Update on IFE Target Fabrication Progress

presented byDan Goodin

HAPL Project ReviewMadison, WisconsinSeptember 24, 2003

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

Topics

1. Foam Insulated Target Fabrication and Assembly

2. Foam Insulated Target Reflectivity

3. Insulating Foam Survival During Acceleration

4. Mass-Production Layering System Design

5. 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 (970C or 2.8 mtorr Xe @ 4000K)

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

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

Rene Raffray will talk more about target thermal…

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

Foam insulated target fabrication and assembly

DT gas

DT solid

DT + foamDense plastic(not to scale)

“Basic” NRL Target

~ 1 m holesHigh-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

• 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

Foam

Glue joint1) Hemi-shells (demonstrated, but not for IFE…)

There are potential insulating-foam fabrication methods

Injection molding, W. Steckle LANL

Foam layer over shell by emulsification, M. TakagiCH

Advantages

• Reproducible (same diameter & wall)• Standard industry

practices

Foam with Pb

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

Mold

RetractableCentering Pins (3)Injection Pathway

“Basic”NRL

Target

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

FOAM HEMI

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

pulse

Microencapsulation turns emulsification into mass-production

4 mm150 m

Want but Excess precursor resultsin 289 m thick foam

Bubble injection

Two approaches

1) Alternate with “beads”

2) Add Bubbles

10 % DVB + polymerization initiator(V70) in DEP

One issue may be shrinkage rate of each

layer after drying?

“bead”

Insulated foam target

0.05% PAA (or PVA)

Stripping Flow

289 m

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

“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?)

R1

R2R3

Insulatingfoam

DT fuellayer

Outer sealcoat

DT target values for example targetdrain time problem.

Variable ValueR1 1.5 mmR2 1.95 mmR3 2.05 mmD 1 mC 0.6Y 0.75

DTTemperature

22 K

LiquidDensity

217 kg/m3

Ga s Density 1.37 kg/m3

SaturationPressure

4.74×104 Pa

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

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

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

PAMS

Bare foam

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

survive injection

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

survive injection

Example of reflectivity - PAMS and DVB

micron-sized foam overcoated with metal is not reflective

PAMS with Al(reflecting illuminator)

Bare DVB with Al

Does the insulating foam collapse during injection?

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”)

NRL “basic” target- 4 mm OD- ~3 mg mass

Insulating foam - 150 m thick - variable density

1000 g’s acceleration

1 5 10

110

Foam Density Ratio (%)

Log Deshpande-Fleck Parameter (DFP) @ 1000g

€

E f

E s

= C1

ρ f

ρ s

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2 E = Young’s modulusf = densityC1 = 0.38Exponent = 2.29

*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

€

pl

σ ys

= C2

ρ f

ρ s

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

3

2pl = plastic stressys = yield stress of solidC2 = 0.15Exponent = 1.85

Room temperature(conservative)

~10X

Support film

€

Log σ pl [collapse stress]

Target remains centered in foam

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

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

E=0.76 MPa

100 mg/cm3 DVBHeight = 4.5 mm

Area = 63 mm2

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

€

Deflection=FHEA

=maΔrEπr2 ≅0.6 μm

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

“Scale” (Force)

Foam

Micrometer

Simple and classicmaterials test

Force vs compression

0

50

100

150

200

250

300

350

400

450

0 0.1 0.2 0.3 0.4 0.5

DVB foam compression (mm)

Forc

e (

gra

ms)

Layering beds

Plant Experiment

Targets per bed 65,000 700

Diameter bed 320 mm 34 mm

Bed height, settled 44 mm 44 mm

Bed expansion 2 2

Operating temperature 18 - 19.7 K to ~15K

Pressure of levitating fluid

380 torr 380 torr

Mass flow 140 g/s 1.8 g/s

Velocity of fluid 133 cm/s 150 cm/s

T across bed (1 QDT; native layering)

0.054K 0.067K

Temperature change at inner surface of DT ice

<0.003K <0.003K

N. Alexander, HAPL Mtg., 4/2003

Mass-production layering system design

•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

HX

Typical cryo-circulator

bed

Cryo-circulator

Design uses many borrowed ideas and commercial devices

Standard Evaporation Chamber Components

Bell Jar Design (OMEGA, CPL)

Cryocoolers (CPL, OMEGA)

External Vacuum Manipulators (OMEGA)

Permeation Cell (D2TS, OMEGA, CPL)

Transfer Arm (OMEGA)

Heat Exchangers on Second Stage

(OMEGA)

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

Cryogenic Compressor

24”ø

Fluidized Bed Layering Device

Operating Steps (1 of 2)

1) Basket w/700 empty capsules placed on inserter

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

basket

inserter

permeation cell

Bell Jar

filled/cooled targets

Operating Steps (2 of 2)

6) Basket (w/ filled capsules) grasped by

transfer arm

7) Transfer arm rotated 90 degrees

Top View

Note: view rotated 90˚ from other

views

8) Basket placed on fluidized bed lower half

9) Fluidized bed lower half raised and sealed

with upper half

10) Capsules layered and characterized

filled/cooled targets

transfer arm

filled/cooled targets

cryogenic fluidized bed gas

supply lines

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

• Characterization– take image of moving capsule (baseline)– capture single capsule and characterize when stationary

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

Summary and conclusions

1. We think the insulated-foam target can be reasonably fabricated for IFE

2. The insulated-foam target reduces issues associated with filling time

3. The insulating foam can be “drained” of DT

4. Insulating foam will survive the acceleration during injection and remain centered

5. Demonstration system for mass-production layering is being designed

DT gas

DT solid

DT + foam

~ 1 m holesHigh-Z coat

Insulating foam