Direct-Drive Implosions Using Cryogenic D2 Fuel

Transcription

1 Direct-Drive Implosions Using Cryogenic D2 Fuel Distance (μm) 200 View from H11 +zω Time (ms) Y-TED Distance (μm) T. C. Sangster OMEGA Experiments Group Leader University of Rochester Laboratory for Laser Energetics 35th Annual Anomalous Absorption Conference Farjardo, Puerto Rico 27 June 1 July 2005

2 Summary Direct drive is a robust alternative for ignition on the National Ignition Facility The baseline symmetric direct-drive cryogenic D 2 campaign has demonstrated target performance consistent with 1-D and 2-D hydrocode predictions. Laser and cryogenic target uniformity are approaching the requirements for scaled ignition validation. DT cryogenic implosions will be performed before the end of FY05. OMEGA EP will be completed by the end of FY07. E13846

3 OMEGA cryogenic targets are energy scaled from the NIF symmetric direct-drive point design NIF: 1.5 MJ DT ice DT gas ~3 μm CH 1.69 mm 1.35 mm Energy ~ radius 3 ; power ~ radius 2 ; time ~ radius E11251g Gain (1-D) = 45 OMEGA: 30 kj ~4 μm CH D 2 ice D 2 gas 0.46 mm 0.36 mm Power (TW) α = P fuel P Fermi OMEGA α ~ 4 NIF α ~ Time (ns)

4 Target gain A stability analysis* defines the ignition-scaling performance window for low adiabat implosions The NIF gain and OMEGA yield can be related by σ 2 = 0.06 σ 2 l<10 + σ 2 l 10, where the σ l s are the rms amplitudes at the end of the acceleration phase*. Normalized yield OMEGA (α = 6) OMEGA (α = 4) NIF (α = 3) THz, 2-D SSD with PS, 1-μm-rms ice roughness, 840- outer-surface roughness, 2% rms power imbalance σ (μm) DRACO results α = Incident laser energy (MJ) E12008l *P. W. McKenty et al., Phys. Plasma 8, 2315 (2001).

5 The best layer to date is 1.2-μm rms (all modes) with the best regions below 1.0-μm rms 24 shadowgraphic views of x and y Radius (pixels) Unwrapped Image X (pixels) Spectrum (μm 2 ) X (pixels) Primary bright band Multiple secondary bright bands Inner 0.8-μm rms Outer 0.3-μm rms Angle ( ) Mode l 10 2 T1905e

6 Absorption measurements for cryogenic D 2 shots agree with 1-D hydrodynamic simulations for all pulse shapes Relative absorption difference [measured absorption 1D/1D (%)] SG1018 α402p α402 Mean±σ mean Shots (pulse shapes) The average difference between 1-D predictions and absorption measurements is 1±2%. E13392

7 The reaction history and bang time are close to the 1-D predictions for cryogenic D 2 implosions Neutron rate (1/s) Shot (α ~ 25) 86-μm offset, 6.4-μm ice rms Experimental uncertainty Simulation Experiment Neutron rate (1/s) Shot (α ~ 4) 15-μm offset, 4.1-μm ice rms Experimental uncertainty Simulation Experiment Time (ns) Time (ns) { Exp.: 0.55±0.02 { f abs f Exp.: 0.57± D: 0.57 abs 1-D: 0.55 E13394a

8 Preheat estimates for cryogenic targets are well below the threshold of concern (0.1%) 10 3 Preheat in CH shells and CRYO targets Fractional preheat 10 4 CH Cryo Laser irradiance ( )(W/ W cm 2 ) E13627 B. Yaakobi et al., Measurement of Preheat Due to Fast Electrons in Laser Implosions of Cryogenic Deutrium Targets, to be published in Physics of Plasmas.

9 Low-l-mode drive nonuniformities due to OMEGA beams have been significantly reduced μm rms New DPP s, better overlap, and beam re-pointing have minimized low-l-mode (l < 6) contributions. E Standard pointing μm rms After re-pointing Beam position error (μm) σ 2 tot = σ2 size + σ2 pntg + σ2 balance SG3 = (1.5) 2 + (2.2) 2 + (1.3) 2, σ tot = 3.0% SG4 = (0.6) 2 + (0.7) 2 + (0.6) 2, σ tot = 1.1% Normalized intensity ETP s on OMEGA SG3 (n = 2.3) SG4 (n = 3.7) Distance (mm)

10 Hydrodynamic simulations are consistent with implosion data over a wide range of ice roughness and target offset YOC μm offset (42 μm) α ~ 6 Performance with NIF requirements (32 μm) DRACO (no offset) (38 μm) (28 μm) (28 μm) (23 μm) μm offset α ~ 4 with imprint Performance with NIF requirements DRACO (no offset) (18 μm) (15 μm) rms ice roughness (μm) modes l = 1 to 16 rms ice roughness (μm) modes l = 1 to 16 Average error of offset = 10 μm E13085e

