Effect of the amplitude and rise time of a voltage pulse on the formation of an ultrashort avalanche electron beam in a gas diode

The effect of the amplitude and rise time of a voltage pulse from a RADAN-303 pulser on the formation of an ultrashort avalanche electron beam (UAEB) in a gas diode is experimentally investigated. It is shown that, when the open-circuit voltage of the pulser exceeds an optimum value, the beam current amplitude and the gap voltage under which the UAEB is generated decrease.     

High-Voltage Ka-Band Gyrotron Experiment

A new high-voltage, intense-beam, Ka-band gyrotron experiment is underway using a 350-400-keV 0.5-1-kA beam from a short-pulse Febetron pulser. High-power operation at 35 GHz has been observed, with 20 MW (±3 dB) produced at ~8.5-percent efficiency in a "whispering-gallery" TE62 mode. Operation in other modes and at other frequencies has also been studied.     

Single-bunch emittance dilution in the perfect ILC main linac

In the ILC (International Linear Collider) main linac, low emittance preservation is the most important issue for beam dynamics study. As the main sources of emittance dilution, the dispersive and wakefield effects were studied in this paper. The theoretical calculations and numerical simulations of these two effects on single-bunch emittance dilution, without any misalignment errors, are presented in detail.     

Anomalous hollow electron beams in a storage ring

This Letter reports the first observations of an anomalous hollow electron beam in the Duke storage ring. Created by exciting the single-bunch beam in a lattice with a negative chromaticity, the hollow beam consists of a solid core inside and a large ring outside. We report the detailed measurements of the hollow beam phenomenon, including its distinct image pattern, spectrum signature, and its evolution with time. By capturing the postinstability bursting beam, the hollow beam is a unique model system for studying the transverse instabilities, in particular, the interplay of the wakefield and the lattice nonlinearity. In addition, the hollow beam can be used as a powerful tool to study the linear and nonlinear particle dynamics in the storage ring.     

Single-bunch emittance dilution in the perfect ILC main linac

In the ILC(International Linear Collider)main linac, low emittance preservation is the most important issue for beam dynamics study. As the main sources of emittance dilution, the dispersive and wakefield effects were studied in this paper. The theoretical calculations and numerical simulations of these two effects on single-bunch emittance dilution, without any misalignment errors, are presented in detail.     

Head-tail instability caused by electron clouds in positron storage rings

In positron or proton storage rings with many closely spaced bunches, an electron cloud can build up in the vacuum chamber due to photoemission or secondary emission. We discuss the possibility of a single-bunch two-stream instability driven by this electron cloud. Depending on the strength of the beam-electron interaction, the chromaticity and the synchrotron oscillation frequency, this instability either resembles a linac beam breakup or a head-tail instability. We present computer simulations of the instabilities, and compare the simulation results with analytical estimates.     

High-power transverse flow CW CO2 laser for material processing applications

A transverse flow transversely excited (TFTE) CW CO₂ with a maximum output power about 15 kW has been developed. This is excited by pulser sustained DC discharge applied between a pair of multi-pins anodes and a common tubular cathode. Though the laser power in convective cooled CO₂ laser scales proportionally with the volumetric gas flow, it did not increase in this laser when the volumetric gas flow was increased by increasing the electrode separation keeping the flow velocity constant. The discharge voltage too remained almost unchanged with increase of the electrode separation. These observations are explained considering the electrical discharge being controlled by ionization instability. Laser materials processing applications often demand programming facilities for laser power modulation. A four-stage cascaded multilevel DC–DC converter-based high-frequency switch mode power supply has been developed to modulate the output power of the laser. Laser was operated up to 15 kW output power in four different modes viz. continuous wave mode, pulse periodic mode, single shot mode and processing velocity-dependent power mode with 1.2 kHz modulation bandwidth. We describe briefly the laser system, the SMPS, and the temporal behavior of laser beam.     

双近贴管纳秒单幅高速摄影机

作为一种性能优越的二维图象记录设备,双近贴管纳秒单幅高速摄影机在高速摄影领域已越来越受到人们的重视。这方面的研究成果已经而且正在为核物理研究及其它学学科的发展提供有效的测量工具。     

Excess-energy electrons in a nanosecond electron beam from a vacuum diode

The characteristics of an IMA3-150É sealed-off vacuum diode connected to a RADAN-220 nanosecond pulser are investigated. It is found that the electron beam behind the foil contains electrons with an energy exceeding the voltage applied to the diode. It is shown that the elevated-energy electrons appear at the leading edge of a current pulse, the FWHM of the current pulse of these electrons is 200–450 ps, and the pulse amplitude reaches several tens of amperes.     

