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.     

An Improved Parallelogram Hysteresis Loop Used in the HVDC Snubber

The snubber is a transformer-like fault-protection device in the heating neutral beam of the fusion device, such as ITER, which is designed to suppress the short-circuit current and protect the device during HV sparking. In process of modeling the nonlinear equivalent inductance of the snubber, the permeability changes stepwise at the turn points of the parallelogram hysteresis loop. Due to the step change of the permeability, the overshoot of the short-circuit current occurs in simulation. In order to eliminate the current overshoot, the piecewise linear interpolation method is adopted to optimize the hysteresis loop. Simulation results show that the current overshoot is eliminated and its good accordance with the test result verifies the feasibility and accuracy of the improved parallelogram hysteresis loop.     

A new approach to passive protection against high energy and high current breakdowns in the ITER NBI accelerator

The energy stored in the 1 MV ITER Neutral Beam Injector power supply system will exceed by far the energy stored in the existing largest NB Injectors; as a consequence, the limitation of the grid breakdown effects–grids damage and Electro Magnetic Interference emission–are critical issues. In the present ITER NBI reference design the mitigation system is based on the concept of the concentrated core snubber which, due to the large amount of stored energy, is a huge component. Furthermore, in the NBI a relatively large part of HV capacitance to ground remains downstream the core snubber, so neither the arc peak current nor the high-frequency oscillations can be effectively limited. Moreover, the concentrated core snubber is ineffective in limiting the voltage reversal caused by internal insulation fault, increasing the risk of cascade failures in components like HV bushing and transmission line. The paper proposes an alternative approach to limit the grid breakdown effects, based on the concepts of Damper Resistor- substituting the direct connection to ground of the zero-potential accelerating grid – and of Distributed Core Snubber (DCS) – installed along the whole length of the transmission lines. The DCS concept has been subjected also to experimental validation by a small scale setup supported by electrical modelling.     

Experimental and computed results for fluid-structure interactions with impacts in the HDR blowdown experiment

The HDR experimental facility has been used for several blowdown experiments in order to study fluid-structure interactions and loadings on the pressure vessel internal structures of a pressurized water reactor. We have developed the code FLUX to analyse the motions in the initial blowdown period.This paper describes a new type of HDR experiments (V34) and compares the experimental results with the FLUX-code results. As novel feature, the core barrel is not rigidly clamped to the vessel as in earlier experiments but supported with gaps such that the core barrel can move freely upwards for about 2 mm and horizontally for 0.3 mm at the upper flange. At the lower core-barrel edge, snubbers restrict the horizontal motion to about + 1.4 mm and −2.8 mm.The experimental results show that the core barrel is deflected sidewards until it hits the snubber at the lower edge and then swings back to hit the opposite snubber. By this some kinetic energy is lost due to plastic snubber deformations. At the same time, the measurements show that the core barrel lifts rather uniformly from its support upwards until it hits the upper constraint. Several bounces up and down are observed until the core barrel becomes fixed probably due to friction from the side.This situation has been pre- and post-computed with the new FLUX-version which contains a very effective algorithm to treat supports with gaps and resultant impacts. For treatment of plastic supports, a simple model is added. Pre-computations were not meaningful because of large deviations in the pre-estimated initials gaps. However the computed pressure-field is not influenced very much by these parameters and predicted very well. This was favoured by the isothermal fluid initial conditions. Post-computations show sufficient agreement with respect to computed core barrel motion. The axial motion is described very well. Some problems remain which are due to the model for the upper flange support.Impacts do not results in greatly enlarged loadings, strains or accelerations for this situation.     

Decreasing snubber inservice inspection costs through snubber reduction and improved test limits

Snubber inservice inspection (ISI) requirements, along with a history of snubber malfunctions, has made inspection and maintenance of snubbers a significant part of a nuclear power plant's ISI budget. These expenses can be minimized through snubber reduction and the use of improved test limits for snubber functional testing. This paper presents a snubber overview and reviews snubber ISI requirements. Examples are given of the high cost that maintaining a snubber in an operating nuclear plant represents.Snubber reduction refers to reducing a plant's snubber population by eliminating snubbers shown not to be required to restrain piping for design basis dynamic loadings, and by replacing snubbers with other types of restraints, such as rigid struts. Snubber reduction is discussed in terms of what makes removing snubbers practical along with approaches to, and results of recently implemented snubber reduction programs.Improved or increased test limits for snubber functional testing are discussed along with an approach to, and results of an Electric Power Research Institute sponsored program to develop improved limits that would not significantly affect piping response. Improved piping acceptance criteria can be used to justify the use of increased test limits provided by snubber manufacturers. An additional use is to justify the operability of piping on which faulty snubbers were found.     

