Planning for the National Ignition Campaign on NIF

Transcription

1 Planning for the National Ignition Campaign on NIF Presentation to Fusion Power Associates Annual Meeting Dec 3-4, 2008 Lawrence Livermore National Laboratory John Lindl NIF Programs Chief Scientist Lawrence Livermore National Laboratory LLNL-PRES Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

2 We have a clearly defined path forward to achievement of ignition on NIF An extensive scientific data base forms the foundation for the NIF ignition point design target and experimental campaign We have requirements in place for the first ignition attempt in 2010 A margin formalism allows us to evaluate the performance of the targets, and to assess and manage risk A copper-doped Be capsule driven at 285 ev is sufficiently robust to achieve yields>1 MJ (an ignition margin >1) with the expected precision of target experiments, laser performance, and target fabrication A simulated ignition campaign has verified our ability to achieve the required precision in the presence of physics uncertainties After the first ignition campaign, we have several paths forward to develop a robust ignition platform

3 The NIF point design has a graded-doped, beryllium capsule in a U hohlraum driven at 285 ev by 1.22 MJ Cryo-cooling rings Laser Beams: 24 quads through each LEH arranged control symmetry U hohlraum with B doped Au surface layer to reduce LPI and enhance fabrication yield Cu doped Be Capsule with cryo fuel layer 10.8 mm Laser Entrance Hole sized to balance LPI and radiative losses Capsule fill tube ~10 µm He0.2H0.8 gas fill to control symmetry and minimize LPI

4 We have developed detailed specifications for the point design hohlraum and capsule

5 We have begun productions of targets for the National Ignition Campaign (NIC) 5

6 We have selected a copper doped Be capsule driven at 285 ev for the first ignition experiments (Cu doped Be shell for 285eV, 1.22 MJ) Efficient ablator results in 1/3 more capsule absorbed energy than for an equivalent CH capsule Ablation front instability substantially reduced compared to CH Crystalline structure effects mitigated by melting with the first shock We predict an ignition margin >1 at the point design laser energy

7 A CH capsule at 300eV is the principal alternate to Be at 285 ev Ge doped CH capsule for 300 ev Hohlraum simulations at 300 ev indicate LPI equivalent to Be at 285eV Amorphous material with no crystal structure issues Large data base from Nova and Omega Less efficient ablator and higher ablation front instability result in margin <1 at 1.22 MJ

8 A Uranium hohlraum and Be capsule are chosen to optimize capsule absorbed energy 10-20% of the laser energy to capsule Au with Be Capsule (285) U with Be Capsule (285) U with CH Capsule (300) Laser light (MJ) Absorbed xrays wall loss hole loss capsule efficiency (%) % % %

9 Ignition point design optimization must balance LPI effects, laser performance impacts, and capsule robustness Max allowed hotspot ΔR/R TR(eV) 225 SSD and Polarization smoothing to be incorporated on NIF raises this threshold 285 ev Point design Laser Energy (MJ) Initial operations Design Optimum for initial ignition experiments Experimental lower limit for 1% scatter 300 Tang linear theory 10% scattering SBS Gain Exponent

10 Success of ignition is crucially dependent on Mix, Velocity, Entropy and Shape ( MVSS ) S Entropy " <1.5 Velocity V > 350 km s V R HS "R "R mix "R shell < 0.2 "R HS R HS < 0.18 M Mix Shape S

11 Achieving ignition requires constraining or adjusting multiple lower level parameters that roll up to set the ignition conditions ~150 lower parameters Higher level quantities 1D quantities, e.g: Peak Laser Power Foot Laser Power Velocity of 1 st shock Mix Velocity ρr Total T Ignition 3D quantities, e.g: Ice Perturbations Capsule Roughness Intrinsic Asymmetry Laser Power Balance Entropy Shape ρr hot spot We can adjust or constrain the lower level parameters to affect the higher level parameters Multivariable Sensitivity Studies of the 1D and 3D quantities allow us to specify acceptable values and reproducibility

12 We can define a Margin based on Mix Velocity Entropy Shape that correlates with the likelihood of ignition Margin 1 2 Yield (MJ) Nominal Point Design 1D clean Within 15% in energy, targets with ψek>3.9kj have Y>1.2 MJ Gain The Margin formula is based on a fit to a data-base of 1D and 2D calculations 10 5 ψek(kj)= Effective Fuel Kinetic Energy E fuel E fuel # < v > & M argin = *" = % ( $ 3.9kJ 3.9kJ 365km /sec ' Velocity # &, 0.5+Rmix / +Rhotspot % %%1* (( 1*. 1 % Rhotspot ' +Rshell 0 $ $ - *3.9 # # < ) >& % ( $ 1.46 ' Entropy Shape Mix & ( ( '

13 Success of ignition is crucially dependent on Mix, Velocity, Entropy and Shape ( MVSS ) S Entropy " <1.5 V > 350 km s Velocity V Shock pressures Shock timing Hot electrons T R Laser power Backscatter Hohlraum efficiency Ablator thickness R HS "R M Ablator-fuel interface roughness Photon preheat Ablator dopant Mix "R mix "R shell < 0.2 Ice surface perturbations Ablator low mode surface Laser power balance Hohlraum geometry "R HS < 0.18 R HS Shape S

14 Targets must be made to tight tolerances so MVSS requirements can be met reproducibly S Entropy Ablator thickness Fuel layer thickness Contaminant reproducibility Ablator thickness Contaminant reproducibility Velocity V ΔR R HS "R Ablator-fuel interface roughness Photon preheat 20 nm Ablator dopant Capsule roughness Dopant layer M Mix 0.3 µm Ice perturbations Hohlraum assembly Capsule Shape location S

