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.     

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.     

Application of an impedance matching transformer to a plasma focus

A plasma focus was constructed using an impedance matching transformer to improve power transfer between the pulse power and the dynamic plasma load. The system relied on two switches and twelve transformer cores to produce a 100 kA pulse in short circuit on the secondary at 27 kV on the primary with 110 J stored. With the two transformer systems in parallel, the Thevenin equivalent circuit parameters on the secondary side of the driver are: C = 10.9 μF, V(0) = 4.5 kV, L = 17 nH, and R = 5 mΩ. An equivalent direct drive circuit would require a large number of switches in parallel, to achieve the same Thevenin equivalent. The benefits of this approach are replacement of consumable switches with non-consumable transformer cores, reduction of the driver inductance and resistance as viewed by the dynamic load, and reduction of the stored energy to produce a given peak current. The system is designed to operate at 100 Hz, so minimizing the stored energy results in less load on the thermal management system. When operated at 1 Hz, the neutron yield from the transformer matched plasma focus was similar to the neutron yield from a conventional (directly driven) plasma focus at the same peak current.     

Synchronization algorithm for three-phase voltages of an inverter and a grid

This paper presents the results of designing a joint phase-locked loop for adjusting the phase shifts (speed) and Euclidean norm of three-phase voltages of an inverter to the same grid parameters. The design can be used, in particular, to match the potentials of two parallel-connected power sources for the fundamental harmonic at the moments of switching the stator windings of an induction AC motor from a converter to a centralized power-supply system and back. Technical implementation of the developed synchronization algorithm will significantly reduce the inductance of the current-balancing reactor and exclude emergency operation modes in the electric motor power circuit.     

A High-Frequency Discharge Unit for Pumping Systems of Semiconductor Lasers

The electric circuit of a high-frequency discharge unit for pumping semiconductor lasers and the calculation of the unit pumping regime are presented. The unit ensures a high efficiency of conversion of the power-supply energy into the pump-pulses energy at constant current amplitudes within the entire pump pulse. The transients in the circuit are analyzed, and the main parameters of the converting system at a specified current and pulse duration are determined. A control circuit ensuring a programmable current-source mode is proposed.     

Analysis of a modular generator for high-voltage, high-frequency pulsed applications, using low voltage semiconductors (< 1 kV) and series connected step-up (1:10) transformers

This article discusses the operation of a modular generator topology, which has been developed for high-frequency (kHz), high-voltage (kV) pulsed applications. The proposed generator uses individual modules, each one consisting of a pulse circuit based on a modified forward converter, which takes advantage of the required low duty cycle to operate with a low voltage clamp reset circuit for the step-up transformer. This reduces the maximum voltage on the semiconductor devices of both primary and secondary transformer sides. The secondary winding of each step-up transformer is series connected, delivering a fraction of the total voltage. Each individual pulsed module is supplied via an isolation transformer. The assembled modular laboratorial prototype, with three 5 kV modules, 800 V semiconductor switches, and 1:10 step-up transformers, has 80% efficiency, and is capable of delivering, into resistive loads, -15 kV1 A pulses with 5 micros width, 10 kHz repetition rate, with less than 1 micros pulse rise time. Experimental results for resistive loads are presented and discussed.     

The critical aspects in the design of high-current inductors

High-voltage high-current inductors are important components of power-supply systems that are based on capacitor banks with a high energy capacity. The main aspects of designing high-current inductors that were obtained via numerical simulation are presented. A harmonic analysis was performed to take the influence of eddy currents on the inductance value and mechanical stresses into account. It was shown that the choice of materials significantly influences the parameters of the inductor. Calculations of the stray magnetic field in a quasi-toroidal assembly of inductors were performed. It is shown that the leakage magnetic field in the far-field zone is two orders of magnitude lower for an assembly of four inductors than for one inductor.     

TEA CO2激光器主放电延迟时间对效率的影响

介绍了TEA CO₂激光器火花针紫外预电离与主放电之间的延迟时间对激光器输出电光转换效率影响的实验研究结果。通过改变放电回路中的感抗值,可以改变预电离与主放电之间的延迟时间。实验结果表明:当预电离与主放电的延迟时间在200~600 ns范围变化时,激光器输出的电光转换效率存在最佳点,在注入能量相同的情况下,单脉冲能量从24.0 J提高到45.6 J,激光器的电光转换效率从8％提高到15％。经过进一步的参数优化,该激光器的电光转换效率最高可以达到17％以上。     

Longitudinally excited N(2) lasers without high-voltage switches

We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N(2) lasers (wavelength: 337 nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8 microJ and the efficiency was 0.16% at 18 Torr (2.4 kPa) when a slow-rising voltage pulse of -28 kV was applied (rise time: 21.3 micros). In the tandem-tube system, the laser output energy was 259.4 microJ and the efficiency was 0.11% at 18 Torr when a slow-rising voltage pulse of -48 kV was applied (rise time: 27 micros).     

