SRF2013 - List of Authors (van Rienen, U.)

Paper	Title	Page
MOP092	Computation of Wakefields and HOM Port Signals by Means of Reduced Order Models	364
	J. Heller, T. Flisgen, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	The investigation of wakefields is an important task in the design and operation of particle accelerators. Computer simulations are a reliable tool to extend the understanding of these effects. This contribution presents an application example of a new method to compute wakefields as well as parameters derived from those fields, such as higher order mode (HOM) port signals. The method is based on a reduced order model of the structure created by as set of 3D eigenmodes, a set of 2D waveguide port modes and the current density of the beam. In contrast to other wakefield computations, the proposed method operates directly on the reduced order model. Therefore, once having established this model, the beam-excited fields can be determined quickly for different beam parameters. As a matter of fact, only a small part of the reduced system has to be recomputed for every sweep point. From these advantages it is obvious, that the method is highly compatible for beam parameter studies. In a proof of principal the effectiveness of the method compared to established methods of wakefield computations in terms of computational time and accuracy is shown.

THP040	3D MULTIPACTING STUDY FOR THE ROSSENDORF SRF GUN	991
	E.T. Tulu, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany A. Arnold HZDR, Dresden, Germany
	Funding: *This work is supported by Federal Ministry for Research and Education BMBF Electron multipacting is still observed in the Rossendorf SRF gun which limits the cavity fields (accelerating gradient). To better understand this process, a three-cell 1.3 GHz elliptical-shape cavity with cathode was modeled in CST Studio Suite® 2013 at the University of Rostock. All parameters are provided by Helmholtz-Zentrum Dresden-Rossendorf. The multipacting simulations have been performed with CST Microwave Studio® (CST MWS) [1] and CST Particle Studio® (CST PS) which is suitable and powerful for 3D electromagnetic designs and provides the most advanced model of secondary emission. The radio frequency fields are calculated using the frequency domain solver of CST MWS, whereas the CST PS is used for particle tracking simulation [2]. The purpose of these numerical simulations is to better comprehend multipacting in the Rossendorf SRF gun and make a detailed analysis. The midterm goal is to find a new cavity shape, which might suppress the electron amplification so that the SRF Gun will be able to operate up to an accelerating gradient of 50 MV/m. #eden.tulu@uni-rostock.de [1] CST AG, Bad Nauheimer Str. 19, D-64289 Darmstadt, Germany [2] F. Hamme, U. Becker and P. Hammes, Proc. of ICAP 2006, Chamonix, France

THP064	HOM Couplers for CERN SPL Cavities	1066
	K. Papke, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Gerigk CERN, Geneva, Switzerland
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.

Paper

Title

Page

Computation of Wakefields and HOM Port Signals by Means of Reduced Order Models

364

J. Heller, T. Flisgen, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

The investigation of wakefields is an important task in the design and operation of particle accelerators. Computer simulations are a reliable tool to extend the understanding of these effects. This contribution presents an application example of a new method to compute wakefields as well as parameters derived from those fields, such as higher order mode (HOM) port signals. The method is based on a reduced order model of the structure created by as set of 3D eigenmodes, a set of 2D waveguide port modes and the current density of the beam. In contrast to other wakefield computations, the proposed method operates directly on the reduced order model. Therefore, once having established this model, the beam-excited fields can be determined quickly for different beam parameters. As a matter of fact, only a small part of the reduced system has to be recomputed for every sweep point. From these advantages it is obvious, that the method is highly compatible for beam parameter studies. In a proof of principal the effectiveness of the method compared to established methods of wakefield computations in terms of computational time and accuracy is shown.

THP040

3D MULTIPACTING STUDY FOR THE ROSSENDORF SRF GUN

991

E.T. Tulu, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A. Arnold
HZDR, Dresden, Germany

Funding: *This work is supported by Federal Ministry for Research and Education BMBF
Electron multipacting is still observed in the Rossendorf SRF gun which limits the cavity fields (accelerating gradient). To better understand this process, a three-cell 1.3 GHz elliptical-shape cavity with cathode was modeled in CST Studio Suite® 2013 at the University of Rostock. All parameters are provided by Helmholtz-Zentrum Dresden-Rossendorf. The multipacting simulations have been performed with CST Microwave Studio® (CST MWS) [1] and CST Particle Studio® (CST PS) which is suitable and powerful for 3D electromagnetic designs and provides the most advanced model of secondary emission. The radio frequency fields are calculated using the frequency domain solver of CST MWS, whereas the CST PS is used for particle tracking simulation [2]. The purpose of these numerical simulations is to better comprehend multipacting in the Rossendorf SRF gun and make a detailed analysis. The midterm goal is to find a new cavity shape, which might suppress the electron amplification so that the SRF Gun will be able to operate up to an accelerating gradient of 50 MV/m.
#eden.tulu@uni-rostock.de
[1] CST AG, Bad Nauheimer Str. 19, D-64289 Darmstadt, Germany
[2] F. Hamme, U. Becker and P. Hammes, Proc. of ICAP 2006, Chamonix, France

THP064

HOM Couplers for CERN SPL Cavities

1066

K. Papke, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
F. Gerigk
CERN, Geneva, Switzerland

Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.