ARL Commissioning Experiments With 

a 4.5-MJ Pulsed Power Supply 

by Miguel Del Güercio

ARL-TR-2814 September 2002

Approved for public release; distribution is unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position 

unless so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval 

of the use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-2814 September 2002 

ARL Commissioning Experiments With a 4.5-MJ Pulsed 

Power Supply 

Miguel Del Güercio 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

Abstract 

A 4.5-MJ capacitor-based, pulsed power supply has been installed at the U.S. Army Research 

Laboratory, Aberdeen Proving Ground, MD, for railgun operations. The system consists of 18 

independent modules, each with an energy capacity of 250 kJ. Half of the modules were 

modified from their original condition to a pulse-forming inductance of ~24 μH, while the 

remainder maintained their original 60-μH inductance. Another modification included a 

pneumatic-operated shorting system, added to enhance the safety of the system. Simulations 

were conducted for a variety of load conditions using a SPICE-based code. Predicted currents 

and velocities are in reasonable agreement with measured quantities. The complete system 

allows the electromagnetic launch of hypervelocity launch packages to a downrange distance of 

4 km. 
iii

Contents 

List of Figures v

1. Introduction 1

2. Hardware 2

2.1 Inductors..........................................................................................................................2 

2.2 Diodes..............................................................................................................................2 

2.3 Fuses................................................................................................................................3 

2.4 Controls ...........................................................................................................................3 

2.5 Spark Gap........................................................................................................................5 

2.6 HVCPS ............................................................................................................................5 

2.7 Output Cables..................................................................................................................5 

2.8 Charge and Discharge Operations...................................................................................6 

3. Modeling 8

4. Experimental Results 9

5. Railgun Testing 11

6. Summary 12

7. References 13

Report Documentation Page 15 
iv

INTENTIONALLY LEFT BLANK. 
v

List of Figures 

Figure 1. PPS racks.........................................................................................................................1 

Figure 2. Crowbar diodes and spark gap. .......................................................................................2 

Figure 3. Fuses and trigger generators............................................................................................3 

Figure 4. Local controller. ..............................................................................................................4 

Figure 5. Control console/data acquisition. ....................................................................................4 

Figure 6. Dry gas and monitoring panel–Interlock J-box and Interface J-box. ..............................4 

Figure 7. High-voltage (DC) control power supply........................................................................6 

Figure 8. Module resistor/J-box/Ross relay....................................................................................7 

Figure 9. Module shorting system. .................................................................................................7 

Figure 10. Safety soft dump/Ross probe.........................................................................................8 

Figure 11. ICAPS module schematic..............................................................................................8 

Figure 12. Simulation at 9 kV.........................................................................................................9 

Figure 13. Breech............................................................................................................................9 

Figure 14. Module 1 data vs. simulation.......................................................................................10 

Figure 15. Rack 6 data vs. simulation...........................................................................................10 

Figure 16. Railgun. .......................................................................................................................11 

Figure 17. Current from railgun firings vs. code simulations.......................................................11 
vi

INTENTIONALLY LEFT BLANK. 
1

1. Introduction 

A 4.5-MJ pulsed power system (PPS), previously owned and operated by GDLS (General 

Dynamics Land Systems) for use on electrothermal-chemical (ETC) programs [1, 2], was 

acquired some time ago by the U.S. Army Research Laboratory-Weapons and Materials 

Research Directorate (ARL-WMRD). The system was recently modified to operate with an 

electromagnetic (EM) railgun, and the output of the pulser was modeled with a SPICE-based 

code (Intusoft ICAP/4Rx) [3]. 

This software reduces the long run times usually involved in these kind of simulations by means 

of a variable time-step control algorithm. The code [4] determines the in-bore projectile 

position, velocity, voltage and current at the breech all as a function of time up to muzzle exit. 

The code also includes a detailed model developed by the Institute for Advanced Technology 

(IAT) for the railgun [5]. The pulser’s hardware consists of eighteen 250-kJ independently 

triggered modules. Pairs of these modules (see Figure 1) are symmetrically placed in nine racks 

(3 ft 7 in wide H 13 ft long and 4 ft high). Each of the eighteen 250-kJ modules contains five 

Aerovox 11-kV/50-kJ, 830-μF capacitors and two original 116-μH inductors. 

 Figure 1. PPS racks.
2

2. Hardware 

The PPS is composed of many subsystems and components. The following subsections address 

the parameters, physical characteristics and operating characteristics for a few of the most 

important components. 

