High Current Pulse Generator Research Articles

Structure of Self-Powered Modular High-Voltage and High-Current Pulse Generator for Magnetron

Structure of Self-Powered Modular High-Voltage and High-Current Pulse Generator for Magnetron

Generation of magnetosonic waves by electrical explosion of conductors driven by mega-ampere current pulses

An experimental study of the explosion of cylindrical copper rods in the current skinning mode was performed using the GIT-12 high-current pulse generator with currents of amplitude up to 5 MA and rise time about 2 μs. It was observed that the waveforms of the electrical impedance of the exploded rods exhibited low-frequency oscillations with a period of several hundreds of nanoseconds. The results of the experiment with exploded solid copper rods carried out on the GIT-12 facility were interpreted by performing a series of magnetohydrodynamic calculations. It was shown that the experimentally observed low-frequency oscillations of the rod impedance were associated with a fast magnetosonic wave excited in the material of the rod.

A Miniaturized Piezo Stack Impact Actuation Mechanism for Out-of-Plane Freely Moveable Masses.

We present the prototype and analytical model of a miniaturized impact actuation mechanism, providing a fast out-of-plane displacement to accelerate objects against gravity, allowing for freely moving objects and hence for large displacements without the need for cantilevers. To achieve the necessary high speed, we chose a piezoelectric stack actuator driven by a high-current pulse generator, connected to a rigid support and a rigid three-point contact with the object. We describe this mechanism with a spring-mass model and compare various spheres with different masses and diameters and from different materials. As expected, we found that larger flight heights are achieved by harder spheres, achieving, e.g., approx. 3 mm displacement for a 3 mm steel sphere using a 3 × 3 × 2 mm3 piezo stack.

Medium Voltage Pulse Power Generator for Accurate Current Interruption

High power one-shot pulse generators that respond quickly to a trigger are needed for industrial, scientific, and medical applications. A fast-response, flat-top current pulse can help dc circuit interrupters achieve zero current switching, which alleviates arcing, reduces semiconductor device stress, and improves circuit design. We overcome several challenges in designing high-voltage and high-current accurate pulse generators, including the following: first, parasitics from the necessary large physical format that degrade pulse quality and complicate design; second, modularity that is economical in using fewer lower voltage semiconductor switches; third, optimality in the tradeoff among response time, pulse flat-top duration, and component selection. We present a design method and hardware results for a modular 4.5 kV pulse generator that delivers a 100 A peak current pulse for an 800 ns flat-top duration and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 1$</tex-math></inline-formula> % accuracy, which can potentially scale to tens of kilovolts.

High-current space-charge-limited pulses using ultrashort laser pulses.

The maximum current that can be delivered by a 1-D vacuum diode is limited due to the space-charge reduction of the accelerating field. For a steady-state operation, this is given by the Child-Langmuir space-charge limit. However, for pulsed diode sources, the instantaneous current can be much higher than this limit, as long as the pulse length is much less than the transit time across the diode gap. This enables the generation of high current pulses with pulse durations of the order of tens of picoseconds using photocathodes driven by ultrashort laser pulses. The generation of such short and powerful electromagnetic pulses is important for numerous applications such as ultrawideband radar or as photocathode sources for accelerators. In this work, the limiting current pulse is investigated in the case of a very short, square-top initial pulse and it is found that these pulses propagate in a self-similar manner, remaining as a square-top charge cloud in space throughout their acceleration and propagation. The resultant current and pulse duration turn out to be dependent on only three parameters, which are the applied voltage, the vacuum transit time, and the fraction of the saturation charge density in the initial charge cloud. The resultant scaling of the resultant peak current and pulse duration are calculated numerically as a function of starting sheet-charge density, allowing the calculation of the resultant pulses for any ultrashort, pulse-driven vacuum photodiode design.

