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The planned China fusion engineering test reactor (CFETR) needs one or more negative-ion-based neutral beam injectors (N-NBIs) with a beam energy of 500 or even 1000 keV. In order to prepare for CFETR, a prototype of CFETR N-NBI is being designed. The prototype needs an acceleration grid power supply (AGPS) rated at 200 kV/25 A with a maximum pulselength reaches to 3600 s. The AGPS adopted a single-stage inverter-type high-voltage power supply (HVPS). The output voltage ripple is an important specification of the AGPS, which can affect the efficiency and stability of N-NBI system by influencing the beam divergence. However, the conventional methods cannot be used to limit the output voltage ripple of the inverter-type HVPS used as AGPS of CFETR N-NBI prototype. This paper simplified the AGPS to an insulated three-phase three-level (TPTL) dc–dc converter connected with a dual dc link. The working process of the TPTL dc–dc converter with duty-cycle modulation has been analyzed, and two main continuous conduction modes are described. The influence of key parameters such as duty cycle of inverter, leakage inductance of transformer, and output current on output voltage ripple is analyzed. Based on the analysis results, a so-called combined control strategy was proposed to keep the output voltage ripple at a level. The proposed strategy is suitable for the cases where the object output voltage is below 175 kV. Some simulations were carried out by using MATLAB/Simulink. The results showed that the analysis in this paper is reliable and the proposed control strategy has a good performance. [ABSTRACT FROM AUTHOR]

This paper proposes unconventional control techniques for a portable power supply consisting of electric double-layer capacitors (EDLCs), a dc–dc converter, and a low-impedance load such a plasma load. Between the EDLCs and the plasma load consuming high power, a dc–dc converter is required to control the output voltage from the rapidly decreasing voltage of EDLCs. In addition, the dc–dc converter should maintain a set point by responding to arcs occurred in plasma process. This paper proposed hybrid analog and digital controls for a nonideal boost converter which was setup by theoretical analysis. The proposed system is verified with experiment and simulation. As a result, the proposed control method can maintain the constant output voltage longer than a traditional analog pulsewidth modulation control. [ABSTRACT FROM AUTHOR]

DC arc evolution is a complicated and rapid time-dependent process. To better demonstrate the mechanism of the dc arc without external interference factors, a test circuit was built for the entire process of arc generation, maintenance, and extinction. Two different adjustment models were adopted. The macroscopic performance and characteristics of the arc were analyzed. The discharging and extinguishing conditions were measured and compared to the results of a burning candle located under a rod–rod air gap. This paper shows that the dc arc’s color changes from blue to purple and then yellow, finally forming a flame as the current increases. The macroscopic performance can be divided into eight periods in the first adjustment model, while only three periods are included in the second model. The arc discharging condition only depends on the applied high voltage, but the extinguishing condition may depend on either the limiting current or the drop-down voltage. Dynamic volt–ampere characteristics appear only if adjusted by the first model. The arc-root voltage is constant to 0.32 kV. The degradation of the ground electrode is far worse than that of the high-voltage electrode. This paper can be regarded as the first-step research for further studies on large-current dc arcs in arcing horns used in dc transmission grounding lines. [ABSTRACT FROM AUTHOR]

This paper discusses the control of a modular multilevel converter (MMC) used as a grid interface for the klystron modulators in the compact linear collider (CLIC). The converter has a DC side load which takes short-duration power pulses, causing high DC side power fluctuations that are not tolerable if seen by the AC grid. The DC–AC power decoupling capability of the MMC enables mitigation of the power ripple on the AC side, guaranteeing compliance with power quality requirements. However, the pulse repetition rate of the CLIC modulators is synchronized the 50-Hz AC grid and this induces permanent power imbalance in the arms of the MMC, causing voltage deviation and overmodulation unless appropriate balancing strategies are implemented. Unlike existing arm balancing methods that control 50-Hz circulating currents to balance the arm powers, the method proposed in this paper introduces an augmented modulation strategy where modulation signals are redistributed among arms based on the demand from a balancing controller. The resulting controller has lower complexity and its simple structure enables an easier design of the balancing loop, which guarantees predictable dynamics in operation. The effectiveness of the method has been demonstrated in simulation for the full-scale CLIC converter ratings and experimentally on a 7-kW MMC prototype operating with a 3.3-kA pulsed DC load. [ABSTRACT FROM AUTHOR]

This paper introduces the work undertaken to reliably use off-the-shelf differentiating voltage probes attached to coaxial transmission lines. The results obtained prove that indeed such probes are a valid and simple instrument for measuring nanosecond and subnanosecond voltage impulses. As a bonus, this paper also highlighted an important challenging phenomenon that appears whenever an attempt is made to measure fast voltage impulses with a differentiating probe positioned too close to the closing switch of a pulse forming line generator. [ABSTRACT FROM AUTHOR]

