John SethianNaval Research Laboratory

April 4, 2002

Electra title page

ElectraElectraNRL

J. Sethian M. Friedman

M. MyersS. ObenschainR. LehmbergJ. Giuliani

JAYCOR S. Swanekamp

Commonwealth TechF. Hegeler

SAIC M. Wolford

Titan PSD, IncD. Weidenheimer

Work sponsored by DOE//NNSA/DP

The Electra Laser Facility500 keV, 100 kA, 100 nsec @ 5 Hz (x 2 sides = 50 kW)

The Electra Laser Facility500 keV, 100 kA, 100 nsec @ 5 Hz (x 2 sides = 50 kW)

Laser GasRecirculator

Topics This Time

RearMirror

OutputOptics

Laser Cell(Kr + F2)

PulsedPowerSystem

ElectronBeam Foil

Support(Hibachi)

AmplifierWindow

Cathode

Bz

Front runner for Advanced Pulsed Power should meet IFE requirements (< $10.00/J, >80% eff)

Notes:Cost: $ / e-beam Joule, for 100 kJ systems in quantities, NOT Electra; Efficiency: Flat top e-beam/wall plug

TTIDIODE

Marx/PFN

Marx / Pulse Forming Network

too new to evaluatecost and efficiency

XFMRS1 DIODEPFL

Laser-gated switch stack/array

Transformer + PFL + HV laser output switch

$ 8.35/J 87% eff

TTIDIODE

MC-1

Fast Marx

Fast Marx w/ laser gated switches + 1 stage Magnetic Compressor

$ 7.15/J 85% eff

Burst mode @ 5pps – 104 shotsShots to failure of chip under test – 1.36 x 105

Max voltage – 3.2 kV (limited by external insulation)Max current density – 2.7 kA/cm2

(121% of IFE requirement)Max di/dt – 1.36 x 1010 A/sec/cm2

(154% of IFE requirement, limited by circuit) > 10 x higher than non laser triggered devices

Max charge transfer per pulse – 1.7 mCb/cm2

(152% of IFE requirement)Laser output ~40% of maximum (tested at >107 shots)Successful demo of thyristor/ laser diode integration

Advanced Pulse Power Switch Development-1

RESULTS TO DATE

LGPT (Laser Gated and Pumped Thyristor)

Flood entire switch volume &junction with laser light…Gives high turn-on (dI/dt)

*Photon 1105 nm = 1.36 eV I.E. Just above the band edge of the PN junction

DiodeLaser*

Si Switchp

n+n

n++

p++

CONCEPT

Prototype has demonstrated concept

Switch

Lasers (hidden)

Feed Electrodes

Pulse Sciences Division

Advanced Pulse Power Switch Development-2

Full required performance (16.7 kV)NEXT GENERATION

Generation 2 Forecasts

Maximum voltage > 16.7 kV (IFE requirements) Thicker device with two sided laser pumping Design allows use of advanced encapsulants (insulation) (soldered or alloyed interface of silicon and electrodes)

Action (I2t) in excess of IFE requirements

Integration of larger area reverse parallel co-planar diode to meet 100% of IFE reverse current requirement

Extrapolates to “rail gap” aspect ratio easily (full IFE scale)

EXPECT TO BE READY FOR TESTING WITHIN 6 MONTHS

Pulse Sciences Division

1 cm2 silicon thyristorand co-planar diode

Laser array in electrode(anode and/or cathode)

(Single sided system shown)

Advanced Pulse Power Switch Development-3

Rail Gap GeometryFINAL CONFIGURATION

Pulse Sciences Division

Full-Stage Switch Assembly (16.4 kV)

11cm

108 cm total length

End View Side View

16 kVSi Switch

7 cm 1/2 Capacitor

1/2 Capacitor

1/2 Capacitor

1/2 Capacitor

Laser Drive Electronics

Si Switch

Laser

Application- Ultra Fast Marx (+/- 16.4 kV stage)

Oil Insulation

Test bed is evaluating lifetime of capacitor dielectric systems

Capacitor/Switch Test Bed Results· 2 x 108 shots on CSI capacitors (~0.03 J/cm3) – no failures· 1 x 108 shots on GA capacitors ( ~0.015 J/cm3) – no failures· 2 x 108 shots on ABB thyristor in service comparable to 3 stage MPC for IFE

Rep-rate: 55 Hz

Modified SLIA Rep Pre-Compression Stage

HV Transformer

Parallel Plate Test Volume

Coaxial Test Volume

Liquid Breakdown Dielectric Test facility nearing completion

Pulsed Power Systems use liquids to store electrical energy

V = V0

V =0

Oil or water

Electrodes, area A

d

E = V0.d

Electrical Breakdown strengthdetermines size of the system:

Oil (+): E = .48/(1/3 A.075)Oil (-): E = .72/(1/3A.075)Water (+): E = .23/(1/2 A.058)Water (-): E = .56/(1/3 A.070) ( is time voltage is above 63% of peak)

IFE driver..A(oil) = 108 cm2, A (water) = 3 x 108 cm2

Above formula derived for single shotevents, not long term repetitive operation.

