LA-UR -96-3319,,

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TITLE:

LA-UR--86-3319

DE87 000164

LARGE EXCIMER LASERS FOR FUSION

AUTHOR(S): Jensen, Reed J.

SUBMITTED TO: !hciety of Plloto-Optical Instrumentation EngineersPel.linghum, WA

I)ISC1.AIMER

I’his Icport W;IS prcpurml J\ on uccmm[ ofwurk spnw)rcd hyon agcncyorlhe (JnihxlStutcsfhwcrnn)cnl, Ncilhrr thr Ilni[cd .SIIIICS Guvcrnment nor urry agency thereof, rmr uny u( their

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LOSAualmmsMAm

LosAlamos National LaboratoryLosAlamos,New Mexico 87545

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Large Excimer Lasers for Fusion

Ueed J. Jensen

Loe Alamos National LaboratoryLoe AlamoS, Neu Mexico 87545

Introduction

Important goals in DOE and DoD programn require ❑ultimegajoule laner pulaee. Forinertial confinement fusion there is aloo a requirement to deliver the pulse in about 25

naec with ● very particular power V- time profile --all at high overall efficiency and 10V

coat per joule. After exhaustive coneideratioo of various alternative, our acudiea haveohown that the moat coat ●ffective approach to energy scaling in to increaae the ●ize of

the final ●mplifiers up to the 200 to 300 kJ level. Thio conclusion derivea largely frvmthe fact that, at a given complexity, Coacn increase nlowly with increasing part citewhile output energy should increaae dramatically. Extrapolation to low coet by draaticcute in the unit coot of cmaller devices through ❑ ass production are considered highly

risky. At a ❑inimum tha requirement co provide, opace, optics and ❑ ounto for ●uchayscemn will remain ●xpenrnive.

In recent yeara there have been dramatic advancea in ncaling. The Loo Alamoa LAM haaproduced over 10 kJ in ● single 1/2 naec pulse. In this paper we ●xplore the innues

involved in scaiing to higher ●nergy while ●till maintaining high ●fficienc~ea. In theremainder of thin paper we will discuan KrF laoer scaling for the t,leion mission. Wewill omit ❑ ont of the discuaoion of the lanmr syntem design, but addresa only KrFmmplifie~o.

Scalina

Fig. 1 rnhow- the relationship between laser co-t ●nd the co-t of ●lectricity.1●aoily

It ianeen that f~r driver coet of $2001J ●nd efficiency greatmr than 5Z favorable

ele~trical costs ● re possible. Fig. 2 shows how laaer ●yatem cost decreanes with moduleoize ●nd total driver nnergy. ttodule s~zeo leoa than 100 kJ ●re probably uneconomicbecause of the very large number of beam lines needed. Arguments for unit coat reductionbecauae of large quantities are considered very cenuoun ● t Ieaat until the cpecificdaeign is known in great detail.

[n constructing ● very large ●mplifier it is very ●dvancaueoua to ●dopt ● ❑odulardesign. In this ●chem~ the ●mplifier La produced by stacking a sufficient number of

modules. Fig. 3 ahowo the ● lectron beam pumping footprint for saveral design

options.z Tha most favorable of thene ia the negmented ●xpanding flow diode oyatam.

Fig. 4 shows ❑ore detail for the systam. The ●xpanding flow pattern for the ●mitted● lectrons allow- for close stacking of the diode structures ●nd better uniformity of the

pumped medi~m. Th* high voltage mechanical ●upport buahingo ●re of ● new design ●nd willrequire development. Fig. 5 ahowc how the > 100 kJ amplifler ia integrated from itscomponents. At Loo Alamoa we, ●long with AVCO Everett, have completed the design forsuch ●n amplifier. It is referred to ●- the powar ●mplifier module or PAt’1. Someparameters of the system ● re shown in Figt. 6 ●nd 7. Pi#. 8 ohova one of the ten diode

■ooules to be ●tacked together to constitute the PAH oyatem. Notice that the ●efiment ic

over ? meterm high, but aarvlcea an ●lectron uindov ● rea only 60 cm wide. Th~sarrangamenc ~ake~ Lt possible to ●chieve the total pump current required and yet control

●lectron beam pinch with ●pplled ❑egnetlc fields of only a few kC. This overall ●pproachto scaling incorpor~tec ●nough adjustable parameter to aasura scalin~ to the level-raquired by the application. A related iaaue is ●mplifier energy ●fficiency.

