Showing papers on "Marx generator published in 2004"

Solid state Marx generator using series-connected IGBTs

Abstract: Pulsed power supplies using solid state switches have been widely studied recently. Use of high power semiconductors such as IGBTs and IGCTs have become an area of interest today. To make this, several type of pulse generators using solid state devices have been adopted and tested in many papers. In this paper, a boost converter array using series-connected switches is presented. The electrical circuit is made of a boost converter array to produce high voltage pulses. To verify the proposed converter, an experimental equipment with a 20 kV, 300 A pulse generator was made and food treatment results are shown.

Investigation of a multichanneling, multigap Marx bank switch

Abstract: There is increasing interest in the pulsed power community for understanding the complex phenomena of multichannel spark gap switches. Extracting the potential advantages of these switches is necessary for upgrades to large, high current, high voltage machines. A previously designed, multichanneling spark gap (MCSG), with toroidal electrodes, for Marx bank applications, is investigated to determine which factors effect its multichannel operation. To date, thorough research does not exist for multichanneling gas switches with toroidal electrode geometry. The following results are the first of their kind. Gas type, gas pressure, trigger voltage, and trigger polarity are varied to study their effects on multichanneling in the MCSG. The fill gas is varied between air and an Ar/SF6 (90%/10%) mixture, from 3 to 10 psig. There are more channels for the mixture than for air for similar pressures. Trigger voltage amplitude and polarity are varied negatively from −60 to −100 kV and positively from +75 to +95 kV. Tr...

Solid-state Marx bank modulator for the next linear collider

Abstract: In this paper, we will discuss the design of a solid-state Marx bank modulator (Figure 1) for the NLC, which will deliver 150 ns risetime (10-90%) for a 500 kV, 530 A pulse (for two klystrons), with efficiency over 90%. The use of a common mode inductive charging system allows transfer of filament power without separate isolation transformers. The combination of these features supports future compact, inexpensive, very high voltage pulsed power systems

Prototype development progress toward a 500 kV solid state Marx modulator

Abstract: Recent advances in IGBT and SiC technology have made possible a range of solid-state modulator concepts that were unthinkable a decade ago. Power densities and speeds of pulsed-power circuits have increased dramatically due to the commercial introduction of fast, multikilovolt IGBT silicon and SiC diodes featured in PCB-style packages. A solid-state modulator concept that stands to benefit considerably from recent IGBT and SiC breakthroughs is the Marx configuration-where an array of stacked modules generates high-voltage output pulses directly from a low voltage DC supply. The Marx scheme avoids the large, inefficient and costly magnetic cores inherent in standard modulator designs, resulting in a considerably simpler, cheaper and more compact mechanical solution. The main disadvantage to this approach is that the individual cells in a Marx bank must float at high voltages during the pulse, complicating the distribution of power and timing signals. This paper examines in closer detail the practical advantages and pitfalls of a solid-state Marx configuration, and explores a design approach with emphasis on performance, wall-plug efficiency, cost of manufacture, availability and ease of service. The paper presents electrical diagrams, mechanical CAD layout and preliminary prototype test data.

Design of a laser-triggered driver for fast capillary discharge

Abstract: We are developing a new upgraded capillary discharge device. The assembled set-up consists of a Marx generator, a pulse forming line, a gas-filled laser-triggered spark gap and a ceramic capillary. The special attention has been paid to the design of the spark gap. The laser triggering of this spark gap ensures a very low jitter in comparison with the present capillary discharge device CAPEX, where the main spark gap works in a self-breakdown regime. The description of the assembled apparatus, the main predicted parameters of the designed device (such as capillary current, capillary current rise-rte, and/or voltage at the end of pulse forming line) are presented.

A compact MV Marx generator

Abstract: A compact MV Marx generator is presented. The generator employs a modular geometry designed for decreased volume, enhanced performance ease of maintenance. The generator is very well suited for the direct generation of narrow band and ultra wide band energy, as a high voltage trigger generator or as a flash X-ray source. The characteristics of the generator are discussed

Nanosecond Marx pulsed generator with semiconductor switches

Abstract: The concept of Marx high voltage pulse generator with semiconductor switches is considered in the paper. Use of semiconductor switches in Marx generator allows increasing the efficiency of the generator and extending the range of output voltage adjustment. The primary results of tests of the 100 kV pulse generator are presented as well as the prospective of short coming 1 MV pulse generator. The potential applications for high voltage generators are discussed.

Marx generator GIN-1000 with 1 MV output voltage and 80 kJ energy stored

Abstract: The results of development and study of Marx generator with output voltage of 1 MV and stored energy of 80 kJ are reported. The measured value of generator inductance is ~ 1.3 μH, the measured effective ohmic resistance ~ 1 Ohm.

