Investigation of the Si Cooling Arm to TMP Bond and its Impact on Low Mode Imperfections in NIF Cryogenic

LayersJ.D. Sater, S. Bhandarkar , B. Haid, B. Kozioziemski, J.W. Pipes, R.J. Strauser

National Ignition Facility • Lawrence Livermore National Laboratory • Operated by the US Department of Energy

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and by General Atomics under contract DE-NA0001808.

• Capsules in cylindrical hohlraums are cooler at the mid-plane relative to the poles

—Results in a thicker layer at the

equator than at the poles.

• Adding heat to the hohlraum equator will approximate a spherical thermal profile at the capsule

• The uniformity of the resulting thermal profile about the hohlraum axis depends upon:

— consistent thermal conductivity of the 16 individual bonds between each Si cooling arm and the TMP

— uniform axial thermal conductivity of the TMP

Cooling arm

Heaters

T(z)

Temp. profile

with shim

heaters on

Power Spectral Density plot

Power in modes > 3 is below the Haan spec.

Mode Amplitude vs Shim Power

De-centering of the layer occurred at higher shim powers as a result of azimuthal thermal asymmetry of the hohlraum

LEH view

Wedge analysis predicted a de-centering drift towards the

fill tube with 34 degree off axis component

Actual ice layer drift was towards the fill tube with 16

degree off axis component

…. Smoothed data___ Raw data

Arm 1

Arm 2

Degree of azimuthal bond asymmetry

Pad angle (rad)

Bo

nd

Th

ickn

ess

(µm

)

Si arm’s integral flexures being bonded to the Al TMP

Heater

Shim heatersTemp.

Sensor

Layered

Target

Prototype

Sub title

Sub title

Sub title

Sub title

Sub title

0

1

2

-1 -0.5 0 0.5 1

Max

we

dge

(u

m)

M1 Cos

Al DBs

0

1

2

-1 -0.5 0 0.5 1

Max

we

dge

(u

m)

M1 Cos

Cu DBs

0

1

2

-1 -0.5 0 0.5 1

Max

we

dge

(u

m)

M1 Sin

Cu DBs

0

1

2

-2 -1 0 1

Max

we

dge

(u

m)

M1 Sin

Al DBs

M1 vs max wedge from both TMP halves

Spec M1 < 0.68 µm amplitude

Targets occasionally still fail to meet requirements.

A sampling of M1s for targets with different diagnostic bands

Simulation of TMP thermal asymmetry for two

different conductivities

∆T < ±0.5 mK at inner heater edge to meet M1 spec.

Based upon thermal modeling, we

derive the requirement that

∆T < ±0.5mK at the inner heater edge

to meet M1 spec.

The figures at left illustrates the effect

of bond thickness variation on the

inner heater edge ∆T for two materials

of differing thermal conductivities (k).

Temp sensors

Heaters

1 cm Al puck is bonded to a silicon

arm with sample material

50 µm bond thickness

Gen 1 apparatus

TO BOBBIN-2HEAT SINK WIRES

HT1

TT1

TO BOBBIN-2

TO

HEAT SINK WIRES

HEAT SINK WIRESTO BOBBIN-2

TT5HEAT SINK WIRES

RED

H6MEASUREMENT.

BLU

TARGET STALK AND BOBBIN

TT13

HT3, HT7

AS THERMAL STAND OFF.

CRYOSTAT

T6

BOBBIN-1

& TT7FOR HT3, HT7

4 LEADCHIP HEATER

BLKSOLDER JOINTS

INSTALL LAYER OFCAPTON TAPE BETWEEN

EXISTING BASETHERMOMETER

HT5HEAT SINK WIRESTO BOBBIN-2

TT7HEAT SINK WIRESTO BOBBIN-1

TT5TT1HT5HT1

WIRING NOTSHOWN(TT5)

(HT5)

WIRING NOTSHOWN

5012

TT7HT7HT3

BOBBIN-2

(TT1)(TT7)

BOBBIN-1

HEAT SINK ADHESIVE:

ZONENOTES, UNLESS OTHERWISE SPECIFIED:

2. DIMENSIONS AND TOLERANCING PER ASME Y14.5M-1994

OR BETTER ON ALL MACHINED SURFACES.

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4. REMOVE BURRS AND BREAK SHARP EDGES 0.127/0.254 CHAMFER OR RADIUS.

TOLERANCE ARE:

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DESCRIPTIONREVCLASSIFICATION:

SH

REV

DR

AW

ING

NU

MB

ER

A

B

C

D

8 7 6 5 4 3 12

±±

DECIMALS ANGLESTHIRD ANGLE PROJECTION

MATERIALOR DESCRIPTION/MATERIAL

QTYNO

PARTS LIST

PIPES1

SATER1

7/6/15

7/6/15

7/6/15

APPLICATIONS

NEXT ASSY USED ON

--

-- --

--

THERMAL ADHESIVE TESTING

AAA15-501333-AA

AA

A15

-501

33

3-A

A

AA

A1

5-5

013

33-A

AA

AA

_1

5_5

01333

.005 2

1 -- -- --

8 7 6 5 4 3 2 1

D

C

B

A

UNCLASSIFIED

CLASSIFICATION:

DRAWN

CLASSIFICATION: UNCLASSIFIED

PIPES1 SATER1 7/6/15INITIAL RELEASEAA

SO

LID

WO

RK

SD

RA

WIN

G:

SCALE

MO

DEL:

SATER1 14067

LSOTUNLESS OTHERWISE SPECIFIED

6. MAXIMUM TOOL RADIUS ALLOWED IN CORNERS 0.04.

ADHESIVE TEST ASSEMBLY

SUBASSEMBLY

MAJOR UNIT

SATER1

THIS DRAWING WAS CREATED BY THELAWRENCE LIVERMORE NATIONAL SECURITY, LLC

(LLNS) WHICH OPERATES LAWRENCE LIVERMORE NATIONAL LABORATORY (LLNL)

FOR THE U.S. DEPARTMENT OF ENERGY UNDERCONTRACT NO. DE-AC52-07NA27344.

ANY REPRODUCTION, DISSEMINATION AND/ORFABRICATION IS PROHIBITED WITHOUT THE

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Gen 2 apparatus

Similar apparatus that thermally guards thermometer

and heater leads on the sample bobbin.

0

5

10

15

0 0.02 0.04 0.06 0.08

De

lta

T

power (W)

Delta T vs Heater Power

• 50 µm bond thickness

• Unfilled clear epoxy

• k18K=0.006 W/mK

• k was ~20x lower than

expected

• Measurement performed

with Gen 1 apparatus

0

50000

100000

150000

200000

250000

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8

electrical conductivity 1

electrical conductivity 2

viscosity

Typical behavior

Sorted through various alumina and silver filled adhesives

H20E appeared to meet requirements for building targets:

particle size was stated as <17µm, but we found this was due to

agglomeration of Ag particles

chemical cured

viscosity 3200 cP

silver filled - 35 vol% (82wt%) => electrically conductive

H20E should have good thermal conductivity

y = 18.966x + 0.3387

y = 19.541x + 0.79

0

0.5

1

1.5

2

2.5

0 0.05 0.1

De

lta

T (

K)

Power (mW)

k=0.08 W/mK

Gen1 apparatus

k=0.08 W/m•K => the glue bonds must be uniform to within 0.1 µm

Estimated Thermal Conductivity Based Upon Layering Target Thermal Resistance Measurements

R = 55 K/W

Number of Pads = 16

Pad width = 0.7 mm

Area of Pad = 4.9 *10-7m^2

Glue Thickness = 3.5*10-6 m

A/L (pad) = 0.14 m

A/L (total) = 2.24

Glue Conductance = 0.0081 W/m•K

Temperature drop is measured across TMP -> Si

arm interface at several powers

Estimated Thermal Conductivity Based Upon

Layering Target Thermal Resistance

Measurements

The bond thickness not measured, but is chosen as a ”reasonable” value based upon

other measured bond thicknesses.

The gen 1 measurement above performed on H20E had a 50 µm thick bond. There may

be poorly understood effects due to either changes in percolation behavior of the

silver loading material or due to differences in bonding behavior.

Control of the bond between Al

can and Si arm is important

Switch from Al to Cu DBs

removed the outlier M1s but still

leave a significant number of

layers out of spec.

Improving the thermal

conductivity of the TMP to silicon

arm bond can improve M1.

Low temperature conductivity of

composite adhesives have

unexplained sample to sample

variation.

Need to investigate thickness

effects on k.

Inconsistent measurements of

k are not understood and

require further investigation.

We plan to evaluate low melting point

solders

There are a number of

commercially available solder

alloys with Tmelt < 200C and

good tensile strength.

M1 has been improved by modifying the

diagnostic band material from Al to Cu and

minimizing wedging.

Thermal conductivity was measured for Stycast

1266 bonded between Si and Al at 18K.

We also estimated H20E conductance from

thermal measurements made on D-T layering

targets

The thermal profile quality depends upon

uniform bonds between the Si cooling arm and

the TMP

Layers in prototype targets met the high mode

spec.Larger bond thermal conductivity (k) relaxes

requirements on bond to bond thickness

variation.

Thermal conductivities have been measured for

several potential glues.

Composite “metal loaded” epoxy is expected to

behave as a percolated system

Thermal conductivity was measured for Ag loaded

epoxy Epotek H20E directly using the two different

apparatus.Summary and future directions for M1 mitigation

Uniform solid D-T layers in spherical

capsules require a spherical thermal

environment

Thermal asymmetry

induces M1

WarmLEH

VIEW

Capsule

. .

M1 = 0

. .

Mode 1 (M1) is dominated by thermal

symmetry of the TMP/Hohlraum

Layer

Surface

Cool

Temp (K)

k (W

/m•K

) *

10

4

0

2

4

6

8

10

15 16 17 18 19 20

Thermal Conductivity vs. Temp.

k=0.0008 W/mK

Gen2 apparatus

H20E @ 18K

Norm

aliz

ed e

lectr

ical conductivity

Vis

cosity (

cP

)

Vol Fraction

solid phase