Abstract
Electron cloud ($e$-cloud) mitigation is an essential requirement for proton circular accelerators in order to guarantee beam stability at a high intensity and limit the heat load on cryogenic sections. Laser-engineered surface structuring is considered a credible process to reduce the secondary electron yield (SEY) of the surfaces facing the beam, thus suppressing the $e$-cloud phenomenon within the high luminosity upgrade of the LHC collider at CERN (HL-LHC). In this study, the SEY of Cu samples with different oxidation states, obtained either through laser treatment in air or in different gas atmospheres or via thermal annealing, has been measured at room and cryogenic temperatures and correlated with the surface composition measured by x-ray photoelectron spectroscopy. It was observed that samples treated in nitrogen display the lowest and more stable SEY values, correlated with the lower surface oxidation. In addition, the surface oxide layer of air-treated samples charges upon electron exposure at a low temperature, leading to fluctuations in the SEY.
Highlights
Electron cloud (e-cloud) mitigation is an essential requirement in proton circular accelerators for beam stability and reduction of the heat load in cryogenic sections at a high intensity [1,2]
The analysis indicates the presence of copper oxide (CuO) on the sample treated in air, visible from the Cu2þ satellite around 943 eV and the Cu 2p3=2 binding energy as well as from the Cu LMM transition at 917.6 eV kinetic energy (KE) [15] resulting in an Auger parameter of 1851.2 eV, to the previous CH-patterned sample
Laser surface structuring for secondary electron yield (SEY) reduction has been performed on copper samples, in different gas atmospheres
Summary
Electron cloud (e-cloud) mitigation is an essential requirement in proton circular accelerators for beam stability and reduction of the heat load in cryogenic sections at a high intensity [1,2]. In the Large Hadron Collider (LHC) at CERN [3], this requirement is achieved using activated nonevaporable getter coatings [4] in the room-temperature sections and via beam scrubbing of the copper beam screen surfaces in the cryogenic sections. Both solutions provide a low enough secondary electron yield (SEY) of the beamfacing surfaces below the e-cloud multiplication threshold, effectively suppressing the e-cloud. Because of the modified HL-LHC beam parameters, a reduction of the SEY below what may be achieved with beam scrubbing is needed in order to maintain the heat load on the cryogenic system within
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