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 ManagementF. Najmabadi

Les Waganer (Operations)

Mark Tillack (System Integration)

Program ManagementF. Najmabadi

Les Waganer (Operations)

Mark Tillack (System Integration)Advisory/Review

Committees

Advisory/Review

Committees

OFESOFESExecutive 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

ConceptsCharacterization

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

DriverDriver

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 wallSolid wall with

sacrificial layerThick 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)

85˚

stiff, lightweight, actively cooled, neutron transparent substrate

40 cm

4.6 m

Grazing incidence mirrors

Si2O or CaF2 wedges

Final Optic Damage Threats

• Damage that increases absorption (<1%)

• Damage that modifies the wavefront –

– spot size/position (200m/20m) and spatial uniformity (1%)

Two main concerns:

Final Optic Threat Nominal Goal

Optical damage by laser >5 J/cm2 threshold (normal to beam)

Sputtering by ions Wavefront distortion of </3 * (~100 nm)Ablation by x-rays (6x108 pulses in 2 FPY: (~25 mJ/cm2, partly stopped by gas) 2.5x106 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/cm2 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 ns @1064 nm;800, 500, 300 mJ @532, 355, 266 nmPeak power density ~1014 W/cm2

Shack-HartmannProfiling

Class 100cleanroomenclosure

100 ppm accuracy

Reflectometry

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

Dimensional Defects Compositional Defects

Gross deformations,

δ>Surfa cemor ,phology

δ <

Gros s surfacecontamination

Loca l contamination

CONCERNS

• Fabricat ion quality• Neutr onswelling• Therma l swelling• Gravit y loads

• Lase -r induceddamage

• Thermomechanicaldamage

• Transmutations• B ulkredeposition

• Aerosol, dus t&debris

MODELLIN G TOOLS

Optical designsoftwar e(ZEM )AX

Scatterin g byroughsurface s (Kirchhoff)

Fresn elmulti-layersolver

Scatterin g byparticles

Laser propagation near or beyond the breakdown threshold is uncertain

Laser intensity near the target:1013 – 1014 W/cm2

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: 100-200 ms).

Understanding Chamber Dynamics and Clearing is a Critical R&D Item

Chamber Wall

Vapor, Fragments

X-rays

Neutrons

Ion Debris

Target

Non-uniform pressure distribution

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 wallRelaxation 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

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 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