Nov 5-9, 2006 IAEA meeting, Vienna, Austria 1 Target and Chamber Technologies for Direct-Drive Laser-IFE Presented by A. René Raffray Scientific Investigators:

Nov 5-9, 2006 IAEA meeting, Vienna, Austria 1

Target and Chamber Technologies for Direct-Drive Laser-IFE

Presented by A. René Raffray

Scientific Investigators: M. Tillack, R. Raffray, F. Najmabadi

University of California, San Diego

1st RCM of the CRP on Pathways to Energy from Inertial Fusion - an Integrated Approach

IAEA HeadquartersVienna

November 5-9, 2006


Electricity Generator

Targetfactory

Modular LaserArray

• Modular, separable parts: lowers cost of development AND improvements

• Conceptually simple: spherical targets, passive chambers

• Builds on significant progress in US Inertial Confinement Fusion Program

Proposed Work Within Context of High Average Power Laser (HAPL) Program

Target injection

(engagement and surviva)

Chamber conditions (physics)

Final optics (+ mirror steering)

Blanket (make the most of MFE design and R&D info)

System (including

power cycle)

Dry wall chamber (armor

must accommodate ion+photon threat and

provide required lifetime)

• Multi-institution Activities led by NRL with the Goal of Developing a New Energy Source: IFE Based on Lasers, Direct Drive Targets and Solid Wall Chambers


Proposed Research(as part of HAPL Program)

a) Target engagement. We will develop and demonstrate systems to track direct-drive targets in flight and to steer multiple driver beamlets onto the targets with the precision required for target ignition. Bench-top experiments will be performed in order to demonstrate the feasibility of these systems and to characterize their performance.

b) Chamber design studies. We will develop chamber design concepts that integrate armor and structural material choices with a blanket concept providing attractive features of design simplicity, fabrication, maintainability, safety and performance (when coupled to a power cycle). Advanced concepts (including magnetic intervention) that could result in smaller less costly chambers, better armor survival and lower cost of electricity also will be investigated.

c) Chamber armor thermomechanics. We will perform modeling and experiments on candidate chamber armor materials. The goal of this work is to develop solid armors capable of withstanding cyclic thermomechanical loading expected in direct-drive IFE chambers.


Target Engagement


Year 1:Utilize lab-scale injection equipment to support the development of target engagement methods. Field and test individual elements, including Poisson spot detection, Doppler fringe counting, glint alignment, fast mirror steering and real-time software integration.

Year 2:Combine benchtop systems and extend performance.

Year 3:Perform integrated demonstration of target engagement. Install all engagement systems on a prototype injector using full-speed electronics, full-power light sources and full-aperture optics.

Proposed Work Plan for: a) Target Engagement


Target engagement research is performedin collaboration with General Atomics

L. Carlson1, M. Tillack1, T. Lorentz1, J. Spalding1

N. Alexander2, G. Flint2, D. Goodin2, R. Petzoldt2

(1UCSD, 2General Atomics)

Power plant requirements:• 20 µm engagement accuracy in (x,y,z) • ~20 m standoff to final optic• 5-10 Hz rep rate

• Purpose: To individually demonstrate successful table-top experiments of key elements, then integrate together.

• Final goal: Provide a “hit-on-the-fly” target engagement demo meeting accuracy requirements.


Benchtop experiments simulate all of the key elements of a power plant engagement system

• Poisson spot, fringe counting, crossing sensors, verification:

– Provide in-flight steering instructions & diagnostic, backup.

• Glint & coincidence sensor:

– Aligns beamlets & provides final steering instructions

crossingsensorsC2C3C1pulsed glint

laser (1064 nm)alignment & driver beam

(635 nm)

verification camera

retroreflectorcoincidence sensor

Poisson spot

camera

fast steering mirror

focusing mirrorwedged dichroic mirror

chamber center

Poisson (632 nm) & fringe counting

(1540 nm) beams

fringe counter

microlens array

collimating lens

drop tower R. Petzoldt, et al., "A Continuous,

In-Chamber Target Tracking and Engagement Approach for Laser Fusion," 17th ANS Topical Meeting, to be published in Fusion Science and Technology.

