ESS, Lund, Sweden
ORNL, Oak Ridge, Tennessee, USA
Linac dynamics simulation capabilities of the PyORBIT code are discussed. The PyORBIT is an open source and a further development of the original ORBIT code that was developed and used for design, studies, and commissioning of the SNS ring. The PyORBIT code like the original one has a two layers structure. The C++ is used to perform time consuming computations, and a program flow is controlled from the Python language shell. The flexible structure allowed using the PyORBIT also for linac dynamics simulations. The benchmark of the PyORBIT with Parmila and the XAL Online model is presented.
TEMF, TU Darmstadt, Darmstadt, Germany
The design and optimization of particle accelerator components are fundamentally based on beam dynamics simulations. The knowledge of the interaction of moving charged particles with the surrounding materials and fields enables to optimize individual devices and consequently to take the best advantage of the entire machine. Among the essential accelerator components are radio-frequency cavities which are utilized for acceleration as well as for beam diagnostics. In these applications, precise beam dynamics simulations urgently require high-precision data of the electromagnetic fields. Numerical simulations based on Maxwell’s equations have to represent the resulting fields on an acceptable level of quality even with limited amount of degrees of freedom. On the other hand, the particle beam itself gives rise to the excitation of undesired modes which have to be extracted from the cavities. In the current work, some of the challenges faced in high precision cavity simulations are summarized. Based on high-performance eigenvalue calculations, important features like "low-noise" field evaluations or port-mode boundary approximations to enable traveling-wave transport are addressed.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
Geometry perturbations affect the eigenmodes of a resonant cavity and thereby can improve but also impair the performance characteristics of the cavity. To investigate the effects of both, intentional and inevitable geometry variations parameter studies are to be undertaken. Using common eigenmode solvers involves to perform a full eigenmode computation for each variation step, even if the geometry is only slightly altered. Therefore, such investigations tend to be computationally extensive and inefficient. Yet, the computational effort for parameter studies may be significantly reduced by using perturbative computation methods. Knowing a set of initial eigenmodes of the unperturbed geometry these allow for the expansion of the eigenmodes of the perturbed geometry in terms of the unperturbed modes. In this paper, we study the complexity of a numerical implementation of perturbative methods. An essential aspect is the computation and analysis of the unperturbed modes since the number and order of these modes determine the accuracy of the results.
SLAC, Menlo Park, California, USA
Track3P is the particle tracking module of ACE3P, a 3D parallel finite element electromagnetic code suite developed at SLAC which has been implemented on the US DOE supercomputers at NERSC to simulate large-scale complex accelerator designs. Using the higher-order cavity fields generated by ACE3P codes, Track3P has been used for analyzing multipacting (MP) in accelerator cavities. The prediction of the MP barriers in the ICHIRO cavity at KEK was the first Track3P benchmark against measurements. Using a large number of processors, Track3P can scan through the field gradient and cavity surface efficiently, and its comprehensive postprocessing tool allows the identifications of both the hard and soft MP barriers and the locations of MP activities. Results from applications of this high performance simulation capability to accelerators such as the Quarter Wave Resonator for FRIB, the 704 MHz SRF gun cavity for BNL ERL and the Muon cooling cavity for Muon Collider will be presented.
TUD, Darmstadt, Germany
TEMF, TU Darmstadt, Darmstadt, Germany
GSI, Darmstadt, Germany
In a synchrotron, particles are accelerated by repeatedly passing through RF cavities. In the SIS18 synchrotron at GSI, ferrite cavities are used. Each cavity is equipped with local control systems to adjust the amplitude and phase of the accelerating field. In this paper, we consider ferrite cavities of the type that is currently used in the SIS18 at GSI and will be used in the future SIS100 which is being built in the frame of the FAIR project. We analyze the dynamics of the cavities in conjunction with their local control loops. An emphasis is put on the cavities' reaction to changes in the desired amplitude or resonant frequency. Using simulations, we show that the cavities' dynamics hardly influence longitudinal dipole oscillations, and conclude that a high-level model for the RF cavities is sufficient.
