Old Dominion University, Norfolk, Virginia
Muons, Inc, Batavia
Fermilab, Batavia
Funding: Supported in part by USDOE STTR Grant DE-FG02-08ER86350 Supported in part by USDOE STTR Grant DE-FG02-08ER86352 and in part by FRA DOE contract number DE-AC02-07CH11359
In earlier reports, microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 805 MHz RF cavity experiments were used to investigate the mechanism of RF breakdown of tungsten, molybdenum, and beryllium electrode surfaces. Plots of remnants were consistent with the breakdown events being due to field emission, due to the quantum mechanical tunnelling of electrons through a barrier as described by Fowler and Nordheim. In the work described here, these studies have been extended to include tin, aluminium, and copper. Contamination of the surfaces, discovered after the experiments concluded, have cast some doubt on the proper qualities to assign to the metallic surfaces. However, two significant results are noted. First, the maximum stable RF gradient of contaminated copper electrodes is higher than for a clean surface. Second, the addition of as little as 0.01% of SF6 to the hydrogen gas increased the maximum stable gradient, which implies that models of RF breakdown in hydrogen gas will be important to the study of metallic breakdown
ANL, Argonne
We developed a moving window algorithm for the SEDG time-domain code, NekCEM, for wake field calculations. NekCEM is a highly efficient and spectrally accurate electromagnetic solver using the spectral element discontinuous Galerkin (SEDG) method based on body-fitted spectral element hexahedral meshes. When the domain of interest is around a moving bunch within a certain distance, one does not need to carry out full domain simulations. Moving window approach has been a natural consideration in such circumstance to have significant reduction in computational cost for the conventional low-order methods such as FDTD method. However, there have not been studies on the high-order methods, especially the SEDG method, based on the moving window approach. We implemented 3D moving window option for wake field calculations on various conducting cavities including the 9-cell TESLA cavity. We will demonstrate the performance of the SEDG simulations on moving window meshes.
Uni HH, Hamburg
DESY, Hamburg
Based on TE/TM splitting algorithm a new (longitudinally) dispersion-free numerical scheme is developed to evaluate the wake fields in structures with finite wall conductivity. The impedance boundary condition in this scheme is modeled by the one dimensional wire connected to boundary cells. A good agreement of the numerical simulations with the analytical results is obtained. The developed code allows to calculate multipole wake potentials of arbitrary shaped geometries with walls of finite high conductivity.
ANL, Argonne
Transition radiation is frequently used to determine the time profile of a bunched relativistic particle beam. Emphasis is usually given to diagnostics sensitive to wavelengths in the infrared-to-optical portion of the spectrum. In this study, CST Particle Studio simulations are used to make quantitative statements regarding the low-frequency (DC to microwave) behavior of coherent transition radiation from a mirror inclined at 45 degrees relative to the particle beam trajectory. A moving Gaussian bunch confined within a cylindrical beam pipe is modeled. Simulation results are presented.
JLAB, Newport News, Virginia
Tech-X, Boulder, Colorado
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In this paper, we present benchmarking results for high-class 3D electromagnetic (EM) codes in designing RF cavities today. These codes include Omega3P [1], VORPAL [2], CST Microwave Studio [3], Ansoft HFSS [4], and ANSYS [5]. Two spherical cavities are selected as the benchmark models. We have compared not only the accuracy of resonant frequencies, but also that of surface EM fields, which are critical for superconducting RF cavities. By removing degenerated modes, we calculate all the resonant modes up to 10 GHz with similar mesh densities, so that the geometry approximation and field interpolation error related to the wavelength can be observed.
SLAC, Menlo Park, California
Funding: Work supported by US DOE contracts DE-AC03-76SF00515.
A remarkable progress over the last decade in development of computer codes significantly advanced our capabilities in calculation of wakefields and impedances for accelerators. There are however a number of practical problems that, when approached numerically, require a huge mesh, and hence memory, or an extraordinary CPU power, or both. One class of such problems is related to wakes of ultra short bunches, typical for many next generation electron/positron accelerators and photon sources. Another class is represented by long shallow collimators and tapers, often with non round cross sections. The numerical difficulties with these problems can be traced to a small parameter in the system, such as, e.g., a ratio of the bunch length to the length of a taper. It is remarkably, however, that the same small parameter often allows developing approximate analytical methods that provide a simplified solution to the impedance problem. In this paper, we review recent results in the analytical theory of wakefields, which include calculation of the wakes of very short bunches, long transitions and some special cases of the resistive wall impedance.
PPRC, Tehran
IPM, Tehran
2D potential profiles for uniformly populated discs of charged particles with circular and elliptical cross sections inside a perfectly conducting ring are simulated using the method of images. The results are compared with the problem of infinitely long linear charge distribution inside a conducting cylinder with a dependence only on the two transverse coordinates*.
*Miguel A. Furman Phys. Rev. ST Accel. Beam 10, 081001(2007)
Tech-X, Boulder, Colorado
Funding: This project was in part supported by DOE Office of Advanced Scientific Computing Research SBIR Phase II grant #DE-FG02-07ER84731, SciDAC Grant #DE-FC02-07ER41499, and Tech-X Corporation.
In order to meet the design and budget constraints of next generation particle accelerators, individual components have to be optimized using numerical simulations. Among the optimizations are the geometric shape of RF cavities and the placement of coupler and dampers, requiring large numbers of simulations. It is therefore desirable to accelerate individual cavity simulations. Finite-Difference Time-Domain (FDTD) is a widely used algorithm for modeling electromagnetic fields. While being a time-domain algorithm, it can also be used to determine cavity modes and their frequencies. Weak scaling of parallel FDTD yields good results due to the algorithm locality, but the maximum speedup is determined by the usually small problem size. Graphics Processing Units (GPUs) offer a huge amount of processing power and memory bandwidth, well suited for accelerating FDTD simulations. We therefore developed an FDTD solver on GPUs and incorporated it into the plasma simulation code VORPAL. We will present GPU accelerated VORPAL simulations, provide speedup figures and address the effect of running these simulations in single precision.
Commanding Communications Academy, Wuhan
CIAE, Beijing
Under the influence of applications using virtual reality in accelerator R&D, this paper discusses the complete process of developing Communication Equipment Operation Simulation (CEOS) based on Creator/Vega Visual Scenery Simulation Technology, operation rules modeling and solutions to its key problem. The virtual scene model for communication equipment is designed with 3D modeling software MultiGen Creator, especially its DOF technology and Switch node. The basic graphs such as wires are drawn through OpenGL call-back functions. By the virtual scene drive Vega, the application of CEOS comes true. Its simulation example shows greatest traits on building similar simulation system e.g. cyclotron virtual prototyping system as well as virtual cyclotron control system.