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Phase II Considerations:Diode Pumped Solid State Laser (DPSSL) Driver
for Inertial Fusion Energy
Steve Payne, Camille Bibeau, Ray Beach, and Andy BayramianNational Ignition Facility Directorate
Lawrence Livermore National LaboratoryLivermore, California 94550
HAPL ReviewFebruary 6, 2004
Atlanta, GA
Outline
• Comparison of DPSSL with NIF- Requirements- Technologies
• Critical Phase II science and technology issues- Beam energy- Nonlinear beam propagation- Stimulated Raman scattering - Crystal growth- Diode cost- Frequency conversion- Beam bundling
• ROM cost and schedule
• Energy• Pulse shape• Smoothness• Wavelength
Target Gain
• Efficiency• Reliability• Diode cost• Repetition rate
IFE Power Plant
Fusion laser architectures are predicated on meeting target physics and power plant system-level requirements
• Target requirements similar to NIF
• Additional system-level requirements imposed on IFE lasers
Gain Medium
NIF
(stockpile stewardship)
IFE
(energy)
Integrated Research Exp.
(scaling)
Mercury
(prototype)
Energy 2 MJ
192 beams x 10kJ
2 MJ
700 beams x 3kJ
6kJ
2 beams x 3kJ
100 J
1/30 aperture
Pulse shape,
wavelength
3 ns at <0.4 m
Smoothness < 0.1 % in 1 ns
(beams overlapped)
< 3 %
in 1 nsec
< 10 %
in 1 nsec
Efficiency 0.8%,
no utilities
5 - 10%,
wall-plug
5 - 10%,
no utilities
Cost $1000/J; Flash lamps used
$500/J - laser;
$0.05/W - diodes
$40k/J - laser;
$1/W - diodes
$400k/J - laser;
$5/W - diodes
Rep-rate 10-4 Hz 10 Hz
Reliability 104 shots • 1010 for diodes• 108 for optics
• 109 - diodes• 107 - optics
• 108 - diodes• 106 - optics
NIF
/ I
FE
ar
e sa
me
En
han
cem
ents
nee
ded
Solid state laser driver requirements forInertial Confinement Fusion
Amplifiers
Flashlamps
TelescopeMirror
Diodes
Reflectors
Our new architectural layout of optics and amplifiers
• Collinear diode pumping and beam path extraction - improves gain uniformity and pump efficiency - integrates spatial filter and pump cavity
• Closely-spaced slabs and lenses in compact amplifier cavity - reduces “B-integral” or beam intensity modulations - optics located where damage probability is lowest
Our new architectural layout of optics and amplifiers
• Collinear diode pumping and beam path extraction - improves gain uniformity and pump efficiency - integrates spatial filter and pump cavity
• Closely-spaced slabs and lenses in compact amplifier cavity - reduces “B-integral” or beam intensity modulations - optics located where damage probability is lowest
Comparison of NIF and Mercury amplifiers
Gas cooled
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
V
Flash lampsPulsed
power
DC power20 kV
Flash lampsPulsed
power
DC power20 kV
Eff. (%) NIF Hg IFE
Power 82 85 95
Pump 50 45 70
Xport 60 85 95
Absorption 40 90 90
Quant Def 60 86 86
Emission 67 80 80
ASE 67 N/A 67
Extraction 60 65 70
Fill 85 85 92
Xport 93 N/A 95
Freq Conv 60 75 75
Total (%) 0.75 8.3 12.0
Efficiency comparison NIF andMercury-like architectures (estimates)
Higher efficiency of DPSSL is achieved through many enhancementsHigher efficiency of DPSSL is achieved through many enhancements
Radiative cooling
Convection
Nd:glass
Frequency conversion
Radiative cooling
Yb:S-FAP
Frequencyconversion
Reflector
Yb:S-FAP
Turbulentcooling
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
V
Pulsed power
DC power100 V Diodes
Pulsed power
DC power100 V Diodes
Mercury
Gain medium deployed in solid state laser hasfundamental consequences on cost and performance
Energy Levels Storage time determines diode cost
GainSaturation fluence is FSAT = h / G
2 MJ laser and 5¢/W diodesCdiode ($B) = 0.5 / ST (ms)
Peak fluence: FPEAK = 4.5 FSAT
Bandwidth for smoothing: G
Beam EnergyBalances amplified spontaneous emssion (ASE) and nonlinear ripple growth
Ebeam = (EXT / 12 FSAT) (3 P / 4)2
nonlinear indexextraction efficiency
laser pulse widthSaturation fluence
Pump LaseG
Storage time = ST
Pump LaseG
