• B. Steiner, W. Ackermann, W. F.O. Muller, T. Weiland
  TEMF, Darmstadt

The Wien filter is well known as a common energy analyzer and is also used more and more as a compact variant of a spin rotator at low energy for electrons. The Wien filter based on a homogenous magnetic and electric field that are perpendicular to each other and transverse to the direction of the electrons. The rotation of the spin vector is caused by the magnetic field. If the force equilibrium condition is fulfilled the beam should not be deflected at the Wien filter. Simulations show that in the fringe fields the electrons get a kick. Therefore full 3D simulations of the electromagnetic fields and beam dynamics simulations are studied in detail at the example of the Wien filter at the new polarized 100 keV electron injector at the S-DALINAC. The results of the simulations with CST Design Environment(TM), MAFIA and V-Code are presented.

• W. Ackermann, W. F.O. Muller, B. Steiner, T. Weiland
  TEMF, Darmstadt
• J. Enders, C. Heßler, Y. Poltoratska
  TU Darmstadt, Darmstadt

Beam dynamics simulations for computationally large problems are challenging tasks. On the one hand, to accurately simulate the electromagnetic field distribution within the whole device and the surrounding environment it is essential to consider all necessary device components including even small geometry details, complicated material distributions and the field excitations. On the other hand, further computational effort has to be put into precise modeling of the injected particle beam for detailed beam dynamics simulations. Under linear conditions, it is possible to separate the field calculation of the device from the computation of the particles self-field which can result in the proper application of diverse numerical schemes for the individual field contributions. In the paper it is demonstrated how the static electric and magnetic fields of a Wien filter beam line element can be treated as applied external fields within the beam dynamics simulation tool V-Code under the assumption that the interaction of the particle beam with the surrounding materials can be neglected.

• A. Paech, W. Ackermann, T. Weiland
  TEMF, Darmstadt
• O. Grimm
  DESY, Hamburg

One method to measure the bunch shape at the FLASH facility at DESY, Hamburg is based on the observation of synchrotron radiation generated at the first bunch compressor. For the correct interpretation of the results it is mandatory to know how various parameters of the real setup, in contrast to theoretical assumptions, influence the observed spectrum. The aim of this work therefore is to calculate the generation of synchrotron radiation of a moving point charge inside the bunch compressor with the emphasis of including the effects of the vertical and horizontal vacuum chamber walls in the vicinity of the last dipole magnet. Because of the small wavelength in comparison with the chamber geometries this is a demanding task. One idea to cope with the difficulties is to use optical methods such as the uniform theory of diffraction (UTD). In this paper the applicability and limitations of the proposed method are discussed. Furthermore a comparison of simulated and new measured fields is shown.

• E. Arevalo, W. Ackermann, R. Hampel, W. F.O. Muller, T. Weiland
  TEMF, Darmstadt

The computation of wake fields excited by ultra short electron bunches in accelerator components with geometrical discontinuities is a challenging problem, as an accurate resolution for both the small bunch and the large model geometry are needed. Several computational codes (PBCI, ROCOCO, CST PARTICLE STUDIO etc.) have been developed to deal with this type of problems. Wake field simulations of the RF electron gun of the Photoinjector Test Facility at DESY Zeuthen (PITZ) are performed whith different specialized codes. Here we present a comparison of the wake potentials calculated numerically obtained from the different codes. Several structures of the photoinjector are considered.