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Naval Research Laboratory Plasma Physics Division Washington, DC 20375 13 th HAPL Meeting November 8, 2005 University o PowerPoint Presentation
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NRL J. Sethian M. Myers J. Giuliani R. Lehmberg S. Obenschain SAIC M. Wolford R. Jaynes Commonwealth Tech F. Hegeler M. Friedman RSI P. Burns S. Searles. KrF Lasers: Electra Laser Overview. Naval Research Laboratory Plasma Physics Division Washington, DC 20375

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slide1

NRL

J. Sethian

M. Myers

J. Giuliani

R. Lehmberg

S. Obenschain

SAIC

M. Wolford

R. Jaynes

Commonwealth Tech

F. Hegeler

M. Friedman

RSI

P. Burns

S. Searles

KrF Lasers: Electra Laser Overview

Naval Research Laboratory

Plasma Physics Division

Washington, DC 20375

13th HAPL Meeting

November 8, 2005

University of Rochester (LLE)

Work supported by DOE/NNSA/DP

slide2

Electra KrF Laser Layout

pre-amp 10 cm x 10 cm

main amp 30 cm x 30 cm

seed osc 1cm x 3 cm

slide3

Electra 30 cm x 30 cm Amplifier stage

Electra title page

730 J Plano-Parallel Oscillator ~100 ns FWHM

slide4

Laser gas recirculates

(provides cooling

and quiescent flow)

Capacitor charging to +/- 43 kV

(>160 ms)

E-Beam KrF Pump Source

500 kV, 110 kA

140 ns pulse

Discharging through the

1:12 step-up transformer

Charging of the

PFL to 1 MV

(3-4 ms)

slide5

Currently in use

Gas Velocity

Foils

Rib

Rib

gas flow

“V” plate mimics “ideal” closed louvers

optimum gas flow velocity at foil

Rep-rated oscillator laser output was not influenced by fixed “V” plate

More Far-Field Experiments needed

Electra Foil Cooling Concepts

Foil Cooling concepts being examined

See Georgia Tech Poster on “Investigation of Mist Cooling for the Electra Hibachi“

Demonstrated 5 Hz at full power for 10,000 shots continuous in module

See John Giuliani Poster “Foil Cooling for electron beam pumped KrF lasers “

Louvers

Thermal

Conduction

Mist Cooling

slide6

Laser resonator and Rep-Rate Diagnostics

All Optics Standard Grade Fused Silica 1F

Photodiodes

Pump Source (electrons)

Output

Coupler

Mirror

Pickoff Window

Graphite

Beam

Dump

E-Beam Pumped Region

(Gain Media)

1 m

Tilted Windows

Rear Mirror

Photodiode

Pump Source (electrons)

Calorimeter Positions

Real Time F2 monitor with Nitrogen laser attached to recirculator

slide7

Electra KrF laser is very consistent in long duration, repetitively pulsed, runs

300 J @ 1 Hz

(300 W)

10,000 shots continuous

(2.5 hrs)

700 J @ 1 Hz

(700 W)

400 shots

continuous

400 J @ 5 Hz

(2000 W)

500 shots

continuous

Notable results:

7700 shots @ 5 Hz

four back to back runs

9600 shots @ 2.5 Hz in a multiple segmented run

slide8

Efficiency (9.6%)= PLaser (5.75 GW)/ PE-Beam (60.2 GW)

Intrinsic Efficiency 730 J Laser Shot

E-Beam Power

PLaser (GW)

PE-beam (GW)

Time (ns)

E-Beam Power = (Pressure Rise (E)*Radiation Correction (105%)) + Laser Energy (E)

Distributed over the pulse width measured in the diode

slide9

How we project an amplifier intrinsic efficiency of ~11-12% based on oscillator results of 9.6%

  • Better windows (>99% transmitting vs. measured 93% transmission in oscillator)

Anti-Reflection coating on both side windows

(currently single sided)

KrF or ArF grade (currently standard grade fused silica)

