Untriggered Water Switching

Recent experiments indicate that synchronous untriggered multichannel switching in water will permit the development of relatively simple, ultra-low impedance, short pulse, relativistic electron beam (REB) accelerators. These experiments resulted in the delivery of a 1.5 MV, 0.75 MA, 15 ns pulse into a 2 ? line with a current risetime of 2 x 1014 A/sec. The apparatus consisted of a 3 MV Marx generator and a series of three 112 cm wide strip water lines separated by 2 edge-plane water-gap switches. The Marx generator charged the first line in < 400 ns. The first switch then formed 5 or more channels. The second line was charged in 60 ns and broke down with 10 to 25 channels at a mean field of 1.6 MV/cm. The closure time of each spark channel along both switches was measured with a streak camera and showed low jitter. The resulting fast pulse line construction is simpler and should provide considerable cost savings from previous designs. Multiples of these low impedance lines in parallel can be employed to obtain power levels in the 1014 W range for REB fusion studies.     

Harp, A Short Pulse, High Current Electron Beam Accelerator

A 3 MV, 800 kA, 24 ns electron beam accelerator is described and the results of initial switching experiments are discussed. The generator will provide a source for studying the physics of processes leading to electron beam driven, inertially confined fusion. The major components of the accelerator are two diodes with a common anode, twelve oildielectric Blumleins with low jitter (< 2 ns) multichannel switches, three intermediate storage capacitors, a trigger pulse generator and two Marx generators.     

The novel HVEE 5 MV Tandetron™

Recently, HVEE has extended the voltage range for its Tandetron™ accelerators from 3 MV terminal voltage to 5 MV terminal voltage with the development of an entirely new coaxial Tandetron™. The new 5 MV system is presently in the final test phase and will shortly be installed at the Universidad Autonoma de Madrid (Spain) as part of their new IBA facility. The all-solid-state power supply (parallel-fed Cockroft–Walton type) is constructed around the high-energy accelerator tubes, thereby avoiding the T-shaped tank that was so far characteristic for the HVEE Tandetrons™. During the design of the system special emphasis has been put to minimize the electrical field strength in the complete structure. Using three-dimensional electrostatic field simulations, we were able to identify possible hot spots and to reduce the maximum field strength to 80% compared to that of older designs. This reduction in field strength guarantees more reliable operation at or even above the guaranteed terminal voltage of 5 MV. The electrical power for beam transport is generated by a 10 kW version of a recently in-house developed range of all-solid-state drivers with output powers of up to 25 kW. Apart from IBA applications like heavy element ERDA and NRA, the system is very well suited for other applications like positron emission tomography, deep implants in semiconductors as well as accelerator mass spectrometry of various elements, including ³⁶Cl and ⁴¹Ca.     

A New Collective Effect, High Flux Ion Accelerator

A new type of accelerator capable of producing a large flux of medium energy ions is discussed. The accelerator contains a charge neutral plasma in a magnetic field. Electron currents parallel to B? heat the plasma electrons to an average energy kTe by the Joule process. The electrons try to escape from the plasma into an adjacent vacuum region along the magnetic field lines. In doing so they create a charge separation electric field which collectively accelerates the ions to energies ?10 kTe . The large resistivity necessary to obtain both the rapid heating and impedance matching to high power sources results from electron streaming instabilities in the plasma. Feasibility is investigated using a one dimensional, time dependent fluid model. In this model a realistic circuit is coupled to the plasma electrons. The resultant plasma heating and expansion are numerically followed in time and space. These calculations seem to imply that present day technology utilizing high voltage Blumlein transmission lines (Z ? 1?) seem capable of creating a 10 MeV proton stream with energy >10 kJ, and equivalent current density >10 kA/cm2     

A 3 MV tandetron facility at KFUPM

A 3 MV General lonex Tandetron accelerator has recently been tested at the nearly established Energy Resarch Laboratory at the King Fand University of Petroleum and Minerals. The accelerator features a very stable solid-state power supply which delivers about 3 MV of terminal high voltage. A beam resolution of about 400 eV was measured. Ions of a wide range of masses, ranging from hydrogen to gold, were accelerated. The configuration of this Tandetron will be described along with a discussion of the facility and research programs.     

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.     

Superconducting Niobium Deflectors

The study of S-Band superconducting niobium cavities is being carried out for application to long-pulse rf beam separators in the momentum range of the AGS, whereas, X-Band frequencies are being considered for the NAL accelerator. Results for a 5-cell S-band prototype are: a peak field of 410 G, corresponding to an equivalent deflecting field of over 2 MV/m, and a loss improvement factor of 2 × 105. The fabrication and post-fabrication treatments are described. Perturbation measurements to determine deflector parameters are summarized. A new type of mode stabilizer is suggested. A 7-cell X-Band deflector is under construction.     

