Naval Research Laboratory

Electra title page

A Repetitively Pulsed, High Energy, Krypton Fluoride Laser

ElectraElectra

Presented by John Sethian & John Giuliani

NRLM. FriedmanM. MyersS. ObenschainR. LehmbergP. Kepple

JAYCOR S. Swanekamp

Commonwealth TechF. Hegeler

Pulse Sciences, IncD. Weidenheimer

SAICR. Smilgys

Rep-Rate KrF laser (Electra)----NRLOverall Objective…………. • Develop technologies for low cost, durable

and efficient rep-rate KrF laser.• Technologies will be integrated into a 700 J, 5 Hz laser called ELECTRA.• Technologies scalable to large (50-150 kJ)systems

FY 01 Deliverables……….. 1. Develop cathode, hibachi and gas recirculator

2. Advanced pulsed power component dev.

3. KrF Physics research to maximize efficiency

4. Optics development (amplifier window)

5. Design Advanced Front End (input laser)

PI Experience………………. Leader in e-beam pumped KrF laser R & D. Nike. (POC: J. Sethian)

Proposed Amount………….. $ 9,275,000

Relevance of Deliverables

[X] NIF…………………… High damage optics development

[X] Laser RR Facility…. Rep-Rate laser

[X] Other DP/NNSA…… Advanced Pulsed Power, DEW technology

[X] Energy……………… Potential to meet IFE Driver requirements

Target gain and power plant studies definethe laser requirements

1. S.E. Bodner et al, .“Direct drive laser fusion; status and prospects”, Physics of Plasmas 5, 1901, (1998).2. Sombrero: 1000 MWe, 3.4 MJ Laser, Gain 110; Cost of Electricity: $0.04-$0.08/kWh; Fusion Technology, 21,1470, (1992)

1. 1999 $. Sombrero (1992) gave $180/J and $4.00/J2. Shots between major maintenance (2.0 years)3. Not Applicable: Different technology4. Not Applicable: Nike shoots planar targets

High Gain Target Design (G >100) 1

Power Plant Study 2

Laser IFE Requirements

IFE NIKE

Beam quality (high mode) 0.2% 0.2%

Beam quality (low mode) 2% N/A(4)

Optical bandwidth 1-2 THz 3 THz

Beam Power Balance 2% N/A(4)

Laser Energy (amplifier) 30-150 kJ 5 kJ

System efficiency 6-7% 1.4%

Cost of entire laser(1) $225/J(laser) $3600/J

Cost of pulsed power(1) $5-10/J(e-beam) N/A3

Rep-Rate 5 Hz .0005

Durability (shots) (2) 3 x 108 200

Lifetime (shots) 1010 104

DT Vapor

DT Fuel

Foam + DT

Laser GasRecirculator

The Key Components of a Krypton Fluoride (KrF) Laser

LaserInput

OutputOpticsENERGY + (Kr + F2) (KrF)* + F (Kr + F2) + h (248 nm)

Laser Cell(Kr + F2)

PulsedPowerSystem

ElectronBeam Foil

Support(Hibachi)

AmplifierWindow

Cathode

FY 1999 | FY 2000 | FY 2001 | FY 2002 | FY 2003 | FY 2004 | FY2005

FY 1999 | FY 2000 | FY 2001 | FY 2002 | FY 2003 | FY 2004 | FY2005

The Electra Program PlanELECTRA LASER (700 J, 30 cm, 5 Hz KrF Laser)

First Generation Pulsed Power

Develop Laser components:Emitter, Hibachi, Gas Recirculator

Input LaserIntegrated

Test

ADVANCED PULSED POWER

SystemsDesigns

Component R & D, Component test and evaluation

Design / BuildAdvanced System

Integrateinto Electra

ADV FRONT END (pulse shape/zooming)

Design Build and Test Integrate into Electra

OPTICS DEVELOPMENT

Amp Window Coating Development Steering/focussing Optics

KrF SYSTEMS (architecture for 2 MJ system)

Optimum Amplifier Size Architecture Optimization

KrF PHYSICS (optimize efficiency & develop design tools)

Code integrationElectron beam propagation & KrF Kinetics/ASE CodesExperimental Validation

The Electra Facility is ready for Laser Component R & D

We are evaluating cathodes for uniformity, turn-on and impedance collapse and durability

-10

-8

-6

-4

-2

0

0 10 20 30 40

norm

aliz

ed d

iode

cur

rent

time (ns)