2.1 Inductors 

The pulse-forming inductance was decreased on selected modules in an effort to generate an 

increase in peak launcher current and launch velocity. Nine of the eighteen modules retained 

their two original 116-μH inductors (connected in parallel). Nine 30-μH inductors replaced nine 

of the 116-μH inductors on the remaining nine modules. The final inductance for each of these 

modified modules was 24 μH. In general, many configurations are possible, as nine modules 

may have their twin inductors connected as single 116-μH inductors or in parallel as a 60-μH 

inductor, while the other nine modules can have their inductors connected as a single 116-μH, as 

a 30-μH, or in parallel as a 24-μH inductor (their present configuration). 

2.2 Diodes 

A total of fifteen Brown Boveri BBC Avalanche DSA 908-44 AG diodes, arranged in five stacks 

in parallel, with three diodes in series in each stack, form a crowbar diode set which protects the 

capacitors of each module from damaging voltage reversals (see Figure 2). Each diode is rated 

at 4.4 kV and 50 kA for a 1-ms half-sinusoid surge currents. Each crowbar diode set is clamped 

together and evenly distributed between two identical 1-in-thick aluminum circular plates. 

 Figure 2. Crowbar diodes and spark gap.
3

There are three 0.01-mF capacitors connected in parallel and placed across the diode stacks. 

The capacitors provide extra protection for the diodes during large transients. Each of the five 

crowbar diode stacks is connected in series to a 15-mΩ resistor, providing a total of 3-mΩ

crowbar resistance per module. The resistors limit the peak current through the diodes and 

moderate the action through the diodes, as these diodes become susceptible to failure when 

switching at large voltages. 

2.3 Fuses 

Four fuses are connected in parallel and placed in series with the output of each capacitor to 

enable the handling of large currents while providing isolation in the event of a capacitor short 

circuit at high voltages. Each Maxwell high-voltage fuse (see Figure 3) is rated at 6 kA and 

22 kV, providing a maximum rating of 24 kA per assembly of four. 

Figure 3. Fuses and trigger generators. 

2.4 Controls 

A local controller (see Figure 4) with state-of-the-art fiber-optic linked subsystems provides the 

hand-shake between the control consol (see Figure 5) via the Interface J-box (see Figure 6). All 

communications to and from the control consol to the J-box and to the J-boxes at each module 

are via fiber optics. 

Data acquisition set-up (see Figure 5) includes four 4094A Nicolet oscilloscopes, providing a 

total of 16 channels. Data acquired are transferred from the 4094A oscilloscopes to the adjacent 

via the personal computer RS232 link in DOS mode. 
4

Figure 4. Local controller. 

Figure 5. Control console/data acquisition. 

Figure 6. Dry gas and monitoring panel–Interlock J-box and Interface J-box. 
5

Voltage-to-frequency circuitry boards are at three locations to communicate the optical signals: 

(1) the interlock chassis to allow high-voltage charging power supply (HVCPS) set point 

transmission to the Interface J-box, (2) the Interface J-box for HVCPS charge voltage and 

current transmission to the consol control, (3) the module’s Interface J-box for sensor and 

transmission purposes to the F/V chassis located in the Interface J-box (see Figure 6). 

The control console contains six separate chassis: (1) the control chassis with the on/off system 

key switch and enable buttons, (2) the charge monitor panel displaying the real-time voltage and 

current data, (3) the charge monitor chassis, (4) the output monitor chassis, (5) an 18-channel 

delay generator that allows the firing of the modules at preselected times, and (6) the Interlock Jbox that defeats any attempt of discharging the pulser if any interlock is not closed. 

When the initial sequence of commands for a test has been successfully completed at the control 

consol, a “charge complete” is displayed, indicating that the banks have reached the desired 

charge set-point and are ready to be discharged. At that time, the trigger generator, which 

controls the firing times of the individual modules, is able to be triggered, provided a disconnect 

handshake returns from the HVCPS. However, if the fire pushbutton is not pressed within 4 

minutes, an excess time counter, started when the key switch is turned to run will connect the 

dump resistors across the capacitors to ground depleting the energy stored in the capacitors. 

2.5 Spark Gap 

The discharge of each module is initiated by a high-voltage trigger generator (PI-TG-75S) and 

controlled by a spark gap (PI-ST-300), operating as an output switch. The trigger generators are 

located between the module’s spark gaps (see Figure 3), use dry air (Figure 6) to prevent 

breakdown, and produce over 55 kV into a high-impedance load. Their trigger is enabled via 

fiber optics within a 600-ns time delay. The ST-300 spark gaps (Figure 2) are rated at 500 kA 

with a stand-off voltage of 22 kV at zero pressure and are reliably triggered with the 55-kV pulse 

from the trigger generator. 

