krf laser development - the fire place · 2011. 1. 30. · 3 nrl progress in krf laser development...

1

KrF Laser Development

2

Opening Remarks on KrF Laser Development

Many institutions have had programs ine-beam pumped KrF lasers

Los Alamos National LaboratoryLivermore National LaboratoryAvco TextronRutherford Appeleton Labs, UKETL, Ministry of Technology and Industry, JapanLebedev Institute, Russia

The Naval Research Laboratory is the first to develop routine, high energy, efficient, and repetitive KrF capability

3

NRL Progress in KrF Laser Development

300 M90,000200Durability(continuous shots)

> 6.07.11.9Predicted Efficiency(%)

52.5 to 5.00056Repetition rate(pulses/second)

IFE20102001

Most all of these advances have been made through understanding and controlling the relevant physics

4

Elements of a Krypton Fluoride (KrF)electron beam pumped gas laser

Laser GasRecirculator

Laser cell(Kr+F2+Ar)

Input Laser(Front end)

Window

KrF laserPhysics

e-beamwindow(hibachi)

electronbeam

Cathode

Pulsedpower

Energy + ( Kr+ F2) ⇒ ( KrF)* + F ⇒ Kr + F2 + hν (λ = 248 nm)

Typical e-beam: 500 -700 keV, 100 - 500 kA, 3000 – 12,000 cm2

5

KrF developed with the NRL Electra and Nike Lasers

Electra: (5 Hz)400-700 J laser light500 keV/100 kA/100 nsec30 cm x 100 cm e-beam

Develop technologies for:Rep-Rate,Durability,Efficiency,Cost

Nike: (Single Shot)3-5 kJ laser light750 keV, 500 kA, 240 nsec60 cm x 200 cm e-beam

E-beam physics on full scale diodeLaser-target physics

6

Pulsed Power



Window

KrF laserPhysics


electronbeam

Cathode

Pulsedpower


7

Existing “spark gap based” pulsed power system: Limited to 50,000 – 100,000 shots continuous

92,000 shotsNEW

Discharge through the1:12 step-up transformer

PrimaryEnergyStore

(CapacitorBank) Lifetime

limit isElectrodeErosion

Spark GapPrimary Switch

Lasertriggered

Spark Gapmain switch

Pulse Forming Lines

8

Solid State system should be durable and efficient♦ Concept for Electra, scalable to IFE size system♦ Basic elements tested to > 300 M shots

Primary Energy StoreFast MarxLong Life capacitors

Primary SwitchesNew fast thyristors(Modified commercial units)

Output SwitchSaturable Magnetic Inductor

Modeled system for Electra:Predict Efficiency > 82%(Wall plug to flat top pulsed power)

PLEX, LLC

9

All Solid State Pulsed Power demonstratorContinuous run: 11.5 M shots @ 10 Hz (319 hrs)

PLEX, LLC

200 kV, 4.5 kA, 250 ns,Marx > 80% efficiency Marx

Pulse Forming LineLoad

MagneticSwitch

10

Electron Beam -- Generation and Transport



Window

KrF laserPhysics


electronbeam

Cathode

Pulsedpower


11

ELECTRON BEAM GENERATIONNeed cold cathodes: simplicity, efficiency, durabilityBest so far: Carbon Fibers pyrolized to aluminum

Robust (> 250,000 shots)Low cost ($15 k Electra)Easy to make to patterned cathodes

Cathode dimensions:30 cm x 100 cm

12

ELECTRON BEAM TRANSPORT Two innovations gave high hibachi transmission:

1. Eliminate anode foil2. Pattern the beam to “miss” the ribs

Laser GasKr + F2+ Ar

Vacuum

e-beam

Emitter

PressureFoil

(.001” SS)

Rib

AnodeFoil

(.001” Ti)

EnergyDeposited in gas

Before: ∼ 35%

After: ∼ 76 - 81%

13

Simulations and experiments show iron bars can efficiently guide electron beam past the hibachi ribs

emitter

iron

rib

laser gasfoil

emitter

iron

rib

laser gasfoil

Bz

14

3-D LSP Simulations (Voss Scientific/Albuquerque) ♦ Prescribe the emitter topology ♦ Predict observed electron beam deposition into the gas

