progress towards a compact laser driver for laser … amp slabs compensated ... on today’s...
TRANSCRIPT
Presented by: Andy BayramianLawrence Livermore National Laboratory
High Energy Class Diode Pumped Solid State Lasers Workshop
September 12, 2012
Granlibakken Conference Center, Lake Tahoe, CA
Progress towards a Compact Laser Driver for Laser Inertial Fusion Energy
Progress towards a Compact Laser Driver for Laser Inertial Fusion Energy
LLNL-PRES-581132
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The National Ignition Facility
LIFE is a modular laser system which allows realistic reliability specifications, affecting plant availability by <1%
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1 “Beamline in a box” fits in a semi trailerA >100m NIF beamline is compressed into a <11m box
10.5 x 2.2 x 1.4 m3
Modular, truck-shippable, swappable beamlines enablepractical power plant supply chainhigh availability laser
NIF capability in a very small box:LIFE high average power laser architecture attributes
Provides efficiency (~18%) at high repetition rate (16 Hz)• High brightness efficiency diode pump arrays• Helium gas-cooled amplifiers• High efficiency harmonic conversion using pulse splitting
Will be built with existing materials• Glass slabs: thermal birefringence compensated by architecture• DKDP Pockels cell: polarization switching minimizes heat load
Designed for high availability operation• Robustness: Low 3 fluence operation• Headroom in beamline power to meet operational availability• Optics preparation to mitigate damage
Suitable for remote (off-site) manufacturing• Modular beamlines permit hot-swapping• Separation of laser manufacturing & power generation operations
4 4
55
Laser Bay
Master oscillator / Preamplifier / Multi-pass architecturePassive optical system performanceLine Replaceable Unit (LRU) methodologyWhole-system design, construction, commissioning and operationOptics production and performance experience baseCoupling demonstration to full-scale IFE target
The NIF laser provides the single-shot baseline
NIF Beamline
17 J/cm2 18 J/cm2 3
6
pFlashlamps
pFlashlamps
Laser diodes and helium gas cooling enable a NIF-like architecture to meet LIFE driver requirements
These technologies have been developed as part of the Mercury HAPL Project
High Speed Gas CoolingHigh Power Diode Arrays
3 W/cm2 cooling (average)100 kW peak power
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Diode pumps high efficiency (18%)Helium cooled amps high repetition rate (16 Hz) with low stressNormal amp slabs compensated thermal birefringence, compact ampPassive switching performs at repetition rateLower output fluence less susceptible to optical damage
LIFE combines the NIF architecture with high efficiency, high average power technology
8NIF-0111-20671s2.ppt
16 J/cm2 14.7 J/cm2 3
Rotator /4Diodes Diodes
The entire 1 beamline can be packaged into a box which is 31 m3 while providing 130 kW average power
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10.5 m
1.35
m
2.2 m
Diode array
Pockels cell
Amplifier head
Preamplifier module (PAM)
Deformable Mirror
LIFE Box in NIF Laser Bay
LLNL average power lasers have been proving grounds for several key LIFE technologies
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J. Honig, et. al, Appl. Opt. 46, 3269 (2007)A.J. Bayramian et. al, Fusion Sci. Tech. 52, 383 (2007)
25 kW high average power laser AVLIS 24/7 operational laser
600W, 10 Hz Mercury Laser 300 Hz, 38 W Pulse Amplifier
Efficiency-cost tradeoffs: Nd vs. Yb gain media
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Efficiency vs. Pump Power vs. Cooling Architecture
Erlandson, et al., Invited Paper, Opt. Mat. Express, 2011; Patent filed: IL-12308
Our results quantify the benefits of advanced materialsshow that cooling architecture is critical to capitalize on Yb:YAG
for 2.2 MJ 3LaserYb:S-FAP
Nd:APG-1
Yb:YAG @ 200 K
Yb:YAG @ 150 K
Yb:S-FAP @ 295 K
Yb:YAG @ 200 K
Yb:YAG @ 232 K
Yb:YAG @ 175 K
Yb:YAG @ 150 K
Nd:APG-1 @ 326 K
125 s164 s
Pulselength = 400 s
300s
164 s300 s
600
1000 s
The LIFE laser will achieve high efficiency, optimized at ~18% to balance economic and performance terms
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14
16
18
20
22
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30 40 50 60 70 80 90
Effic
ienc
y (%
)
Diode Power (GW)
223 s
164 s 125 s 106 s
Pump pulselength
Electrical to 3 Optical Efficiency
variability
83 s
Capital Cost →
Diode power conditioning has been made practical for the footprint and efficiency needed for Beam-in-a-Box
