新型准光学可调辐射源研究

本文介绍一种新型毫米波准光学可调辐射源,它采用由面对称三反射镜准光学谐振腔和绕射光栅组成高频互作用系统,利用中等能量级的相对论带状电子注激励,产生频率可调的宽带毫米波、远红外波段的辐射。这种新方案的机理性实验在电子科技大学首次获得成功,其主要实验参数：电子注的能量为400~500kV,电压脉冲宽度70ns,同步脉冲磁场强度1.2T; 磁场脉冲宽度10ms,带状电子注尺寸10nm×1mm;通过热测实验,我们成功地检测到3mm波段的高频信号,其峰值功率达到数十千瓦量级。     

Simulation study of a photo-injector for brightness improvement in Thomson scattering X-ray source via ballistic bunching

Increasing the peak brightness is beneficial to various applications of the Thomson scattering X-ray source. A higher peak brightness of the scattered X-ray pulse demands a shorter scattering electron beam realized by beam compression in the electron beam-line. In this article, we study the possibility of compressing the electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve the peak brightness of the scattered x-ray pulse. Numerical optimization by ASTRA demonstrates that the peak current can increase from 50 A to > 300 A for a 500 pC, 10 ps FWHM electron pulse, while normalized transverse RMS emittance and RMS energy spread increases very little. Correspondingly, the peak brightness of the Thomson scattering X-ray source is estimated to increase about three times.     

High-Power Modulated Intense Relativistic Electron Sources with Applications to RF Generation and Controlled Thermonuclear Fusion

Recent advances in the physics and technology of the modulated intense relativistic electron beams (IREB's) are reviewed in this paper. Bunched dense electron beams can be used to construct high-power RF sources, which may critically affect future progress in fusion technology. In this paper a system is described in which electrical energy can be converted from a single pulse of relatively long duration into a series of subpulses of short duration (nanosecond and subnanosecond) and of high power (~1010 W). This electrical system consists of an IREB propagating through passive structures. The mutual interaction between the electron beam and one passive structure modifies the IREB so that power compression and beam modulation occur. When the modified IREB interacts with the next passive structure, the kinetic energy of the electrons is converted into electrical energy or RF energy. The beam current modulation depends on the injected IREB and the structure parameters. A 100-percent modulation of the current has been achieved. A single-beam source may be used for exciting radiation in a frequency range of 60 MHz to 10 GHz. In the frequency range of 60-750 MHz a modulated beam with power ~1010 W has already been achieved. IREB modulation at a frequency of ~3 GHz was performed and RF energy was extracted from the bunched beam with power output of 5 × 108 W.     

A Novel Smith-Purcell FEL

A novel Smith-Purcell FEL with a relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three mirror reflector is described in this paper. Coherent radiation with peak power of tens of KW at 3 mm waveband is successfully detected from an experimental facility characterized by beam energy of 400-500 KeV, pulse length of 70 ns, pulse beam current of 0.2 KA, and pulse guide magnetic field of up to 1.2 T.     

Generation and Amplification of Cherenkov Superradiance Pulses by Electron Beams with Energy Chirp

We propose a method for increasing the peak power of a superradiance pulse by varying the electron energy along an electron bunch. A one-dimensional time-dependent model describing the evolution of an electromagnetic pulse as well as direct numerical simulations based on the KARAT code show that the power of generated pulses becomes several times greater if the particle energy increases linearly along the bunch. A similar method can be applied to increase the peak power in the case of amplification of a short electromagnetic pulse (and a superradiance pulse generated by an external source) propagated along a quasi-continuous electron beam with a certain particle-energy profile.     

S波段长脉冲相对论速调管放大器的实验研究

介绍了S波段强流长脉冲相对论速调管放大器（RKA）的高频系统设计、长脉冲强流相对论电子束(IREB)的调制及微波提取等方面的实验研究结果。重点阐述了长脉冲IREB调制和输出微波中的自激振荡问题。通过采用高阶工作模式以及参差模式设置的谐振腔、提高系统安装的同心度和调节电子束参数等措施,使自激振荡得到了抑制。采用550 kV,4 kA及210 ns的环行电子束,经过优化调节RKA参数,使强流调制电子束流脉宽由50 ns增加到150 ns,同时得到了3.2 kA的基波调制电流。从该RKA得到了峰值功率580 MW、脉宽140 ns的输出微波,束波转换效率26%,增益34 dB。     

