HAPL 6/05

LASER GATED AND PUMPED THYRISTOR (LGPT) SCALE-UPFOR THE ELECTRA ADVANCED PULSED POWER

TECHNOLOGY DEMONSTRATOR*

*Work sponsored by the Naval Research Laboratory Plasma Physics Division

D. Weidenheimer, G. James, D. Morton, D. Knudsen, R. KnightTitan Pulse Sciences Division, San Leandro CA

D. Giorgi, T. NavapanichOptiSwitch Technology Corporation, San Diego CA

HAPL 6/05

• Flood entire switch channel with laser light…• Optical fluence determines di/dt• Advances in design, construction yield fast thyristor action (» 100 ns)• Near band edge light, high quality silicon enable 20 kV working devices• Continuous illumination reduces forward dissipation in thyristor• Uses relatively low power laser diodes in place of YAG

CONCEPT LGPT (Laser Gated & Pumped Thyristor),

Diode Lasers

On or off-board

Si Switch

p

n-

n+

n++

p++

LGPT Concept

HAPL 6/05

Limited Area Developmental Devices

Diode Lasers LGPT Laser Drive Boards

Development History I

HAPL 6/05

Development History II

16.4kV

162 to 184kA/(us*cm2 ) Active Si 0.7mCoul Charge Transfer

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

Number of 5Hz Shots

kAm

ps/c

m^2

Act

ive

Si

0

0.5

1

1.5

2

2.5

kAm

ps/c

m^2

LG

PT A

rea

kAmps/cm2 (Total LGPT Area)

kAmps/cm2 (Active Si)

No. of shots to failure vs. current density at 162-184 kA/usec/cm2

HAPL 6/05

No. of shots to failure vs. di/dt density at 15 kA/cm2 current density

16.4 kV

15kA/cm2 Active Si0.7mCoul Charge Transfer

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

200.00

1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08

Number of 5Hz Shots

kAm

ps/(u

s*cm

^2) A

ctiv

e S

i

0

2

4

6

8

10

12

14

Date

kAm

ps/(u

s*cm

^2) T

otal

LG

PT

Are

a

kA/us (Active Si)

kA/us (Total LGPT Area)

Development History III

HAPL 6/05

Laser Diode Bars

Development History IV

Circa 2000-2003 – first designs - standard cavity, 1085 thru 1125 nm progression in wavelength,60 x 1500 um x 90 um pitch, 2500 um bar length, stripline package

2004 - first LOC strain-mitigated designs - reduced facet loading, 1125 nm, increased emitter area/packing fraction, 150 x 2000 um x 180 um pitch, 2500 um bar length, increased lifetimes at requisite drive currents

2005 - first LOC designs with single-side confinement, 1125 nm, further reduced facet loading – longer life expectations, 140 x 2000 um x 170 um pitch, same bar length, due 6/05

first direct-coupled double-layer mini-bars, 2 emitter arrays ~150 um c-c, samepackage envelope, due 7/05

HAPL 6/05

Rev 2 Bord Current and Laser Power

0

100

200

300

400

500

600

1.50E-07 2.00E-07 2.50E-07 3.00E-07 3.50E-07 4.00E-07 4.50E-07

sec

Am

ps

0.00E+00

5.00E+01

1.00E+02

1.50E+02

2.00E+02

2.50E+02

3.00E+02

3.50E+02

Watt

s

CURRENT

6 Venkel 2.2uF 48V 0.050 series R180uJ

c

Development History V

Laser Diode Bars

Apparent turn-on delay (fill-time) of diode laser cavities – reproducible for fixed drive parameters

