Simulation and analysis of the transverse spectrum in HIRFL-CSR

Particles in a storage ring oscillate in the longitudinal and transverse dimensions.Therefore,the signal that beam has generated can be analyzed in the frequency domain to extract many beam parameters,such as tune,momentum spread,emittance and their evolution with time and so on.In this paper,the transverse spectrum in HIRFI-CSR was simulated and analyzed under different conditions,including electron cooling,hollow electron beam,solenoid effect,the tune shift caused by power supply ripple and the misalignment between ion and electron beams.The result of the simulation shows that the longitudinal magnetic field of the electron cooling device should be compensated by a "compensation solenoid",and the power supply ripple must be controlled,otherwise the accumulation would be affected and the beam would be lost.     

Simulation and analysis of the transverse spectrum in HIRFL-CSR

Particles in a storage ring oscillate in the longitudinal and transverse dimensions. Therefore, the signal that beam has generated can be analyzed in the frequency domain to extract many beam parameters, such as tune, momentum spread, emittance and their evolution with time and so on. In this paper, the transverse spectrum in HIRFL-CSR was simulated and analyzed under different conditions, including electron cooling, hollow electron beam, solenoid effect, the tune shift caused by power supply ripple and the misalignment between ion and electron beams. The result of the simulation shows that the longitudinal magnetic field of the electron cooling device should be compensated by a “compensation solenoid”, and the power supply ripple must be controlled, otherwise the accumulation would be affected and the beam would be lost.     

HIRFL-CSR电子冷却系统空心电子束性能研究

 电子冷却系统中冷却力的大小与电子束的温度密切相关。由于强流电子束自身产生的空间电荷场,使得电子束的速度离散,增加了电子束温度,降低了冷却效率。为了减小空间电荷效应,HIRFL CSR的电子冷却系统将首次采用空心电子束对储存环中的重离子束流进行冷却。通过分析实心电子束和空心电子束的空间电荷场,研究了其对电子束速度和温度的影响。     

High-frequency emissions during the propagation of an electron beamin high-density plasma

A relativistic annular electron beam passing through a high-density plasma excites Langmuir waves via Cerenkov interaction. The Langmuir waves are backscattered off ions via nonlinear ion Landau damping. At moderately high amplitudes these waves are parametrically up-converted by the beam into high-frequency electromagnetic radiation, as observed in some recent experiments. A nonlocal theory of this process is developed in a cylindrical geometry. It is seen that the growth rate of the Langmuir wave scales as one-third the power of beam density. The growth rate of parametric instability scales as one-fourth the power of beam density and the square root of beam thickness     

离子通道中相对论电子注的切连科夫辐射

对入射等离子体的相对论电子注(REB)在离子通道中可能产生切连科夫(Cherenkov)辐射的问题进行了论证与研究.利用线性理论分析了离子背景下的注-波互作用关系，导出了系统的色散方程与同步辐射条件.结果表明，系统的电磁不稳定性是由离子通道中TM模与电子注模通过电子注耦合所致，其微观机理是离子对电子注的聚焦.对处于运动等离子体状态下的离子-注系统进行了严格地理论分析，获得了通道内辐射波的频偏与波增长率公式，并通过数值模拟计算讨论了系统有关参数对它们的影响. 关键词： 离子通道 等离子体 切连科夫辐射     

The nonlinear theory of slow-wave electron cyclotron masers with inclusion of the beam velocity spread

The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency.     

Study on the effects of chromaticity and magnetic field tracking errors at CSNS/RCS

The Rapid Cycling Synchrotron (RCS) is a key component of the China Spallation Neutron Source (CSNS). For this type of high intensity proton synchrotron, the chromaticity, space charge effects, and magnetic field tracking errors between the quadrupoles and the dipoles can induce beta function distortion and tune shift, and induce resonances. In this paper, the combined effects of chromaticity, magnetic field tracking errors and space charge on beam dynamics at CSNS/RCS are studied systemically. 3-D simulations with different magnetic field tracking errors are performed by using the code ORBIT, and the simulation results are compared with the case without tracking errors.     

