Investigating the role of photoemission in the e-cloud formation at the LHC

Abstract

The presence of electron clouds at the LHC gives rise to sev-eral problems, among them is the heat deposited by the elec-trons on the beam screens of the superconducting magnets,which constitutes a significant load for the cooling system.To improve the understanding of this phenomenon, simula-tion studies of the e-cloud build-up are performed using thededicated simulation tool PyECLOUD. Photoelectrons gen-erated by synchrotron radiation can significantly enhancethe e-cloud formation. In this contribution, the availableliterature on photoelectric properties of the material usedfor the LHC beam screens is reviewed, and the number ofphotons emitted by the beam is calculated. This allows thedefinition of suitable simulation parameters for modeling theelectrons from photoemission within the PyECLOUD code.The simulations with photoemission seeding are comparedto those that neglect photoemitted electrons. The predictedheat loads are compared against measurements from LHCcryogenic cells. Since these cells include several kinds ofmagnets, simulations with dierent configurations of theexternally applied magnetic field had to be combined. Fur-thermore a sensitivity study on the modeling of synchrotronradiation is presented