16th HAPL MeetingPrinceton, New Jersey

December 12, 2006

Naval Research LaboratoryPlasma Physics Division

Washington, DC

Presented by M. Wolford

Work supported by DOE/NNSA/DP

Electra (KrF) Laser Development

NRLJ. SethianM. MyersJ. GiulianiM. Wolford S. Obenschain

Commonwealth Tech

F. HegelerM. Friedman

T. Albert J. Parrish K. Gunlicks

RSIP. Burns

R. Lehmberg S. Searles

SAIC R. Jaynes

• Starting Integration of Electra Laser System– First Stages of Construction

• Pre-Amplifier Laser Energy Measurements– Increased laser yield to 25 J– Time-Dependent characterization of laser pulse– Near-Field Profile

• Cathode & Rep-Rate Durability– Anode Mesh (1st Implementation 12,363 shots)

Summary Since August HAPL Meeting

LPX

Electra ISI Source Options

Electra Laser System

Pre-AMP

Main AMP

PinholeAmplifier

Focus

A. V. Deniz, S. P. Obenschain Opt. Comm. 106 (1994) 113-122

LPX

f f

LPX Diffuser

T. Lehecka et al., Opt. Comm. 117 (1995) 485-491

External Cavity Diffuser w/ additional amplifier

Electra ISI Laser Source Options

See NRL Poster:Large Aperture KrF Discharge Amplifier

Initial experiments and will continue with LPX as is, non ISI

LPX

Large Amplifier optical architecture

Electra Laser System

Pre-AMP

Main AMP

PinholeAmplifier

Focus

AMP

Closely PackedConvex Mirror Array

Large Concave Mirror

Double Pass Large Amp Architecture

Electra Pre-Amplifier Laser Experiments

LPX 305 i

Input 0.5 J10 cm x 10 cm

Cylindrical lens Pair

Telescope

1 cm x 3 cm

3 cm x 3 cm

Calorimeter

OutputInput

Review: First light on Electra Pre-Amp

80% Ar, 0.3% Fluorine

0.0

5.0

10.0

15.0

20.0

25.0

30.0

8 12 16 20Pressure (psi)

Las

er O

utp

ut

(J)

Orestes 0.5 J Input

Measured Input ~0.5 J

25 J Electra Pre-Amplifier Output

80% Ar, 0.3% F2

0.0

5.0

10.0

15.0

20.0

25.0

30.0

8 12 16 20Pressure (psi)

Las

er O

utp

ut

(J)

Orestes 0.5 J Input

Measured Input ~0.5 J

Orestes 0.7 J Input

Measured Input 0.6 J

Timing Electron Beam to Laser, 10 J Yield

Voltage

OutputInput

64.8 ns

-50

0

50

100

150

200

250

300

350

-40 -20 0 20 40 60 80 100 120 140

Time (ns)

Vo

ltag

e (k

eV)

Po

wer

(10

0 M

W)

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Inte

nsi

ty (

arb

.)

Diode VoltageDiode PowerOutputInput

Output Time Dependent Intensity

-1

0

1

2

3

4

5

6

0 20 40 60 80 100 120 140

Time (ns)

Inte

ns

ity (

arb

.)

1 (-36.3 ns) 3.8 J

2 (1.3 ns) 10.0 J

3 (21.5 ns) 15.7 J

4 (40.7 ns) 20.0 J

5 (64.8 ns) 10.0 J

6 (88.0 ns) 2.9 J

Power (10 GW)

1

2

3

4

5

6

-40 -20 0 20 40 60 80 100 120 140

1 2 3 4 56

Input

Output

Pre-Amplifier Energy Function of Input Timing

0

5

10

15

20

25

-50 0 50 100 150Input Time (ns)

En

erg

y (J

)

80% Ar, 0.3% F2@ 16 psi80%Ar, 0.3% F2@ 18 psiOrestes 16 psi

Orestes 18 psi

-30 -10 10 30 50 70 90Time (ns)

Cause of Discrepancy

Progress in realizing long duration laser runs

ceramic honeycomb

primaryemitter • Gas buildup in the diode

• Degradation of the emitter

• Foil failure due to debris and/or plasma arcs in A-K gap

Previous Limits to Laser Durability(< 10 k shots)

March 2006 HAPL meeting

Hibachi

Solved with new all-carbon emitter.As much as 25 k shots

(reported at Aug 2006 meeting)Foil

MAY have been solved withhigh transparency anode screen

Screen

One Possible mechanism limiting foil durabilityElectron emission from Anode

Hypothesis Rationale

Micro particles can stick to the foil Emission is an explosive process.See marks on foil

Voltage reverses in diode Seen on Voltage monitorsafter the main pulse

Voltage reversal causes micro See what may be "cathode spots" onparticles to emit electrons pressure foil

Emission can be an explosive process Known fact.

Can puncture hole in highly stressed Experiments with an anode foil showpressure foil evolution of this process

First experiments with mesh, (90%-95% effective transmission) showa) Minimal degradation in laser energy (i.e. transmission OK)b) First Implementation lasted several multi-thousand shot runs

• Starting Integration of Electra Laser System– First Stages of Construction

• Pre-Amplifier Laser Energy Measurements– Increased laser yield to 25 J– Time-Dependent characterization of laser pulse– Near-Field Profile

• Cathode & Rep-rate Durability– Anode Mesh (1st Implementation 12,363 shots)

Summary Since August HAPL Meeting