猝发强流多脉冲电子束源物理设计

给出一台脉冲间隔100～1 000 ns、脉冲数2~5个、二极管电压3 MV、引出束流强度2.5 kA的猝发多脉冲电子束源的物理设计及初步调试结果。在设计中,采用感应叠加和阻抗匹配方案获得二极管高电压脉冲;试验中分别采用天鹅绒和大发射面储备式热阴极获得猝发多脉冲电子束。调试结果表明：采用大发射面热阴极可避免阴极等离子体产生,确保二极管在猝发多脉冲状态下稳定运行。初步调试获得大于2.7 MV猝发三脉冲二极管高压,并获得1.6 kA的三脉冲电子束流。     

猝发强流多脉冲电子束源物理设计

给出一台脉冲间隔100～1 000 ns、脉冲数2~5个、二极管电压3 MV、引出束流强度2.5 kA的猝发多脉冲电子束源的物理设计及初步调试结果。在设计中,采用感应叠加和阻抗匹配方案获得二极管高电压脉冲;试验中分别采用天鹅绒和大发射面储备式热阴极获得猝发多脉冲电子束。调试结果表明:采用大发射面热阴极可避免阴极等离子体产生,确保二极管在猝发多脉冲状态下稳定运行。初步调试获得大于2.7 MV猝发三脉冲二极管高压,并获得1.6 kA的三脉冲电子束流。     

RF deflecting cavity for bunch length measurement in Tsinghua Thomson scattering X-ray source

An RF deflecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source.The cavity is a 2856 MHz,π-mode,3-cell standing-wave cavity,to diagnose the 3.5 MeV beam produced by photocathode electron gun.With a larger power source,the same cavity will again be used to measure the accelerated beam with energy of 50 MeV before colliding with the laser pulse.The RF design using MAFIA for both the cavity shape and the power coupler is reviewed,followed by presenting the fabrication procedure and bench measurement results of two cavities.     

长脉冲X波段多注相对论速调管放大器的初步实验研究

设计了工作在长脉冲的X波段同轴强流多注相对论速调管放大器, 对长脉冲强流多注电子束在多注器件结构中的传输、电子束经过输入腔和中间腔后的束流调制以及经过输出腔的微波提取等过程进行了实验研究, 采用了相应的设计措施以减轻实验中出现的脉冲缩短现象, 得到了初步的长脉冲实验结果. 在输入微波功率60 kW、频率9.378 GHz、电子束电压700 kV、束流4.2 kA、轴向引导磁感应强度1 T的条件下, 重频5Hz输出微波功率为670 MW, 脉宽89 ns, 效率为23%, 增益为40 dB, 输出微波频率与输入微波一致. 从实验上验证了几十千瓦级输入微波驱动X波段同轴多注RKA输出几百兆瓦长脉冲高功率微波的可行性, 为后续更高功率研究打下了基础.     

硼中子俘获治疗实验装置射频功率源系统

中国科学院高能物理研究所建造了一台基于加速器的硼中子俘获治疗（BNCT）实验装置。射频功率源系统为352.2 MHz射频四极加速器（RFQ）提供高频功率,使束流离开RFQ时,其能量达到3.5 MeV。BNCT射频功率源系统主要包括速调管功率源、数字低电平控制系统、射频传输系统。本文介绍了BNCT射频功率源系统,主要包括物理需求、系统组成、关键设备、安装和调试。目前该装置已进行动物实验,加速器打靶束流功率4.3 kW,加速器射频功率源系统运行稳定。     

S波段长脉冲相对论速调管放大器的实验研究

 介绍了S波段强流长脉冲相对论速调管放大器（RKA）的高频系统设计、长脉冲强流相对论电子束(IREB)的调制及微波提取等方面的实验研究结果。重点阐述了长脉冲IREB调制和输出微波中的自激振荡问题。通过采用高阶工作模式以及参差模式设置的谐振腔、提高系统安装的同心度和调节电子束参数等措施,使自激振荡得到了抑制。采用550 kV,4 kA及210 ns的环行电子束,经过优化调节RKA参数,使强流调制电子束流脉宽由50 ns增加到150 ns,同时得到了3.2 kA的基波调制电流。从该RKA得到了峰值功率580 MW、脉宽140 ns的输出微波,束波转换效率26%,增益34 dB。     

20 GW紧凑Marx型重复频率脉冲驱动源研制进展

介绍了一种基于电触发技术的重复频率脉冲驱动源,其突破了双电容结构脉冲成形、紧凑型结构高压产生、大电流条件下重复频率稳定运行等关键技术,采用电路结构最简单的Marx电压叠加技术,解决了Marx在重复频率运行中的技术难点。脉冲功率驱动源设计输出功率20 GW、脉冲宽度180 ns、重复频率1~50 Hz,输出功率和重复频率在一定范围内可调。研制的脉冲功率驱动源体积仅2.5 m3,重量低至2.2 t,脉冲形成单元储能密度高达23 kJm-3,驱动源单次工作状态下输出功率约20 GW;在重复频率30 Hz工作状态下,输出功率16 GW、连续运行时间10 s、系统抖动约6 ns,系统运行稳定可靠。     

