Showing papers on "Marx generator published in 1998"

Portable hard x-ray source for nondestructive testing and medical imaging

Abstract: A portable hard x-ray source has been developed for nondestructive testing, medical imaging, and flash x-ray radiography. The source is powered by a Marx generator that produces a 200 kV, 1.2 kA pulse of 60 ns full width at half maximum. The x-ray tube is composed of a tungsten anode and a mesh cathode. The time dependence of the voltage, current, and x-ray emission were measured and were in good agreement with computer simulations. The simulation model accounted for the 15 capacitors and 15 spark gap switches of the Marx generator and the perveance of the electron flow across the anode–cathode gap. The simulations indicated that the 5 J energy that was stored in the Marx generator was efficiently delivered to the x-ray tube. The measured x-ray exposure, 34 mR at a distance of 30 cm, was in good agreement with the calculated exposure. X-ray images are presented that demonstrate the capabilities of the x-ray source for medical imaging, nondestructive testing, and flash x-ray radiography.

The principle of operation of the avalanche transistor-based Marx bank circuit: A new perspective.

Abstract: The principle of operation of the transistor-based Marx bank circuit has been examined. It was experimentally observed that stage-wise increase of reverse voltage does not occur. This cannot be explained by the principle of operation understood so far. A new explanation, consistent with the experimental observations and associating current-mode second breakdown of transistors, is proposed. A few experimental observations made by earlier workers have also been justified in light of the new current-controlled mechanism.

Comparison of computed and measured parameters of a driver for fast capillary discharge

Abstract: The authors were attracted by numerous applications of coherent soft X-rays and decided to build a fast capillary discharge, despite it is generally understood as a relatively sophisticated apparatus. From the beginning they paid great attention to its design: they performed a lot of modelling and optimisation. The present paper aims at comparison of the designed (computed) parameters with the measured value.

Capacitor mounting arrangement for marx generators

Abstract: A mobile X-ray machine includes an improved Marx generator. The capacitorssed in the Marx generator are disc capacitors each having opposed side surfaces having electrodes formed thereon and each including a insulative coating provided on the peripheral edge thereof. The capacitors are mounted in slots in a support structure and are supported by spring contact members located within the slots. The spring contact members include spring arms which engage the electrodes on the opposed side surfaces of the associated capacitor. The spring contact members also include support elements from which are suspended the spherical electrodes of spark-gap switches individually associated with each of the capacitors.

Development of high energy induction accelerator, "ETIGO-III"

Abstract: A new induction accelerator "ETIGO-III" has been developed to generate high current relativistic electron beam for applications in materials science, high-power microwave generation and intense X-ray generation. Using the Marx generator of "ETIGO-I", we have produced the initial pulse of 670 kV (60 ns pulse width). Through the four transmission lines, the pulse was fed to four induction cells. Three cores are installed inside each cell. The output voltage of 2 MV was obtained by the initial cell. Specifically, it is possible to obtain the final output parameters of 8 MeV, 5 kA 60 ns. Various diagnostics have been carried out on the characteristics of the electron beam generated by "ETIGO-III".

Development of a high voltage, high PRF PFN Marx generator

Abstract: A PFN Marx generator which has been designed for repetitive operation is described. The device is nominally capable of generating an output voltage of 1 MV into a matched load at a pulse repetition frequency (PRF) of several hundred Hz. The output voltage pulse is rectangular in profile with a duration of 450 ns and a risetime of 40 ns. There are twenty stages in the generator, with each stage comprising 50 m of HVDC 50 /spl Omega/ co-axial transmission line. This results in an overall output impedance of 1 k/spl Omega/ and a stored energy of 500 J at a charging voltage of 100 kV. The generator is operated in repetitive mode using a resonant charging inductor/diode, an in-line triggered charge transfer switch and an intermediate capacitor store.

Four-stage Marx generator using thyristors

Abstract: A small-scale capacitor discharge pulse generator using thyristors in a Marx configuration is described. The four-stage generator is actively triggered in a sequential manner. The application considered is in the firing circuit of a larger switch where the generator is shown to be capable of producing pulses rising to 230 A in less than 1.5 μs from an equivalent open-circuit voltage of 2.3 kV.

Study of repetitive plasma opening switch generator technology

Abstract: Repetitive plasma opening switch (POS) research for X-ray and electron beam generators for commercial applications is reviewed. This research was started on the RS-20 generator in 1991 with submicrosecond conduction times, 100 kA currents, and MV voltages. In the experiments wall-plug to electron beam production efficiency was increased from 10-50%. Maximum voltage obtained at POS was 3 MV starting from 0.8 MV at the Marx generator. POS operation was improved using an applied external magnetic field for the opening phase. Diode current and total generator efficiency were increased by combining the POS and diode system in one technology unit. For the opening phase of the high-impedance, repetitive POS, a set of conditions based on early POS experiments in the Kurchatov Institute were proposed. Repetitive POS generators have obtained peak X-ray dose rates of 1 MGy/s and electron dose rates of 10 GGy/s. This may be important for applications as pulsed irradiation may cause more efficient sterilization at lower doses. An X-ray generator based on repetitive POS technology at 5 MV and 200 kW in the electron beam is proposed.

High brightness electron beam injector for the DARHT facility

Abstract: An injector for the second axis of the Dual-Axis Radiographic Hydrotest Facility (DARHT) is been built at LBNL. The proposed injector consists of a single gap diode extracting 4 kAmps, 3 MV electrons from a thermionic dispenser cathode and powered through a high voltage ceramic insulator column by a Marx generator. The key issues in the design are the control of beam quality to meet the DARHT 2nd axis final focus requirements and to minimize high-voltage breakdown risks. We present the conceptual design of the injector as well as preliminary results on a scaled experiment and breakdown tests in vacuum using the Berkeley RTA facility.