一种新型缓变倒向场大回旋电子枪

提出了一种新的利用缓变倒向场获得大回旋电子注的设计方法,在分析缓变倒向场中电子的运动规律和引起偏心与速度零散的各种原因的基础上,设计了一支大回旋电子枪.与传统设计思路不同,这种大回旋电子枪既不追求形成薄的管状电子束,又不追求突变的倒向磁场,因而极大降低了制管工艺和结构复杂性;阴极发射带可以位于倒向点前的轴向磁场幅值渐减区域,通过控制各条轨迹起始点的正则角动量差异,并利用多种不利因素的相互抵消作用来减小偏心与速度零散.模拟计算结果与理论分析一致,表明通过微调电磁场使各种不利因素相互抵消可以显著提高大回旋电子 关键词： 缓变倒向场 大回旋电子枪 偏心 速度零散     

同轴波导环形相对论电子束空间极限电流

得到了1维条件下电子均匀分布时,环形电子束在同轴波导内轴向传输的空间极限电流解析表达式。通过讨论解析式在薄电子束和波导内导体半径为0等极限条件下的近似情况,分析了其合理性。在电子束非均匀分布的条件下,对空间极限电流进行了数值求解,并与解析计算结果进行了比较。理论研究表明:环形电子束在同轴波导内具有较圆柱波导内更高的空间极限电流,而且当电子束靠近波导壁时,空间极限电流会显著提高。     

Coherent interaction of ion and electron beams in systems with electron cooling

A hydrodynamic approximation is used to study the behavior of dipole modes of the transverse oscillations of an ion beam in a storage ring with an electron cooling section. It is shown that in addition to the finite interaction time of the beams, instability may be caused by a specific interaction effect between the ion and electron beams in the magnetic field which leads to redistribution of energy between the various modes of the ion beam oscillations. In this case, the condition that the determinant of the transfer matrix for the cooling section does not exceed unity no longer guarantees the stability of the transverse coherent oscillations of the ion beam and all the eigenvalues of the complete matrix of the ion motion including the storage ring must be analyzed. Calculations of the stability of ion beam dipole oscillations are presented for the parameters of CELSIUS.     

Theoretical analysis of electron acoustic shock waves in magnetized superthermal plasma with electron beam

We have analysed the small-amplitude non-linear electron acoustic shock waves by taking into account the effects of electron beam in magnetized plasma. Satellite observations in different regions of the Earth's magnetosphere have shown that the electrostatic solitary waves are generally associated with electron or/and ion beams. The nonlinear Korteweg-de-Vries Burgers (KdVB) equation has been derived by considering the basic fluid equations and dissipation effects. The nonlinear coefficient of KdVB equation comes out to be negative. Only dip-shaped potential structures are reported here. For the parameters discussed in this paper, we did not find positive polarity shocks. This could be due to the restrictions on the plasma parameters since we are using the fixed densities of the cold, hot, and beam electrons as observed by the Viking satellite in the auroral region. In this paper, the importance of the cold electron to hot electron temperature in conjunction with the beam speed is pointed out. Increase in beam density, kinematic viscosity, and magnetic field results in increase in the amplitude while the increase in hot electron concentration and superthermality leads to decrease in potential. The numerical analysis is presented for the parameters corresponding to the observation of burst b event by Viking satellite in the dayside auroral zone of the earth's magnetosphere.     

Tune optimization of the third generation light source storage ring based on Frequency Map Analysis

Tune optimization is necessary to optimize the nonlinearity of the third generation light source storage ring. In this paper we summarize the common strategies for choosing a tune and discuss tune op-timization. Frequency Map Analysis (FMA) is applied as a tune scanning tool to reveal information about nonlinear resonances and guide the tune optimization. The Shanghai Synchrotron Radiation Facility (SSRF) storage ring is taken as a test lattice, and the optimum solutions are presented in this paper. Moreover, the third order regular structural resonances excited by sextupoles are particularly investigated, and it is found that these resonances distort the tune shifts with amplitude and show a stop-band like the linear structural resonances.     

