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HAPL Direct Drive Targets: Baseline Specifications

HAPL Direct Drive Targets: Baseline Specifications. L. John Perkins, Max Tabak, Ray Beach With thanks to: S.Skupsky, C.Bibeau, W.Meier, K.Manes, S.Dixit, J.Hunt, E.Moses, J.Murray, R.Town High Average Power Laser Program LLNL, Livermore CA June 20, 2005. convergence ~25 ~3-4x10 7 cm/s.

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HAPL Direct Drive Targets: Baseline Specifications

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  1. HAPL Direct Drive Targets: Baseline Specifications L. John Perkins, Max Tabak, Ray Beach With thanks to: S.Skupsky, C.Bibeau, W.Meier, K.Manes, S.Dixit, J.Hunt, E.Moses, J.Murray, R.Town High Average Power Laser Program LLNL, Livermore CA June 20, 2005

  2. convergence ~25 ~3-4x107 cm/s Indirect Drive Direct Drive Why Direct Drive? Energy Accounting for NIF at 1MJ Bottom line – Get ~3-4 times more energy in shell at max kinetic energy But! – low mode symmetry and high mode stability ???? *S.Skupsky LLE-- Losses includes refraction, LPI (Imax=5e14W/cm2) and zoom (super-Gaussian beams not top-hat)

  3. Laser Power Pulse Shape KrF or DPSSL 1.0 0.1 0.01 0.001 “Picket stake” prepulse Standard 2.4mm DT ablator (+ CH foam) DT fuel Time DT gas LASNEX 2D Stability Results KrF at 0.25mm Standard pulse Picket Standard Yield(MJ) 343 384 Elaser(MJ)2.94 2.4 Gain 117 157 Shell breakup fraction: ~0.15 ~1.8 Growth factor Picket pulse Innovative Laser Pulse Shaping has Significantly Improved Stability of High-Gain Direct-Drive Targets

  4. A Target-Centric View of HAPL Design Optimization: The Target Drives the Driver System economics Target specs Chamber Final optics Energy conversion and B.O.P Freq conversion Laser Laser aux plant and buildings

  5. ? ? ? What is The Optimum l for DPSSL-Driven Targets? 1w 2w 3w 4w l() 1.05 0.53 0.35 0.26  Target gain………………………………..  Laser-plasma interactions……………..  Imprint (standoff ).............................  Target stability…………………………...  Laser efficiency (wallplug  target)…. Optics damage/lifetime………………… Integration complexity…………………. Systems optimum (COE....?)………..... NB: KrF is at 0.25mm

  6. 1-D LASNEX Gain Curve for a Fixed Target Design -1-D LASNEX Results High Gain Direct Drive target. Fixed baseline target, mass = 8.6mg Baseline - 2.94MJ Target gain Marginal ignition Driver energy (MJ)

  7. g e plasma wave g g ion acoustic wave g two e plasma waves g Laser Plasma Instabilities are a Concern at Longer Wavelength (but Hard to Quantify!)  Stimulated Raman Scattering (SRS) Ithreshold ~ 40 / (Lrl)  Stimulated Brillouin Scattering (SBS) Ithreshold ~ 1.7Te(nc/n) / (Ll)  Two-Plasmon Decay (TPD) Ithreshold ~ 0.54Te / (Lrl)  These cause: – Suprathermal electrons that preheat fuel (SRS, TPD) – Reduced efficiency due to scattered light (SRS, SBS) – Filamentation resulting in intensity peaking  instabilities (all) – Net result is Ithreshold ~ 1/ lso factor of ~2 lower for 3w 2w

  8. 6 4 3 1 3 5 4 7 1 2 Determined by shell outer radius (R) Laser intensity ( Drfuel) DR shell thickness (DR) Fuel adiabat Determined by fuel adiabat Time R For a given Edriver and w, contours in 3(4) – space show: velocity,ignitability, rho-R,IFAR, CR , KE margin, yield, gain, ...etc Determining Direct Drive Gain Curves. There are Six (count ‘em...six! ) Independent Variables 4 Gain 3 • @ fixed peak I.l2 • @ fixed peak I 2 Edriver

  9. Previous Understanding High temperature, low density hotspot • Based on isobaric assumption (constant pressure) across hotspot and cold fuel at ignition • Fusion-a energy plays no role in ignition conditions • Hotspot conditions for ignition are fixed, rRign~0.35g/cm2, Tign~10keV • Static model - doesn’t explain partition into hotspot/cold fuel Low temperature, high density cold fuel T Isobaric (constant pressure) Profiles at Ignition P r Radius • The hotspot and cold fuel are not in pressure equilibrium at ignition • Fusion-a energy present at ignition can exceed kinetic energy from stagnating shell • Cold fuel is not at const. density/pressure; partitions into a stagnated tamp mass and a still ingoing mass • Hotspot conditions for ignition depend on the tamping effect of the cold fuel • Requires solution of six coupled, time-dep ODE’s New Understanding T P Profiles at Ignition Stagnated cold fuel r Radius We have Developed a Fast (~3sec) Dynamic 0-D Model of Compression, Ignition and Burn in ICF Capsules This has lead to a new fast (~3s) dynamic 0-D model — consistent with our rad-hydro-burn codes — for use in design optimization of HAPL reactor targets

