High voltage pulses for high impedance loads using explosive formed fuses

It is necessary to make full use of explosive energy and reduce the loss of unnecessary energy when we study high-powered radio frequency explosive magnetic flux compression generator . Therefore, this paper proposed that indirect charging was used in radio frequency explosive magnetic flux compression generator. Based on the equivalent circuit theory, we studied the interaction of two loops in the case of indirect charging. The numerical simulation results showed that we must choose appropriate circuit parameters of charging in order to guarantee the radio frequency explosive magnetic flux compression generator to run steadily.

Vladislav Nikolaevich Mokhov, an outstanding scientist, Doctor of Science in Physics and Mathematics, professor, died on December 27, 2011 after long time of severe disease. Before this illness he was Deputy Scientific Leader of the All-Russian Research Institute of Experimental Physics (VNIIEF). V.N. Mokhov was born on April 12, 1931 in the town of Atkarsk, Saratov region, Russia. In 1955, after graduation from the Moscow Engineering Physics Institute, he in a group of the most brilliant and talented young theoreticians was selected by Academicians Ya.B. Zel'dovich and A.D. Sakharov for work on the nuclear weapons program at VNIIEF. In 1963, he was awarded the Lenin Prize for the development of new principles and new approaches to nuclear and thermonuclear weapons design and controlled fusion; in 1964, he received the degree of Candidate of Science, and four years later, the degree of Doctor of Science. V.N. Mokhov was always inspired by challenging projects that required teamwork of theoreticians, designers, and experimentalists. His major scientific and practical results include: Development of the theory of turbulent mixing in layered structures at intense compression. The results obtained are relevant for studying the processes occurring in inertial confinement fusion (ICF) targets.; Ignition of thermonuclear fuel by its heating with fast compression, which was and continues to be very important for the development of a number of special-purpose nuclear charges and fusion targets.; Development of “clean” nuclear charges for peaceful applications (jointly with the team of colleagues).; The new approach to the controlled thermonuclear fusion - the MAGO (MAGnitnoye Obzhatiye, or magnetic compression) - was proposed and developed jointly with his team. V.N. Mokhov considered MAGO to be a system that now made it possible to achieve the scientific breakeven point for fusion without the large initial capital investment that is required by the two more conventional approaches, magnetic confinement fusion and ICF.; Investigation of physical properties of materials at high energy densities provided by explosive magnetic flux compression generators (EMG). Jointly with his team, V.N. Mokhov proposed and developed methods of this investigation, obtained novel results on dynamic strength of a number of materials (aluminum, copper, polyethylene). In 1998, he and some of his colleagues were awarded the RF Government Prize for the development of EMGs and their application for scientific investigations. V.N. Mokhov was one of the pioneers of scientific cooperation between US and Russian nuclear laboratories. This mutually beneficial cooperation between the two countries produced extremely interesting scientific results obtained during joint research activities, including more than 20 series of experiments, and published in more than 400 papers and presentations. Equally important is that he was a true friend of many US scientists, and this friendship between people from different countries and trust in each other made the world better. V.N. Mokhov was a very interesting person having his original opinion on nearly any issue - whether related to science, history or politics. Many of his ideas on these issues were reflected in his papers available to a broad public and in his book “Nuclear Weapons and Safe Stable World. These ideas were extremely up-to-date in due time, and they continue to be relevant these days.

爆磁压缩发生器与高阻抗负载匹配调制电路

Expendable, explosively driven shock tubes are used to propel aluminum flyer plates toward dense stainless steel plugs to simulate gas compression in explosive magnetic flux compression generators (FCGs). Armature velocity in a typical FCG is calculated using the Gurney method and shock tubes are designed to drive the flyer plates at similar velocities. Experiments with sulfur hexafluoride and synthetic air are presented.

Data are presented describing refined simulations of perturbation growth in a three-layer cylindrical liner system tested with disk explosive magnetic flux compression generators (DEMGs) to study the strength properties of copper and polyethylene at shocklessly applied pressures of up to ~15 GPa. The calculated performance for the same liner system in the experiments to study the strength properties of copper at shockless loading of up to ~40-GPa pressures is presented. The feasibility of similar strength experiments with quasi-isentropic material compression to ~2000 GPa using DEMGs is demonstrated.

This paper presents an overview of publications on numerical simulations of one of the major 2-D effects observed in magnetically driven implosion of cylindrical condensed-matter liners: their interaction with glide planes. We consider liners accelerated to 8-20 km/s by currents of 30-100 MA delivered by disk explosive magnetic flux compression generators with azimuthal magnetic fields of 1-6 MG (magnetic pressures of 0.04-1.4 Mbar): experimental liners HEL-1, ALT-1, 2, and liners HEL-2, ALT-3 proposed for high energy density physics research.

Data of refined perturbation growth simulations of the three-layer cylindrical liner systems, tested during experiments with DEMGs (disk explosive magnetic flux compression generators) to study the strength properties of copper and polyethylene at shockless pressures up to ~15 GPa, and calculated performance data of the same liner systems for the Atlas experiments to study the strength properties of copper at shockless compression to ~40 GPa are presented. The feasibility of similar strength experiments with quasi-isentropic material compression to ~2000 GPa using DEMGs is demonstrated.

The parameters of laser radiation and kinetic processes of plasma formation and production of inverse population are studied. Electrophysical processes proceeding in a feed circuit containing a semiconductor opening switch and intermediate inductive energy storage are also considered. It is shown that the semiconductor opening switch controls the amount of energy in the inductive storage, and a high-voltage short prepulse with a peak pump power density of ∼1 MW cm-3 appearing during the current interruption can produce a volume-discharge plasma and create the inverse population for the time ∼10 ns, providing the conditions for efficient pumping of the active medium from the main capacitor. The time dependences of the pump and emission powers, the concentrations of electrons, excited xenon atoms, HCl(v) molecules in excited vibrational states and of the ionisation, recombination, and attachment rates are calculated. Kinetic processes determining the parameters of laser radiation are analysed. The output energy up to 1.0 J is obtained for 90-ns (FWHM) pulses with the efficiency up to 4.0% with respect to the pump energy. The maximum output power was 11 MW for the lasing efficiency of 4.7% with respect to the pump power. The calculated and experimental time dependences of the voltage across the laser gap, discharge current, and output power are in good agreement.

The characteristics of the differential-output D-dot sensor, which is employed to diagnose the voltage pulse across the water-insulated component of the pulsed power accelerator, are investigated by theory, circuit simulation, and experiments. The leakage current from the D-dot sensor to the inner electrode of the measured component will degrade the low-frequency response property of the monitor. The lower level of the water medium resistivity the worse performance of the sensor’s low-frequency response property will be. The actual lower-limited response frequency of the D-dot sensor is not related to the sensor itself but is mainly determined by the resistivity of the water. These are not only deduced from theory but also approved by the experimental results. Circuit simulation results suggest that the D-dot sensor without consideration of the leakage current will over-evaluate the amplitude and rise time of the voltage pulse across the water-filled element. We have proposed a method to make compensation for such an effect by using a passive resistor–capacitor (RC) integrator instead of the numerical process suggested previously. It is approved both by circuit simulation and experimental results that the output of the D-dot sensor post-processed by the RC integrator could give accurate measurement results providing that the time constant of the RC integrator is identical to the characteristic time of the D-dot sensor.

SUMMARYIn this paper, we propose two control methods of a static impulse voltage generator to lower the influence of dc voltage source fluctuations on the output voltage and to improve its efficiency by reusing discarded inductive storage energy. Introducing output voltage control adjusting the charging period of capacitive and inductive energy in accordance with the source voltage, the output voltage fluctuation by the source voltage decreased by 61.1%. Applying the reusing method, we estimated by circuit simulation that the amount of energy that could be recovered was 21.0% and the efficiency of energy transfer was improved from 60.4% to 76.7%.

Semiconductor opening switches (SOS) are able to interrupt currents at density levels of up to 10 kA/cm 2 in less than 10 ns, operate at repetition rates up to 1 kHz, and possess lifetimes of more than 10 1 1 pulses. 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, obtainable through diffusion from the surfaces. 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 is easy to apply and thus allows to carry out parameter studies to determine the influence of different physical quantities, like doping and impurity levels, on the performance of the device. Applying the code some new interesting results concerning the plasma dynamics during the opening process in the switch have been found. Especially, using realistic values for the charge carrier mobility, it was found that the opening process starts first at the n-n + boundary. Also it has been possible to derive the physical conditions for the occurrence of the SOS-effect. Based on the simulation results a simplified SOS equivalent circuit model has been developed. This model can be used in the circuit simulation program PSpice. A new pulse generator scheme based on inductive storage 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. PSpice simulations of such a scheme based on semiconductor opening switches are presented. 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.

Calculations are carried out on the efficiency of MCG magnetic field production in a system where magnetic flux compression is accomplished with the thick-walled cylindrical liner. The results of these calculations are discussed. Special hammer accelerated to the velocity about ~105 cm/s are used to perform energy transfer from inductive storage into the liner. The efficiency of this process depends on system elements coupling. This system allows to transform about 3% of stored energy into the magnetic field (20 MG).

Pulse power can be used to generate high energy density conditions in convergent hollow cylindrical geometry through the use of appropriate electrode configuration and cylindrical loads. Cylindrically symmetric experiments are conducted with the Pegasus-II inductive store, capacitor energized pulse power facility at Los Alamos using both precision machined cylindrical liner loads and low mass vapor deposited cylindrical foil loads. The liner experiments investigate solid density hydrodynamic topics. Foil loads vaporize from Joule heating to generate an imploding cylindrical plasma which can be used to simulate some fluxes associated with fusion energy processes. Similar experiments are conducted with “Procyon” inductive store pulse power assemblies energized by explosively driven magnetic flux compression.

Hybrid on‐load tap changers (OLTCs) are attractive solutions for the smooth change in voltage without current interruption in the converter transformer. This paper proposes a systematic topology derivation method of hybrid OLTC. To begin with, the topology derivation principle of OLTC is studied according to graph theory and equivalent electrical network theory, and the basic structure of OLTCs is constructed. Based on the topology derivation and optimization method, some hybrid OLTC topologies are derived. Particularly, a new hybrid star‐type parallel three‐switch OLTC topology with independent intellectual property rights is investigated in detail. Then, the optimal timing control is designed to reduce the time of current flow and shorten the overall switching time. Circuit simulation results show that arc‐free and reliable switching can be realized in the new topology. In addition, the losses and the heat generated during the switching process are calculated, and the impact of the phase between the stage voltage and system current on the loss and electrical stress is studied. Furthermore, the comparison between the proposed topology and other topologies is carried out to show the advantages of the proposed topology. Finally, Saber circuit simulation will be carried out to verify the theoretical and numerical analysis results.

Fusion in the magnetically compressed targets