Polar Drive on OMEGA and the NIF

Transcription

1 Polar Drive on OMEGA and the NIF OMEGA polar-drive geometry 21.4 Backlit x-ray image OMEGA polar-drive implosion CR ~ 5 R = 77 nm 4 nm 4 nm P. B. Radha University of Rochester Laboratory for Laser Energetics 54th Annual Meeting of the American Physical Society Division of Plasma Physics Providence, RI 29 October 2 November 212

2 Summary OMEGA and NIF experiments are setting the physics basis for polar-drive (PD) ignition OMEGA experiments are addressing key aspects of PD ignition areal density and symmetry are well-modeled with the hydrodynamic code DRACO PD cryogenic implosion studies will begin in the near term Better scaling of OMEGA implosions with the National Ignition Facility (NIF) PD ignition designs will be obtained with new PD-specific phase plates Early NIF experiments will be used to study the symmetry and laser plasma interactions TC1137

3 Collaborators F. J. Marshall, J. A. Marozas, A. Shvydky, I. Gabalski, T. R. Boehly, P. W. McKenty, T. J. B. Collins, R. S. Craxton, D. H. Edgell, R. Epstein, D. H. Froula, V. N. Goncharov, M. Hohenberger, R. L. McCrory, D. D. Meyerhofer, T. C. Sangster, and S. Skupsky University of Rochester Laboratory for Laser Energetics J. A. Frenje and R. D. Petrasso The Plasma Science and Fusion Center Massachusetts Institute of Technology

4 Outline Polar drive OMEGA experiments Future PD OMEGA experiments Early NIF experiments

5 Outline Polar drive OMEGA experiments Future PD OMEGA experiments Early NIF experiments

6 Polar drive (PD) enables direct-drive ignition experiments on the NIF in the x-ray-drive configuration Repointing for PD* Oblique irradiation near the equator is at lower densities (n = n crit cos 2 i inc ) nonradial beams reduced absorption reduced hydro-efficiency lateral heat flow TC9532h *S. Skupsky et al., Phys. Plasmas 11, 2763 (24).

7 Tailored laser pulse shapes and beam profiles are used to adequately irradiate the equator in the ignition design y (mm) 39 nm CH 18 to 21 nm DT TC1138 DT gas Polar beams x (mm) 1585 nm E V imp MJ (3.5 to 4.3) 1 7 cm/s a inn 2.2 to 2.6 P a inn = P F Equatorial beams x (mm) Relative intensity Power per beam (TW) 2 1 Equator, pole Mid-latitude 5 Time (ns) 1 Custom spot shapes preferentially irradiate the equator, improving symmetry T. J. B. Collins et al., Phys. Plasmas 19, 5638 (211); T. J. B. Collins, JO4.1, this conference.

8 Shimming can provide an additional parameter to control symmetry Radius (nm) Pole CH DT ice DT gas Polar angle ( ) Equator Different shimmed profiles permit variation in symmetry adequate symmetry with lower-intensity equatorial beams than without a shim TC136 T. J. B. Collins et al., Phys. Plasmas 19, 5638 (211); T. J. B. Collins, JO4.1, this conference.

9 PD ignition space is similar to symmetric drive 5 More stable Implosion velocity ( 1 7 cm/s) 4 3 Ignition space Adiabat 4 5 More stable Analytical theories help to identify key parameters that affect the onset of ignition Ignition target designing is based on hydrodynamic simulations Simulation models are continuously being refined based on experimental data from OMEGA and the NIF for symmetric and polar drive TC1358 T. C. Sangster, NI2.2, this conference V. N. Goncharov, JO4.1, this conference

10 Both shocks and the main drive contribute to asymmetry Triple-picket pulse shape 1 Power per beam (TW) Time (ns) Adiabat (shock timing) 2 Implosion velocity Symmetry TC V. N. Goncharov et al., Phys. Rev. Lett. 14, 1651(21); P. B. Radha et al., Phys. Plasmas 18, 1275 (211). 2 P. B. Radha et al., Polar Drive on OMEGA, submitted to the European Physical Journal.

