Electron cloud and beam scrubbing in the LHC

Abstract

An adequate dose of photoelectrons, accelerated by lowintensity proton bunches and hitting the LHC beam screen wall, will substantially reduce secondary emission and avoid the fast build-up of an electron cloud for the nominal LHC beam. The conditioning period of the liner surface can be considerably shortened thanks to secondary electrons, provided heat load and beam stability can be kept under control; for example this may be possible using a special proton beam, including satellite bunches with an intensity of 15-20% of the nominal bunch intensity and a spacing of one or two RF wavelengths. Based on recent measurements of secondary electron emission, on multipacting tests and simulation results, we discuss possible 'beam scrubbing' scenarios in the LHC and present an update of electron cloud effects.

Secondary-electron yields and their dependence on the angle of incidence on stainless-steel surfaces for three energetic ion beams

“…The present experiments can of course be extended to other materials, and coatings that have been suggested [30,31] for the reduction of electron produced secondary electrons will be investigated. Also further improvements are possible in angular accuracy and in the small angle limit for these measurements.…”

Recent advances in multipactor physics and mitigation

“…Multipactor [1][2][3][4][5] is a nonlinear phenomenon that occurs when electrons driven by a high frequency electric field in a high vacuum environment create an avalanche by impacting one or more metallic [2] or dielectric [3,6,7] surfaces. The electron avalanche sustains itself by a rapid charge growth through secondary electron emission [8][9][10][11] from the surfaces and can cause a multitude of problems in radio frequency (rf) and microwave systems, such as satellite communication payloads and spacecraft components [12][13][14], travelling wave tubes (TWTs) [15], high power microwave sources [16], and particle accelerators [17][18][19]. These problems include the breakdown of dielectric windows [20][21][22][23], erosion of metallic structures, melting of internal components, and perforation of vacuum walls [2].…”

“…In addition, multipactor can often detune rf systems, cause multi‐tone coupling and signal distortion [24], limit the transmission or delivery of rf power, and cause a local pressure rise due to the desorption of surface gases [25]. In particle accelerators such as the Large Hadron Collider (LHC) multipactor has been found to be responsible for problems including the rise of pressure inside the beam pipes, heat loads, and beam instabilities [18, 19, 26]. Although there are some beneficial applications of multipactor discharge [3], its various undesirable effects often far outweigh the useful aspects.…”

The Effect of Air Exposure on SEY and Surface Composition of Laser Treated Copper Applied in Accelerators

“…The electron cloud is a key problem in particle accelerators, which can cause the degradation of beam quality and limit the performance of particle accelerators with high energy, high intensity, high luminosity and long beam lifetime [1][2][3][4][5][6][7][8]. The methods of mitigating electron cloud effect have been studied by many researchers from several organizations, such as CERN [9,10], STFC [11,12], NSRL [13], KEK [7,14], INFN [15], etc.…”