A stabilized copper bromide laser with computer-controlled operating modes and a mean lasing power of 20 W

A copper bromide vapor laser with a mean lasing power of 20 W and the computer-controlled pulse-periodic, pulse train, and waiting modes is described. The laser power-supply unit has a modular structure. The effect of operating parameters on the lasing characteristics is shown. The mutual influence of the power-supply units is determined. The laser design and energy characteristics are presented.     

双管反激电源的分析与设计

针对反激电源主开关管关断时候的电压应力过大和变压器气隙漏感导致的电压尖峰过大的问题,对双管反激电源的拓扑结构及工作原理进行了详细分析,构建了双管反激电源工作在DCM模式时的能量传递模型,论证了变压器匝比与变压器原边漏感的磁复位时间及最大占空比和回馈能量大小的关系,推导出了双管反激电源主要参数的通用设计公式;利用其设计公式,设计了一个实际工作于DCM模式的30W双管反激电源,同时利用Saber仿真软件,研究了双管反激电源的主开关管、副边整流二极管和原边续流二极管的工作电流。仿真结果表明：变压器匝比参数选择合适,充分削弱了通过续流二极管回馈的能量,电源工作稳定。将仿真结果与实验样机所测结果进行了比较,结果显示两者基本吻合,说明设计公式可用作双管反激电源主要参数的设计工具。     

Generation of High-Voltage Pulses with a Picosecond Front in a Cascade Kivotron Connection

The possibility of the operation of high-current high-voltage switches based on “open” discharge with the generation of counter-propagating electron beams, that is, kivotrons, in a two-stage pulse compression scheme is demonstrated experimentally. The total degree of the initial-pulse compression, which exceeded 600 at a minimum measured front duration of a generated pulse of at most 100 ps, was achieved at a voltage of up to 18 kV and a pulse-repetition rate of 1 kHz.     

Control systems of high-voltage transistor switches

Control systems of high-voltage transistor switches are described. Possible ways to develop these systems are considered. A control system of the transistors of a high-voltage switch on the basis of a current loop is considered in detail. Signals for turning the transistors on and off arrive to their control boards from their common conductor with bipolar current pulses. A positive pulse turns the transistors on, while a negative pulse turns them off. The time interval between these pulses sets the time during which the switch is in the conducting state. The minimum duration of the conducting state is several microseconds, while the maximum duration is not limited. The results of tests of a switch prototype with an operating voltage of up to 4 kV are presented. The operation of the switch was demonstrated when obtaining rectangular pulses in the microsecond range across a resistive load. We also verified the possibility of forming pulses of damped oscillations at a frequency of 1 MHz by this device. The positive test results make it possible to develop switches for operating voltages of tens of kilovolts using the considered approach.     

Multichannel Spark Gaps with Control Bar Electrodes: Their Development and Application (A Review)

Multichannel low-inductance (1 nH) gas-filled spark gaps (MSGs)¹ with several tens of channels each, bar control electrodes designed for an operating voltage of 100 kV, and a switched current of up to 400 kA are reviewed. The control electrodes, made in the form of narrow thin plates, have an intermediate potential, are positioned in the gap between two common main electrodes (high-voltage and low-voltage (grounded)), and are oriented uniformly along their length. Upon a near-simultaneous change in the bars' potential in a time of <15 ns, applying a signal through trigger circuits disturbs the electric-field distribution in the gas volume. The field strength sharply increases at the electrode surfaces and especially at the edges of the bars, from which breakdowns develop synchronously from one electrode to another or simultaneously to both main electrodes. When the discharge formation is completed, the main electrodes of the MSGs are short-circuited by discharges through parallel channels (whose number is equal to the number of bars). These switches ensure the nanosecond accuracy of the operation delay relative to the trigger pulse at a breakdown-strength margin of up to 100%, determined by the pressure (>0.1 MPa) of the MSG-filling gas. Electrical circuits for initiating the discharge development in the MSGs, the transients in such circuits, and the factors affecting the parameters of processes and the gap-breakdown delay and rate are considered. Particular MSG designs, multicable systems for parallel triggering of a large number of MSGs, and the use of 48 four-channel 50-kV MSGs in the first iron-free LIA-2 linear electron accelerator (2 MeV, 25 kA, and 60 ns) created in 1967 are described. The successful operation of MSGs stimulated further studies and the development of efficient trigatrons for operating voltages of 100 and 500 kV. Up to 3000 MSGs of this type are used in new high-power linear electron accelerators. A low-impedance (0.45 ) generator of high-voltage pulses (50–200 kV) with a multicable output has been developed to synchronously trigger such large numbers of trigatrons as these.     