Efficiency ≡ Energy deposited in laser gas/energy flat portion of e- beam

> 81%*76%66%Simulation

N/A75%67%Experiments

1 mil (SS)1 mil (Ti)2 mil (Ti)Pressure Foil

800 keV500 keV500 keVE-beam Voltage

Deposition EfficiencyEfficiency ≡ Energy deposited in laser gas/energy flat top portion of beam)

*1-D modeling for800 keV full sizeIFE system

15

Hibachi Foil: Cooling and Durability



Window


electronbeam

Cathode

Pulsedpower


KrF laserPhysics

16

FOIL COOLINGNeeded to avoid metal fatigue (470 °C for SS 304)and minimize unwanted chemistry

Two previous concepts we evaluated:

“V” plate Foil Temp = 220 °C @ 2.5 HzPredict 440 °C @ 5 Hz. (A bit warm)

“Mist Cooling”Foil Temp < 140 °C @ 5Hz

ElectronEmitter

RibRib

PressureFoil

e-beam

Laser GasKr + Ar + F2

AnodeFoil

He (air) watermist + film on

foils

ElectronEmitter

RibRib

PressureFoil

e-beam

Laser GasKr + Ar + F2

AnodeFoil

AnodeFoil

He (air) watermist + film on

foils

Foils

E-beam

“V” plate

E-beam

gas flow

17

"Jet" cooling technique developed by Georgia Tech: Effective, efficient, and scalable to large apertures

e-beam

MainGasFlow

foil

Jets

Tube

VIEW FROM GASINTO THE DIODE

TOP VIEW

Tube Jets

foilRib

Laser Gas

18

Jets cool foil while maintaining laser qualitywith minimal power consumption

Jets cool foil

Do not perturb laser gasLaser

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

0 10 20 30 40 50Shot #

Inte

nstiy

(Cou

nts)

9 x 9 pixel

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

0 10 20 30 40 50Shot #

Inte

nstiy

(Cou

nts)

9 x 9 pixel

no decline in energy in focusat 5 Hz for 50 shotsReprate=5Hz, Blower=30 Hz, GT=80 cfm

050

100150200250300350400450

0 2 4 6 8 10 12 14

time (s)

tem

p (C

)

average foil temperature < 370° C(Fatigue limit ∼480 ° C)

Georgia Institute of Technology & Matt Wolford

19

FOIL DURABILITYOne key: Control late time voltage in e - beam diode.Increasing diode impedance 10%, lowering charge voltage 15%:Eliminates voltage reversal, and hence damaging foil emission

No Voltage reversal∼ 100,000 shot runs

time (nsec)

300

200

100

0

-100

-200

-300

-400

-500

-600

Diode Voltage (kV) vs time

time (nsec)

300

200

100

0

-100

-200

-300

-400

-500

-600

Diode Voltage (kV) vs time

80 µmpinhole

Voltage reverses< 10,000 shot runsFoil fails due to pinhole.(“Cathode spots”)

20

Electra now capable of ∼100 k shot runs

Electra Cell after 30,000 shot continuous laser run

90,000 laser shots (10 hrs) continuous @ 2.5 Hz150,000 laser shots on same foils @ 2.5 Hz50,000 laser shots on same foils @ 5 Hz

300,000 laser shots in 8 days of operation

21

A video starring Electra

22

KrF Physics: Simulations and Modeling


Window

KrF laserPhysics


electronbeam

Cathode

Pulsedpower



23

KrF PHYSICS“Orestes” Code includes all relevant phenomena

1-D & 2-D Electron Deposition Plasma Chemistry3-D Laser Transport 3-D Amplified Spontaneous Emission

