强流电子束入射弯曲宏观石英管的导向效应研究

研究了强流（~129 nA）、 高能（1 500～1 900 eV）电子束在大角度(9°)弯曲宏观石英管中的导向效应。 实验分别测量了入射流强及能量对出射电子角分布值（FWHM）和传输效率的影响。 实验观察到出射电子角分布FWHM随着入射电子流强和入射电子能量增加变化均不明显; 发现电子传输效率随入射流强增加而增加, 但随入射能量增加而减小, 这与高电荷态离子导向中离子传输效率随入射能量增加而增加的现象相反。 分析发现, 与高电荷态离子导向机制不同, 电子束导向并非是由电子在石英管内壁的自组织充电过程引起的, 而是入射电子与管内壁弹性和非弹性散射碰撞共同作用的结果。 By using an incident electron beam with the high current and high energy, the guiding effect of the bended macroscopic quartz tube for the electron beam has been investigated. The angular distributions of outgoing electrons depending on the current and energy of incident electrons were measured. The dependences of electron transmitted fraction on energy and current of incident electrons are also shown. As the incident electron energy increasing, the electron transmitted fraction increases, but it decreases while the incident electron current increasing. The results have been compared with the present data. This work presents, the process of guiding electrons is essentially different from that of guiding highly charged ions, the guiding electron beam was caused by both elastic and inelastic collisions between electrons and inner walls of quartz tube, rather than self organized charging effect on the surface of inner wall of quartz tube.     

刻槽绝缘平行板对电子束的导向效应研究

采用不同材质的刻槽绝缘平行板,包括高纯度石英玻璃、聚四氟乙烯（Teflon）、酚醛树脂（电木）和聚甲醛板（赛钢板）,并在15 pA/mm2 ~14.3 nA/mm2范围内改变入射流强,利用1 500 eV电子束入射上述绝缘平行板,实验研究了上述平行板对电子束的导向行为。实验发现,上述电子束通过上述平行板时存在明显的导向现象,其导向行为与束流流强和绝缘材质无关。据此,可排除绝缘平行板内表面沉积电荷自组织充放电过程中,以绝缘材料的面电阻和体电阻对地泄放的线性形式放电过程。Adopting several grooved parallel plates made by different insulators, such as high-purity fused quartz, Teflon, Bakelite and POM (Polyformaldehyde), and further adjusting the electron beam current in a wide range (tens of pA~tens of nA), the discharging mechanism in the self-organizing charge and discharge processes of electron guiding was investigated and discussed by using 1 500 eV incident electron beam. The present results show that, the electron guiding behaviors are obviously existing when such electron beam is transmitted through the above grooved insulating parallel plates, which are independent on beam current and insulators. Our results suggest that, the possibilities of the accumulated charges on inner-surface of grooved parallel plates linearly discharging through surface and bulk resistances of plates into the ground should be excluded.     

Practical 2.45-GHz microwave-driven Cs-free Hˉ ion source developed at Peking University

A practical 2.45-GHz microwave-driven Cs-free Hˉ source was improved based on the experimental Hˉ source at Peking University(PKU). Several structural improvements were implemented to meet the practical requirements of Xi'an Proton Application Facility(XiPaf). Firstly, the plasma chamber size was optimized to enhance the plasma intensity and stability. Secondly, the filter magnetic field and electron deflecting magnetic field were enhanced to reduce co-extracted electrons. Thirdly, a new two-electrode extraction system with farther electrode gap and enhanced water cooling ability to diminish spark and sputter during beam extraction was applied. At last, the direct Hˉ current measuring method was adopted by the arrangement of a new pair of bending magnets before Faraday cup(FC) to remove residual electrons. With these improvements, electron cyclotron resonance(ECR) magnetic field optimization experiments and operation parameter variation experiments were carried out on the Hˉ ion source and a maximum 8.5-mA pure Hˉ beam was extracted at 50 kV with the time structure of 100 Hz/0.3 ms. The root-mean-square(RMS) emittance of the beam is 0.25 Π·mm·mrad. This improved Hˉ source and extraction system were maintenance-free for more than 200 hours in operation.     

Investigation of intense sheet electron beam transport using the macroscopic cold-fluid model and the single-particle orbit theory

The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.     

