Marx generator

About: Marx generator is a research topic. Over the lifetime, 1276 publications have been published within this topic receiving 8970 citations.

Simulation of semiconductor opening switch physics

Abstract: Summary form only given. Semiconductor opening switches (SOS) are able to interrupt currents at density levels of up to 10 kA/cm2 in less than 10 ns. If stacked, SOS diodes can hold off voltage levels above a few 100 kV. They are therefore ideal for the design of compact high voltage pulse generators of the GW-class for industrial applications. The aim of this work was to improve our understanding of the opening process in a semiconductor diode of SOS-type with a doping profile of p+pnn+ structure. To simulate the physical processes inside this diode the code POSEOSS was developed. It contains a detailed physical model of charge carrier transport under the influence of density gradients and electric fields and considers all relevant generation and recombination processes. It possess a large degree of flexibility and allows to carry out parameter studies to determine the influence of different physical quantities, like doping and impurity levels. Applying the code, using realistic values for the charge carrier mobility, it was found that the opening process starts first at the n-n+ boundary, in contradiction to results published by other authors. Based on the simulation results a simplified SOS equivalent circuit model has been developed which can be used in the circuit simulation program PSpice. A new pulse generator scheme based on inductive stores is proposed, in which power multiplication is achieved by unloading the inductors, previously charged in series, in parallel. This scheme can be considered as the inductive equivalent of a Marx generator. We present Pspice simulations of such a scheme based on semiconductor opening switches. The theoretical results were compared to measurements obtained with a simple experimental set-up using two 100 kV SOS-switches. The measurements showed good agreement with the simulation results. Further improvements seem possible by adapting the SOS device structure to the specific generator circuit.

CST Particle-In-Cell Modeling Of A Tunable Reflex-Triode Vircator

Abstract: This study serves to describe three-dimensional particle-in-cell (PIC) simulations of a tunable reflex-triode virtual cathode oscillator (vircator). Experimental data from the compact hard-tube reflex-triode vircator developed at Texas Tech University (TTU) is used to validate simulated results. The vircator developed at TTU is capable of burst-mode operation at pulse repetition rates (PRFs) up to 100 Hz for a period of one second. A pulse energy of 158 J drives the vircator, and 600 kV (open circuit) pulse forming network (PFN) based Marx generator. The vircator is comprised of a bimodal, carbon fiber cathode and a pyrolytic graphite anode, with the ability to quickly change the distance between the anode-cathode (A-K) gap, back wall distance, and bottom plate distance between experiments. The PIC simulations have been performed using CST PIC Solver, by Dassault Systemes. The models detail virtual cathode formation and the subsequent extraction of radiated microwave power for a variety of cavity geometries. A working three-dimensional, relativistic, electromagnetic, particle-in-cell model of a vircator allows for quick, pre dictive results relative to building an experimental setup. The model is used to determine the necessary driving voltages, A-K gap distances, and cathode current densities to extract microwave radiation at a desired. Simulated results aid in identifying mode contributions. Voltage, current, and microwave data are presented and compared against experimental results at different operating conditions.

Rail-gap switch with a multistep high-voltage triggering system.

Abstract: A rail-gap switch with a multistep triggering system was developed. The rail-gap switch consisted of two rail-like electrodes and a knife-edge electrode parallel to each other. It was assembled from many pieces and filled with unpressurized-flowing dry air. Good alignments between all electrodes were achieved by using a special jig and the knife-edge electrode as the spatial reference. Furthermore, to trigger the rail-gap switch, a multistep triggering system was used. The triggering system consisted of three components: an optical trigger-pulse generator, a slow high-voltage trigger-pulse generator using an ignition coil for a car, and finally, a fast high-voltage trigger-pulse generator using a three-stage Marx generator. The triggering system generated a negative high-voltage trigger pulse of less than -40 kV with a falling speed of -6.6 ± 0.4 kV/ns. The falling speed was fast enough to initiate multichannel discharges in the rail-gap switch. Finally, the rail-gap switch was tested using a test bench consisting of a 0.5-μF capacitor bank charged to 20 kV. The rail-gap switch was triggered by the multistep triggering system robustly with a delay of 180 ns. The delay between the time, when the peak current of the test bench occurred, and the trigger pulse was 890 ns with a jitter of 20 ns, i.e., ∼2% uncertainty in time. The inductance of the rail-gap switch was ∼80 nH obtained from the discharge tests. The rail-gap switch with the multistep high-voltage triggering system is suitable for any pulsed-power systems with current rise times in the order of 1 µs.

PIM: Pre-Pulse Minimisation and Considerations

Abstract: In 2002, an inductive voltage adder (IVA) machine called PIM (prototype IVA module) was commissioned, which had been designed and built at AWE. Originally its purpose was to assist the development of a multi-module X-ray machine for high-energy radiography but more recently it has been adapted for 1-3 MV single-module applications, the PIM machine consists of two inductive cavities (or cells) pulsed in parallel by a water dielectric Blumlein, pulse forming line (PFL), of impedance 10Ω, which is charged by a Marx generator consisting of 32 capacitors each of value 1.35 μF. The design incorporates a pre-pulse reduction system comprising a gas switch at the output end of the PFL and a 6 μF inductor which connects the inner Blumlein conductor to ground. The purpose of the gas switch is to isolate the inner Blumlein conductor from the induction cavities and e-beam diode during the charging phase. A fast output pulse from the Blumlein splits and appears across a Perspex-insulated accelerating gap in each cell. The inductively-isolated voltages add along a short vacuum transmission line and are applied to an e-beam diode. Additional inductive and resistive components were installed in the Marx generator, allowing the Blumlein charging rate to be varied and different electrical configurations to be investigated. Electrical modelling has been performed to determine the scope in the Marx characteristics based on the permissible range of output pre-pulse voltage from the Blumlein. This paper presents results which show that the pre-pulse can be kept within acceptable levels by suitable choice of electrical components in the Marx but that unacceptable levels arise if the choice is inappropriate.

A High Energetic Flashlamp-Pumped Dye Laser With a 4-Stage Marx-Bank Driver

Abstract: Since dye lasers are very widely tunable from near ultra-violet to near infrared, so that it had been used in high resolution spectroscopy and many other applications. A linear flashlamppumped dye laser is very useful for its low cost and high output power or high energy, as well as a good beam quality and sharp tunability. However, several flashlamps are required for excitation in order to obtain an output energy over several joules. We have achieved a dye laser output of 18 J with a single flashlamp, by employing a multi-stage Marx-bank driver and optimizing the output mirror reflectivity as well as by choosing appropiate dye cell size and the dye concentration.