11 Scaled ignition performance on OMEGA is approaching the predicted equivalence of high gain on the NIF Normalized yield α = 6 α = 4 DRACO OMEGA data σ (μm) 1-THz, 2-D SSD with PS, 1-μm-rms ice roughness, 840-Å outer-surface roughness, 2% rms power imbalance E13398 Target offset and ice quality presently limit access to low σ for α = 4 campaign

12 The near term cryogenic shot plan will be focused on high ρr n and validating adiabat shaping The working physics plan is geared toward direct-drive ignition on the NIF and includes 1. adiabat shaping validation with pickets 2. high ρr n 3. ignition-scale ρr/dt implosions 4. adiabat shaping validation with Rx drive pulses 5. advanced cryogenic target designs including fill tubes (NIF CTHS baseline) wetted foams saturn targets (best prospect for PDD on the NIF) cone in shell (FI) E13624a These objectives will be met with ~1-μm rms ice and TCC offsets of ~10 μm (or less).

13 Tritium will be introduced gradually, following a readiness review in June A second FTS will be complete in July for concurrent D 2 cryogenic target production. One MCTC will be dedicated to DT operations. At most, one DT implosion per shot day (up to 24/year ). Potential tritium contamination of the characterization station may limit the throughput for D 2 implosions. The initial tritium fraction will be 0.1% and be raised incrementally ( 10) to reach 50:50 DT by fall Layering studies can begin with 10% tritium. A dedicated cryogenic target test stand is being designed for advanced target development. maintain production target throughput E13808

14 The nonuniformity of the inner ice layer at the end of the accelerating phase will be directly inferred using the OMEGA EP HEPW laser system 200 μm Compressed EP beam Monochromatic imager (3-μm resolution)* Compressed EP beam 100 μm Monochromatic imager (3-μm resolution)* LiF target (~900 ev) 5-ps pulse for start of deceleration P target (~2.3 kev) 20-ps pulse for stagnation ΔX motion = ν Δt = = 2.5 μm TC5944g *F. J. Marshall et al., Rev. Sci. Inst. 68, 735 (1997).

15 OMEGA EP will be operational in FY07 (two beams) and ready for target physics in FY08 There are four primary missions. 1. Extend ICF research capabilities with highenergy and high brightness backlighting 2. Perform integrated fastignition (FI) experiments 3. Develop advanced backlighter techniques for HED physics 60-beam OMEGA OMEGA EP 4. Conduct ultrahigh-intensity laser matter interaction research E11888c

16 The two short pulse beams can be delivered to both target chambers OMEGA target chamber OMEGA EP target chamber OMEGA Laser Bay Compression chamber Beam 1 2 Main amplifiers Short-pulse performance Short-pulse Beam 1 Short-pulse Beam 2 Booster amplifiers Short pulse (IR) 1 to 100 ps 35 to 100 ps IR energy on-target (kj) Intensity (W/cm 2 ) ~ OMEGA EP Laser Bay Focusing (diam) > 80% in 20 μm > 80% in 40 μm G5546t

17 The OMEGA EP building was completed in February 2005 April 2004 January 2005 Mechanical room OMEGA Laser bay Target Bay Capacitor bay Laser bay slab, 1 m OMEGA EP Laser Bay E13574c The source laser was installed in April 2005.

18 An OMEGA EP Use Plan is under development The OMEGA EP Use Plan will define the expected operating parameters and availability, the avenues for non-lle users to obtain access, and initial experimental campaigns. The Use Plan will be completed in Spring An informational and informal discussion meeting will be held at the 2005 APS/DPP meeting. A workshop will be held at UR/LLE in December 2005/ January to allow potential users to propose experiments and discuss access availability and - to consider capabilities required to carry out the experiments. If you wish to be informed of, or participate, in this planning activity and be included in the mailing list, contact E13897 David D. Meyerhofer Laboratory for Laser Energetics ddm@lle.rochester.edu

19 Summary/Conclusions Direct drive is a robust alternative for ignition on the National Ignition Facility The baseline symmetric direct-drive cryogenic D 2 campaign has demonstrated target performance consistent with 1-D and 2-D hydrocode predictions. Laser and cryogenic target uniformity are approaching the requirements for scaled ignition validation. DT cryogenic implosions will be performed before the end of FY05. OMEGA EP will be completed by the end of FY07. E13846

20 The measured ρr n is close to 1-D for all but the lowest-adiabat implosions Measured ρr n mg/cm ρl to ρr is a 10% to 15% reduction for the lower-convergence implosions α~4 to 6 α ~ 25 Mid-α s D LILAC ρr n mg/cm 2 TCC offset <60 μm and ice rms <6 μm Ice roughness and target offset appear to limit the measured ρr n for higher-convergence implosions. E13492a F. Marshall et al., Direct-Drive Cryogenic Implosions on OMEGA, to be published in Physics of Plasmas.