Transcript 3.Hund

IFE Target Fabrication Update
Presented by Jared Hund1
N. Alexander1, J. Bousquet1, Bob Cook1, S. Eddinger, D. Frey1,
D. Goodin1, H. Huang, J. Karnes2, R. Luo1, A. Nikroo1, R. Paguio1,
R. Petzoldt1, N. Petta2, N. Ravelo1, K. Saito1, D. Schroen1,
J. Streit2, A. Cheng3, S. Saiedi3
1General
Atomics, Inertial Fusion Technology, San Diego, CA
2Schafer Corporation, Livermore, CA
3UC San Diego, San Diego, CA
HAPL Workshop
IFT\P2008-012
Since the last HAPL Meeting we have:
• Reduced coating thickness for gas tight capsules
– Pinhole free at 15 µm! (63% yield)
– Improved from 25 µm (10/31/07)
• Measured the areal density of foam shell with gas tight
over coating
– Meets specification*
(< 0.3% variation over
high modes)
Thin (300-1200 Å)
High Z coating
10 m CH Overcoat
HAPL Target
Foam + DT
DT
DT Vapor
Foam layer:
0.18 mm thickness Divinyl Benzene
(DVB) or Resorcinol-Formaldehyde (RF)
*Neglecting isolated defects
Glow Discharge Polymer (GDP) is being used to
produce the plastic permeation barrier
• The horizontal rotary GDP coater* (“rotocoater”) has
been able to produce gastight HAPL shells
Good
Good––permeation
permeationleak
leakonly
only
2500
2500
3000
3000
1800
1800
Time (s ec onds )
Time (s ec onds )
1600
1600
600
600
400
400
3000
2500
2000
1500
1000
500
0
-22
200
200
0
0
-20
1400
1400
LN
LN2 2temp
temp
• The shells are tested for gas retention with a
cryogenic leak testing technique
-18
1200
1200
-16
1000
1000
-12
-12
-14
-14
-16
-16
-18
-18
-20
-20
-22
-22
ln (MS ion s ig nal)
ln (MS ion s ig nal)
ln (MS ion s ig nal)
-14
2000
2000
Bad
Bad––pinhole
pinholeleak
leak
800
800
Vacuum
LN2 temp
Pump
Shells
-12
1000
1000
Time (s ec onds )
Time (s ec onds )
Good – permeation leak only
T2B H2
500
500
0
Plasma
Rotary
Union
RF Coil
0
Stepper
Motor
LN
2 temp
LN
2 temp
-12
-12
-14
-14
-16
-16
-18
-18
-20
-20
-22
-22
1500
1500
Geometry different than established ICF technique
Produced the best coatings yet
Scalable to mass production
ln (MS ion s ig nal)
ln (MS ion s ig nal)
–
–
–
Time (s ec onds )
*Vermillion
al., Fusion
Sci & Tech 51, 791 (2007)
Bad – et
pinhole
leak
450
450
400
400
350
350
Time (s ec onds )
Time (s ec onds )
300
300
1800
1600
1400
1200
1000
800
400
200
0
3000
2500
600
Time (s ec onds )
250
250
Time (s ec onds )
2000
1500
1000
500
0
-22
200
200
-20
150
150
-22
LN2 temp
-18
100
100
-20
-16
50
-18
-14
50
-16
Leak
Leaktoo
toofast
fasttoto
test
testat
atcryo
cryotemp
temp
-12
-12
-14
-14
-16
-16
-18
-18
-20
-20
-22
-22
ln (MS ion s ig nal)
ln (MS ion s ig nal)
-12
ln (MS ion s ig nal)
ln (MS ion s ig nal)
-14
0
LN2 temp
-12
Ugly
Ugly–– viscous
viscousflow
flowleak
leak
Bad – pinhole leak
0
Good – permeation leak only
Changing the background pressure during the GDP
coating run affects the outer surface
Standard condition
Background pressure:
500 mtorr
250 mtorr
75 mtorr
• Disadvantages to 250 mtorr coating:
• Shells stick together > 2um
• Coating rate is reduced to 1/3 of std rate
• Solution: 2 step coating (High/Low background
pressure)
The latest capsules have fewer large features
• The latest conditions
– Utilized high/low background pressure coating
• 48 hours (1.5 µm) 250 mtorr, finish at 50 mtorr
– More careful techniques to reduce debris
• Shell transfer, pyrolysis of chamber
WYKO RMS Surface Roughness
RMS Surface
Roughness (nm)
10000
The smaller range in
roughness is due to
fewer large defects
Latest technique
(3/08)
1000
100
11/07 Batch
10
5
10
15
20
25
Coating thickness (um)
30
*Profiles taken over a
200 x 300 µm patch
The surface roughness evolves as the shells are
coated
Shell surface starts like this...
µm
40
0.5
µm
20
0.0
... And finishes like this
40
µm
20
µm
0.5
0.0
-0.5
0
0
20
40
60
0
0
µm
20
40
60
µm
Bare resorcinol-formaldehyde foam
15 µm of GDP on foam shell
• Experiment of the evolution of surface roughness
in progress
Measure surface
Measure surface
roughness
Coat w/GDP
roughness
Repeat
Shells mounted to substrate
Recent improvements in coatings have decreased
the minimum GDP layer for gas retention
250 mtorr/ 50 mtorr
background pressure (3/08)
50 mtorr background
pressure (10/07)
1200.0
1200
Pinhole free
1000.0
D2 Half life (sec)
D 2 Half life (sec)
1000
800
600
Pinholes
400
200
0
0
Predicted D2
permeation rate
10
20
GDP coating thickness (um)
Current barrier specification: 10 µm
30
800.0
600.0
400.0
200.0
0.0
0
10
20
30
GDP coating thickness (um)
Green = pass cryo permeation test
Black = fail cryo permeation test
We have reduced the coating thickness for
gas tight capsules by 40%!
The areal density of shells can be measured by
the precision radiography technique
• X-rays penetrate through 2 walls of shell
– Eq: T  T0 e   x , x is optical depth
• Scintillator converts x-rays into visible light
2 mm
• System counts every x-ray photon
– Noise in counts is
1
(counts)
• 16 detectors in two columns
X-ray beam
• Shell rotates
(144 pixels/row)
1 mm
(16 rows)
detectors
– Shaft encoder => no cumulative error
rotation
S.A. EDDINGER, R.B. STEPHENS, H. HUANG, T.J. DRAKE, A. NIKROO, G. FLINT, C.R. BYSTEDT, “Precision
X-Ray Optical Depth Measurements in ICF Shells” Fusion Sci. & Technol. 51, 525 (2007)
The areal density of thick shells have been measured
Areal density specification:
Single Rotation Scan
< 0.3% over modes 100 - 500
(w/ 13 traces)
Large defects
1.005
1.004
1.002
1.005
1.001
1.003
1
Relative Areal Density
Relative Areal Density
1.003
0.999
0.998
0.997
0.996
0
45
90
135
180
225
270
315
Angle, degrees
4.5 mm RF foam shell
with 25um GDP
overcoating
1.001
0.999
0.997
0.995
360
0.993
0.991
0
45
90
135
180
225
270
315
360
Angle, degrees
Single Rotation Scan
(w/ all 16 traces)
The shells tested meet the areal density
specification (neglecting large defects)
Conclusion
• We have reduced the GDP coating thickness
for gas tight capsules from 25 to 15 um (40%)
–
–
Further improvement are possible
Future work: experiments to better
understand mechanism of background
pressure/ evolution of coating roughness
•
Use this understanding to refine coating parameters