Megawatt, 330 Hz PRF tunable gyrotron experiments

Repetitively pulsed and cw gyrotrons have hitherto used thermionic cathodes, whereas cold cathode gyrotrons have normally operated as single shot devices. The novel results presented here show that cold cathode gyrotrons can be successfully pulsed repetitively. A tunable gyrotron with a pulse repetition frequency (PRF) of 150Hz is demonstrated. This system developed >4MW mm-wave output pulses at 100GHz. The gyrotron is based on a two-electrode configuration comprising a field-immersed, field emission, cold cathode and a shaped anode cavity. A superconducting magnet was used to produce the homogeneous intra-cavity magnetic field and a cable pulser was used to drive the electron beam. This pulser produced up to a (200±20)kV pulse with 10ns rise time, a 100ns flat top, a 10ns decay with a characteristic impedance of 200. The energy storage capacity of the cable pulser was 35J. The charging unit limited the maximum PRF to 330Hz. Due to spark gap switching limitations 330Hz was only obtainable in 5 to 10 pulse bursts. For substantial periods of the order of 30 seconds, 100Hz PRF was achieved over an oscillating range of 28 to 100GHz and 150Hz PRF was achieved at 80GHz. No degradation effects on the mm-wave output pulse was evident due to diode recovery time throughout this series of results. A subsequent conclusion is that the diode recovery time in our cold cathode gyrotron is less than 3ms.     

探地雷达高功率高稳定度脉冲源设计

 对于探地雷达,脉冲源的功率和稳定度直接影响其作用距离和探测精度,对目标成像时进行相干积累有着重要意义。采用雪崩三极管设计的全固态脉冲源具有很高的稳定度指标,但输出功率较低,使用Marx电路可以提高其输出峰值电压幅度。梳状PCB(印刷电路板)电路是一种结构紧凑具有自相似性的电路形式,有利于进一步提高脉冲源的稳定度指标,也有利于脉冲源的小型化设计。根据某探地雷达要求,采用梳状PCB电路形式,实现了12级Marx电路的脉冲源,采用欠电荷法对脉冲波形进行了优化设计,其输出峰值电压大于400 V(50 Ω负载),脉冲宽度为600 ps,重复频率大于25 kHz;并且具有良好的时基稳定度和波形稳定度,脉冲宽带抖动小于1%,峰值抖动小于1%。     

基于雪崩管Marx电路的高稳定度脉冲技术

采用Marx电路提高雪崩管脉冲源输出脉冲幅度,分析基于雪崩管Marx电路脉冲源的时基稳定度和波形稳定度的影响因素。采用适当的优化措施提高稳定度指标,设计了高稳定度的雪崩管脉冲源,脉冲峰值电压2 000 V(50Ω负载),脉冲全底宽度5 ns,上升时间400 ps,重复频率达到25 kHz,具有很高的稳定度指标:短时抖动小于30 ps,长时漂移小于100 ps/min,峰值电压和脉冲宽度抖动小于1%。     

基于虚拟仪器技术开发的超声弹性模量测量系统

本文利用脉冲回波法，通过声速测量材料弹性模量，基于虚拟仪器技术发挥软件算法的优势提高测量精度。通过研制超声脉冲收发卡，编制弹性模量测量系统软件，开发了超声弹性模量测量系统。     

强流电子束二极管陶瓷真空界面

从绝缘和机械强度两方面优化设计了一种应用于强流电子束二极管的陶瓷真空界面。首先,依据真空沿面闪络机理及其影响因素,针对外径220mm的陶瓷板,应用ANSYS静电场模拟,通过对阴极电极形状和阳极外壳尺寸的调整,使得陶瓷沿面电场和阴、阳极三结合点场强均得到了有效控制。模拟结果显示:陶瓷沿面电场分布均匀,阴、阳极三结合点场强小于30kV/cm,电场线与陶瓷表面所成角度基本保持在45°;其次,针对陶瓷与电极的约束结构,通过静力和瞬态冲击分析,确定了该陶瓷界面可承受的最大静压和冲击波最大峰压分别为4.8MPa和60MPa;最后,在脉宽200ns的脉冲功率驱动源上进行了实验研究,陶瓷真空界面平均绝缘场强达到44kV/cm,二极管运行稳定,机械性能可靠,实验结果与理论设计相符。     

