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

Rep-rated high-energy solid-state laser initiatives have sprung up around the world, which is likely to accelerate progress