11 Models of laser deposition and heat conduction are crucial to determining symmetry of implosion Laser energy deposited at end of laser pulse 2 18 NIF ignition design Laser energy ( 1 22 ergs/cm 3 ) 26 R (nm) Smaller conduction zone Pole Polar angle ( ) Larger conduction zone Ablation surface Equator TC114

12 Models of laser deposition and heat conduction are crucial to determining symmetry of implosion Laser energy deposited at end of laser pulse 2 18 NIF ignition design Laser energy ( 1 22 ergs/cm 3 ) 26 R (nm) Smaller conduction zone Lateral heat flow 6 Pole Polar angle ( ) Larger conduction zone Ablation surface Equator TC114a

13 Minimizing asymmetry is an important goal of OMEGA experiments and hydrodynamic modeling Nonuniform shock fronts contribute significantly to the asymmetry R (nm) Density contours at 65 ps Laser Second shock 41 First shock Pole Equator Polar angle ( ) Amplitude (nm) Amplitude at rear shell surface, = Time (ns) 3 6 Main shock Return shock Picket shock TC1357

14 Outline Polar drive OMEGA experiments Future PD OMEGA experiments Early NIF experiments

15 4 OMEGA beams emulate the 48-quad (192-beam) NIF configuration NIF configuration Ring 2 Ring 1 Ring 4 Ring 3 OMEGA PD configuration Ring 1 Ring 2 Ring 3 The remaining beams are used to backlight the shell Ring 1 Ring 2 Dr Ring 3 Beam shifts are parametrized by: Dr 1, Dr 2, Dr 3, TC7194e R. S. Craxton et al., Phys. Plasmas 12, 5634 (25). F. J. Marshall et al., J. Phys. IV France 133, 153 (26).

16 Several low-adiabat laser pulse shapes have been studied in the PD configuration nm CH D 2 24 to 27 nm Power (TW) t (mg/cm 2 ) I = W/cm 2 CR ~ 12 E ~ 14 kj a ~ Higher areal density is obtained by eliminating shell coasting after the laser drive is off. Power (TW) tr (mg/cm 2 ) I = W/cm 2 CR ~ 19 E ~ 14 kj a ~ 3 Time (ns) TC1141

17 Areal density 1 is well modeled over a range of different pulse shapes in the PD configuration tr exp (mg/cm 2 ) Power (TW) Time (ns) Time (ns) (Reference 2) Areal density depends on the adiabat 3 tr n 13 / L ^ E. MJh = a TC9479i tr 1-D (mg/cm 2 ) 1 F. H. Séquin et al., Phys. Plasmas 9, 2728 (22). 2 F. J. Marshall et al., Phys. Rev. Lett. 12, 1854 (29). 3 C. D. Zhou and R. Betti, Phys. Plasmas 14, 7273 (27).

18 Symmetry Good agreement is obtained in the symmetry of the compressed shell* CH 27 nm Ring 1 Ring 2 Ring 3 Ring 1 Ring 2 Ring 3 9 nm, 15 nm, 15 nm 3 nm, 15 nm, 15 nm 43 nm D 2 Experiment DRACO/Spect3D** Experiment DRACO/Spect3D CR ~ 5 CR ~ 5 Power (TW) Time (ns) tr (mg/cm 2 ) Mode amplitude (%) nm R ~ 79 nm R ~ 82 nm R ~ 76 nm R ~ 72 nm 5 nm , mode, mode TC1355 * P. B. Radha et al., Polar Drive on OMEGA, submitted to the European Physical Journal. ** Spect3D J. J. MacFarlane et al., High Energy Density Phys. 3, 181 (27).

19 Symmetry has been studied with shimmed shells A pointing scheme that minimizes nonuniformity is chosen with DRACO Ring 1 nm Ring 2 12 nm Ring 3 12 nm Radius (nm) CH D 2 gas Polar angle ( ) TC1144 F. J. Marshall, JO4.15, this conference

20 Improved symmetry has been demonstrated with shimmed shells Mode amplitude (%) 5 nm nm, 12 nm, 14 nm No shim (67343) Shimmed (67345) Experiment DRACO/Spect3D Experiment DRACO/Spect3D CR ~ 5 CR ~ 5 R ~ 76 nm 5 nm DRACO, = 4 DRACO, = 2 Experiment, = 4 Experiment, = 2 Mode amplitude (%) R ~ 77 nm DRACO, = 4 DRACO, = 2 Experiment, = 4 Experiment, = Time (ns) Time (ns) TC1362