High current fast Marx generator and vircator experiments

Abstract: This paper describes a compact pulsed power generator. This system stores 10 kJ and is capable of delivering up to 40 GW to an electron diode. It has been optimized to drive high power microwaves devices that require high current. In order to limit the parasitic inductance and to reduce the rise time of the current to less than 100 ns, two Marx generators have been associated in parallel. Some typical results of vircator operation in S band are also presented.

Upgrade of a 350 kV NEMP HPD pulser to 1.2 MV

Abstract: This paper will describe the upgrade of the 350 kV NEMP HPD pulse generator of the WIS in Munster, Germany to an output voltage of 1.2 MV by using a commercially available 1.2 MV Marx generator. The results of a PSpice investigation of the influence of the peaker capacitance and the line inductance on the pulse rise time, amplitude and width will be presented. The design, production and testing of the HV elements as feed through, pulse line and peaking capacitor under the restrictions of a short isolation distance and a high voltage will be discussed. The paper will conclude with a presentation of the measured electrical field parameters such as rise time, field strength, reproducibility etc. reached after the integration of the modified pulse generator into the existing dipole hybrid antenna construction in Munster

Experimental optimization of a Reflex Triode Virtual Cathode Oscillator

Abstract: Experimental findings on a high power Reflex Triode Virtual Cathode Oscillator (Vircator) at Texas Tech University are reported. In order to optimize performance, changes to the AK gap distance were made. The AK gap was varied from 0.5 to 1.5 cm. The type of cathode material employed was velvet. Cathode radius was 2.5 cm. The Reflex Triode Vircator is driven by a 350 kV Marx generator with a 60 ns, 20 ohm pulsed forming line. Typical peak input power is 4 GW. The output microwave power is measured in the far-field with a waveguide to coax adapter. Thus far we have observed microwave peak power output as high as 330 MW corresponding to a peak power efficiency of ~ 11 %. In an effort to provide premodulation to the vircator region, reflecting strips were added in the downstream waveguide. This technique has been employed with success by this group with a coaxial Vircator.

Pulsed power - principles and applications

Abstract: Pulsed power originated with the invention of the Marx bank in the early 1920s, enabling the simulation of lightning strikes and switching operations on power system components. Between the 1960s and the beginning of the twenty-first century, the demands of high energy pulsed power applications have stretched Marx bank techniques enormously. Refinements of triggering and switching techniques, and control and exploitation of the stray capacitances in the systems, enable 100-200 ns rise times to MV levels and above with MJ of energy being stored and delivered. The requirements of exotic radiographic, e-beam and plasma pinch loads have demanded the use of pulse forming networks or lines interposed between the Marx and the load to provide the requisite pulse shaping and power levels. Meanwhile the rise time capability of low energy Marxes has been reduced to nanosecond levels as a result of developments in capacitor and switching technologies. The latest direction is now for the development of ultrafast high energy Marxes with adequately low inductance for direct feed of compact e-beam loads.Pulsed power has principally developed in response to high energy physics and weapons programme requirements; plasma drivers, x-ray drivers, magnetron drivers, laser drivers, ion beam steering and acceleration. However, the industrial application of pulsed power is increasing.

Spontaneous pulse width limitation in S-band two-sectional vircator

Abstract: The paper presents a review of continuing studies on production of S-band microwave pulses in a two-sectional single-mode vircator [1, 2] based on long-pulse (sub-microsecond) high-voltage generators. The two pulsers were used (a) generator with inductive energy store and fuse opening switch and (b) generator based on Marx bank and water forming line. The peak microwave output was on the range of ~1 GW. Substantial spontaneous shortening of the microwave pulse was observed (50-100 ns). Possible mechanisms for this phenomenon are discussed and supported by 3-D KARAT simulations.

ZR Marx capacitor lifetime test results

Abstract: The ZR upgrade to the Z machine at Sandia National Labs (SNL) has a total output current requirement of at least 26 MA for a 100-ns standard z-pinch load. To accomplish this with minimal impact on the surrounding hardware, the existing Marx generator capacitors must be replaced with identical size units with twice the capacitance. Before the 2005 six-month shut down and transition from Z to ZR occurs, 2500 of these capacitors will be delivered. This paper summarizes the results of our lifetime testing of the selected General Atomics P/N 32896. 11/spl times/14/spl times/25-inch, Scyllac-style insulator bushing, 2.65-/spl mu/F, 100-kV, 30-nH, 35% reversal capacitor. We have completed lifetime tests with twelve capacitors at 100 kV and with fourteen capacitors at 110-kV charge voltage. The means of the fitted Weibull distributions for these two cases are about 17,000 and 10,000 shots, respectively. As a result of this effort plus the rigorous vendor testing prior to shipping, we are confident in the high reliability of these capacitors and have acquired information pertaining to their lifetime dependence on the operating voltage. One result of the analysis is that for these capacitors lifetime scales inversely with voltage to the 6.28/spl plusmn/0.9 power, over this 100 to 110-kV voltage range. Accepting the assumptions leading to this outcome allows us to predict the overall ZR system Marx generator reliability at the expected lower operating voltages of about 85 to 90 kV.

