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.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
HZB, Berlin, Germany
Energy Recovery Linacs (ERLs) being the most promising candidates for next-generation light sources put very high demands on preservation of beam brightness and reduction of beam losses. Thus, it is mandatory to avoid the impact of ionized residual gas considered as a source for instabilities in accelerators. Recently, we have presented simulations for the clearing of ionized residual gas with electrodes performed with an upgraded version of software package MOEVE PIC Tracking [1] which is being currently further developed to model the interaction of the ions with the electron beam in presence of external electromagnetic potentials such as the field of clearing electrodes. The tracking code allows for studies on clearing times for electrodes with different voltage as well as detailed studies of the behavior of the ions in the environment of the electrodes. In this paper we take further steps to study possible designs of clearing electrodes. Especially, we will consider the influence of different gas mixtures on clearing times and possible configurations for the clearing electrodes. We use parameters planned for BERLinPro as an example for our studies.
[1] G. Pöplau, A. Meseck, U. van Rienen, Simulation of the Behavior of Ionized Residual Gas in the Field of Electrodes, IPAC 2012, New Orleans.