2.6 HVCPS 

The time for charging this system to full voltage (11 kV) is about 60 s, with a maximum current 

of 15 A. Initially, the charging process starts in a constant current mode to reach the desired set 

point. Once the set point voltage is reached, the HVCPS (see Figure 7) switches to a constant 

voltage mode to regulate and hold the set-point voltage. 

2.7 Output Cables 

The pulser's discharge is conducted through 18 single coaxial cables (see Figure 15), which are 

10.7 m long, six of which have a resistance of 6 mΩ (560 μΩ/m) and an inductance of 2.02 μH 

(189 nH/m). These coaxial cables connect each module to the breech of the railgun. 
6

Figure 7. High-voltage (DC) control power supply. 

2.8 Charge and Discharge Operations 

Each module is charged and discharged safely through a heavy-duty 50-Ω (Allen Bradley) 

resistor (Figure 7). This operation is controlled by the module J-box as a Ross relay opens or 

closes. The resistor is capable of depleting 3 charges to full voltage within an hour period 

(Figure 8). A pneumatic shorting system was added at each module to eliminate the “hands on” 

shorting required after each firing. In the event of residual stored energy, the pneumatic system 

remotely depletes the energy in a rapid manner by physically lowering a grounded aluminum 

channel, thereby shorting the capacitor’s terminal to the capacitor’s case (rack’s ground bus). 

Each of the aluminum channels are mechanically operated by two air cylinders positioned at 

opposite ends. At the lower position, the channel presses on an array of copper contacts 

(Figure 9) secured to each of the five mounting brackets that lock each set of four fuses to each 

capacitor's output terminal. Thus, in the event that a set of fuses for a capacitor is open circuited, 

the stored energy will be shorted directly to ground, possibly destroying the copper contacts but 

assuring that the energy in the capacitors is depleted. Previous to any work on the modules, a 

soft dump-rod (Figure 10) is used. A high-voltage Ross probe is also available for any potential 

troubleshooting hazard. 
7

Figure 8. Module resistor/J-box/Ross relay. 

Figure 9. Module shorting system. 
8

Figure 10. Safety soft dump/Ross probe. 

3. Modeling 

A non-net schematic of a module architecture is shown in Figure 11. The ICAPS software 

provided results in agreement with the initial tests, with a low impedance load connected at the 

breech. This initial data provided a coarse verification of the circuit performance. A simulation 

at an initial charge voltage of 9 kV (Figure 12), with a mass of 190 g and a rail length of 3 m, 

predicts a peak armature current of ~1.2 MA and an exit velocity of 2300 m/s. 

5

4

C1

4242.2E-06

6

RS

3.65E-03

4

7

6

LS

0.3E-06 9

7

CBDIODE

DSA908

10

LCB

97E-09

4

RCB

6.65E-03

7

7 7

4

4 4

7 8

3

S1

SPARKGAP

14

V1

3

8

12

LIND

60E-06

2

RIND

2.0E-03

11 201

L1C

1.2E-06

22

R1C

3.18E-03

11

7 7

11 201

VM1

11

11 201

201

Figure 11. ICAPS module schematic. 
9

0

200

400

600

800

1000

1200

1400

0 0.5 1 1.5 2 2.5 3 3.5

Time (ms)

Current (kA)

0

0.4

0.8

1.2

1.6

2

2.4

2.8

Velocity (km/s)

Current Velocity

C

Figure 12. Simulation at 9 kV. 

4. Experimental Results 

Initial tests were done by discharging the individual modules into a low-impedance load at the 

breech (Figure 13). In general, good agreement was obtained between the ICAPS simulations 

and the current output. 

Figure 13. Breech.
10

At an initial charge voltage of 3 kV, the experimental data from module 1, rack 1 with a 30-μH 

inductor, and a 116 μH in parallel (~24 μH), show a lower peak of 29.3 kA at 519 μs than its 

simulated value of 31.1 kA (Figure 14). 

0.50 1.50 2.50 3.50 0.00 1.00 2.00 3.00 4.00

Time (ms)

5.00

15.00

25.00

35.00

0.00

10.00

20.00

30.00

Current (kA)

Simulation

Data

Figure 14. Module 1 data vs. simulation. 