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns （FWHM） electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm （FWHM） in diameter and the corresponding beam divergence is about 10.5 mrad.     

High-transmittivity non-periodic sub-wavelength high-contrast grating with large-angle beam-steering ability

We present a high-transmittivity non-periodic sub-wavelength high-contrast grating （HCG） with large-angle beam-steering ability for transmitted light. The phase front profile of transmitted light is a decisive factor to the beam-steering property of the HCG. By designing the structural parameters of the HCG, both beam steering and high transmittivity can be achieved. The properties of the beam steering and transmission are numerically studied with the finite element method. The results show that the transmittivity is up to 0.91 and the steering angle is 27.42° which is consistent with the theoretical 30°.     

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.     

ECR离子源外电子注入技术研究

使用电子枪对ECR（Electron Cyclotron Resonance）等离子体注入外电子束是继铝衬弧腔、偏压盘之后,对等离子体电子的额外补充的又一种手段,通过向弧腔中注入一定能量与流强的电子束,以期提高引出束流的流强与电荷态。但由于该方法可控参数繁多,经验积累与报道资料都很少,且设计与操作远不如偏压盘等手段简便,故一直未能得到深入研究。通过以三维仿真软件CST粒子工作室对注入到弧腔电子束的运动轨迹的模拟结果为依据、以18 GHz ECR蒸发冷却源为平台,进行了ECR等离子体注入电子束的实验,结果表明:在一定实验条件下,当注入电子束能量超过1 800 eV时,会产生一种引出的离子束流的激增现象。在这个现象中,脉冲与直流的流强均比未注入电子时要高,束流电荷态向高价方向移动,且可通过控制实验条件来控制这种现象。最后对于这种电子并未通过共振面,却能起到提高电荷态与流强的作用进行了分析与讨论,并认为该现象在改善直流束与脉冲束性能的方面都有着积极的意义。The injection of the electron beam into the ECR (Electron Cyclotron Resonance)plasma by electron gun is a new method for the additional supplementary of the plasma electron, following the aluminum chamber wall and the bias plate, we are expecting for the higher current and charge state of the ion beam with it. However, because of the controllable parameter's variety, the lack of the accumulation of experience and data, and the shortage of convenience in designing and experimental practicing compared by biased disk and other means,it has always not been intensively studied. In this article, we take the 18 GHz ECR Ion Source using evaporative cooling technique as experimental platform, do the experiment of injecting electron into ECR plasma base on the simulation result of the electron beam's path in ECR's chamber by the 3D simulation software CST the particle studio. It shows that a pulsing leap of the current of the extracting ion beam appears when the injecting electron's energy is above 1 800 eV. In the mean time, the top of the pulse and the average current of the ion beam rises, the ionization state moves to a higher level. This phenomenon can be turned on and off by controlling the experimental condition. At the last part of the article, we discuss this improvement of the current and charge state of the ion beam despite of the position's missing between the injection of electron beam and the resonance surface, and hold the opinion that this phenomenon is positive to both pulsed and direct beam.     

64通道一维位置灵敏电流分布探测器及其数据获取系统

针对高流强粒子束与绝缘毛细管相互作用的特点, 设计制作了一套64通道一维位置灵敏电流分布探测器及其配套的数据获取系统, 该探测器可分辨最小直径为1 mm的束斑, 通过数据获取系统可实现可视化自动数据采集。 用2 nA和200—2000 eV电子对探测器进行了定标, 并用10 μA和2000 eV的电子束穿越锥形毛细管后的出射电子, 对探测器及数据获取系统进行测试, 获得了出射粒子的位置分布谱及能量信息。 A 64 channel position sensitive current distribution detector with 1 mm position resolution was developed, while the data acquisition system is based on the LabVIEW software. The test result obtained by using a 2 nA, 200—2000 eV electron beam deflecting by different voltages and the position spectra of 10 μA, 2000 eV electrons transmitted through a glass capillary was measured. The result indicated that the detector can be used to detect the charged particles with strong beam current through the capillary.     

