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.
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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.
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