This paper proposes an active resonance circuit based on multiple series gaps (MSG) with voltage-dividing network and self-charging trigger device. The working principle of active resonance circuit, MSG, and triggering device is described in detail. To determine the optimal parameter setting of MSG, the effects of the voltage frequency, equalizing resistance, and voltage-dividing capacitance on the voltage distribution of MSG are analyzed by simulation. To realize the interrupting process of short fault current and determine the operation requirements of the main devices of precharge direct current (dc) circuit breaker, a simulation model of interrupting short fault current is performed. Furthermore, an experiment of four-series gaps is presented to verify the turn-on characteristic of the MSG and an experiment of artificial current zero is set up to testify the feasibility of the active resonance circuit. The simulation and experimental results show that the active resonance circuit proposed in this paper can generate an artificial zero current and is suitable for precharge dc circuit breaker. [ABSTRACT FROM AUTHOR]

This paper shows how to use modular Marx multilevel converter diode ( \textM^3 CD) modules to apply unipolar or bipolar high-voltage pulses for pulsed power applications. The \textM^3 CD cells allow the assembly of a multilevel converter without needing complex algorithms and parameter measurement to balance the capacitor voltages. This paper also explains how to supply all the modular cells in order to ensure galvanic isolation between control circuits and power circuits. The experimental results for a generator with seven levels, and unipolar and bipolar pulses into resistive, inductive, and capacitive loads are presented. [ABSTRACT FROM AUTHOR]

In this paper, the functional aging of gas-filled surge arresters (GFSAs) is addressed. Aging is determined by the features of the lifetime. Statistical samples of the random variables of breakdown time and breakdown voltage have been recorded. Experiments on the model of a GFSA were carried out in controlled laboratory conditions. The parameters of the experiment were: 1) gas type; 2) gas pressure; 3) interelectrode distance; 4) electrode material; and 5) treatment method of the electrode surface. The results indicate that the GFSA shows slower functional aging provided that: 1) the operating point is to the right of the Paschen minimum in the area of breakdown initiation with streamers mechanism; 2) the pressure is lower, i.e., at a constant pd value (product of pressure and interelectrode distance); 3) the electrode material has a higher melting point and thermal conductivity; and 4) the electrodes have a built-in topography. In addition, it was established that aging of the GFSA does not depend on the noble gas type. Finally, the production of a GFSA with optimal characteristics in terms of functional stability is proposed. [ABSTRACT FROM AUTHOR]

High-power current sources with high dynamic performance, ultralow current ripple, and absolute reference tracking accuracy are the key elements for magnets (bumper and septum) that are used in accelerators. Similar requirements are also encountered in plasma research applications in fusion reactors, as well as plasma research for the future high voltage direct current circuit breakers. Therefore, the current source must be able to drive resistive/inductive and highly fluctuating loads without any compromise in its performance. In this paper, such a flexible, dynamic, and accurate current source is introduced, which able to provide amplitudes up to 30 kA and bipolar voltages up to 10 kV. The system’s operating concept is presented and its design procedure in order to fulfill a list of demanding specifications is demonstrated. In addition, a detailed description of its near-optimal, advanced control system is presented. Finally, the theoretical considerations are verified by extensive simulation results for various operating scenarios, including driving chaotic arc loads. [ABSTRACT FROM AUTHOR]

This paper proposes the equivalent circuit of postarc dynamic voltage distribution (PDVD) in multibreak vacuum circuit breakers (VCBs). The equivalent circuit is composed of controlled postarc sources, postarc resistors, and equivalent capacitors. The sheath growth and the postarc process of double-break VCBs are analyzed. The PDVD is divided into four processes: the initial transient recovery voltage (TRV) process, the oscillating TRV process, the stable TRV process, and the power-frequency voltage process, which can be analyzed by the equivalent circuit. The novel equivalent circuit of the PDVD in multibreak VCBs is gained by introducing the controlled postarc current source. The test platform is set up in the synthetic circuit. The postarc current, grading capacitor current, and the TRV are measured to analyze the PDVD in the above four processes. The test results verify the theoretical analysis. Therefore, the mechanism of the PDVD in multibreak VCBs is obtained and described by the equivalent circuit, which is useful to gain even voltage distribution and improve the breaking capacity of multibreak VCBs. [ABSTRACT FROM AUTHOR]

Electromagnetic launchers (EMLs) including railguns, helical guns, and coilguns have been proposed for numerous applications. However, the scaling characteristics of EMLs are unknown. This paper examines the nonlinear operating characteristics of EMLs and derives the operating voltage and current scaling relationships as determined by the mass and velocity of the projectile and the length of the launcher. The scaling relationship is derived using the kinetic power relationship common to all types of EMLs. The scaling relationship is expressed as a simple function of the projectile velocity, projectile mass, and launcher length. This paper also defines the impedance of an EML. The accuracy of the scaling relationship and the EML impedance are verified in a comparison with the experimental results of practical EMLs. The effects of resistive losses and inductive energy storage on the scaling relationship are included in the analysis. [ABSTRACT FROM PUBLISHER]