1

2

3

4

5

5


Poisson spot

camera


(1540 nm) beams

• Goal is to know centroid position to ± 5 µm every 5 ms

• Looks achievable

#1. Transverse target motion is tracked using Poisson spot centroiding

2) Brightness/contrast adjustment ~1 ms

1) Capture image ~1 ms

3) Threshold pixels above a certain value ~4 ms

4) Remove border objects ~2 ms

6) X,Y centroid computed with < 5 µm error (1) ~1 ms

5) Particle filter ~1 ms



(1540 nm) beams

fringe counter

reference leg

• A Michelson interferometer is used, with noise mitigation, signal processing and modifications for plane/spherical wave mixing.

#2. Fringe counting provides continuous z-axis tracking, with accuracy goal of ~1 part in 106

0

2

4

6

8

10

12

14

-7.65 -5.15 -2.65 -0.15 2.35 4.85 More

Scale (µm)

Frequency

Fringe count repeatability over 5 m using a 4-mm steel sphere

• So far, operation is limited in range and standoff (power, noise, bandwidth, …)

• May predict velocity (vs. full z-axis tracking)


crossingsensorsC2C3C1drop tower

#3. Crossing sensors initiate fringe counting and may be sufficiently accurate to supplant the interferometer

C1

C2

C3

Real-time Position Prediction Repeatability at C3

0

1

2

3

4

5

6

7

8

Prediction Discrepancy (µm)

Number Observed

-75 -50 -25 0 25 50 75

• New real-time operating system reports on-the-fly placement repeatability of 45 µm (1) at C3.

=> Sufficiently precise to trigger glint laser

Sphere dropping mechanism


alignment & driver beam

(635 nm)

verification camera

chamber center

microlens array

collimating lens

4 mmfalling targetSide viewsimulated

driver/alignment beam

camera/PSDmicro lens array

collimating lens

micro lens array

collimating lens

simulated driver beam

#4. To demonstrate successful engagement, we developed a high-precision verification system

target target eclipses eclipses

verification verification beamletsbeamlets

(Diffraction-limited beamlet waist ~75 µm)

PSD Y Signal+V-Vtime0

Camera triggers here if timing prediction is perfect

1 µm precision when the target is within the 4 beamlets


pulsed glint laser (1064 nm)alignment & driver beam

(635 nm)

retroreflectorcoincidence sensor


focusing mirrorwedged dichroic mirrormicrolens

arraycollimating

lens

4 mmChopper wheel alternates between alignment signal... Driver/alignment

beam is steered to coincide with glint

signal

...and glint signal.

#5. The glint system provides final position update and closes the beam steering loop

Optics In Motion FSM

• Stationary demo performed with 18 µm accuracy in 8 ms

• Full demonstration in progress

1) Fast steering mirror keeps alignment beam

centered in the coincidence sensor.

2) Glint return provides error between alignment

beam & actual target position 1-2 ms before

chamber center.

3) Error signal provides final correction to FSM.1 2 3

7 ns


Time sequence of tracking & engagement demo - START

target is injected


alignment & driver beam

(635 nm)

Poisson spot

camera

chamber center


(1540 nm) beams

microlens array

collimating lensPoisson spot

centroiding system begins transverse

tracking


chamber center



chamber centerretroreflectorcoincidence

sensorFSM maintains alignment

beam on coincidence sensor, which represents position where simulated

driver beam enters chamber


chamber centerzero-

crossingsensor

fringe counter

begin axial tracking by counting

interference fringes


chamber center

C2-C1 determines

velocity

C2C3C1


chamber center

C3 verifies timing

prediction

C3


chamber center

glint laser fires 1-2 ms before chamber

center, alignment beam turns off

pulsed glint laser (1064 nm)


chamber center

focusing mirrorwedged dichroic mirror

glint return registers on

sensor, providing final steering instructions


chamber centerFSM steers driver beam to coincide with glint return

FSM


Time sequence - ENDchamber

centersimulated pulsed

driver beam engages target

verification camera confirms accurate

engagement

verification camera


Chamber Design Studies


Year 1:Perform initial scoping studies of advanced chamber options (including blanket and armor). Possible design scenarios range from large chambers without a protective chamber gas to smaller chambers with magnetic intervention. Studies include concept development and sufficient scoping design analysis to allow for a reasonable assessment of each concept based on key criteria including performance (when coupled to a power cycle), lifetime, fabrication, safety and maintenance.

