Progress Towards Mass-Production Layering

Presented by Neil Alexander

Don Bittner, Kurt Boehm, Amy Bozek, Dan Frey, Dan Goodin, Jim Kulchar, Ron Petzoldt,

Robert Stemke and Emanuil Valmianski

San Diego HAPL meetingAugust 8-9, 2006

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Summary of progress on Layering

• Mass Production Layering Experiment (MPLX) Cryostat being assembled at GA– It is being outfitted for layering

• Uses cryogenic fluidized bed• Can be outfitted for alternate methods including bounce-pan, rolling, micro-wave heating et al

• Fluidized Bed loop tests at room temperature– Capsules rotate fast enough

• Will produce the high average thermal symmetry• Should produce uniform fuel layers

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MPLX objectives

Fuel Layer Goal: Total rms < 5 µm; for l-mode ≥ 10, rms < 0.5 µm

Design

Build

Shakedown

Layering

2003 – 2004Initial Fluid Bed calculationsCryostat preliminary designCryo-helium circulator built

2005 – mid-2006Cryostat final designFabrication and installation of cryostat

mid-2006 – mid-2007Cold Circulation empty targetsPermeation cell and pressure system brought upInitial capsule fills and cool-downs

mid-2007 – 2009IR system brought upMass layering experiments

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MPLX has been installed near the target injector front end

Target InjectorMPLX Cooling Plant Dome

MPLX Layering DomeVacuum Vessel

MPLX Layering DomeThermal Shield

Target Crossing Sensor“Target Chamber Center”

Dome Lift

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The cryostat is first being outfitted for fluidized bed layering

• General systema. Cooling Plant for cold, circulating heliumb. Permeation cell for source of D2 filled targetsc. Target manipulator to transfer targets into layering device d. Fluidized bed

Cooling Plant Dome (a)

Cold Helium Blower

Cryocoolers(b)

(c)

(c)

Target Vacuum Pickup

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Status of subsystem installation (1 of 3)

1. Cryocoolers — tested, installed

2. Cryogenic Helium Blower — custom design, in-house, tested

3. Heat Exchangers — designed, out to fab

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Status of subsystem installation (2 of 3)

4. Fluidized Bed — cryoseal prototyped, designed, out to fab

5. Target Manipulator — being assembled

6. Permeation Cell (17,000 psi) — design complete, material passed ultrasonic inspection, out to fab

MPLX Cell is copy of SFS cell shown here

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Status of subsystem installation (3 of 3)

7. Target Pickup — Prototyped, in design

8. Cryovalves — prototype tested, in-house

9. Characterization cameras and lenses — lenses in-house

10.Lower Cost IR System — designed around blackbody source

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For initial layering we plan to use a low cost IR system

• Typical – IR optical parametric oscillator laser– ~$180K for 1 W of 3 µm output– Narrow band width reduces capsule imprint on fuel layer

• Alternative – black body source based system– Cost reduced more than order of magnitude– Larger band width increases capsule imprint on fuel layer• Band width selected where PAMS capsule absorption is small — minimize capsule absorption

• PAMS prefilter to eliminate capsule absorption peaks

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Design provides ~1QDT equivalent heating to 700 deuterium filled targets

• Cone ‘collimator’ redirects rays to near normal for filter

Wavelength (microns)

Coefficient of

absorption (cm-1)

D2

PAMS

IR Filter Band

Peak Absorption of PAMS

•Not in filter band•Reduces extra heating

IR Filter and PAMS sheet

Continuesto fluid bed

Blackbody sourceBoston Electronics Corp

IR-563Operating at 1300K

20°

Gold plated cone“Collimator”

Sapphire vacuum window Gold plated tube

1”

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Prototype tests have been successful for key items• Cryoseal of fluidized bed

– Seal made at 22K – Chain clamp and gearbox mechanism used to squeeze indium based seal

– Torque required for seal is low (30 in-lbs)

