Investigation of Arc Regulation of Hot Cathode Ion Source with Langmuir Probe

The neutral beam injector (NBI) is one of the main plasma heating methods for nuclear fusion devices. For the hot cathode high current ion source, the arc current and beam current tends to increase during the beam pulse. In order to gets long pulse beam extraction, the arc regulation technology is employed. The Langmuir probes are installed on the experimental advanced superconducting tokamak-NBI ion source, to feedback control the arc discharge and beam extraction. The experimental results show that, the long pulse of 100 s ion beam is extracted with beam energy of 30 keV with arc regulation. More the results are presented in this paper.     

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.     

Long-pulse power-supply system for EAST neutral-beam injectors

The long-pulse power-supply system equipped for the 4 MW beam-power ion source is comprised of three units at ASIPP (Institute of Plasma Physics,Chinese Academy of Sciences):one for the neutralbeam test stand and two for the EAST neutral-beam injectors (NBI-1 and NBI-2,respectively).Each power supply system consists of two low voltage and high current DC power supplies for plasma generation of the ion source,and two high voltage and high current DC power supplies for the accelerator grid system.The operation range of the NB power supply is about 80 percent of the design value,which is the safe and stable operation range.At the neutral-beam test stand,a hydrogen ion beam with a beam pulse of 150 s,beam power of 1.5 MW and beam energy of 50 keV was achieved during the long-pulse testing experiments.The result shows that the power-supply system meets the requirements of the EAST-NBIs fully and lays a basis for achieving plasma heating.     

Progress of the RF negative hydrogen ion source for fusion at HUST

Huazhong University of Science and Technology has developed an experimental setup of a radio frequency (RF) driven negative hydrogen ion source, to investigate the physics of production and extraction of the H− ions for neutral beam injection in nuclear fusion reactors. The main design parameters of the ion source are: RF power ≤40 kW; extraction voltage ≤10 kV; accelerator voltage ≤20 kV. This paper gives an overview of the progress of the ion source with particular emphasis on some issues. The RF driver and source plasma are analyzed and optimized in terms of impedance matching, plasma characteristics and power coupling. In regard to the simulation analysis, a plasma model based on the particle-in-cell method and a beam trajectory model considering beam stripping loss are developed to investigate the plasma and negative ions transport inside the ion source. Furthermore, a collisional radiative model of H and H2 is built for plasma optical diagnosis.     

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。     

Effect of radio-frequency substrate bias on ion properties and sputtering behavior of 2 MHz magnetron sputtering

The effect of radio-frequency substrate bias on ion properties and sputtering behavior of 2 MHz magnetron discharge was investigated. The ion velocity distribution function(IVDF), the maximum ion energy and ion flux density were measured at the substrate by a retarding field energy analyzer. The sputtering behavior was investigated by the electric characteristics of target and bias discharges using voltage–current probe technique. It was found that the substrate bias led to the decrease of sputtering power, voltage and current with the amplitude 7.5%. The substrate bias also led to the broadening of IVDFs and the increase of ion flux density, made the energy divergent of ions impacting the substrate. This effect was further enhanced by increasing bias power and reducing discharge pressure.     

Experimental Results of Ion Beam Extraction of High-Current Ion Source for EAST Neutral Beam Injector

The first campaign of ion beam extraction tests are completed for EAST NBI high current ion source. The hydrogen ion beam with beam voltage of 80 keV is extracted from tetrode accelerator system. During the experiment, the characteristics of arc discharge and ion beam extraction are studied. The arc power reaches 120 kW and the extracted ion beam power reaches 3 MW. The relationship of some key parameters of arc and beam are investigated, and the details are described in this paper.     

Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF) discharge sustained at low pressures, typical of the operating modes of RF gridded ion sources. The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source. The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared. The experimental data were also compare...     

基于Saber的5MW中性束注入弧电源仿真设计

强流离子源是HL-2M装置5 MW中性束注入加热系统的核心部件,离子源通过弧电源加速初级电子至高能态,碰撞气体分子,产生等离子体。所以,弧电源对于离子源维持稳定的弧放电非常重要。本文利用Saber软件建立了弧电源的主电路模型,设计并仿真了弧电流的恒流控制、打坑控制以及超级电容的恒流充电控制、恒功率放电控制等。这种方法不仅提高了弧电源电路的分析和设计效率,缩短了系统研制的周期,还可用于实际系统的故障分析和控制参数的整定,降低实验风险。实验结果表明,弧电源的真实输出与仿真输出结果相符。     

Preliminary analysis of back-streaming electrons on the source plasma region of ion sources for the EAST-NBI