• Smart Pulser— “A more compact and efficient diode pulser”— High average power (12.5 kW)— High current (1000A)— High efficiency (90%) (95% efficiency possible with double size pulser— Low volume diode pulser (713 cm3)— Benefit: 10X average power, 10X decreased volume
• Licensing— This technology is currently being developed by a commercial company
Size: 3.66 x 4.76 x 40.96 cm3
Single pulser unit of Diode Power Conditioning for LIFE
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These pulsers are now being used in the lab for diode laser testing
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0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
WA
TTS
AMPS
10C0C-17C
0 50 100 150 200 250 300 3500
200
400
600
800
1000
Time (us)
Cur
rent
(am
ps)
97% of energy between 0 and 208 us
0 50 100 150 200 250 300 350 4000
100
200
300
Time (us))
Cur
rent
(am
ps)
1000A dummy load
10-bar diode stack
• Once characterized, these early bar analogs similar to those needed for LIFE will undergo Mshot to Gshot lifetests
• Mshot testing underway now
Example of a bar test with temperature study
0
100
200
300
400
500
600
700
800
900
0.00E+00 5.00E+04 1.00E+05 1.50E+05 2.00E+05
WAT
TS
SHOTS
Optical Power (W)
Early Lifetime testing
Diode technology will meet Beam-in-a-Box cost targets
• White paper co-authored by 14 key laser diode vendors• 2009 Industry Consensus: 3¢/W @ 500 W/bar, with no new R&D
• Power scaling to 850 W/bar provides $0.0176/W (1st plant) • Sustained production of LIFE plants reduces price to ~$0.007/W• Diode costs for first plant: $880M• Diode costs for sustained production: $350M
0.1
1.0
10.0
100.0
0.000 0.001 0.010 0.100 1.000 10.000 100.000
Price (¢/W
at 5
00W/bar)
Diode Volume (GW)
1
ONE TIME PRODUCTION
SUSTAINEDPRODUCTION
One LIFE Plant
LIFElet1¢ /W
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Each beam box includes ~130 MW of polarization combined diode pumps
Schematic of pump delivery methodDiode relay telescope
Polarizer
Amplifier
Solid model of the LIFE amplifier system
Diode array
Gas-cooled amplifier
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Dio
de
arra
y
Diode array
7.0
5.5
4.0
2.5
1.0
Amplifier Diode Pump Profile (Gain)
-12-10 -8 -6 -4 -2 0 2 4 6 8 10 12
-12-10-8-6-4-202468
1012
X(cm)
Y(cm
)
Ray-trace data
Amplifier heads employ gas-cooled glass slabs to remove heat longitudinally mitigating thermal lensing
This amplifier design was prototyped and thermal / gas cooling codes benchmarked on the Mercury laser system
amplifierslabs
Helium
Pump
Pump
Gas Cooled Amplifier Head
Details
• 20 glass slabs • Aerodynamic vanes• 5 atm Helium • Flow rate Mach 0.1
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Thermally induced depolarization in isotropic media (Nd:glass) can be minimized with polarization rotation
, 4-wave platepolarizers
Pockels cell
Quartz rotator
Spatial filterRelay
RelayAmp 1
Amp 2
Architecture
Polarized transmission of amplifier components
1 slab 1 amplifier(20 slabs)
2 amplifiers(compensated)
1.00.90.80.70.60.50.40.30.20.10.0
1.00.90.80.70.60.50.40.30.20.10.0
1.00.90.80.70.60.50.40.30.20.10.0
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The materials chosen for the LIFE laser are based on today’s availability to meet schedule
KDP and DKDP frequency conversion crystals
Nd3+: phosphate laser glassHEM Sapphire & EFG Sapphire
waveplates
Quartz crystal rotators
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LIFE requires a 25 x 25 cm2 aperture quartz rotator, however, quartz is not yet available in this size
• Quartz crystals can produce a 15 x 15 cm aperture today (Sawyer Corporation)
• Bonding of 4 parts together will yield a full size optic.• We are doing our first test bonds in collaboration with
Precision Photonics Corporation• Polished parts bonded with CADB (Chemically Activated Direct
Bonding)
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Validation experiments on quartz rotator material indicate potential to meet LIFE beamline requirementsFirst characterization of a bonded quartz rotator shows promise
• Transmitted wavefront (<lambda/14 without MRF correction) & rotation (>99.9%) are reasonable for this first demo
• Raster scan damage testing was carried out at SPICA Inc. on three different samples using a 1064 nm 3 ns Nd:YAG laser system.
• First initiation sights were observed at 16 J/cm2, 16 J/cm2 and 49 J/cm2
respectively. • An additional test for 105 shots was successfully carried out at 10 J/cm2
(nominal LIFE operational point for the rotator).
