Summary of Research in the Advanced Energy Technology Group at UC San Diego Farrokh Najmabadi and Mark Tillack March

Our Research Staff and Students Sophia Chengraduate studentElectrical & Computer Engineering Brian Christensengraduate studentMechanical & Aerospace Engineering Kevin CockrellundergraduateElectrical & Computer Engineering Zoran Dragojlovicproject scientistElectrical & Computer Engineering Andres Gaerisproject scientistElectrical & Computer Engineering S. S. Harilalproject scientistElectrical & Computer Engineering Tak Kuen Mauresearch scientistElectrical & Computer Engineering Farrokh NajmabadiprofessorElectrical & Computer Engineering Beau O’Shaygraduate studentElectrical & Computer Engineering John PulsiferengineerCenter for Energy Research René Raffrayresearch scientistMechanical & Aerospace Engineering Kevin Sequoiagraduate studentMechanical & Aerospace Engineering Dai Kai Szeresearch scientistCER/MAE Mark Tillackresearch scientistMechanical & Aerospace Engineering Phyllis Voigtsadministrative specialistCenter for Energy Research Xueren WangengineerCenter for Energy Research

Summary of Research Activities ARIES Fusion Concept Studies High Average Power Laser Program – final optics – chamber clearing – dry-wall armor thermomechanics – cryogenic target survival Inertial Fusion Energy Chamber Physics – magnetic diversion of ablation plumes – phase change physics Laser-Matter Interactions –laser ablation plume dynamics and cluster formation –laser plasma EUV light source Thermal Sciences

1. ARIES Fusion Concept Studies

The ARIES Team has examined several magnetic and inertial fusion power plant concepts during the past 15 years TITAN reversed-field pinch (1988) ARIES-I first-stability tokamak (1990) ARIES-III D- 3 He-fueled tokamak (1991) ARIES-II and -IV second-stability tokamaks (1992) Pulsar pulsed-plasma tokamak (1993) SPPS stellarator (1994) Starlite study (1995) (goals & technical requirements for power plants & Demo) ARIES-RS reversed-shear tokamak (1996) ARIES-ST spherical tokamak (1999) ARIES-AT advanced tokamak (2001) ARIES-IFE IFE chamber studies (2003) ARIES-CS compact stellarator (ongoing)

Concept studies incorporate customer require- ments and the existing database to assess concepts, innovate, and guide the base program Customer Input Mission and Goals Evaluation Based on Customer Attributes Attractiveness Characterization of Critical Issues Feasibility Design Options Assessment Present Data Base Redesign R &D Needs, Development Plan Concept Studies R&D Program

Objectives:  Analyze & assess integrated and self-consistent IFE chamber concepts  Understand trade-offs and identify design windows for promising concepts. The research was not aimed at developing a point design. Approach:  Six classes of realistic target were identified. Advanced target designs from NRL (laser-driven direct drive) and LLNL (Heavy-ion-driven indirect-drive) were used as references.  To make progress, the activity was divided based on 3 chamber classes: Dry wall chambers; Solid wall chambers protected with a “sacrificial zone” (such as liquid films); Thick liquid walls.  These classes of chambers were researched in series with the entire team focusing on each. ARIES integrated IFE chamber analysis and assessment research was a 3-year exploration study, recently completed

History of the UCSD IFE program OFES proposallab YAG Staff ramp-up excimer laser vacuum system new lab LLNL-funded studies of chamber simulation experiments OFES grant on chamber physics, modified to address final optics ARIES-IFE DP HAPL programs GA target engineering OFES grant on chamber physics (terminated) dry walls liquid walls

2. High Average Power Laser Program

Our IFE research is focused on the key issues for IFE chambers and chamber interfaces Prometheus-L Reactor Building Final optics that survive the environment Understanding of residual chamber medium and propagation of targets and beams through it – Chamber dynamic response, chamber clearing – Beam & target interactions Chamber walls that survive or are renewable Cryogenic targets that survive injection

We are developing damage-resistant final optics based on grazing-incidence metal mirrors Objectives: Measure laser-induced damage threshold and demonstrate long-term operation of a grazing incidence metal mirror at laser fluence of ~5 J/cm 2 normal to the beam. Determine limits due to contamination & other target threats. Determine effects of damage on beam quality.

The SPARTAN chamber dynamics and clearing code was developed for studies of the post-blast chamber environment 2-D Transient Compressible Navier-Stokes Equations. Second order Godunov method, for capturing strong shocks. Diffusive terms (conductivity, viscosity) depend on local state variables. Adaptive Mesh Refinement for uniform accuracy throughout the fluid domain. Arbitrary boundary resolved with Embedded Boundary method.

Cyclic thermomechanical behavior of dry- wall chamber armor is under investigation Temperature is calculated from measurement of radiated energy at two wavelengths: A fast (nanosecond) optical thermometer was developed to assist the project with time-resolved surface response measurements

+ Survival of cryogenic direct-drive targets in hot, turbulent chambers is a challenging problem Pre-existing vapor bubbles could close if initial bubble is below a critical size and the heat flux above a critical value t = s T init = 18 K DT Vapor Core Plastic Shell Local Vapor Bubble Rigid DT Solid t v,o roro Thermal, mechanical and phase change studies were performed on cryogenic DT targets subjected to chamber heating

3. Inertial Fusion Energy Chamber Physics

Magnetic diversion of expanding laser plasma is being studied as a possible means to mitigate target debris

Phase change physics is important for under- standing the generation of impulse and behavior of aerosols in liquid-protected IFE chambers Homogeneous nucleation and growth from the vapor phase – Supersaturated vapor – Ion-seeded vapor – Impurity-seeded vapor Phase decomposition from the liquid phase – Thermally driven phase explosion – Pressure driven fracture Hydrodynamic droplet formation (flow conditioning) Spinodal decomposition of Si (Craciun)

4. Laser-Matter Interactions

Laser ablation plume dynamics is extremely complex, involving laser interactions, phase change, gasdynamics, atomic and plasma physics 0.01 Torr 1 Torr 0.1 Torr 10 Torr 100 Torr

Ionization was shown to play a dominant role in nanocluster formation in laser ablation plumes 5x10 9 W/cm 2 Polyimide laser ink-jet printer head (courtesy of HP)

We recently began a program of research on next-generation semiconductor lithography based on laser-plasma EUV emission Achieving higher efficiency and lower contamination are key issues for EUV light sources

5. Thermal Sciences

Studies of heat transfer enhancement techniques are equally important in high heat flux applications (like fusion) and energy efficiency Heat transfer in porous and granular media – Energy recovery ventilator – High heat flux devices Coaxial heat exchanger

UCSD Laser Plasma and Laser- Matter Interactions Laboratory