A Design Model of Core Snubber for EAST NBI

A transformer type iron core snubber, as a protective device against the stray capacitance during the breakdown in EAST, is analyzed in detail. Three kinds of topology are presented. Then with the analysis for equivalent circuit, the ranges of three key parameters, i.e., secondary side resistance, leakage inductance and snubber inductance, are determined. By considering the saturation of the magnetic material, a design principle is also presented. A nearly 1:10 core snubber is tested. It is proved that a high permeability core with secondary resistor can restrain the discharge current effectively.     

LLC谐振恒流恒压高压充电电源技术研究

高压充电电源输出电压的稳定性是脉冲调制器的关键技术指标,需对其进行研究,以提高其输出稳定性。基于激磁电感、谐振电感、谐振电容（LLC）谐振变换器的工作原理,根据LLC等效电路得到了LLC谐振电路的电压增益曲线,分析了LLC谐振变换器工作区间的特性,提出了平面绝缘芯变压器的选择依据和设计方法,通过测量实际变压器得到变压器的参数;根据变压器参数选择了LLC谐振变换器谐振频率和工作频率,并通过LLC谐振变换器电路的推导,详细计算了高压充电电源输出电压的纹波幅值。结果显示,计算结果优于设计指标。经实验验证,叠层磁芯LLC谐振变换器高压充电电源的稳定性能达到了设计要求。     

Some Generalised Characteristics of the Electro-dynamics of the Plasma Focus in Its Axial Phase: Illustrated by an Application to Independantly Determine the Drive Current Fraction and the Mass Swept-Up Fraction

We describe the axial phase of the Mather plasma focus by two coupled equations of motion and circuit. We non-dimensionalised these equations resulting in two coupled equations which are characterised by only three scaling parameters α, β and δ which are ratios of electrical to transit times, inductances and impedances respectively. The normalised current waveform, trajectory and speed profile are unique for each combination of α, β, δ which are the ratios of characteristic times (electrical discharge vs. axial transit), inductances (tube inductance vs. static inductance) and impedances (stray resistance vs. electrical surge impedance). This leads to important information and insight into various aspects of the axial phase. In the present work we show that in a time-matched plasma focus shot we deduce the value of axial phase current fraction f_c simply by measuring the calibrated voltage waveform and the uncalibrated current waveform. The scaling parameters β and δ are fixed; and by form-fitting the measured current waveform to the normalised current waveform using the value of α of the shot is determined uniquely; from which the peak current and the ratio of peak to average speed [the speed form factor (SFF)] are obtained. The average transit speed is measured by time-of-flight using the voltage upturn as indicator of end of axial phase. Then the SFF yields the peak speed. The measured voltage (back EMF), peak current and peak axial speed (all at the end of axial phase) allows the unambiguous measurement of f_c. The value of the mass swept-up fraction f_m is deduced from α which is the ratio of the characteristic discharge and the characteristic transit times, both deduced during the non-dimensionalisation of the equations. Analysis of a time-matched shot in the INTI PF at 15 kV, 3 Torr D₂ gave f_c = 0.68 and f_m = 0.05.     

Research on resonance parameters matching based on partitioned operation method of atmospheric pressure plasma reactor array

Matching optimization of resonant parameters among the high power inverters, low power transformers and plasma reactors have significant effects on the performance and output of the reactor array when applying the partitioned operation method. In this paper, the Matlab/ Simulink electrical model was established based on the method of partitioned operation. The matching relation between resonant parameters is analyzed on the basis of experimental result. As a consequence, transformer leakage inductance and working frequency are the important parameters influencing the operational efficiency of system, leakage inductance of transformer should be adjusted based on the equivalent capacitance of plasma reactor to realize the matching optimization of resonant parameters.     

Magnetic flux leakage analysis and compensation of high-frequency planar insulated core transformer

A novel high-frequency and high power density planar insulated core transformer(PICT) applied to high voltage DC generator is introduced. PICT's operating principle and fundamental configuration are described,and preliminary experimental results in self-designed PICT apparatus are presented. Emphatically, magnetic leakage flux(MFL) giving rise to the output voltage drop is analyzed in detail both theoretically and by finite element method(FEM). Showing good consistency with experimental result, FEM simulation is considered to be practicable in physical design of PICT. To cancel out leakage inductance and improve the voltage uniformity,compensation capacitor is adopted and experimental verification is also presented. All shows satisfactory results.     

