P1258836327YTXSO

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Final Optic Research Progress and Plans
M. S. Tillack
with contributions from
Z. Dragojlovic, F. Hegeler, E. Hsieh, J. Mar, F.
Najmabadi, J. Pulsifer, K. Sequoia, M. Wolford
HAPL Project Meeting, PPPL 27-28 October 2004
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Overview

1. Final optic program summary
2. New mirror fabrication and testing
3. Larger scale testing
4. Contaminant transport modeling
5. Gas puff modeling

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The steps to develop a final optic for a Laser
IFE power plant (1 of 2)
1. Front runner final optic Al coated SiC
GIMM UV reflectivity, industrial base,
radiation resistance
Contamination Optical quality Fabrication
Radiation resistance
Key Issues Shallow angle stability Laser
damage resistance goal 5 J/cm2, 108 shots
2. Characterize threats to mirror LIDT,
radiation transport, contaminants
3. Perform research to explore damage mechanisms,
lifetime and mitigation
Microstructure
Bonding/coating
Fatigue
Ion mitigation
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The steps to develop a final optic for a Laser
IFE power plant (2 of 2)
4. Verify durability through exposure experiments
10 Hz KrF laser UCSD (LIDT)
XAPPER LLNL (x-rays)
ion accelerator
neutron modeling and exposures
6. Perform mid-scale testing
5. Develop fabrication techniques and advanced
concepts
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Diamond-turned, electroplated mirrors survived
105 shots at 18 J/cm2 on a small scale (mm2)

1. Relatively small grains (10-20 mm)
2. Relatively dense, thick coating

Still, these mirrors ultimately fail due to grain
motions, ...
... and we would like to improve the high-cycle
fatigue behavior
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Post-processing after thick (35-50 mm) thin-film
deposition should provide good optical quality
with a damage-resistant microstructure
rough substrate
polish/turn
coat
final polish/turn
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Ringdown reflectometry (now _at_266 nm) indicates
somewhat high absorption at 85
reflectivity of 35 mm Schafer mirror
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Diamond turning lines are too deep 50 nm rms
(A new Pacific Nanotechnolgy AFM has been added
to our surface analysis capabilities)
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Peaks grow during exposure (unlike earlier
results which exhibited etching)
etching observed previously in diamond-turned
polycrystalline foils
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Its time to start making smoother mirrors
MRF systems are popping up all over the
place(this one is at Edmund Optics)
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Larger mirrors are being fabricated with
increasing emphasis on surface quality

• Mid-scale 4 optics
• Thick e-beam coatings
• Electroplated Al

1. Other improvements under consideration

• MRF surface finishing
• Hardening techniques
• nanoprecipitate, solid solution hardening
• friction stir burnishing (smaller grains)

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Scaled testing was initiated at Electra during
late August
we spent 1 week assembling the optical path,
developing test procedures, and exploring issues
for large scale testing
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Experimental Layout
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Laser energy measurements showed dramatic energy
loss along the beam path
Electra oscillator
2 graphite aperture
3 lead aperture
0.14 J to 5.2 J (measured with a 2 calorimeter)
80 cm
periscope
10 cm
5.2 J
polarizer cubes
Nike mirror
telescope
1/2 waveplate
3.9 J
p-polarized
10 cm
0.14 J
14.2 15.3 J (measured with a 30 cm x 30
cm calorimeter) 13.2 J with a 2 dia. aperture
12.8 J (measured with a 30cm x 30 cm calorimeter)
1 aperture
0.57 J
1.04 J
vacuum chamber
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We dont see this with our Compex laser
1 86 mJ 2 84 mJ
3 86 mJ 4 85 mJ
1 228 mJ 2 119 mJ 3 95 mJ 4 92 mJ
5 13 mJ 6 75 mJ 7 58 mJ 8 56 mJ
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An alternative idea for scaled testing large-aper
ture uncoated FS window _at_56
12 FS window(5250)
beam dump
700 J blunderbuss
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30 cm squareaperture
10 roundaperture
10 diameter, 6-m fl Nike lens
6.7
8 port
10
30 cm
assume 700 J in 900 cm2 0.75 J/cm2 25 of
s-light reflected 0.09 J/cm2 10 round on 6x12
rectangle 362 cm2 35 Joules (polarized)
available
chamber
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Another alternative idea for scaled
testingContrast is gt1001 over a 7 range
10 diameter, 6-m fl Nike lens
beam dump
700 J blunderbuss
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30 cm squarebeam with 9 round aperture
12 FS window
8 port

• assume 700 J in 900 cm2 0.75 J/cm2
• 25 of s-light reflected 0.09 J/cm2
• 9 round 410 cm2
• 37 Joules (polarized) available

chamber
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Contamination transport from the chamber to the
final optic was explored using Spartan

• 160 MJ NRL target
• 50 mTorr Xe _at_RT
• Bucky hand-off at 500 ms

Displacement field after 1st shot

• Net flow toward chamber center is predicted
• we need to include rad-hydro displacements
• Net flow toward optic?

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Particles transport rapidly toward the final optic
Test particle trajectories
Pressure at 100 ms
Pa
4
3
2
1
We need to run multiple shots to establish the
long-term behavior
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Gas puffing was examined as a posssible optic
protection technique

• 1 Torr-m may help reduce ion and x-ray damage
• Fast gas puff could be used immediately preceding
  implosions
• Might also help cool chamber gas

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A gas puff sufficient to protect optics would
increase the base pressure beyond 100 mTorr

• Pump speed per duct 1.5x105 l/s
• Duct diameter 75 cm
• Duct length 3 m
• Number of ducts 64
• Orifice conductance 44 l/s/cm2
• Target mass 4 mg
• Rep rate 5 Hz
• Chamber radius 7 m

It doesnt look promising!
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5-yr plan and progress to date
2001
2002
2003
2005
2006
2004
start
KrF
larger optics
Phase I evaluation
electroplatesuccess
initial promising results at 532 nm
new lab,cryopump
extended database,mid-scale testing,radiation
damage, mirror quality, design integration
lower limits at 248 nm, chemistry control
attempts at thin film optics