Efficiency

FLR. 9 shout the ●nticipated lmprovam,nt~ in KrF ●mplifier ●fficiency whan tha intendedtechnology improvement are Lncorporetad. Improvement An ●lectron optics should raoultin ●n ovarall ●fficiency of 5.13% inctead of the prenenc 3.5:. The 5.8% should thenimprova to 10.22 by ua~IIg both highar ❑ulo percent Kr ●nd higher ●xtraction incknoity tothwart tha formation of Kr2F,

Th@ ❑ain idea behind thn attempt co lmprova elactron optlca 10 to prevent ●b~orptioll by

● lectron window nupportz. This Ln to be done by d@mLgning tho emitter surfaun to wmitonly in ● rea- thdt m-p into high trannmitoinn areas for th~ alwctron window. T,) (io thii,

●ccount mu-t b~ tak-n UC pattern rotation cailred by the salf [leltl of thr amin~loil. Alno

tachnoluRy must be davclopad tu ● now non ●misnion in tits ● reec intandcd not to @mitt

Fig. 11 shows the aalien~ ●xci tat ion paths to the cpper laser level, ●nd some patlle to

formation of performance degrading ●pecie5. It muac be stressed that unless the

● xtraction intensity is sufficiently high, no performance improvement will be observed

for Kr ricn ❑ixcurea. Fig. 10 shows how ●xtraction ●fficiency improved with go/a where

so is the small nignal gain and a ie the nonsatulable abaorpcion. Once the electrical

performance of the syecem ia perfecced, the system ●fficiency becomes very sensitive co

nonsaturable ●bsorption that inevitably ●riseJ from F- ●nd some Kr2F.

However, chc notorious ●beorber Ar2a is purposely omitted. Performance io ● lso

●aaily degraded by a host poesible fluoride im~uritiee. Highest efficiencies can be

●xpecced only when the gas handling ayotem ie tl~t-lly stabilized ●nd debugged, ●nd che

sbsence of unwtnt.’d abeorbers is confirmed.

LAP!

The large ●perture module (LAM) represents ● first obvioue ocep toward rcaling of KrF

lasars for fusinn. In that project there was no ●ttempt to adv.~nce the stsce of the ● rt

of e beam driven amplifiers. Rather it wec only ●n effort to apply known technology to

the KrF system sc sn aff~rdzble COEC. T>ac device ham produced over 10 kJ in a 600 ns

pulne and has laid che foundation for denigns that scale to larger outputs.2

Referencc~

1. Harrin, D. B., Berggren, R. R., Kurnic, N. A., Lo- Alamoa Nationai Laboratory,

Lowenchml, D. D., Burger, R. G., Eggle~con, G. B., Ewing, J. J., Kuohner, H. J., SPec~raTechnology, Inc. , Uaganer, L. H., Bower-, D. A., Zuckerman, D. S., HcDonnell Douglae

4stronautice Company, Fucurd Developments ●nd Ap placations of KrF Laaer-Funion Syeceme,

LA-UR-86-1837, Loe Alamos National Laboratory.2. Sullivan, J. A., KrF Power Amplifier f40dule Scaling”, Fusion Technology, accepted

for publication.

3. Jensen, R. J., Rosocha, L. A., Sullivan, J. A., High Power KrF Laeere for Funiorru

Lon Akamos National Laboratory.

c

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m1-0Lu-1w

IL01-U)c0

200

150

100

50

0

ICF DRIVER COSTS LESS THAN $200/JAND EFFICIENCIES GREATER THAN 5%CAN RESULT IN A COMPETITIVE COE

F“y’’’’’’’Af’/” ‘‘“’’”/A1000 MWe

ED=5 MJGAIN =1OO

5.0% TYPICAL COE7—— —. ——

1

——

rLMJl10

-

I 1 I I 11111 1 I I 1 1111,100 1000 10,00 0

DRIVER COST ($/JOULE)

P. VG -95:

LASER SYSTEM C42ST DECREASES FOR LARGE AMPL8F1ERMODULES AND H!GHER ENERGY ON TARGET

200 W AMPLIF/ER MODULES REAPMOST OF THE COST ADVANTAGE OF SIZE

400+

g — 100 kJ MODULES

: ---- zoo kJ MODULES

730(3 .m ● -0— 300 kJ MODULES

z 90 \

i

{“%k

“--.:--“-Gm-

‘-o~m 9909 --- m------.9*- ●-.-, m,m g-a

0 2 4 6 8 10

ENERGY (MJ)

F-vG-9C)5

DIODE TECHNOLOGY CHOICES

● MONOLITHIC

● SZGMENTED PLANARWITH APPLIED FIELD

● SEGMENTED PLANAR,NO APPLIED FIELD

● SEGMENTEDFLOW

EXPAND/NG

ISSUES

B-FIELD REQUIRED B a J h/2

FORMATION OF STREAMERSHIGH CLOSURE VELOCITIESMFG/MAlftTENANCE/REPAIRHIGH RISK/HIGH COST

EXCESSIVE UNPUMPEDREGIONS (standoff plus return)

LOW q APPROACH

SELF-PINCH LIMITS SIZEMANY DIODES REQUIREDMAINTENANCE/REPAIR

EMISSION CONTROLB-FIELD SHAPING

BUSHING AND SWITCHDESIGNS

P-vG-715C

AVCO/LAHL SEGMENTED EXPAND9NG FLOW DIODE DESIGN

ANODE

A

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-v--.. —-—= ..............................................—.. ............................................ ....-, -_ ...........................................................................................................L ..................................................................................... ..................................-tt-

Tr4=

LASER mCAVITY

u

H

I56 cm

FRADIATION............................... ........................................................... ...................................... . ................ .............................. ................. ...........................................................................................................................................