Trigger / ignition device in a Marx generator provided with N step capacitors

Abstract: The invention relates to a trigger / ignition device in a Marx generator provided with n step capacitors, wherein n is a natural number higher than 1 of switches / spark-gaps and 2(n-1) charging branches, said switches / spark-gaps operating in a self-charging mode. The inventive trigger / ignition device is provided with at least one pulse transmitter connected to a pulse generator. An overvoltage is generated in a chronological matter and for short term on an adjacent spark gap in at least one charging branch of the Marx generator, said overvoltage being sufficient for one self-charging. The charging branch short-circuits the spark gap by means of an associated step capacitor arranged on the output side. The output winding of the pulse transmitter operates during charging in a charging coil / inductance mode and is connected to the pulse generator. Voltage pulse generated by the pulse transmitter during igniting / triggering of the pulse generator is added to a charging voltage of the associated step capacitor, thereby producing a short-term overvoltage required for the spark gap self-discharging.

Electron gun for powerful large orbit gyrotron

Abstract: One of the most important tasks in high power electronics is the development of RF sources in the submillimeter wavelength region. One of the most promising sources is the large orbit gyrotron (LOG). But the efficiency of LOGs is rather small - usually a few percent only. So, to obtain a high enough value of the output power, it is necessary to use a powerful electron beam as the RF radiation energy source. Recently in the Nagaoka Institute of Technology, a Marx generator with accelerating voltage U/sub o/ of about 400 kV was developed. The combination of such a power supply with a pulse magnet providing an operating magnetic field of 12 T opens the possibility of a LOG to reach the border of the Terahertz frequency range with output power above 1-2 MW. This paper presents a project designing an electron beam formation system with the mentioned power supply. The operation of a LOG at third to fifth cyclotron harmonics is also discussed.

A laser-triggered driver for fast capillary discharge device

Abstract: We are developing a new upgraded capillary discharge device. The assembled set-up consists of a Marx generator, a pulse forming line, a gas-filled laser-triggered spark gap and a ceramic capillary. Special attention has been paid to the design of the spark gap. The laser triggering of this spark gap ensures a very low jitter in comparison with the present capillary discharge device CAPEX, where the main spark gap works in a self-breakdown regime. The description of the assembled apparatus, the main predicted parameters of the designed device (such as capillary current, capillary current rise-rate, and voltage at the end of pulse forming line) are presented

Solid-state Marx modulator development

Abstract: A solid-state Marx modulator is under development to supply regulated voltage and current to a high-power magnetron. A primary goal of this design is for the modulator to have low volume and low weight. The modulator is required to provide 5-/spl mu/s-wide rectangular pulses of approximately 45 kV and 145 A at a repetition frequency of 120 Hz. The Marx is composed of 12 circuit boards, with 4 IGBT switched Marx stages per board, for a total of 48 stages. The IGBT Marx switches can be closed and then opened at full-load current, allowing the production of a rectangular pulse from a Marx generator. Single boards and three-board stacks have been tested into a resistive load at operational voltages and currents. Results of the resistive load test are shown.

Versatile test environment for compact pulsed power system evaluation

Abstract: This paper describes our efforts to develop a test environment that accurately approximates elements of several battery-driven compact Marx generator (CMG) systems currently in use, but which avoids the high-voltage and electromagnetic interference (EMI) issues of operating the actual CMG's. A triggering circuit, lumped capacitance, and load resistor housed in a cart filled with SF6 provide the necessary elements to represent the CMG. Two 20 kW AC-DC supplies were used to substitute for battery packs and furnished the medium voltage (hundreds of volts) required to drive the high voltage (HV) capacitor charging power supplies (CCPS). The prime motivation of this work is to explore rep-rate operation at tens of Hz and provide guidance for optimizing HV power supply settings and battery design. The test stand provides a unique testing environment for several applications. We report verification of the test bed operation using a well understood configuration of power supplies with well documented control and trigger systems. The performance of a series/parallel combination of multiple HV power supplies for rep. rate operation is also examined. Battery pack voltage droop effects on HV power supply calibration are described. We then discuss use of the test bed to explore the operating characteristics of a novel 100 kV (plusmn50 kV) capacitor charging power supply recently developed by North Star Research, Corp. (NSRC)

Intense nanosecond duration source of x rays for resolving cavitation-induced trauma in human tissue