Velvet (1.0e-01) HC/Ceramic Carbon Fiber Carbon Flock Carbon Foam 100 ppi RHEPP

CATHODE t rise (ns) Impedance Collapse Large Scale I/I Small Scale10% - 90% Z start Z finish I <ave> I I/I

Std. Green Velvet 41 4.14 4.14 629 40.2 +/- 7%RHEPP 63 3.93 3.93 652 41.2 +/- 9%V; 2:1 HCarbon Flock 64 3.75 3 662 51 +/- 15%Carbon fiber 64 3.84 3.1 650 45 +/- 100 %Carbon Foam (500 ppi) 75 3.2 2.65 554 39 +/- 10 %

Green Velvet

Carbon flock

We are developing the emitter and hibachi as a single systemPattern emitter to miss hibachi ribs

Vac

.001” TiAnode

He Laser Gas

.001”Al +Main FoilRib

e-beam

1.40 W/cm2

160º C40 m/sec

Emitter

Base

Hibachi Emitters0 5 10 15 20 25 30

0

5

10

15

20

25

30

35

Ed

epo

site

d (

keV

/ele

ctro

n)

X (CM)

Predicted Performance on ELECTRA (1 mil Ti+1 mil Al foil, @ 500 keV) 61.5% (0.9 atm) Kr 38.3% (1.1 atm) Ar 0.2%F

Lost to Foils: 20.6%1 mil Ti Foil: 10.9%1 mil Al Foil 7.7%He gas (1.0 atm) 1.4%Transmitted to other foil: 0.6%

Absorbed by gas: 78.6%Reflected: 0.0%Radiation: 0.7%

1-D Energy deposition profile

RECIRCULATOR:Textron Systems has installed a system that will allow repetitive amplification of a high quality laser beam

Gas recirculator.ppt

RMS Variation 10 % Open Cavity Mufflers, 2.5 % Open Cross-leg Mufflers Rev3

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 10 20 30 40 50 60

Transits (1m)

RMS Density

RMS Pressure

/ 10-4 @ 51 passes (= 5 Hz)

HoneycombThermal

Equalizers (4)

Design based on EMRLD laser--demonstrated1.3 XDL

Fan

Heat Exchanger

LaserCell

RearMirror Optical

Axis

Contraction Muffler

Diffuser Muffler

PerforatedPlate (2)

Cross-leg Muffler (4)

6 m

Flow3.75 m/sec

Advanced pulsed power development plan

Pick nominal module size of 100 kJ pulsed power = 80 kJ e-beam

First design RangeVoltage: 800 kV 650-900 kVCurrent: 150-200 kA 150-350 kAModule size: 100 kJ (electrical) 50-150 kJPulse Length: 600 nsec 200-1500 nsec

Evaluated pulsed power concepts that can meet the requirements:

Cost: $5.00-10.00/electron beam JouleEfficiency: > 80%Durability: > 3 x 108 shots

Use systems studies to determine feasibility and define R & DDeveloped three systems

Develop the required components - 3 yrs

Integrate into system that demonstrates technology on Electra - 2 yrs

Pick nominal module size of 100 kJ pulsed power = 80 kJ e-beam

First design RangeVoltage: 800 kV 650-900 kVCurrent: 150-200 kA 150-350 kAModule size: 100 kJ (electrical) 50-150 kJPulse Length: 600 nsec 200-1500 nsec

Evaluated pulsed power concepts that can meet the requirements:

Cost: $5.00-10.00/electron beam JouleEfficiency: > 80%Durability: > 3 x 108 shots

Use systems studies to determine feasibility and define R & DDeveloped three systems

Develop the required components - 3 yrs

Integrate into system that demonstrates technology on Electra - 2 yrs

We are evaluating three advanced pulsed power systems, and performing R & D to develop the required components

TTIMC-1 MC-2 MC-3DIODE

XFMRS1

TTIMC-1 MC-2DIODE

Fast Marx

XFMRS1 DIODEPFL

Laser-gated switch stack/array

1. $ / e-beam Joule, for 100 kJ system in quantities, NOT Electra; 2. Flat top e-beam/wall plug

Transformer + 3 stage Magnetic Compressor Cost 1 Efficiency2

$11.30/J 81%

Fast Marx w/ laser gated switches + 2 stage Magnetic Compressor

$ 7.65/J 85%

Transformer + PFL + HV laser output switch

$ 8.35/J 87%

Meeting the IFE efficiency requirements is a challenge…but achievable

Efficiency allocation: How we get there Current status

Pulsed power 80% Advanced PP design RHEPP 63%

Hibachi 80% Lattice Hibachi Nike 50%

Ancillaries 95% Electra + Study1 N/A

Intrinsic 10-12% KrF physics2 14-15%(small systems)3,4 12% predicted from Nike kinetics code5

