Fast Marx Generator Research Articles

A trigger source for linear transformer driver

A repetitive low jitter trigger source applied in triggering the multi-gap gas switch of the linear transformer driver (LTD) stage, is designed and developed in this paper.The pulse source based on fast Marx topology can repetitively output a low jitter high voltage pulse into a 50 Ω resistance load with peak value of 150 kV, rising time of 7 ns, width of 260 ns and rep-rate 0.1 Hz. Proper design of stray capacitance to peak the output pulse and employing the UV light to pre-ionize each consequent stage gap to reduce the switch delay time and jitter have been proposed. All those have been demonstrated feasible and reliable. A software program control unit has been developed for operation and control of fast Marx generator. The software gives full remote control by a computer via optical fiber communication. The experimental results show that the trigger source can continuously and reliably generate a 150 kV/260 ns pulse into a resistive load every 10 s with 1-σ jitter less than 2.7 ns. The trigger source is compact and portable and agrees well with the trigger demands of LTD for new fusion energy.

Modeling and system improvements for a fast rise time Marx generator

This paper discusses the modeling of fast Marx generators particularly with reference to improve the performance in terms of output current pulse characteristics, namely peak current, rise time and full width half maximum (FWHM) duration. As the inductance of the circuit critically influences the characteristics of the output current pulse, possible reduction in inductance of the Marx by bringing the current return path closer to the Marx generator and other practical issues, particularly the need of electrical insulation, are discussed. Characterization of the Marx capacitors & optimization of the Marx generator have been studied.

Development of a Fast Marx Generator for High Power Ultra Wideband Pulse Radiation

We present in this paper the design and realisation of two autonomous, ultra wideband radiation sourcesconsisting of a high gain broadband antenna driven by two subnanosecond pulsed power sources. Each one ismade of a Marx generator and a pulse forming device based on the use of gaseous spark gap. The main pulsedsource is a ten stage subnanosecond Marx generator which delivers pulses in the range of 250 kV/1.5 J, with a300 ps rise time, subnanosecond pulse duration at a pulse repetition frequency of 350 Hz. The antenna combinedwith the pulsed source is a travelling wave antenna called Valentine antenna. Some mechanical modiflcations weremade to improve the dielectric strength of this radiation element. A 3D model of the antenna, on a time domainelectromagnetic software, was flrst performed to study the in°uence of these modiflcations on the main radiatingcharacteristics of the antenna. Its high gain and its capability to radiate short pulses without dispersion allow usto achieve a high measured flgure of merit.PACS numbers: 84.70.+p, 07.57.Hm, 84.30.Ng

Fast discharge energy storage development for advanced X-ray simulators

Design studies have been completed to investigate the impact of improvements in fast energy storage systems on the designs of: larger future simulators (such as a 15-MA plasma radiation source (PRS) simulator), simulator upgrades of operational machines (such as Double-EAGLE), and for very compact, smaller simulators. The fast energy storage system that has been investigated and is presently under development is a fast Marx generator (FMG) with inductance capacitance (LC) 1/2=200 ns and LC 1/2=300 ns, depending on the capacitance per stage. This new fast Marx energy storage system uses newly developed, low-inductance rail switches and low-inductance capacitors. These components are configured in a low-inductance FMG stage and then stacked in series to form a unit for the voltage required and a number of units in parallel for the required system inductance and stored energy. A four-stage fast Marx prototype has been demonstrated with a total of 60-kJ energy stored and an output voltage of 680 kV. This new FMG technology will provide the capability to build X-ray machines in a significantly more compact configuration. The new FMG technology minimizes or eliminates the need for storing the energy in a large water transfer capacitor. A design sketch of a 15-MA PRS machine driven by a fast Marx will be presented. This generator would consist of 48 eight-stage FMG units and would drive the PRS directly without further pulse compression. We will also present the concept of a high voltage (2-3 MV), compact X-ray machine that uses a nine-stage fast Marx module to directly charge a vacuum inductive store. A plasma opening switch (POS) is used to switch the inductive store and deliver the electron beam to the load.

An Observation of Energetic Electron Beams in Low-Pressure Linear Discharges

Experimental observations of energetic axial electron beams in a linear Z pinch operating in the pseudospark mode are presented. The device is driven from a fast Marx generator and allows reproducible production of electron beams over a wide pressure range. Evidence of the importance of electrons generated in the cathode recess in the formation of the beams is presented. An electron beam of high energy which is not associated with formation of the discharge is identified. A second beam of high current density and lower energy associated with gas breakdown is also observed.

Overvoltage and Breakdown Patterns of Fast Marx Generators

Spark gap overvoltages of fast Marx generators in the 100-300 kv range were studied as a function of stray and interstage capacitance for several circuit designs. Overvoltage measurements were made at low voltages by simulating the spark with a silicon-controlled rectifier. Breakdown times were measured to nanoseconds by viewing the light flash from the sparks with a fast photomultiplier. The influence of the ultraviolet irradiation on breakdown time was studied by masking the first gap. Practical conclusions for Marx generator design are presented.