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 several problems, among them is the heat deposited by the electrons on the beam screens of the superconducting magnets, which constitutes a significant load for the cooling system. To improve the understanding of this phenomenon, simulation studies of the e-cloud build-up are performed using the dedicated simulation tool PyECLOUD. Photoelectrons gen- erated by synchrotron radiation can significantly enhance the e-cloud formation. In this contribution, the available literature on photoelectric properties of the material used for the LHC beam screens is reviewed, and the number of photons emitted by the beam is calculated. This allows the definition of suitable simulation parameters for modeling the electrons from photoemission within the PyECLOUD code. The simulations with photoemission seeding are compared to those that neglect photoemitted electrons. The predicted heat loads are compared against measurements from LHC cryogenic cells. Since these cells include several kinds of magnets, simulations with dierent configurations of the externally applied magnetic field had to be combined. Furthermore a sensitivity study on the modeling of synchrotron radiation is presented.