TU Darmstadt, Darmstadt, Germany
In order to test RF control systems for accelerator cavities without being dependent on available prototypes, a resonator-simulator has been developed. The Simulator is based on a Xilinx-VIRTEX-4 FPGA-module and has been configured using MATLAB-Simulink with a special Xilinx-Blockset. The underlying model for this configuration is a parallel RLC-circuit that has been parameterised with common RF-quantities like the resonance frequency, driving frequency, bandwidth and quality factor. This approach allows to simulate the behaviour of normal conducting cavities with quality factors up to 104 as well as superconducting cavities with quality factors up to 109. Besides, it can as well be operated in a continuous-wave as in a pulsed mode. We report on the mathematical model, its digital representation and on the benchmarking against real cavity behaviour.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
HZB, Berlin, Germany
DELTA, Dortmund, Germany
The main scope of this work is the automation of the extraction procedure of the external quality factors Qext of Higher Order Modes (HOMs) in Superconducting (SC) radio frequency cavities [*]. The HOMs are generated by charged particle beams traveling at the speed of light through SC cavity. The HOMs decay very slowly, depending on localization inside the structure and cell-to-cell coupling, and may influence succeeding charged particle bunches. Thus it is important, at the SC cavity design optimization stage, to calculate the Qext of HOMs. The Traveling Poles Elimination (TPE) scheme has been used on scattering parameters spectra to obtain external quality factors. The combination of Coupled S-Parameter Calculations (CSC) method and vector fitting procedure allows us to study very complicated structures in much better details and almost automated extraction of HOMs' Qext factors. The results are also reasserted by careful eigenmode analysis of the SC cavity. The S-Parameter and eigenmode simulations were performed using CST Microwave Studio.
*Axel Neumann et al., "Status of the HOM Calculations for the BERLinPro Main Linac Cavity", FRAAC3 (this conference)
KU Leuven, Kortrijk, Belgium
The dependence of the eigenfrequencies of a superconductive cavity on its geometry are represented by a stochastic response surface model. The model is constructed on the basis of both information on the eigenfrequencies as on their sensitivities with respect to the geometry. The eigenmodes are calculated using the 2D or 3D finite element method or finite integration technique. The stochastic representation does not only model uncertainties on the geometrical parameters but also inaccuracies of the eigenmode solvers, e.g. due to remeshing. Variations or optimisations of the geometry are carried out on the surrogate model. The model allows an efficient evaluation of microphoning and Lorentz detuning of accelerator cavities.
PSI, Villigen, Switzerland
ETH, Zurich, Switzerland
The new X-ray Free Electron Laser (SwissFEL) at the Paul Scherrer Institute (PSI) employs, among many other radio frequency elements, a transverse deflecting cavity for beam diagnostics. Since the fabrication process is expensive, an accurate 3-D eigenmodal analysis is indispensable. The software package Femaxx has been developed for solving large scale eigenvalue problems on distributed memory parallel computers. Usually, it is sufficient to assume that the tangential electric field vanishes on the cavity wall. To better approximate reality, we consider the cavity wall conductivity is large but finite, and thus the tangential electrical field on the wall is nonzero. We use the surface impedance boundary conditions (SIBC) arising from the skin-effect model. The resulting nonlinear eigenvalue problem is solved with a nonlinear Jacobi–Davidson method. We demonstrate the performance of the method. First, we investigate the fundamental mode of a pillbox cavity. We study resonance, skin depth and quality factor as a function of the cavity wall conductivity. Second, we analyze the transverse deflecting cavity to assess the capability of the method for technologically relevant problems.
DELTA, Dortmund, Germany
HZB, Berlin, Germany
Elliptical cavities have been a standard in SRF linac technology for 30 years. In this work, we present a novel approach [1] using Bezier spline profile curves. By using different degrees of spline curves, the number of free parameters can be varied to suit a given problem (endcell tuning, basecell figures of merit), thus leading to a high flexibility of the spline approach. As a realistic example, a cubic spline SRF multicell cavity geometry is calculated and the figures of merit are optimized for the operational mode. We also present an outline for HOM endcell optimization that can be realized using available 2D solvers.
[1] B. Riemann et al., "SRF multicell cavity design using cubic and higher order spline cavity profiles", T 80.9, Verhandlungen DPG Göttingen 2012
CIAE, Beijing, People's Republic of China
PSI, Villigen, Switzerland
TEMF, TU Darmstadt, Darmstadt, Germany
For acceleration of charged particles at the heavy-ion synchrotron at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt two ferrite-loaded cavity resonators are installed within the ring. Their eigenfrequency can be tuned by properly choosing a bias current and thereby modifying the differential permeability of the ferrite material. The goal of the presented work is to numerically determine the lowest eigensolutions of accelerating ferrite-loaded cavities based on the Finite Integration Technique. The newly developed solver includes two subcomponents: Firstly, a magnetostatic solver supporting nonlinear material for the computation of the magnetic field which is excited by the specified bias current. This enables to linearize the constitutive equation for the ferrite material at the current working point, at which also the differential permeability tensor is evaluated. Secondly, a Jacobi-Davidson type eigensolver for the subsequent solution of the nonlinear eigenvalue problem. Particular emphasis is put on the implementation to enable efficient distributed parallel computing. First numerical results for biased ferrite-filled cavity resonators are presented.