HAPL 6/05

Development History VI

CEO from 9-08-04 Experiment 12uF Driver

-71

-69

-67

-65

-63

-61

-59

-57

-55

-53

-51

1110 1115 1120 1125 1130 1135 1140 1145 1150

nm

dB

m

100A 61uJ

200A 125uJ

25A 12.2uJ

50A 30uJ

400A 225uJ

700A 265uJ

10A 2uJ from 9-10 data

Laser Diode Bars

Thermal CWL Shift and Spectral Broadening with Current

HAPL 6/05

Development History VII

Silicon Thyristors

• Basic design has remained unchanged since late 2002 – quasi-symmetric thyristor, 16.4 kV working • Continuous iterations/improvements made to passivation and encapsulation, optical interface, current contacts

• Co-planar anti-parallel diodes added 2004

HAPL 6/05

Diagnostics/Test Fixtures

Development History VIII

Circuit L

Circuit C

Circuit Load ( Twelve 55W Rs)

Floating Laser Power/Trigger

LGPT V Monitor

Three Tek HV probes for Charge, Load R,

and LGPT R

B-dot

• Improved diagnostics measure forward voltage drop with confidence – forward dissipation

• SF6 device immersion enables rapid turn-around between failures, maintenance and inspections

HAPL 6/05

Recent Conclusions

• Experimental measurements/data, Medici modeling, absorption profiles, ray-tracing, plasma-spread theory all point to active silicon volume being confined to that defined by the window/cell dimensions.

• Devices must be scaled by the cell unit – presently ~.0167 cm2

• Current density of ~15 kA/cm2 and di/dt density of ~90 kA/usec/cm2, corresponding to illumination levels of ~25 kW/cm2 (gross-active) are sustainable for ~107 shots at 5 pps by both silicon device and latest design lasers – 800 nsec half-sine pulseshape

• Reduction in current and di/dt density by a factor of 2, with commensurate reduction in optical illumination levels should be sufficient for ~109 shot service at 5 pps

• Scaled-up integrated device design must have flexibility to accommodate a range of 7-15 kA/cm2 active area and the requisite laser diode bars to provide illumination levels from ~12-25 kW/cm2 (active) in a device with an overall peak current rating of 10-20 kA, di/dt of 60-200 kA/usec

• Cell/laser bar counts for such a device will be from 40-80 at present cell dimensions – fewer if cell/laser bar size increases

• Scale-up requires direct-mount double bar laser packaging and series drive

HAPL 6/05

LGPT Scale-Up

Anode

Cathode

Anode Cathode

5x1 Test Bed

Cross Section Shows 4 of 40 Laser Channels

Adjustable Laser Holder

Low Inductance Strip Line connecting Drive Board to Laser

Top View Shows 20 of 40 Laser Laser Channels

Side View

• ~ 5 cm x 1 cm contact area device accommodates 42 cells in first iteration• Staggered patterning of cells for greater active area packing fraction• Expandable to 84 cells as necessary• Single laser diode bar each cell in first iteration – 5-10 kA peak current - 7/05• Direct-coupled double laser package upgrade - >10 kA peak - 8/05• Expansion to 84 cells – if necessary – 9/05

5 x 1 cm LGPT

LGPT Integrated with Electrodes/Lasers

HAPL 6/05

Scaled-Up Test Capability

• Integrated LGPT inserts into scaled- up test fixture

• Fast turn-around features

• Peak currents to >25 kA

• Full diagnostics as in small scale testbed

• Easy access to all internal components

• Components to undergo miniaturization phase after scaling demonstrated

HAPL 6/05

Near-Term: FE2 Retrofit

HAPL 6/05

KrF IFE Building Block

HAPL 6/05

Summary/Conclusions

• Understanding of LGPT performance/scaling is sufficient to move ahead with 5 x 1 cm KrF IFE building-block device

• Scaled-up device and test fixture designs completed ~April, 2005

• Silicon devices are in process at Optiswitch, due for first delivery by end of June, 2005

• Electrodes/laser drive hardware for 1st prototype due end of June

• First single bar packaged limited confinement LOC laser bars due end of June

• Direct double bar packaged lasers due in July, 2005

• Subsystem testing to begin early July

• Full integrated device testing in late July

• Engineering iterations/optimizations through 2005-2006

• Target retro-fit of FE2 in 2006-2007