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Update on IFE Target Fabrication Progress. N. Alexander. L. Brown, R. Gallix, D. Geller, C. Gibson, J. Hoffer, A. Nikroo, R. Petzoldt, R. Raffray, D. Schroen, J. Sheliak, W. Steckle, M. Takagi, E.Valmianski, B. Vermillion . presented by Dan Goodin HAPL Project Review Madison, Wisconsin

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Update on IFE Target Fabrication Progress

N. Alexander. L. Brown, R. Gallix, D. Geller, C. Gibson, J. Hoffer, A. Nikroo, R. Petzoldt, R. Raffray, D. Schroen, J. Sheliak, W. Steckle, M. Takagi, E.Valmianski, B. Vermillion

presented by

Dan GoodinHAPL Project Review

Madison, Wisconsin

September 24, 2003



  • Foam Insulated Target Fabrication and Assembly
  • Foam Insulated Target Reflectivity
  • Insulating Foam Survival During Acceleration
  • Mass-Production Layering System Design
  • Summary and Conclusions

NRL Basic High Gain Target


The foam insulated target could significantly open the chamber design window!

Basic target (18K): <0.68 W/cm2 (970Cor 2.8 mtorr Xe @ 4000K)

Foam-insulated (100 m, 10%): <3.7 W/cm2 (970Cand 12.5 mtorr @ 4000K)

Foam-insulated and 16K: <9.3 W/cm2 (970Cand 40 mtorr @ 4000K)

Rene Raffray will talk more about target thermal…


~ 1 m holes

High-Z coat

Insulating foam

  • Full-density CH “seal coat”
  • Permeable at room temperature
  • Seal at cryo to prevent DT loss
  • High-Z here increases fill time

DT + foam

Dense plastic

(not to scale)

DT solid

“Basic” NRL Target

DT gas

Foam insulated target fabrication and assembly

Additional advantage = reduces issue of DT inventory (filling time)

  • Moving high-Z to outside allows multiple ~ 1 m holes
    • - holes let DT enter and cover full area of seal coat, reducing fill time
    • at cryo, holes are necessary to “dry” the foam after filling


Glue joint


There are potential insulating-foam fabrication methods

1) Hemi-shells (demonstrated, but not for IFE…)

2) Injection molding with NRL target (conceivable ….)

  • Advantages
  • Reproducible (same diameter & wall)
  • Standard industry practices

Injection molding, W. Steckle LANL

3) Chemical process (likely best for IFE …..)

Foam layer over shell by emulsification, M. Takagi

Foam with Pb

By “shake and toss” (8 to 170 m walls)…



Microencapsulation turns emulsification into mass-production

Excess precursor results

in 289 m thick foam



4 mm

150 m

289 m

2) Add Bubbles

Two approaches

Bubble injection

10 % DVB + polymerization initiator(V70) in DEP

1) Alternate with “beads”

One issue may be shrinkage rate of each layer after drying?

0.05% PAA (or PVA)

Stripping Flow



Conclusion = microencapsulation to make insulating foam seems feasible, next we should try it

Insulated foam target


“Draining” (drying) the outer foam

  • Outer foam needs drying after the fill
  • Calculated DT flow thru one 1 m hole
    • liquid = 4.6 minutes
    • gas = 77.8 minutes
    • Ron Petzoldt
  • Prior experimental data also indicate a single 1 m hole will drain very fast (Jim Hoffer)

Conclusion = filling & drying the outer foam shouldn’t be a problem if there are “many” approximately one micron sized holes (kHz laser?)



Bare foam

Side-by-side PAMS and “bare” foam coated with Al

Reflectivity of outer layer

  • Outer “reflective” layer on outer foam is still needed
    • total IR heat flux (970°C) = ~14 W/cm2 (too high)
    • reflectivity in the mid-90% desirable
  • Micron-sized foam cells simply overcoated with metal is “black”
    • “smoothing” coat needed - what parameters?
  • Test series to demonstrate reflectivity and find parameters
    • CH coating thickness (surface finish)
    • high-Z coating thickness

Result = “design window” curves for insulating foam and high-Z parameters to survive injection


Example of reflectivity - PAMS and DVB

Bare DVB with Al

PAMS with Al

(reflecting illuminator)

micron-sized foam overcoated with metal is not reflective


Does the insulating foam collapse during injection?