Detailed Analysis of the Transient Voltage in a JT-60SA PF Coil Circuit

A superconducting coil system is actually complicated by the distributed parameters, e.g. the distributed mutual inductance among turns and the distributed capacitance between adjacent conductors. In this paper, such a complicated system was modeled with a reasonably simplified circuit network with lumped parameters. Then, a detailed circuit analysis was conducted to evaluate the possible voltage transient in the coil circuit. As a result, an appropriate (minimum) snubber capacitance for the Switching Network Unit, which is a fast high voltage generation circuit in JT-60SA, was obtained.     

影响De-Qing线路稳压效果的因素分析

一、影响De-Qing线路工作的几种因素在电子直线加速器中,脉冲调制器输出脉冲电压的稳定度会影响速调管的相位调制,从而影响束流能散度。北京正负电子对撞机(BEPC)对电子直线段的能散度要求相当高,为±0.6%。因此,提高电压稳定度成为脉冲调制器研制工作中的一个重要方面。     

Simulations of W7-X magnet system fault scenarios involving short circuits

The stellarator Wendelstein 7-X (W7-X) which is presently under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald [(C. Beidler, G. Grieger, F. Herrnegger, E. Harmeyer, J. Kißlinger, W. Lotz, H. Maassberg, P. Merkel, J. Nührenberg, F. Rau, J. Sapper, F. Sardei, R. Scardovelli, A. Schlüter and H. Wobig., Physics and engineering design for Wendelstein 7-X, Fusion Technol., 17 (1990)148–168)], uses 70 superconducting coils, arranged in 7 groups to create the magnetic confinement for the plasma. A wide variety of tests and investigations are performed in order to ensure the later safe operation of the device. Much attention is also paid to the proper insulation of all the parts. These measures are costly and time consuming but are necessary in order to avoid the severe consequences of faults–—especially short circuits–—during operation. If a short circuit would happen during an emergency switch-off, the discharge of any shorted inductance would be delayed, and the coupled magnetic flux of the discharging system would induce additional currents into this shorted part. The currents and forces developing in such a case depend not only on the short circuit resistance and the critical current of the superconductor, but also on the shorted inductance itself, its magnetic coupling to other inductances, and its position within the system. The paper describes the influences of these factors and presents simulation results for different fault scenarios involving short circuits across a coil group, a single coil, different double layers, and a single turn. Maximum currents result from a shorted outer double layer, maximum forces from a shorted coil group, depending on its position in the magnet system.     

Experimental Study of the Multi-gap Multi-channel Gas Spark Closing Switch

1. IntroductionHigh-voltage and high--current closing switch is oneof the key elements in pulsed-power systems. It hasextensive applications in generating high--voltage andhigh-current pulses With the recent development ofpulsed-X-r8y simulator and high--power Z--pinch tech-nology [l,2], it is required that the closing switch is ofsmall inductance, low jitter, high conducting currentand long operating life.One of the methods for the reduction of switchlnductance, jitter and electrode erosion …     

Leakage Flow Characteristics of Highly Effective Graphite Seal Mechanism for HTGR Core Support Blocks

The prevention of leakage flows of coolant gas is important for a thermal hydraulic design of HTGR core which consists of prismatic graphite blocks. In particular, a seal mechanism for the core support blocks is necessary because gaps between core support blocks induce leakage flows in the core. Here, a seal mechanism, which consists of graphite seal element with triangular cross section and V-shaped seal seat, has been proposed. Air flow experiments were conducted to study the leakage flow characteristics of this seal mechanism. It is shown that the present seal mechanism is highly effective in preventing leakage flows as compared with the plate-type seal mechanism. It is also found that most of the leakage flow occurs at the seal element end-gaps and the pressure loss coefficient factor of this seal mechanism can be predicted with the use of the effective flow area of the end-gaps.     