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.     

Response spectrum analysis of piping systems with elastic-plastic gap supports

A new seismic support device and its application in piping systems is described. The device, E-BAR (patented), can be cost effectively used for snubber replacement programs, mitigation of hydraulic transients, pipe whip and as a thermal stop. The device has pre-set gaps to allow free thermal movement. During a seismic or other dynamic load event, if the pipe movement exceeds the gap dimension, the device acts as an elastic or elastic-plastic restraint. The device also has a unique design feature for not exceeding the restraint force beyond a specified limit design value. To analyze piping systems with gap supports having elastic-plastic characteristics, modal analysis procedures for both response spectrum and time history methods are developed. The comparison of responses obtained from the procedures with nonlinear time history analysis and test results available in the literature shows excellent correlation. A pilot program conducted for snubber replacement with E-BARs demonstrates that the limit force feature of E-BAR makes them very attractive for snubber replacement. This is because a particular E-BAR with a specified limit design force can be selected, such that, the E-BAR replacing the snubber does not require any modifications be made to the existing support steel and hardware.     

HT-7 超导托卡马克铜壳在等离子体放电中的作用分析

在对铜壳在等离子体发生位移扰动时平衡机理和对外垂直磁场的屏蔽作用分析中，对于每个铜壳采用水平和垂直方向两对正反串的线圈等效，用集中自感、互感和电阻来表示铜壳的参数，并重新建模进行分析，其分析结果和实验结果符合较好。     

Design and Development of a Power Supply System for NBI Test Stand of EAST

A neutral beam injector (NBI) test stand was constructed to develop a multi-megawatt prototype ion source as an auxiliary heating system on experimental advanced superconducting tokamak. A power supply system for the NBI test stand components such as a set of dc power supplies for plasma generator, a dc high voltage power supply of a tetrode accelerator, a transmission line and a surge energy suppressor. Stable arc discharges of the plasma generator with hydrogen gases for 100 s long pulse have been produced by six Langmuir probes feedback loop regulation mode to control the arc power supply. The 4 MW hydrogen ion beam of 1 s is extracted with beam energy of 80 keV and the beam current of 52 A. The dc high voltage power supply for the plasma grid of the prototype ion source was designed to contribute maximum voltage of 100 kV and current of 100 A. The high voltage power output is continuously adjustable to satisfy with plasma physics experiment in operation frequency of 10 Hz. To prevent damage of the beam source at high voltage breakdown, core snubber using deltamax soft magnetic materials have been adopted to satisfy the input energy into the accelerator from the power supply can be reduced to about 5 J in the case of breakdown at 80 kV. For the transmission line, a disc shape multi cable coaxial configuration was adopted and which the dimension of the diameter is 140 mm at the core snubber. The major issues of discharge characteristics with long pulse and beam extraction with high power for the prototype ion source were investigated on the NBI test stand.     

Dependence of the internal inductance on the radial distance between the primary and secondary X-point surfaces in the EAST tokamak

In view of their advantage in long-pulse high-performance operations, low internal inductance scenarios are being developed and tested for the EAST and other tokamaks. Dependence of the internal inductance on several main plasma configuration parameters are statistically analyzed. It is found that the internal inductance of the plasma is closely related to the radial distance dR_sep between the primary and secondary X-point surfaces on the outer mid-plane as well as the poloidal field of the last closed flux surface. Moreover,dR_sep is also related to the distribution of the fast electrons driven by the injected lower-hybrid waves, which is partially responsible for the observed relation betweendR_sep and the internal inductance. The results here should therefore be helpful as a guide for future experiments on internal inductance control and long-pulse operations of the EAST and other tokamaks, as well as for detailed theoretical study of the underlying physics.     

