Simulation of the electron-cloud build up and its consequences on heat load, beam stability, and diagnostics

Abstract

Photoemission and secondary emission are known to give rise to a quasistationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate the electron-cloud build up and related effects via computer simulation. In our model, macroparticles representing photoelectrons are emitted synchronously with the passing proton or positron bunch and are subsequently accelerated in the field of the beam. As they hit the beam pipe, new macroelectrons are generated, whose charges are determined by the energy of the incoming particles and by the secondary emission yield of the beam pipe. A quasistationary state of the electron cloud is eventually reached due to space charge. The equilibrium density is used as an input parameter for a second program that analyzes the electron-cloud driven single-bunch instability. The electron cloud simulation also allows the evaluation of the heat load on the cold Large Hadron Collider beam screen, which must stay within the available cooling capacity, and the electron charge deposited on or emitted from the electrodes of the beam-position monitors.

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

“…No appreciable shift is observed in the horizontal plane. Simulations of electron-cloud build up were performed following the recipe described in [6]. Good agreement with observations is obtained if a substantial component of elastically scattered low-energy electrons is included.…”

Examining mitigation schemes for synchrotron radiation in high-energy hadron colliders

“…At high proton-beam energies, beam-induced synchrotron radiation is an important source of heating, of beam-related vacuum pressure increase, and of primary photoelectrons, which can give rise to an electron cloud [1][2][3][4][5][6][7].…”

Beam Instabilities in Hadron Synchrotrons

“…28. Schematic of the formation of an electron cloud in a particle accelerator (a similar sketch can be found in [191]). …”

“…A qualitative picture of the EC buildup at a section of an accelerator operated with bunches of positively charged particles is sketched in Fig. 28 (see also [191]). Fig.…”

“…Moreover, the demand for extensive parameter scans gave quite stringent requirements in terms of speed and reliability. CERN has a long experience in the EC build-up simulation, mostly carried out with the ECLOUD code, developed and maintained at CERN since 1997 [191,198,199,150] and, more recently, a fully reorganized simulation code has been developed in order to better fulfill the aforementioned requirements. The new code has been called PyECLOUD, since it is almost entirely written in Python and inherits the physical models of the ECLOUD code.…”