Effect of Neutron Irradiation on Mechanical Properties of Niobium and Nb-Y Alloy

In a high-temperature gas-cooled reactor core, which consists of prismatic graphite fuel elements, leakage flows of coolant gas occur through gaps between blocks. Since the effects of these leakage flows on the total flow distribution are significant, their flow features must be clarified. In this paper, the leakage flows (crossflow through the interface gap between contacting fuel elements and the permeation flow through the fuel elements) in the normally stacked fuel elements were studied. In the basic experiments, leakage flow rates were measured using small-scale graphite blocks to determine the equivalent interface gap width and the permeability. The experiments using the full-scale fuel element were also carried out and the results agreed well with those of the basic experiments. Furthermore, a simple flow model was devised to predict the leakage flow in the fuel element.     

秦山三核发电机重大故障处理

发电机故障分为20多类,主要为漏水、漏油、温度高、短路等重要缺陷。本文分为两节,第一节重点阐述秦山三核在发电机漏水、温升、短路典型故障方面处理实例,第二节为结论。通过阐述发电机冷却水管处理、铁芯温度高处理和匝间短路处理,详解在发电机典型故障（漏水、温升、短路）方面的处理方案和经验,力图掌握发电机设备的整体性能和参数,为未来发电机故障维修提供有利的处理手段和方案。本文将为未来发电机故障维修提供有益的借鉴意义。     

基于超级电容储能的中性束注入系统弧电源设计

弧电源是中性束注入加热系统中最关键的设备之一,它的性能决定了弧放电的稳定性及束流引出的品质。为提高弧放电稳定性,降低电网容量,减少对电网的冲击,弧电源拓扑设计采用了基于超级电容储能和开关电源技术的DC/DC变换器结构。利用多个IGBT功率模块并联工作,可提高电源工作频率,实现更快的动态响应速度。在详细分析电源工作过程的基础上,设计了滤波电路和电流快速转移电路,根据电源的要求和具体参数,由一阶RL电路的电流响应特性,精确计算出滤波电感的最小值。最后,利用Matlab对电源性能指标进行了仿真验证,结果表明电源性能完全符合设计要求。     

Passive protections against breakdowns between accelerating grids in SPIDER experiment

In the SPIDER experiment a ITER-like full size plasma source will be realized with the target to extract a Dˉ beam of 70 A and then to accelerate it to 100 keV energy. The reduction of the effects due to the frequent breakdowns between the accelerating grids is needed, because of grids damage due to energy deposition by arcing and strong electromagnetic noise (EMI) emission. The solution proposed is a comprehensive design of the circuit. Two passive components are installed: a Damping Resistor and an Output Filter in series to the Power Supplies. Then a doubled screened structure will be adopted for the 30 m long – 100 kV Transmission Line TL, which connects the Ion Source and Acceleration Power Supplies to their loads: the Inner Screen will be connected to the reference ground (the vessel) by a resistive link, the Outer Screen acting as a low-impedance ground. Finally, a Distributed Core Snubber DCS (magnetic snubber) will be installed onto the TL, aimed to increase the damping of the oscillations due to the stray inductances and capacitances. The DCS is composed of 10 magnetic alloy cores and is equipped by a biasing circuit to enhance the flux swing in unsaturated condition during the breakdown. A detailed model of the circuit is developed to evaluate the passive components parameters for protection against breakdown, in which all the magnetic and capacitive couplings between components are modeled as well as the magnetic core snubber saturation.     

Recent results of an experimental study on the impact of smoke on digital I & C equipment

A program to assess the impact of smoke on digital instrumentation and control (I & C) safety systems began in 1994, funded by the US Nuclear Regulatory Commission Office of Research. Digital I & C safety systems are likely replacements for today’s analog systems. The nuclear industry has little experience in qualifying digital electronics for critical systems, part of which is understanding system performance during plant fires. The results of tests evaluating the performance of digital circuits and chip technologies exposed to the various smoke and humidity conditions representative of cable fires are discussed. Tests results show that low to moderate smoke densities can cause intermittent failures of digital systems. Smoke increases leakage currents between biased contacts, leading to shorts. Chips with faster switching times, and thus higher output drive currents, are less sensitive to leakage currents and thus to smoke. Contact corrosion from acidic gases in smoke and stray inductance or capacitance are less important contributors to system upset. Transmission line coupling was increased because the smoke acted as a conductive layer between the lines. Permanent circuit damage was not obvious in the 24 h of circuit monitoring. Test results also show that polyurethane, parylene, and acrylic conformal coatings are more effective in protecting against smoke than epoxy or silicone. Common sense mitigation measures are discussed. Unfortunately we are a long way from standard tests for smoke exposure that capture the variations in smoke exposure possible in an actual fire.     