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Bonded Quartz Rotator Transmitted wavefront error(8.0 x 9.0 x 1.4 cm3)
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A cylindrical spatial filter can mitigate manyissues associate with high average power / intensity
• Spatial filters are essential for high energy laser systems– Reset high frequency B-integral effects– Provide gain isolation– Improve laser beam quality
• High intensity in spatial filters is an issue– Exceeds pinhole melt / vaporization
threshold– Pinholes degrade over time– Vaporized material can coat telescope
optics
High Intensity Issues
Cylindrical Filter Approach
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The calculated intensity profile on the cylindrical filter appears acceptable with real aberration files
0 100 200 300 4001x10-2
1x10-1
1x100
1x101
1x102
1x103
1x104
1x105
left right
Flue
nce
(J/c
m2 )
Half Angle (rad)
Fluence map on slit
Design point
Complex field for final pass sent through Cylindrical Telescope in Miro
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Cylindrical filter experiments are proceeding well
Testing apparatus at SPICA showing active test
• Slit filter substrates manufactured using NIF high damage threshold substrate, finishing, and cleaning procedures.
Raster scan test results:
• Successful ramp from 0 - 300 J/cm2 in dry air (RH 5%)
• Successful ramp from 0 - 300 J/cm2 in vacuum (mtorr)
• Single damage spot at 150 J/cm2 in vacuum – no other damage
• Lifetime testing underway to demonstrate 105 shots – so far 3.6x104 shots no damage
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PROP Model with New Optics Aberration Files: Results at Converter Input
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Mean 1 fluence: 6.25 J/cm2
Peak 1 fluence: 6.99 J/cm2
Contrast: 2.23%
• More realistic aberrations using NIF optics database with no scaling• Filtering of files to remove interferometer defects• Wavefront improved slightly compared to original model
High resolution 1024x1024 (500 micron pixels)
Detailed propagation simulation (based on measured NIF optics aberrations) shows excellent performance
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Energy = 5.5 kJMean fluence = 1.55 J/cm2
Contrast = 6.5%
Beam contrast at the final Fresnel optic is reasonable
Focal spot at hohlraum clears the laser entrance hole
Fluence (J/cm2)
2.5
2.0
1.5
1.0
0.5
0.0-30 -20 -10 0 10 20 30X (cm)
30
20
10
0
-10
-20
-30
Y (c
m)
Outer illumination cone shown with allowances for pointing/plasma closure
3 optical damage can be mitigated using existing NIF technologies and fluence scaling
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Fused Silica Lenses
Tremendous progress has been made improving the damage resistance of
optics for NIF
0 5 10 15 20 25100
101
102
103
104
105
106
107
AfterMitigation
2009finish
1997finish
3w Fluence Distribution 1.8MJ NIF, 1000 Shots
2010 AMPTreatment
Initi
atio
ns p
er N
IF-s
ize
Opt
ic
3 3ns fluence (J/cm2)
Beam Contrast 10%
LIFE: average fluence reduced by >2X to add margin against modulation for
high average power
Fused Silica Lenses
0 5 10 15 20 25100
101
102
103
104
105
106
107
3w Fluence Distribution LIFE, 1e9 Shots
After Mitigation
2010 AMPTreatment
Initi
atio
ns p
er N
IF-s
ize
Opt
ic
3 3ns fluence (J/cm2)
Beam Contrast 10%KDP
Final optic
NIF capability in a very small box:LIFE high average power laser architecture attributes
Provides efficiency (~18%) at high repetition rate (16 Hz)• High Brightness efficiency diode pump arrays• Helium gas-cooled amplifiers• High efficiency harmonic conversion using pulse splitting
Will be built with existing materials• Glass slabs: thermal birefringence compensated by architecture• DKDP Pockels cell: polarization switching minimizes heat load
Designed for high availability operation• Robustness: Low 3 fluence operation• Headroom in beamline power to meet operational availability• Optics preparation to mitigate damage
Suitable for remote (off-site) manufacturing• Modular beamlines permit hot-swapping• Separation of laser manufacturing & power generation operations
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Bob DeriAndy BayramianGlenn BeerChuck BoleyJeff BudeAmber BullingtonDiana ChenAl ErlandsonSteve FulkersonGlenn HueteTravis LangeRod Lanning
Mark HenesianKen Manes
Naresh MehtaShahida Rana
Margareta RehakSam Rodriguez
Kathleen SchaffersMary Spaeth
Chris StolzTayyab SuratwalaJohn Trendholme
Steve Telford
LIFE laser/laser materials team