  10. Isobaric Hotspot Ignition Model (Meyer-ter-Vehn) At ignition At time of maximum kinetic energy High temperature, low density hotspot Low temperature, high density cold fuel Th Ed (off)  v, Kc Profiles at Ignition m Isobaric (constant pressure) P Radius h Radius rh rc • Based on isobaric assumption (constant pressure) across hotspot and cold fuel at ignition • Fusion energy plays no role in ignition conditions • Hotspot conditions for ignition are fixed, e.g., rrign~0.35g/cm2, Tign~10keV • Doesn’t explain partition into hotspot and cold fuel

  11. Thus need 6 coupled differential equations: Hotspot mass balance Hotspot energy balance System mass balance System energy balance Tamp shock velocity System inertia The New, Non-Isobaric O-D Model is Fully DynamicThrough Compression, Ignition and Burn Isobarichotspot Tamp cold fuel Unstagnated cold fuel max Low temperature, high density, stagnated tamp mass Th Ed (off) P v, Kc m Radius fmarginKc Th(0)=T0 c h Radius r(0)=r0 At time of maximum kinetic energy rh rc rT At ignition Need to determine dynamically: Th(t), rh (t), rh (t), rT(t), rc(t), rc (t) 

  12. Just Need to Solve Six Coupled Differential Equations – Takes ~3s with Mathematica Need to determine : Th(t), rh (t), rh (t), rT(t), rc(t), rc (t)

  13. Edriver = 2.94 MJ Shell radius-v-time plot with burn “off” IFAR=24 Single region fuel/ablator Radius (cm) v=3.3e7cm/s Conv. Ratio=27 1-D LASNEX density @ ignition Time (ns) @ max KE Time Time evolution of density profiles from max kinetic energy to ignition Density profiles at ignition. (Arbitrarily normalized in peak height and radius) Model: density pressure Density (arb scale) Density (g/cm3) Radius (arb scale) Radius (cm) 0-D Model: Dynamics for Baseline Target

  14. OD Model - Shell Dynamics rR at tign =2.17g/cm2 mtamp +mcold rRhot at tign =0.31g/cm2 Radii (cm) rc Mass (g) rT rh mhot Time (ns) Time (ns) tign tign tmax KE tmax KE Time evolution of mass components Time evolution of region radii

  15. OD Model: Burn Dynamics -vs- Drive Energy Hotspot Temperatures (keV) Hotspot Radii (cm) Edriver = 2.9MJ Edriver = 2.9MJ 2.7MJ 2.7MJ Hotspot temperature (keV) Hotspot radius (cm) 2.5MJ 2.5MJ tmax KE tign Time (ns) Time (ns) Fusion Energies (J) Edriver = 2.5, 2.7, 2.9, 4.0 MJ Edriver = 2.9MJ 2.7MJ Fusion energy (J) DT+CH foam DT fuel High Gain Direct Drive Reactor Target 2.5MJ DT gas Time (ns)

  16. Normalize at baseline point O-D Model Gain Curve at Fixed Mass/Dimensions -O-D Model Locates Marginal Ignition! High Gain Direct Drive target. Fixed target, mass = 8.6mg Target gain 1-D LASNEX Driver energy (MJ)

  17. 5 4 3 1 1 2 4 6 3 Determined by shell outer radius (R) Laser intensity shell thickness (DR) Determined by fuel adiabat Time Fix R and scan shell thickness DR Determining Direct Drive Gain Curves. There are Six (count ‘em...six! ) Independent Variables 4 Gain 3 • @ fixed peak I.l2 • @ fixed peak I 2 Edriver DR R

  18. 4w (0.25mm) 3w (0.35mm) Velocity (cm/s)/107 IFAR/10 Velocity (cm/s)/107 IFAR/10 Conv. Ratio/10 Conv. Ratio/10 Yield(MJ)/100 Yield(MJ)/100 Gain/100 Gain/100 Shell thickness DR (cm) Shell thickness DR (cm) Ignition/burn threshold Initial Parametric Results for Gain Curves:Fix R=0.238cm, Scan Shell Thickness DR Edriver=2.94MJ, Il2=1e15(0.25)2 Wcm-2mm2

  19. Gain Decreases with Increasing Wavelength Gain Curves (Picket Pulses) 4w (0.25mm) 3w (0.35mm) 2w (0.53mm) Target gain 350MJ yield Driver energy (MJ)

  20. HAPL Direct Drive Target :First Cut at Laser/Target Specs – June ‘05 Sources: J.Perkins HAPL w/shop presentations UCLA (June 2004), PPPL (Oct 2004); D.Eimeral “Configuring the NIF for Direct Drive” UCRL-ID-120758 LLNL (1995); R.McCrory “NIF Direct-Drive Ignition Plan” plus briefing VGs (April 1999); LLE Reviews 98 p67, 79 p121, 84 181. S.Skupsky(LLE) pvte comm. (May 2005) * NIF indirect drive specs: 12nm (CH), 33nm (Be/Cu), 0.5mm (inner ice l>10)

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