Dynamic dielectric recovery performance of serial vacuum and SF6 gaps in HVDC interruption and its regulation method

Vacuum gaps have rapid dynamic dielectric recovery speed while SF₆ gaps have high insulation strength. The series-connected vacuum and SF₆ gaps are used as the main switch (MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF₆ gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance (DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker (VCB) and SF₆ gas circuit breaker (GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker (CB) based on series-connected vacuum and SF₆ gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage (TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.     

一种核磁共振测井信号强度的确定方法

核磁共振测井信号较为微弱,其信号强度直接决定着探头设计的成败,同时也为电子线路设计的重要依据.从核磁共振理论出发,结合互感概念提出一种确定核磁共振信号的方法,该方法可有利于核磁共振探头设计和电子线路设计.     

遗传算法在HFETR堆芯优化设计中的应用

研究遗传算法在HFETR堆芯优化设计中的应用。计算程序中部分参数采用岷江试验堆堆芯优化程序中已采用的参数，计算方法上引入了对称变异算子与虚拟堆芯技术。虚拟堆芯技术的引入减少了获得优化方案的计算时间，而对称变异算子的应用增加了优化方案的工程实用性。从优化结果可以看出，转换比与同位素总产量都可提高10％以上，优化堆芯装载方案对称实用。满足工程要求。     

Transient Radiation-Induced Response of MOS Field Effect Transistors

It was found that the radiation-induced leakage current across the gate-to-substrate and the drain-to-substrate semiconductor junction dominates the behavior of MOS field effect transistors for small gate impedances. The smaller radiation-induced gate leakage current consists, to a large extent, of components due to secondary emission and air ionization effects. For large gate impedances, the gate leakage current can be important because of a modulation of the gate bias. The voltage dependence of this leakage current is also discussed. Based upon these findings and the physical structure of the device, an equivalent circuit model has been developed to predict the behavior of devices of this type in a transient radiation environment. The model consists of a standard nonradiation equivalent circuit modified by the inclusion of elements to describe the substrate junctions and the addition of current generators in parallel with the gate-to-substrate and the drain-to-substrate capacitances to account for transient radiation effects. A voltage dependent gate-to-channel current generator can also be included to describe the gate leakage current. The utility of the model was confirmed by comparing the predicted behavior of radiation-induced responses with responses observed at a flash X-ray. The equivalent circuit model developed is suitable for use with existing automated circuit prediction techniques and contains parameters measurable with standard instrumentation procedures.     

High-order cross-section homogenization method

A high-order cross-section homogenization method based on boundary condition perturbation theory is developed to improve the accuracy of nodal methods for coarse-mesh eigenvalue calculations. The method expands the homogenized parameters such as the cross-sections and the neutron flux discontinuity factor in terms of the node surface current-to-flux ratio. The expansion coefficients are evaluated during the nodal calculations using additional precomputed homogenization parameters. As a result, it is possible to correct (update) the homogenized parameters to arbitrary order of accuracy for the effect of reactor core environment (fuel assembly neutron leakage) with very little computational effort in the core calculation. The reconstructed fine-mesh flux (fuel-pin power) is a natural byproduct of the new method. A benchmark problem typical of a BWR core is analyzed in one dimension, monoenergetic diffusion theory by modifying a nodal method based on a bilinear, flat as well as a fine-mesh intranodal flux shape. The homogenized parameters are first computed using exact (fine-mesh) albedos and compared to those determined from a fine-mesh core calculation. Two nodal (coarse-mesh) examples are given to show how well this approach works as a higher-order perturbation method is utilized. The paper concludes by showing that this method succeeds in giving excellent results for cores that may be difficult to model using standard nodal methods.