Simulation of single bunch instabilities driven by electron cloud in the SPS

Abstract

Photoemission, or gas ionization, and secondary emission can give rise to a quasi-stationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate single bunch instabilities driven by a quasi-stationary electron cloud by means of a computer simulation. The model that we apply makes use of two sets of macroparticles for both the bunch particles and for the electrons, which interact at one or more locations along the beam orbit. Two different schemes have been implemented for the electron cloud field calculation (PIC and soft-Gaussian), and their efficiencies are compared. The code is used to simulate possible instability mechanisms in the SPS. The options of a broad-band wake-field and space charge induced tune spread have been also introduced in order to follow the bunch evolution under the combined effect of the electron-cloud and a broad-band impedance.

Transverse behaviour of the LHC proton beam in the SPS: an update

“…In the vertical plane the tail fills-up the physical aperture of the machine producing beam losses. The results of simulations [8] of the growth rate of the single-bunch instability and of the induced emittance blow-up (Fig. 3) are consistent with the observations.…”

“…The single-bunch instability driven by the electroncloud wake-field is expected to produce emittance growth in both planes [7] [8]. Profile measurements performed at injection (integrated over a few ms) indicate a significant blow-up (by more than a factor 2.5 in the horizontal plane and by a factor 4 in the vertical plane) of the tail of the batch.…”

Some Key Issues of Vacuum System Design in Accelerators and Colliders

“…And in the case of synchrotron radiation, the instability caused by EC is analogous to the transverse mode coupling instability (TMCI) [50]. The impacts of space charge, magnetic field, the chromaticity, the amplitude detuning, and the broad-band resonator are also considered in the study of the bunch instability caused by EC [50][51][52][53].…”

“…The single bunch instability caused by EC with different densities in LHC and SPS was investigated by E. Benedetto et al [52] based on the HEADTAIL simulation code [53,63]. The EC effect on transverse single bunch instabilities in the bending region was simulated and compared with observations in the SPS.…”