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”

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

Part I. Chamber Physics

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

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

Multi-dimensional effects have been explored For all cases: Tmin = Twall = 973.16 K Time = 0.5 ms Time = 3 ms Time = 8 ms Tmax = 2.2 105 K Tmax = 1.3 105 K Tmax = 5.3 104 K Cartesian Tmax = 3.1 105 K Tmax = 2.2 105 K Tmax = 5.3 104 K Cylindrical

Effects of chamber geometry, cont’d For all cases: Tmin = Twall = 973.16 K Time = 20 ms Time = 65 ms Time = 100 ms Tmax = 1.2 105 K Tmax = 2.3 104 K Tmax = 2.8 104 K Cartesian Tmax = 1.3 105 K Tmax = 5.1 104 K Tmax = 3.2 104 K Cylindrical

Plasma conductivity and radiation play a major role in chamber recovery (chamber state at 100 ms, for all cases Tmin=Twall=973.16 K) Case I: Neutral Gas Case II: Neutral Gas + Electron Conductivity Case III: Gas + Electron Conductivity + Radiation Tmax = 23.3 103 K Tave = 6.3 103 K Tmax = 14.3 103 K Tave = 5.6 103 K Tmax = 4.37 103 K Tave = 1.41 103 K Cartesian Tmax = 31.6 103 K Tave = 4.1 103 K Tmax = 16.9 103 K Tave = 3.4 103 K Tmax = 4.36 103 K Tave = 1.42 103 K Cylindrical

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

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

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

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 30-40 ns is ballistic, followed by plume drag The plasma beta initially is large, but falls quickly

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)

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

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?

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

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

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

Part II. Final Optics for Laser-IFE

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

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

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

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