天光Ⅱ-B光源的初步实验

天光Ⅱ-B是在天光Ⅱ-A的油箱侧面建立而成,利用原有的Marx发生器,以及新建的脉冲形成线、主开关、脉冲传输线、负载腔构成一条新的实验线路。在保留装置原有泵浦激光能力的基础上,可同时进行X-pinch相关实验研究。脉冲形成线内导体为同轴线结构,特征阻抗6 Ω,工作介质为去离子水,研制了一种真空水压的方式对形成线进行灌注,有效消除形成线内水中的气泡。采用Rogowski线圈对流过金属丝负载的电流进行测量。本文进行了天光Ⅱ-B在真负载下的初步实验。结果表明,在对Marx电容器充电70 kV时,输出电流269 kA,脉宽约50 ns,上升沿≤30 ns,丝负载对电流利用率约80%。     

1 MV杆箍缩二极管辐射特性实验研究

依据现有的实验室驱动源能力建立杆箍缩二极管（RPD）粒子模拟计算模型,获得了工作电压为1 MV的RPD电参数特性及电子、离子时空分布特性,并设计了RPD实验装置。在1 MV驱动源平台上开展了实验研究,实验中采用B dot、D dot、热释光剂量片和SiPin二极管测试了RPD电流、电压、辐射剂量和光脉冲信号,分析了RPD电参数及X射线辐射特性。结果表明,阳极采用1.5 mm钨时,1 MV电压下1 m处辐射剂量约1 R,并得出剂量与电压Ud、电流Id的关系式D(R=1 m)=120U1.55d∫Iddt;二极管阻抗范围为26.4~36.7 Ω,空间电荷限制阶段平均阻抗下降率大于2 Ω/ns,磁绝缘阶段平均阻抗下降率小于0.5 Ω/ns;光脉冲宽度较电压脉冲宽度约缩短20%~30%,与电压、电流的关系为∝IdU1.55 d。实验测试的剂量和光脉冲信号结果与拟合计算式计算结果符合较好。     

2×6 MV串列加速器头部附近电场设计优化

为了给2×6 MV串列加速器提供高压电极与均压环尺寸，根据设计要求及已有参数，采用电磁场仿真软件计算了串列加速器的二维电场强度分布，针对高压电极结构、均压环截面形状及环间距等因素对串列加速器电场强度分布的影响提出了优化措施。仿真结果表明：直筒结构的高压电极与均压环接壤处电场强度分布不均匀，而圆弧过渡结构的高压电极具有屏蔽作用，比直筒时电场强度分布更均匀；优化均压环截面形状与减小环间距可降低环间电场畸变，但后者对减小均压环表面的电场贡献更大。最终优化后得到高压电极与均压环的尺寸可满足新研制的串列加速器要求。     

低能加速器开关电源研制

利用直流脉宽调制技术以及半桥变换电路,为一种低能电子直线加速器成功研制阳极开关电源。根据开关电源的特点,对该电源中低压和高压部分进行详细设计。低压部分采用SG1525A为控制核心,实现脉宽调制、软启动、稳压调节以及过压保护功能。该开关电源主要指标:输出电压0~800V,最大电流400 m A,工作频率为18.5 k Hz,纹波峰值系数为0.9‰,达到设计要求。     

天光Ⅱ-B强流脉冲电子加速器的设计

为了驱动X箍缩负载,在天光Ⅱ-A的Marx油箱侧面建立了一条新的实验线路天光Ⅱ-B。它在保留装置原有泵浦激光能力的基础上,还可进行X-pinch相关实验研究,达到了一器两用的目的。天光 Ⅱ-B主要由Marx发生器、脉冲形成线、主开关、脉冲传输线和负载构成,形成线工作介质为去离子水,形成线特征阻抗6 Ω,传输线采用变阻抗线设计,负载特征阻抗1.25 Ω。本文介绍了天光Ⅱ-B新线的设计、全电路模拟及在电阻负载下的调试结果。模拟和调试结果显示,天光Ⅱ-B装置在负载电阻为1.25 Ω时,负载上的电流峰值约269 kA,脉宽约50 ns,电流上升时间小于30 ns。以上结果证实,天光Ⅱ-B具有驱动低阻抗X-pinch实验线路的能力。     

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.     