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.     

Equivalent circuit model for the insulated core transformer

The design of the insulated core transformer(ICT)needs to consider the flux leakage effects.An equivalent linear circuit model is proposed based on the principle of duality.It is composed by two types of leakage inductances:conventional leakage between windings and special leakage introduced mainly by the insulation gaps.The values of leakage inductances depend on the dimensions of the core,gaps,or windings and the property of magnetic materials.The circuit allows for quantitatively evaluating influences of ICT internal parameters on its output properties.The winding self- and mutual inductance matrix is mathematically converted to derive the inductance formula.As an example,the leakage parameters of a sixstage two-dimensional(2D) ICT are calculated and analyzed.     

An approximate method for calculating secondary criticality following LMFBR meltdown accidents

A major concern following a meltdown accident in an LMFBR is the possibility of secondary criticality. In this paper an approximate method is presented for determining criticality as a function of pool depth, geometry and reflectivity of the surrounding material. Using this method, ramp rates are determined for the case of a subcritical pool being filled by core debris falling from above. It is shown that in addition to the very large ramps which are normally considered, several configurations lead to much smaller ramps, which should also be considered in subsequent safety analyses.     

Electrical Parameters of the Vacuum Vessel in HT-7U Tokamak

1. IntroductionThe time-t'arying currents in plasma and poloidalfield coils induce the eddy current on the vacuumvessel of tokamak- The magnetic field produced bythe eddy currents has an effect on the penetrationof poloidal field, the position and the shape of theplasma: t'.hich is related to the structure of the yao-uum vessel and the distribution of the eddy currentsThe level of the effect can be described by the electrical parameters of the vessel, being of very importance in the study Of t…     

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。     

Piping extreme dynamic response studies

Results are presented for a series of high-amplitude dynamic tests of a simple pressurized piping system excited through various multiple piping supports. The four-inch diameter piping achieved response levels above yield when subjected to earthquake-like time history inputs and withstood — without leakage or gross distortion — dynamic inputs that were factors of three to five times greater than those inputs required to just exceed the ASME Class 2 stress limit for Service Level D, the Safe Shutdown Earthquake condition. Despite intentionally induced support failures in several tests, piping pressure integrity was maintained, and no plastic collapse occurred. Selected snubber hardware likewise exhibited large design margins under transient loads.     

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 …     

电荷分配法用于丝室的若干问题

本文讨论了阻容扩散模型的局限性;给出了考虑丝电感时的电荷分配过程的解析解;证明了有终端负载电阻时的电荷分配公式Q_a/Q_b=R(l-x_0) R_L/Rx_O R_L。     

LMFBR system analysis: Impact of heat transport system on core thermal-hydraulics

In discussing LMFBR thermal-hydraulic analysis, this paper focuses on the heat transport system and its impact on the predicted core behavior, particularly during off-normal or protected accident transients. Following a brief background of related work in the area of system simulation for both loop and pool-type LMFBR designs, modeling considerations for individual components such as reactor core, piping, pumps, heat exchangers and check valves, together with the overall integrated approach to system simulation, are discussed. The need for, and current approaches to, modeling pool stratification are also examined. The role of buoyancy forces in the system is clarified, with particular emphasis on its increasing influence during flow decay. Sample results are presented to illustrate the influence of system modeling details, and selection of component parameters and operational mode, on predicted core thermal-hydraulic response during protected loss-of-flow transients. From a systematic study of the effect of pump inertia for a flow coastdown to natural circulation event in a loop-type design, it is found that certain combinations of primary and secondary pump inertias can lead to core flow reversal for a sustained period, and eventual boiling in the hot fuel channel. This effect, based on its impact on core flow, is even more pronounced in pool-type designs.     

Diagnostics of Internal Inductance in HT-7

1. IntroductionMagnetic measurements have been used exten-sively since the early days of tokamaks. Many prop-erties of a tokamak plasma can be determined byusing simple loops or coils of wire. Basic measurements aJre for the plasma current, loop voltage,plasma position and shape, stored plasma energy,and current distribution. InfOrmation about instabilities [l] is also obtained. For efficient operationsof these tokarnaks, it is essentiaJ to have a fast, y6tan accurate method for the deterndn…