Yerevan synchrotron injector electron beam transversal scan with vibrating wire scanner

We have developed extended-aperture (20 mm) vibrating wire scanner (VWS) for transversal scanning of electron beams with large transversal size. Test experiments were performed in open atmosphere on the 40 MeV electron beam of the Yerevan synchrotron injector with the 4–10 μA at outlet. A construction of VWS is elaborated for scanning beams with larger transversal size. This elaboration is a new precision tool for diagnostics of beams in accelerators, which may be successfully employed, because of universality of the used operation principle, for profiling of as well large-aperture proton and ion beams.     

2MeV注入器脉冲电子束时间分辨能谱诊断研究

介绍了利用磁分析器和电子束产生的契伦科夫辐射光诊断直线感应加速器脉冲电子束时间分辨能谱的原理、方法及诊断系统,对中物院2MeV感应叠加型注入器的2kA强流脉冲电子束时间分辨能谱进行实验诊断,并与二极管电压进行对比分析。测得能量约2.2MeV,60ns内最大能量变化为4%。     

2MeV注入器脉冲电子束时间分辨能谱诊断研究

 介绍了利用磁分析器和电子束产生的契伦科夫辐射光诊断直线感应加速器脉冲电子束时间分辨能谱的原理、方法及诊断系统，对中物院2MeV感应叠加型注入器的2kA强流脉冲电子束时间分辨能谱进行实验诊断，并与二极管电压进行对比分析。测得能量约2.2MeV，60ns内最大能量变化为4%。     

Problems of magnetic field distortions caused by eddy currents in Yerevan synchrotron

The effects of eddy currents on the design value of magnetic field in accelerators are investigated analytically. A program is developed for calculation of magnetic field distortions caused by eddy currents. The numerical results are given for the accelerator in Yerevan Physics Institute, if it will be used to accelerate the ions.     

Convective loss cone instability in electron beam injected mirror plasmas

It is shown that in electron beam injected mirror plasmas, the convective loss cone instability gets modified substantially and so reduces the critical length by at least an order of magnitude. This will seriously jeopardize the open ended confinement schemes employing electron beams.     

A particle-in-cell mode beam dynamics simulation of medium energy beam transport for the SSC-Linac

A new linear accelerator system, called the SSC-Linac injector, is being designed at HIRFL (the heavy ion research facility of Lanzhou). As part of the SSC-Linac, the medium energy beam transport (MEBT) consists of seven magnetic quadrupoles, a re-buncher and a diagnose box. The total length of this segment is about 1.75 m. The beam dynamics simulation in MEBT has been studied using the TRACK 3D particle-in-cell code, and the simulation result shows that the beam accelerated from the radio frequency quadrupole (RFQ) matches well with the acceptance of the following drift tube linac (DTL) in both the transverse and longitudinal phase spaces, and that most of the particles can be captured by the final sector focusing cyclotron for further acceleration. The longitudinal emittance of the RFQ and the longitudinal acceptance of the DTL was calculated in detail, and a multi-particle beam dynamics simulation from the ion source to the end of the DTL was done to verify the original design.     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

Longitudinal beam distribution and coherent synchrotron radiation of relativistic electron clouds

The effect of the form of the longitudinal distribution of an electron beam on the characteristics of coherent synchrotron radiation is investigated. The spectral density and total power of the coherent synchrotron radiation are studied as functions of the dispersion and excess of the longitudinal distribution, as well as of the energy of the radiating particles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 17–20, February, 1977.     

超快电子衍射装置的束流能量反馈控制

上海交通大学的超快电子衍射（UED）装置由一台电子直线加速器作为驱动,电子枪为一台光阴极微波电子枪。加速器在运行中电子枪会偶尔打火,腔体失谐,造成束流损失,束流能量产生变化,束流需要很长时间才能恢复到初始状态,影响了用户的使用。为此,对低电平控制器（LLRF）的幅度相位控制环路进行了改进,增加了能量反馈,代替了幅度反馈,通过对束流的中心位置进行实时的反馈以控制低电平控制器输出信号的幅度,保证了电子束流的能量稳定和电子枪加速场强的稳定。长时间的稳定性测试表明,电子枪在打火产生时,束流能量可以很快恢复,能量抖动由4.293 3×10⁻⁴（RMS）提高到2.855 7×10⁻⁴（RMS）,实现了束流能量的长期稳定。     

The distribution of liberated energy and injected charge under normal incidence of a fast electron beam on a target

Formulas for the distributions of the liberated energy and injected charge are derived within the diffusion model of the kinetic equation for an electron beam normally incident on the target. The theory does not involve empirical adjustable parameters. The calculation of the liberated energy for the case of a planar directional electron source in an infinite medium (C, Al, Sn, and Pb) correlates well with the Spencer data, obtained from the exact solution of the Bethe equation, which is also used as the basis in the diffusion model.     