21 The best symmetry in PD implosions on OMEGA has been achieved with shimmed shells X-ray radiographs with peak fits Shot 6661 No shim 9 nm, 133 nm, 133 nm CR ~ 6 R = 65 nm Shot With shim nm, 12 nm, 14 nm CR ~ 5 R = 77 nm Mode amplitude (%) Shim No shim , mode 4 4-nm regions TC1145

22 Outline Polar drive OMEGA experiments Future PD OMEGA experiments Early NIF experiments

23 Near-term experiments will address some limitations of current OMEGA experiments CH D 2 24 to 27 nm CH DT Cryogenic CH a $ 2 V imp # cm/s Warm CH I = W/cm 2 a = 3 V imp = cm/s I = W/cm 2 9 to 1 nm 35 to 65 nm Warm CH a = 3 V imp = cm/s I = W/cm 2 Cryogenic DT a $ 2 V imp # cm/s I = W/cm 2 E ~ 14 kj R t = 43 nm R t = 3 nm TC1146

24 PD warm and cryogenic implosions will be studied with new phase plates on OMEGA Circular spot shape Elliptical spot shape y (nm) 2 2 Pole and mid-latitude rings Relative intensity Equatorial ring 2 x (nm) x (nm) Single-beam power (TW).3 E = kj.25 Ring Rings 1, Time (ns) 3 nm 1 nm CH 65 nm DT z (nm) t (g/cc) r (nm) TC1356 P. B. Radha et al., Phys. Plasmas 19, 8274 (212).

25 Outline Polar drive OMEGA experiments Future PD OMEGA experiments Early NIF experiments

26 Early NIF experiments will address key issues for PD ignition The goal is to demonstrate drive uniformity measure laser coupling identify and address laser plasma interactions - longer coronal density scale lengths in NIF implosions may result in larger effects of cross-beam energy transfer 1 and fast-electron preheat from two-plasmon decay 2 These experiments will use the existing NIF configuration (phase plates and beam smoothing) The designs use a combination of beam defocus, repointing, and independent ring pulse shapes to achieve the required symmetry The first shot will be performed a few weeks from now TC J. A. Marozas, JO4.15, this conference D. H. Edgell, UO5.1, this conference 2 J. F. Myatt, TO5.5, this conference D. T. Michel, YI2.2, this conference

27 The primary goal of early NIF experiments is to predictably change implosion symmetry Implosion symmetry is varied by changing ring energies CH.7 atm air 8 nm Simulated x-ray self-emission images* (ho L 2 kev) 5 Power (TW) nm 2 4 Time (ns) 6 P 2 mode amplitude (%) 5 5 E L ~ 35 kj Oblate Prolate Time (ns) Spherical y (nm) y (nm) y (nm) x (nm) Relative intensity TC1148 *T. Michel et al., Rev. Sci. Instrum. 83, 1E53 (212).

28 Polar-drive platforms on the NIF have been used for diagnostic development 1 and mix studies nm SiO 2 Exploding-pusher targets have been used to produce neutrons 1 1 atm D 2.75 mm Power (TW) Incident (13 kj) 1 2 Time t (ns) N12328 High-adiabat (a ~ 5) and high-intensity (I ~ W/cm 2 ) PD implosions have been used to study mix on the NIF 2 3 y (nm) Gated framing camera images t E = 1.14 ns ho L 2 kev Image x (nm) N Relative intensity TC R. S. Craxton, JO4.12, this conference; P. W. McKenty, JO4.11, this conference. 2 M. J. Schmitt, YI2.5, this conference; N. Krasheninnikova, TO4.6, this conference; T. Murphy, TO4.2, this conference; G Kyrala, TO4.7, this conference.

29 NIF experiments will systematically explore the physics before the ignition campaign Cryogenic target system Ignition experiments Beam smoothing Target performance warm shells PD-specific phase plates ID phase plates Energy coupling Preheat Symmetry Shock timing Energy coupling Preheat Symmetry Time TC1386

30 Summary/Conclusions OMEGA and NIF experiments are setting the physics basis for polar-drive (PD) ignition OMEGA experiments are addressing key aspects of PD ignition areal density and symmetry are well-modeled with the hydrodynamic code DRACO PD cryogenic implosion studies will begin in the near term Better scaling of OMEGA implosions with the National Ignition Facility (NIF) PD ignition designs will be obtained with new PD-specific phase plates Early NIF experiments will be used to study the symmetry and laser plasma interactions TC1137