Investigation on current loss of high-power vacuum transmission lines with coaxial-disk transitions by particle-in-cell simulations

Coaxial-disk transitions can generate non-uniform magnetic fields and abrupt impedance variations in magnetically insulated transmission lines(MITLs),resulting in disturbed electron flow and non-negligible current loss.In this paper,3D particle-in-cell simulations are conducted with UNPIC-3d to investigate the current loss mechanism and the influence of the input parameters of the coaxial-disk transition on current loss in an MITL system.The results reveal that the magnetic field non-uniformity causes major current loss in the MITL after the coaxial-disk transition,and the non-uniformity decreases with the distance away from the transition.The uniformity of the magnetic field is improved when increasing the number of feed lines of a linear transformer driver-based accelerator with coaxial-disk transitions.The number of input feed lines should be no less than four in the azimuthal distribution to obtain acceptable uniformity of the magnetic field.To make the ratio of the current loss to the total current of the accelerator less than 2％at peak anode current,the ratio of the current in each feed line to the total current should be no less than 8％.     

Numerical Simulation of Non-Inductive Current Driven Scenario in EAST Using Neutral Beam Injection

For achieving the scientific mission of long pulse and high performance operation,experimental advanced superconducting tokamak(EAST) applies fully superconducting magnet technology and is equiped with high power auxiliary heating system.Besides RF(Radio Frequency) wave heating,neutral beam injection(NBI) is an effective heating and current drive method in fusion research.NBCD(Neutral Beam Current Drive) as a viable non-inductive current drive source plays an important role in quasi-steady state operating scenario for tokamak.The non-inductive current driven scenario in EAST only by NBI is predicted using the TSC/NUBEAM code.At the condition of low plasma current and moderate plasma density,neutral beam injection heats the plasma effectively and NBCD plus bootstrap current accounts for a large proportion among the total plasma current for the flattop time.     

Experimental study of current loss of a single-hole post-hole convolute on the QG I generator

The post-hole convolute(PHC), which is used to transport and combine the pulse power flux, is a key component in huge pulsed power generators. Current loss at the PHC is a challenging problem for researchers. To explore a method of reducing the current loss, a single-hole PHC was designed for experiments on the current loss on the Qiang Guang I generator. The experimental results showed that the current loss at the single-hole PHC is related to the distance l between the vicinity of the cathode hole and the surface of the downstream side of the post.Meanwhile, a single-hole PHC with a blob cathode hole transmitted current more effectively than the PHC with a circle cathode hole. The relative current loss at the single-hole PHC with the cathode coated with gold foil was about 30%–50% of that with the cathode coated with nickel and titanium foil. The gap closing speed was also obtained from the current waveforms in the experiments. The speed was 5.74–14.52 cm μs~(-1) which was different from the classical plasma expansion velocity of 3 cm μs~(-1) .     

ITER中的电子回旋波电流驱动模拟

通过将相对论Fokker-Planck方程与波迹方程联合求解,对ITER(国际热核实验反应堆)参数下的电子回旋波电流驱动进行了数值模拟。结果表明,当波的环向发射角度不太大时,波功率沉积将发生在ITER的强场侧。当环向发射角度为21°时,电子回旋波的能量在等离子体中心区域被吸收并驱动起等离子体中心区域的电流。当发射角度变大时,电子回旋波将在弱场侧沉积功率。当发射角度为20°～30°时,能够驱动归一化的径向位置(r/a)小于0.35区域内的等离子体电流,并有较高的电流驱动效率。     

脉冲电流相位检测与反馈系统设计

大多数环型加速器引出束流方向受冲击磁铁的磁场控制,引出冲击磁铁脉冲电源输出的脉冲励磁电流抖动和漂移过大会降低束流引出效率,主要来源于触发系统、闸流管、环境温度变化等[1]。国内抑制引出脉冲电源输出电流相位偏移的相位检测及反馈系统尚属空白。针对中国散裂中子源(CSNS)快循环同步加速器(RCS)引出脉冲电源的需求,设计一种TDC芯片+FPGA结构的输出脉冲电流相位检测及反馈系统,通过研究TDC芯片和FPGA间的数据传输方式、基于FPGA的串口通信及反馈控制算法,实现电源输出电流相位ps级精度实时检测及偏移量反馈,反馈调整步长5 ns,为脉冲电流高精度相位检测与锁定提供了新方法。     

