HAPL Direct Drive Targets: Baseline Specifications

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
Why Direct Drive? Energy Accounting for NIF at 1MJ
NIF Indirect Drive_at_ 3? NIF Indirect Drive_at_ 3? NIF Direct Drive_at_ 3? NIF Direct Drive_at_ 3?
1MJ 1MJ
Backscatter / laser loss 0.9 0.9MJ
Laser ? x-ray 0.84 0.76MJ
Capsule absorption fraction 0.18 0.14MJ 0.9 0.9MJ
Hydro efficiency? shell KE 0.17 0.024MJ 0.10 0.09MJ
(Target gain) ( 10) ( 10) ( 30) ( 30)
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
(Imax5e14W/cm2) and zoom (super-Gaussian beams
not top-hat)
3
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
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
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
Determining Direct Drive Gain Curves. There are
Six (count em...six! ) Independent Variables
4?
Gain

3?
_at_ fixed peak I.l2 _at_ fixed peak I
2?
Edriver
9
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., rrign0.35g/cm2,
Tign10keV Doesnt explain partition into
hotspot and cold fuel
11
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
rh
At time of maximum kinetic energy
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
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)
DTCH foam
DT fuel
High Gain Direct Drive Reactor Target
2.5MJ
DT gas
Time (ns)
16
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
Determining Direct Drive Gain Curves. There are
Six (count em...six! ) Independent Variables
4?
Gain

3?
_at_ fixed peak I.l2 _at_ fixed peak I
2?
Edriver
DR
R
18
Initial Parametric Results for Gain CurvesFix
R0.238cm, Scan Shell Thickness DR
Edriver2.94MJ, Il21e15(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
Energy on target (MJ) 2.5-3.5MJ dependent on wavelength (2-3w)
Pulse lengths (ns) Total20, picket0.6, foot6,accel phase8,av. peak power4.5
Power (W) 5.5e14(peak), 4e14(av.peak), 2.8e13(foot), 1.1e14(picket) Contrast ratio20
Intensity (W/cm2) 8e14(over accl phase), 1e15 (over av. peak power)
Pulse shock precision time/power 0.05ns ( 0.3ns ? -7 in gain) 3 ( 10 ? -7 in gain)
Beam-beam power bal 8 in 0.5ns
Quad-quad power bal 4 in 0.5ns (indep quads)
Individual beam non-uniformity 3 in 0.5ns (all modes)
Bandwidth/smoothing/RMS imprint 1THz(3w) 2D SSD 50nm (picket may relax this)
Polarization smoothing 2x50mrad (needed?)
Overall uniformity low modes (beam-beam variation pointing, power-bal.....) dI/I1.5 (for CR29, Drh/rH1/3)
Overall uniformity high modes l10-120 (from individual beam structures) lt0.5 RMS for tsmooth0.5ns (indiv beam uniform. 3)
Capsule outer CH surface finish lt50nm
Inner ice layer uniformity/ roughness 5mm ( 20mm ? -7 in gain) lt0.5mm for l 10
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 lgt10)