A radiation foil bolometer for measuring the energy losses of fast Z-pinches

A radiation foil bolometer intended for measuring radiation-energy fluxes and plasma flows in high-power pulsed plasma X-ray sources is studied. In the bolometer, the radiation or ion-flow energy is absorbed by a 13-μm-thick niobium foil preliminarily heated to T ≈ 1900 K by a quasi-constant current lasting 2 s. Radiation from the foil was fed through an 8-m-long light guide to a semiconductor photodetector. The sensitivity of the instrument obtained from the results of calibrations is 0.56 J/V cm². The time resolution of this technique (∼2.5 μs) is determined by the foil heating time. In experiments with megaampere Z-pinches, the time resolution attained allows detection of the radiation energy independently of the energy of expanding plasma flows. In this case, the photoelectric effect from X-rays and the conductivity of expanding plasma do not affect the operation of the radiation bolometer. The working capacity of the bolometer was demonstrated at the Angara-5-1 facility in experiments with high-current Z-pinches with a radiation output energy of 50–100 kJ/pulse. The measurements performed have shown that the energy flux density of plasma expanding in the direction perpendicular to the pinch axis is at most 5% of the energy flux density of soft X-rays.     

A current source with an inductive energy storage for measuring pulse impedances of grounding connections

A pulse generator with an inductive energy storage for measuring pulse impedances of grounding connections is developed. The generator produces current pulses with a rise time of 200–300 ns and an amplitude of up to 8 A. In contrast to the capacitive storage sources, it is fully controllable, allows one to adjust the amplitude, and ensures a constant current-pulse shape regardless of the load parameters. The different operation modes of the source are described. The experimental load-current waveforms are presented.     

An ИЛТИ transportable high-power pulse X-ray radiation source

Characteristics of the ИЛТИ pulse (～50 ns) X-ray radiation generator with a boundary quantum energy of ～700 keV and a dose of ～1 R at 1 m from the target are presented. The ИЛТИ is intended for prompt checking of the response of the studied object at its location to the radiation effect at specified time moments at an ambient temperature from +40 to ?10°C and also for the x-ray radiographic monitoring (diameter of the beam focus is ～5 mm) of positions of an object’s parts behind an opaque shield. The jitter in delays of the source’s response times with respect to the start pulse is < ±30 ns. The ИЛТИ is based on an electron-beam accelerator with a pulse current of ～80 kA. A double forming line (DFL) with glycerin insulation serves as the energy storage and former of accelerating-voltage pulses. The DFL is charged from a six-stage Marx generator for 280 ns. The charging current of the DFL internal line passes through the resistance of the prepulse plasma formed in the volume of a strong-current electron diode between its specially shaped electrodes. In order to ensure ≥20 serial startups of the ИЛТИ without replacing anode and cathode parts, a backward diode with a massive anode and electron-beam pinching in the interelectrode gap was used. X rays are extracted into the air through a polyethylene window withstanding ≥200 source startups. The ИЛТИ has a modular demountable structure and, hence, can be quickly dismantled and moved to a new place. The ИЛТИ can be put into operation within ～2 h. Two ИЛТИs used for radiation studies since 1998 have demonstrated performance stability and ease of service.     

用于金属拔丝的调频调幅大电流窄脉冲电源

介绍了一种将电流脉冲的电塑性效应应用于金属拔丝的调频调幅大电流窄脉冲电源系统。电源初级储能环节采用常规三相桥式整流和LC滤波;中间二次储能电路采用Buck变换器,利用全控型功率开关器件IGBT调节电热电容的充电电压,进而控制输出脉冲电流的幅值;而窄脉冲的形成则由电热电容、输出回路电感和等效负载电阻决定,由高频晶闸管进行控制。电源输出脉冲电流的频率和幅值可实时调节、数字显示。运行及测试结果表明,电源系统工作稳定,脉冲电流幅值和频率调节方便,控制准确。     

A High-Power Semiconductor Generator for an Atomic Injector

An atomic injector with a beam power of 1 MW for heating plasma in the TCV tokamak (Lausanne, Switzerland) by a beam of neutral atoms was developed and put into operation in 2015–2016 at the Budker Institute of Nuclear Physics SB RAS (Novosibirsk). Plasma in the injector is formed in a plasma emitter by a high-frequency magnetic field, which is created by a high-power semiconductor generator with an output power of 40 kW at a frequency of 4 MHz. The facility operates in the pulse mode with a pulse duration of 2 s and a pause of 5 min. The generator is manufactured in the form of a modular system consisting of 16 identical generator modules, whose high-frequency power is summed, control modules, and a power-supply source. The generator allows modulation of the output power in the range of 30–100% by changing the power-supply voltage. The general structure of the generator and its elements and the results of its commissioning are presented.     

An inductive voltage divider positioned near the liner

An inductive divider for measuring voltages near a radiating load, which is a hollow cylindrical assembly compressed by a 3-MA current pulse, is described. Some results that were obtained in experiments on the Angara-5-1 facility using this divider are presented. The nanosecond resolution of the sensor and closeness of its position to the load allow observation of the moment of breakdown of wires using the obtained voltage signals. Analysis of voltage and current signals allows evaluation of the energy deposition to the wires before the breakdown and the parameters of plasma that is generated around them.     

Pulsed blowdown-electron gun facility for low-temperature and high-pressure supersonic flow electronic transition lasers

The design of a small compact pulsed blowdown apparatus coupled to a cold cathode electron gun is described. This system allows the excitation of a gas mixture in supersonic flow at temperatures of 80 and 120 K and density of 1 amagat with a maximum electron beam current density of 20 A cm(-2) at 300 kV and pulse length of 0.5 mus. With this facility it has been possible, using aerodynamic cooling, to achieve high-power, long-pulse ultraviolet laser operation in a high-pressure active medium on XeF and Ne ii ion transitions. A strong increase in fluorescence intensity was also obtained for numerous atomic lines and molecular bands of interest for the developement of high-power, high-efficiency, visible and ultraviolet lasers.     

A Modernized PC-20 Facility for Studying the Characteristics of a Plasma-Opening Switch

Abstract-A modernized PC-20 facility with a plasma opening switch (POS) is described. It contains a four-module voltage pulse (Marx) generator (MXG) connected via a high-voltage feedthrough to a POS. The energy stored in the MXG is increased by a factor of 12.5 and amounts to 240 kJ at a maximum voltage of 1 MV. At such a voltage, the POS current amplitude is 320 kA and the current rise time is 2 s. The breakdown strength of the high-voltage insulator is raised to a significant degree. The modernized facility was used in experiments in which the maximum accessible POS parameters (the obtained voltage, passed charge density, etc.) were evaluated. A voltage of up to 3.5 MV was obtained in the first experiments at a MXG voltage of 0.84 MV and a current of 300 kA.     

The Use of a Magnetic Switch for Commutation of High-Current Pulse Circuits

The switching of high-current pulse circuits by using a magnetic switch is analyzed. The use of the magnetic switch, which is an inductor on a toroidal ferromagnetic core, allows for the change to simple and reliable two-electrode spark gaps. They are triggered by a high-voltage igniting pulse, and the nonlinear inductance of the switch serves as an isolation between the high-current and low-current (ignition) circuits. The device was tested by switching the discharge of a capacitive storage with an energy of up to 100 kJ and millisecond pulse duration.     

A high-voltage nanosecond pulse generator based on a barrier discharge

One of the specific features of the barrier electric discharge is the short duration of microdischarge processes that last about tens of nanoseconds. A high-voltage nanosecond pulse generator based on a barrier electric discharge is presented. A voltage of tens of kilovolts is usually applied to electrodes of the discharge cell. The peak values of the current pulse may be very high (from a few amperes to several tens of amperes). The presented high-voltage nanosecond pulse generator, having a sufficiently simple design, ensures quite good pulse repetition stability, and, when necessary, allows one to easily tune characteristics of pulses and their repetition rates by changing the geometrical, electrical, and physical-chemical parameters of the setup.     

An experimental setup for exciting semiconductors and dielectrics with picosecond electron-beam and electric-field pulses

An experimental facility for forming high-voltage pulses with amplitudes of 30–250 kV and durations of 100–500 ps and electron beams with a current density of up to 1000 A/cm² is described. The facility was built using the principle of energy compression of a pulse from a nanosecond high-voltage generator accompanied by the subsequent pulse sharpening and cutting. The setup is equipped with two test coaxial chambers for exciting radiation in semiconductor crystals by an electron beam or an electric field in air at atmospheric pressure and T = 300 K. Generation of laser radiation in the visible range under field and electron pumping was attained in ZnSSe, ZnSe, ZnCdS, and CdS (462, 480, 515, and 525 nm, respectively). Under the exposure to an electric field (up to 10⁶ V cm^?1), the lasing region was as large as 300–500μm. The radiation divergence was within 5°. The maximum integral radiation power (6 kW at λ = 480 nm) was obtained under field pumping of a zinc selenide sample with a single dielectric mirror.     

A prototype of a superconducting magnet for a 170-GHz gyrotron

Within the framework of the “International Thermonuclear Experimental Reactor” (ITER) program, a prototype of a superconducting magnet for a 170-GHz gyrotron has been developed, manufactured, and tested. The operating induction value (7.1 T at the center of a 219-mm-diameter cold hole and 8.1 T on the winding) is reached at a current of 185.2 A. In the final version of the magnet, the required induction value was reached without aging. Special requirements are imposed on the distribution of the magnetic field along the axis, including an abrupt field decrease on both sides of the magnet. Axial forces are additionally taken by a special device. The magnet’s sections are wound with multifiber conductors based on niobium-tin and niobium-titanium alloys. Seventeen resistive shunts are provided for protecting sections during their transition to the normal state. The magnet is equipped with a device for removing a part of energy from the sections. Mechanical stresses in the magnet’s sections and the structure’s power elements have been measured during tests.     

Synchronized and configurable source of electrical pulses for x-ray pump-probe experiments

A method is described for the generation of software tunable patterns of nanosecond electrical pulses. The bipolar, high repetition rate (up to 250 MHz), fast rise time (<30 ps), square pulses are suitable for applications such as the excitation sequence in dynamic pump-probe experiments. Synchronization with the time structure of a synchrotron facility is possible as well as fine control of the relative delay in steps of 10 ps. The pulse generator described here is used to excite magnetic nanostructures with current pulses. Having an excitation system which can match the high repetition rate of a synchrotron allows for utilization of the full x-ray flux and is needed in experiments which require a large photon flux. The fast rise times allow for picosecond time resolution in pump-probe experiments. All pulse pattern parameters are configurable by software.     

Studying a spark discharge in the ground during reproduction of a negative lightning-current pulse using magnetic cumulation generators

Using an energy source based on a single BMΓ-160 generator, a current pulse with an amplitude of 50 kA and a rise time of 2 μs has been formed in a grounding rod electrode with a length of 1 m in the ground with a resistivity of 160 Ω m. The maximum length of spark channels on the ground surface from the point of current injection is 3–4 m. An energy source based on two BMΓ-160 generators connected in series allows an increase in the current pulse amplitude to 90 kA, the rise-time duration being the same, 2 μs. In this experiment, the maximum length of spark channels on the ground surface from the point of current injection exceeds 8 m.     

A 1-MJ capacitive energy storage

A capacitive energy storage is intended for generating high-power current pulses. The setup consists of two capacitive energy storage modules, a control console, and a cable collector for connecting a load to the setup. Each module is a capacitive energy storage with a 0.5-MJ stored energy and 18-kV voltage, which is based on eight capacitor cells with reverse switch-on dynistors as switches. The module volume is 1.3 m³. The semiconductor switches in the capacitor cells are activated by light pulses, which are transmitted from the control console through fiber-optic cables. The unit is designed for operating in the programmable discharge mode, at which the semiconductor switches in the capacitor cells are switched on nonsimultaneously but in accordance with a specified program. When the discharge of all the cells is switched on simultaneously and the load is short-circuited, the maximal amplitude of the output current pulse is 800 kA. The rise time of the discharge current pulse of the cell is 150 μs.     

A new current hybrid inertia friction welding for nickel-based superalloy K418–alloy steel 42CrMo dissimilar metals

The nickel-based superalloy K418 and alloy steel 42CrMo dissimilar metals friction welding joints lack strength and toughness due to high hardening and poor joining quality at the friction interface. To resolve this issue, a new current inertia friction welding (CIFW) method is carried out by hybrid an external additional electronic current in inertia friction welding (IFW) process. The characteristics of welding formation, the elements’ diffusion, and the mechanical properties of K418–42CrMo dissimilar metal joints are studied by scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer tools. The experimental results show that hybrid additional electronic current has a significant positive influence on interface characteristics of IFW joints. The required welding time for CIFW to complete a good qualified joint is shortened due to mixture actions of both friction heat and resistance heat. The width of the element diffusion zone increases in CIFW joints, and elements in 42CrMo side diffuse through the K418/42CrMo interface into the K418 side in CIFW joints. The width of the K418/42CrMo bonding interface increases in CIFW joints. The microhardness at the K418/42CrMo bonding interface is decreased in CIFW joints. The mechanical tensile property of CIFW joints is increased obviously. The interface bonding pattern becomes jagged and interlocking perfect formations. These above changes improve the joining quality of K418–42CrMo dissimilar metal friction welding joints. The heat treatment effect and resistance heat effect originated from hybrid external electronic currents are discussed by comparing CIFW with IFW. A new model is proposed to illustrate the interface’s evolution and development mechanism in K418–42CrMo dissimilar metal CIFW.     

Linear induction accelerators made from pulse-line cavities with external pulse injection

Two types of linear induction accelerator have been reported previously. In one, unidirectional voltage pulses are generated outside the accelerator and injected into the accelerator cavity modules, which contain ferromagnetic material to reduce energy losses in the form of currents induced, in parallel with the beam, in the cavity structure. In the other type, the accelerator cavity modules are themselves pulse-forming lines with energy storage and switches; parallel current losses are made zero by the use of circuits that generate bidirectional acceleration waveforms with a zero voltage-time integral. In a third type of design described here, the cavities are externally driven, and 100% efficient coupling of energy to the beam is obtained by designing the external pulse generators to produce bidirectional voltage waveforms with zero voltage-time integral. A design for such a pulse generator is described that is itself one hundred percent efficient and which is well suited to existing pulse power techniques. Two accelerator cavity designs are described that can couple the pulse from such a generator to the beam; one of these designs provides voltage doubling. Comparison is made between the accelerating gradients that can be obtained with this and the preceding types of induction accelerator.     

A high-voltage power supply based on a distributed capacitive energy storage

For the corpuscular plasma heating in the MST plasma device (Madison, United States), an injector of hydrogen atoms with 25-keV energy, equivalent at omic current of >45 A, and 20-ms pulse duration was designed and put into operation at the Budker Institute of Nuclear Physics (Novosibirsk, Russia) in 2009. The pulse repetition rate is 5 min. The output current of the ion source in the atomic injector exceeds 50 A. A high-voltage source with a 1.5-MW power was design ed for the high-voltage powering of the atomic injector. The run duration of the power supply with rated characteristics is >20 ms. The power supply is based on a distributed capacitive energy storage, which allows the power consumption from the industrial network to be reduced down to 10 kW at a pulsed load power of 1.5 MW. The high-voltage power supply smoothly regulates the output voltage from 0 to 30 kV and is capable of being quickly deenergized if high-voltage breakdown of the load takes place. The diagram and structural components of the high-voltage power system of the atomic injector are described, and its test results are given.     

A KPU-200 movable capacitor installation

A movable electrophysical capacitor installation with a 250-kJ maximum bank energy, which generates intense neutron pulses, is described. A current pulse generator with a capacitive energy storage forms the basis of the installation. When the initial voltage at the capacitor bank is up to 35 kV, the installation ensures a flow of current pulses with amplitudes of up to 2 MA in a gas-discharge plasma-focus chamber, which is filled with an equal-component deuterium-tritium (DT) mixture. Under these conditions, the chamber is capable of repeatedly generating single fast-neutron pulses with an energy of 14.1 MeV, a duration of ～70 ns, and an integral yield over 1013 neutrons/pulse.