24 species, 146 reactions, 53 vibrational states

NeutralChannel

IonChannel

e-beam e-beam

Kr

KrF2 F-

e-

Kr

F-F2

2Ar 2Kr

γ, F2, e-

harpoon ion-ion recex

chan

ge

GAIN, go

γ, Ar, Kr, F2, e-

γ, Ar, Kr, F2, e-

absorption, σ = σF2ηF2+ σF-ηF- + σKrF2 ηKrF2 + σArF2 ηArF2

Kr,Ar,F2

Ar* Ar+

Kr* Kr+

ArF*

KrF*

ArKrF* Kr2F*

Kr,Ar,F

Good

Bad

24

Orestes accurately predicts Electra Main AmplifierLaser Pulse

0 50 100 150 200 250

Pe-beam (expt)ILaser (expt)Pe-beam (Orestes)ILaser (Orestes)

Shot OSC080404_11ELaser = 731 Joules

9

8

7

6

5

4

3

2

1

0

25

Orestes predicts performance of many KrF Lasersoperating over a wide range of parameters

(c) Lebedev's Garpunsingle pass amp(b) NRL's NIKE

double pass amp(a) Keio Univ.'ssingle pass amp

no ASE

inI =52.5 kW/cm2

Orestes

E(laser)out (kJ)

Pbeam=1.3 MW/ cc

no ASE

Pbeam=1.3 MW/ cc

no ASE

0.62 MW/ccno ASE

Iout (MW/cm2)

Orestes

Orestes

Pbeam=1730 kW/cc

Iout-Iin (MW/cm2)

[Suda, et.al., Appl.Phys. Lett., 51, 218 (1987)]. [McGeoch, et.al., Fusion Tech., 32, 610 (1997)]. [Zvorykin, et.al., Final Report,

Lebedev Institute (2002)].

26

Efficiency (9.8%)= ELaser (71.5 J)/ Ee-Beam (730 J)

0 50 100 150 200

P E-b

eam

(GW

)

10203040506070

0

3

012

4567

Total laser energy 730 Joules

Laser energye-beam energyIntrinsic Efficiency ≡ (in flat part of pulse)

Electra: ∼ 10% intrinsic efficiency as oscillatorexpect ∼ 12 % as an amplifier

P Las

er(G

W)

27

Based on our research, an IFE-sized KrF system should have a wall plug efficiency > 7%

Pulsed Power All solid state 82%(wall plug- flat top e-beam)

Hibachi No Anode, Pattern Beam 81%(e-beam in diode into gas)

KrF Electra Experiments 12%(e-beam to laser) (literature ∼ 14%)

Optics to target Estimate 95%

Ancillaries Pumps, recirculator 95%

Total 7.1%

For fusion energy want ηG > 10.with KrF and advanced targets: ηG = 7.1% x 300 ~ 21

28

18 kJ, 5 Hz, KrF laser amplifier:Extrapolate Nike, using Electra Technologies

electron beamLaser

MirrorWindow

800 keV, 500 kA, 250 nsec60 cm x 100 cm window60 cm x 250 cm each beamStrip cathode

FTF - 18,000 J 650 keV, 500 kA, 240 nsec60 cm x 60 cm window60 cm x 200 cm each beamMonolithic Cathode

Nike - 5000 J

Iout [MW/cm2]

Pe-beam[MW/cc x 10]

Iin [MW/cm2]

250 nsec

0 100 200 300 400

15

10

5

0time (nsec)

Iout [MW/cm2]

Pe-beam[MW/cc x 10]

Iin [MW/cm2]

250 nsec

0 100 200 300 400

15

10

5

0time (nsec)

efficiency ∼ 12%

29

Summary of Achievements.

• Durable, efficient, all solid state pulsed power

• Generation, transport, efficient deposition of electron beam

• Jet foil cooling

• Should meet efficiency, based on experiments

• Meets pulse shaping, zooming, uniformity requirements

• Orestes KrF physics code to design future systems

30

Main outstanding issue: >> 1M shot durability

• Windows (now quartz):• Exploring degradation mechanisms• Can use Calcium Fluoride, as in commercial units

• Foils: • Improve pulsed power durability• Mitigate all late time voltage

• Long term integrated demonstration at IFE class size

SHORT TERM

LONG TERM

krf laser development - the fire place · 2011. 1. 30. · 3 nrl progress in krf laser development...

Documents