The output current for modules 11 and 12, also at an initial charge voltage of 3 kV (rack 6) and 

each with two parallel 116 μH inductors (~60 μH), is shown in Figure 15. The larger inductance 

of these modules produced a later peak at 820 μs with a good match of peak values between 

experimental and simulated data (42.6 kA vs. 42 kA). 

0.50 1.50 2.50 3.50 0.00 1.00 2.00 3.00 4.00

Time (ms)

5.00

15.00

25.00

35.00

45.00

0.00

10.00

20.00

30.00

40.00

Current (kA)

Simulation

Data

Figure 15. Rack 6 data vs. simulation. 
11

5. Railgun Testing 

Two initial tests at 5 and 6.5 kV were performed with a simple electromagnetic railgun, a 230-g 

solid armature, and a target placed at 50 m. Figure 16 shows the railgun and its connection to the 

breech. 

Figure 16. Railgun. 

Data show muzzle velocities and peak currents of 880 m/s at 722.5 kA and 1000 m/s at 481 kA 

(delayed pulse), respectively. The code-generated simulations (Figure 17) reveal good 

agreement with the experimental data. 

Data at 6.5kV

Data at 5kV

Simulation at 6.5kV

Simulation at 5kV

1.00E-3 3.00E-3 5.00E-3 0.00E+0 2.00E-3 4.00E-3 6.00E-3

Time (s)

100.00

300.00

500.00

700.00

0.00

200.00

400.00

600.00

800.00

Current (kA)

Figure 17. Current from railgun firings vs. code simulations. 
12

6. Summary 

A capacitor-based power supply previously used for ETC launchers and placed in storage for six 

years was successfully recommissioned. Additionally, the supply was used to provide currents 

and pulse shapes amenable to solid armature experiments. Peak performance to date included an 

8-kV charge voltage. With all banks discharged at time zero and a 5-kV initial charge voltage, 

the peak current was 871 kA; using a time delay for each module, a nearly flat pulse was attained 

with a peak current of 611 kA and an initial charge voltage of 6.5 kV. Firings with different 

configurations of solid armatures of diverse weight (133–371 g), with all banks discharged 

simultaneously or delayed, showed a close agreement with their code simulations. 
13

7. References 

1. Hammon, H. G., D. Bhasavanich, and F. T. Warren. “Design Approaches to Pulsed Power 

for Electromagnetic and Electrothermal Gun Systems.” Proceedings Pulsed Power 

Conference, San Leandro, CA, 1991. 

2. Bhasavanich, D., D. F. Strachan, and R. Ford. “4.5 MJ Modular Pulse Power Supply for 

ETC Gun Applications.” Proceedings Pulsed Power Conference, San Leandro, CA, 1993. 

3. ICAP/4Rx, ICAPS, and ISPICE4 are trademarks of Intusoft, San Pedro, CA, 90733-0710. 

4. Del Güercio, M. “A SPICE-Based Code for ARL’s 4.5-MJ Electromagnetic Launcher 

Pulsed Power Supply System.” ARL-TR-2592, U.S. Army Research Laboratory, Aberdeen 

Proving Ground, MD, September 2001. 

5. Schroder, K. A. “Study of Possible Power Supply Module Upgrade at the IAT 

Electromagnetic Research Laboratory.” IAT.TM 0051, IAT at The University of Texas at 

Austin, February 2000. 
14

INTENTIONALLY LEFT BLANK.
15

electromagnetic launcher, pulsed power system, EM gun experiments 18

ARL-TR-2814

U.S. Army Research Laboratory

ATTN: AMSRL-WM-BC

Aberdeen Proving Ground, MD 21005-5066

Miguel Del Güercio

ARL Commissioning Experiments With a 4.5-MJ Pulsed Power Supply 1L1622618AH80

September 2002 Final, February - April 2002

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project(0704-0188), Washington, DC 20503.

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE

6. AUTHOR(S)

5. FUNDING NUMBERS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES)

8. PERFORMING ORGANIZATION

 REPORT NUMBER

10.SPONSORING/MONITORING

 AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

13. ABSTRACT

14. SUBJECT TERMS 15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION

 OF REPORT

18. SECURITY CLASSIFICATION

 OF THIS PAGE

19. SECURITY CLASSIFICATION

 OF ABSTRACT

20. LIMITATION OF ABSTRACT

(Maximum 200 words)

UL

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18 298-102

NSN 7540-01-280-5500 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED

Approved for public release; distribution is unlimited.