Storage time = ST G
Peak G value
G
G
Peak G value
Ripplegrowth
Laser slab
ASElosses
Yb:S-FAP laser material offers advantages over Nd:glass for IFE
Gain Medium
Diode Cost0.5 /st
Damage4.5 Fsat
Beam Energy, Ebeam (3 nsec pulse)
1 Band Width,
NIF
(Nd:glass)
$1.25B
(hypothetically diode-pumped)
24 J/cm2 5.6 kJ
(10 kJ with higher ASE losses)
1 THz
IFE
(Yb:S-FAP)
$0.45B 14 J/cm2 4.4 kJ 0.3 THz
1.0 THz @ 3
Comparison of Nd:glass and Yb:S-FAP gain media in fusion lasers
Longer lifetime reduces cost
Lower fluencereduces damage
Beam energiesare similar
• Yb:S-FAP has 2.5x greater thermal conductivity than Nd:glass better for rep-rated operation• However, crystals are more difficult to produce in large size
• Yb:S-FAP has 2.5x greater thermal conductivity than Nd:glass better for rep-rated operation• However, crystals are more difficult to produce in large size
Bandwidthis adequate
Outline
• Comparison of DPSSL with NIF- Requirements- Technologies
• Critical science and technology issues- #1 - Beam energy / amplified spontaneous emission- #2 - Nonlinear beam propagation / optical damage- #3 - Stimulated Raman scattering - #4 - Crystal growth- #5 - Diode cost- #6 - Frequency conversion- #7 - Beam bundling
• ROM cost and schedule
• Amplified spontaneous emission rates are accelerated for larger slabs
• Greater extraction efficiency leads to higher B-integral (i.e. beam modulation)
• Diode efficiency of ~60% and 3-conversion of ~75% to be included
• Reduced losses and higher diode efficiency possible
S&T issue #1: Models indicate that multi-kilojoule output is feasible from a single coherent aperture
0 1 2 3 4 5 6 70.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0 1 2 3 4 5 6 70.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
10 x 15 cm2
20 x 30 cm2
30 x 45 cm2
Op
tica
l-O
pti
cal E
ffic
ien
cy
B-Integral, radians (beam modulation)
Quadrant ofdesired
operation
Design point
4.2 kJ
1.7 kJ
8.3 kJ
Ripplegrowth
Laser slab
ASElosses
S&T issue #2: Mercury “closely-spaced slab” architecture has reduced nonlinear beam breakup relative to “widely-spaced” (NIF-like) architecture
Optical damage risk is mitigated in Mercury architecture two ways:• Closely-spaced-slab architecture reduces nonlinear ripple growth • Lower saturation fluence of Yb:S-FAP vs. Nd:glass reduces average fluence
Widely-spaced slabs have more
intensity on pinhole
Focal spots
Mercury:Closely-spaced slabs
B = 3.8 radians
B = 3.8 radians
Fitting function: Peak-to-Ave = Static · (1 + Alpha · eB)
0 1 2 3 4 5 6 70
1
2
3
4
5
6
7
Data: NIF1xRPH_P0XModel: B-integral Chi^2/DoF = 0.01565R^2 = 0.89509 Static 1.7349 ±0.04798alpha 0.0007 ±0.0001beta 1 ±0
Data: Relay1XRPH_P0XModel: B-integral Chi^2/DoF = 0.02025R^2 = 0.77415 Static 1.51115 ±0.05837alpha 0.00091 ±0.00021beta 1 ±0
Data: Relay1X_P0XModel: B-integral Chi^2/DoF = 0.01724R^2 = 0.99196 Static 1.18188 ±0.05188alpha 0.00357 ±0.00024beta 1 ±0
Data: NIF1X_P0XModel: b-integral Chi^2 = 0.14123R^2 = 0.88469 Static 1.84205 ±0.17213alpha 0.00933 ±0.00198beta 1 ±0
B limitfor NIF
No phase distortion Mercury NIF-like architecture
Pea
k to
Ave
rag
e In
ten
sity
at
th
e o
utp
ut
B (radians)
Widely-spaced architecture
0 20 40 60 80 100 120 140 160 1800.0
0.2
0.4
0.6
0.8
1.0
SR
S g
ain r
educt
ion fac
tor
Stokes angle relative to Pump (degrees)
SRS gain as a function of Stokes angle for 3 GW/cm2
S&T issue #3: Stimulated Raman Scattering (SRS) in S-FAP, or unwanted nonlinear frequency conversion, must be controlled in the IRE
Quantitative modeling yields: - Aperture limit is >20x30 cm2 at 3 GW/cm2
- Longitudinal SRS is controlled by: - inserting Tm:YAG absorber in amps - adding a small wedge to the slabs
Tm:YAG absorber suppresses SRS
Gain lowers with angle between laser and SRSSRS is predicted for the IRE based on gain
900 950 1000 1050 1100 1150 12000
20
40
60
80Absorption @1163.5 nm = 26.9 cm-11047.7 nm = 0.29 cm-1900 nm = 0 +/- 0.03 cm-1
Ab
sorp
tio
n c
oef
fici
ent
(cm
