Be Coating on Spherical Surface for NIF Target Development H. Xu, J. Wall, and A. Nikroo General Atomics 3550 General Atomics Court San Diego, CA 92121.

Be Coating on Spherical Surface for NIF Target Development

H. Xu, J. Wall, and A. NikrooGeneral Atomics

3550 General Atomics CourtSan Diego, CA 92121

Beryllium Targets are essential for Inertial Confinement Fusion because of high x-ray absorption with stable implosions

300 eV design

1000

radii in µm(not to scale)

915

900

850

845

840

760

Cu dopantatom %

0%

0.35%

0.35%

0.70%

0%

DT

10-1

100

101

102

103

104

105

Po

wer

, n

m 2

2 4 6 810

2 4 6 8100

2 4 6 81000

mode number

Graded Be NIF spec Graded CH NIF spec

1 MJ graded Be:Cu design

It requires ~160μm Be/Be(Cu) coatings.

better stability for Be capsule

Magnetron Sputtering is One Way of Making Be Coatings on Sphere Mandrels

Be sputter

targets

Bounce pan

Piezoelectric

oscillator

Cu sputter

target

CH mandrels

voltage

bias

Vacuum

Chamber

- energetic deposition beam- low temperature- relative high rate

Be Coatings Characterized by X-ray Radiograph and SEM

CH

Be

27µm

X-ray radiograph shows ~100μm Becoating and inside CH mandrel.

SEM showed columnar grain growthof Be coatings.

0.4-0.5μm/hr

Higher Coating Rates Lead to Twisted Grain Structure

0.75 μm/hr

0.5 μm/hr

More directional beam at higher power plays a role here.

Be Coating Density Measurements

Be shells Density (g/cc)+3%

Be050325, 49μm

1.74

Be041206-2, 95μm

1.77

Be050414, 43μm

1.74

Be050420, 53μm

1.74

ρ = M/V

94-95% bulk density

TEM showed low void density and small void size

voids

Low void density and small void size are consistent with density measurements,which indicate Be films are a few percent from bulk density.

Roughness Evolution versus Thickness

y = 9.5272x0.7931y = 4.88x1.1908

1

10

100

1000

0 20 40 60 80 100 120

Thickness (um)

RM

S (

101-

1000

) n

m

2004

2005

Power (2004)

Power (2005)

Roughness RMS ~ dβ and β is 0.8-1.2, which is consistent with shadowing dominated roughening.

Evidence of Self-shadowing

Striations seen at high magnificationare consistent with shadowing effects.

J. Appl. Phys. 91, 1963 (2002)

20º

40º

60º

FIB cross section

Film Growth Structure Zone Model

Microstructure of sputter-deposited coating

At 3.7-10mTorr and deposition temperature of 130ºC-150ºC (T/Tm~0.25)microstructure of our Be film is consistent with a transition regime betweenZone I and Zone II.

Structure Zone Model (SZM) proposed by Thornton (1977)

T/Tm~0.25

Challenge for full thickness capsule-beyond thin film regime

• High density up to 150μm thickness: repeatedly demonstrated at ~50μm; what will be the density at ~150μm?

• Some problems for getting thicker films (100-150μm):agitation, stoppage etc.power law predicts rougher surface with increasing thickness; one approach is to divide full thickness growth into a few thinner layer growth and apply polishing/ion etching at each interfaces.

• Smooth surface finish: polishing has been demonstrated to improve surface finish.

• High accuracy film density and doping level measurements.

~100μm coating with nodular growth~100μm coating with columnar grains

Summary

• Be coatings on sphere mandrels have been demonstrated.

• Columnar grain growth was obtained up to 100μm.

• Higher density columnar structure has been demonstrated repeatedly up to 50μm.

• Film roughening mechanism on spherical surface is analyzed and believed to be dominated by shadowing effect.

• Future efforts are focused on obtaining full thickness NIF capsule with high density and smooth finish.