Transcript 24 HUND - HAPL Oct 08 Coating Fabrication (corrected)

Progress on HAPL Foam Shell
Overcoat Fabrication
Presented by Jared Hund1
N. Alexander1, J. Bousquet1, Bob Cook1, D. Goodin1,
D. Jasion1, R. Paguio1, K. Saito1
1General
Atomics, Inertial Fusion Technology, San Diego, CA
19th HAPL Workshop
University of Wisconsin
Madison WI
October 22 - 23, 2008
IFT\P2008-088
Since the last HAPL meeting we have made
progress on overcoats:
• Improved surface defects on foam – which
has resulted in fewer defects on the overcoat
surface
• Measured parameters important for fill
cycle/tritium inventory
– permeation rate at elevated temp
• Built 2nd high capacity GDP(roto)coater for
more experiments
We are focusing on low yield steps of the foam
target fabrication process
Foam fabrication cumulative yield (pre-coating)
~90%
Droplet
survival
DVB
RF
Curing/
Drying
DVB
RF
Sphericity
DVB
RF
Wall
uniformity
(NC)
DVB at 3% NC
DVB at 1% NC
RF at 3% NC
RF at 1% NC (zero yield)
65%
We are also focusing on the overcoat yield
Capsule fabrication cumulative yield
65%
Foam
Fabrication
Gas
Retention
Surface
Finish
DVB
RF
11%
DVB w/15 µm 0%
RF w/15 µm 8%
RF w/10 µm 0%
HAPL Target
Thin
5-10 µm CH
High Z coating
Overcoat
DVB 0%
RF 0%
Foam + DT
DT
DT Vapor
Foam layer:
0.18 mm thickness
Divinyl Benzene (DVB) or
Resorcinol-Formaldehyde (RF)
We are working to reduce the overcoating
thickness to 5-10 µm
• We are continuing our parametric evaluation
of GDP coating conditions on foam
– Background pressure
– Foam surface
– Reactant flow rates
3” dia.
chamber
GDP “Rotocoater”
• The essential function of the overcoating is to be
permeable at RT yet hold the fuel at cryo
LN2 temp
-12
-14
-16
-18
-20
3000
2500
2000
1500
1000
-22
500
– Measured with Interferometric Profiler
MS Signal of Good Shell
Cycled between 20°C and
– permeation
LN2 temperaturesleak
0
• Surface roughness
Good
ln (MS ion s ig nal)
• At 20°C
• At cryo (LN2) temperature
Time (s ec onds )
Bad – pinhole leak
-12
ion s ig nal)
– Test permeation with mass spectrometer
-14
-16
on
We can successfully make gas tight
overcoatings at 15 microns thickness
Improved parameters
April 2008
Plot of gas retention
Oct 2007
1200
1200
Pinhole free
1000
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)
30
800
600
400
200
0
0
10
20
30
GDP coating thickness (um)
Green = pass cryo permeation test
Black = fail cryo permeation test
• The improvement came from tailoring the
coating pressure ranges
We have reduced the isolated defects
appearing on the overcoated shells
~30 nm RMS RF
Coated with GDP
~60 nm RMS RF
Coated with GDP
Both areas ~115 nm RMS
• Reducing defects on the foam reduced defects in the
overcoating
• But - the background roughness is the same
The foam surface roughness is now below the spec, but
coating parameters need to be improved
A number of items need to be optimized for
good surface finish and gas retention
• Coating pressure
– Evaluated background pressures for
smoothing effect
• Experiments of 50 – 500 mtorr showed 250 mtorr was
smoother
– 250 mtorr background pressure for entire run
• Sticking was a problem we were able to overcome
• Stress in the coating is a problem
– Use variable pressure: 250 then 50 mtorr
– Current experiments: high pressure for more of
the coating thickness (but not all)
The tritium inventory required is set by the
coating characteristics
• The temperature of the fill can affect the properties of the
coating (and fill rate)
Plot of tritium
inventory as a
function of
temperature for
various Ea and
reduction in buckle
strength
Tritium Inv (kg)
– Buckle strength (can decrease with T)
– Permeation rate (increases with T)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Ea=20; 10%
Ea=40; 10%
Ea=20; 50%
Ea=40; 50%
300
320
340
360
380
400
Temperature (K)
High temperature fill will be necessary to keep the
tritium inventory low
The permeation rate through GDP was measured
as function of temperature
• The permeation rate through GDP was
measured as function of temperature
Ea= 15 kJ/mole
Permeability x10^14
7
6
5
Lit Value*
4
3
2
1
0
250
300
350
400
450
Temperature (K)
• ~4x faster permeation at 100°C
•~10x faster permeation rate at 130°C
But the actual fill rate may be reduced because of a
reduction in buckle strength of the shell, but that will
no greatly affect tritium inventory
Conclusion
• Foam yields are progressing with systematic,
parametric studies
• We are evaluating the mechanisms to
improve coatings parameters for thinner,
gastight, smooth coatings
• We will evaluate the needed Tritium inventory
due to fill cycle
– measure effect of temperature on buckle
strength