Operation of repetitively pulsed virtual cathode oscillators on theTEMPO pulser

The design and performance characteristics of two virtual cathode oscillators operated at a 1-Hz repetition rate for a 10-shot burst using the TEMPO pulser are presented. The 2.4-GHz hardware generated a 300 MW per pulse (radiated) in the TM₀₂ mode with a 1.3% total energy conversion efficiency and with a 10.5% frequency bandwidth. A 2:1 scale-tip of this hardware was used to achieve an 840-MHz operation, but it only radiated 70 MW per pulse in the TM₀₁ mode with a 7.3% bandwidth, since hardware constraints prevented the TM₀₂ component from being radiated. The relatively low beam current density of the TEMPO VCOs yielded a low diode gap closure rate that should make them suitable for long-pulse operation. In addition, the low beam current density minimized damage to the thin anode screen     

紧凑型L波段磁绝缘线振荡器的实验研究

 设计加工了一个紧凑型L波段磁绝缘线振荡器(MILO)并进行了实验研究。该MILO具有一个新型收集极和一个新型模式转换器，射频扼流腔减为一个，同时将阴极杆设计成变阻抗结构，该MILO由一台自建的600kV,8Ω，100ns加速器SPARK01驱动。在二极管电压为515～538kV, 二极管电流为58～61kA的条件下, 该MILO在实验中获得了1.76～1.78GHz， 2.2～2.5GW的TM₀₁模高功率微波辐射, 功转换效率为7.3%～7.9%。在30ns的有效电压脉宽下，实验中测得微波脉冲半高宽为15ns。实验结果与模拟结果符合得较好。     

形成线脉冲压缩技术在超宽谱技术中的应用

分析了基于同轴Blumlein线的高功率脉冲源对低阻抗短形成线充电、实现脉冲压缩的基本原理,给出了理想情况下,脉冲压缩后输出的高功率超宽谱脉冲电压、功率增益及能量效率计算公式。利用电路仿真软件建立了脉冲压缩电路模型,通过模拟验证了理论分析。模拟了实际主脉冲波形对输出脉冲的影响,结果表明:低阻抗压缩线充电时间变长、充电电压峰值降低;通过在前级脉冲源与脉压形成线之间增加一定长度传输线,可以有效提高压缩线充电电压。针对典型的同轴Blumlein线高功率脉冲源紧凑Tesla型高功率脉冲源CKP-1000,设计了脉冲压缩装置和测量系统,建立了完整的脉冲压缩实验系统,开展了脉冲压缩试验。该脉压系统可将4.5 ns输入脉冲压缩为前沿940 ps、半高宽约1 ns的亚纳秒脉冲,实现了约2.2倍的功率增益。实验数据与理论分析基本吻合。     

Short pulse,x-ray preionization of a high pressure XeCl gas discharge laser

A short pulse (35 ns), high energy X-ray source, driven by a coaxial Blumlein pulser, has been used to preionize a 2.5 × 3 × 30 cm³ active volume XeCl avalanche discharge laser. A maximum output energy of 1 J has been extracted at 0.9% efficiency (including X-ray preionization). Measurements have been performed to investigate the influence of the X-ray pulse timing on laser output and discharge quality.     

基于PFN-Marx技术的200 keV脉冲X射线源设计与实验

基于PFN-Marx技术路线研制了200 kV脉冲驱动源,采用了超前触发技术,实现了在40 Ω水电阻负载上输出电压约200 kV、前沿约25 ns、脉冲宽度约62 ns的脉冲高压。设计了工作电压为200 kV的“Washer-Needle”型二极管,在二极管电压210 kV、电流5 kA条件下,输出X射线脉冲宽度约40 ns,X射线焦斑直径1.2 mm,1 m处照射剂量约15 mR。     

A Radially and Axially Extracted Virtual-Cathode Oscillator (Vircator)

Experiments are described in which a 5-? 1-MeV pulser drives virtual-cathode systems optimized to emit microwave radiation in the X band. Radiation is extracted both axially in TM modes and radially in TE modes. The threshold for microwave emission is found to be several times the space-charge limited current. The radiating frequency is approximately proportional to the electron beam plasma frequency with a proportional constant of (27?)1/2. Anode/cathode spacing is varied to demonstrate the frequency tunability of the virtual cathode as a microwave source. The radiation is broad band and frequency chirping is observed. Radiation patterns of the axially extracted radiation are described. The instantaneous efficiency of energy conversion from electrical to microwaves is ~2 percent. External excitation from an external source does not alter microwave generation.