Showing papers on "Marx generator published in 2017"

Design of a 6-MW Solid-State Pulse Modulator Using Marx Generator for the Medical Linac

Abstract: The linear accelerators (linacs) producing high energy and high power of electron-beam or X-ray beam have been used in medicine, industry, national security, etc. In the linac, the electrons are generated by the electron gun and accelerated in the accelerating column with the high-power RF fields. The high-voltage pulses from the pulse modulator are supplied to the RF power source and the electron gun. The pulse modulator is one of the big and expensive components in the linac. The commercial medical linacs commonly use the pulse modulator based on the thyratron-switched pulse-forming network. In order to improve the power efficiency, achieve the system compactness, and optimize the cost and space, the solid-state pulse modulator based on the Marx generator was proposed. The low-power solid-state pulse modulator was developed for the electron gun operation. The conceptual design and functional results were confirmed. In order to apply it to the RF power source, such as a magnetron or a klystron, the 6-MW pulse modulator with the same Marx scheme is proposed. It consists of 40 storageswitch stages and one high-voltage pulse transformer, producing the pulse of 50 kV and 120 A required by the magnetron in the medical linac. A storage-switch stage was designed for insulated gate bipolar transistors to switch high current of 280 A and 720 V and to use the capacitor of 25 μF which was chosen for the voltage droop of 10% with the pulsewidth of 5 μs. The prototype system with eight storage-switch stages was fabricated and tested with a load system. The performance results show that it can be extended to be the 6-MW solid-state pulse modulator. In this paper, we describe the design features, and discuss the results and also the future plan to optimize the solid-state pulse modulator in the medical linac.

Modified High-Power Nanosecond Marx Generator Prevents Destructive Current Filamentation

Abstract: A traditional Marx circuit (TMC) based on avalanche transistors with a shortened emitter and a base was investigated numerically by using a two-dimensional (2-D) physics-based approach and experimentally, and compared with a special Marx circuit (SMC) suggested here, in which an intrinsic base triggering of all the stages protects the transistors, especially the second one, from thermal destruction due to current filamentation. This is because the entire emitter–base perimeter in the SMC participates in switching, whereas in a TMC the switching is initiated across the entire area of the emitter but then changes to current filamentation due to certain 3-D transient effects reported earlier. Very significant difference in local transient overheating in the transistors operating in TMC and SMC determines the difference in reliability of those two pulse generators. The results suggest a new circuit design for improving reliability and explain the difference in the operating mode of different transistors in the chain which makes the second transistor most prone to destructive thermal filamentation. This new understanding points additionally to ways of optimizing the design of the transistors to be used in a Marx circuit.

Performance Analysis of an All Solid-State Linear Transformer Driver

Abstract: The performance of an all solid-state linear transformer driver (LTD) is evaluated based on experimentally verified behavior of a single stage. The single-stage LTD utilizes a low-profile design with robust thyristor switches and high-energy-density mica capacitors to minimize overall system inductance. Subnanosecond jitter is achieved with simultaneous thyristor triggering. The stage is magnetically coupled to a secondary winding through a central nanocrystalline core. A dc current source, decoupled with a large inductance, actively resets the core between pulses. The overall result is a low-impedance ( $ per stage) pulse generator that rivals the performance of traditional Marx systems with the improved reliability, increased lifetime, and fast rep-rate capabilities of solid-state switches. The stage is tested with charging voltages up to 8 kV into various loads and compared with simulations based on an analog behavioral thyristor switch model previously developed at Texas Tech University. The simulation is expanded into a full-scale, multistage LTD simulation and compared with a previously constructed Marx generator.

New Marx Generator Architecture With a Controllable Output Based on IGBTs

Abstract: In this paper, a new architecture of a high-voltage Marx pulse generator based on isolated gate bipolar transistors (IGBTs) is proposed. It allows continuous control of the output voltage by acting on the IGBTs activation time: “on-time.” The final after-charging capacitors’ voltage can be higher than the double of the input voltage. A simplified mathematical description of the system was developed in order to find a relation between the output voltage and the “On-time” (an open-loop control law). A SPICE simulation was implemented to check the expected performances and to verify the developed model. A three-stage generator was built according to the proposed structure using commercial IGBTs with a maximum output voltage of 3.6 kV. All results were compared to check and confirm the validity of the proposed architecture.