HZB, Berlin, Germany
[1] M. Venturini, et al., Phys. Rev. ST-SB, 8, 014202(2005)
[2] K.L.F. Bane, et al., “Comparison of Simulation Codes for Microwave Instability in Bunched Beams“, IPAC 2010, Kyoto, Japan
Fermilab, Batavia, USA
The computational approaches assure essential guidance and order for the design of a superconducting cavities and cryomodules. The nature of superconductivity requires precise surface electromagnetic fields computation in order to design the cavity shape with a maximum accelerating gradient. At the same time the thickness of the cavity shell is limited by the ability to cool it down the temperature of liquid He, which makes the mechanical stability of the cavity and liquid He vessel assembly extremely important. Hence, it demands a self consistent electro-mechanical optimization in order to minimize microphonics and/or Lorentz force detuning phenomena. Specific challenges are an estimation of RF losses caused by the interaction of the passing beam with SC cavity and a multipactor analysis in the SC cavity and RF coupler. Finally the irregular time structure of a beam train with its own dense spectra may stochastically induce HOM fields in a cavity which results the beam emittance dilution. The study of these effects leads to specifications of SC cavity and cryomodule and can significantly impact on the efficiency and reliability of the superconducting linac operation.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
For the design and optimization of Higher-Order-Mode Coupler, used in RF accelerator structures, numerical computations of electromagnetic fields as well as scattering parameter are essential. These computations can be carried out in time domain. In this work the implementation and investigation of a time integration scheme, using the Arbitrary high-order DERivatives (ADER) approach, applied on the Discontinuous Galerkin finite-element method (DG-FEM) is demonstrated for solving 3-D electromagnetic problems in time domain. This scheme combines the advantage of high accuracy with the possibility of an efficient implementation as local time stepping scheme, which reduces the calculation time for special applications considerable. It is implemented in NUDG++*, a framework written in C++ that deals with the DG-FEM for spatial discretization of the Maxwell equations. Accuracy and performance is analyzed by a suitable benchmark.
* Nodal Unstructured Discontinuous Galerkin in C++
HZB, Berlin, Germany
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
DELTA, Dortmund, Germany
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 (ERLs). Strongly higher order mode (HOM) damped multicell 1.3 GHz cavities are required for the main linac. The cavity under study is an integrated design of the Cornell base cell with JLab HOM waveguide couplers. Modifications to the end group design have also been pursued, including the substitution of one waveguide by a HZB-modified TTF-III power coupler. In this talk the progress in HOM calculations to avoid beam-breakup instabilities for the favored cavity structure will be presented.
HZB, Berlin, Germany
ANL, Argonne, USA
RPI, Troy, New York, USA
We examined hybrid parallel infrastructures in order to ensure performance and scalability for beam propagation modeling as we move toward extreme-scale systems. Using an MPI programming interface for parallel algorithms, we expanded the capability of our existing electromagnetic solver to a hybrid (MPI/shared-memory) model that can potentially use the computer resources on future-generation computing architecture more efficiently. As a preliminary step, we discuss a hybrid MPI/OpenMP model and demonstrate performance and analysis on the leadership-class computing systems such as the IBM BG/P, BG/Q, and Cray XK6. Our hybrid MPI/OpenMP model achieves speedup when the computation amounts are large enough to compensate the OMP threading overhead.
TEMF, TU Darmstadt, Darmstadt, Germany
Efficient and accurate computation of eigenvalues and eigenvectors is of fundamental importance in the accelerator physics community. Moreover, the eigensystem analysis is generally used for the identifications of many physical phenomena connected to vibrations. Therefore, various types of algorithms such that Arnoldi, Lanczos, Krylov-Schur, Jacobi-Davidson etc. were implemented to solve the eigenvalue problem efficiently. In this direction, we investigate the performance of selected commercial and freely available software tools for the solution of a generalized eigenvalue problem. We choose two setups by considering spherical and billiard resonators in order to test the robustness, accuracy, and computational speed and memory consumption issues of the recent versions of CST, Matlab, Pysparse, SLEPc and CEM3D. Simulations were performed on a standard personal computer as well as on a cluster computer to enable the handling of large sparse matrices in the order of hundreds of thousands up to several millions degrees of freedom. We obtain interesting comparison results with the examined solvers which is useful for choosing the appropriate solvers for a given practical application.