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TECHNOLOGY DEVELOPMENT PROGRAMME IN PULSEELECTRON ACCELERATORS AND UTILISATION IN

COMPACT HPM SOURCES

Archana Sharma

Accelerator and Pulse Power Division, Beam Technology Development Group

Dr. Archana Sharma is the recipient of the DAE Homi Bhabha Science &

Technology Award for the year 2011

IntroductionIntroductionIntroductionIntroductionIntroduction

The pulsed power program has been started in BARC

since 1970s, it was developed for fusion related research

(till 1980s) and then focus was shifted to NEMP (nuclear

electro- magnetic pulse) simulation, hardening and

surge suppression. Pulse power systems were developed

for generation of high power microwave and Flash X-

rays for strategic applications. Power capability was

increased from 0.5GW in KALI-75 to 30GW in KALI-

30GW systems where KALI stands for Kilo Ampere

Linear Injector. During 1990s, in association with DRDO

development of compact and mobile system with

repetitive pulsed output and systems like Linear

Induction Accelerator (LIA-200) was taken up. Later

Pulsed power developments include repetitive 1kJ Marx

system and LIA-400 were also developed.

In last four decades various technologies and high

energy pulsed power systems have been developed

indigenously. It includes design and development of

marx generator, tesla transformer, pulse forming line,

AbstractAbstractAbstractAbstractAbstract

This work involves the design and development of high intensity pulsed power systems from multi MW to GW

capacity, single shot to repetitive shots and devices for high power microwave (HPM) generation. These systems

are ready for deployment to various users in defence, electronic industries and test laboratories. The techniques of

generating high pulsed power needs a critical optimization of high voltage and low inductance, fast switching

and fast recovery, efficient conversion from electrical power to electron beam pulsed power. It is also critical to

match the frequency and power of microwave pulses to get coupled effectively with electronics circuitry and

create temporal/operational or permanent damage depending on their circuit configuration frequency and threshold

electric field. Keeping these strategic and industrial applications as target, a variety of pulsed power systems have

been developed viz. KALI series, LIA series and UWB sources.

Fig.1: Block Diagram of Pulsed power Systems and year wise growth

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Founder’s Day Special Issue October 2013

blumlein, fast acting sparkgap switches, magnetic pulse

compression, solid state modulators and relativistic

electron beam diodes. These systems have been

demonstrated to its full capacity from single shot to

repetitive operation and utilized for the generation of

high power microwaves (HPM) and flash X-rays. In this

paper a few developed systems are described based on

different topology for compact HPM sources

successfully and operational as milestones of this long

and uninterrupted technical path of achievements.

The essence of pulsed power system is to convert slow

charging pulse into fast discharging pulse such that

peak power increases manifold. This can be achieved

using various techniques of energy storage and power

transition switches.

A few Marx based systems were developed as described

below:

KALI-5000KALI-5000KALI-5000KALI-5000KALI-5000

For multi gigawatt peak output

power, Marx generator based

systems are developed, where

capacitors are charged in parallel

and discharged in series for single

shot system operation it can be

resistive charging but for repetitive

pulsed power system it is inductive

charging charged based system. To

reduce the no. of charging stages

and sparkgap switches, bipolar

charging is utilized. To have control

of different operating output

Fig.2: Schematic and Photograph of KALI-5000

parameters, pressurised sparkgaps are used to vary its

breakdown voltage in the sparkgap switches, by

changing gas pressure. Thus KALI-5000 system was

developed using hybrid insulated Marx generator (gas

in the switches and transformer oil for the rest assembly)

was developed. It has castor oil filled Blumlein type pulse

forming line with prepulse switch along with charging

inductor and REB gun. Typical output and photograph

of the system is shown in Fig. 2.

It was used for generating high power microwaves

(HPM), and Flash X-rays generations with suitable

diagnostics. Experiemnts were conducted with

300-600kV designed Axial and Coaxial vircators

(Virtual Cathode Oscillatrs) using this system as shown

in Fig.3, and HPM signals were measured and

characterised.

Fig.3: Typical Vircator assembly and Pulsed output sugnals with KALI-5000

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At this output power capacity(>10GW), weight, size

and reprate are limited to make it a static system for

hardening and development of diagnostics etc.

Reprate 1kJ Marx SystemReprate 1kJ Marx SystemReprate 1kJ Marx SystemReprate 1kJ Marx SystemReprate 1kJ Marx System

In order to make the Marx based system compact and

repeatable, high pressure gas filled repetitive marx

generator was developed using inductive charging viz.

1kJ Reprate Marx generator has characteristic

impedance of ~25 ohms. Instead of using axial or

coaxial vircators in this system, a new type of HPM

device namely reflex triode was designed and developed

for HPM generation directly fed by Marx source. There

was no PFL used in this system except a peaking gap

after the Marx generator to make the system compact.