双脉冲电子束源实验研究

 利用现有2MeV直线感应注入器，通过改造，将其次级功率源和8个感应腔分成2组，使之交替工作，建立了一台双脉冲电子束源。二极管电压脉冲幅度达到1MeV，电子束脉冲持续时间为120ns，脉冲间隔可以根据需要在100~500ns间进行调节。实验结果表明：该双脉冲电子束源可以产生双脉冲电子束，其电压幅度差值小于2%，束流可达3kA，并且工作稳定，利用该装置可以进行多脉冲二极管物理和天鹅绒多脉冲发射特性实验研究。     

双脉冲电子束源实验研究

利用现有2MeV直线感应注入器,通过改造,将其次级功率源和8个感应腔分成2组,使之交替工作,建立了一台双脉冲电子束源。二极管电压脉冲幅度达到1MeV,电子束脉冲持续时间为120ns,脉冲间隔可以根据需要在100~500ns间进行调节。实验结果表明：该双脉冲电子束源可以产生双脉冲电子束,其电压幅度差值小于2%,束流可达3kA,并且工作稳定,利用该装置可以进行多脉冲二极管物理和天鹅绒多脉冲发射特性实验研究。     

折叠型平板Blumlein线高功率微波驱动源

 介绍了一种使用折叠型平板Blumlein线为主体的紧凑型高功率微波驱动源,Kapton薄膜和纯净变压器油分别作为折叠型平板Blumlein线的传输线介质和绝缘介质,Blumlein线的整体尺寸为1.00 m×0.40 m×0.15 m。采用一个特征阻抗大约是12 W的C波段磁绝缘振荡器作为高功率微波源。折叠型平板Blumlein线传输的能量可以使磁绝缘振荡器的阴极发射出电压550 kV,电流40 kA ,脉宽90 ns的电子束,从而产生峰值功率350 MW,脉宽40 ns的高功率微波。     

X波段短脉冲相对论返波管设计与初步实验

对基于短电子束脉冲超辐射机理的X波段相对论返波管进行了优化设计和粒子模拟,结果表明：在超辐射机理作用下,该器件能实现高峰值功率和高功率转换效率的微波辐射。在小型Tesla脉冲源基础上设计了阻抗变换段、二极管、磁场系统等装置,建立了一套小型窄脉冲电子加速器,以此为实验平台在低磁场条件下进行了器件的初步实验研究。在磁场0.73 T、束压约380 kV、束流约4.5 kA、脉宽3.1 ns条件下,实验获得的微波脉冲峰值功率约360 MW,脉宽1.10 ns,上升沿800 ps,频率9.15 GHz,功率转换效率为21%。     

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm³, a density of the discharge current at the anode of up to 3 kA/cm², and specific energy deposition of ∼1 J/cm³ over 3 to 5 ns is created.     

X波段短脉冲相对论返波管设计与初步实验

 对基于短电子束脉冲超辐射机理的X波段相对论返波管进行了优化设计和粒子模拟,结果表明：在超辐射机理作用下,该器件能实现高峰值功率和高功率转换效率的微波辐射。在小型Tesla脉冲源基础上设计了阻抗变换段、二极管、磁场系统等装置,建立了一套小型窄脉冲电子加速器,以此为实验平台在低磁场条件下进行了器件的初步实验研究。在磁场0.73 T、束压约380 kV、束流约4.5 kA、脉宽3.1 ns条件下,实验获得的微波脉冲峰值功率约360 MW,脉宽1.10 ns,上升沿800 ps,频率9.15 GHz,功率转换效率为21%。     

Preliminary experiment of the Thomson scattering X-ray source at Tsinghua University

The X-ray source based on Thomson scattering of ultrashort laser pulse with a relativistic electron beam is a means of generating a tunable, narrow bandwidth and ultrashort pulse of hard X-rays. Such a sub-picosecond hard X-ray source is proposed at Tsinghua University, and a preliminary experiment with a 16 MeV Backward Traveling electron linac and a 1.5 J, 6 ns Q-switched Nd:YAG laser is carried out first. A 6 ns pulse X-ray with a peak energy of 4.6 keV and an intensity of 1.7×104 per pulse is generated successfully in the experiment. The experimental setup, result and discussion are reported in this paper.