Overview of Inertial Fusion Energy

Technology Activities at UC San Diego

Mark S. Tillack

Briefing to the Advanced Energy Technology GroupJune 2001

IFE Technology Program Relationships

National CollaborationsARIES TeamIFE Technology:

Target Engineering (GA) Chamber Materials (SNLA Team) Chamber Physics (ANL/INEEL) Final Optics

(UCLA/LANL/LLNL/GA)

International Collaborations

Local OrganizationJSOE: MAE and ECE Departments

Center for Energy ResearchPlasma Experimental ProgramsPlasma Theory and ComputationVirtual Laboratory for TechnologyAdvanced Energy Technology:

1. Fusion Design Studies2. IFE Technology3. Thermal Sciences

Collaborations

DOE Office of Fusion Energy SciencesScience DivisionTechnology Division (VLT, Baker)

Design Studies: ARIES (Dove, Najmabadi)IFE Technology (Nardella, Meier)

DOE Defense ProgramsHigh Avg. Power Laser Program (Schneider)

Naval Research Laboratory (Sethian)Lawrence Livermore National Lab (Payne)

CA State ProgramsCalifornia Energy CommissionUC Energy InstituteNational Laboratory collaborative programs

Industry ProgramsSBIR contracts (PPI)GA contracts (Goodin)

Funding and Oversight

History of the IFE Technology Program

Sept. 1996 Initial contact with LLNL

June 1997-99 Funded studies of chamber simulation experiments

July 1999 OFES 3-year grant initiatedLab space obtained (3703 EBU-I), laser ordered

December 1999 Delivery of 2J Nd:YAG laser

April 2000 Initial experiments performed;Collaboration with GA on optics fab. & characterization started

June 2000 ARIES IFE study kick-off

July 2000 First new researcher hired into the IFE technology program

April 2001 DP grants awarded, chamber physics & materials programs initiated

June-July 2001 Arrival of 5 new staffGA collaboration initiated on target engineering

IFE Technology Program Organization, June 2001

Driver interface

Chamber physics

IFEengineering

IFE power plantstudies

Collaboration w/ General Atomics

J. Pulsifer(thermal analysis)

E. Abu-Nada(integratedmodeling)

F. Najmabadi

Final OpticsBeamPropagation

Experiments

M. Tillack

M. Tillack F. Najmabadi

R. Raffray

Z. Dragojlovic(integrated modeling)

Collaboration w/ ANL, INEEL

A. Gaeris

S. S. Harilal

B. Harilal

M. Zaghloul(materialsresponse)

R. Miller

E. Abu-Nada

System ModelChamber Eng.

R. Raffray

T. K. Mau(modeling)

M. Zaghloul(testing)

Integration

M. Tillack

M. Zaghloul

X. Wang

Final optics

T. K. Mau

J. Pulsifer

M. Tillack

S. S. Harilal(spectroscopy)

J. Pulsifer(vac. eng.)

A. Gaeris(smoothing)

F. Najmabadi

Numericalmodeling

Engineeringresponses

F. Najmabadi

Targetengineering

R. Raffray

Chamber wallengineering

Collaboration w/ Sandia Albuquerque

T. K. Mau(radiation)

M. Tillack

D. Blair

M. Tillack R. Raffray

M. Zaghloul

X. Wang

M. Tillack

Collaboration w/ UCLA, LANL,

LLNL, GA

Prometheus-L Reactor Building Layout

Driver Interface R&D: Final Optics(Tillack, Zaghloul, Mau)

Problem StatementThe final beam steering optic in a laser-IFE power plant is subjected to a variety of

threats, including neutrons, -rays, x-rays, high-energy ions, chamber contaminants and the laser itself. Robust optics that can survive for extended periods of time (108 shots) without degrading the laser beam quality are needed.

Objectives • Measure laser-induced damage threshold and demonstrate stable long-term operation of

a grazing incidence metal mirror at laser fluence of ~5 J/cm2 normal to the beam. • Determine limits on damage due to contamination and other target threats.

