R. Verma

Nanosecond rise time air-core current transformer for long-pulse current measurement in pulsed power

A slow-wave delay line type air-core (nonmagnetic Nylon former) current transformer fabricated using silver epoxy for the measurement of currents of long pulse durations and few nanoseconds rise times is reported in this article. The advantage of using silver epoxy is that it fills all the voids between coil and shield and enhances the proximity of the coil to the shield, leading to a high value of distributed capacitance. Thus the transit time of the coil increases and it can measure fast current pulses of longer durations. Increasing the inductance of the coil can compensate for the resulting reduction in the sensitivity of the coil for matched termination. An easy experimental technique to find the value of the matched terminating resistor is also reported in this article. We have also done simulations of the slow wave current transformer using PSPICE.

Characterization of High Power Microwave Radiation by an Axially Extracted Vircator

Characterization results of high-power microwave radiation, from an axial vircator driven by pulsed electron beam accelerator AMBICA-600 are reported in this paper. We present a study on variation in pulsed microwave power output and dominant frequency by discretely varying anode-cathode (A-C) gap. While keeping the cathode diameter fixed at 40 mm, for the A-C gap distance in the range 5-9 mm, dominant frequencies have been measured to be lying in the range 4.7-9.8 GHz. The trend of a subsequent increase in the dominant frequency at lower A-C gap distances (and vice versa) revealed that center frequency is mainly governed by the longitudinal size of the potential well. The highest microwave power of ~ 14 MW for ~ 75-ns pulse duration was obtained at A-C gap of 7 mm having the dominant frequency in C-band at ~ 6.9 GHz. The beam-to-microwave power conversion efficiency of ~ 1.2% has been demonstrated in our experiments. On the basis of power distribution pattern obtained by the gas breakdown technique, the dominant mode of emission is believed to be transverse magnetic mode. Relative analysis of frequency spectrums obtained for various A-C gap distances evidenced experimental recognition of optimum A-C spacing as a generation of narrowband distinct frequency peak of large magnitude with minimal mode hopping.

Impulse electromagnetic interference generator

Electromagnetic interference (EMI) related malfunctioning of equipment containing electronic control devices has become a serious problem these days, as it couples to wires and PCBs in the equipment, reflecting and resonating and then being amplified by an IC finally resulting in malfunction. In order to test and simulate the immunity of electronic circuits to an EMI environment, an electrical fast transient/burst generator has been developed which generates broadband interference spectrum in the range of 20 MHz to 600 MHz. The burst generator is mainly comprised of coaxial cables, pressurized spark gaps, a HV Power Supply, a terminating resistor and a TEM horn which acts as load. For pulse sharpening, switching has been done at two stages. Depending upon the delay time of coaxial line, the width of the square wave pulse has been kept at 50 ns. The total energy of the portable system is 34 Joules, and it weighs less than 50 kg. In the presented paper we describe the system design, results of measurements and areas of further improvements in energy transfer efficiency.

Battery operated portable 300 kV pulsed power system

We have developed a compact, portable, high-voltage, pulsed power source. Such systems can have a range of industrial applications, such as driving portable x-ray sources. The primary source is a series-parallel bank of dry-cell batteries. A dc to dc converter SMPS converts the 30V-dc output from the battery-bank to a 30kV, 2mA output. This, in turn, is used to charge a 0.24 /spl mu/F capacitor to 30kV. The whole power supply, excluding the capacitor weighs only 3 kg and is compact. The capacitor weighs 5.5 kg. We are trying to use more compact capacitors to further reduce the weight. The capacitor is discharged into the primary of a pulse transformer to step-up the voltage. By immersing the pulse transformer in oil we have obtained 300 kV from the pulse transformer. Such an output will be enough for our applications. Details of the system and its performance are reported in the paper.

200 kJ Pulsed Power System for Pulsed Plasma Device

A 200 kJ pulsed power system (PPS) has been built up to drive pulsed plasma devices. This PPS consists of two 100 kJ capacitor bank modules, each comprising of five capacitors of each

Results of Ultracompact Plasma Focus Operating in Repetitive Burst-Mode

178~\mu \text{F}

Generation of EM radiations using intense electron beam produced in vacuum

, a discharge switch, and a pulse-shaping unit. When both the banks are charged simultaneously to −15 kV using full charging technique, it delivers a peak current 100 kA at the load (damping resistor and pulse-shaping inductor). Later on, a plasma system will be attached at the load which will also have an inductive and resistive effect. A fiber-optic triggering unit controls both the modules and there exists a flexibility of sometimes operating a single module only, besides there are provisions for further up gradation of the PPS to a targeted 600 kJ. Prior to this development, PSpice simulation was carried out to estimate the parameters of the circuit components to achieve the required wave pulse with precision. Using these parameters, a design of the PPS was made keeping into account about the critical issues involved and the ratings of the components, some of which were fabricated in house. This paper basically includes the criticality surrounding the operation of a high-energy long-pulse PPS under negative operating voltage.