In this paper, NH3 plasma directly applied to the surface of poly-Si channel is studied for the development of high-performance low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) with HfO2 high- \kappa gate dielectric. The reduction of threshold voltage from 1.52 to 0.62 V, the decrease of subthreshold swing from 227 to 151 mV/decade, and the enhancement of field effect mobility \mu _{\mathrm {FE}} from 31 to 65 cm ^{\mathrm {\mathbf {2}}}$ /Vs are observed after NH3 plasma surface treatment. It can be attributed to the NH3 plasma surface treatment enabling defect passivation and plasma-induced interfacial layer (PIL) growth. To decouple the impacts of defect passivation and PIL growth, the device without PIL is also fabricated. This paper demonstrates the important impacts of NH3 plasma surface treatment on the improvement of electrical characteristics of LTPS-TFTs. [ABSTRACT FROM PUBLISHER]

This paper presents a 100-kV high frequency transformer/rectifier package, which is capable of a dual output polarity operation. An H-Bridge inverter drives the primary of the high voltage (HV) transformer at a frequency of 20 kHz. The inverter is driven by a Microchip dsPIC33F digital signal controller using peak current mode control with adaptive slope compensation. The HV-tank has two HV-coax output cables with a grounded shield on each cable. If the center conductor of the coax cable designated as negative output is grounded, positive voltage is obtained from the coax cable designated as positive output and vice versa. This paper provides design details and experimental results from tests of the entire system. [ABSTRACT FROM PUBLISHER]

Multipole field reconnection electromagnetic launchers are highly efficient electromagnetic transmitters, which can solve the inherent flaws in conventional electromagnetic launchers such as the small axial thrust and the sliding contact. In addition, there are many tunable parameters for this launch mode. In order to improve the acceleration performance, the axial acceleration force, the efficiency of the system and influence of capacitor parameters on the emission performance is focused in this paper. Some theories about this launch mode is introduced. A finite-element model of the system was constructed and the commercial finite-element software Ansys Maxwell was applied. The simulation results indicate that increasing the voltage and capacitance of the capacitor can improve the axial acceleration force of the projectile, but the efficiency of the system may not be enhanced. We proposed that it should be appropriate to reduce the capacitance, while increasing the charging voltage value at high-speed launch. [ABSTRACT FROM AUTHOR]

To set up an automatic hot test platform of gyrotron traveling wave tubes (gyro-TWTs), feedback controls of proportional–integral–derivative (PID) were applied. Simulation of the controlling process of operating voltage on the gyro-TWT cathode had been carried out by MATLAB and then was verified as well as compared by the hot test experiment. The PID control on cathode–anode voltage is typical and similar to the control of beam current achieved by the heater filament. The operating voltage controlling process includes two different stages, i.e., the voltage rise and voltage maintenance phase. By optimizing the operating parameters of the PID algorithm, the simulated voltage rise has a good agreement with the one in the hot test controlling. Furthermore, PID responses after feedback control with sinusoidal and random fluctuations are, respectively, investigated. This paper indicates that the proposed strategy can easily achieve a stable operating voltage. [ABSTRACT FROM AUTHOR]

JT-60SA is a superconducting tokamak in the framework of the broader approach agreement between Europe and Japan. For this international project among its various procurements, the Italian National Agency for new technology energy and sustainable economic development (ENEA) is providing four ac/dc converters for the central solenoid (CS) superconducting magnets, two ac/dc converters for the equilibrium field (EF) superconducting magnets, and two ac/dc converters for the fast plasma position control coils (FPPCC). Furthermore, ENEA is also providing six converter transformers of which four are of the dry type for FPPCC power supplies (PSs) and two of oil type for CS PSs. CS/EF PSs feed poloidal superconducting magnets of JT-60SA, whose purpose is the generation of strong magnetic fields able to induce and confine the plasma current in a prefixed geometrical configuration. The control system of CS/EF PSs has to be able to reproduce in real-time a reference current or voltage profile, known as “scenario” and these are particularly critical in these systems for the high currents required and for the high magnetic energy stored in the superconducting magnets. All performed type tests, carried out in accordance to the IEC60146 Standards, pointed toward a good dynamic behavior of the control system both for forward and for reverse rectifier bridges, assuring the smooth transitions between different operating modes: single mode, circulating current mode and dual mode. This is the focus of this paper. [ABSTRACT FROM AUTHOR]

The extraction grid power supply (EGPS) is important for neutral beam injection of tokamak, which is used to extract the negative ions from the plasma source. A set of power supply with pulse step modulation topology at 16 kV/20 A has been designed for the negative ions extraction at the Institute of Plasma Physics, Chinese Academy of Sciences, which meets the requirements of fast dynamics, low ripple, and good output operation. The development of EGPS is presented in this paper. Two different voltage ratings and series-connected switched power supply (SPS) modules are fed from multisecondary transformer. Insulated-gate bipolar transistors are applied to the switch of SPS module. Rise time and fall time of EGPS out voltage can be set from few microseconds to milliseconds. When the overcurrent occur, the output voltage falls to zero less than $5~\mu \text{s}$. The dynamic performance tests with dummy load of EGPS are presented. The testing results indicate that the power supply meets the demands of negative ions extraction. The design provides a foundation for the next phase of extraction experimental operation for radio frequency ion source. [ABSTRACT FROM AUTHOR]