Key Program Elements• Fabrication and characterization of mirrors (including subcontract with GA)• Testing in the UCSD Laser Plasma and Laser-Material Interactions Laboratory• Modeling of the effects of damage on beam characteristics• Neutron irradiation testing in collaboration with LANL and LLNL• Target injection system integration in collaboration with General Atomics

Status and Opportunities • Initial LIDT data have been obtained • Models of Fresnel and Kirchhoff scattering have been developed • New research opportunities exist in several terrestrial, airborne and space applications

• Damage occurs at a higher fluence as compared with normal incidence

• Silicide occlusions in Al 6061 preferentially absorb light, causingexplosive ejection and melting

• Fe impurities appear unaffected

• Exposure of Al 1100 to 1000 shots at 85˚ exhibited no damage

Several shots in Al 6061 at 80˚, 1 J/cm2 peak

Damage to aluminum at grazing angles

Fe

Fe MgSi

1000x

Al GIMM with in-situ reflectometry

Driver Interface R&D: Beam Propagation (Najmabadi, Harilal, Gaeris, Pulsifer, Tillack)

Problem StatementThe chamber environment following a target explosion contains a hot, turbulent gas

which will interact with subsequent laser pulses. Gas breakdown occurs in the vicinity of the target where the beam is focussed. A better understanding of the degree of gas ionization and the effects on beam propagation are needed. The effect of aerosol and particulate in the chamber must be understood in order to establish clearing criteria. Objectives

• Determine the laser breakdown threshold in pure and impure chamber environments at low pressure.

• Determine the effect of chamber environmental conditions on beam propagation.

Key Program Elements• Construction of a multi-purpose vacuum chamber• Breakdown emission detection and spectroscopy• Laser beam smoothing and accurate profiling (goal of 2-5%)

Status and Opportunities• Chamber and vacuum system parts have been ordered• Interaction of laser with chamber media is related to laser interactions with ablation

plumes and atmospheric beam transport (LIDAR, free-space optical communications, ...)

Beam propagation experiments will be performed in a multi-purpose vacuum chamber under construction

Initial measurements:• Visible light emission from the focal spot

• Variation in laser energy profile (CCD) & temporal pulse shape (photodiodes) • Wavefront variation (Shack-Hartmann)Planned: • Emission spectroscopy

• Changes in spatial profile with 2% accuracy

Chamber Physics: Numerical Modeling (Dragojlovic, Najmabadi, Raffray)

Problem StatementThe chamber condition following a target explosion in a realistic chamber geometry is not well

understood. The key uncertainty is whether or not the chamber environment will return to a sufficiently quiescent and clean low-pressure state to allow another shot to be initiated within 100–200 ms. A modeling capability is needed to predict the behaviour of an IFE power plant chamber, to ensure that all relevant phenomena are taken into account and to help plan experiments. Objectives

• Develop an integrated, state-of-the-art computational model of the dynamic response of IFE chambers following target explosions and make it available to the community

• Benchmark the code• Use the code to plan experiments and study IFE chambers

Key Program Elements• Construction of the initial, extensible numerical framework with core fluid dynamics model• Inclusion of wall interactions and radiation transport modules in collaboration with ANL• Inclusion of aerosol & particulate production and transport models in collaboration with INEEL• Implementation of adaptive mesh routines, if necessary

Status• Code methodology is currently under development• Initial code writing to begin in summer 2001

Multi-physics model of chamber dynamics

ChamberTarget Wall

Momentum Conservation

Impulse

Energy ConservationPhasechange

Conduction

ImpulsePressure (T)

Pressure(density)

Mass Conservation(multi-phase, multi-species)

Evaporation,sputtering ...

CondensationEvacuation

Energy deposition

Heattransfer Thermal stress

Driver Beams

Energy Input

Momentum Input

Mass Input

Fluidhydrodynamics

Erosion/redeposition

Viscous dissipation

Transport & deposition

Radiation transport

Phase change

Mechanicalresponse

Convection

Eqns. of state

Thermalresponse

Chamber Physics: Engineering Responses (Raffray, Zaghloul, others TBD)

Problem StatementMany physical phenomena with different time scales occur in the chamber following a target

explosion. The aim of research on engineering responses is to improve our predictive capabilities of the chamber dynamics and to understand the constraints imposed on the rep-rate of an IFE power plant. Objectives

• Explore chamber dynamic phenomena to understand most critical issues for select IFE chambers• Develop and benchmark physics modules for the integrated modeling effort

Key Program Elements• Develop improved “wall-interaction” models• Develop aerosol and particulate production and transport models• Develop a detailed radiation transport package• Quantify R&D needs and define experiments• Benchmark models using experimental data

Status and Opportunities• Literature survey and scoping of individual response models has begun• Implementation will be coupled with numerical model development activity

• Close ties with experimental programs should be maintained

Aerosol and droplet production is a key issue for wetted wall IFE chambers

liquid

vapor

X-ray, gamma & neutron preheating phase:

Ion heating phase: background 2-phase

Possible mechanisms for droplet production:surface vapor explosionbulk boilingisochoric heatingconvective flow & shocksin-flight recondensation

Transport phase: radiation

convection

Chamber Physics: Experiments (Harilal, Harilal, Gaeris, Blair, Tillack, Najmabadi)

Problem StatementThe chamber condition following a target explosion in a realistic chamber geometry is not well

understood. A key uncertainty is whether or not the chamber environment will return to a sufficiently quiescent and clean low-pressure state to allow a second shot to be initiated within 100–200 ms. A capability is needed to predict the behavior of IFE power plant chambers, to ensure that all relevant phenomena are taken into account and to help benchmark numerical models.

Objectives • Demonstrate validity of scaling and simulation experiments • Develop chamber experimental capabilities • Benchmark chamber dynamics models • Provide new data relevant to IFE chamber responses

Key Program Elements• Study potential energy sources and simulation capabilities• Build or obtain access to needed energy sources• Define and, when needed, develop diagnostics• Perform simulation experiments

Status and Opportunities• Initial characterization of simulation experiment opportunities have been performed• Synergism between IFE and laser ablation

Chamber Physics: Experiments

HYADES simulation of laser irradiation of Au

Direct surface illumination

x-ray source w/close-in targets

Shaped chambers

Micro-enclosureBeamline effects

IFE Engineering: Target Engineering (Tillack, Raffray, Pulsifer, Abu-Nada)

Problem StatementCryogenic targets require strict control over symmetry in order to assure that fusion will take

place. Thermal and mechanical responses of direct and indirect drive targets during fabrication (layering), injection and transport through the chamber environment are important factors in determining the survival of the delicate targets. An integrated thermal, fluid, mechanical and optical model is needed to guide R&D programs and to predict the behavior of IFE targets in power plant chambers.

Objectives• Develop an integrated, state-of-the-art computational model of the response of IFE targets

during fabrication, injection and transport through the chamber• Use the code to plan experiments and study IFE targets

Key Program Elements• Construction of the initial, extensible numerical framework • Inclusion of various interaction modules in collaboration with General Atomics

Status and Opportunities• Code methodology is currently under development• Initial code writing to begin in Summer/Fall 2001

Integrated Engineering Model of IFE Targets

Input ParametersInitial target configurationProperties databaseImposed accelerationsThermal environmentChamber gas, aerosol and particulate speciesChamber hydrodynamic environment

Computed ParametersTarget temperature distributionTarget trajectoryTarget internal stress distributionInternal mass transport

Layering Injection Chamber TransportFree Flight

Thermal radiation

Hydrodynamicinteractions

Convective heat transfer

Acceleration in sabot

Gravity

Mass transferTransient stresses

IFE Engineering: Wall Engineering (Raffray, Zaghloul, Wang, Tillack)

Problem StatementThe walls of an IFE chamber are subjected to intense energy sources from repeated target

explosions. Survival and reliability of materials in this environment are important for the feasibility of dry wall chamber concepts. Objectives

• Develop innovative design solutions for robust, damage-resistant wall materials• Evaluate response of materials to simulated IFE target explosions

• Assist SNLA, ESLI and others field experiments and perform pre- and post-test analysis

Key Program Elements• Modeling of energy deposition and thermal response of engineering surfaces• Experimentation at the SNLA Z x-ray source and RHEPP/MAP ion beam facility• Diagnostic development

Status and Opportunities • This program is carried out in collaboration with Sandia National Laboratories, and

includes participation of the University of Wisconsin, UC Berkeley, and Energy Science Laboratories Inc.

IFE Engineering: Wall Engineering

RHEPP/MAP ion beam facility, SNLA

ESLI carbon fiber flocked surface

Structured surfaces may offer superior thermal response and improved erosion behavior under exposure to pulsed energy sources

Related Studies: Laser Micromaching*

* work partially supported by Hewlett Packard

• Laser absorption in surface

• Thermal response of surface

• Liquid hydrodynamics

• Evaporation

• Unsteady gas dynamics

(including chamber environment)

• Condensation

• Laser-cluster interaction

Governing physics is very similar to IFE

Closing Remarks

• The UCSD IFE Technology Program has grown from a simple idea to a diversified program of 12 researchers in less than 5 years.

• We are now poised to make our most rapid progress ever, developing models and experimental capabilities and helping to demonstrate the feasibility of inertial fusion energy.

• Numerous opportunities exist for expanding into new areas of study.