• Cryovalve (made by Thermionics)– Shocked to LN2 temperatures, leak checked

– Valve stem mechanism operates at LN2

Chain ClampFor Cryoseal

Gearbox

G10 Shaft

Cryovalve

CL

Chain Clamp

Indium O-ring

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Suitable capsules for first layering experiments are available

• Size: Ø4000 µm x 35 µm wall• Material: PAMS• Measured key parameters

– Buckle strength: 200 psi• Similar to polystyrene

– Deuterium permeation time constant = 60 min

• These capsules will take 7 days to fill to 17Ksi at room temperature– Ramp fill, safety factor S=2

Once we can layer in clear capsules, we can move on to layering foam capsules using x-ray phase contrast characterization

€

t fill =S⋅PFill ⋅τPBuckle

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Pressurization system design is based on the prototype of OMEGA cryotarget system

• Previously used to fill capsules with aspect ratio of– Ø900 µm / 3.3 µm wall = 270– Our capsules: Ø4000 µm / 35 µm wall = 110– Improves buckling resistance by (270/110)^2 = 6

• Booster pump up to 6,000 psi, regulator bleed to cell• Syringe pump micro-steps up to 17,000 psi design pressure

Booster pump

Syringe pump

Permeation cell

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Characterization optics are being tested on the MPLX

• Improve lighting with micro-optic diffuser• Improve image fill and resolution with new camera

K2 lens and fast camera on MPLXBacklight is Xe lamp with Fiber optic bundle

Ø4 mm Empty Target Capsule imaged through MPLX

windows

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A fluidized bed test loop is being used to test bed configuration• Room temperature, closed loop using cryo-helium blower

• Cryo compatible frit design verified to produce good fluidization (no channeling)

• Alternate bed frits tested to change: capsule spinning, circulation in bed, and interactions

Successful Frit:HCP array of Ø0.5 mm orifices

With 2 mm nearest neighbor spacing

Static cling of capsules controlled with Polonium strip on wall of bed

**Without Polonium, fluidization only lasts 45 sec until capsules lock

together**

Replicable Fluidized Bed Section

Capsules

Frit

Closed loop plumbing circuit

Polonium Strip

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Capsules move rapidly through the bed

• Note capsules not filled

Normal Speed Video

Slow Speed Video (x17)

HCP frit HCP frit

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Whirling bed* enhances capsule spin and circulation within the bed

• Whirling bed uses a wedge on the orifice plate

Slow Speed Video (x17)

HCP frit Whirling bed frit

HCP Frit vs Whirling Frit Performance with Symmetric Capsule

0

5

10

15

20

25

0 1 2 3 4 5

Bed Expansion

Frequency, Hertz

Spin Rate HCP Frit Circulating Rate HCP FritSpin Rate Whirling Frit Circulation Rate Whirling Frit

Whirling bed frit

*Rios, G.M., Baxerras, J.L. and Gilbert, H., in Fluidization, Eds. Grace, J.R. and Madsen, J.M., 529, Plenum Press, New York (1980)

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Offset mass capsules also have significant spin rates

• 2 mg offset mass injected into capsule– Similar to a starting condensed capsule

Slow Speed Video (x17)

Symmetric Capsule Offset Mass Capsule

Fluidized Bed Performance Wedge

0

5

10

15

20

25

0 1 2 3 4 5

Bed Expansion

Frequency,

Hertz

Spin Rate Offset Mass CapsuleSpin Rate Symmetric CapsuleCirculating Rate Offset Mass CapsuleCirculating Rate Symmetric Capsule

Injected Whiteout

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There is enough kinetic energy in the capsules to allow collision induced overturning rotation

D2 Filled Ø4 mm Capsule

1 2 3 4 5CASE

0

5

10

15

20

25

30

35

40

45

Ekinetic/Egravity

Layering reduces gravitational potential for rotation to zero(0) —> Layering makes rotating easier

Kinetic energy based on 25% of free stream gas velocity.

Need ratio to be at least one (1) to have overturning rotation

Deuterium will start out in case 3.