Three flywheel energy-stored impulse motor-generators (MGs) are used in the power supply system of HL-2A tokamak to produce short high-voltage or high-current pulse of desired parameters that are usually used for magnetic field coils and auxiliary heating equipment loads. The operation changing of these loads will cause disturbances in generator’s terminal voltage and the remarkable drop in MG’s rotating speed. This paper describes the implementation of an excitation controller using LabVIEW and CompactRIO for a 125-MVA impulse MG in power supply system of HL-2A/2M. Both a staged control strategy and digital PID algorithm built in LabVIEW are applied to the excitation controller that runs preciously in a 1-ms cycle to achieve voltage feedback control. The excitation controller, composed mainly of host computer and CompactRIO embedded reconfigurable system, is available to restore and stabilize terminal voltage in accordance with the desired voltage curves set by operators when pulsed loads and motor speed change quickly. It also implements real-time monitoring of the working condition and some electrical parameters of excitation system and communicates with central control system via Ethernet to either download discharge control files at time interval between two impulse discharges or upload waveform data generated in control process after a pulsed discharge. Engineering experiment results show that the use of excitation controller improves the voltage stiffness of the power supply system and provides the effective control of generator’s terminal voltage under the management of central control system. [ABSTRACT FROM AUTHOR]

Recent circuit driven electromagnetic particle in cell simulation of the United Nations University-International Centre for Theoretical Physics plasma focus device revealed regular oscillations in both the voltage and current profiles. The simulated voltage waveform agreed well with the experimental profile, where similar unaccounted oscillations were also observed. In this paper, the oscillations are attributed to the plasma inductance, whose value was calculated by circuit analysis and agreed reasonably well with the computed experimental value. A circuit simulation of the prebreakdown and postbreakdown phases, with the plasma inductance incorporated, reproduced with sufficiency accuracy the electromagnetic particle in cell generated waveforms and consequently confirmed our finding. [ABSTRACT FROM AUTHOR]

In this paper, a new architecture of a high-voltage Marx pulse generator based on isolated gate bipolar transistors (IGBTs) is proposed. It allows continuous control of the output voltage by acting on the IGBTs activation time: “on-time.” The final after-charging capacitors' voltage can be higher than the double of the input voltage. A simplified mathematical description of the system was developed in order to find a relation between the output voltage and the “On-time” (an open-loop control law). A SPICE simulation was implemented to check the expected performances and to verify the developed model. A three-stage generator was built according to the proposed structure using commercial IGBTs with a maximum output voltage of 3.6 kV. All results were compared to check and confirm the validity of the proposed architecture. [ABSTRACT FROM PUBLISHER]

When the poloidal field (PF) magnet power supplies (MPSs) of 11 units are operated, maximum power of 200 MVA is required to achieve long pulse operation of Korea superconducting tokamak advanced research (KSTAR). Motor generator (MG) system was installed to resolve the power shortage because the available grid power is only 100 MVA at the National Fusion Research Institute site. MG system is composed of mechanical devices (stator, rotor, bearings, etc.), power control devices (variable voltage variable frequency and exciter), power facilities (transformers, switchboard, uninterruptible power system, filter, dynamic brake, etc.), utilities (cooling water pump, heat exchangers, cooling fans, oil circulation pump, mechanical brake, etc.), and control systems. MG system supplies power to the PF MPS of 11 units. And we configure the reactive power compensator (RPC) and harmonic filter (HF) system to stabilize the MG power system. After installing the MG system, individual tests and dummy coil tests were conducted to determine the safety and performance of MG system. And we completed the commissioning of the MG system by carrying out the superconducting magnet coil load tests for the 2014 KSTAR experiment. MG system was operated up to 150 MVA of PF MPS with the RPC and HF system. And the maximum operating duration was about 100 s. In this paper, we discuss about the power characteristic results of the MG system according to the superconducting magnet coil load tests. [ABSTRACT FROM PUBLISHER]

High-voltage (HV) pulses are used in pulsed electric field (PEF) applications to provide an effective electroporation process, a process in which harmful microorganisms are disinfected when subjected to a PEF. Depending on the PEF application, different HV pulse specifications are required such as the pulse-waveform shape, the voltage magnitude, the pulse duration, and the pulse repetition rate. In this paper, a generic pulse-waveform generator (GPG) is proposed, and the GPG topology is based on half-bridge modular multilevel converter (HB-MMC) cells. The GPG topology is formed of four identical arms of series-connected HB-MMC cells forming an H-bridge. Unlike the conventional HB-MMC-based converters in HVdc transmission, the GPG load power flow is not continuous which leads to smaller size cell capacitors utilization; hence, smaller footprint of the GPG is achieved. The GPG topology flexibility allows the controller software to generate a basic multilevel waveform which can be manipulated to generate the commonly used PEF pulse waveforms. Therefore, the proposed topology offers modularity, redundancy, and scalability. The viability of the proposed GPG converter is validated by MATLAB/Simulink simulation and experimentation. [ABSTRACT FROM PUBLISHER]

