Chamber Dynamic Response, Laser Driver-Chamber Interface and System Integration for Inertial Fusion Energy Mark Tillack Farrokh Najmabadi Rene Raffray First IAEA-CRP-RCM on “Elements of Power Plant Design for Inertial Fusion Energy” May 21-25, 2001 IAEA Headquarters, Vienna

Outline ARIES power plant studies program Assessment of IFE chambers Laser driver-chamber interface studies Final optics damage Beam propagation through chamber media Chamber dynamic response and clearing Numerical modeling Simulation experiments

 Analyze & assess integrated, self-consistent IFE chamber concepts  Understand trade-offs and identify design windows for promising concepts. The research is not aimed at developing a point design.  Identify existing data base and extrapolations needed for each promising concept. Identify high-leverage items for R&D: What data is missing? What are the shortcomings of present tools? For incomplete database, what is being assumed and why? For incomplete database, what is the acceptable range of data? Would it make a difference to first order, i.e., does it make or break the concept? Start defining needed experiments and simulation tools. Goals of ARIES Integrated IFE Chamber Analysis and Assessment Research

ARIES-IFE is a Multi-Institutional Effort Program Management F. Najmabadi Les Waganer (Operations) Mark Tillack (System Integration) Program Management F. Najmabadi Les Waganer (Operations) Mark Tillack (System Integration) Advisory/Review Committees Advisory/Review Committees OFES Executive Committee (Task Leaders) Executive Committee (Task Leaders) Fusion Labs Fusion Labs Target Fab. (GA, LANL*) Target Inj./Tracking (GA) Chamber Physics (UW, UCSD) Chamber Eng. (UCSD, UW) Parametric Systems Analysis (UCSD, BA, LLNL) Materials (ANL) Target Physics (NRL*, LLNL*, UW) Drivers* (NRL*, LLNL*, LBL*) Final Optics & Transport (UCSD, LBL, PPPL, MIT, NRL*,LLNL*) Safety & Env. (INEEL, UW, LLNL) Tritium (ANL, LANL*) Neutronics, Shielding (UW, LLNL) Tasks * voluntary contributions

An Integrated Assessment Defines the R&D Needs Characterization of target yield Characterization of target yield Target Designs Chamber Concepts Characterization of chamber response Characterization of chamber response Chamber environment Chamber environment Final optics & chamber propagation Final optics & chamber propagation Chamber R&D : Data base Critical issues Chamber R&D : Data base Critical issues Driver Target fabrication, injection, and tracking Target fabrication, injection, and tracking Assess & Iterate

Status of ARIES-IFE Study  Six combinations of target and chamber concepts are under investigation: Nearly Complete, Documentation Direct drive target Work started in March 2001 Dry wall Solid wall with sacrificial layer Thick Liquid Wall Indirect drive target Work started in March 2001 *Probably will not be considered *

Driver-Chamber Interface & Final Optic Damage Prometheus-L reactor building layout (30 m) (SOMBRERO values in red) (20 m) Grazing incidence mirrors Si 2 O or CaF 2 wedges

Final Optic Damage Threats Damage that increases absorption (<1%) Damage that modifies the wavefront – – spot size/position (200  m/20  m) and spatial uniformity (1%) Two main concerns: Final Optic ThreatNominal Goal Optical damage by laser>5 J/cm 2 threshold (normal to beam) Sputtering by ionsWavefront distortion of < /3 * (~100 nm) Ablation by x-rays(6x10 8 pulses in 2 FPY: (~25 mJ/cm 2, partly stopped by gas) 2.5x10 6 pulses/allowed atom layer removed) Defects and swelling induced by Absorption loss of <1%  -rays (~3) and neutrons (~18 krad/s)Wavefront distortion of < /3 * Contamination from condensable Absorption loss of <1% materials (aerosol and dust) >5 J/cm 2 threshold * “There is no standard theoretical approach for combining random wavefront distortions of individual optics. Each /3 of wavefront distortion translates into roughly a doubling of the minimum spot size.” (Ref. Orth)

The UCSD laser-plasma and laser-material interactions lab is used for damage tests Spectra Physics YAG laser: 2J, 10 nm; 800, 500, , 266 nm Peak power density ~10 14 W/cm 2 Shack-Hartmann Profiling Class 100 cleanroom enclosure 100 ppm accuracy Reflectometry

Modeling the effects of damage on beam characteristics helps us establish damage limits

Laser propagation near or beyond the breakdown threshold is uncertain  Laser intensity near the target: – W/cm 2  Threshold intensity is not well- defined; laser light partially ionizes chamber gas at any intensity  Gas “breakdown” occurs when plasma density is high enough that a substantial amount of laser light is absorbed (avalanche process).  Previous work: breakdown threshold defined as intensity at which visible light is emitted from the focal spot (most of the visible light is generated by the interaction of electrons generated by ionization of the background gas with the neutral gas atoms).  Wavefront distortion can occur at lower (or higher) plasma densities and laser intensities, changing the beam profile on the target. This “threshold” intensity will depend on the required degree of beam smoothness on the target, f number of the lens, beam coherence, etc.  Multi-species and contaminated environmental conditions further complicate the physics. Data for Xe, except Turcu

 The rep-rate is limited by the time it takes for the chamber environment to return to a sufficiently quiescent and clean, low-pressure state following a target explosion to allow a second shot to be initiated (goal: ms). Understanding Chamber Dynamics and Clearing is a Critical R&D Item Gas dynamics: Compressible Radiation heat transport Dissipative processes … Volume interactions: In-flight evaporation In-flight re-condensation Chemistry … Surface Physics: Melting & melt layer behavior Evaporation/sublimation Sputtering Macroscopic erosion Condensation and redeposition …  Many complex phenomena must be understood and modeled.

 “First pass” of target-released energy through the chamber – “fast” time scale (ns to several  s). Propagation of X-rays and ions through the chamber; Re-radiation of the ions & X-ray energy deposited in the chamber gas. At the completion of this phase, the chamber volume is in a non-equilibrium state and material is released from the wall.  Relaxation of chamber environment to a equilibrium state – “slow” time scale (several  s to hundreds of ms). Mass and heat transport in the chamber & to/form chamber wall Relaxation to “residual” chamber environment (“pre-shot” environment) The “pre-shot” environment affects target injection & tracking, laser propagation, … Response of Chamber to Target Explosion Covers Two Vastly Different Time Scales

Multi-Physics Model of Chamber Dynamics

Chamber Dynamics Simulation Experiments – Exploration and Planning  Simulation experiments are essential to: Benchmark simulation codes; Ensure all relevant physical phenomena is taken into account  Relatively new field: Previous experimental work focused on shock propagation and/or condensation of wetted chamber walls.  Eventually, we need scaled experiments to screen concepts for implementation on integrated research experiments (IRE’s).  Two major areas need to be investigated first: 1.A source of energy to produce prototypical environments for experimentation, 2.Experiment characterization and array of diagnostics.

Scaled Simulation Experiments Can Help Address Many Chamber Issues 100–500 J Large-volume tests for geometrically prototypical testing 1–10 kJ Integrated (simultaneous) surface and volume effects Chamber dynamics in limited volume (~1 liter) 1–10 J Beam propagation and focusing Near-surface physics Diagnostic development and experimental techniques >10 MJ Integrated prototypical chamber testing Incl. neutrons

Many Opportunities Exist for International Collaboration Design studies ARIES-IFE Laser driver-chamber interface studies Modeling and experiments on optics damage Breakdown and beam propagation through chambers Chamber dynamic response and clearing R&D Numerical modeling Simulation experiments