1. M. S. Tillack and F. Najmabadi
Report on Chamber Physics, Final Optics and IFE Power Plant Conceptual Design Studies
M. S. Tillack and F. Najmabadi
14-15 October 2004
Third IAEA Research Coordination Meeting on
“Physics and Technology of Inertial Fusion Energy Targets and Chambers”

2. During the past 4 years, we have made excellent progress in our CRP activities
Chamber Physics
Spartan was developed, validated and used to study laser-IFE chambers
A new lab was constructed, and experiments on ablation plume dynamics, phase change physics and magnetic diversion were performed
Laser-plasma and atomic physics modeling capabilities were added
Programs on EUV lithography and XUV plasma diagnostics were spawned
Final Optics for Laser-IFE
Numerous fabrication techniques were explored
A KrF laser was added and extensive laser testing was performed
Results were reported at the 3rd TM
Design Studies
ARIES-IFE was completed in November 2003
Our final report was presented at the 2nd RCM in Vienna

3. Part I. Chamber Physics

4. IFE chamber response to target explosions covers vastly different time scales
Target injection,
Laser propagation, …
“Pre-shot” Chamber
Environment
“Fast” time-scale
processes
“Slow” time-scale:
processes
Non-Equilibrium
Environment
First pass of x-rays and ions through the chamber (a few ms)
1-D codes such as Bucky are used
SPARTAN Code

5. The Spartan code models longer time scale hydrodynamics and transport phenomena
Transport processes:
Photon and ion heat deposition; chamber gas conduction, convection and radiation; chamber wall response; cavity clearing
Numerical algorithms:
Godunov solver of Navier-Stokes eqns with state-dependent transport properties
Embedded boundary
Adaptive Mesh Refinement y z
Cartesian
Cylindrical
chamber dimensions:
radius: 6.5 m
height: 13 m
beam sheet dimensions:
length: 20 m
width: 1 m f q x r Xe Xe
initial conditions
from BUCKY q

6. Multi-dimensional effects have been explored
For all cases: Tmin = Twall = K
Time = 0.5 ms
Time = 3 ms
Time = 8 ms
Tmax = K
Tmax = K
Tmax = K
Cartesian
Tmax = K
Tmax = K
Tmax = K
Cylindrical

7. Effects of chamber geometry, cont’d
For all cases: Tmin = Twall = K
Time = 20 ms
Time = 65 ms
Time = 100 ms
Tmax = K
Tmax = K
Tmax = K
Cartesian
Tmax = K
Tmax = K
Tmax = K
Cylindrical

8. Plasma conductivity and radiation play a major role in chamber recovery (chamber state at 100 ms, for all cases Tmin=Twall= K)
Case I: Neutral Gas
Case II: Neutral Gas + Electron Conductivity
Case III: Gas + Electron Conductivity + Radiation
Tmax = K
Tave = K
Tmax = K
Tave = K
Tmax = K
Tave = K
Cartesian
Tmax = K
Tave = K
Tmax = K
Tave = K
Tmax = K
Tave = K
Cylindrical

9. Chamber physics experiments are performed using lasers to simulate short-pulse energy deposition
Laser plasma expansion dynamics
Modeling of laser plasma
Ablation plume experiments
Magnetic diversion
Aerosol generation in liquid-protected walls
Explosive phase change (evaporation)
Homogeneous nucleation in ablation plumes
Laser propagation in background gas
These experimental studies are helping to prepare us for larger, more prototypical tests on major facilities

10. Laser ablation plumes provide a surrogate environment to study magnetic diversion of IFE target emissions
1.5 cm

11. An aluminum ablation plume is confined by a moderate magnetic field
5 GW/cm2, 8 ns, Al target Rb
0.64 T

12. The expansion is slowed after the thermal beta falls
5 GW/cm2
free expansion velocity v=6x106 cm/s
Similar to results without B, the initial ns is ballistic, followed by plume drag
The plasma beta initially is large, but falls quickly

13. Rapid condensation of vapor ejected from liquid-protected IFE chamber walls was modeled numerically and experimentally
0.15 Torr
The processes also occur in pulsed laser deposition (PLD)

14. The homogeneous nucleation rate and critical radius depend on saturation ratio & ionization
High saturation ratios result from rapid cooling during plume expansion
Extremely small critical radius and high nucleation rates result
Ion jacketing (dielectric behavior of vapor) reduces the energy barrier
# of atoms
Si, n=1020 cm–3, T=2000 K
Si, n=1020 cm–3, T=2000 K, Zeff=0.01
Without ionization
With ionization

15. The condensate size distribution was measured at stagnation using atomic force microscopy
500 mTorr He
5x108 W/cm2
5x109 W/cm2
5x107 W/cm2
5x108 W/cm2
5x109 W/cm2
Correlation between laser intensity and cluster size is observed.
Is it due to increasing saturation ratio or the presence of ions?

16. The saturation ratio is inversely proportional to laser intensity
As laser intensity increases, ionization increases but saturation ratio decreases
• 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
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.
The saturation ratio is inversely proportional to laser intensity

17. Spin-off research on EUV lithography began in 2004
EUV spectroscopy has been added to our diagnostic capabilities
Jen-Optik TGS, energy monitor
Modeling capabilities and personnel have been added
Hyades, Helios, Cretin, Hullac
Experimental and modeling studies of underdense Sn foams
Related Activities
SBS cell for pulse compression
Density interferometry
High-field electromagnets

18. New research on non-LTE plasmas and XUV emissions was started in September 2004
Collaboration with LLNL (Tina Back, Howard Scott)
The goal is a quantitative understanding of non-LTE plasmas
Address a class of problems in which temperature cannot be uniquely related to the energy
Long-standing problems modeling radiation from low-density plasmas will be addressed
3-year project goal is to benchmark spectroscopic data of a well-characterized non-LTE plasma

19. Part II. Final Optics for Laser-IFE

20. High-cycle thermomechanical behavior of Al mirrors was studied (results were reported at TM)
Basic stability
Differential thermal stress
S-N curve for Al alloy
High cycle fatigue

21. Several fabrication techniques were 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

22. Extensive testing has been performed at UCSD; Initial testing has begun on Electra (700 J KrF)

23. Future Plans Chamber Physics Final Optics for Laser-IFE Design Studies
OFES-sponsored work on chamber physics has been terminated
HAPL will continue to support chamber clearing studies
Non-fusion programs (EUVL, XUV laser plasma) are growing
Final Optics for Laser-IFE
Under the HAPL program, we will continue to acquire higher shot counts, test larger optics, and perform system integration
Design Studies
ARIES-IFE was completed
Our power plant studies are no longer funded by OFES