IPAC2011 - List of Authors (van Rienen, U.)

Paper	Title	Page
MOPC080	First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro	259
	B. Riemann, T. Weis DELTA, Dortmund, Germany W. Anders, J. Knobloch, A. Neumann HZB, Berlin, Germany H.-W. Glock, C. Potratz, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Marhauser JLAB, Newport News, Virginia, USA
	Funding: work supported by BMBF under contracts 05K10PEA and 05K10HRC The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate.

WEPC096	Calculation of High Frequency Fields in Resonant Cavities Based on Perturbation Theory*	2235
	K. Brackebusch, H.-W. Glock, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10HRC. The knowledge of the eigenmodes of resonant accelerator cavities is essential for the determination of their performance characteristics, comprising resonant frequencies and field distributions inside the cavities. Apart from the material properties the eigenmodes of a cavity depend on its geometry. In spite of the high elaborateness during the complex fabrication process, minor deviations of the actual cavity shape from the desired one are inevitable. Moreover, especially superconducting cavities are subject to extreme operating conditions that may cause deformations of their shape. Any geometry perturbation results in a shift of the resonant frequencies and modified field distributions. In this paper, we will analyze a generalization of Slater's theorem proposed in literature. The method should allow for the calculation of resonant frequencies and field distributions of a slightly perturbed cavity by using a set of precomputed eigenmodes of the unperturbed cavity. We will evaluate the practicability of the method by applying it to cavity geometries for which the eigenmodes are analytically known, ascertain the effort of reasonable calculation results and describe its limitations.

WEPC097	A Concatenation Scheme for the Computation of Beam Excited Higher Order Mode Port Signals	2238
	T. Flisgen, H.-W. Glock, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Ongoing studies investigate in how far higher order mode (HOM) port signals of superconducting RF cavities can be used for machine and beam diagnostics. Apart from experiments e.g. at the FLASH facility at DESY in Hamburg, numerical modelling is needed for the prediction of HOM coupler signals. For this purpose, the RF properties of the entire accelerating module have to be taken into account, since higher order modes can propagate along the cavity chain. A discretization of the full chain, followed by a wake field simulation is only feasible with powerful and expensive cluster computers. Instead, an element wise wake field simulation of sub-sections of the chain, followed by a suitable concatenation scheme can be performed on standard hardware assuming the beam to be sufficiently stiff. In this paper a concatenation scheme for the computation of beam excited HOM port signals is derived as a generalization of the Coupled S-Parameter scheme CSC. Furthermore, the validity of the method is shown for a sample structure.

WEPC098	Automatic Pole and Q-Value Extraction for RF Structures	2241
	C. Potratz, H.-W. Glock, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Marhauser JLAB, Newport News, Virginia, USA
	The experimental characterization of RF structures like accelerating cavities often demands for measuring resonant frequencies of Eigenmodes and corresponding (loaded) Q-values over a wide spectral range. A common procedure to determine the Q-values is the -3dB method, which works well for isolated poles, but may not be applicable directly in case of multiple poles residing in close proximity (e.g. for adjacent transverse modes differing by polarization). Although alternative methods may be used in such cases, this often comes at the expense of inherent systematic errors. We have developed an automation algorithm, which not only speeds up the measurement time significantly, but is also able to extract Eigenfrequencies and Q-values both for well isolated and overlapping poles. At the same time the measurement accuracy may be improved as a major benefit. To utilize this procedure merely complex scattering parameters have to be recorded for the spectral range of interest. In this paper we present the proposed algorithm applied to experimental data recorded for superconducting higher-order-mode damped multi-cell cavities as an application of high importance.

WEPC099	Coupler Design and Optimization by GPU-Accelerated DG-FEM	2244
	C. Potratz, H.-W. Glock, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	The numerical optimization of rf-components like couplers is a common task during the design phase of particle accelerators. Typically, these optimizations involve the simulation of a multitude of very similar structures with minor geometric variations. Nevertheless, this process is in its entire extend rather demanding on both the invested time and hardware budget. With recent advancements in the field of numerical electromagnetic field simulation and consumer graphic processors, an interesting alternative for the time-consuming simulation part of the optimization is available. In this contribution we show, how the Discontinuous Galerkin FEM method in conjunction with consumer graphic cards can be used to build moderately prized cluster solutions for the parallel simulation of rf-components. The contribution will mainly focus on, but is not limited to, Higher Order Mode couplers as a typical application example, where the DG-FEM method accelerated by a graphic processor might be used to significantly reduce the overall time necessary for the optimization.