This system has positive output for anode mesh and

cathode is at ground potential. Typical results and

system details are given in Fig.4.

This system is quite user friendly due to gaseous

insulation and compact assembly it is mobile also. The

system was used for HPM characterisation and

Intentional Electromagnetic Interference (IEMI) studies

on Electronics circuiry viz. Susceptability threshold,

hardening techniques etc.

Linear Induction Accelerator (LIA)Linear Induction Accelerator (LIA)Linear Induction Accelerator (LIA)Linear Induction Accelerator (LIA)Linear Induction Accelerator (LIA)

In order to make the high voltage pulsed power system

operation at higher repetition rate, switching is

performed by magnetic pulse compression switches and

no sparkgaps are used. This switches are made with

special toroidal cores having square B-H characteristics

with large permeability and low coercive force at high

pulse frequency. APPD,BTDG has developed two such

systems as decribed below.

LIA-200 is a repetitive pulsed power system rated for

200kV,5kA,100ns,100Hz. A soild state modulator was

used to charge this system and circuit schematic and

photograph of this system is shown in Fig.5. Here, 3-

stage Induction cavities are used in Linear Inductive

Adder configuration using DM-water capacitors

(10nF,200kV) and water PFL. Russian cores were

procured for 2-pulse transformers, 4-magnetic switches

and 3-stage induction cavities. This system was developed

for the technology demonstration of new reprate

techniques based on magnetic elements and operated to

full rated capacity (LIA-200) as shown in Fig.5.

Challenges involved in this developemnt program was

to make magnetic cores saturate at desired volt-time

Fig. 4: (a) Photograph of the 1kJ Marx system (b) with Reflex triode assembly (c)and output waveshapes of HPMpower (d), filed and frequency

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level, reset them before the arrival of next pulse, thermal

management over 100Hz. The amorphous cores were

tested for its characteristic parameters under pulse

excitation such as core loss, change in permeability and

total flux swing. The size and shape of the oil/vacuum

Fig.5: Electrical Circuit (a) and Photograph (b) of LIA-200(200kV,5kA,100ns,100Hz)

interface insulators was optimised betwen core based

induction cavities to mitigate any flashover under 100ns

pulses in 100Hz reprate. Water capacitors were

designed for the first time to store energy at 200kV

with low inductance at 10nF capacity. Water PFL was

Fig.6: Typical output of LIA-200 at various MPC stages (a) and HPM output @30Hz,160kV,12 shots (b) from B-dotprobe

(a) (b)

Fig. 7: Schematic (a) and Photograph (b) of LIA-400 with output waveshape in single shot (c) and 100Hz operation(d) for REB generation

(d) Reprateshots

(c) Singleshots

(a) Schematic of lIA-400

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also used to shape the output pulse followed by a core

based sharpening switch. The typical output of this

system is shown in Fig.6 at various stages of pulse

compression by magnetic switching. Pulse compression

gain (T2/T

1) was maintained at 3-4 to optimise the core

volume (core volume gain2).

The enabling technology with this systems (LIA-200)

were magnetic switching, reset techniques, induction

cavities adder configuration, fast charging CCPS, core

characterisation, surface flashover phenomenon in oil/

vacuum interface and toroidal pulse transformer. Based

on these experience another system was designed (LIA-

400) and successfully developed. Core based elemnets

in this system were jointly developed under BARC-Russia

Collaboration. It is also completed in stipulated time

period as shown in Fig.7.

Overall systems developed in APPD, BTDG are

deployable for various HPM and UWB irradiation to

see the effect of high frequency impulse electric and

magnetic field coupling with sensitive electronics

circuitry, their susceptability level and hardening

techniques

AcknowledgementAcknowledgementAcknowledgementAcknowledgementAcknowledgement

I extend heartfelt gratefulness to Dr.P.H.Ron, pioneer

of this programme. I also want to acknowledge the

encouragement and support given by Dr.L.M.Gantayet,

Director, BTDG. My sincere thanks to Dr.K.C.Mittal,

Head, APPD, Shri. D.P.Chakravarthy, Dr.K.V.Nagesh and

Dr. A.K.Ray for valuable guidance. Lastly all APPD

colleagues are gratefully acknowledged for their

cooperation.

Pulse Diode Diode A-K Microwave E-field HPM

Power Voltage Current Gap HPM Device Peak power @10m frquencySystem (kV) (kA) (mm) @window from (GHz)

(MW) window

KALI-1k 250 12 6 Axial Vircator 87 5.1 4-6.6

KALI-5k 300 20 12.5 Coaxial Vircator 26 2.8 2.8

KALI-5k 300 15 12 Reflex Triode 43 3.6 6.5

1kJ Marx 200 4 15 Reflex Triode 100 5.3 2.2-4

IES-1 300 10 15 Reflex Triode —— 7@3m 0.9 & 2.6