Polarization of coherent synchrotron radiation from an electron beam rotating in a plasma

After eliminating reflections from the walls of the plasma container, we observed polarization of the coherent synchrotron radiation from a relativistic electron beam rotating in a plasma. Several features of the polarization agree well with calculations based on the single particle synchrotron radiation theory. A particular polarization ratio (Fig. 3) does not, however. We deduce from this direct diffraction of the radiation by the beam electrons. This is strong evidence for beam-particle bunches of size cm. Also, there must be some absorption of the extraordinary wave to account for the observations. We suggest a way to apply these results to measure the pitch angle of the beam.Work supported by Army Research Office.     

Proposal for an x-ray free electron laser oscillator with intermediate energy electron beam

Harmonic lasing of low-gain free electron laser oscillators has been experimentally demonstrated in the terahertz and infrared regions. Recently, the low-gain oscillator has been reconsidered as a promising candidate for hard x-ray free electron lasers, through the use of high reflectivity, high-resolution x-ray crystals. In this Letter, it is proposed to utilize a crystal-based cavity resonant at a higher harmonic of the undulator radiation, together with phase shifting, to enable harmonic lasing of the x-ray free electron laser oscillator, and hence allow the generation of hard x-ray radiation at a reduced electron beam energy. Results show that fully coherent free electron laser radiation with megawatt peak power, in the spectral region of 10-25 keV, can be generated with a 3.5 GeV electron beam.     

Monochromaticity of the Smith-Purcell optical radiation generated by a 75-keV electron beam

The monochromaticity of the Smith-Purcell optical radiation generated by a 75-keV electron beam with a final emittance of ε = 0.65 × 10^?4 mm rad that passes over a grating with a period of D = 0.833 μm has been analyzed. It has been shown that the monochromaticity of Smith-Purcell radiation is determined not only by the angular aperture of a monochromator but also by the divergence of the electron beam.     

Resonant transition radiation in the X-ray region from a low emittance 855 MeV electron beam

The interference of transition radiation coherently produced from a periodic stack of four polyimide foils of 7.2 μm thickness and a separation of 162 μm was investigated. This stack has been brought into the low emittance (3 π nm rad) electron beam of the 855 MeV Mainz Microtron MAMI. Transition radiation was observed in the energy range from 2 to 15 keV with a LN₂-cooled pin photodiode. A good energy resolution of 0.8 keV and angular resolution of 0.15 mrad was achieved simultaneously allowing for the first time to quantitatively study the interference pattern. Good agreement with theoretical calculations is found. Prospects to exploit transition radiation in the x-ray region from a low emittance electron beam as a high brilliant radiation source are discussed.     

Structure formation and tearing of an MeV cylindrical electron beam in a laser-produced plasma

The stability of a cylindrical, solid hot electron beam propagating in a high density plasma has been studied using a two-dimensional, hybrid Darwin code. The initially solid beam evolves into a hollow, annular beam due to the Weibel instability and generates strong magnetic fields on both sides of the annular ring. The annular structure subsequently breaks up into several beamlets via a mechanism similar to a tearing instability. It is found that the magnetic fields parallel to the direction of beam propagation also grow due to the tearing process.     

超强飞秒激光尾波场加速产生58MeV准单能电子束实验

超短超强激光与等离子体相互作用产生的激光尾波场可以在毫米尺度上加速产生高能量的准单能电子束.在SILEX-Ⅰ激光装置上进行的激光尾波场加速实验中,利用超强飞秒激光与超声速锥形喷嘴产生的2.7mm直径氦气气体柱相互作用,获得了能散为15.5%、发散角为15mrad、能量为58MeV的准单能电子束.在70TW激光照射下获得的电子束总电量达到15.4nC.介绍了实验条件、方法和主要实验结果.     

Free electron laser spectral dynamics with a modulation of electron beam energy

Recent experimental and theoretical works on free electron laser spectral dynamics have pointed out the difficulty to obtain a narrow and stable spectrum operation. This goal can only be achieved by avoiding the sideband generation leading to a broadband and unstable spectrum. Tapered wiggler and two-frequency wiggler are well suited for combining sharp spectrum and high efficiency but are not really compatible with a wide tunability of laser light. Filtering sidebands is a good way for lower power experiments but it seems to be difficult to conceive wideband filters, specially in the far-infrared region. Modulation of electron energy is a new potential soft way for controlling the spectral dynamics of longpulse free electron laser. Spectral dynamics under the modulation is investigated in the linear and non-linear regimes in the far-infrared region. Simulations show that a pulsed and sharp spectrum behavior can be obtained by optimizing the modulation parameters. The interest of such a method for the far-infrared experiments is discussed.