E = Young’s modulus

f = density

C1 = 0.38

Exponent = 2.29

NRL “basic” target

- 4 mm OD

- ~3 mg mass

Insulating foam

- 150 m thick

- variable density

pl = plastic stress

ys = yield stress of solid

C2 = 0.15

Exponent = 1.85

Support film

1000 g’s acceleration


ANSYS to evaluate survival

  • Ozkul* model (0.1 - 20 m cells, 40 - 270 mg/cc)
  • Use “Deshpande-Fleck Parameter+ (DFP) from ANSYS results
  • DFP< pl (foam will “spring back”)


Log Deshpande-Fleck Parameter (DFP) @ 1000g

Room temperature






Foam Density Ratio (%)

*M.H.Ozkul, J.E.Mark, and J.H.Aubert. The Mechanical Behavior of Microcellular Foams, Mat. Res .Soc. Symp. Proc. Vol.207.1991

+V.S.Deshpande, N.A.Fleck. 2000.J.Mech.Phys.Solids 48:1253-1283


Force vs compression






Force (grams)












DVB foam compression (mm)

Target remains centered in foam

  • Must “spring back” from any significant de-centering “quickly”
  • Simple experiments

100 mg/cm3 DVB

Height = 4.5 mm

Area = 63 mm2

E=0.76 MPa

1-D estimates for compression of foam by accelerated target:

Data at RT, E at cryo typically 2 to 10 times higher (i.e., conservative)

…these data indicate the insulating foam will withstand acceleration and will remain centered


Mass-production layering system design

Layering beds

N. Alexander, HAPL Mtg., 4/2003

  • Since last meeting
    • selected full-size for capsule, drafted SDD and specs for cryo-circulator
    • prepared cryostat and operating concepts
  • Goal = demonstrate thermal environment in a cryogenic fluidized bed
    • IR replaces -decay heat
    • start with 40 m wall CH shell (transparent & easier to fill)
    • can also use transparent foams
design of mass production layering system is progressing
Demonstration will use 4 mm targets

strong desire to demo full-size components

precludes “once-through” and RT circulator designs

Will use cryogenic compressor

requires “minor” modification of existing design

have agreement with Barber-Nichols on basic operating parameters (e.g. T, pressures, heat load)

Overall status:

conceptual drawings are completed

System Design Description out for internal review

Design of mass production layering system is progressing




Typical cryo-circulator

design uses many borrowed ideas and commercial devices
Design uses many borrowed ideas and commercial devices

Heat Exchangers on Second Stage (OMEGA)

Fluidized Bed Layering Device

Bell Jar Design (OMEGA, CPL)

One unique feature is that internal environment is vacuum

  • OMEGA & CPL use low pressure helium
  • This device is not intended for DT use
  • Greatly simplifies design


Standard Evaporation Chamber Components

Permeation Cell (D2TS, OMEGA, CPL)

Transfer Arm (OMEGA)

External Vacuum Manipulators (OMEGA)

Cryogenic Compressor

Cryocoolers (CPL, OMEGA)

operating steps 1 of 2
Operating Steps (1 of 2)

Bell Jar

permeation cell

filled/cooled targets



2) Bell jar is lowered and vacuum pumped

3) Inserter raised and permeation cell breech lock engaged

4) Capsules permeation filled and cooled to cryogenic temperature

5) Breech lock disengaged and inserter lowered

1) Basket w/700 empty capsules placed on inserter

operating steps 2 of 2
Operating Steps (2 of 2)

filled/cooled targets

Top View

cryogenic fluidized bed gas supply lines

filled/cooled targets

Note: view rotated 90˚ from other views

transfer arm

6) Basket (w/ filled capsules) grasped by transfer arm

7) Transfer arm rotated 90 degrees

8) Basket placed on fluidized bed lower half

9) Fluidized bed lower half raised and sealed with upper half

10) Capsules layered and characterized

remaining design is standard engineering however there are several developmental areas
Capsule Static Cling

mesh basket ensures that capsules arrive at layering device

several ideas to eliminate cling in layering device:

ionizer (baseline), radiation source, alternating current

Layering Method

fluidized bed (baseline)

bounce pan


take image of moving capsule (baseline)

capture single capsule and characterize when stationary

Remaining design is standard engineering, however, there are several developmental areas:

Approach is to have a baseline design, yet keep things simple and modular, so that different concepts can be substituted

summary and conclusions
We think the insulated-foam target can be reasonably fabricated for IFE

The insulated-foam target reduces issues associated with filling time

The insulating foam can be “drained” of DT

Insulating foam will survive the acceleration during injection and remain centered

Demonstration system for mass-production layering is being designed

~ 1 m holes

High-Z coat

Insulating foam

Summary and conclusions

DT + foam

DT solid

DT gas