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M. S. Tillack
IFE Technology Research at UC San Diego
MAE Departmental Seminar6 October 2004
http://aries.ucsd.edu
Many people have contributed to this research
Faculty and
Staff:
C. V. Bindhu
Z. Dragojlovic
A. C. Gaeris
S. S. Harilal
F. Najmabadi
T. K. Mau
J. E. Pulsifer, MS’98
A. R. Raffray
X. R. Wang
M. R. Zaghloul
Students:
N. Basu, MS’98
D. Blair, PhD’03
L. Carlson
S. Chen
B. Christensen,
MS’04
K. Cockrell
M. Mathew
J. O’Shay
K. Sequoia
New kids
on the block:
K. Boehm
J. Hanft
J. Mar
R. Martin
E. Simpson
The inertial confinement fusion concept
The goal of “ICF” research is to ignite DT targets in order to explore high energy
density physics
Indirect DriveDirect Drive Z-pinch
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Omega
2 mm
DT ice
Au cone
Be+Cu
ρ=3. -5e gcm-3
Ignition scale“fast ignition”
1.95 mm1.69 mm1.50 mmDT Vapor0.3 mg/ccDT FuelCH Foam + DT1 mm CH+500 Å Pd
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NIF
60 beams/40 kJ
192 beams/2 MJ@3
2 MJ of x-rays
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Z
The goal of “IFE” research is to generate power economically
• HAPL: Laser driver (DPSSL or KrF) with direct drive targets and dry walls
• HI-VNL: Ion accelerator, indirect drive targets, liquid chambers
• Z-IFE: Z-pinch driver
In addition to target physics, key issues include efficient rep-rated drivers, target mass production, target injection, reliable chambers and optics
Our IFE research is focused on the key issues for IFE chambers and chamber
interfaces
Prometheus-L Reactor Building
1. Chamber walls that survive long-term exposure
2. A residual chamber medium which allows propagation of targets and beams through it
3. Final optics that survive long-term exposure
4. Cryogenic targets that survive injection and are properly illuminated
neutrons & gammas
x-rays
ions
1.Prompt transport of energy through and deposition into materials (ns-s)
2.Radiation fireball & shock propagation, mass loss from walls (1-100 s)
3.Afterglow plasma & hydrodynamics (1-100 ms)
4.Liquid wall dynamics (ms-s)
5.Long-term changes in materials
Following target explosions, several distinct stages of chamber response occur:
Wall protection and target/driver propagation depend on the details of target
emissions
Fireball forms from captured x-ray and ion energy, re-radiates on
a slower timescale
Fireball forms from captured x-ray and ion energy, re-radiates on
a slower timescale
200-400 MJ released per target
Our chamber wall research simulates thermomechanics of armor and energy
transport from ablation plumes
• High-cycle fatigue of tungsten armor
– simulations with short-pulse lasers– phenomena similar to optics
damage
• Laser plasma expansion dynamics– modeling of laser plasma– ablation plume experiments– magnetic diversion
We use laser ablation plumes to provide a surrogate plasma to study IFE target
emissions
1.5 cm
Time-resolved imaging and spectroscopy are performed with 2-ns gated camera
and PMT
An aluminum ablation plume is confined by a moderate magnetic
field5 GW/cm2, 8 ns, Al
target
0.64 T Rb
free expansion velocity v=6x106 cm/s
5 GW/cm2
The plasma beta initially is large, but
falls quickly
Similar to results without B, the initial 30-40 ns is
ballistic, followed by plume drag
The expansion is slowed after the thermal beta falls
Our IFE research is focused on the key issues for IFE chambers and chamber
interfaces
Prometheus-L Reactor Building
1. Chamber walls that survive long-term exposure
2. A residual chamber medium which allows propagation of targets and beams through it
3. Final optics that survive long-term exposure
4. Cryogenic targets that survive injection and are properly illuminated
We seek to understand the residual chamber medium and the propagation of
targets and beams through it
• Chamber dynamic response modeling and “chamber clearing”
• Target transport through the perturbed chamber
• Aerosol generation in liquid-protected walls
– explosive phase change (evaporation)– homogeneous nucleation in laser
ablation plumes (condensation)
• Laser propagation in background gas
Spartan simulation
Rapid condensation of vapor ejected from liquid-protected IFE chamber walls was
modeled numerically and experimentally
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0.15 Torr
These processes also occur in laser machining, pulsed laser deposition, and other applications
Again, lasers are used to simulate ion & x-ray deposition and response
The homogeneous nucleation rate and critical radius depend on saturation ratio &
ionization
# of atoms
• Ion jacketing (dielectric behavior of vapor) reduces the energy barrier
Without ionization With ionization
Si, n=1020 cm–3, T=2000 K
• High saturation ratios result from rapid cooling during plume expansion
• Extremely small critical radius and high nucleation rates result
Si, n=1020 cm–3, T=2000 K, Zeff=0.01
W(r)=- 34 r r3 nDn_ i +4r r2v + 1- 1/f c_ i Q2/8r f o_ i 1/r - 1/ra_ i
The condensate size distribution was measured at stagnation using atomic force
microscopy
500 mTorr He
5x108 W/cm2 5x109 W/cm2
5x109 W/cm25x108 W/cm2
5x107 W/cm2
• Correlation between laser intensity and cluster size is observed.
• Is it due to increasing saturation ratio or the presence of ions?
• Plasma temperature and density were measured spectroscopically using Stark broadening and line ratios
• Saturation ratio and ionization state were computed using these measurements and assuming local thermodynamic equilibrium
The saturation ratio is inversely proportional to laser intensity
As laser intensity increases, ionization increases but saturation ratio decreases
Maximum charge state at 50 ns, 1 mm from Al target, as derived from spectroscopy and assuming LTE.