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Temperature variations of helium gas are only partially impressed onto fuel

•Model shell as semi-infinite slab with a fluid at the surface whose temperature is varying sinusoidally*

•Differences in the thermal properties of fuel and helium gas lead to impedance mis-match at surface

•Diffusivity, density, thermal conductivity, heat capacity

Helium gas: 0.5 atm, <18K>Temperature variations of fuel capsule

are less than that of surrounding helium

Fuel

Capsule Fuel Temperature

at an instant

*B Gebhart, Heat Transfer, McGraw Hill, 1961, eq 3-22, pg 68

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Experiment spin rates indicate fuel layer will be uniform • Previous modeling of bed circulation led to

– 3.7 Hz circulation in 54 mK bed top to bottom, with bed expansion of 2

– Thermal impedance mis-match implies fuel surface variation will be 0.26 mK

– 1-D layering analysis predicts that 0.26 mK top to bottom on fuel layer will produce layer uniformity of 1.2%

• Experimental spin rates lead to– 10 Hz capsule spin rate – Gas varies 2 mK across capsule (local gradient; bed expansion 2)

– Thermal impedance mis-match at surface predicts surface temperature variation will be 0.006 mK

– 1-D layering analysis predicts that 0.006 mK top to bottom on fuel layer will produce layer uniformity of 0.026% • 0.1µm thickess difference

This is less than layer spec of 5 µm rms

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Summary

• MPLX Cryostat has been delivered to GA– It is currently being outfitted for layering using a fluidized bed (subsystems designed and in fab)

– Mass layering is a significant project, made possible by our previous experience with ICF community designing cryotarget systems

• Prototype frit produced good fluidization of capsules– Polonium continues to control static ‘cling’ issue

• RT tests indicate fast capsule rotation– Indicates high average thermal symmetry necessary for uniform fuel layers is achievable

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Backup and old slides follow

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Optical modeling is being used to analyze the effect of vibration on bright band analysis

• Based on 1D analysis, shifts in the BB peak position are minimized for:– Vibration amplitudes <

peak width– Image integration time >

vibration period.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

500 600 700 800 900 1000

relative position

relative intensity

Motion degrades image

Bright band from fuel inner surface

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The ~0.26mK temperature variation should lead to ≤1.2% layer non-uniformity

δ 0.0117

dummy

Fraction of the average layer thickness by which the layers deviate

dummy

in thickness.

=R o 1.951 mm =R i 1.5 mm =R i1 1.503 mm =R i2 1.497 mm

=R i1 R i2

t L0.0117

=.1

6

qdot

k LR o

2 R i22 ..2 R i2

3 1

R i2

1

R oR o

2 R i12 ..2 R i1

3 1

R i1

1

R o0.261 mK

Ro

Ri

Ri1

Ri2

1.2% non-uniformity is sufficient

•Temperature difference produced by offset void (from UR/LLE)

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At 3.7 Hz, the surface of the capsule varies ~0.26mK

e par

....k DT 2 π 1 ρcDT

.2 hsphere2

=epar 144.9

a1

.2 e par2 .2 e par 1

=a 4.863 10 3

=...0.054 K exp ...2 π

0.27 sec

1.2 D

00 μm a 2.626 10 4 K

dummy

00 microns is the surface of the semi-infinite slab.

dummy

See B Gebhart, Heat Transfer, McGraw Hill, 1961, eq 3-22,

dummy

page 68.

=D 3.636 10 7 m2

sec

Model shell as semi-infinite slab with a fluid at the surface whose temperature is varying sinusoidally

sin(t)

0.5 atm

Helium

h sphere.Nu sphere

k gas

D target

=h sphere 12.766watt

.m2 K

Thermal impedance of the film coefficient causes less variation on the surface of the slab than of the fluid itself

0.054K is temperature variation in bed helium, top to bottom

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We have begun to port/adapt bright band analysis algorithms into Labview

• LNLL bright band analysis routines are being adapted into LANL sphlinder analysis code that is already Labview based– Save porting time

Add Labview VI picture

Add Bright band picture

Add sphlinder picture

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