E = Vo/d

d

Cathode(V =Vo)

Anode(V = 0)

Cathode development: Edge effect

0 20 40 60 80 current density (A/cm2)

Prediction

Elimination

Field-Shaper

Problems with this solution

1. Field shaper emits in rep-mode or longer pulse

3 cm x 30 cm“Strip” Cathode

2. Tough to do with strip cathode

0 0.5 1.0Cumulative charge (AU)

Verification

Radiachromicfilm

E = C-L

e-beam

Base

Emitter

“Floating Edge Removers” eliminate edge, fit strip geometry, and don’t emit (over 3000 shots)

(a)

(a)

(b)

(b)

Cathodebase

Cathode

Emitter (velvet)

Edge removers

Anode

0 50 100 current density (A/cm2)

(a)

(a)

(b)

(b)

Radiachromic Film

SeeFrank HegelerPoster

Expts & theory show beam subject to “transit time” instability. 2D PIC simulations predict resistive slots stabilize beam

dN

/dE

(A

rb.

un

its

) 1.0

0.5

0.00.0 0.5 1.0

E (MeV)

Not stoppedby gas

stopped by foils

0 2 4 6 8 10 12 14 160.0

0.2

0.4

0.6

0.8

FFT (B-dot signal)

2.5 GHz

Frequency (GHz)

0 5 10 15 20-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

B-dot signal (Arb. units)

Time (ns)

Cathode

Anode

e-

Before

0 50 100 150 200 Time (ns)

V (

MV

) 0.8

0.4

0.0

f=2.5 GHz

Experiment (Nike 60 cm AMPLIFIER_

Simulation

0 50 100 150 200 Time (ns)

0.4

0.2

0.0

1.0

0.5

0.0

-0.5

-1.0

X (

m)

/4

Slot withResistiveWire

-5 0 5 Z (cm)

Cathode

After

dN

/dE

(A

rb.

un

its

)

0.0 0.5 1.0E (MeV)

1.0

0.5

0.0

Not stoppedby gas

stopped by foils

Simulation

7

cu

rre

nt

de

ns

ity

A/c

m2

time (100 ns/div)

0

14

frequency (GHz)

am

pli

tud

e

0 1 2 3

0

.02

.04

-7

0

7

14

time (100 ns/div)

cu

rre

nt

de

ns

ity

A/c

m2

0 19

2 30

.02

.04

am

pli

tud

e

frequency (GHz)

e-

e-

The slotted cathode suppresses the transit-time instability on NIKE 60 cm Amplifier

Slotting cathode in other direction may completely eliminate instability

e-

Nike-Solid Cathode

cathode

anode

ribs

pressure foil

Nike-solid cathodeVOLTAGE LOSSESEnergy Lost/Electron Calculation Experiment

Instability 50 kV 50 kV

Anode foil 100 kV 60 kV

Pressure foil 50 kV 170 kV

Total 200 kV 280 kV

Energy Trans@ 500 kV

60% 44%

CURRENT LOSSES(Transmission)Hibachi 80% 90%

Beam Rotation, Edge 90% 90%

TOTALTRANSMISSION

48% 35%

e-

Nike-Slotted cathode

Nike-solid cathode Nike-Slotted CathodeVOLTAGE LOSSESEnergy Lost/Electron Calculation Experiment Calculation Experiment

Instability 50 kV 50 kV 0 15 kV

Anode foil 100 kV 60 kV 50 kV 60 kV

Pressure foil 50 kV 170 kV 75 kV 120 kV

Total 200 kV 280 kV 125 kV 200 kV

Energy Trans@ 500 kV

60% 44% 75% 60%

CURRENT LOSSES(Transmission)Hibachi 80% 90% 80% 90%

Beam Rotation, Edge 90% 90% 90% 90%

TOTALTRANSMISSION

48% 35% 73% 55%

Reducing instability increases hibachi transmission efficiency

See Matt Myers Poster

Nike-solid cathode Nike-Slotted Cathode Electra/IFEVOLTAGE LOSSESEnergy Lost/Electron Calculation Experiment Calculation Experiment Calculation

Instability 50 kV 50 kV 0 15 kV 0

Anode foil 100 kV 60 kV 50 kV 60 kV 0

Pressure foil 50 kV 170 kV 75 kV 120 kV 60 kV

Total 200 kV 280 kV 125 kV 200 kV 60 kV

Energy Trans@ 500 kV

60% 44% 75% 60% 88%

CURRENT LOSSES(Transmission)Hibachi 80% 90% 80% 90% 98%

Beam Rotation, Edge 90% 90% 90% 90% 98%

TOTALTRANSMISSION

48% 35% 73% 55% 79%

e-

Electra/IFE:Noanode

Pattern,rotate beam

ShallowRibs

10 ms 60 ms 100 ms 200 ms Concept & Modeling:

A.Banka & J.Mansfield, Airflow Sciences, Inc

Cell Exit

Cell Entrance

Contours of Stream Function--flow is quiescent for next shot

gasflow

louvers

After 1st shotAfter 1st cycle After 2nd shot

200F 400F 600F

0

10

20

Foil Temperature below required 650F

cm alongfoil

The recirculating laser gas can be used to cool the Hibachi

Foils

e-beame-beam

Rib

LouversOpen

gasflow

Louversclosed

gasflow

FOR REFERENCE ONLY, DOES NOT VIOLATE

“NO OLD VIEWGRAPH” RULE

Recirculator to both cool and quiet laser gas plus provide hibachi cooling has been designed

HeatExchanger

Blower

LaserCell

Homogenizers &Turning Vanes Static Pressure Contours

varies by 14 Pa (10-4) over laser cell

Louvers

Other accomplishments

Turn Electra into a laser:Start with oscillator, then add discharged pump commercial inputLaser on order, optics awaiting in-house damage testing

Rear Mirror stand here:

Front end for Electra:Prescription from Orestes KrF kinetics code

30 cm x 10 cm aperture, 100 cm long1.0 J input.30-45 J output (enough to give 700 J output on main amp)

e-beam pumpedMay be first demonstration of advanced switch technology

Big issue:We still don’t have a cathode with the require durability