A staggered double vane circuit for a W-band traveling-wave tube amplifier

Based on the combination of a staggered double vane slow wave structure(SWS) and round electron beam,a 200-W W-band traveling-wave tube(TWT) amplifier is studied in this paper.The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced.It operates in the fundamental mode at the first spatial harmonic.The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube.Then a TWT model is established and the particle-in-cell(PIC) simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz,on the assumption that the input power is 0.1 W and the beam power is 5.155 kW.The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB,respectively.Such amplifiers can potentially be used in high power microwave-power-modules(MPM) and for other portable applications.     

测量电子束流的小型法拉第筒

介绍一种测量束流强度不大于50kA,能量不超过0.8MeV的小型法拉第筒。经标定,此法拉第筒上升前沿小于6ns。已用于契伦柯夫自由电子激光的传输束流测量。     

Time resolved studies on X-rays and charged particles emission from a low energy plasma focus device

The time resolved studies on soft X-ray, hard X-ray, electron beam and ion beam emissions from a low energy plasma focus device are carried out simultaneously by employing a photodiode X-ray spectrometer, a scintillator photomultiplier tube, a combination of Faraday cup and Rogowski coil assembly and a biased Faraday cup, respectively. The soft X-ray is seen to be emitted in short multiple pulses corresponding to different pinch stages where as it is a single for hard X-ray, which corresponds to only maximum pinch stage. Similarly, multiple pulses of electron beam is found, which also corresponds to different pinch stages and these pulses are analogous with the soft X-ray pulses. The effective hard X-ray photon energy is estimated by foil absorption technique and found to be around 110 keV, which is consistent with the observed electron beam energy distribution. The simultaneous investigation of the electron and ion beam shows that both are accelerated by the same local field generated during the pinching process. The detailed results of time resolved studies on various radiations are incorporated in this Letter.     

法拉第筒阻抗对二极管电子束流性能的影响

 分析了法拉第筒阻抗对二极管电子束流性能的影响, 研制了一种安装在阳极座中测量阳极吸收束流的法拉弟筒, 并用它测量了81-7M -01强流相对论电子束加速器二极管阳极吸收束流。     

Mutual electron-ion interactions in electron impact ionization of a Ca beam

Summary We evaluate the role of electron-ion mutual interactions as a possible source of systematic errors in an experiment of electron impact ionization and excitation of an effusive Ca beam. By monitoring photons resulting from the impact excitation of a Ca resonant transition, the transmitted electron beam current by a sectored Faraday cup and total ion yields, we extract information about elementary processes responsible for ionization. We show that our diagnosis allows us to monitor the influence of the produced ionization on the elementary processes and on the density profile of the electro beam.     

Electron scattering cross section measurements in a variable pressure scanning electron microscope

Scattering of the incident electron beam in the variable pressure scanning electron microscope (VPSEM) affects the ability to perform quantitative chemical measurements. However, the manner in which the sum of the elastic and inelastic scattering cross sections varies as a function of gas type and accelerating voltage in the VPSEM is not well understood. A dual Faraday cup was constructed to measure the scattered fraction of the primary beam as a function of gas pressure, working distance, and accelerating voltage in air, water vapor, and argon environments. Experimentally measured values of the scattering cross section agree with previous experimental work, and agree within a factor of two with those values calculated carefully from theory.     

高流强电子束在锥形SiO2毛细管中的导向效应

 研究了高流强电子束(1～10 μA)在单根锥形SiO₂毛细管中的导向效应,测量了出射电子的角分布,分析了入射能量对电子传输效率的影响。实验发现：出射电子呈高斯分布且时间稳定性好,随着入射能量增加,电子在毛细管中的传输效率降低,传输效率与入射能量呈负指数关系。实验结果与导向效应模型符合得很好。     

12MeV LIA轫致辐射靶面回流离子测量

 强流高功率脉冲电子束聚焦成mm量级的束斑后，打击到轫致辐射靶的过程中会产生回流离子，它会导致电子束被提前聚焦，在预定的靶面形成散焦。描述了法拉第筒对12MeV 直线感应加速器的轫致辐射靶面可能产生的离子及其参数进行的实验测量，并对实验结果进行了分析讨论。结果表明在靶前60°~70°方向未发现回流离子。     

强流短脉冲电子束束剖面测量技术

 束流剖面信息的获得对于加速器的研究有着重要的意义。对强流短脉冲电子加速器束剖面测量技术作了评述。目前，发展时间分辨的快响应的光学测量技术及实时在线测量为主要发展趋势。