University of Tokyo, Tokyo
KEK, Ibaraki
Recently, calculation of wake field and impedance has become more important. In many cases they are usually calculated numerically by using a mesh. It will be shown here that the mesh calculation based on the paraxial approximation can be much faster than ordinary methods when the bunch is very short. There are two advantages. One is to be able to choose the longitudinal mesh size independent of the bunch length. The other is that the problem can be solved as an initial-value problem in spite of frequency domain calculation.
ORNL, Oak Ridge, Tennessee
IUCF, Bloomington, Indiana
As SNS continues to ramp toward full intensity, we are acquiring a wealth of experimental data. Much effort is being applied to understand the details of the beam accumulation process under a variety of experimental conditions. An important part of this effort is the computational benchmarking of the experimental observations. In order to obtain quantitative agreement between the calculations and the observations, and hence a full understanding of the machine, a great deal of care must be taken to incorporate all the relevant experimental parameters into the calculation. These vary from case to case, depending upon what is being studied. In some of these cases, the benchmarks have been critical in unearthing flaws in the machine and in guiding their mitigation. In this paper we present the results of benchmarks with a variety of experiments, including coupling in beam distributions at low intensities, space charge effects at higher intensities, and a transverse instability driven by the impedance of the ring extraction kickers.
GSI, Darmstadt
The head-tail instability represents a potential intensity limitation for bunched beams in the synchrotrons of the FAIR project. Parametrical studies with numerical simulations over very long time scales are necessary in order to understand the effect of direct space charge, nonlinear synchrotron oscillations and image charges, which are all important in FAIR synchrotrons. Existing analytic approaches either neglect space charge or describe simplified models, which require a numerical or experimental validation. For our simulation studies we use two different computer codes, HEADTAIL and PATRIC. In this work we verify models for wake-field kicks and space-charge effect using the analytic solution for head-tail mode frequencies and growth rates from the barrier airbag model.
KEK, Ibaraki
Recent progress of KEKB and nano beam scheme adopted in KEKB upgrade are discussed. For the present KEKB, chromatic x-y coupling, which was the key parameter to improve luminosity, is focussed. Beam-beam simulations with weak-strong and strong-strong models for nano beam scheme are presented. A weak-strong simulation was done in the presencee of the longitudinal micro-wave instability. Finally status of beam simulations in KEK supercomputers is presented.
KEK, Ibaraki
Two methods were investigated to study microwave instability in LER of KEKB and SuperKEKB. One is macroparticle tracking code based on PIC. The other one solves the VFP equation directly. First we compare the two methods using a resonator impedance model of KEKB LER. Then we use the calculated impedance including CSR to study the beam instability of LER of KEKB and SuperKEKB. Convergence properties of these two methods due to numerical noise are discussed.
KU Leuven, Kortrijk
TEMF, TU Darmstadt, Darmstadt
The modeling of eddy-current phenomena in superconductive accelerator magnets is challenging because the large differences in geometrical dimensions (skin depth vs. magnet size) and time constants (ramping time vs. relaxation time). The paper addresses modeling issues as e.g. the ferromagnetic saturation of the iron yoke, the eddy-current losses in the yoke end parts, the eddy-current losses in the beam tube and possible eddy-current losses in the windings. Heavy saturation, small skin depths and small time constants render simulations of this kind to be challenging. The simulation approach is used in combination with an optimization procedure involving both continuous and integer-valued parameters.
SLAC, Menlo Park, California
High current B-Factory BPM designs incorporate a button type electrode which introduces a small gap between the button and the beam chamber. For achievable currents and bunch lengths, simulations indicate that potentials can be induced in this gap which are comparable to the breakdown voltage. This study characterizes beam induced voltages in the existing PEP-II storage ring collider BPM as a function of bunch length and beam current.