A portable dc power supply based on electric double-layer capacitor (EDLC) bank was established for high-power applications. EDLC bank needs a dc–dc converter to maintain a constant output voltage and current. Especially, a low-impedance load makes the voltage of capacitors discharge faster, and their discharging time is determined by RC time constant. The proposed system is designed as a fundamental concept, and deals with some issues occurring in a large-scale system. Also, this paper provides detailed information and consideration for a real establishment. Last, we performed a full-scale experiment using basic techniques. [ABSTRACT FROM PUBLISHER]

Pulsed power supply (PPS) applied in the electromagnetic launch system must have a compact design and high reliability. In this paper, a PPS for electromagnetic launch system is built up. The main parts in a pulse forming unit (PFU) of a PPS are energy storage capacitors (8 kV/75 kJ), pulse-shaping inductor (10 \muH), pulse thyristor, crowbar diode, and a Rogowski coil for current measuring. The energy storage density of the PFU is 0.74 MJ/m^3. Eight PFUs form a pulse forming network (PFN) of 600 kJ. In many cases, the discharge current waveform of the PFN must be adjusted for lower peak value and lower electromagnetic force. On the basis of this PFN, in this paper, we analyze the effect of sequence discharge on the semiconductors. To prevent diode from overvoltage during the recovery process, different parameters of snubber circuit have been researched in the experiments. Finally, we set up a model of the serial augment rail gun in a personal simulation program with integrated circuit emphasis, and the safety of PFU can be affirmed by simulation if the voltage of the rail gun keeps positive during the course of the discharge. [ABSTRACT FROM PUBLISHER]

Electromagnetic launch (EML) system needs pulse power supply (PPS) as the energy source for discharging in EML experiments. The EML system’s work effectiveness is decided by the PPS’s parameters, such as the charging precision of the voltage, the energy density of the energy storage module, and the charging rate. As the development of EML technology, the experiment needs more and more energy and the number of energy storage module is increasing rapidly. However, the output power of the charging power supply cannot hold up the requirement energy at the same time. So, how to charge the numerous modules rapidly and accurately becomes a key problem to be solved. In this paper, the load is divided to several groups and a controller to manage the multigroups of load is designed, with the function of voltage feedback and isolation driving. The design of the isolation drive technology is introduced, which include the design of the pulse signal amplification and shaping circuit, the isolation pulse transformer, the drive circuit, and the optical fiber communication circuit. The voltage feedback system is also introduced and the control strategy of the multigroup loads’ switchover and voltage measuring method is designed. The digital signal process controller that used to achieve these functions is introduced and the controller is applied in the charging experiment for multigroups of load and the results prove that the controller can be used effectively. [ABSTRACT FROM PUBLISHER]

Electromagnetic launch (EML) system needs large energy to realize the high current discharge for launching, so that the requirement of pulse power energy increases rapidly in the EML experiments. In recent years, some scientists focus on provide enough energy for the EML system and a new method of charging the power module by the battery cascade charging power supply (BCCPS) is proposed. By using the BCCPS, the fast charging with high-voltage and large-current can be realized, but some restrictions of the BCCPS need to be dealt with, such as the fault protection, the sequential control, and the insulation of the battery. In this paper, a BCCPS’s control system is designed, which uses the digital signal processor as the main controller. The components of the control system, such as fiber communication system, voltage feedback system, protection circuits, loads grouping system, and sequence setting system, are used to enhance the performance of the BCCPS. The control system is used in a ten levels BCCPS and the experiment waveforms proved that it can work effectively. [ABSTRACT FROM PUBLISHER]

Many studies have demonstrated the utility of surface dielectric barrier discharge (SDBD) plasma actuators driven by different voltage waveforms for airflow control. In this paper, a new dual-power supply voltage consisting of ac high voltage with a superimposed positive or negative pulse bias voltage is applied to a two-electrode structure SDBD actuator to compare the actuator performance with that driven by a single ac voltage waveform. The ionic wind velocity, the thrust force, and the schlieren visualization images are studied under three types of voltage waveforms: single ac voltage, ac voltage superimposed with a positive pulse bias voltage (ACPP), and ac voltage superimposed with a negative pulse bias voltage (ACNP). The influences of different pulse parameters including pulse voltage, pulse repetition frequency (PRF), and pulsewidth on the actuator performance are studied in detail. Experimental results show that pulse voltage and PRF have more notable influence on the actuator performance when the actuator is driven by ACPP, while the pulsewidth has little effect on the actuator performance. In contrast, the actuator performance is little changed when the actuator is driven by ACNP. The positive and negative pulse discharges have different effects on the actuator performance, the reason is positive pulse discharge increases the discharge of glow-like region while negative pulse discharge increases the discharge of streamer region in the following ac cycle. The schlieren images further indicate pulse discharge exerts its effects on the SDBD actuator performance by affecting the electric field of ac discharge. [ABSTRACT FROM PUBLISHER]

