TEMF, TU Darmstadt, Darmstadt
DESY, Hamburg
The rf and wakefield transverse kicks resulting from the asymmetry of input and HOM couplers in the third harmonic module for the XFEL are investigated. The fundamental mode is computed using eigenvalue analysis. The short range wakefields in a string of cavities are simulated with the PBCI code. Using the simulation data, the transverse kick factors associated with the presence of cavity couplers are evaluated.
* P. Pierini, "Third Harmonic Superconducting Cavity Prototypes for the XFEL", LINAC08.
** T. Khabiboulline, "New HOM Coupler Design For 3.9 Ghz Superconducting Cavities At FNAL", PAC07.
TEMF, TU Darmstadt, Darmstadt
GSI, Darmstadt
Funding: This work is supported by the GSI.
Beam coupling impedances have been identified as an appropriate quantity to describe collective instabilities caused through beam-induced fields in heavy ion synchrotron accelerators such as the SIS-18 at the planned SIS-100 at the GSI facility. The impedance contributions caused by the multiple types of beamline components need to be determined to serve as input condition for later stability studies. This paper will present an approach exploiting the abilities of commercial FDTD wake codes such as CST PARTICLE STUDIO® for a benchmark problem with cylindrical geometry. Since exact analytical formulae are available, the obtained numerical results will be compared. Special attention is paid towards the representation of the particle beam as the source of the EM fields and conductive losses.
TEMF, TU Darmstadt, Darmstadt
TU Darmstadt, Darmstadt
Funding: This work was supported by DFG through SFB 634.
Based on the moment approach a fast tracking code named V-Code has been implemented at TEMF. Instead of using the particle distribution itself this method applies a discrete set of moments of the particle distribution. The time evolution of each moment can be deduced from the Vlasov equation when all essential external forces are known. These forces are given by the Lorentz equation in combination with the distribution of electric and magnetic fields. For efficiency reasons the 3D fields in the vicinity of the bunch trajectory are reconstructed in V-Code from one-dimensional field components by means of proper multipole expansions for the individual beam line elements. The entire beam line is represented in the code as a successive alignment of separate independent beam line elements. The proximity of some beam forming elements may lead to overlapping fringe fields between consecutive elements. In order to simulate even such beam lines with the V-Code, its database of disjunctive beam line elements has to be enhanced to deal also with superposed fields. In this paper a summary of issues regarding the implementation complemented with simulation results will be provided.
TEMF, TU Darmstadt, Darmstadt
We report on a new numerical technique for the computation of geometrical wakes in three-dimensional LINAC structures. The method utilises an explicit Finite-Volume Time-Domain (FVTD) formulation. The numerical dispersion in all three axial directions is completely eliminated by choice of an appropriate staggering of the field components on the grid. Thus, contrary to most of the previously reported techniques no splitting of the time-evolution operator is necessary. This results in large savings in computational time as well as in an improved numerical accuracy. We have implemented this new technique in PBCI code and present some preliminary results.