TOTAL 6-7% 7% Nike (not optimal )

1. Electra will validate technology. Efficiency and cost will be established with modeling from Electra results2. intrinsic = formation (25-28%) x extraction; (40-50%) = (10-14%). Optimize extraction by increasing gain-to-loss

3. “KrF Laser Studies at High Krypton Density” A.E. Mandl et al, Fusion Technology 11, 542 (1987).4. Characteristics of an electron beam pumped KrF amplifier with atmospheric pressure Kr-rich mixture in

strongly saturated region”, A. Suda et al, Appl. Phys. Lett, 218 (1987)5. M.W. McGeoch et al, Fusion Technology, 32, 610 1997

Efficiency Goal: 6-7%

Electron Beam Propagation - transport in diode & hibachi, - deposition in gas 2-D, 3-D PIC code modeling 2-D simulations Experiments

Electron Beam Propagation - transport in diode & hibachi, - deposition in gas 2-D, 3-D PIC code modeling 2-D simulations Experiments

KrF Physics: develop science base to meet the requirements for rep-rate, durability and efficiency.

Laser Amplifier Physics- e beam to KrF*

- laser transport 1-D kinetics, 3-D ASE chemistry & plasma physicsExperiments

Laser Amplifier Physics- e beam to KrF*

- laser transport 1-D kinetics, 3-D ASE chemistry & plasma physicsExperiments

KrF Physics done on both Nike and Electra

Laser Amplifier Physics code: Kinetics coupled to a 3D, time dependent, radiative transport of the ASE

e-beam..........presently uniform, change to 3D w/ e-beam code.

plasma..........1-D axially resolved complete energy accounting Te and Tg, ne, species, ...

lasing.............method of characteristics for laser transport.

kinetics..........automated chemistry solver e.g, 25 species + 20 KrF(v), 429 reactions.

ASE...............3-D, discrete ordinate, time dependent: i) local look back approach; ii) FFT for parasitics.

objective........understand details of laser gain and kinetics -> predict and optimize ELECTRA efficiency.

mirror

inputlaser

ASE

x

y

z

Laser Amplifier Physics code: KrF kinetics coupled toa 3-D, time-dependent, rad transport of ASE.

NRL

Radiation Hydrodynamics

Laser Physics

outputlaser

e beam e beam

KrF Kinetics includes a multi-species plasma chemistry

.

e- beam

Ar*

Ar2*

Kr* KrF*F2 Kr+F-

ArKr*

Kr2*

ArF*

Ar2F*

ArKrF*

Kr2F*

2Ar

Kr

2Ar

KrKr+Ar

Kr

F2

2Ar

2Ar

Kr

Neutral Channel

F

F2

F2

F

F2

Kr Kr

Ar+

Ar2+

ArKr+

Kr2+

2Ar

Kr

2Ar

Kr

F-

F-

F-

F-

Ion Channel

Kr+Ar

F-

Kr

2Kr

Kr+Ar

KrF* kinetics includes a multi-species plasma chemistry.

harpoon exch

ange

recombination

Vibrational Kinetics Model for KrF

.

12

10

8

6

4

2

0

1 2 3 4 5 6 7

X1 2

A=I , II3 2

1 2B=III

C=II3 2

R(A)

1 2

24

8 n

m

KrF potentialenergy curves

E (

eV

)Vibrational kinetics model for KrF*

kv+1,v = kelCB

-E/Tgkv,v+1 = kel* eBC

kv+1,v = kvibBB

-E/Tgkv,v+1 = kvib* eBB

.

v+1

v

v-1

v+1

v

v-1

v=0v=0

top v top v

KrF(C) KrF(B)

0.0

41

eV

0.0

16

eV

0.0

43

eV

kv+1,v

ABQAC Q se

BB

kv+1,vCB

data-1.

chemset= kan1 quadset=RL_16 runname=NIKE 1991 comparison test

NP NL NI NJ NK NS NR MP NPASS NBEAM NLASR LPMP XAMP YAMP ZAMP AR% KR% F2% Ptot 20 20 5 5 20 61 429 8 T 0.0 0.0 0.0 56.45 56.45225.80 68.5

PB0 EB0 EL0 PL0 RX1 RY1 RZ1 RZNSPCLR 426.0 62.1 50.0 70.4 0.10 0.00 1.00 0.00 1.00

200 ns

Iout

10Peb

<go>

10<>%/c

mI

Isat

Iaseoc

form = = ~ 21%go* Is

Pdep

hRp*

Pdep

ext = ~ 44%Iout - Iingo* Is L

eff = form ext ~ 9%

(MW

/cm

3)

(MW

/cm

2)

(MW

/cm

2)

The Kinetics/ASE model compares favorably with experimental data under diverse conditions

Iin (MW/cm2)

The kinetics/ASE model compares favorably withexperimental data under diverse conditions.

