A Target Fabrication and Injection Facility for Laser-IFE

M. S. Tillack, A. R. Raffray, UC San Diego

D. T. Goodin, N. B. Alexander, R. W. Petzoldt, General Atomics

D. Schroen and J. E. Streit, Schafer Corporation

J. D. Sethian Naval Research Laboratory

20th IEEE/NPSS Symposium on Fusion Engineering14-17 October 2003

San Diego, CA

Laser-IFE with direct drive targets and dry chambers is under development in the High

Average Power Laser Program

• Modular, separable parts allows for lower development costs and economical upgrades

Spherical target

Electricity Generator

Dry wall (passive) chamber

Targetfactory

Modular LaserArray

Final optics

The Path to Develop Laser Fusion Energy

Phase IIValidatescience &technology2006 - 2014

Phase IIIEngineeringTest Facilityoperating 2020

Full size laser: 2.4 MJ, 60 laser lines Optimize targets for high yield Develop materials and components. 300-700 MW net electricity Resolve basic issues by 2028

Phase I:Basic fusionscience &technology1999- 2005

Ignition Physics Validation

• MJ target implosions• Calibrated 3D simulations

Target Design & Physics

• 2D/3D simulations• 1-30 kJ laser-target expts

Full Scale Components

• Power plant laser beamline • Target fab/injection facility • Power plant design

Scalable Technologies

• Krypton fluoride laser• Diode pumped solid state laser• Target fabrication & injection• Final optics• Chambers materials/design

Phase-I R&D includes a room-temperature capsule injector and various separate-effects R&D tasks to

demonstrate target fabrication and survival

Elements of the injector facility:

Plastic capsules injected with sabots

Target tracking and verification

Target transport through a surrogate cylindrical chamber

Related R&D:

Target fabrication steps

DT properties

Chamber interactions

Beam steering

D1 Detector Station

Photodiode Triggers

LinescanCamera

Targetfab labs

Cryogenic targetsupply systems

Differentialvacuum pumping

Sabotdeflector

Surrogatetargetchamber

In-chambertracking

Low powerhit on fly laser

Positiondetectors

Gun barrelLoadingchamber

The TFIF – Target Fabrication and Injection Facility – will validate the science and technology of full-scale

components of an IFE power plant in an integrated system

Elements of the facility:

1. Mass production (batch mode) of cryogenic targets that meet the specifications of high gain

2. Target handling & transfer

3. Cryogenic target injection into the chamber

4. In-chamber target tracking

5. Chamber environment (backround gas, wall temperature, etc.)

6. Steering of a pulsed laser onto the target in flight

Key Features:

• Full cryogenic capabilities

• Interfaces and integration

• Repeatable and reliable

Expected Direct Drive Target Specifications

Capsule Material CH (DVB) foam

Capsule Diameter ~4 mm

Capsule Wall Thickness 290 m

Foam shell density 100-120 mg/cc

Out of Round <1% of radius

Non-Concentricity <1% of wall thickness

Shell Surface Finish ~20 nm RMS

Ice Surface Finish <1 m RMS

Temperature at shot~15-18.5 K

Positioning in chamber ± 5 mm

Alignment with beams <20 m

Reference target design and specifications

NRL High Gain Target Design

Laser driven foam shell is CH-only

Divinyl benzene is being developed.

Outer foam insulation is also possible.

DT Vapor0.3 mg/cc

DT Fuel

CH Foam + DT

1 m CH +500 Å Pd/Au

1.95 mm

1.50 mm

1.69 mm

CH foam = 20 mg/cc

1. Manufacturing and characterization steps will be demonstrated with processes scalable to mass production

Step Methods Comments/Remaining Issue

Capsule Production Microencapsulation Suitable for mass-productionIssue = non-concentricity

Metal Overcoat Sputter Coating Standard industrial processOptimization needed

Filling with DT Permeation Optimize for min. DT inventory

Layering -layering, IR enhance Mass-production demo in TFIF

Cryo Handling Cryostats Critical part of TFIF

Injection Gas-gun, EM Analyses of survival now - demo in TFIF

InjectorLayering DemoLab-scale microencapsulation

2. Cryogenic target handling will be addressed in the TFIF

HELIUM/DTSEPARATION

DTPRESSURIZATIONSYSTEM

TO INJECTOR

REVOLVER

DIFFUSER

IR ORµWAVEINJECTION

COOLER

He

Issues

• Static “cling”

• Self charging

• Cryo-layer degradation

• Physical damage

• Component wear in vacuum

3. The target injector will develop and demonstrate cryogenic target survival during accurate, high speed injection

Target speed up to 400 m/s (to reduce heating time in chamber)Repetition rate 6 HzFree flight distance up to 16 mPlacement accuracy ±5 mmTrajectory prediction at DCC ±14 micron

Acceleration ~10,000 m/s2 (limited for target survival)Wall temperature up to 1800 KChamber gas temperature up to 5000 K

Current target protection sabot design

Sabot (fully engaged) Sabot (disengaged)

A gas gun or EM accelerator may be used

The gas gun is a more developed and simpler technology

An EM accelerator eliminates propellant gas and is more compatible with cryogenic targets

End of Gun Barrel

4. In-chamber tracking will be added to deal with non-uniform gas density, turbulence, and “wind”

Ex-chamber In-chamber

DetectorD2

DetectorDCC

DetectorD1

OPTIONS:

• Add more detectors

• Add interferometeric position change

detectors• Being developed by

POC under an SBIR.

DetectorDCC

DetectorD2

DetectorD1

InterferometricallyGenerated light sheets

PhotodetecterQuartz Tube

• Reflections of light sheets from target picked up by photodetector.

• Use 3 orthogonal sets of light sheet sources and detectors, each in a different color.

5. Target survival in the chamber is a critical issue to be addressed in TFIF

• TFIF will help demonstrate acceptable symmetry in simulated chambers

• In-chamber diagnosis (e.g., shadowgraphy) is very limited; complementary R&D is essential

• Radiation heating from hot chamber walls

• Friction and condensation from chamber gas

• Residual plasma recombination Baseline target/chamber conditions:To=18 K, Tmax=19.79 K

15 ms transit time (400 m/s)

1000 K wall

gas at 10 mTorr, 4000 K, Zeff=0

6. Laser driver integration requires precise metrology and timing, as well as rapid control signal transfer

• Goals: ±5 mm location, 20 m target/laser accuracy @20-30 m (~1 radian mirror aiming precision 0.4 m mirror displacement)

• Continuous corrections based on tracking info

• In-chamber tracking

• Final correction at 11 s, or ~4 mm from implosion location

xyzt

trackingelectronics

target tracking

injector

timing

laser driver

trigger

steering control

targetchamber

VxVyVz

Target tracking/beam steeringinterface

xyzt

pointing laser

PSDxyzt

20-30 m

confocal tracking

Summary

An integrated Target Fabrication and Injection Facility is an essential element of the plan to develop IFE based on lasers and direct drive targets

The facility will integrate all of the systems and interfaces relevant to IFE power plant fuelling:

– Mass production of cryogenic targets – Target handling & transfer – Target injection – Target tracking – Target survival – Integration with the final optic

Independent R&D is well underway, and is expected to provide the necessary data to proceed with TFIF in a time frame consistent with the transition to Phase II