Transverse wakefield suppression using cell detuning assisted by manifold damping for high gradient linear colliders

Transverse wakefields excited by multiple bunches in ultra-relativistic charged particle beams in a linear collider must be adequately damped in order to preserve the luminosity of the colliding beams and to prevent a beam break up instability developing. Means of achieving this wakefield suppression are discussed in detail for high gradient normal conducting linacs. In particular the features of a damped and detuned series of structures (DDS) are described. Analytical expressions for the wakefield on short time scales are presented together with the circuit analysis required to rapidly analyse the general long-range behaviour in these linacs. A conspectus of experimental results along with theoretical predictions for this series of accelerating structures developed for the NLC/GLC is presented together with recent results on wakefield suppression for CLIC.     

A high-charge and short-pulse RF photocathode gun for wake-field acceleration

In this paper we present a design report on 1- cell, L-Band RF photocathode gun which is capable of generating and accelerating electron beams with peak currents> 10 kA. We address several critical issues of high-current RF photoinjectors such as longitudinal space charge effect, and transverse emittance growth. Unlike conventional short electron pulse generation, this design does not require magnetic pulse compression. Based on numerical simulations using SUPERFISH and PARMELA, this design will produce 100 nC beam at 18 MeV with r.m.s. bunch length 1.25 mm and normalized transverse emittance 108 mm mrad. Applications of this source beam for wake-field acceleration are also discussed.     

束流尾场效应引起消色差系统中色散系数的变化

从已有的消色差系统中的束流尾场效应公式，变换成六维传输矩阵的形式，并扩充束流传输计算机程序ＴＲＡＮＳＰＯＲＴ－ＥＭ／ＰＣ的功能，使之能用以计算尾场效应。最后，通过计算机数值计算，给出了一些实例的束流尾场效应对消色差系统中轨道色散和角色散变化的图表曲线。     

合肥光源的新高频腔阻抗谱计算

用电磁场计算软件MAFIA，在时域和频域两种情况下，对高频腔的耦合阻抗及电子束在此结构中产生的尾场进行了计算。结果表明，新高频腔里存在较强的高次模，需要采取措施加以抑制。     

Utilizing asymmetric laser pulses for the generation of high-quality wakefield-accelerated electron beams

Employing temporally asymmetric laser pulses in the interaction with plasma has been recently proposed for controlling the pointing angle of an electron beam produced by a laser wakefield acceleration at low plasma density and moderate laser intensity. In this paper, results on the electron beam parameters for both symmetric and asymmetric laser pulses are presented. These results show that the highest-quality (well-pointed, well-collimated and bright) electron beams are generated in the current regime only using asymmetric laser pulses, which are longer than the plasma wave’s acceleration period, τ>λ_p/2c. The interaction between the laser pulse and the accelerated electron beam in the first plasma-wave period is extracted from the experimental results and observed in preliminary two-dimensional particle-in-cell simulation.     

Specific heat of Wakefield thermal compound from 2 to 40 K

This paper reports on the measurement of the specific heat of Wakefield thermal compound from 2 – 40 K     

Near- and long-term applications of plasma-based accelerators

A variety of near-term applications has been suggested and several long-term goals, including high-energy colliders, have been discussed. Applications of laser (or beam)-driven accelerators along with applications of advanced laser itself have been considered, such as for X-ray sources. Some of the near term applications are realistic and exciting enough that they deserve serious further investigations. We point out some of these future opportunities.     

损失阻抗测量装置数据采集处理系统研制

电子储存环中真空部件的损失阻抗是表征该元件性能的重要参数,该参数的测量对于真空部件的设计,性能评估都有很大的意义。介绍了合肥储存环二期工程中损失阻抗测量的研制情况。     

Stimulated regenerative BBU instability of a bunch train in a single linac section

Stimulated multi-bunch transverse instability caused by hybrid dipole mode is studied using single cavity model. An accurate solution for the transverse displacement is found for sequence of bunches at presence and in absence of the input of signal. Threshold currents are calculated for resonant and non-resonant instability build-up including interaction with backward wave and Lorentz’ force contribution into the transverse wakefield. Linear amplification gain below the threshold was analyzed analytically. Transition from the cavity model to the waveguide model and validity of single-mode approximation is considered. It is shown, that for resonantly stimulated BBU the increment can be higher and threshold current lower than that for spontaneous instability.     

Design and applications of an X-band hybrid photoinjector

An INFN-LNF/UCLA/URLS collaboration is developing a hybrid photoinjector in X-band. This device is an integrated structure consisting of initial standing wave gun cells connected at the input coupler to a traveling wave section. This design nearly eliminates RF reflections from the SW section; further, a 90° phase shift in the accelerating field at the coupling cell gives strong velocity bunching. The current initiative in X-band follows an S-band hybrid, now proceeding to construction at LNF and high power testing/beam production measurements at UCLA. This S-band hybrid has 1.5 cell SW and 9 cell TW sections, and produces strongly compressed 3.5 MeV beam. It can be used for novel applications; here we discuss the production of an exponential energy spectrum extending from 1 to 12 MeV to simulate the effects of radiation belt environments on space-craft. It can be optionally used with a 3 m TW linac fed from RF output of the hybrid, to boost the energy to 22 MeV. While scaling the design from S-band to X-band is conceptually simple, practical limits require changes in both RF and magnetostatic designs. As the field is limited by RF breakdown to 200 MV/m peak field, the SW section must be expanded to 2.5 cells to reach 3.5 MeV; this permits flexibility in the solenoid design. We present beam dynamics simulations that show 6D phase space compensation at 7 pC: sub-0.1 mm mrad at the emittance minimum that occurs simultaneously with a longitudinal focus of <20 fs rms. We discuss applications ranging from multi-THz coherent radiation production to ultra-fast electron diffraction.