The Experiment of Modulated Toroidal Current on HT-7 and HT-6M Tokamak

The Experiments of Modulated Toroidal Current were done on the HT-6M tokamak and HT-7 superconducting tokamak. The toroidal current was modulated by programming the Ohmic heating field. Modulation of the plasma current has been used successfully to suppress MHD activity in discharges near the density limit where large MHD m = 2 tearing modes were suppressed by sufficiently large plasma current oscillations. The improved Ohmic confinement phase was observed during modulating toroidal current (MTC) on the Hefei Tokamak-6M (HT-6M) and Hefei superconducting Tokamak-7 (HT-7). A toroidal frequency-modulated current, induced by a modulated loop voltage, was added on the plasma equilibrium current. The ratio of A.C. amplitude of plasma current to the main plasma current △Ip/Ip is about 12% ～ 30%. The different formats of the frequency-modulated toroidal current were compared.     

PIG Ion Source with Permanent Magnets: Model Based Anode Current Return Circuit

Ion sources are widely used in fusion technologies. A new high voltage pulsed power supply for use in penning ion gauge ion sources is proposed in this paper. To use discharge current, a diode-capacitor bank is included. The power supply is composed of 3 stages. A fast switching transistor is used as a single switch which is trigged by a pulse generator. A transformer is used to level up the voltage up to 2?kV without power loss. It is also used to isolate input and high voltage output. Also; the proposed high voltage power supply implementation uses a diode-capacitor bank whose capacitors are charged during plasma discharge. This system structure gives compactness and easiness to implement the total system which in combination with inexpensive commercially available components, makes the unit versatile and inexpensive.     

Effect of pulse parameter on preparation of W coating on V alloy

The tungsten coatings were prepared on vanadium alloy substrate by pulse electroplating in Na₂WO₄–WO₃ molten salt. A series of tungsten coatings with compact and smooth morphologies were successfully obtained under various conditions. Orthogonal experimental design method was used to analysis the influence degree of current density, duty cycle and period on tungsten grain size, coatings thickness and current efficiency. The results demonstrated that current density was the most important factor influencing tungsten grain size and tungsten coatings thickness, which all had a positive correlation with current density. The pulse duty was the most important factor influencing current efficiency; the result also showed a positive correlation between current efficiency and pulse duty factor.     

动态膜电解制备四价铀中电流效率的讨论

进行了不同电流密度（40～160 mA/cm²）下电解制备四价铀的研究。研究结果表明,采用动态膜电解制备四价铀,能在保证六价铀转化率的前提下维持较高的电流效率,最终保证了四价铀制备过程的高效率。但在电解过程后期（大部分六价铀已转化为四价铀）,若采用高电流密度,电流效率迅速下降,而采用低电流密度时仍能维持较高的电流效率。为进一步提高四价铀制备过程的电流效率,研究了程序控制电流密度阶梯减小的电解方式对电解过程后期的电流效率的影响。研究结果表明,与恒定电流密度电解方式相比,采用阶梯形减小电流密度的电解方式,可有效地提高电解过程的电流效率,有助于减少副反应的发生。     

HT-7低杂波相控天线阵的耦合特性分析

HT-72.45GHz低混杂波系统利用相控波导阵列将微波能量耦合到等离子体中。本工作基于二维线性耦合理论,主要利用Step+Ramp的等离子体密度剖面模型,详细分析了HT-7装置上各种关键参数(如边缘密度、密度梯度、相邻主波导相位差等)下低杂波波导阵列天线的耦合特性。分析表明,通过调节主波导之间－90°～90°的相差,天线的n_∥谱可在1.93～3.15之间灵活调节;当天线口边缘密度为0.5×10¹⁸～2×10¹⁸m^-3时,波导阵天线的反射系数可保持在5%以下,方向性系数很大;主波导之间相位差的改变对波导阵的驱动效率有很大影响。     