Simple method of determining plasma impedance of streamer discharge in atmospheric air

For atmospheric streamer discharges using a lightning impulse generator, we demonstrate a method of determining the plasma impedance in a streamer region by analyzing the periodic attenuated discharge waveforms having high-frequency components. When the streamer region in the plasma can be treated as an equivalent series circuit model including resistance and inductance elements, the regression waveforms obtained by reducing and smoothing the discharge waveforms are analyzed in the equivalent circuit. We found that the streamer resistance increased exponentially with time after the discharge, whereas the streamer inductance and series impedance were constant at 4.0 Ω for longer than the first period of the discharge waveforms. Moreover, the slope of the regression curve increases more rapidly for the positive streamer resistance than for the negative resistance. Finally, the absolute values of the streamer impedance versus time were 3.3-19 Ω and 3.5-9.0 Ω for positive and negative discharges, respectively.     

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.     

基于参数辨识的内置式永磁同步电机最大转矩电流比电流预测控制

为了实现对内置式永磁同步电机的高效准确控制,解决电机运行过程中参数变化对控制性能的影响,提出了一种基于在线参数辨识的内置式永磁同步电机最大转矩电流比电流预测控制方法。根据内置式永磁同步电机的转矩特性对最大转矩电流比的d-q电流最优关系进行化简以便于工程计算;并针对电机参数变化对最大转矩电流比工作点偏移的影响进行了分析。同时,对MTPA算法影响较大的关键参数q轴定子电感,转子永磁体磁链进行基于参考模型的自适应辨识,以确保实时的最优d,q轴电流分配。在得到准确辨识的参数和最优电流指令的基础上进行电流的鲁棒预测控制,使实际电流更快地跟踪指令,提高系统的动态性能。实验结果表明q轴定子电感,转子永磁体磁链在线辨识的误差分别小于3%,3.5%,收敛时间小于20 ms;电机能有效跟踪最大转矩电流比工作点,电流响应时间小于30 ms,能够满足内置式永磁同步电机系统稳定可靠、高效快速等运行要求。     

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.     

Influence of parameters and optimization of EDM performance measures on MDN 300 steel using Taguchi method

Maraging steel (MDN 300) exhibits high levels of strength and hardness. Optimization of performance measures is essential for effective machining. In this paper, Taguchi method, used to determine the influence of process parameters and optimization of electrical discharge machining (EDM) performance measures on MDN 300 steel, has been discussed. The process performance criteria such as material removal rate (MRR), tool wear rate (TWR), relative wear ratio (RWR), and surface roughness (SR) were evaluated. Discharge current, pulse on time, and pulse off time have been considered the main factors affecting EDM performance. The results of the present work reveal that the optimal level of the factors for SR and TWR are same but differs from the optimum levels of the factors for MRR and RWR. Further, discharge current, pulse on time, and pulse off time have been found to play a significant role in EDM operations. Detailed analysis of structural features of machined surface was done by using scanning electron microscope (SEM) to understand the influence of parameters. SEM of electrical discharge machining surface indicates that at higher discharge current and longer pulse on duration give rougher surface with more craters, globules of debris, pockmarks or chimneys, and microcracks than that of lower discharge current and lower pulse on duration.     

Investigation of vibrations in multimodule drives of cyclic machines with a branched-ring structure

The technique of dynamic investigations of multimodule cyclic machines which form vibrating-branched and ring-structured systems with constraints depending on time is developed. The spectrum of eigenfrequencies and gain-frequency characteristics in the case of kinematic excitation due to the programmed motion of execution elements is determined using continual idealization and regular system properties.