HIBACHI - “

FOIL- -

1

I HIGH VOLTAGE GRADING SOLUTION ‘BUSHING

P. VG -901

LARGE KrF AMPLIFIER TECHNOLOGY REQUIRESADVANCEMENT AND DEMONSTRATION

IN THE FOLLOWING AREAS

DEMONSTRATE HIGHINTRINSIC EFFICIENCY

ACHIEVE REDUCED B-FIELD REQUIREMENTS

DEMONSTRATEDIODE SEGMENTATION[EXPANDING FLOW)

DEMONSTRATE MAINTENANCE

P DEMONSTRATE CATHO

-J PERFORMANCE[J> 50 A/cm2 FOR 400

dDEMONSTRATE IMPROVEDDIODE EFFICIENCY

ADVANCE LARGE WINDOW AiiDMIRROR TECHNOLOGY(CONSTRUCTION & DAMAGE THRESHOLD]

DE

ns)

RELIABILITY, REPARABILITY FORLARGE MOCULAR MARX’s AND PFL’s

PAM LASER CAVITY PREDICTED ANDSPECIFIED PERFORMANCE PARAMETERS

PARAMETERS

PuL.SE LENGTH

RISE TIME

PEAK POWER DEPOSITED

PRESSURE

Kr/F2 RATIO

OUTPUT COUPLING (start UP)

GAS TEMPERATURE (initial)

OUTPUT ENERGY

FORMATION EFFICIENCY

EXTRACTION EFFICIENCY

VALUE

400 ns

S45 ns

250 kW/cm3

585 Torr

250

0.84

300 K

>100 kJ

> 26%

> 50%

INTRINSIC EFFICIENCY >13%

P. )IC - I065B

PAM DESIGN SPEC9F9CAT90NS

ENERGY OUTPUT

PULSE LENGTH

OUTPUT FLUENCE

LASER CAVITY DIMENSIONS

GUIDE FIELD MAGNETIC STRENGTH

RISE TIME/FALL TIME LOSSES

RISE TIME

OVERALL EFFICIENCY

KRYPTON-RICH MIX OPERATING AT 585 TORR

PUMPING POWER (average)

USE A SEGMENTED MIRROR AND OUTPUT WINDOW

THE AMPLIFIER WILL OPERATE PARASITIC FREE

ASE LOSS

INSTANTANEOUS VOLUMETRIC PUMPING UNIFORMITYPARALLEL TO THE LASING DIRECTION

VOLUMETRIC PUMPING UNIFORMITY OVER THE DURATIONOF THE USEFUL PUMP PULSE PARALLEL TO THE LASINGDfRECTION

RELIABILITY GOAL

MAXIMUM TIME TO REPAIR FOR ANY ONE FAILURE

& 100 kJ

400 ns

<3,5 J/crn2

h ~- 325 c:n

w= 130 cm

L = 300 cm

1.5-3 TIMES Bse[f

< 20 PERCENT

~ 45 ns

3- 5 PERCENT--—-

250 kw/cm3-----

-.---

< 10 PERCENT

~ ~o PERCENT

t 10 PERCENT

1 FAILURE/300

TWO WEEKS

SHOTS

THREE-DIMENSIONAL CUTAWAY

OF THE PAM PROTOTYPE DIODE

+

P. VG -397

DEFINITE STEPSWILL. IMPROVE KRF EFFICIENCY

10

8

6

4

2

0

. . . . . . . . . . . . .. . . . . . . . . . . ........ . . . . ... ,. . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . .. . . . . . .. . . . . . . .“. ”.”.”.”.. . . . . . . . . . . . I............................................”. ”.”.”.”. “.”. ”.”.... . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .

. .. ”.”. ”.”. ”.”.”. “.”. ”..... . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. .. ”.”. ”. ”.”.”.”. “.”. . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .

,“..... ”.”.....”.” .“. ”...”. . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . .

ts!

EEEBl

u........”...... . . . .

STANDARD CASE

IMPROVEDELECTRON OPTICS

IMPROVEDELECTRICALCOUPLING &. . . . . . . . . .. . . . . . . . .............. . . .. . . I

.................-.. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . ,. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .. . . . . . . . . .. . . . . . . . .

TECH IMPROVEMENTS

MAJOR IMPROVEMENT IN KrF EFFICIENCY

HAS RESULTED FROM ADJUSTING Kr/Ar MIX

ELECTRON BEAMe-+ F2

An &’\

PRODUCTS zF2,e-, .~r

$)hv+.4r+F

Ar2 F’

F2, e-

hv+2Ar+F

PRODUCTS hv+2Kr+F

PRODUCTS

F-v G-504B

1.0

z

xU!

REDUCED ABSORPTION BY THE LASING MEDIUMENABLES HIGHER EXTRACTION EFFICIENCY

go= SMALL SIGNAL GAINSQ = ABSORPTION COEFF.

e ‘0’’=40

10 20 30 40

EXTRACTION FLUX MW/cm2