EASTICRF天线电流带电磁分析

为了实现EAST托卡马克1000s以上的稳态先进模式运行的最终物理目标,两电流带双环共振(RDL)离子回旋共振（ICRF）天线被选择用来加热,电流带是ICRF天线关键部件,它通过近场区的耦合把能量传输到等离子体中。本文通过有限元方法对电流带在等离子体破裂和等离子体垂直位移事件两种工况下进行了电磁计算,给出了电流带感应电流密度大小分布情况、磁感应强度大小分布情况以及电流带所受的电磁力。利用电流带所受的电磁力作为载荷对电流带进行了结构分析,分析结果为验证电流带结构的可行性提供理论依据,分析方法对未来更高功率的ICRF天线电流带进行电磁分析具有一定的借鉴价值。     

PIN探测器贯穿辐射与非贯穿辐射线性特性

采用脉冲X射线源和脉冲氙灯光源实验研究了PIN探测器对贯穿辐射和非贯穿辐射响应的最大线性电流输出特性,并与理论计算结果进行了比较。PIN探测器输出的最大线性电流随外加反向偏置电压线性变化,对贯穿辐射响应的最大线性电流输出比对非贯穿辐射响应的最大线性电流输出约大20%,理论计算的最大线性电流值比实验值小。在脉冲辐射探测中,采用可见脉冲光源获得的PIN探测器最大线性电流不会超出探测器对贯穿辐射的线性响应。     

双脉冲法精确测量PMT脉冲线性电流的实验设计

PMT脉冲线性电流是PMT在脉冲工作方式下的重要参数,它直接关系到实验结果的可靠性。本文对比各种测量PMT脉冲线性电流方法的优缺点,从提高测量精度方面考虑,设计了基于双脉冲法的测量PMT脉冲线性电流的实验,通过挑选稳定性高的LED作为光源,利用DG2020信号发生器给LED灯供电,采用通道循环功能加长信号时间间隔,使用分路输出到两台示波器接收信号,应用示波器多次采集自动取平均的功能等方法在实验细节上进行设计,提高测量精度。通过实验测到了PMT脉冲输出电流偏离线性直线1%处的电流,并获得了PMT脉冲输出的mA级至A级电流全曲线。     

电子回旋波Ohkawa机制电流驱动计算

从电子回旋波电流驱动的机制出发,理论推导出了Boozer-Fisch电流与Ohkawa电流的计算表达式,并给出了具体的计算方法。数值模拟结果表明:电子回旋波的波功率沉积在托卡马克高场侧的离轴位置时,Ohkawa电流较小,Boozer-Fisch电流能达到较大值;波功率沉积在低场侧的离轴位置时,通过调整波参数,有效抑制Boozer-Fisch电流,能充分利用Ohkawa电流的优势使离轴驱动电流同样能达到较大值。     

微型X射线管灯丝电源的研制

根据微型X射线管的特点,设计了基于推挽电路和闭环反馈电路的灯丝驱动电源。采用了UCC3808脉宽调制(Pulse Width Modulation,PWM)控制芯片产生两路相位相反的PWM信号,并经由UCC37324金属氧化物半导体(Metal-Oxide-Semiconductor,MOS)管大电流驱动器提高驱动效率,实现推挽结构的后端驱动电路。闭环反馈电路的设计采用精密电阻将管电流的信号转换为等比例的电压信号引入到反馈环节,通过系统自身的闭环控制实现管电流的恒定,并保持高效率和低功耗。实验首先通过外接1.5?的功率电阻测量系统功率,测得输入功率为11 W,效率超过80%,符合灯丝电源的功耗指标要求;然后连接实际的X光管灯丝,经测试可正常工作,管流稳定度为0.227%。     