Abstract: A pulsed nanosecond x-ray generator based on an actively pumped field emission x-ray tube is described. The x-ray source is based on a high voltage Marx generator that drives a field emission tube without the need for an intermediate energy store. The Marx generator stores 12 Joules in ceramic capacitors and produces a voltage pulse > 380 kilovolts with a rise time of < 4 nanoseconds from an equivalent generator-impedance of 52 W. A numerical model is used in which the x-ray tube's cathode width and anode-cathode gap (AK) are permitted to change with time while electron current between the cathode and anode is treated as non relativistic and space-charge-limited (SCL). By coupling this model to an equivalent circuit representation of the Marx generator a calculation of the cathode current, anode-cathode potential and the output x-ray spectrum can be made. The radiation dose is 55 millirems at 30.4 cm from the anode of the x-ray tube and is Gaussian in shape with a 35 nanosecond (full width at half maximum) FWHM. The measured x-ray dose, pulse shape and width are consistent with model predictions. The source was successfully used to study high-velocity projectile induced cavatation in human tissue.

Feedback stabilized pseudospark switch for fast rise marx generator application

Abstract: Design and operation of a compact floating housekeeping system for pseudospark switches in high-voltage multiswitch applications is presented. The system provides isolated power to the pseudospark reservoir heater, the keep-alive gas discharge and the high-voltage trigger pulse generator. The floating HV trigger pulse generator receives its external trigger command signal via an optical fiber. The keep-alive discharge current, representing the gas pressure in the pseudospark switch, is monitored via an optical fiber as well. Pseudospark switch operation in Marx generator applications depends on the precise adjustability of the trigger to main discharge delay. This delay, in turn, is a strong function of the gas pressure inside the switch. A feedback circuit, adjusting the heater current in response to change in the keep-alive current, stabilizes the pressure. Class-E high frequency power amplifiers provide the electric power for the floating assembly through ferrite core transformers that have 40 kV insulated secondary windings

Marx generator using dense plasma switches

Abstract: Summary form only given. The design and preliminary operation of a Marx style pulse generator using advanced dense plasma switches (Pseudospark) are presented. The bank consists of three 150 nF/40 kV capacitors connected with three floating plasma switches. These switches can hold off 35 kV and pass up to 10 kA at repetition rates approaching 1 kHz. The expected lifetime of >200 kC and the relatively low housekeeping power of <50 W make the dense plasma switch an excellent candidate in compact Marx generator applications. In the Marx bank application the important issues to be resolved are the stability and reproducibility of delay and jitter among all the switches and the practicality of a highly efficient, compact floating power supplied to each switch. These are interrelated issues, as the delay is a strong function of the trigger pulse shape and amplitude as well as of the exact gas pressure inside the switches. Thus, the main design and implementation problem lies in the floating housekeeping power units of each switch.

Research on pinches driven by SPPED 2 generator : hard X-ray and neutron emission in plasma focus configuration

Abstract: SPEED2 is a generator based on Marx technology and was designed in the University of Dusseldorf. SPEED2 consists on 40 +/- Marx modules connected in parallel (4.1 mF equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt~1013 A/s). Currently the SPEED2 is operating at the Comision Chilena de Energia Nuclear, CCHEN, Chile, being the most powerful and energetic device for dense transient plasma in the Southern Hemisphere. Most of the previous works developed in SPEED2 at Dusseldorf were done in a plasma focus configuration for soft X-ray emission and the neutron emission from SPEED2 was not completely studied. The research program at CCHEN considers experiments in different pinch configurations (plasma focus, gas puffed plasma focus, gas embedded Z-pinch, wire arrays) at current of hundred of kiloamperes to mega-amperes, using the SPEED2 generator. The Chilean operation has begun implementing and developing diagnostics in a conventional plasma focus configuration operating in deuterium in order to characterize the neutron emission and the hard X-ray production. Silver activation counters, plastics CR39 and scintillator-photomultiplier detectors are used to characterize the neutron emission. Images of metallic plates with different thickness are obtained on commercial radiographic film, Agfa Curix ST-G2, in order to characterize an effective energy of the hard X-ray outside of the discharge .

Method for the computer-assisted process control of a fragmentation system

Abstract: Disclosed is a fragmentation system comprising a Marx generator and two electrodes which are connected thereto and the tips of which are placed at an adjustable distance from each other. Said fragmentation system is used for electrodynamically fragmenting fracture-like, solid material, wherefore the entire intermediate space between the electrodes is located in a processing liquid. A discharge channel is created in the intermediate space between the electrodes when the spark gap of the Marx generator breaks down. The point in time TD when such a fully distinct discharge channel has been created and the electric resistance RE of said discharge channel make up the two variables RE, TD for controlling the fragmentation system.