Pulsed Electrical Power

at

100 Megawatt Levels

TABLE OF CONTENTS

HISTORY and STATUS [Not Installed]

CONCEPT [Not Installed]

Excerpt from ARTICLE #1 presented at the Technical Conference AMEREM '96 held in

Albuquerque, NM June 12-15, 1996.

BibliographyReturn to MAIN Table of Contents

PHOTOCONDUCTIVE SWITCHING

of

STACKED BLUMLEIN PULSERS

In recent years photoconductive semiconductor switches have gained much attention and have

become competitors to the conventional high-power switches for certain applications. These new

devices operate jitter-free with optical isolation of the trigger. They have switching speeds which

either match or greatly exceed the risetimes of the the optical pulses triggering them. Suchphotoconductive switches are described as LINEAR or AVALANCHE, respectively.

The application of linear switches has been limited by the relatively high optical power required to

obtain their closure. In the avalanche type switches, the electron-hole pair produced by each

trigger photon is multiplied through an avalanche process, thus reducing the optical energy levels

necessary for initiation of the switch closure. The nonlinearities of the multiplication accelerates

the pace of commutation so that the switch closes faster than the trigger power rises. It is

interesting to note that Blumleins may be the most appropriate pulse-forming line for use with

photoconductive switches. They provide faster output pulse risetimes and reduce the percentage of

stored energy deposited in the switch.

Recent efforts in the Center for Quantum Electronics at UTD have been directed toward

commuting Blumlein pulsers with GaAs switches in the avalanche mode. Adaptation of the design

and fast charging schemes haveenabled the stacked Blumleins to

produce extremely high-power

nanosecond pulses of electrical

energy with sub-nanosecond

risetimes.

A 2-line stacked Blumlein pulser

shown in the photograph was

designed and constructed for

commutation by photoconductive

switches. A low-profile switching

assembly was constructed to

distribute the switching current toeach of the two Blumleins with line

impedances of about 100 ohms eachand line lengths of 15 cm.

During operation, the pulser was resonantly pulse charged using the charging circuit seen in the

figure to voltages in the range of 30-60 kV and repetition rates of 1 to 10 Hz.

The Charging Pulse Compression (CPC) moduleshown in detail in the figure was resonantly charged

by the slower pulse charge supply after which itsconventional thyratron was triggered to generateshorter charging waveforms for the main stacked

Blumlein pulser. About 80 nsec. later, when the main pulser was fully charged, the laser systemproduced a short burst of photons for commutation of the GaAs switch in the avalanche mode

causing a rapid discharge of the Blumleins. In this way output pulses were produced with very fastrisetimes and peak powers approaching 100 Megawatts.

Typical output waveforms obtained from this pulser

using either a Nd:YAG laser or a low-power laserdiode are seen in the figure reproducing typical data.

These measurements were obtained using an SCD5000 oscilloscope capable of recording single

electrical transients with risetimes of under 100 psec.The particular data shown corresponded to thelaunch of a pulse carrying 70 Megawatts peak power

from the system in the photograph that is as small as hand luggage.

These results prove that with small photoconductive switches,stacked Blumleins can provide nanosecond electrical pulses atpowers approaching 100 Megawatts with risetimes faster than300 picoseconds.

References

C.B. Collins, F. Davanloo and T.S. Bowen, Rev. Sci. Instrum. 57,863 (1986).

F. Davanloo, T.S. Bowen and C.B. Collins, Rev. Sci. Instrum. 58,2103 (1987).F. Davanloo, J.J. Coogan, T.S. Bowen, R.K. Krause and C.B. Collins, Rev. Sci. Instrum.

59,2260 (1988).F. Davanloo, J.J. Coogan, R.K. Krause and C.B. Collins, Nucl. Instrum. Methods,

B40/41,912 (1989).J.J. Coogan, F. Davanloo and C.B. Collins, Rev. Sci. Instrum. 61,1448 (1990).C. Cachoncinlle, J.M. Pouvesle, F. Davanloo, J.J. Coogan and C.B. Collins, J. Phys. D: Appl.

Phys. 23,984 (1990).F. Davanloo, J.J. Coogan, R.K, Krause, J.D. Bhawalkar and C.B. Collins, Nucl. Instrum.

Methods, B56/57,1068 (1991).F. Davanloo, R.K. Krause, J.D. Bhawalkar and C.B. Collins in Proceedings of the 8th

International Pulsed Power Conference, pp 971-974 (1991).F. Davanloo, J.D. Bhawalkar, C.B. Collins, F.J. Agee and L.E. Kingsley in Conference

Record of the 1992 Twentieth Power Modulator Symposium, pp 364-367 (1992).J.D. Bhawalkar, F. Davanloo, C.B. Collins, F.J. Agee and L.E. Kingsley in Proceedings of

the International Conference on Lasers '92, pp 360-364 (1992).J.D. Bhawalkar, F. Davanloo, C.B. Collins, F.J. Agee and L.E. Kingsley in Proceedings ofthe 9th International Pulsed Power Conference, pp 857-860 (1993).

J.D. Bhawalkar, D.L. Borovina, F. Davanloo, C.B. Collins, F.J. Agee and L.E. Kingsley in

Proceedings of the International Conference on Lasers '93, pp 712-717 (1993).F. Davanloo, D.L. Borovina, J.D. Bhawalkar, C.B. Collins, F.J. Agee and L.E. Kingsley in

Conference Record of the 1994 Twenty- first Power Modulator Symposim, pp 201-205

(1994).

D.L. Borovina, F. Davanloo, C.B. Collins, F.J. Agee and L.E. Kingsley in Proceedings of theInternational Conference on Lasers '94 (in press).

F. Davanloo, D.L. Borovina, C.B. Collins, F.J. Agee and L.E. Kingsley in Nucl. Instrum.

Methods, B99, 1995, pp 713-716.

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