Pulsed-power generator based on linear transformer driver (LTD) technology has been used to demonstrate waveform control for pulsed atmospheric discharge. This kind of discharge load is known for its time-varying impedance where constant voltage usually does not result in constant current. In this paper, an LTD system has been combined with a field-programmable gate array in order to generate a flexible voltage waveform which, in turn, dictates the discharge current. The experimental results have proved that the current of a discharge load can be arbitrarily controlled, to a certain extent, by properly adjusting the applied voltage. This kind of current waveform control should have significant implications for various applications of discharge-generated plasmas. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of the axial magnetic field (AMF) arc control on voltage distribution (VD) of double-break vacuum circuit breakers (VCBs) in order to gain balanced VD, and thus enhance the breaking capacity. The interaction of vacuum arc plasma, postarc current (PAC), and AMF is discussed. We conduct the breaking test of double-break VCBs with externally applied AMF of a different pulsewidth, magnitude, and a different moment. The PAC, postarc charge, and the VD are measured to analyze the relationship between the AMF arc control and the VD. The optimal AMF arc control and the relationship between the AMF magnitude and the unbalanced voltage ratio are gained when the grading capacitors were 400 pF. The experimental test showed that the proper AMF arc control can improve the unbalanced VD. The mechanism is that the proper AMF arc control can make the postarc charge small and stable, so the unbalanced postarc charge, which caused the unbalanced VD is limited. [ABSTRACT FROM AUTHOR]

During a disruption, plasma electromagnetic energy usually damages tokamak devices severely. Thus, this paper presents a five-part energy processing system (EPS) to dispose this energy. The five parts of the EPS are as follows: the metal oxide varistors employed to limit overvoltage and to absorb energy, the resistor module applied to consume energy, the pulse capacitor module used to store energy, the inverter module used for energy feedback, and the controller. These parts are described, and their key design features are introduced. The influence of different capacitances and resistances on the amount of energy transferred is investigated. The simulation results obtained by the Power Simulation program are given. The experimental and simulation results show that about 20%–30% of the total plasma electromagnetic energy can be transferred out of the tokamak device and effectively disposed by the EPS during the disruptions in the Joint Texas Experimental Tokamak (J-TEXT) tokamak. Moreover, the loop voltage during a disruption can be inhibited and decreases about 40%. [ABSTRACT FROM AUTHOR]

The acceleration grid power supply (AGPS) is an important part of the neutral beam injector (NBI) system. With the increase in NBI power, the requirement for output voltage of the AGPS is becoming higher and higher, even reaching to 1000 kV. As the inverter-type high voltage power supply uses inverters located at the lower voltage side to regulate and cut off the output voltage, it is very suitable for high-voltage applications. The proposed scheme for the AGPS of the International Thermonuclear Experimental Reactor (ITER) NBI system comprises five stages, where each stage has an inverter-type power supply with an output voltage of 200 kV. This paper investigates the inverter-type power supply based on neutral point clamped three-phase three-level (TPTL) inverter and three-phase step-up transformer, which is equivalent to an insulated TPTL dc–dc converter connected with a dual dc link. In order to design a preferable controller for the inverter-type power supply, the topology and principles of the TPTL dc–dc converter with duty cycle modulation have been analyzed. It indicates that only when the converter operates at a large duty cycle, the output voltage ripple can be limited to ±5%. Hence, the small signal model of the converter at a duty cycle larger than 2/3 is established. Following the mathematical model, a single-loop PID controller has been designed and a 400 V/6 A prototype has been built. Simulation and experimental results verify the correctness of the theoretical analysis. The system achieves a lower output voltage ripple and fast dynamic response. [ABSTRACT FROM AUTHOR]

Nuclear fusion reactors, such as the tokamak in the International Thermonuclear Experimental Reactor (ITER) project, usually involve extremely sophisticated high-voltage power supply systems, which provide exciting research challenges. In the short term, the major challenges in power supplies of the ITER and other fusion reactors include the following: 1) fast current control of vertical stabilization (VS) coils and 2) dynamic compensation of reactive power and harmonics. In the long term, the power supply systems in fusion reactors provide opportunities for optimizations at both component and system levels. In this paper, modular multilevel converters (\M^2\LCs) are adopted to tackle the short-term challenges. Circuit structures, pulsewidth-modulation methods, and fault-tolerant operation strategies are presented. The configuration and control strategies of \M^2\LC in VS coils are fully studied and verified with real-time simulations. Compared with existing circuit solutions in fusion reactors, the \M^2\LC -based circuits will have better dynamic response, higher reliability, smaller footprint, and reduced weight. As an outlook to the long-term developments of the fusion power supplies, comprehensive real-time simulations are also discussed. Furthermore, as the future development direction of power electronic devices, the wide band gap devices are discussed at the end of this paper. [ABSTRACT FROM PUBLISHER]

