The 1-D Campaign on OMEGA: A Systematic Approach to Find the Path to Ignition

Transcription

1 The 1-D Campaign on OMEGA: A Systematic Approach to Find the Path to Ignition Normalized intensity R. Betti University of Rochester Laboratory for Laser Energetics Core self-emission Radius (nm) 2 3 8th Annual Meeting of the American Physical Society Division of Plasma Physics San Jose, CA 31 October 4 November 216 1

2 Summary The 1-D campaign on OMEGA uses systematic changes and looks for trends to improve physics understanding and find the optimal target design The 1-D campaign uses ON/OFF systematic changes in cryo implosions to understand the implosion behavior The 1-D campaign looks for 1-D trends in qualitative features of the experimental observables to elucidate the physics and assess the dimensionality of the implosion A short-term goal is to find the optimum 1-D performance at high adiabat (~7) using two-shock (single-picket) pulse shapes The ultimate goal is to find the optimum target design through an adiabat and velocity scan TC1392 2

3 Collaborators J. P. Knauer, A. V. Maximov, T. J. B. Collins, C. Stoeckl, A. Bose, J. Woo, A. R. Christopherson, A. Shvydky, W. Theobald, J. A. Delettrez, F. J. Marshall, P. B. Radha, S. P. Regan, E. M. Campbell, W. Shang, W. Seka, and S. X. Hu University of Rochester Laboratory for Laser Energetics 3

4 The time history of the hot-spot radius R 17% monitors deviations from one-dimensional behavior 6 Low modes (, ~2) increase the hot-spot size Intermediate modes (, ~1) decrease the size 1-D bang time, = 2 R 17% (nm) Clean, = 2, YOC = 6%, = 1, YOC = 6% Clean, = Time (ps) TC1393 The time history of the hot-spot radius reveals what modes are dominant. A. Bose et al., UO.1, this conference. YOC: yield over clean 4

5 The shape of the hot-spot self-emission is another measure of the deviations from a one-dimensional implosion 2 y (nm) y (nm) TC x (nm) x (nm) Rayleigh-Taylor (RT) spikes from intermediate modes lead to a peaked self-emission profile. 2 1-D YOC = %.4 Z (nm) Normalized intensity Radius (nm) r (nm) 3 R. Nora, Lawrence Livermore National Laboratory, private communication (213).

6 A necessary condition for a one-dimensional implosion is that the neutron yield follows the 1-D formula based on stagnation properties 1-D yield-formula Y an mg T 47. M 6. kev stag = _ trgcm / 2i c m D yield analytic ( 1 13 ) a > a 3 a 3 ( Gbar) This is a necessary but not sufficient condition for a one-dimensional implosion Y exp Y an This is only true if our stagnation physics models are correct. TC8777a D yield LILAC ( 1 13 ) R. Betti et al., Phys. Plasmas 17, 812 (21). 6

7 A typical cryogenic shot day of the 1-D campaign uses sets of systematic ON/OFF pairs of shots 43 nm OMEGA CD DT ice DT gas 8 nm nm 372 nm Power (TW) Shock-timing test Change pulse shape Hot e ON/OFF ON/OFF (RT test) Power (TW) Fixed pulse shape HXR e Change target (different payload, same ablator) fuel-preheat evaluation* e e CD DT DT gas 8. nm.2 nm nm CD DT gas e 17.6 nm nm TC139 *A. R. Christopherson et al., NO.7, this conference. 7

8 The first high-adiabat targets are designed for a 7 and compared to best performer* a 3 43 nm OMEGA CD DT ice DT gas 8 nm nm 372 nm Power (TW) a a (a 3) > Gbar 882 (a 7) Adiabat t a a t Density (g/cm 3 ) CR = 18 CR = Mass coordinate 1 (g) Radius (nm) TC1396 S. P. Regan et al., Phys. Rev. Lett. 117, 21 (216); A. Bose et al., Phys. Rev. E 94, 1121(R) (216). 8

9 2-D post-shot simulations including low-mode perturbations show little degradation from low modes 2 t (g/cm 3 ) t (g/cm 3 ) T e (kev) Bang time, 2. ns z (nm) 2 Port geometry only Laser-beam imbalances Laser-beam imbalances, ice roughness, target offset Offset = 1. nm v rms, ice =.6 nm.3% power imbalance 8-nm mispointing -ps mistiming x (nm) x (nm) Simulations including beam mistiming, mispointing, and.3% power imbalance, with measured ice roughness and target offset, show a reduction in yield of 17% from the clean yield Even when the power imbalance is doubled to 1%, the yield degradation is just 26% TC1397 Multidimensional simulations are used to assist our strategy and help the interpretation of the results, but are not used to reach final conclusions. T. J. B. Collins et al., PO.9, this conference. 9