A device for combined thermal and pulsed electric field treatment of food

Abstract: The application of pulsed electric fields to biological tissue enables both ohmic heating of the material and a permeabilisation of the biological cells at ambient temperature due to electroporation. To what extend each of both mechanisms is effective can be controlled via the applied electric field strength and duration of treatment. A device for batch treatment of biological material with pulsed electric fields for studying both effects has been set up and tested successfully. It comprises a pulse circuit based on a RLC circuit and a 30-stage Marx generator with IGBT switches. The generator has been designed with only one closing switch per stage, capable of active voltage clamping. The charging voltage per stage and pulse current are 1 kV and 500 A, respectively. Soft-switching conditions of the IGBTs are ensured by the inductance of the circuit. The operation of the device has been demonstrated with a combined treatment of an apple by electroporation and ohmic heating.

Compact solid-state Marx-bank sub-nanosecond pulse generator based on gradient transmission line theory

Abstract: For non-invasive treatments in the biomedical field, sub-nanosecond pulse electric field matching ultra-wideband antennas have aroused great interest for their excellent directivity and targeted treatment. Sub-nanosecond pulse generators have proved difficult to control in pulsed power technologies despite many studies of pulse generators based on avalanche transistor theory and the Marx circuit. However, no solution exists to the problems of non-ideal waveform of the output sub-nanosecond pulse and the relatively low effectiveness of the Marx circuit. To resolve these problems, the paper describes a sub-nanosecond pulse generator simulation model based on gradient transmission line theory in PSPICE simulation software and the development of a compact solid-state sub-nanosecond pulse generator (18 cm×18 cm×4 cm). From experimental tests, trigger signals of 5-V amplitude, 5-ns rise and fall times (pulse-width 10 ns-50 ns) were generated by Field-Programmable Gate Array (FPGA). A pulse with 1600-V voltage amplitude, 300-ps full width at half maximum, 150-ps rise time, and 10-kHz high-stability repetition rate was generated in an attenuator load with high-bandwidth (8 GHz, 50 Ω). The effectiveness (Output pulse voltage amplitude / Charge voltage × Stages) of this Marx circuit reached to 41.7%, improving considerably on previous efforts.

High current nonlinear transmission line based electron beam driver

Abstract: A gigawatt-class nonlinear transmission line based electron beam driver is experimentally demonstrated. Four experimental series, each with a different Marx bank charge voltage (15, 20, 25, and 30 kV), were completed. Within each experimental series, shots at peak frequencies ranging from 950 MHz to 1.45 GHz were performed. Peak amplitude modulations of the NLTL output voltage signal were found to range between 18% and 35% for the lowest frequency shots and between 5% and 20% for the highest frequency shots (higher modulation at higher Marx charge voltage). Peak amplitude modulations of the electron beam current were found to range between 10% and 20% for the lowest frequency shots and between 2% and 7% for the highest frequency shots (higher modulation at higher Marx charge voltage).

PWM Voltage Droop Compensation for Bipolar Solid-State Marx Generator Topologies

Abstract: This paper presents a novel technique for the voltage droop compensation of long pulses in solid-state bipolar high-voltage Marx generators. Considering the modularity of Marx generators the compensation consists in adding one extra stage to perform as a pulsewidth modulation circuit. This stage voltage is added to the output positive or negative pulses, and an output $L_{f}C_{f}$ filter is included to smooth the voltage pulse waveform. A five-stage laboratory prototype of this circuit has been assembled using 1200-V Insulated Gate Bipolar Transistors and diodes with 1000-V dc input voltage. The circuit was operated at 50-Hz bipolar pulse rate, giving 4-kV bipolar pulses, into a resistive load, with 100- $\mu \text{s}$ pulsewidth and 9.5-ms relaxation time. The circuit was able to compensate 10% of bipolar pulse voltage droop.

Comparison of pulse forming networks for Marx generator

Abstract: Pulse Forming Network (PFN) is a network consisting of capacitor and inductor in series and parallel. A true squared shape pulse can be achieved using PFN and also pulse width, pulse power etc. can be adjusted by varying number of PFN sections and their connections. This paper deals with six different PFN connections and their simulation results. Comparisons of all six PFNs are done based on type, output voltage, pulse power, load resistance and rise time. A 20 kV input DC supply is used and it is found that output voltage for ten sections and one stage of PFN is varied between 10kV to 20 kV. Rise time of output pulse is achieved in the range of 350 ns to 1.8 μs.

Research of compact repetitive pulsed power system based on Marx generator

Abstract: By adopting Marx generator technology, a compact repetitive pulsed power system has been developed which consists of a high power repetitive power supply and a Marx generator. By utilizing inverter, resonance, 10-stage step boost, rectification and output in series, a high power repetitive power supply has been designed and tested which can transform 300V DC. to 100kV DC and charge the capacitor to 100kV repetitively. The Marx generator consists of 16 stages with integrated folder configuration. Each stage consists of three 20nF capacitors in parallel. By integrating the Marx with the high power repetitive power supply. A compact repetitive pulsed power system has been developed and tested. We have obtained 5 pulses with repetition rate of 5Hz on a 14Ω load. The peak voltage and peak power are more than 700kV and 35GW respectively.