Back-streaming electrons gain significant energy due to the high voltage of the extraction system for a high-current ion source.By theoretical calculation,the particle flux accounts for 13.88％ of the total beam current,and the power flux accounts for about 7.5％ of the total beam power.This shows that back-streaming electrons are very destructive to the plate of electron absorption that is installed opposite of the accelerator.At the same time,as particles impinge on grids,the energy level that the grids absorb will be really high.Compared with the water flow calorimetry data of ion sources on the ASIPP-NBI testbed,it can be found that,as the high voltage of the extraction system rises,the particle flux and the power flux of the back-streaming electrons are essentially in the same proportions.Therefore,the corresponding energy deposited on the components of the ion source will grow by the same percentage with the increase in high voltage,which demonstrates strong inhibition to improving the neutral beam power injected into a tokamak.     

Commissioning of the first KSTAR neutral beam injection system and beam experiments

The neutral beam injection (NBI) system was designed to provide plasma heating and current drive for high performance and long pulse operation of the Korean Superconducting Tokamak Advanced Research (KSTAR) device using two co-current beam injection systems. Each neutral beam injection system was designed to inject three beams using three ion sources and each ion source has been designed to deliver more than 2.0 MW of deuterium neutral beam power for the 100-keV beam energy. Consequently, the final goal of the KSTAR NBI system aims to inject more than 12 MW of deuterium beam power with the two NBI for the long pulse operation of the KSTAR. As an initial step toward the long pulse (～300 s) KSTAR NBI system development, the first neutral beam injection system equipped with one ion source was constructed for the KSTAR 2010 campaign and successfully commissioned. During the KSTAR 2010 campaign, a MW-deuterium neutral beam was successfully injected to the KSTAR plasma with maximum beam energy of 90 keV and the L-H transition was observed with neutral beam heating. In recent 2011 campaign, the beam power of 1.5 MW is injected with the beam energy of 95 keV. With the beam injection, the ion and electron temperatures increased significantly, and increase of the toroidal rotation speed of the plasma was observed as well. This paper describes the design, construction, commissioning results of the first NBI system leading the successful heating experiments carried in the KSTAR 2010 and 2011 campaign and the trial of 300-s long pulse beam extraction.     

Simulation,Design, Construction of Duoplasmatron and Diagnostic Neutral Beam System for Alborz Tokamak

Diagnostic Neutral Beam (DNB) has been used for measuring plasma parameters of tokamaks such as ion and electron temperature, safety factor, impurity concentration and etc. Ion source and electrical power supply specification are the main part of DNB. Arc discharge current value is affected by filament current and anode voltage. Beam current changes with arc current signal in our experiment that agree with theoretical relations. Sixty milli-ampere (60 mA) pulse beam current is because of arc current of about 40 A and extraction voltage of about 20 kV. The increase of beam current with arc current has been reported experimentally and effect of arc current on beam current has been investigated for several high extraction voltages. Optimum condition, which means having a telescopic beam (minimum divergence) for specific parameters of duoplasmatron, has been simulated and verified with experimental test. The best extraction voltage for these parameters has been found to be about 16-kV. The ratio of the perpendicular velocity to parallel velocity has been calculated to be about 0.012. It has been shown experimentally with optical emission spectroscopy that increase in arc current and magnetic current increase proton content of beam.     

Control of Beam Energy and Flux Ratio in an Ion-Beam-Background Plasma System Produced in a Double Plasma Device

Plasmas containing ion beams have various applications both in plasma technology and in fundamental research. The ion beam energy and flux are the two factors characterizing the beam properties. Previous studies have not achieved the independent adjustment of these two parameters. In this paper, an ion-beam-background-plasma system was produced with hotcathode discharge in a double plasma device separated by two adjacent grids, with which the beam energy and flux ratio(the ratio between the beam flux and total ion flux) can be controlled independently. It is shown that the discharge voltage(i.e., voltage across the hot-cathode and anode) and the voltage drop between the two separation grids can be used to effectively control the beam energy while the flux ratio is not affected by these voltages. The flux ratio depends sensitively on hot-filaments heating current whose influence on the beam energy is relatively weak,and thus enabling approximate control of the flux ratio     

基于多元线性回归模型的中性束质子比分析

中性束质子比的高低对其注入等离子体后的加热效果具有重要的影响。实验中,强流离子源的灯丝电压、弧压、进气量等宏观运行参数决定了中性束质子比的大小。以东方超环中性束注入测试台束引出实验为基础,利用多元线性回归模型对引出中性束质子比进行分析,建立了影响中性束质子比的预测方程,并对该模型的正确性进行了检验。结果表明,中性束质子比可利用以灯丝电压和弧压为自变量的多元线性回归模型进行分析,灯丝电压是影响质子比的关键参数,弧压次之。     

