Wolfgang Franz Otto Müller

Time Domain Boundary Element Analysis of Wake Fields in Long Accelerator Structures

We present an explicit time domain boundary element method (TDBEM) scheme with moving window technique for short-range wake field simulations of long accelerator structures. The proposed scheme is formulated by Kirchhoffs boundary integral equation of the scattered electromagnetic field in interior region problems. Implementation of a moving window technique in the framework of TDBEM is achieved by taking into account the causality and the retardation properties of the boundary integral equation. A parallelization algorithm for this moving window implementation is also proposed. The proposed TDBEM code with the moving window technique is applied to several practical examples of long accelerator structures. Numerical results obtained with the TDBEM code are compared with those of several finite integration codes.

Wien filter as a spin rotator at low energy

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 is based on homogenous magnetic and electric fields which 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 Environmenttradeand V-Code are presented.

Status and recent developments at the polarized-electron injector of the superconducting Darmstadt electron linear accelerator S-DALINAC

At the superconducting Darmstadt electron linac a 100 keV source of polarized electrons has been installed. Major components had been tested prior to installation at an offline teststand. Commissioning of the new source at the S-DALINAC will take place early in 2011. We report on the performance of the teststand, simulations, developments on the laser systems, new radio-frequency components for the S-DALINAC injector, and the status of the implementation of the source.

Combined Simulation of a Micro Permanent Magnetic Linear Contactless Displacement Sensor

The permanent magnetic linear contactless displacement (PLCD) sensor is a new type of displacement sensor operating on the magnetic inductive principle. It has many excellent properties and has already been used for many applications. In this article a Micro-PLCD sensor which can be used for microelectromechanical system (MEMS) measurements is designed and simulated with the CST EM STUDIO® software, including building a virtual model, magnetostatic calculations, low frequency calculations, steady current calculations and thermal calculations. The influence of some important parameters such as air gap dimension, working frequency, coil current and eddy currents etc. is studied in depth.

Simulation for a New Polarized Electron Injector (Spin) for the S-DALINAC

The Superconducting DArmstädter LINear ACcelerator (S-DALINAC) is a 130 MeV recirculating electron accelerator serving several nuclear and radiation physics experiments. For future tasks, the 250 keV thermal electron source should be completed by a 100 keV polarized electron source. Therefore a new low energy injection con cept for the S-DALINAC has to be designed. The main components of the injector are a polarized electron source, an alpha magnet, a Wien filter spin-rotator and a Mott polarimeter. In this paper we report about the first simulation and design results. For our simulations we used the TS2 and TS3 modules of the MAFIA programme which are PIC codes for two and three dimensions and the CST PARTICLE STUDIO™.

Explicit time domain boundary element scheme for dispersion-free wake field calculation of long accelerator structures

This paper introduces a new explicit scheme with a moving window option for wake field calculation of long accelerator structures. This scheme is based on a time domain boundary element method (TDBEM) which uses a retarded Kirchhoff boundary integral equation for interior region problems. As a corollary of this boundary integral equation, our approach allows a conformal modeling of a structure and time domain wake field simulation without numerical grid dispersion errors in all spatial directions. The implementation of a moving window technique in the framework of TDBEM is presented and it is shown that this moving window technique allows to significantly reduce memory requirement of the TDBEM scheme in the short range wake field calculation. Several numerical examples are demonstrated for the TESLA 9-cell cavity and tapered collimators. The results of the new TDBEM scheme are compared with those of finite difference codes.

A dispersionless algorithm for calculating wake potentials in 3D

Accurate computations of wake potentials are an important task in modern accelerator design. Short bunches used in high energy particle accelerators excite very high- frequency fields. The geometrical size of accelerating structures exceeds the wavelength of the excited fields by many orders of magnitude. The application of codes such as TBCI, MAFIA[1] or tamBCI are limited due to numerical dispersion effects and memory needs. Recently new codes like PBCI have been developed to overcome these problems. In this work the utilization of dispersionless directions in the leap-frog update scheme on a Cartesian grid are proposed for accurate simulations. In conjunction with a conformal modeling technique which allows for the full Courant time step a moving window technique can be applied. This was previously implemented in a 2D code [2]. In this publication an extension to arbitrary three dimensional problems is presented.

Calculating trapped modes in TESLA cavities with time and frequency domain methods

We report the development of different algorithms for the calculation of quality factors of trapped eigenmodes in accelerating cavities, which have resonance frequencies above the cutoff frequency of the beam tubes. The analysis is based on a discretization of such cavity structures by the Finite Integration Technique (FIT), and the radiation at the open boundaries is systematically taken into account by different approaches in time and frequency domain. Comparison with the conventional method of analyzing closed cavities and identifying modes with little change in frequency as function of boundary condition show qualitative differences. Some modes from the closed cavity model do not exist in the open structure and thus would be misinterpreted as trapped modes when only a closed cavity analysis is employed. Results indicate that even single cell cavities of the TESLA type show Q-values above 10/sup 3/. And for the TESLA. 9-cell cavity trapped modes with Q-values in excess of 10/sup 6/ are found, which correspond to recent measurement results from the TESLA Test Facility at DESY.

Simulations of a quadrupolar pick-up at GSI SIS-18

This report presents the simulation results for an asymmetrical capacitive pick-up installed at GSI SIS-18. In the past, it was used as BPM (Beam Position Monitor) and is planned to be used for measuring the transverse beam size oscillations at SIS-18. The main goal of this project consists in estimating the properties of the pick-up and evaluating its usage as a quadrupole signal monitor. Due to the fact that the bunch for the SIS-18 operation is long compared to the pick-up electrode, first simulations have been performed with the electrostatic solver of the simulation software CST EM Studio to estimate the pick-up properties [1]. Now, to study the pick-up behavior in the frequency range of insterest for GSI, some simulations have been performed using the PIC solver of CST PS (Particle Studio) [2] and the results are presented in this report.

Planung von Braunkohlentagebauen

Bergbauprojekte setzen wirtschaftlich gewinnbare Vorrate voraus und sind standortgebunden. Ihre Planung muss auser den Gegebenheiten der Lagerstatte auch alle weiteren Einflussfaktoren einbeziehen. Durch die bei Tagebauen auf flozartigen Lagerstatten sukzessiv fortschreitende Inanspruchnahme groser Flachen verstarkt sich die Anforderung an Umweltvertraglichkeit. In Folge der uberwiegend engen Koppelung der Braunkohlennutzung an die Stromerzeugung ubertragt sich die Standortbindung auch auf die Verwertungsanlagen, i.e. im Wesentlichen die braunkohlebefeuerten Kraftwerke.