Numerical Calculation of Coherent Synchrotron Radiation Effects Using TraFiC4

Coherent synchrotron radiation (CSR) occurs when short bunches travel on strongly bent trajectories. Its effects on high-quality beams can be severe and are well understood qualitatively. For quantitative results, however, one has to rely on numerical methods. There exist several simulation codes utilizing different approaches. We describe in some detail the code TraFiC4 developed at DESY for design and analysis purposes, which approaches the problem from first principles and solves the equations of motion either perturbatively or self-consistently. We present some calculational results and comparison with experimental data. Also, we give examples of how the code can be used to design beamlines with minimal emittance growth due to CSR

Periodic Poisson Solver for Particle Tracking

A method is described to solve the Poisson problem for a three dimensional source distribution that is periodic into one direction. Perpendicular to the direction of periodicity a free space (or open) boundary is realized. In beam physics, this approach allows to calculate the space charge field of a continualized charged particle distribution with periodic pattern. The method is based on a particle mesh approach with equidistant grid and fast convolution with a Green's function. The periodic approach uses only one period of the source distribution, but a periodic extension of the Green's function. The approach is numerically efficient and allows the investigation of periodic- and pseudo-periodic structures with period lengths that are small compared to the source dimensions, for instance of laser modulated beams or of the evolution of micro bunch structures. Applications for laser modulated beams are given.Comment: 33 pages, 22 figure

Transverse self-fields within an electron bunch moving in an arc of a circle

As a consequence of motions driven by external forces, self-fields (which are different from the static case) originate within an electron bunch. In the case of magnetic external forces acting on an ultrarelativistic beam, the longitudinal self-interactions are responsible for CSR (Coherent Synchrotron Radiation)-related phenomena, which have been studied extensively. On the other hand, transverse self-interactions are present too. At the time being, existing theoretical analysis of transverse self-forces deal with the case of a bunch moving along a circular orbit only, without considering the situation of a bending magnet with a finite length. In this paper we propose an electrodynamical analysis of transverse self-fields which originate, at the position of a test particle, from an ultrarelativistic electron bunch moving in an arc of a circle. The problem will be first addressed within a two-particle system. We then extend our consideration to a line bunch with a stepped density distribution, a situation which can be easily generalized to the case of an arbitrary density distribution. Our approach turns out to be also useful in order to get a better insight in the physics involved in the case of simple circular motion and in order to address the well known issue of the partial compensation of transverse self-force.Comment: 23 pages, 14 figure

Impact of Optics on CSR-Related Emittance Growth in Bunch Compressor Chicanes

Abstract The dependence of emittance growth due to Coherent Synchrotron Radiation (CSR) in bunch compressor chicanes on optics has been noticed and empirically studied in the past. We revisit the subject, suggesting a model to explain slice emittance growth dependence on chicane optics. A simplified model to calculate projected emittance growth when it is mainly caused by transverse slice centroid offsets is presented. It is then used to find optimal compensation of centroid kicks in the single chicanes of a two-stage compression system by adjusting the phase advance of the transport in between and the ration of the compression factors

Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers

Some features of accelerating section field computation presented by the development of power and HOM couplers for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the beam area, thus causing transverse kick. For this kick and its influence on beam under acceleration parameters estimation the dynamics modelling calculations were done. 3D-simulation code MAFIA was used for field computation. These data were further used in beam dynamics calculations by means of TRMTrace code. Standing wave mode was simulated while considering HOM couplers, and travelling wave in case of power couplers. Transverse kicks and focussing forces are calculated for one HOM coupler design and two coaxial FM couplers

Algorithm for calculating spectral intensity due to charged particles in arbitrary motion

An algorithm for calculating the spectral intensity of radiation due to the coherent addition of many particles with arbitrary trajectories is described. Direct numerical integration of the Lienard-Wiechert potentials, in the far-field, for extremely high photon energies and many particles is made computationally feasible by a mixed analytic and numerical method. Exact integrals of spectral intensity are made between discretely sampled trajectories, by assuming the space-time four-vector is a quadratic function of proper time. The integral Fourier transform of the trajectory with respect to time, the modulus squared of which comprises the spectral intensity, can then be formed by piecewise summation of exact integrals between discrete points. Because of this, the calculation is not restricted by discrete sampling bandwidth theory, and hence for smooth trajectories, time-steps many orders larger than the inverse of the frequency of interest can be taken.Comment: 19 pages, 6 figures, submitted to J. Comp. Phys. Changes in new version: axis labels of figure 3 correcte

RF thermal and new cold part design studies on TTF-III input coupler for Project-X

RF power coupler is one of the key components in superconducting (SC) linac. It provides RF power to the SC cavity and interconnects different temperature layers (1.8K, 4.2K, 70K and 300K). TTF-III coupler is one of the most promising candidates for the High Energy (HE) linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR value of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along the warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using 60mm coaxial line; the corresponding multipacting simulation studies have also been investigated.Comment: 5 pages, 12 figures. Submitted to Chinese Physics C (Formerly High Energy Physics and Nuclear Physics

First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]

Isolated terawatt attosecond hard X-ray pulse generated from single current spike

Isolated terawatt (TW) attosecond (as) hard X-ray pulse is greatly desired for four-dimensional investigations of natural phenomena with picometer spatial and attosecond temporal resolutions. Since the demand for such sources is continuously increasing, the possibility of generating such pulse by a single current spike without the use of optical or electron delay units in an undulator line is addressed. The conditions of a current spike (width and height) and a modulation laser pulse (wavelength and power) is also discussed. We demonstrate that an isolated TW-level as a hard X-ray can be produced by a properly chosen single current spike in an electron bunch with simulation results. By using realistic specifications of an electron bunch of the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), we show that an isolated, >1.0 TW and similar to 36 as X-ray pulse at 12.4 keV can be generated in an optimized-tapered undulator line. This result opens a new vista for current XFEL operation: the attosecond XFEL