Design strategies for a SiC Marx generator for a kicker magnet

Abstract: This paper discusses various design strategies and preliminary test results for a Marx generator with specifications of 40 kV, 3.2 kA, 3 μs pulse width, 30 ns rise and fall-times, and 1 Hz repetition rate, for possible replacement of a thyratron and PFL in an existing kicker system. The proposed topology will use 50 stages, each 800 V stage comprising 24 SiC MOSFETs in parallel, each MOSFET conducting about 140 A pulses. First tests using parallel SiC MOSFETs are described and results discussed in light of the proposed topology. Also the overall structure is discussed, as the parasitic inductances are a key issue for this application.

Development of cable fed flash X-ray (FXR) system

Abstract: Flash X-ray sources driven by pulsed power find applications in industrial radiography, and a portable X-ray source is ideal where the radiography needs to be taken at the test site. A compact and portable flash X-ray (FXR) system based on a Marx generator has been developed with the high voltage fed to the FXR tube via a cable feed-through arrangement. Hard bremsstrahlung X-rays of few tens of nanosecond duration are generated by impinging intense electron beams on an anode target of high Z material. An industrial X-ray source is developed with source size as low as 1 mm. The system can be operated from 150 kV to 450 kV peak voltages and a dose of 10 mR has been measured at 1 m distance from the source window. The modeling of the FXR source has been carried out using particle-in-cell and Monte Carlo simulations for the electron beam dynamics and X-ray generation, respectively. The angular dose profile of X-ray has been measured and compared with the simulation.

Pulse forming network for Marx generator with boosting operation

Abstract: This paper presents Solid State Marx Generator in which capacitors are replaced by Pulse Forming Network (PFN) through which we can get controlled pulse. The magnitude of output square impulse wave can be increased to high value with the low supply voltage without using converter or transformer. To achieve high voltage the PFN inductors and capacitors are connected in boost converter mode temporarily. It increases the capacitor voltage up to its desired value. The proposed topology of single stage Marx generator using six sectionPFN with boosting operation is simulated in MATLAB and satisfactory results are obtained.

Reconfiguration of 3 MV Marx Generator into a Modern High Efficiency System

Abstract: High voltage impulse generators are intended to last for long periods of time. Upon reaching the end of their technical lifetime, decisions concerning decommissioning, replacement, refurbishment or upgrading are needed. A new generator is a considerable investment. Significant reductions in material and labor costs can be made by repurposing still functional elements of the existing generator and redesigning the circuit for higher efficiency requiring fewer components. This paper describes the process of refurbishing the Mississippi State University (MSU) High Voltage Laboratory 3 MV, 56 kJ impulse generator originally built in 1962 into a modern digital impulse generator system.

Circuit-PIC coupled model of 3D simulation for magnetically insulated transmission line system

Abstract: In this work, a circuit-PIC coupled model for 3D simulation is developed, which can be used in pulsed power system with magnetically insulated transmission lines (MITLs). The circuit-PIC coupled algorithm consists of an external circuit algorithm and an algorithm which counts the jounced interface of the circuit and the grids for PIC simulation. The circuit-PIC coupled model has been demonstrated and implemented in a 3-D conformal finite-difference time-domain PIC code, UNIPIC. In this paper, the coupled model of 3D simulation is applied in a coaxial MITL system with a helical supporter, and this MITL is driven by Marx Generator. This work provides an approach to simulating MITL system which is azimuthal asymmetry in the power flow or structure.

All-solid-state Marx generator

Abstract: The invention provides an all-solid-state Marx generator The all-solid-state Marx generator comprises at least one circuit unit Each circuit unit comprises a diode, a capacitor, a first MOSFET (metal-oxide-semiconductor field-effect transistor) power tube and a second MOSFET power tube, wherein one end of the capacitor is connected with a cathode of the diode and a drain electrode of the first MOSFET power tube, the other end of the capacitor is connected with a source electrode of the second MOSFET power tube, and a source electrode of the first MOSFET power tube is connected with a drain electrode of the second MOSFET power tube The all-solid-state Marx generator has the advantages of small size and high stability

A switch combination structure for marx generator

Abstract: The utility model discloses a switch combination structure for marx generator, the marx generator includes a plurality of grades of pulse form moulding pieces, and a spark gap switch is connected to the interstage, and all spark gap switches are for puncture the spark gap switch certainly, and first order spark gap switch adopts even field plate switch, all the other spark gap switches adoption non -uniform field electrode switches, airtight pressure vessel is wholly arranged in to the marx generator, adopt the utility model provides a switch combination form, under the condition of not using the source of triggering, can be under higher insulating atmospheric pressure establish from puncturing. Under the same output, can make the marx generator further miniaturized.

