m. s. tillack final optic research – progress and plans hapl project meeting, pppl 27-28 october...
TRANSCRIPT
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:
Overview
1. Final optic program summary
2. New mirror fabrication and testing
3. Larger scale testing
4. Contaminant transport modeling
5. Gas puff modeling
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˚
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
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
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
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
Diamond turning lines are too deep – 50 nm rms –
(A new Pacific Nanotechnolgy AFM has
been added to our surface analysis
capabilities)
Peaks grow during exposure (unlike earlier results which exhibited etching)
etching observed previously in diamond-turned polycrystalline
foils
It’s time to start making smoother mirrors
MRF systems are popping up all over the place(this one is at Edmund Optics)
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
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
Experimental Layout
43”12”
Lens
Beam Dump
Wave Plate
Cube
Mirror
Beam Sampler
Beam Profiler
UV Window
WindowCamera
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)
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
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
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
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
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
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
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!
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