低能高束流氩离子源的结构及性能

离子源技术是等离子体研究中的一项重要内容,而低能大束流源则是离子源技术研究中的一个重要方向,因为这样的源在离子束刻蚀、离子束溅射镀膜以及荷能粒子与物质相互作用方面都有广泛的应用;本文采用空心阴极空心阳极结构,用热阴极电子发射弧放电驱动并用磁场约束产生等离子体,用曲面发射引出离子束,研制成了氩气放电溅射离子源;研究了灯丝加热电流、弧压对弧流的影响和弧流与工作气体压力对离子束引出的影响规律.离子源的引出电压在0-4.0 kV之间连续可调,最大引出束流为100 mA,束斑面积为φ6.0 cm,以Ti为溅射靶时的最大溅射沉积率为0.45 nm/s,离子源可连续工作160 h.     

Properties of Ion Beams Generated by Nitrogen Plasma Focus

Numerical experiments have been systematically carried out using the modified Lee model code on various plasma focus devices operated with nitrogen gas. The ion beam properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor) of the plasma focus have been studied versus gas pressure for each plasma focus device. The results show that, for these studied plasma focus devices, the mean ion energies decrease with increasing gas pressure, while the beam ion number increases with higher pressure. The fluence, flux, ion current, power flow density and damage factor have maximum values at the optimum pressure. It is shown that, the maximum power flow densities range from 10¹² to 10¹⁴ W m^?2 and the damage factor values reach almost 10⁹–10¹¹ W m^?2 s^0.5. The obtained results provide much needed benchmark reference values and scaling trends for ion beams of a plasma focus operated in nitrogen gas. These results could be used as an indicator for ion properties emitted from nitrogen plasma focus for various applications including material processing.     

Ion Extraction Characteristics from Photoionized Plasma by Radio-Frequency Resonance Method

In order to raise ion extraction efficiency in laser isotope separation, we have developed a radio-frequency (rf) resonance method. Then, to confirm feasibility of this method to a photoionized plasma, we experimentally studied the ion extraction characteristics.

When the rf frequency was swept under a weak magnetic field (5mT), the plasma-sheath resonance was found to occur at about 12MHz which was almost the same value as the theoretical one. Moreover, it was confirmed that the ion extraction time at the resonance frequency became the minimum.

When the magnetic field strength decreased from 5mT to zero, the ion extraction time became long. From the simulation results, this was because the plasma potential decreased with the magnetic field strength. Therefore, a magnetic field strength of more than 1mT was required to obtain a sufficient ion extraction efficiency.

To obtain the same extraction time as when applying a ?3kV dc voltage in the electrostatic method, the rf resonance method needed a voltage more than 70V_rms, in which the dc bias was ?1kV. Therefore, we confirmed that this method is feasible for the ion extraction from the photoionized plasma.     

A Multi-Scale Study on Silicon-Oxide Etching Processes in C4F8/Ar Plasmas

A multi-scale numerical method coupled with the reactor,sheath and trench model is constructed to simulate dry etching of SiO_2 in inductively coupled C_4F_8 plasmas.Firstly,ion and neutral particle densities in the reactor are decided using the CFD-ACE+ commercial software.Then,the ion energy and angular distributions(IEDs and IADs) are obtained in the sheath model with the sheath boundary conditions provided with CFD-ACE+.Finally,the trench profile evolution is simulated in the trench model.What we principally focus on is the effects of the discharge parameters on the etching results.It is found that the discharge parameters,including discharge pressure,radio-frequency(rf) power,gas mixture ratios,bias voltage and frequency,have synergistic effects on IEDs and IADs on the etched material surface,thus further affecting the trench profiles evolution.     

Ion Collection from Resonance-Photoionized Plasma by Applying Radio-Frequency Voltage

Ions were collected on electrodes from laser resonance photoionized plasma by applying 2 MHz radiofrequency voltage to the electrodes. It was demonstrated that the ions are collected in a shorter time at the same kinetic energy of the collected ions compared with ion collection by applying DC voltage to the electrode. A simple one-dimensional model was extended for prediction of ion collection times in the cases of applications of not only DC voltage but also radio-frequency voltage. The ion collection times estimated with the simple one-dimensional model agreed with the experimental values in the case of application of radiofrequency voltages as well as DC voltage. Though the experimental conditions such as ion density are far from those of the plant of atomic vapor laser isotope separation (AVLIS), the simple one-dimensional model shows that radio-frequency voltage method is effective under the conditions close to those of the AVLIS plant.