15

A 4.5-MJ capacitor-based, pulsed power supply has been installed at the U.S. Army Research Laboratory, Aberdeen 

Proving Ground, MD, for railgun operations. The system consists of 18 independent modules, each with an energy 

capacity of 250 kJ. Half of the modules were modified from their original condition to a pulse-forming inductance of 

~24 μH, while the remainder maintained their original 60-μH inductance. Another modification included a 

pneumatic-operated shorting system, added to enhance the safety of the system. Simulations were conducted for a 

variety of load conditions using a SPICE-based code. Predicted currents and velocities are in reasonable agreement 

with measured quantities. The complete system allows the electromagnetic launch of hypervelocity launch packages 

to a downrange distance of 4 km. 
16

INTENTIONALLY LEFT BLANK. 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

1

 2 DEFENSE TECHNICAL 

 INFORMATION CENTER 

 DTIC OCA 

 8725 JOHN J KINGMAN RD 

 STE 0944 

 FT BELVOIR VA 22060-6218 

 1 COMMANDING GENERAL 

 US ARMY MATERIEL CMD 

 AMCRDA TF 

 5001 EISENHOWER AVE 

 ALEXANDRIA VA 22333-0001 

 1 INST FOR ADVNCD TCHNLGY 

 THE UNIV OF TEXAS AT AUSTIN 

 3925 W BRAKER LN STE 400 

 AUSTIN TX 78759-5316 

 1 US MILITARY ACADEMY 

 MATH SCI CTR EXCELLENCE 

 MADN MATH 

 THAYER HALL 

 WEST POINT NY 10996-1786 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL D 

 DR D SMITH 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CI AI R 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 3 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CI LL 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 3 DIRECTOR 

 US ARMY RESEARCH LAB 

 AMSRL CS IS T 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

ABERDEEN PROVING GROUND

 2 DIR USARL 

 AMSRL CI LP (BLDG 305) 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

2

 1 US ARMY TACOM ARDEC 

 J BENNETT 

 FSAE GCSS TMA BLDG 354 

 PICATINNY ARSENAL NJ 

 07806-5000 

 1 US ARMY TACOM ARDEC 

 D LADD 

 AMSTA AR FSP BLDG 354 

 PICATINNY ARSENAL NJ 

 07806-5000 

 2 INST FOR ADVANCED TECH 

 UNIV OF TX AT AUSTIN 

 I MCNAB 

 F STEPHANI 

 3925 WEST BRAKER LANE 

 SUITE 400 

 AUSTIN TX 78759-5316 

 3 UNIV OF TX AT AUSTIN 

 CENTER FOR ELECT 

 J KITZMILLER 

 S PRATAP 

 J PAPPAS 

 PRC MAIL CODE R7000 

 AUSTIN TX 78712 

 2 LOCKHEED MARTIN VOUGHT 

 N WELLS 

 K COOK 

 PO BOX 650003 

 MS WT 21 

 DALLAS TX 75265-0003 

 1 UNIV AT BUFFALO 

 SUNY AB 

 J SARJEANT 

 PO BOX 601900 

 BUFFALO NY 14260-1900 

 1 UDLP 

 B GOODELL 

 MS M170 

 4800 EAST RIVER RD 

 MINNEAPOLIS MN 

 55421-1498 

 1 SAIC 

 K A JAMISON 

 1247 B N EGLIN PKWY 

 SHALIMAR FL 32579 

 1 IAP RESEARCH INC 

 D BAUER 

 2763 CULVER AVE 

 DAYTON OH 45429-3723 

 2 TITAN 

 PULSED SCIENCES DIV 

 P REIDY 

 T WOLFE 

 4855 RUFFNER ST 

 SUITE A 

 SAN DIEGO CA 92111 

 1 GENERAL ATOMICS ENERGY 

 PRODUCTS 

 F MCDOUGAL 

 4949 GREENCRAIG LN 

 SAN DIEGO CA 92128 

ABERDEEN PROVING GROUND

 20 DIR USARL 

 AMSRL WM 

 E SCHMIDT 

 AMSRL B 

 A HORST 

 AMSRL WM B 

 B FORCH 

 D LYON 

 AMSRL WM BC 

 P PLOSTINS 

 J GARNER 

 V OSKAY 

 M BUNDY 

 G COOPER 

 J SAHU 

 S SILTON 

 P WEINACHT 

 B GUIDOS 

 A ZIELINSKI 

 D WEBB 

 T ERLINE 

 J NEWILL 

 M DEL GÜERCIO 

 AMSRL WM WD 

 J POWELL 

 C HUMMER