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M. S. Tillack
Final Optic Research – Progress and Plans
HAPL Project Meeting, PPPL27-28 October 2004
Z. Dragojlovic, F. Hegeler, E. Hsieh, J. Mar, F. Najmabadi,
J. Pulsifer, K. Sequoia, M. Wolford
with contributions from:
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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
2. Characterize threats to mirror:LIDT, radiation transport, contaminants
Key Issues:• Shallow angle stability• Laser damage resistance
goal = 5 J/cm2, 108 shots
• Contamination• Optical quality• Fabrication• Radiation resistance
3. Perform research to explore damage mechanisms, lifetime and mitigation
MicrostructureBonding/coating
q”=10 mJ/cm2Al: 20-500 nmSiC: 10 μm
Fatigue Ion mitigation
~50 cm85˚
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6. Perform mid-scale testing5. Develop fabrication techniques and advanced concepts
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 laserUCSD (LIDT)
XAPPERLLNL (x-rays)
ion accelerator neutron modeling and exposures
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Diamond-turned, electroplated mirrors survived 105 shots at 18 J/cm2 on a small scale
(mm2)
... and we would like to improve the high-cycle
fatigue behavior
Still, these mirrors ultimately fail due to grain
motions, ...
1.Relatively small grains (10-20 μm)2.Relatively dense, thick coating
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35 μm “thick thin-film” mirror,
turned at Schafer Corp. and exposed to 104 shots at 5
J/cm2
no damage to elecroplated mirror (turned at GA)
under the same exposure conditions
Post-processing after thick (35-50 μm) 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 @266 nm) indicates somewhat high
absorption at 85˚
<1 nsnanolaserpolarizertest specimenphotodiodeoutput coupleroutput couplerlens
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
reflectivity of 35 μm 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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It’s 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
2. Other improvements under consideration
• MRF surface finishing
• Hardening techniques• nanoprecipitate, solid solution hardening• friction stir burnishing (smaller grains)
1.Mid-scale 4” optics• Thick e-beam coatings• Electroplated Al
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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
43”12”
Lens
Beam Dump
Wave Plate
Cube
Mirror
Beam Sampler
Beam Profiler
UV Window
WindowCamera
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Laser energy measurements showed dramatic energy loss along the beam
path
vacuumchamber
telescope
Nikemirror
periscope
1” aperture
1/2waveplate
polarizer cubes
3” lead aperture
2” graphite aperture Electra oscillator
0.57 J
5.2 J
3.9 J
0.14 J
p-polarized
1.04 J
10 cm
10 cm
12.8 J(measured with a
30cm x 30 cmcalorimeter)
14.2 – 15.3 J(measured with a30 cm x 30 cm
calorimeter)13.2 J
with a 2” dia.aperture
80 cm
0.14 J to 5.2 J(measured with a2” calorimeter)
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We don’t see this with our Compex laser
1 2 3 4
1 = 86 mJ2 = 84 mJ
1
2
3 45
6
78
1 = 228 mJ2 = 119 mJ3 = 95 mJ4 = 92 mJ
5 = 13 mJ6 = 75 mJ7 = 58 mJ8 = 56 mJ
3 = 86 mJ4 = 85 mJ
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An alternative idea for scaled testing:large-aperture uncoated FS window
@56˚
10” diameter, 6-m fl Nike lens
700 J blunderbuss
8” port
12” FS window($5250)
30 cm squareaperture
34˚
10” roundaperture
30 cm
6.7”
10”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
beam dump
chamber
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Another alternative idea for scaled testing:
Contrast is >100:1 over a 7˚ range
10” diameter, 6-m fl Nike lens700 J
blunderbuss
8” port
12” FS window
30 cm squarebeam with 9” round aperture
32˚
12”
6”
• 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
beam dump
chamber
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Displacement field after 1st shot
• Net flow toward chamber center is predicted
– we need to include rad-hydro displacements
• Net flow toward optic?
Contamination transport from the chamber to the final optic was explored using Spartan
• 160 MJ NRL target
• 50 mTorr Xe @RT
• Bucky hand-off at 500 μs
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Particles transport rapidly toward thefinal optic
• We need to run multiple shots to establish the long-term behavior
Test particle trajectories Pressure at 100 ms
Pa
1
2
3
4
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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 doesn’t look promising!
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electroplatesuccess
5-yr plan and progress to date
2001 2002 2003 2005 2006
start KrF larger optics
initial promising results at 532 nm
attempts at thin film optics
Phase I evaluation
lower limits at 248 nm, chemistry control
new lab,cryopum
p
extended database,
mid-scale testing,radiation damage,
mirror quality, design integration
2004