15 S ±5% The laser must perform reproducibly to meet requirements Entropy ±100 ps R HS "R Velocity ±3% Laser power balance ± 3% quad to quad V Laser Beam pointing ±80 µm M Mix Shape S

16 S To compensate for physics uncertainties the laser and target parameters must be experimentally tuned Entropy Velocity V Power & timing ΔR R HS Dopant level "R ΔR Relative power Length M Mix Shape S

17 S MVSS is adjusted using an array of measurement techniques using 6 surrogate targets and different diagnostics Entropy FFLEX (hot electrons) GXD (shock sphericity) VISAR SOP (shocks) FABS/ NBI (laser coupling) Velocity DANTE (T R ) SXD Shell velocity V R HS "R ARC Radiography (compressed DT shape in THD targets) RadChem (THD targets) M Mix DANTE (Drive spectrum) GXD (shape of gas filled surrogate implosion) Shape S

18 Our ignition campaign is focused towards DT implosions in J F M A M J J A S O N D J F M A M J J A S O N D Drive Drive temperature T rad Learning Symmetry, shock timing and ablation rate technique valn 100 shot Tritium-free tuning campaign Tuning Layered THD implosions with dudded capsules Validation DT Ignition Implosions Yield

19 The National Ignition Campaign must bring together all of the components for the first ignition experiments We are using simulated campaigns to test our strategy

20 Ignition experiments require management and coordination of complex processes Campaign Management Campaign Management Tool Shot plan Requirements Decisions Facility prepares & executes shot Shot Data Analysis 0.4 PostShot (3w w/ mix) PostShot (2.75w w/mix) Data Wavelength Shift (Angstroms) Archiving & visualization Laser - target interaction & outputs

21 To test our experimental strategy and to improve our readiness, we carried out a simulated campaign (SimCam) Campaign Management Campaign Management Tool Shot plan Requirements Decisions Facility prepares & executes shot Shot Data Analysis 0.4 PostShot (3w w/ mix) PostShot (2.75w w/mix) Data Wavelength Shift (Angstroms) Archiving & visualization Numerical modeling is used to simulate facility & target Laser - target performance interaction & outputs

22 The SimCam exercises the real preparation & decision making processes but simulates the facility & target performance Campaign Management Campaign Management Tool Shot plan Requirements Decisions Targets Facility prepares & executes shot Shot Data Analysis 0.4 PostShot (3w w/ mix) PostShot (2.75w w/mix) Data Wavelength Shift (Angstroms) NIF ppt Archiving & visualization NIF DRC_John Edwards, Laser - target interaction & outputs 22

23 The Red Team developed an alternate 2D target physics reality based on model uncertainties Red Team Model ablator EOS ablator contaminant opacity Cu opacity Non-LTE collisonal bound-bound Liner EOS Red Team Physics wall opacity Be opacity Units of 1σ uncertainty DT EOS electron flux limit Non-LTE collisional bound-free Wall EOS Blue Team Model A roll of the dice determined the model off-set compared to the standard (blue team) model Typical model uncertainties are 10-20% Non-LTE collision rates & electron flux limiter are factor 2 NIF ppt NIF DRC_John Edwards,

24 The target failed to ignite after the red team physics was introduced & before retuning Blue team physics (nominal pt design) Red team physics (before tuning) Margin Margin terms Velocity Entropy Shape Mix NIF ppt NIF DRC_John Edwards,

25 The red team was able to re-optimize the ignition target performance using the new physics model using about 10% higher inner cone power Laser Power Required with Alternate Model 192 Beam Power (TW) Inner cone Outer cone Hotspot RMS = 5% Time (ns) 5% hotspot rms Changes in plasma conditions resulting from the red team model would imply a few percent more scatter

26 Add errors to synthetic data 0.4 PostShot (3w w/ mix) PostShot (2.75w w/mix) Data Simulate the shot with red team physics model Shot request Laser pulse Target ID Diagnostics Wavelength Shift (Angstroms) Data Analysis Decision making Shot request Laser pulse Target ID Diagnostics Shot set-up Campaign Management Tool NIF ppt NIF DRC_John Edwards,

27 The Blue Team achieved the required precision using its scaling predictions and expected diagnostics without knowledge of the source of observed discrepancies Laser power DANTE to measure drive Measured DANTE drive (GW) [GW] Experiment to measure X-ray drive vs laser power in first 2 ns Requirement Blue team model #1 #3 adjusted wall opacity Total laser power[tw] Laser power [TW] #2 Red team data time The blue team succeeded in tuning symmetry and shock timing in a similar way

28 The goal for is to achieve a robust ignition platform Margin Nominal Point Design 1D clean robust ignition 10 5 Point design campaign for 2010 ψek(kj)= Effective Fuel Kinetic Energy Gain Yield (MJ) 1 Several paths can take us to a robust ignition platform: Improve the precision of the experimental campaign Reduce the statistical variability of the targets and laser performance Increase the capsule absorbed energy using: - more laser energy - optimized coupling efficiency, e.g larger capsule in a fixed hohlraum

29 We have a clearly defined path forward to achievement of ignition on NIF An extensive scientific data base forms the foundation for the NIF ignition point design target and experimental campaign We have requirements in place for the first ignition attempt in 2010 A margin formalism allows us to evaluate the performance of the targets, and to assess and manage risk A copper-doped Be capsule driven at 285 ev is sufficiently robust to achieve yields>1 MJ (an ignition margin >1) with the expected precision of target experiments, laser performance, and target fabrication A simulated ignition campaign has verified our ability to achieve the required precision in the presence of physics uncertainties After the first ignition campaign, we have several paths forward to develop a robust ignition platform

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