Optimization of the secondary electron yield of laser-structured copper surfaces at room and cryogenic temperature

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.

Energy-resolved secondary-electron emission of candidate beam screen materials for electron cloud mitigation at the Large Hadron Collider

“…Qualitatively, the SEY evolves similarly for Cu OFE and a-C-coated samples and follows common trends of SEY curve shape [76,77], with the material-dependent parametersδ andÊ p listed in Table III. It is important to note that the properties of the characterized samples are in very good agreement with earlier SEY analyses of these different surfaces [15,16,20,64,78]. In particular, the SEY maximum ofδ ¼ 1.45 for the Cu OFE-ci surface, Fig.…”

“…For these conditions the signal-tonoise ratio was optimized, as quantified by electron emission spectroscopy of a clean Au(111) surface, where the primary peak of elastically reflected electrons exhibited a full width at half maximum of 3.3 eV at E p ¼ 1008 eV [63]. The samples exhibit a homogeneous lateral surface composition [15,20,64]. The onset of electron emission is defined by the work function of the sample, i.e., by the energy difference between Fermi energy E F and vacuum level E V .…”

Reflectivity and photoelectron yield from copper in accelerators

“…Samples No. 5, 6 are potentially interesting materials that could be used for the construction of HL-LHC, HE-LHC and FCC-hh [2,12,15,16,[33][34][35]37,39,[47][48][49][50].…”

“…6C). This morphology is able to significantly reduce SEY [47,48] and is a potential candidate to be used in FCChh BS [49][50][51].…”

“…This sample is a candidate material for the construction of the beam screen for FCC-hh, since its nanostructured surface grants a low secondary electron yield, hence it is promising to mitigate electron cloud related effects [15,32,[47][48][49][50]. Its specular reflectivity and its photo yield as function of photon energy are shown in Fig.…”