WEPC100	Simulation of the Single Bunch Instability due to the Electron Cloud Effect by Tracking with a Pre-computed 2D Wake Matrix*	2247
	A. Markoviḱ, G. Pöplau, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Supported by DFG Contract Nr. RI 814/20-1. The passage of a positron bunch through an initially homogeneous electron cloud (e-cloud) changes the distribution of the e-cloud in a way that the concentration of electrons in the proximity of the beam axis grows rapidly. The electrons are primarily moving in the transverse plane and are very sensitive on the beam centroid position in that plane. Thus the transverse kick of the e-cloud on the tail particles depends on the centroid position of the head particles of the same bunch. A PIC simulation of the interaction of a positron beam with an e-cloud yields the wake kick from the electrons on the tail particles for a certain offset in the transverse centroid position of the head parts of the bunch. With such a pre-computed 2D wake matrix, for a certain e-cloud density, we investigate the stability of a single bunch by tracking it through the linear optics of the storage ring while at each turn applying the kick from the e-cloud. We examine the positron bunch stability of KEKB-LER and PETRAIII for a certain electron cloud density.

WEPC101	Simulation of the Interaction of an Electron Beam with Ionized Residual Gas	2250
	G. Pöplau, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany A. Meseck HZB, Berlin, Germany
	Funding: Supported by BMBF under contract number 05K10HRC Light sources of the next generation such as ERLs require minimal beam losses as well as a stable beam position and emittance over the time. Instabilities caused by ion accumulation have to be avoided. In Rostock the tracking code MOEVE PIC Tracking has been developed for the simulation of space charge influenced beam dynamics, which is recently applied for simulations of the interaction beam - e-cloud. In this paper we apply MOEVE PIC Tracking for simulation of the interaction of the ionized residual gas with an electron bunch. We demonstrate numerical results with parameters planed for the ERL BERLinPro.

WEPC102	Recent Developments for Efficient 3D Space Charge Computations Based on Adaptive Multigrid Discretizations	2253
	G. Pöplau, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany M.J. de Loos TUE, Eindhoven, The Netherlands S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	Funding: Partly supported by BMBF under contract number 05K10HRC Efficient and accurate space-charge computations are essential for the design of high-brightness charged particle sources. Recently a new adaptive meshing strategy based on multigrid was implemented in GPT and the capabilities were demonstrated. This new meshing scheme uses the solution of an intermediate step in the multigrid algorithm itself to define optimal mesh line positions. In this paper we discuss further developments of this adaptive meshing strategy. We compare the new algorithm with the current meshing scheme of GPT, where the mesh line positions are based upon the projected charge density.

Paper

Title

Page

First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro

259

B. Riemann, T. Weis
DELTA, Dortmund, Germany
W. Anders, J. Knobloch, A. Neumann
HZB, Berlin, Germany
H.-W. Glock, C. Potratz, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
F. Marhauser
JLAB, Newport News, Virginia, USA

Funding: work supported by BMBF under contracts 05K10PEA and 05K10HRC
The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate.

WEPC096

Calculation of High Frequency Fields in Resonant Cavities Based on Perturbation Theory*

2235

K. Brackebusch, H.-W. Glock, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10HRC.
The knowledge of the eigenmodes of resonant accelerator cavities is essential for the determination of their performance characteristics, comprising resonant frequencies and field distributions inside the cavities. Apart from the material properties the eigenmodes of a cavity depend on its geometry. In spite of the high elaborateness during the complex fabrication process, minor deviations of the actual cavity shape from the desired one are inevitable. Moreover, especially superconducting cavities are subject to extreme operating conditions that may cause deformations of their shape. Any geometry perturbation results in a shift of the resonant frequencies and modified field distributions. In this paper, we will analyze a generalization of Slater's theorem proposed in literature. The method should allow for the calculation of resonant frequencies and field distributions of a slightly perturbed cavity by using a set of precomputed eigenmodes of the unperturbed cavity. We will evaluate the practicability of the method by applying it to cavity geometries for which the eigenmodes are analytically known, ascertain the effort of reasonable calculation results and describe its limitations.

WEPC097

A Concatenation Scheme for the Computation of Beam Excited Higher Order Mode Port Signals

2238

T. Flisgen, H.-W. Glock, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Ongoing studies investigate in how far higher order mode (HOM) port signals of superconducting RF cavities can be used for machine and beam diagnostics. Apart from experiments e.g. at the FLASH facility at DESY in Hamburg, numerical modelling is needed for the prediction of HOM coupler signals. For this purpose, the RF properties of the entire accelerating module have to be taken into account, since higher order modes can propagate along the cavity chain. A discretization of the full chain, followed by a wake field simulation is only feasible with powerful and expensive cluster computers. Instead, an element wise wake field simulation of sub-sections of the chain, followed by a suitable concatenation scheme can be performed on standard hardware assuming the beam to be sufficiently stiff. In this paper a concatenation scheme for the computation of beam excited HOM port signals is derived as a generalization of the Coupled S-Parameter scheme CSC. Furthermore, the validity of the method is shown for a sample structure.