Commissioning of 3.7 GHz LHCD system on ADITYA tokamak and some initial results

To drive plasma current non-inductively, a lower hybrid current drive (LHCD) system has been designed, fabricated and successfully installed on ADITYA tokamak. The system is designed to launch 120 kW of RF power, at a frequency of 3.7 GHz. The system mainly consists of a high power CW klystron source, a long waveguide transmission line of about 100 m length, a UHV compatible modular waveguide line of about 2.65 m, and a conventional grill type antenna. Independent phase shifters, one each in the eight lines, are used to adjust the antenna phasing and also provides the flexibility to launch a composite spectrum. The antenna is designed to launch lower hybrid waves (LHW) with parallel refractive index (N_||), in the range, 1 < N_|| < 4.5, by appropriately phasing the antenna. Antenna is positioned in the shadow of the poloidal limiter and is provided with 100 mm radial movement to achieve optimum coupling conditions.The complete system development includes design, fabrication and testing of number of waveguide components, modular waveguide lines and their integration. Different cost effective fabrication techniques are adopted to achieve good RF performance. Special attention is paid on the flanged joint seals in the long transmission line to minimize the RF losses. The entire LHCD system is calibrated, especially, in terms of phase, insertion loss and return loss measurements.After the successful integration of the system on ADITYA tokamak, some initial experiments have been carried out to assess the system commissioning and its performance. The experiments were done with a plasma (hydrogen) density of 2-5 × 10¹² cm⁻³ at a toroidal magnetic field of 0.8 T with 10-25 kA of plasma current. Initial results indicate that, good coupling is achieved in the presence of proper edge density. Measurements obtained from second harmonic electron cyclotron emission (ECE) and hard X-ray diagnostics suggest generation of suprathermal electrons in the presence of LH pulse. Plasma current pulse elongation with LH power is observed but needs further investigation to derive conclusions.This paper presents the design, fabrication, testing and integration of the waveguide lines, waveguide components and UHV compatible modular transmission lines of the LHCD system on ADITYA tokamak and discusses some of the initial results.     

正脉冲电镀法制备φ33 mm模拟镍源

mA量级直流恒流电源具有过保护电压较低的缺点,不适于制作大面积、高活度⁶³Ni放射源。本文以正脉冲电源为解决方案,系统研究在简单组分的镀镍溶液中,各工艺条件对电镀结果的影响。研究结果表明,在阴极电流密度为18 mA/cm²、室温、脉宽80%、频率5 kHz条件下电镀2.5 h,可获得95%以上的⁵⁸Ni沉积率。     

EAST4.6GHz/4MW低杂波电流驱动系统隔直器优化设计

为了研究全超导托卡马克稳态高参数等离子体性能,2008年在EAST托卡马克装置上研制并成功建成了一套能最大传输2兆瓦,工作频率是2450MHz的低混杂波电流驱动系统,要实现低杂波长时间地维持等离子体电流,还需要对低杂波系统的输出功率大小及运行时间长度提出更高要求,拟研制一套波源输出功率4 MW,中心频率4.6GHz,波谱范围为1.7< N_(//)< 2.5,运行脉冲宽度0～1000秒低杂波电流驱动系统.在EAST4.6GHz/4MW低杂波电流驱动系统中,因为速调管放大器和低杂波天线有共同的接地点,速调管放大器电源为负高压,有接地点,低杂波天线有接地点,并且和EAST托卡马克相连,在系统中要求不能有两个接地点,所以要通过隔直器来隔断托卡马克和速调管之间的的直流通路.论文详细介绍了隔直器的原理和设计过程,在以4.6GHz为中心频率,150MHz的频带范围内,隔直器各个端口微波性能良好.     

Methods of Power Balance Analysis and Estimation of Current Density Profile for LHCD and IBW Discharges in HT-7 Tokamak

In this paper a simple code has been developed to analyze power balance and qualitatively evaluate current profiles for discharges with lower hybrid current drive （LHCD） and ion Bernstein wave （IBW） heating in the HT-7 tokamak. Electron and ion thermal diffusivity, profiles of the bootstrap current density and total plasma current density can be estimated by this code using the experimental data. This code offers an easy and reasonable means to understand plasma transport in HT-7.     

Estimation of the sheath power dissipation induced by ion cyclotron resonance heating

During ion cyclotron resonance heating, the sheath power dissipation caused by ion acceleration in the radio frequency(RF) sheath is one of the main causes of RF power loss in the tokamak edge region. To estimate the power dissipation of an RF sheath in the ion cyclotron range of frequency(ICRF), a 1 D fluid model for the multi-component plasma sheath driven by a sinusoidal disturbance current in the ICRF is presented. By investigation of the sheath potential and ion flux at the wall, it is shown that the larger frequency and lower amplitude of the disturbance current can cause smaller sheath power dissipation. The effect of the energetic ion on the sheath power dissipation depends on the disturbance current. For large amplitude of disturbance current, the increase in the concentration and energy of the energetic ion leads to a decrease in sheath power dissipation. While for a small disturbance current, the sheath power dissipation demonstrates non-monotonic variation with the concentration and energy of the energetic ion. In addition, the sheath power dissipation is found to have a small increase in the presence of light impurity ions with low valence.