考虑到束-波相互作用的速调管离子噪声二维模拟

采用粒子模拟的方法并考虑电子束与电磁波的相互作用，首次直接得到了速调管输出信号的离子噪声图像，阐述了束电子、二次电子、离子、电磁场之间的相互作用的动力学过程. 指出离子噪声所表现出来的相位波动是由电子束速度的波动引起的，电子束速度的变化来源于管内离子数量的变化，离子的数量的变化又与电子束状态变化相互影响，这是离子噪声产生的根本原因. 二次电子对离子噪声产生过程的影响甚微，但是其行为却反映了离子噪声的形成机理. 离子噪声引发的输出信号幅度波动取决于电子束速度和半径的改变，与离子行为密切相关. 关键词： 离子噪声 速调管 粒子模拟 电子束     

The theoretical simulation of magnetized electron beam effects on radially polarized of an annular cylindrical piezoelectric crystal

By using the equilibrium equations for a hollow cylindrical piezoelectric layer in absence of body forces and taking into the account a magnetized electron beam in hollow region of this system the effects of thermal pressure, electrostatic self field and the strength of external magnetic field of a non-relativistic magnetized electron beam column on radially polarized of an annular cylindrical piezoelectric crystal in the steady state are simulated. The electrostatic potential profile in piezoelectric layer due to the mechanical pressure and electrostatic self field of electron beam are studied. Furthermore the graphs of the difference of potential Δϕ between inner and outer surfaces of piezoelectric versus to electron temperature, density of beam and the strength of external magnetic field are presented.     

Nonlinear theory of resonant beam-plasma interaction: Nonrelativistic case

Analytic and numerical methods are used to study the nonlinear dynamics of the resonant interaction between a dense nonrelativistic electron beam and a plasma in a spatially bounded system. Regimes such as collective (Raman) and single-particle (Thomson) Cherenkov effects are considered. It is shown that in the first case, the motion of both the beam and plasma electrons exhibits significant nonlinearities. However, because of the weak coupling between the beam and the plasma, the nonlinear dynamics of the instability can be studied analytically and it can be strictly shown that saturation of instability is caused by a nonlinear shift of the radiation frequency and loss of resonance. In the second case, the nonlinear instability dynamics can only be studied numerically. In this regime, at low beam densities significant nonlinearity is only observed in the motion of the beam electrons while the plasma remains linear and saturation of the instability is caused by trapping of beam electrons in the field of the beam-excited plasma wave.     

RF trapping and acceleration in CSNS/RCS

In this paper, two injection scenarios with different chopping rate are discussed. The waveforms of the RF voltage are studied and optimized, respectively. Some suggestions are made, concerning chopping and momentum painting of the injected beam. Furthermore, the momentum spread and transverse tune shift are calculated so that the beam aperture and the beam loss can be estimated. Finally, the beam loss with magnet field error is analyzed.     

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.     

Magneticresonant three dimensional kinetic theory of the free electron laser with waveguide cavity

Vlasov kinetic theory of the free electron laser employing waveguide frifting tube and helical pump is presented. Distinct from the former theories this theory has (1) taken into account the 3-d structure of the scattering field; (2) applied the plasma kinetic theory, which is more accurate than the other methods, to analysing the effect of the longitudinal. field; (3) taken account of the influence of the annular structure of the beam. The magnetic resonant effect appearing when the cyclotron frequency of electrons approaches the effective frequency of the magnetic pump is analysed and the growth rate formula in the linear regime derived. Results show that on taking into account the 3-d structure of the field and beam, one cannot arbitrarily choose the radius of the hollow beam, or else within certain range the instability may disappear altogether. Lastly, the equation for determination of the optimum beam radius is given and the possibility of raising growth rate by operating in high order modes shown.     

Effective mass of an electron in an electromagnetic field

The effective-mass formalism is shown capable to describe the fully relativistic motion of an electron in a strong, locally plane, electromagnetic wave, determining the drift caused by the wave inhomogeneity and by additional weaker fields. The limits of this approach are discussed, in connection with the occurrence of resonances.     

低速度零散会切电子枪的设计和数值仿真

根据拉格朗日方程对电子在平滑会切磁场中的径向波动与速度零散的关系进行讨论。运用Matlab,Magic软件相互结合的方法设计电子枪结构和磁场。用Matlab程序模拟单电子在给定电场、磁场中的运动,分析了单电子径向速度对零散的影响,并优化磁场分布。设计的磁场可以有效地减小单电子束径向速度,降低电子束速度零散。用Magic软件对电流为1 A、能量为30 keV的电子束在优化磁场中的运动进行仿真,得到的电子束速度比约为2,速度零散小于2.5%,轴向速度零散小于8.5%。