Design of self-triggering parallel Marx generator with thyristor

We use a thyristor with a charging direct current (DC) power of 600 V as the circuit switching element and a Marx generator structure combined in series and parallel to design a high current pulse generator for long magnetic lens. According to the current driving characteristic of thyristors, the gate electrode is grounded through the current stabilizing inductance and current limiting resistance to form a self-triggering structure. The circuit output and the self-triggering waveform of thyristors at all levels are simulated. Under the load resistance of 500 mΩ and load inductance of 1.14 mH, a pulse current with amplitude of -1.1 kA and pulse width of 2.68 ms is obtained. The current pulse is used to excite a long magnetic lens, and a magnetic field with a duration of 1.2 ms and an intensity higher than 0.6 T is obtained. The influence of parameters such as charging voltage, energy storage capacitor, and the number of parallel stages of the circuit on the amplitude and width of the pulse current is studied. When the charging voltage increases, the pulse current becomes larger and the width remains unchanged. When the value of the energy storage capacitor and the number of parallel stages increase, the amplitude of the pulse current becomes larger and the pulse width becomes wider.

Studies on the implosion of pinches with tailored density profiles

This paper presents the results of experimental and theoretical studies of imploding metal-puff Z-pinches. The experiments were carried out on the MIG high-current pulse generator at a current level of about 2 MA and a current rise time of about 100 ns. A plasma gun was used to produce a plasma column with a tailored density profile through which the main electromagnetic pulse of the MIG generator was passed. The experiments have shown that pinches of this type, being compressed, are resistant to dynamic magneto-Rayleigh–Taylor (MRT) instabilities. The experimental results were analyzed using one-dimensional radiation magnetohydrodynamic simulations. It has been shown that in a pinch with a tailored density profile, the formation of a high-temperature plasma at the pinch axis and the generation of x-rays occur at the stagnation stage, i.e. under conditions close to Bennett equilibrium. At this stage, flute-like MRT instabilities develop, causing the pinch to decay.

Compact high-current pulse generator for laboratory studies of high energy density matter.

We present the design and parameters of a compact and mobile high-current pulse generator, which can be applied in the study of warm dense matter in university laboratories. The generator dimensions are 550 × 570 × 590mm3, the weight is ∼70kg, and it consists of four "bricks" connected in parallel. Each brick, made up of 2 × 40 nF, 100 kV low-inductance capacitors connected in parallel, has its own multi-gap and multichannel ball gas spark switch, triggered via a capacitively coupled triggering by a positive polarity pulse of ∼80 kV amplitude and ∼15ns rise time. At a charging voltage of ∼70 kV, the generator produces a ∼155 kA current pulse with a rise time of ∼220ns on a ∼15 nH inductive short-circuit load and a ∼90 kA amplitude current pulse in the underwater electrical explosion of a copper wire.

Electromechanical installation based on high power current pulse generator

Electromechanical installation containing electromagnetic s noid with a piston operating in reciprocating motion mode has been developed. Technologies with similar operating modes are widely used in various industries (mechanical engineering, metallurgy, mining, mechanics, robotics, as presses for forging and stamping, as well as jack-hammers in crushing devices for coal, ore and rock). An economically effective generator of high power unipolar current pulses (with unique systems that allow adjustment of the main parameters in a wide range and with high speed: the frequency of pulse reproduction, amplitude) was used as a power source for electromechanical installation. The principle of operation of the generator is based on periodic discharge of pre-charged capacitors to a low-resistance active-inductive load. Generator contains power unit, consisting of a capacitor discharge unit for load; a generator control system (GCS), consisting of a capacitor charging unit (reversible thyristor converter with counter-parallel connected thyristor bridges); a recharge unit and an automatic control system of the ACS. According to the known equations, parameters of mechanical and electrical parts of the electromechanical installation were calculated: initial coordinate of the piston; magnetomotive force arising from change in inductance L(x) ; spring force; the force of resistance to the piston, proportional to the speed of its movement; force action on the piston; amplitude, duration and frequency of reproduction of current pulses. A simulation model of the installation has been developed in the MATLAB-SIMULINK environment. The graphs of transient processes during operation of the installation at idle and under load were built. Analysis of the operating modes of the installation was carried out. Developed electromechanical installation for influencing load with the aim of its destruction or deformation with a system of automatic control of parameters makes it possible to regulate process parameters with high speed: force and distance traveled by the piston.

A repetitive high current pulse generator for high flux electrothermal plasma jets.

Power sources play an important role in the characteristics and the applications of the electrothermal (ET) plasma as an edge localized mode (ELM) heat flux simulator. A repetitive high current ET plasma source with the capability of working at a 10 Hz repetition rate and peak current 7.5 kA is presented in this paper. By controlling the sequence of discharge of ten pulse power modules, a repetitive high heat flux plasma jet can be generated. A two-stage capillary structure is presented, and its repetitive trigger driving circuit based on surface flashover ignition is designed to achieve reliable and repetitive discharge. The topology of the inductive and capacitive (LC) series resonant circuit is applied to the charging system of the pulsed power source. The charging current is limited to 500 A with a charging time of 3.5 ms, and the ratio of the charging voltage to the operating voltage is 1.85. A diode and a power resistor in series are used to suppress the negative overvoltage, which is helpful to increase the thyristors' operating reliability. Using the designed repetitive ET plasma source, the characteristics of the ET plasma jet are investigated by measuring the voltages and currents and by obtaining images of the discharges. Experimental results show that the repetitive ET plasma generator can be used as an appropriate way to simulate the ELM-like heat flux plasma.

A Repetitive High-Current Pulse Generator Circuit Based on Multistage Pulse Transformers

The application of inductive energy storage in the generation of high-current pulses has attracted considerable attention during recent years. In this article, a new inductive high-current pulse generator circuit is proposed based on XRAM (MARX spelled backword) current multiplier converter concept and multistage pulse transformers by using power electronic switches. This circuit is capable to recover the residual energy and generate repetitive high-current pulses with a flexible output pattern. To verify the circuit operation, simulation and experimental results of a two-stage laboratory prototype are presented. The results confirm the theoretical analysis and show the validity of the converter scheme.

High power current pulse generator based on reversible thyristor converter

In metal forming using high power current pulses, it becomes necessary to control both reproduction frequency and pulse amplitude. Description of a generator of high power current pulses with controlled thyristor converter is provided as a power source of charging device (charger) for regulating voltage (pulse amplitude) of capacitor charge. Faults of the generators associated with inrush current in capacitor charge modes are revealed, which reduces quality of supply network. To reduce time of transient processes while lowering voltage across capacitors, application of reverse thyristor converter is applied as a power source. Structural diagram of generator is considered, which includes reversible thyristor converter with separate control, power unit, capacitor recharge device, charger parameters automatic control system and capacitor charge process control system. Calculation of parameters of automatic control system regulators is presented. To obtain optimal transients, standard methodology for setting regulators to a modular optimum was used. In order to reduce overshoot at time of disturbances appearance, which can reach 100 % and higher, socalled logical device was introduced into the automatic control system. It blocks control pulses on thyristors of converter and simultaneously reduces signal at the output of current regulator to zero. Simulation model of high power current pulse generator in MatLab – Simulink environment was synthesized. Analysis of the model was carried out, and graphs are given that explain principle of device operation and transition processes under various operating modes. Generator application will allow user to adjust amplitude of current pulses with high speed and to obtain sufficiently high-quality transient processes of capacitors charge (discharge), which will have beneficial effect on supply network. Application of better converters will significantly increase frequency of reproduction of current pulses.

A New Modular XRAM-Like Inductive High- Current Pulse Generator Circuit Topology

XRAM (MARX spelt back words) is currently a very important circuit for high current pulse generators. In our previous studies, an XRAM-like circuit was proposed based on multiple pulse transformer modules and a capacitor connected in parallel. Compared with the traditional XRAM circuit, the same number of inductive energy storage modules can be used to generate higher current pulses. This circuit is also capable to recover the residual energy and generate repetitive high-current pulses. However, this circuit topology requires more power electronic switches (three IGBT switches per pulse transformer module). In order to reduce the number of switches, by adding two IGBT switches in the capacitor module, a new modular XRAM-like circuit with reduced switches (one IGBT switch per pulse transformer module) is proposed in this paper. The change of the circuit topology makes the capacitor discharge the primary inductors of the pulse transformer in series during the residual energy recovery stage, instead of the parallel discharge in the previous circuit. This requires the closing time of the IGBT switch in each pulse transformer module ahead of the discharge start time of the capacitor. Working process of the proposed circuit was described in detail and simulations of a 12-module circuit were carried out to verify the circuit operation. Finally, the preliminary experimental results of a two-module laboratory prototype are presented. The results confirm the theoretical analysis and show the validity of the converter scheme.

Generation of high-current pulses by a magnetized squeezed electron beam

The space charge limited current of an electron beam generated in a magnetically insulated foil-less diode by a cylindrical or hollow cathode and injected into a cylindrical drift tube depends on the energy of the electrons and on the ratio of the beam radius to the tube radius. When this beam drifts into a tube of larger radius, it exceeds the corresponding space charge limit. This leads to the formation of a virtual cathode and to the reduction of the energy of the beam. The latter is known as a squeezed beam state. When the cylindrical tube consists of more segments of different radii and lengths, the dynamics of the beam can be manipulated. We propose a simple configuration resulting in the production of a high-frequency periodic train of high-current electron beam pulses.

Design and Experiments of Electromagnetic Heating Forming Technology

Electromagnetic forming (EMF) has been widely applied in industries. However, it's still hard to form thick or hard metal work pieces due to the limitation of its system power. Moreover, increasing the input voltage or capacitors may cause the problem of insulation, reduce the lifetime performance of devices, and lead to the cost increase and safety issue. Therefore, this paper proposes a novel technology named electromagnetic heating forming (EMHF), which combines EMF with electromagnetic induction heating (EIH) based on their similar working principles to make it easier to form the thick or hard metal work pieces. The EMHF can reduce the deformation resistance of work pieces by preheating treatment, and produce small discharge energy to deform work pieces. A 5kV/1.68kJ/135μ F EMHF system with a high-current pulse generator and a high-frequency heating source, which consists of an autonomous currentfed push-pull resonant inverter based on a zero voltage switching circuit and a resonant network, has been designed, built, and tested successfully. A finite element model coupling with the electromagnetic field, solid mechanics field, thermal field, and deformed geometry has also been built in COMSOL Multiphysics to analyze the EMHF process. Tube compression EMHF experiments of different input voltages, thicknesses, and temperatures have been carried out. The experimental and simulation results demonstrate that the EMHF can reduce the requirements of the deformation process by preheating treatment, which can't be done by EMF. Besides, the deformation can be controlled by the preheating temperature during the EMHF process. Therefore, the EMHF has great potential in industrial applications.

Finite-Element Simulation and Experiments on Plastic Heating in the Process of Electromagnetic Pulse Forming

Electromagnetic pulse forming (EMPF) is an attractive manufacturing method using pulse power techniques. Temperature rise of the work piece is usually neglected in previous studies because the forming process is regarded as a cold process. Nevertheless, the temperature rise (if not high) also has influence on the forming process. It is important to study the temperature rise for exploring the related law in the process of EMPF. In this paper, the thermal effect in the process of EMPF, caused by the joule heating generated by the high current and the plastic work produced by the plastic deformation of the work piece in the forming process, is discussed though simulations and experiments. A finite-element simulation coupled with the electromagnetic field, plastic mechanics, deformed geometry, heat transfer, and thermal expansion based on COMSOL multiphysics is established to show the detailed thermal effect in this process. The relationship between parameters of work piece and the thermal effect has been analyzed by comparing different materials and thicknesses of work pieces. The simulation results show that the temperature of work piece has changed because of the thermal effect. A high-current pulse generator has been developed for the experiment of EMPF to verify the results of simulations. This paper describes the forming experiments of different materials and thicknesses. And the experimental results verify that the materials and thickness of work piece affect thermal effect during the process of EMPF. Compared with the Joule heating, the plastic work is the main cause of the thermal effect. Moreover, the thermal expansion caused by temperature rise could affect the forming results and material property.

A high current pulsed power generator CQ-3-MMAF with co-axial cable transmitting energy for material dynamics experiments.

A high current pulsed power generator CQ-3-MMAF (Multi-Modules Assembly Facility, MMAF) was developed for material dynamics experiments under ramp wave and shock loadings at the Institute of Fluid Physics (IFP), which can deliver 3 MA peak current to a strip-line load. The rise time of the current is 470 ns (10%-90%). Different from the previous CQ-4 at IFP, the CQ-3-MMAF energy is transmitted by hundreds of co-axial high voltage cables with a low impedance of 18.6 mΩ and low loss, and then hundreds of cables are reduced and converted to tens of cables into a vacuum chamber by a cable connector, and connected with a pair of parallel metallic plates insulated by Kapton films. It is composed of 32 capacitor and switch modules in parallel. The electrical parameters in short circuit are with a capacitance of 19.2 μF, an inductance of 11.7 nH, a resistance of 4.3 mΩ, and working charging voltage of 60 kV-90 kV. It can be run safely and stable when charged from 60 kV to 90 kV. The vacuum of loading chamber can be up to 10(-2) Pa, and the current waveforms can be shaped by discharging in time sequences of four groups of capacitor and switch modules. CQ-3-MMAF is an adaptive machine with lower maintenance because of its modularization design. The COMSOL Multi-physics® code is used to optimize the structure of some key components and calculate their structural inductance for designs, such as gas switches and cable connectors. Some ramp wave loading experiments were conducted to check and examine the performances of CQ-3-MMAF. Two copper flyer plates were accelerated to about 3.5 km/s in one shot when the working voltage was charged to 70 kV. The velocity histories agree very well. The dynamic experiments of some polymer bonded explosives and phase transition of tin under ramp wave loadings were also conducted. The experimental data show that CQ-3-MMAF can be used to do material dynamics experiments in high rate and low cost shots. Based on this design concept, the peak current of new generators can be increased to 5-6 MA and about 100 GPa ramp stress can be produced on the metallic samples for high pressure physics, and a conceptual design of CQ-5-MMAF was given.

Demanding response time requirements on coherent receivers due to fast polarization rotations caused by lightning events.

Lightning events can cause fast polarization rotations and phase changes in optical transmission fibers due to strong electrical currents and magnetic fields. Whereas these are unlikely to affect legacy transmission systems with direct detection, different mechanisms have to be considered in systems with local oscillator based coherent receivers and digital signal processing. A theoretical analysis reveals that lightning events can result in polarization rotations with speeds as fast as a few hundred kRad/s. We discuss possible mechanisms how such lightning events can affect coherent receivers with digital signal processing. In experimental investigations with a high current pulse generator and transponder prototypes, we observed post FEC errors after polarization rotation events which can be expected from lightning strikes.

Mobile Electric-Discharge Blasting Unit for Splitting off and Destruction of Rocks and Concrete

The article describes the pulse power system for electric-discharge blasting of rocks and concrete, the main equipment of which is a high current pulse generator with operating voltage up to 15 kV. The test of short-circuit experiment was produced, the main parameters of the discharge circuit L = 1.01 μH, R = 9 mΩ were calculated. Based on the results of the experiments the impedance Z = 42.5 mΩ of discharge circuit was defined. The pulse power system with mentioned parameters has maximum power condition deviation of about 8.6 %.

Conversion of high explosive chemical energy into energy of powerful nanosecond high-current pulses

This study is a contribution into the development of physicotechnical foundations for generation of powerful nanosecond high-current pulses on the basis of explosively driven magnetic flux compression generators. This problem is solved by using inductive storage of energy for matching comparatively low-voltage explosively driven magnetic flux compression generators and high-impedance loads; short forming lines and vacuum diodes. Experimental data of charging of forming lines are given.