Year 2:Conclude scoping studies and perform assessment and comparison of different chamber options to converge on the most attractive concept(s). Develop possible design solutions for ion dumps in the case of magnetic intervention.

Year 3:Perform detailed design analysis of preferred concept(s) including more detailed study of chamber integration (blanket, armor and ion dumps as required in the case of magnetic intervention) and design interfaces (ancillary coolant, power cycle and assembly & maintenance requirements).

Proposed Work Plan for:c) Chamber Design Studies


Design and Analysis Based on 350 MJ-Class Baseline Direct-Drive Target Spectra

• Energy partition:- Neutron ~75%- Ions ~24%- X-rays ~1%


Energy Deposition Profile in W, SiC and C Armor for 350 MJ-Class Baseline Target Spectra Spectra in a 10.75 m

Chamber

Target micro-explosion

Chamber wall

X-rays Fast & debris ions Neutrons

• Lifetime is a key issue for armor- High T and dT/dx- Ion implantation (in

particular He)


Ion Power Deposition Profile in W Armor

• Time of flight effect due to energy range of ions

Calculation based on 0.1 s time increment

Fast ions

Debris ions


Temperature History and Gradient for W Armor in a 10.75 m Chamber Subject to the 350 MJ-Class Baseline Target Threat Spectra

• 1-mm W on 3.5 mm FS at 580 °C• No chamber gas• Peak temperature ~2400°C

1 mm thick W armor

Coolant at 580°C

3.5 mm thick FS Wall

EnergyFront

h= 10 kW/m2-K


Required PXe as a Function of Yield to Maintain TW,max<2400°C for 1800 MW Fusion Power and Different Rchamber

0

10

20

30

40

50

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350 400 450

Xe

Pre

ssu

re (

@S

T)

(mto

rr)

Rep

etit

ion

Rat

e

Yield (MJ)

3.5 mm FSTcoolant=572°C

h=67 kW/m2-K

chamber60 40

1 mm WR (m)5.7

6.5

7

8

10

Armor Survival Constraints Impact the Overall IFE Chamber Design and Operation

• W temperature limit of 2400°C assumed for illustration purposes (~1.2 J/cm2 roughening threshold from RHEPP results)

• Limit to be revisited as R&D data become available

• Example chamber parameters for 0 gas pressure:- Yield = 350 MJ; R=10.5 m; Rep. rate ~ 5 for 1750 MW fusion

• Desirable to avoid protective chamber gas based on target survival and injection considerations

• Large chamber for W survival

• Other advanced concepts for more compact chamber and armor survival, e.g.- Magnetic intervention- Phase change armor


Self-Cooled Li Blanket for Large Chamber

• The design is based on an annular geometry with a first Li pass cooling the walls of the box and a slow second pass flowing back through the large inner channel.

• Large chamber size led to the division of blanket modules in two (upper and lower halves).

Inner Li Channel

Annular LiChannel

Sandwich insulator: FS-SiC-FS


IP LPHP

Pout

Compressors

RecuperatorIntercoolers

Pre-Cooler

Generator

CompressorTurbine

To/from In-ReactorComponents or Intermediate

Heat Exchanger

1

2

3

4

5 6 7 8

9 10

1BPin

TinTout

η ,C ad η ,T ad

εrec

Self-Cooled Li Blanket Coupled to Brayton Cycle through a Heat Exchanger

Example results for regular FS (Tmax<550°C) and ODS FS

(Tmax<700°C)


Advanced Chamber Based on Magnetic Intervention Concept Using Cusp Coils

• Use of resistive wall (e,g SiC) in blanket to dissipate magnetic energy (~70% of ion energy can be dissipated in the walls).

• Dump plates to accommodate all ions but at much reduced energy (~30%).

• Dump plates could be replaced more frequently than blanket.

Chamber/blanket study underway: - SiCf/SiC as structural material - Pb-17Li and flibe as breeder/coolant- Other?