McGeoch, et al.,Fusion Tech., 32, p.610 (1997)

Suda, et al.,Appl. Phys. Lett., 51, p.218 (1987)

P(beam) (kW/cc)

Kr/F2/Ar=99.4/0.6/0%1 bar

Kr/F2/Ar=10/0.4/89.6%1 bar

Kr/F2/Ar=35/0.4/64.6%1.1 bar

no vib no ASE

full

single pass amp at Keio Univ. NIKE double pass amp at NRL

Pbeam =1730 kW/cc

1000 kW/cc

Iin=62 kW/cm2

I out -

Iin (

MW

/cm

2 )

(M

W/c

m2 )

When the ionization efficiency is constant…

Rex

c /R

ion

NRL

Radiation Hydrodynamics

Laser Physics

100 101 102 1030.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 2010-7

10-6

10-5

10-4

10-3

10-2

10-1

100

103

102

101

100

Kr

Ar

used forAr & Krsince '76

Pdep (kW/cm3)

Pdep (kW/cm3)

u (eV)

While the ionization efficiency is constant,the excitation efficiency depends on theelectron distribution function resultingfrom the e-beam deposition..

f(u)

(e

V-3

/2)

Advanced Coatings & Optics are needed in the amps, mirrors and final optic

Coatings for KrF amplifier windows*

Long life in the amplifier cell:

HF, F2, UV, X-rays, e-beam.

High damage threshold*

long life, optics:

Threshold > 5 J/cm2

Final optic for IFE power plant (UCSD,LLNL, LANL, etc)

Evaluate candidates (optical, debris, x-ray)

Neutron testing, if we can establish source

TARGET

AMPLIFIER WINDOWLASER

MIRROR

GRAZING INCIDENCEMIRROR

We have developed a test cell to evaluate optic resistance to HF, F2 , and UV (@ 248 nm)

5% F2 in Ne

2% H20 in Air

Lumonics 1/2J KrF Laser(induce UV damage @ 1-2 J/cm2)

RGA mass spectrometer (measure HF, impurities)

Heater &temperature control

CELL

SAMPLE

Mixer

Integrated test

Can increase exposures to to accelerate damage

Test SiO2 samples Coatings Al2O3

HfO2

MgF2

SiO2

….?

Simulates Environmentof KrF Laser Cell

Also performing experiments to determine effect of x-rays

Determine Non linear index effect on laser profile (should affect envelope only, not speckle) >>> Two photon absorption @ 4 nsec Degradation in transmission

Experiments showed profile broadening and degradation of transmission ..Probably due to poor materials

Will repeat with high quality optics Envelopes of object and image for ~5 XDL with and without self phase modulation

Optical Sample (Quartz) (5-10 cm long)

Nike Laser beam10 J / 4 nsec

CCD camera• focal profile• spectrum• pulse shape

Measure beam with and without optical sample

4.8 cm2 = 2 J/cm2

1.2

1.0

0.8

0.6

0.4

0.2

0

Flu

en

ce

(a

rb u

nit

s)

-100 1000 50- 50

OBJECT B = 0

B = 0.4

We have developed a way to measure the distortion of an ISI-smoothed laser beam in optical materials

(Deniz, Lehmberg, Chan, Pawley, 1999)

10 J, 20-30 nsec pulse, 5-10 Hz

Distortion free amplification of 200 XDL ISI

High-contrast pulse shaping

Zoomed focal profiles

E-Beam pumped

Input for Electra AND Nike

10 J, 20-30 nsec pulse, 5-10 Hz

Distortion free amplification of 200 XDL ISI

High-contrast pulse shaping

Zoomed focal profiles

E-Beam pumped

Input for Electra AND Nike

The Advanced Front End will be sizedto drive several ~ 100 kJ Laser Beam lines

Front End

NS

Beam line 1

Beam line 2

Beam line 3

Beam line N

Summary

Electra Program is well underway

“Platform” for component R & D is finishedFirst generation pulsed power installedRecirculator installedFully operating facility

Electron beam experiments have been started

Companion programs in KrF Physics, Opticsand Advanced Front End.