Utilization of Rigrod analysis implies an expected increase of 17% in efficiency( )

A properly designed amp would have:

  • Lower laser light absorption due to fluorine, less passes through e-beam unpumped regions (~2%)
  • Full laser extraction of the created gain media, data here is 31.5 cm deposition in electron beam propagation direction and utilization of a 30 cm laser extracting (~4-5%)
  • Amplification from input laser, no oscillator build-up time (~1%)
slide11

TC

TN

1”

CN

CC

Gain Media Uniformity Measurements(Single Pass Gain)

248 nm bandpass filter

Parasitic Light Attenuators

Neutral Density Filter

KrF output

12”

Photodiode

(1 ns risetime)

Iout

Iin

PD2

PD3

ND

E-Beam Pumped

Region

KrF input

PD1

PD4

Beam Cube Polarizer

Gas Composition: 60% Ar, 39.7% Kr, 0.3% F2

slide12

Oscillator Yield 730 J

TC

TN

TC

TN

CN

CN

CC

CC

g0 = 6%/cm

α = 0.6%/cm

Isat = 10 MW/cm2

Rigrod Analysis

Uniform Amplification Gain Across the entire 30 cm x 30 cm aperture @ 20 psi

slide13

CC

Addition of He does not significantly reduce output …. Increases foil cooling

Single Pass Gain (Amplifier) results and Oscillator results

slide14

KrF Laser Calculations (Orestes)

e-beam: ionization and excitation from Boltzmann analysis.

plasma: 1D axially resolved, separate electron and gas temperatures, enthalpy balance.

kinetics: 24 species, 144 reactions, Includes KrF vibrational structure.

lasing: method of characteristics.

ASE: 3D, discrete ordinates, time dependent, ASE gain narrowing.

slide16

KrF Kinetics Calculations (Orestes) Agree with Experiment

9

8

7

6

5

4

3

2

1

0

Pe-beam (expt)

ILaser (expt)

ILaser (Orestes)

Shot OSC080404_11

ELaser = 731 Joules

Pe-beam (100 kw/cc)

ILaser (MW/cm2)

0 50 100 150 200 250

time (ns)

slide17

Orestes has been used to predict the performance of a 25 kJ amplifier

four e-beams per side

800 kV

200 kA

225 nsec

100 x 50 cm each

40 cm

100 x 100 cm

window

10 cm

1.1 atm, 40% Kr, 0.35% F2

TWIN = 99%, RMIR = 100%

210 kJ e-beam deposition flat (250 kJ total)

PEB = 526 kW/cc (105 J/liter) in flat portion

Laser EIN(t1 to t2) = 1.0 kJ

Laser EOUT(t1 to t2) = 27.4 kJ (32.4 kJ total)

Intrinsic Efficiency(t1 to t2) = 13.0%

slide18

Key stresses in the 25 kJ KrF amplifiers are within existing Electra and Nike parameters

25 kJ Laser Amplifier

Marx

1st stage

1st Mag Switch

2nd stage (PFL)

TTI

2nd Mag Switch

Laser Cell

25 kJ Nike Electra

E-beam voltage (kV) 800 640-750 500

E-beam pulse (ns) 225 225 140

Cathode size (cm) 50 x 100 60 x 200 30 x 100

5 Hz Foil Load (W/cm2) 4.1 N/A 4.1

Pump Power (kW/cc) 526 326-430 700

Window Load (J/cm2) 2.5 1.0 0.78

slide19

Summary

  • Measured flat-top intrinsic efficiency of 9.6% with an oscillator yield of 731 J Yield, plus advances in pulsed power and hibachi gives a basis for the projection of 7% wall plug efficiency in amplifier configuration
  • Orestes Code agrees with Electra Oscillator measurements over wide range of parameter space (F2 concentration, pressure dependence, absolute yield)
  • 3) 2.5 hour operation rep-rate (durability, with high reproducibility) at 1 Hz with 5 Hz capability
  • 4) Gain Media Uniformity over entire 30 cm x 30 cm has been measured