperimental results fo r 1.6mm, 1.2 mm nd 1O mm diameter cavities areshown by the closed circles, triangles and squares respectively. LASNEXcalculations are open circles. Th e lines are fits to the data using the powerbalance equation.

Capsule image distortion vs. initial pointing from a series using Ni-linedhohlraums irradiated by a 2.2 nsec shaped laser pulse, ps22. Inset: Relativelaser power vs time for ps22.Pointing of best symm etry in experiment vs. pointing of best symmetry fromour modeling for 1 ns flat top, 2.2ns 3:l ps 22, nd 3.2ns 5 1 ps 32.Thelonger the pulse shape, the further in we m ust move the beams to get goodsymmetry.

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J. D. Kilkenny et al- Hohlraum Drive and Implosion Experiments on Nova

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