It Could Be More Advantageous to Position Dump Plate In Separate Smaller Chamber

• Could use W dry wall dump, but would require large surface area and same problem with thermomechanical response and He implantation

• Could allow melting (W or low MP material in W)

Hybrid case•Dry wall chamber to satisfy target and laser

requirements•Separate wetted wall

chamber to accommodate ions and provide long life•Have to make sure no

unacceptable contamination of main chamber

Ion Dump Ring Chamber


b) Chamber armor thermomechanics


Year 1:Perform armor thermomechanics simulations experiments for a range of laser energy (peak sample temperature) and a variety of shot rates (10 to 105) for powder metallurgy tungsten samples.

Year 2:Perform armor thermomechanics experiments on different candidate armor material such as single-crystal tungsten.

Year 3:Perform armor thermomechanics experiments on candidate armor material bonded to candidate first wall material (e.g., tungsten bonded to ferritic steels).

Proposed Work Plan for:b) Chamber armor thermomechanics

Nov 5-9, 2006 IAEA meeting, Vienna, Austria

Chamber Armor Thermomechanics Experiments: Dragonfire Laser Facility

F. Najmabadi, J. PulsiferUC San Diego

Objective:Develop and field simulation experiments of the thermo-mechanical response of the

first wall armor of an IFE chamber to target fusion yield.

Description:A laser generates on the test specimen similar surface temperature and temperature

gradients found in an IFE chamber wall (e.g. YAG laser with a rep rate of 10 Hz). Surface temperature as well as mass ejecta from the specimen is measured in-

situ and in real time. Material response of specimen is determined after laser exposure by a variety of

microscopy techniques.

Objective:Develop and field simulation experiments of the thermo-mechanical response of the

first wall armor of an IFE chamber to target fusion yield.

Description:A laser generates on the test specimen similar surface temperature and temperature

gradients found in an IFE chamber wall (e.g. YAG laser with a rep rate of 10 Hz). Surface temperature as well as mass ejecta from the specimen is measured in-

situ and in real time. Material response of specimen is determined after laser exposure by a variety of

microscopy techniques.


Facility Description

In-situ microscopy <25 m resolution large standoff K2 Infinity

optics

translator electronics

Sample heater 500˚C base temperature

Optical thermometer collector

Sample manipulator xy translation external control located close to window

INSIDE VACUUM:

OUTSIDE VACUUM:


Optical thermometer measures surface temperature while QCM measures mass ejecta

Sample holder at 5000C base temperature

Window allows both IR and UV lasers

Quartz Crystal Microbalance (QCM) for measuring ejecta.


In-situ microscopy allows us to monitor microstructure evolution during testing

Basler camera and K2 Infinity microscope

– 1280x1024 resolution– 25 fps– STD objective

(higher mag available)

USAF resolution target:

- 64 line pairs/mm- 16 m resolution


Some results with powder metallurgy tungsten: Sample behavior changes at ~2,500K

1000

1500

2000

2500

3000

3500

0 50 100 150 200 250

Laser Energy (mJ)

Maximum Temperature (K)Room Temperature Sample

500oC Sample

5% Error size


Damage appears at 2,500K (not correlated with T)

12A, 100mJ, 773K, Max: 2,200K (~1,400K T)14A, 150mJ, RT, Max: 2,500K (~2,200K T)

11A, 200mJ, 773K, Max: 3,000K (~2,200K T)15A, 150mJ, 773K, Max: 2,700K (~1,900K T)


Effects of Shot Count and Temperature Rise

103 shots 105 shots104 shots

15A, 150mJ, 773, Max: 2,700K (~1,900K T)

14A, 150mJ, RT, Max: 2,500K (~2,200K T)


Effects of Shot Count and Temperature Rise

103 shots 105 shots104 shots

14A, 150mJ, RT, Max: 2,500K (~2,200K T)

11A, 200mJ, 773K, Max: 3,000K (~2,200K T)


Summary of Possible Collaborative Areas of Interest

• Target engagement

• Chamber armor material development and testing

• Advanced chamber/blanket design study

• Power plant studies

Documents

Nov 5-9, 2006 IAEA meeting, Vienna, Austria 1 Target and Chamber Technologies for Direct-Drive Laser-IFE Presented by A. René Raffray Scientific Investigators: