Prototype of the 1/6 MOL Module of a Superpower Pulse Generator

This paper considers problems related to the creation (as part of the Baikal Program) of a super-power pulse generator intended for inertial confinement fusion applications and having pulse parameters of ～10 MV, ～50 MA, and ～150 ns. A MOL facility (3.7 MA, 5 MV, and 150 ns) with a six-module plasma opening switch (POS), operating as an output pulse compression stage, is being developed to test the circuit solutions of this generator. The design for the prototype of one POS module, referred to as the 1/6 MOL test bench, is presented. The results from experimental tests related to POS performance within the MOL facility are reported.     

A scheme of a modular plasma-opening-switch-based generator of megaampere currents for experiments with Z-pinches

A modular scheme of a megaampere current pulse generator on the plasma opening switch (POS) basis with insulation of the POS interelectrode gap by a magnetic field created by an external source is proposed for experiments with wire liners and other applications. The POS is fed from independent modules that are switched on in parallel. On the basis of an НК-50-3 (50 kV, 3 μF) capacitor, a supply module with a current through the equivalent part of the POS of up to 200 kA is designed and tested. The limiting POS parameters and the maximum permissible number of modules are determined, and circuit designs of the basic units of the generator are presented.     

Filling the gap of a plasma opening switch with plasma from an electroexploding wire in an external magnetic field

The dynamics of filling the interelectrode gap of a plasma opening switch (POS) using an electroexploding wire with a diameter of 4 μm (tungsten) and 6 μm (carbon) is considered. The wire was connected to coaxial electrodes of the POS perpendicular to the force lines of a longitudinal magnetic field, which was created by an external source. When a current was transmitted through the wire, the longitudinal speed of produced plasma was ≈10⁶ cm/s, and the azimuthal speed was ≈10⁷ cm/s (for tungsten) and ≥1.3 × 10⁷ cm/s (for carbon). As a result, a plasma “washer” was formed and the total quantity of particles in it was determined by the parameters of the wire and the POS gap. This result is the first step in a solution of “the first shot” problem.     

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.     

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.     

Radio frequency discharge with control of plasma potential distribution

A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.     

Electric strength of a vacuum gap during breakdown in an inhomogeneous electric field for switching high-power pulses

A system for matching the output of a multimodular plasma opening switch (POS) to a “liner”-type load having a small initial impedance is described. The main element of this system is an isolating spark gap that allows synchronization of the POS modules and prevents a repeated POS closure cutting off the inductive storage from the load. A spark gap based on a multigap explosive-emission diode, which was proposed and tested earlier, is insufficiently strong electrically to be used in the Baikal project aimed at the development of a superpowerful pulsed generator. An urgent problem of increasing the electrical strength of a 1-mm-wide vacuum gap, which is a basic element of the aforementioned spark gap, is being solved. It is proposed to use electrodes of the point (anode)-plane (cathode) type that allow the electric field to be concentrated at the point-type anode, thereby increasing the gap’s electrical strength. The results of experiments aimed at the study of vacuum breakdown in this system of electrodes are presented. It is shown that this design allows the gap’s strength to be raised by several times, a long service life of electrodes to be ensured thanks to the low energy-deposition density, and a multichannel (i.e., low-inductance) breakdown to be stably attained. A diagram of the spark-gap prototype is presented, its breakdown characteristics are obtained, and a full-scale scheme of the spark gap is presented.     

Small barium rail gun for plasma injection

A small rail gun with a barium electrode can be operated at higher than one shot per second to produce more than 2x10(16) barium ions with energy 10-20 eV. The operation of the gun takes advantage of the external magnetic field for cross-field plasma injection into a trap. Up to 7 kG of the magnetic field examined, the gun performance improves with the increased magnetic field strength.     

A facility for permeation measurements under plasma irradiation

An PIM (magnetic plasma source) experimental facility for investigation of permeation of hydrogen isotopes through the structural and plasma-facing materials, which are used in fusion devices, is described. The facility allows investigation of the hydrogen permeation through metal and porous (carbon and carbon composites) membranes in a temperature range of 290–1000 K during interaction of membranes with gaseous hydrogen (the pressure difference between the membrane sides is up to 0.1 atm) and also under irradiation with microwave plasma with a flux density of up to 3 × 10²⁰ atoms/(m² s). The permeability of ChS-68 austenitic steel was investigated. The experimental data confirmed the correctness of the operation of the facility and the reliability of the results.     

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.     

A nanosecond SOS-generator with a 20-kHz pulse repetition rate

A nanosecond SOS-generator with a 20-kHz pulse repetition rate in the continuous operating mode and with a 100-kHz pulse repetition rate in the pulse burst mode is described. The generator contains a low-voltage module with a primary capacitive storage and a transistor switch, and a high-voltage module with a magnetic compressor and a semiconductor opening switch (SOS diode). The generator forms pulses with amplitudes of 40–100 kV with a 20- to 30-MW peak power and a 10- to 14-ns duration across a 50- to 500-Ω external load. The output average power in the continuous operating mode is 5 kW. The electric circuit, principle of operation, and design of the generator’s elements are described. The test results are given.     

Design and Performance of Plasma Injectors for the Generation of High-Power Pulses (Review)

Pulsed plasma injectors, which are plasma generators for plasma opening switches and plasma-filled diodes, are described. Various types and design features of plasma injectors, the main characteristics of the injected plasma and its dynamics, and the performance of coaxial, multigap, and gas plasma injectors in high-power pulsed generators are considered. Methods for increasing the lifetime of multigap plasma injectors are proposed. The results of applying coaxial plasma injectors in repetitive-pulse generators with plasma opening switches are reported. The results for a switch operating in an applied external magnetic field are also presented. The design of plasma sources that show promise for use in Russia's Baikal Program for the creation of a superpower generator with parameters of 10 MV, 50 MA, and 150 ns is considered.     

Measurement of the plasma electron temperature with microsecond resolution

A probe method for determining the instantaneous electron temperature in a rarefied plasma in a magnetic field with a resolution below 2μs is described. The measurement circuit and principles of its operation are described. The experimental results obtained on a model of a stationary plasma engine with a dielectric channel are presented.     

基于Maxwell的磁场发生装置设计及分析

为了实现混有钕铁硼粉末的水凝胶磁化,设计了一种基于亥姆霍兹线圈的新式磁场发生装置。利用Maxwell软件3D模块绘制出磁场系统的三维模型,采用Magnetostatic静磁场求解器分析了增设的辅助线圈距离变化对场强的影响,得到了磁场发生装置的优化结构;再对比磁场发生装置和亥姆霍兹线圈的中心磁场强度和磁感线分布密度,验证结构优化的可靠性。结果表明:当辅助线圈距离为70 mm时,中心磁场强度最大;安匝数相同时,磁场发生装置的中心磁场强度要明显高于亥姆霍兹线圈,最终优化后的磁场发生装置中心磁场强度可达到1.37 T,磁感线分布更加均匀、密集。该仿真结果能够对磁场发生装置结构设计与工作特性分析提供参考,缩短了磁场发生装置设计成本与开发周期。     

Plasma characterization of the superconducting proton linear accelerator plasma generator using a 2 MHz compensated Langmuir probe

The CERN study for a superconducting proton Linac (SPL) investigates the design of a pulsed 5 GeV Linac operating at 50 Hz. As a first step towards a future SPL H(-) volume ion source, a plasma generator capable of operating at Linac4 or nominal SPL settings has been developed and operated at a dedicated test stand. The hydrogen plasma is heated by an inductively coupled RF discharge e(-) and ions are confined by a magnetic multipole cusp field similar to the currently commissioned Linac4 H(-) ion source. Time-resolved measurements of the plasma potential, temperature, and electron energy distribution function obtained by means of a RF compensated Langmuir probe along the axis of the plasma generator are presented. The influence of the main tuning parameters, such as RF power and frequency and the timing scheme is discussed with the aim to correlate them to optimum H(-) ion beam parameters measured on an ion source test stand. The effects of hydrogen injection settings which allow operation at 50 Hz repetition rate are discussed.     

Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments

A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.     

Magnetic multipole line-cusp plasma generator for neutral beam injectors

The magnetic multipole line-cusp device developed by MacKenzie and associates has been adapted for use as a neutral beam ion source. It has produced high-density, large volume, quiescent, uniform hydrogen plasmas, which makes it a potential candidate for use as a plasma generator for neutral beam injectors. The device is a water-cooled cylindrical copper discharge chamber (25 cm in diameter by 36 cm long) with one end enclosed by a set of extraction grids with a 15-cm-diam multi-aperture pattern. The chamber wall serves as an anode and is surrounded by an external system of rare-earth cobalt magnets arranged in a line-cusp geometry of 12 cusps; plasma is produced by electron emission from a hot cathode assembly. This source has achieved extracted beam currents of 12 A at 18.5 kV, radial plasma density uniformities of +/-5% over a 15-cm diameter, noise levels of less than +/-0.5%, and arc efficiencies (beam current/arc power) of 0.6 A/kW.     

激光测距仪时序发生器设计

以提高测距精度为目的,研究激光测距仪内部时序模块,对影响激光测距仪测距精度的因素进行分析。使用以外部延迟链芯片作为延迟线的方法,设计并制作了时序发生器的现场可编程门阵列（FPGA）开发板。测试结果表明,所设计的时序发生器能够实现11 ps的时序分辨率与最大600 Mbit/s的数据速率,达到了预期的目的。     

A high-current plasma emitter of electrons based on a glow discharge with a multirod electrostatic trap

Pulsed electron guns that produce 170-mm-diameter beams with currents of up to 700 A, electron energies of 300 keV, and a pulse width of ～200 μs at a gas pressure of ～0.01 Pa are experimentally studied. Glow-discharge plasma with electron confinement in an electrostatic trap is used as the electron emitter. The trap is formed by a hexagonal prism that consists of 204 cathode rods, which are 5 mm in diameter, 200 mm in length and are spaced by 1.5 mm, as well as 780 cathode rods, which are 5 mm in diameter and 98 mm in length, the spacing between their axes amounting to 15 mm. The latter rods are inside the former system of rods. The plasma emitter fills the hexagonal prism, which is free of rods, at the trap center with a distance of 280 mm between opposite sides and a height of ～200 mm between the emissive grid connected to the anode and the trap bottom covered with 23-mm-diameter cathode disks. All the cathode rods and disks are insulated from one another and connected to the discharge power supply through TVO-2 430-Ω resistors. The current limitation in the circuit of each cathode element by a value of ～2 A at a pulse width of ～5 ms of the glow-discharge current of up to 1 kA fully excludes its glow-to-arc transitions and allows production of continuous pulsed electron beams with an energy capacity of up to 40 kJ and a uniform distribution of the current density over its cross-sectional area of ～0.025 m².     

A compact repetitive high-voltage nanosecond pulse generator for the application of gas discharge

Uniform and stable discharge plasma requires very short duration pulses with fast rise times. A repetitive high-voltage nanosecond pulse generator for the application of gas discharge is presented in this paper. It is constructed with all solid-state components. Two-stage magnetic compression is used to generate a short duration pulse. Unlike in some reported studies, common commercial fast recovery diodes instead of a semiconductor opening switch (SOS) are used in our experiment that plays the role of SOS. The SOS-like effects of four different kinds of diodes are studied experimentally to optimize the output performance. It is found that the output pulse voltage is higher with a shorter reverse recovery time, and the rise time of pulse becomes faster when the falling time of reverse recovery current is shorter. The SOS-like effect of the diodes can be adjusted by changing the external circuit parameters. Through optimization the pulse generator can provide a pulsed voltage of 40 kV with a 40 ns duration, 10 ns rise time, and pulse repetition frequency of up to 5 kHz. Diffuse plasma can be formed in air at standard atmospheric pressure using the developed pulse generator. With a light weight and small packaging the pulse generator is suitable for gas discharge application.