Saturation ratio at 1 mm, derived from spectroscopy and assuming LTE.
Our IFE research is focused on the key issues for IFE chambers and chamber
interfaces
Prometheus-L Reactor Building
1. Chamber walls that survive long-term exposure
2. A residual chamber medium which allows propagation of targets and beams through it
3. Final optics that survive long-term exposure
4. Cryogenic targets that survive injection and are properly illuminated
The final optic in a laser-IFE plant sees line-of-sight exposure to target emissions
• Laser-induced damage
• x-rays
• ions
• neutrons and -rays
• contaminants
Damage threats:
• 5 J/cm2
• 2 yrs, 3x108 shots
• 1% spatial nonuniformity
• 20 m aiming
• 1% beam balance
Mirror requirements:
We are developing damage-resistant final optics based on grazing-incidence metal
mirrors
The reference mirror concept consists of a stiff, light-weight, radiation-resistant substrate with a thin metallic coating optimized for high reflectivity (Al for UV, S-polarized, shallow )
Al reflectivity at 248 nm
~50 cm85˚
Laser damage is thermomechanical in nature: high-cycle fatigue of Al bonded to
a substrate
300 nm Coating
300
305
310
315
320
325
330
335
340
0.E+00 1.E-08 2.E-08 3.E-08 4.E-08 5.E-08 6.E-08Time, s
Temperature, K
SurfaceInterfaceSiC (0.5 um)SiC (1 um)SiC (2.5 um)SiC (5.0 um)
q”=10 mJ/cm2Al: 20-500 nmSiC: 10 m
S-N curve for Al alloy
Basic stability
High cycle fatigue
Differential thermal stress
Testing is performed at the UCSD laser plasma and laser-matter interactions laboratory
cubedumpcube1/2 waveplatebeam diagnosticsdumpviewing portspecimenmount
400 mJ, 25 ns, 248 nm
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Pure Al can have large grains, resulting in slip plane transport and grain boundary
separation (data at 5 J/cm2, 50 shots)
)(in
)(is
)(in
)(is)(in
)(is
)(in
)(is)(* in
)(* is
⊥
*
C
Several fabrication techniques have been explored to enhance damage
resistance
• Monolithic Al (>99.999% purity)
• Thin film deposition on polished substrates
– sputter coating, e-beam evaporation
– Al, SiC, C-SiC and Si-coated substrates
• Electroplating
• Surface finishing
– polishing, diamond-turning
– magnetorheological finishing
– friction stir processing
• Advanced Al alloys
– solid solution hardening
– nanoprecipitation hardening
Finer-grained electroplated Al withstands higher fluence, but eventually goes unstable
At 18.3 J/cm2 laser fluence: Grain boundaries still separate Damage is “gradual” at 18.3 J/cm2
Mirror survived 105 shots
At 33 J/cm2 laser fluence: Rapid onset (2 shots) Severe damage (melting) probably starts with grains
High shot count data extrapolates to acceptable LIDT; end-of-life exposures are
still needed
In addition, we are continuing to develop improve- ments such as “Al-on-Al”, hardened alloys, etc.
Our IFE research is focused on the key issues for IFE chambers and chamber
interfaces
Prometheus-L Reactor Building
1. Chamber walls that survive long-term exposure
2. A residual chamber medium which allows propagation of targets and beams through it
3. Final optics that survive long-term exposure
4. Cryogenic targets that survive injection and are properly illuminated
Targets play a central role in many of the critical issues for
IFE
MIRROR R 50 m
TRACKING10 m STAND-OFF
5 m
CHAMBERR 5 mT ~1500 C
ACCELERATOR8 m1000 gCapsule velocity out 400 m/sec
INJECTORACCURACY
TRACKINGACCURACY
GIMM R 30 m
R 6.5mT ~ 1000C
1.Mass production 500,000/day, $0.25/target, sub-m uniformity
2.Injection 400 m/s, 1-5 mm accuracy
3.Tracking/steering 20/200 m accuracy, ~64 beams
4.Survival 18˚K target in a 1000˚C turbulent chamber
We collaborate with General Atomics on several target-related
tasks
1.Target fabrication• indirect drive target layering
via external thermal control
2.Target injection• sabot transport• capsule steering
3.Target tracking/beam steering• interface with beam steering
system
4.Target survival
Target steering is possible in the chamber using a short-pulse guide laser
• Use shortest pulse possible for minimum ablation depth: 15 fs
• Use highest pulse energy to achieve maximum impulse (subject to total power and rep rate constraint)
• assume 100 kW for 15 ms, 100 kHz – 1 J pulses• assuming 1 mm2 contact, 1016 W/cm2 if the full beam hits• 1014 W/cm2 is a more likely value
• Instead of steering 64 heavy mirrors, why not steer one 4-mg target?
• Can be accomplished using an annular guide-laser beam in the chamber
• Biggest concern is amount of ablation needed and degradation of target surface due to that ablation
Analysis of ablation depth and impulse was performed using the 1D Hyades rad-hydro
code
• 850-nm laser pulse, 15 fs FWHM, 1014 W/cm2
• 500-nm Au coating, 100 m CH substrate
• run code until plume heating of surface is negligible and acceleration phase is complete (1 ns)
DT CH
Au
feathered grid
3 nm
16 nodes
Ablation depth and expansion velocity of Au
d ~2.5 nm total ablationm ~2.5 g/cm2 accelerated to
<v> ~ 2x105 cm/smv ~0.5 (g-cm/s)/cm2
assuming 1 mm2 contact and 5 mg target, each “kick” results in 1 cm/s correction of the target transverse velocity
For more information on our research and student
opportunities,visit our web sitehttp://
aries.ucsd.edu