-1)
Wavelength (nm)
SRS
Laser
2.6 2.8 3.0 3.2 3.4 3.6 3.81E-7
1E-6
1E-5
1E-4
1E-3
SR
S O
utp
ut E
ne
rgy
(J)
Pump Intensity (GW/cm2)
g = 1.23 ± 0.12 cm/GW
3.5 cm boules (standard)
Onyx - high temperature Schott - “glue” bondingBonding choices
S&T issue #4: Combination of bonding and large diameter growth provides pathway to 20x30 cm2 Yb:S-FAP slabs
Approximately 10 cm boules will be needed to bond three parts together for each 20x30 cm2 slab
6.5 cm boules (last year)
10 cm boulesneeded for IRE
10k 100k 1M 10M 100M0.01
0.10
1.00
10.00
100.00Data: Data1_WcostModel: econscale Chi^2/DoF = 0.05077R^2 = 0.99933 Price 25.2 ±0Vol1 10800 ±0alpha -0.80017 ±0.01237
Pri
ce (
$ / W
)
Cumulative # of bars
19941995
19961997
2001
Mercury price
2007
2020
IFE goal
“Soft” quote of 35 ¢/W
59% learning curve
10k 100k 1M 10M 100M0.01
0.10
1.00
10.00
100.00Data: Data1_WcostModel: econscale Chi^2/DoF = 0.05077R^2 = 0.99933 Price 25.2 ±0Vol1 10800 ±0alpha -0.80017 ±0.01237
Pri
ce (
$ / W
)
Cumulative # of bars
19941995
19961997
2001
Mercury price
2007
2020
IFE goal
“Soft” quote of 35 ¢/W
59% learning curve
S&T issue #5: Learning curve analysis suggests that diode bar prices will drop as the market grows
Low duty cycle diode bars
Diode packaging house created from LLNL tech-transfer
HeatsinksDiode laser bars Backplanes
- High production rate reduced cost- Higher efficiency diodes are desired
S&T issue #6: Average power frequency conversion with >80% efficiency can be obtained for ~ 1 THz bandwidth using BBO crystal
• Main challenge is to “tile” multiple BBO crystals to cover aperture of beam- Based on current technology, four crystals must be tiled for Mercury
Conversion vs. detuning @ 0.7 GW/cm2
KDP, YCOB
BBO
0
20
40
60
80
100
3
Co
nv
Eff
(%
)
0.0 0.2 0.4 0.6 0.8 1.0
Incident 1 (GW/cm 2)
BBO Single CrystalConversion Efficiency
Thermally loaded
Conversion vs. Intensity (thermally loaded)
He cooling
BBO doubler2.5 mm
BBO tripler4 mm
He cooling
S&T issue #7: Amplifier can be integrated into bundles and clusters to simplify cooling and minimize the footprint
36 kJ bundle of 12 apertures 4 kJ beam lines
Clusters of bundles
Management of high average power likely to be
very challenging
Phase I resolves:• Yb:S-FAP performance• Laser architecture and gas-cooling• Pockels cell design• Optical damage• Diode package• Diode commercialization• Laser operations• Beam smoothing• Control system architecture• Nonlinear beam propagation (#2)• Frequency conversion (#6)
Phase II resolves:• Beam energy (#1)• Stimulated Raman scattering (#3)• Scale-up of crystals & bonding (#4)• Mass production of diodes (#5)• Beam bundling (#7)
• Higher diode eff., 45 60%• Management of higher power
Phase I resolves most issues associated with component design and functionality
20 cm
30 cm
IRE
Mercury4x6 cm2 20 cm
30 cm
IRE
Mercury4x6 cm2
Cost Breakdown for Phase II: DPPSL
Vendor Readiness ($22M): - Contracts ($10), Crystal growth ($6.5), Overhead ($5.3)
Design ($12M): - Personnel ($7.2), Overhead ($4.8)
Procurement and Construction ($135M): - Personnel ($10) - Diodes (assumed cost $1.2 / Watt, 30 MW) ($39.6) - Crystals ($10) - Laser Hardware ($12.9) - Power Conditioning ($17) - Facilities and Utilities ($22.9) - Overhead ($22.3)
Activation ($22M): - Personnel ($8.1), Crystals ($4.8), Procurements ($1.2), Overhead ($7.6)
Integrated experiments ($36M): - Personnel ($12.0), Crystals ($3.6), Procurements ($1.8), Overhead ($18.6)
$277M Personnel and Laser Hardware ($168M + $50M contingency) - LLNL Overhead ($59M; Assumes 30% reduction in tax base)
Vendor readiness $22M
Construct &Procure $135M
LaserDesign $12M
Laser Activation$22M
Integrated experimentsLaser:$36M; Chamber:$10M
Timeline for DPSSL- IRE (6 kJ) development and operation (rough estimate)
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Construct & Procure $6M
ChamberDesign $0.5M
Chamber Activation $9.5M
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