In this paper, research studies on the breakdown progresses of multigap pseudospark discharge under nanosecond pulsed voltages are reported. The experimental results show great differences from dc voltages. The discharge mechanism of the pseudospark under nanosecond pulsed voltages has been successfully explained by the fast electron ionization effect. In each gap, collision ionizations caused by the fast electron start step by step, and development progresses are almost the same and approximately simultaneous until the main gap breaks down. [ABSTRACT FROM PUBLISHER]

This paper presents the design and experimental validations of a system of three new high-voltage (HV) pulsed-power converters for the H− sources. The system requires three pulsed voltages (50, 40, and 25 kV to ground) at 2-Hz repetition rate, for \(700~\mu \) s of usable flat-top. The solution presents ripple-free output voltages and minimal stored energy to protect the ion source from the consequences of arc events. Experimental results on the final full-scale prototype are presented. In case of short-circuit events, the maximal energy delivered to the source is in the Joule range. HV flat-top stability of 1% is experimentally achieved with a simple Proportional-Integral-Derivative regulation and preliminary tuned H− source (e.g., radio frequency control, gas injection, and so forth). The system is running since more than a year with no power converter failures and damage to the source. [ABSTRACT FROM PUBLISHER]

To supply the cathode voltage for the two gyrotrons (140 GHz/1 MW/3 s) of the electron cyclotron resonant heating system on HL-2A, a high-voltage power supply (HVPS) based on pulse step modulator (PSM) with rated output of 80 kV/200 A has been built. Because the storing energy of the PSM HVPS is much lower than traditional HVPS, it is beneficial to load protection. In the PSM HVPS, there are eight dry-type multiwinding transformers; each transformer has 14 secondary windings. The main insulation of the multiwinding transformer reaches to 150 kV. There are 112 switch power supplies in the PSM HVPS; the output voltage can be regulated from 0 to 80 kV by modulating their delay time and pulsewidths. To realize two gyrotrons parallel operating and respective quick protection for the loads, two solid-state high voltage modulators (SSHVM) based on insulated gate bipolar transistor are applied in the power supply. The over-current and over-voltage protection are executed by turning off the PSM HVPS and the SSHVM. The protection time is <10~\mus . A fully digital controller based on digital signal processor and field programmable gate arrays has been developed to ensure the stability of the output voltage of the PSM HVPS. The design circuit and elements are described, and the test results of the PSM HVPS are given in this paper. [ABSTRACT FROM PUBLISHER]

Utilization of power electronics converters in pulsed power applications introduced a new series of reliable, long life, and cost-effective pulse generators. However, these converters suffer from the limited power ratings of semiconductor switches, which necessitate introduction of a new family of modular topologies. This paper proposes a modular power electronics converter based on voltage multiplier as a high voltage pulsed power generator. This modular circuit is able to generate flexible high output voltage from low input voltage sources. Circuit topology and operational principles of proposed topology are verified via experimental and simulation results as well as theoretical analysis. [ABSTRACT FROM PUBLISHER]

Turbulence and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, destabilizing mechanisms, such as gradients and currents, and stabilizing mechanisms like shear. Active control of fluctuations is investigated in this paper via manipulation of flow profiles in a magnetized laboratory plasma device helicon–cathode (HELCAT). Fluctuations are monitored by electrostatic probes, and E\times B flow profiles are controlled via bias ring electrodes. First, a nonmodel-based extremum-seeking optimal control algorithm is implemented in HELCAT to seek the bias ring voltages that minimize a cost function related to the fluctuation amplitude. The experimental results in HELCAT show that the proposed controller is able to not only suppress the fluctuations but also to regulate their average amplitude around a predefined desired level. It is anticipated that this controller can become a valuable tool for physics-oriented studies designed to elucidate the relationship between the shape of the azimuthal flow profile and the amplitude of the fluctuations once the capability of measuring the flow profile in real time becomes available in HELCAT. Second, with the assistance of a HELCAT-tailored transport code capable of predicting the evolution of the azimuthal flow at several radial points within the plasma, the potential of an extremum-seeking controller for directly regulating the azimuthal flow profile around a prescribed target profile is illustrated numerically. [ABSTRACT FROM PUBLISHER]

The U.S. Naval Research Laboratory is developing a battery-powered rep-rate charger for a 60-kJ capacitor bank. The goal is to charge a 4800-\muF capacitor to 5 kV in <5~s for a 50-shot burst at 10 shots/min. A bank of LiFePO4 batteries is used with a full H-bridge converter, a transformer, and a rectifier to transform the 600 V battery voltage to 5-kV secondary voltage. There are two major aspects to the charger design: battery energy store and the dc–dc converter. A stable battery pack requires active cooling, management, and feedback for proper and safe operation. A design study has been performed to identify an appropriate dc–dc converter that can minimize the weight and volume of the system while maintaining high electrical efficiency. An LLC is being evaluated, as it has the possibility of eliminating a discrete inductor using the magnetizing inductance of the transformer in the resonant circuit. Work has also been performed in the design and evaluation of a battery pack, specifically on characterizing the operational parameters of the pack as applied to the desired load. This paper will present simulation data and results from the experiments. [ABSTRACT FROM AUTHOR]