WEPC098

Automatic Pole and Q-Value Extraction for RF Structures

2241

C. Potratz, H.-W. Glock, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
F. Marhauser
JLAB, Newport News, Virginia, USA

The experimental characterization of RF structures like accelerating cavities often demands for measuring resonant frequencies of Eigenmodes and corresponding (loaded) Q-values over a wide spectral range. A common procedure to determine the Q-values is the -3dB method, which works well for isolated poles, but may not be applicable directly in case of multiple poles residing in close proximity (e.g. for adjacent transverse modes differing by polarization). Although alternative methods may be used in such cases, this often comes at the expense of inherent systematic errors. We have developed an automation algorithm, which not only speeds up the measurement time significantly, but is also able to extract Eigenfrequencies and Q-values both for well isolated and overlapping poles. At the same time the measurement accuracy may be improved as a major benefit. To utilize this procedure merely complex scattering parameters have to be recorded for the spectral range of interest. In this paper we present the proposed algorithm applied to experimental data recorded for superconducting higher-order-mode damped multi-cell cavities as an application of high importance.

WEPC099

Coupler Design and Optimization by GPU-Accelerated DG-FEM

2244

C. Potratz, H.-W. Glock, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

The numerical optimization of rf-components like couplers is a common task during the design phase of particle accelerators. Typically, these optimizations involve the simulation of a multitude of very similar structures with minor geometric variations. Nevertheless, this process is in its entire extend rather demanding on both the invested time and hardware budget. With recent advancements in the field of numerical electromagnetic field simulation and consumer graphic processors, an interesting alternative for the time-consuming simulation part of the optimization is available. In this contribution we show, how the Discontinuous Galerkin FEM method in conjunction with consumer graphic cards can be used to build moderately prized cluster solutions for the parallel simulation of rf-components. The contribution will mainly focus on, but is not limited to, Higher Order Mode couplers as a typical application example, where the DG-FEM method accelerated by a graphic processor might be used to significantly reduce the overall time necessary for the optimization.

WEPC100

Simulation of the Single Bunch Instability due to the Electron Cloud Effect by Tracking with a Pre-computed 2D Wake Matrix*

2247

A. Markoviḱ, G. Pöplau, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Supported by DFG Contract Nr. RI 814/20-1.
The passage of a positron bunch through an initially homogeneous electron cloud (e-cloud) changes the distribution of the e-cloud in a way that the concentration of electrons in the proximity of the beam axis grows rapidly. The electrons are primarily moving in the transverse plane and are very sensitive on the beam centroid position in that plane. Thus the transverse kick of the e-cloud on the tail particles depends on the centroid position of the head particles of the same bunch. A PIC simulation of the interaction of a positron beam with an e-cloud yields the wake kick from the electrons on the tail particles for a certain offset in the transverse centroid position of the head parts of the bunch. With such a pre-computed 2D wake matrix, for a certain e-cloud density, we investigate the stability of a single bunch by tracking it through the linear optics of the storage ring while at each turn applying the kick from the e-cloud. We examine the positron bunch stability of KEKB-LER and PETRAIII for a certain electron cloud density.

WEPC101

Simulation of the Interaction of an Electron Beam with Ionized Residual Gas

2250

G. Pöplau, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A. Meseck
HZB, Berlin, Germany

Funding: Supported by BMBF under contract number 05K10HRC
Light sources of the next generation such as ERLs require minimal beam losses as well as a stable beam position and emittance over the time. Instabilities caused by ion accumulation have to be avoided. In Rostock the tracking code MOEVE PIC Tracking has been developed for the simulation of space charge influenced beam dynamics, which is recently applied for simulations of the interaction beam - e-cloud. In this paper we apply MOEVE PIC Tracking for simulation of the interaction of the ionized residual gas with an electron bunch. We demonstrate numerical results with parameters planed for the ERL BERLinPro.

WEPC102

Recent Developments for Efficient 3D Space Charge Computations Based on Adaptive Multigrid Discretizations

2253

G. Pöplau, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
M.J. de Loos
TUE, Eindhoven, The Netherlands
S.B. van der Geer
Pulsar Physics, Eindhoven, The Netherlands

Funding: Partly supported by BMBF under contract number 05K10HRC
Efficient and accurate space-charge computations are essential for the design of high-brightness charged particle sources. Recently a new adaptive meshing strategy based on multigrid was implemented in GPT and the capabilities were demonstrated. This new meshing scheme uses the solution of an intermediate step in the multigrid algorithm itself to define optimal mesh line positions. In this paper we discuss further developments of this adaptive meshing strategy. We compare the new algorithm with the current meshing scheme of GPT, where the mesh line positions are based upon the projected charge density.