Numerical simulations studies on single-bunch instabilities driven by electron clouds at the LHC

Abstract

Instabilities driven by electron clouds in the LHC are studied by means of numerical simulations performed with the PyECLOUD-PYHEADTAIL suite. Particular attention is given to instabilities driven by e-cloud in the quadrupole magnets at injection energy, which are found to be the most critical case. The numerical parameters of the simulation (grids, number of macroparticles) are defined based on extensive convergence scans, which provide useful guidelines also for future simulation studies. The dependence of the beam stability on RF voltage, bunch intensity, transverse emittance, chromaticity and octupoles settings is investigated. The spectral properties of the unstable motion are analyzed. Simulations are also performed for less critical cases, namely instabilities driven by the quadrupoles at collision energy and instabilities driven by the dipoles at injection energy