In this paper, we describe a novel multiple-switch pulsed-power technology. The basic idea is that the heavy switching duty is shared by multiple switches. The multiple switches are interconnected via a transmission line transformer, in such a way that all switches can be synchronized automatically and no special external synchronization trigger circuit is required. It can produce either exponential or square pulses, with various voltage and current gains and with a high degree of freedom in choosing output impedances. The topology has been implemented on a prototype with ten spark-gap switches. Pulses with a rise time of 10 ns, a width of 55 ns, a peak power up to 810 MW, a peak voltage of 77 kV, and a peak current of 11 kA have been achieved at a repetition rate of 300 pps. The energy efficiency of the circuit is about 93%. In addition to spark gaps, any overvoltage-controlled switch can be applied in this topology. As an example, we demonstrate the synchronous switching of multiple thyristor switches for current multiplication. The proposed multiple-switch topology can also be applied in a Blumlein configuration for an inductive voltage adder and a linear transformer driver. [ABSTRACT FROM AUTHOR]

The acceleration grid power supply of the ITER neutral beam injector is designed to deliver up to 200 kV to each of the five stages of the electrostatic accelerator, producing a total voltage up to -1 MV with respect to ground. In the present design, the output voltages of the dc generators are independently controlled by five closed control loops. The output voltage measurements are obtained from the difference between the grid potential measurements, referred to local ground. Therefore, the control accuracy for each stage is affected by the amplification of the measurement errors. Thus, an alternative control scheme, based on a single closed control loop and regulator, has been considered. In this paper, the performance of the two control methods in terms of systematic errors, dynamic performance, and sensitivity to load variations is evaluated and compared. [ABSTRACT FROM PUBLISHER]

Metal–oxide–silicon (MOS)-gate-structure-based power semiconductors, such as MOS field-effect transistors, insulated-gate bipolar transistors, and MOS controlled thyristors, are widely used as high-voltage switch and power modulator components in pulsed-power applications. The power semiconductors are generally connected in series and in parallel in order to increase their maximum switching voltage and current, respectively. It is important to suppress overvoltage or switching stress on power semiconductors connected in series and parallel during an extremely short switching time and at fast operating frequency. Generally, gate drive control techniques and methods for the suppression of high voltage are required. To suppress overvoltage and switching stress, this paper proposes a simple and effective active clamping method rather than the use of a snubber circuit with free switching condition modulation. Based on comparative switching experiments, the active clamping method is expected to suppress switching stress and overvoltage while load and switching conditions are changed without modification of the high-side auxiliary circuit for pulsed-power applications. [ABSTRACT FROM AUTHOR]

When small currents are interrupted by a vacuum switch, it is well known that the chopping current and the associated overvoltage are observed. Many investigations on the current-chopping phenomena in alternating-current (ac) circuits have been carried out, but there are no data available on inverter circuits in spite of their recent wide application to synchronous motor systems. In this paper, chopping-current levels and the overvoltages in an inverter circuit under a simple three-level pulsewidth-modulated control are investigated. As a result, the mean chopping-current level is three to four times higher than that in an ac circuit. In particular, high chopping currents occur only when the timing of the current interruption by the vacuum switch synchronizes with that of the inverter's switching, which we call “double chopping.” High chopping current due to double chopping might be harmful since the high overvoltage proportional to the chopping-current level could damage the insulation of electric equipment. However, we experimentally confirmed that a typical surge suppressor could reduce overvoltage. [ABSTRACT FROM AUTHOR]

This paper presents a novel crowbar system of 10/350-\mu\s pulse current. The crowbar pulse current system includes a crowbar pulse current waveform forming circuit, a controlling unit, and a measuring unit. The crowbar pulse current circuit consists of a main air triggered switch, a triggered vacuum switch (TVS) which is used as the crowbar switch, and two trigger signal generators. A kind of TVS is designed and fabricated. Its triggering characteristics are tested, and experimental results show that, compared with other reported similar switches, the TVS has excellent characteristics such as wide operating voltage scope from 1.3 to 120 kV, short discharging delay time with maximum delay time at 400 ns, and its jitter at \pm10 ns. Based on the TVS, the crowbar 10/350- \mu\s pulse current circuit and its controlling circuit are designed. With a 36-\mu\F storage capacitor C and a 6-\mu\H waveform forming inductance L, a 10/350- \mu\s pulse current waveform with a maximum of 150 kA can be generated. [ABSTRACT FROM AUTHOR]

In this paper, a new dimmable electronic ballast for metal-halide (MH) lamps based on a three-stage structure is proposed. The presented dimmable electronic ballast can dim smoothly without acoustic resonance from 50% to 100% brightness. A novel current-control method with constant-power capability is also presented to solve the power-drifting problem resulting from the V– I characteristic variations between lamps or caused by the aging of lamp. The dimming capability allows the ballast to adjust its working condition according to the environments or the dimming command; this further improves the energy efficiency. Finally, a 150-W MH lamp ballast prototype is built to verify the feasibility of the proposed methods. [ABSTRACT FROM PUBLISHER]