10 The ion temperature is below the predictions of the 1-D code Experiment [T i (kev)] Texp= Max > Tmin, Tmin Tavg TavgH T i comparison LILAC versus experiment Measure of T i variations 4. a > single picket a 3 single picket 3.6 a 3 ( Gbar) LILAC [T i (kev)] 4. T i (kev) Shot 1 T avg T min T exp These shots exhibit small T i variations among detectors. TC1321 1

11 For high-adiabat shots, the measured yield closely follows a T 4 power law YOC Y Y Y exp exp Formula 1-D YLILAC 1-D Y exp ( 1 13 ) Yield versus fitting formula a > single picket a 3 single picket a 3 ( Gbar) a LILAC T. kev 394 Y fit = 6.6 c m ( 1 13 ) 3. The -Gbar shots do not follow the T 4 power law; LILAC fit of the yield is T 4.7. TC

12 Preliminary analysis of the hot-spot framed images indicate the presence of RT spikes from mid-, modes after stagnation R 17% (nm) The size of the self-emission becomes smaller after stagnation 3 3 2, = 2, YOC = 6%*, = 1, YOC = 6%* 1 1 Time (ps) 1-D* KBFramed 8372** h 2 1 The self-emission profile becomes peaked with time h = 2 h = Time (ps) Ae r c R 2 h m TC1323 This analysis will make it possible to generate a multidimensional picture of the hot-spot dynamics (error bars are large " look at trends). *A. Bose et al., UO.1, this conference. **F. J. Marshall, Laboratory for Laser Energetics, private communication (216). 12

13 Summary/Conclusions The 1-D-campaign on OMEGA uses systematic changes and looks for trends to improve physics understanding and find the optimal target design The 1-D campaign uses ON/OFF systematic changes in cryo implosions to understand the implosion behavior The 1-D campaign looks for 1-D trends in qualitative features of the experimental observables to elucidate the physics and assess the dimensionality of the implosion A short-term goal is to find the optimum 1-D performance at high adiabat (~7) using two-shock (single-picket) pulse shapes The ultimate goal is to find the optimum target design through an adiabat and velocity scan TC

14 No clear signatures of imprinting are observed, indicating stable implosions to short wavelengths TC1398 Arbitrary units (normalized to peak) Arbitrary units (normalized to same yield) Low I 887 ON Laser. Low I 887 ON NTD NTD 2 ps Laser Experiment LILAC BW = 12 ps BW = 91 ps Low I 8811 OFF Low I NTD 887 OFF In warm targets, OFF leads to earlier bang times and wider burn histories.* NTD BW = 12 ps BW = 91 ps ps *S. X. Hu et al., Phys. Plasmas 23, 1271 (216). 14

15 The measured yield is about 6% of the LILAC yield and ~8% of the 1-D yield formula based on measured T and tr 3. LILAC Experiment 1. Y exp /Y LILAC Y exp /Y 1-D formula 2..8 T i (kev) off Low-I on off off High-I on Shots (first 1-D campaign set) YOC off Low-I on off off High-I on Shots (first 1-D campaign set) The measured T i is slightly lower than LILAC T i and explains ~1/2 of the discrepancy; early indication of a 1-D-code over-prediction of 1-D yield. TC1399 1

16 A comparison between YOC s from LILAC and the 1-D formula gives preliminary indications of the 1-D code over-estimating the 1-D yield Y sim /Y 1-D formula Multimode, $ 2, = 8, = 6, = 4 EXP, = 2, = 2 Differences between LILAC YOC and 1-D formula can be reconciled using high-mode distortion -ON/OFF experiments indicate implosions stable to high modes Possible explanation is that LILAC overpredicts the 1-D yield.2...2, = The yield formula also provides a lower bound for the 1-D yield in implosions degraded by nonuniformities. Y sim /Y 1-D sim TC131 16

17 Similar trends are observed for higher intensity shots (but larger bang-time differences) TC1311 Arbitrary units (normalized to peak) Arbitrary units (normalized to same yield) High I 882 ON Laser. High I 882 ON NTD NTD 3 ps Laser NTD Experiment LILAC NTD BW = 91 ps BW = 84 ps High I 881 OFF High I 881 OFF BW = 97 ps BW = 86 ps ps 17