Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
At the synchrotron radiation facility at DESY transversal tune spectra have been observed which are characteristic for an interaction of the positron beam with possible electron clouds in the ring. The filling patterns at which this incoherent tune shifts happen are favourable to the growth of the electron density, i.e. long bunch trains with short intra-bunch distances or filling with short trains but also short distances between the trains. Eventually the vertical emittance growth with the originally designed equidistant filling (with 8 or 16 ns bunch spacing) has been avoided by fillings with shorter trains and longer gaps between the trains by still achieving the designed beam current of 100 mA. In this paper we examine the positron bunch stability of PETRA III for certain e-cloud densities and bunch parameters. A PIC simulation of the interaction of the bunch with an e-cloud yields the wake kick on the tail particles for an offset in the transverse centroid position of the head parts. With such a pre-computed wake matrix, we investigate the stability of a single bunch by tracking it through the linear optics of the ring while at each turn applying the kick from the e-cloud.
LBNL, Berkeley, California, USA
An efficient numerical method for computing wakefields due to coherent synchrotron radiation (CSR) has been implemented using a one-dimensional integrated Green function approach. The contribution from CSR that is generated upstream and propagates across one or more lattice elements before interacting with the bunch is included. This method does not require computing the derivative of the longitudinal charge density, and accurately includes the short-range behavior of the CSR interaction. As an application of this method, we examine the importance of upstream transient wakefields within several bending elements of a proposed Next Generation Light Source.
IS, Beijing, People's Republic of China
IMP, Lanzhou, People's Republic of China
ANL, Argonne, USA
Electromagnetic simulations are fundamental for accelerator modeling. In this paper two high-order numerical methods will be studied. These include continuous Galerkin (CG) method with vector bases, and discontinuous Galerkin (DG) method with nodal bases. Both methods apply domain decomposition method for the parallelization. Due to the difference in the numerical methods, these methods have different performance in speed and accuracy. DG method on unstructured grid has the advantages of easy parallelization, good scalability, and strong capability to handle complex geometries. Benchmarks of these methods will be shown on simple geometries in detail first. Then they will be applied for simulation in accelerator devices, and the results will be compared and discussed.
Saint-Petersburg State University, Saint-Petersburg, Russia
We analyze radiation of a small bunch crossing a boundary between two dielectrics in a cylindrical waveguide. The total energy of radiation was studied earlier for such problem but dynamics of an energy loss as well as a field structure was not investigated. Meanwhile these questions are of essential interest for the wakefield acceleration technique and for new methods of generation of microwave radiation. Our research is based on original approach used previously for the case of the vacuum-plasma boundary*. The principal difference of presented work consists in generation of Cherenkov radiation in dielectric and so-called Cherenkov-transition radiation in vacuum. Algorithms of computations for the field and the energy loss are founded upon certain transformations of integration path. Comparison of analytical results with numerical ones shows a good coincidence. We consider two instances in detail: the bunch is flying from vacuum into dielectric and from dielectric into vacuum. In both cases we compare the energy losses by transition radiation and by Cherenkov one. Our investigation shows, for example, that energy loss can be negative at certain segments of the bunch trajectory.
* T.Yu. Alekhina and A.V. Tyukhtin, Phys. Rev. E. 83, 066401 (2011)
LBNL, Berkeley, California, USA
Numerical modeling of laser-plasma accelerators using the ponderomotive approximation allows efficient modeling of 10 GeV and beyond laser-plasma accelerators. The time-averaged ponderomotive force approximation also allows simulation in cylindrical geometry which captures relevant 3D physics at 2D computational cost. In this talk I will present the code INF&RNO (INtegrated Fluid & paRticle simulatioN cOde). The code is based on an envelope model for the laser while either a PIC or a fluid description can be used for the plasma. The effect of the laser pulse on the plasma is modeled with the time-averaged poderomotive force. These and other features, such as dynamical resampling of the phase space distribution to reduce on-axis noise and boosted-Lorentz-frame modeling capability, allow for a speedup of several orders of magnitude compared to standard full PIC simulations while still retaining physical fidelity. The code has been benchmarked against analytical solutions and 3D PIC simulations and a set of validation tests together with a discussion of the performances will be presented. Applications to the BELLA PW laser-plasma accelerator experiments at LBNL will be discussed.
CERN, Geneva, Switzerland
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.