PFN-Marx generator output waveform shaping method

Abstract: The invention relates to a novel Marx generator technology, to be specific, relates to a shaping method of adjusting a PFN-Marx generator output waveform by using a single-stage network parameter, and belongs to the pulse power technology field. By changing any stage unit form of a routine equal capacitance equal inductance PFN-Marx into an equal inductance non-equal capacitance form, except the unit adopts the equal inductance non-equal capacitance network form, other stage networks still adopt the equal capacitance equal inductance network form, and then the fine adjustment of the Marx output waveform is realized by adjusting only one stage of the Marx generator. The leading edge, the flattop quality, the lagging edge, and the pulse width of the PFN-Marx output pulse are adjusted conveniently, and the defect of the multi-stage Marx waveform of difficult adjustment is overcome. A substantial value is also provided to realize the compact and small size of the pulse power system.

160 J, 100 HZ repetition rate, compact Marx generator and high power microwave system

Abstract: This paper presents the electrical and mechanical hardware considerations of a compact, 160 J modular pulse forming network (PFN) Marx generator used to drive a high-power microwave (HPM) source that is a time variant load at a PRF of 100 Hz The modular Marx generator is designed to produce an open-circuit output voltage of 600 kV from a 50 kV source using twelve stages Each stage of the Marx was constructed from a PFN fashioned from five, 21 nF, high voltage capacitors in parallel Each Marx module was machined out of acetyl copolymer or Delrin© to provide optimal strength, rigidity, and a dielectric constant that closely matches transformer oil These Marx modules include air supply lines that are machined directly into each block of Delrin© allowing airlines to connect to each module chamber rather than every spark gap Each module has two electrode inserts placed into the sealed pressure vessel contained within the module After the Marx erects, the energy is directed into the virtual cathode oscillator (vircator) where subsequent frequency generation is manipulated through a rectangular waveguide contained within a new resonator cavity design The new design allows the bottom wall, back wall, and anode cathode gap to be moved by two linear actuators, a linear bellows, and another linear actuator, respectively The cavity is contained within a 10-inch circular vacuum chamber with a round stainless steel sleeve running from the back wall to the linear bellows Contained within the round sleeve is a rectangular waveguide where the bottom wall and the cathode are housed The anode is connected to the Marx generator via a nickel shaft that feeds through the back wall into the circular sleeve and into the rectangular waveguide The anode made from pyrolytic graphite, remains stationary while the bottom wall, and carbon fiber velvet cathode move relative to its position The benefit of this design is the height and depth of the cavity resonator can be controlled independently of each other while still allowing the A-K gap to be manipulated on its own

Microsecond Electron Beam Source with Electron Energy Up to 400 Kev and Plasma Anode

Abstract: A new high-power source of electrons with plasma anode for producing high-current microsecond electron beams with electron energy up to 400 keV has been developed, manufactured, and put in operation. To increase the cross section and pulse current duration of the beam, a multipoint explosive emission cathode is used in the electron beam source, and the beam is formed in an applied external guiding magnetic field. The Marx generator with vacuum insulation is used as a high-voltage source. Electron beams with electron energy up to 300–400 keV, current of 5–15 kA, duration of 1.5–3 μs, energy up to 4 kJ, and cross section up to 150 cm2 have been produced. The operating modes of the electron beam source are realized in which the applied voltage is influenced weakly on the current. The possibility of source application for melting of metal surfaces is demonstrated.

Marx Generator Based High Voltage Using MOSFETs: A Review

Abstract: This paper shows the development of a reliable and easy to carry compact 4 stages Marx Generator that can produce impulse voltage 4 times of input voltage with some minor losses. In addition, three different experimental circuits of DC supplies have been made. The highest output was 100 V DC for which input was taken as the main supply for the experimental and simulated Marx generator circuit. This generator is useful in small scale industries and academic institutions to demonstrate impulse voltages and also to perform testing on insulators and transformers of lower rating in laboratory. A total of 4 stages of both simulated, experimental Marx impulse generator circuit is designed and the impulse waves are recorded. The simulated recorded impulse waveform, is compared with the standard impulse wave. Both of circuits, the efficiency of each stage was calculated and the percentage of error in the front and tail time was also found out as well as the effects of the circuit parameters on the impulse waveform characteristics were also studied. The simulation was done with the help of Proteus 8 Professional. In this work, the comparison in terms of magnitude of the experimental and simulated 4 stages Marx generator circuit has been carried out.