The novel ultrastable HVEE 3.5 MV Singletron accelerator for nanoprobe applications

Recently, HVEE has completed a novel 3.5 MV single ended accelerator (Singletron^™) for the University of Leipzig, Germany. For one of the main applications, the system will be connected to a nanobeamline to achieve submicron resolution. Because the energy stability and ripple of the beam, and beam brightness are of vital importance for the performance of a nanoprobe, special care has been taken in optimizing these parameters. The system consists of an RF source which is directly mounted on the accelerator tube, a switching magnet to bend the beam into a chamber for standard analysis purposes and an analysis magnet that directs the beam into the nanoprobe. The stability of the beam energy was measured at a terminal voltage of 1.881 MV. These measurements were taken during factory acceptance with large production equipment operational, which negatively influenced the stability of the mains. The measured stability was found to be approx. ±50 eV over 5 h, but it is anticipated that this figure will be as good as ±20 eV (i.e. 10⁻⁵) under normal laboratory conditions. The terminal voltage ripple was measured at 2.25 MV to be 25 V_pp (i.e. 1.1 × 10⁻⁵). Finally, the beam brightness of a 2.25 MeV hydrogen beam was measured by the use of two micrometer slit systems. A brightness of approx. 18 Amps · rad⁻² m⁻² eV⁻¹ was obtained. In this article we will describe the considerations which have led to the layout of the present system.     

Thermal analysis of EAST neutral beam injectors for long-pulse beam operation

Two sets of neutral beam injectors(NBI-1 and NBI-2) have been mounted on the EAST tokamak since 2014. NBI-1 and NBI-2 are co-direction and counter-direction, respectively. As with indepth physics and engineering study of EAST, the ability of long pulse beam injection should be required in the NBI system. For NBIs, the most important and difficult thing that should be overcome is heat removal capacity of heat loaded components for long-pulse beam extraction. In this article, the thermal state of the components of EAST NBI is investigated using water flow calorimetry and thermocouple temperatures. Results show that(1) operation parameters have an obvious influence on the heat deposited on the inner components of the beamline,(2) a suitable operation parameter can decrease the heat loading effectively and obtain longer beam pulse length, and(3) under the cooling water pressure of 0.25 MPa, the predicted maximum beam pulse length will be up to 260 s with 50 keV beam energy by a duty factor of 0.5. The results present that, in this regard, the EAST NBI-1 system has the ability of long-pulse beam injection.     

Impedance matching for repetitive high voltage all-solid-state Marx generator and excimer DBD UV sources

The purpose of impedance matching for a Marx generator and DBD lamp is to limit the output current of the Marx generator,provide a large discharge current at ignition,and obtain fast voltage rising/falling edges and large overshoot.In this paper,different impedance matching circuits (series inductor,parallel capacitor,and series inductor combined with parallel capacitor) are analyzed.It demonstrates that a series inductor could limit the Marx current.However,the discharge current is also limited.A parallel capacitor could provide a large discharge current,but the Marx current is also enlarged.A series inductor combined with a parallel capacitor takes full advantage of the inductor and capacitor,and avoids their shortcomings.Therefore,it is a good solution.Experimental results match the theoretical analysis well and show that both the series inductor and parallel capacitor improve the performance of the system.However,the series inductor combined with the parallel capacitor has the best performance.Compared with driving the DBD lamp with a Marx generator directly,an increase of 97.3％ in radiant power and an increase of 59.3％ in system efficiency are achieved using this matching circuit.     

4.5MV静电加速器离子聚束电路的设计

在加速器中产生脉冲中子源需要对离子源脉冲化。采用10MHz聚束和2.5MHz扫描频率，通过在交叉场分析器设置直流偏置电压和变频切割电压，改变离子束脉冲频率，使之从2.5MHz到39KHz可调。本文介绍了脉冲频率可调，幅度可调的脉冲化电路的改进设计及初步实验结果，并给出功放热设计参考。     

Sub-ns Jitter, 1ns Risetime and 10kV Rectangular Pulse Trigger Generator

A new rectangular pulse trigger generator has been developed which can generate two 10 kV pulses with a risetime less than 1 ns, a jitter of 0.2 ns and a width of about 10 ns and 40 ns, respectively. This generator uses two polymer-foil switches and 25 ohm Blumlein transmission lines composed of two-parallel standard coaxial cables discharging into two 50 ohm output cables. The pulse width and the delay between two pulses can be adjusted by changing the length of the cables.     

A model for electrical fast transient analyses of the ITER NBI power supplies and the MAMuG accelerator

The design of ITER Neutral Beam Injector (NBI) is based on a five-stage electrostatic accelerator, known as Multi-Aperture Multi-Grid (MAMuG) and characterised by an overall acceleration voltage of ?1 MV. The MAMuG accelerator requires a five-stage power supply system under strict load protection requirements, being subjected in operation to breakdowns. In this paper a circuit model of ITER Neutral Beam Injector power supplies and MAMuG accelerator is illustrated, for the simulation of fast transients related to accelerator breakdowns in particular. Consideration of the high voltage involved and of the complex inductive and capacitive couplings implied careful assessment of stray parameters by calculations with finite element techniques. The circuit model, developed to address a number of design issues requiring simulations at system level, is now ready for use—the optimisation of passive protections being the most significant application.