Results of ultra compact plasma focus operating in repetitive burst-mode

The results of a miniature plasma focus are presented in this paper which is operated with energy less than or equal to 150 J. The miniature plasma focus is driven by a small capacitor bank and the peak current delivered in the focus is 75-80 kA. The deuterium gas is filled with a pressure range of 5-7 mbar inside the plasma focus chamber. The quartz glass is used for generating initial surface breakdown at a 4-5-kV discharge, which is a typical value for low-voltage plasma focus discharges. The repetitive operation (record 50 Hz) of the device is achieved by a combination of a simple and high power (5 kW) supply with the synchronized triggering of the capacitor bank at the time of isolation between supply and the capacitor bank. The diameter of cathode is 25 mm and anode diameter is 8-12 mm and both of them are made of stainless steel. The length of anode and gas pressure is adjusted in such a way that the pinching occurs at the time of occurrence of the peak of current. It enhances the neutron emission from the device. The time-of-flight diagnostic is used to distinguish neutron and X-ray emission from the plasma focus. The neutron measurement using a helium-3 detector and also a fast-scintillator-backed photomultiplier tube demonstrates production of neutron pulses in the time separated by nearly 20 ms, which corresponds to 50 Hz in the burst mode. The device can serve the purpose of being a portable and compact repetitive neutron source for various applications as the flux of the radiation is comparable with that of bigger plasma focus operating at the similar current.

Design and development of a portable flash X-ray source driven by battery powered compact Marx generator

The results of a pulse power generator driving an axial virtual cathode oscillator are being presented in this paper as a source of high power microwave (HPM) radiations. The electron beam generator is also modified to attain the intense X-ray burst. The pulse power generator used for these applications is common and is having 10 ohms as its characteristic impedance with 50nS of pulse width. The peak charging voltage of the pulse forming line is 450kV and hence 225kV and 22.5kA is peak voltage and peak current delivery capabilities respectively for the pulse power generator. The peak electrical power of the generator is 5GW for a matched load. The charging power supply for the pulse forming line consists of a high voltage generator made by pulse transformer and charging the pulse forming line in the first cycle of the charging pulse. To utilize the energy of the primary capacitive storage efficiently the pulse transformer is having 0.8 coupling coefficient between its primary and the secondary. The axial vircator chamber is evacuated to attain the vacuum of 2×10-4 torr for the HPM application. In the case of modified electron beam chamber for the generation of X-rays the vacuum of same order is used. The pulse forming line is made using equal lengths of high voltage transmission lines, each having a length of 10 meters, connected in the parallel to give a net source impedance of 10 ohm. The pulse power generator can operate in repetitive mode and hence the HPM as well as X-rays may be generated in the repetitive burst.

Design and development of compact pulsed power driver for electron beam experiments

The results of a miniature plasma focus are being presented in this paper which is operated with energy less than or equal to 150Joules. The miniature plasma focus is driven by a small capacitor bank and the peak current delivered in the focus is 75kA. The deuterium gas is filled with a pressure range of 5-7mbar inside the plasma focus chamber. The quartz glass is used for generating initial surface breakdown at 4-5kV discharge which is a typical value for low-voltage plasma focus discharges. The repetitive operation of the device is achieved by a combination of a simple and high power (5kW) power supply with the synchronized triggering of the capacitor bank at the time of isolation between supply and the capacitor bank. As the plasma focus chamber volume is very low, in order to achieve reduced after-shot contamination effects, the gas pressure inside the plasma focus is maintained by continuous pumping which is disallowed at the time of shorts rather having a sealed type plasma focus assembly. The results of such scheme are also discussed in the paper. The diameter of cathode is 25mm and anode diameter is 8-12mm and both of them are made of stainless steel. The length of anode and gas pressure is adjusted in such a way that the pinching occurs at the time of occurrence of the peak of current. It enhances the neutron emission from the device. The time-of-flight diagnostic is used to distinguish neutron and X-ray emission from the plasma focus. The device as can serve the purpose of being a portable and compact repetitive neutron source for various applications as the flux of the radiation is comparable with the bigger devices of same type. The modeling results of plasma focus are also compared with experimental results to give a broader picture of the device.