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

M Taborelli,G Hartung,S Schulte,V Petit,J Kröger,M Himmerlich

doi:10.1103/physrevaccelbeams.23.103101

Abstract

Energy-resolved secondary electron spectroscopy has been performed on air-exposed standard Cu samples and modified Cu surfaces that are tested and possibly applied to efficiently suppress electron cloud formation in the high-luminosity upgrade of the Large Hadron Collider at CERN. The Cu samples comprise pristine oxygen-free, carbon-coated and laser-structured surfaces, which were characterized prior to and after electron irradiation and rare-gas ion bombardment. Secondary-electron and reflected-electron yields measured with low charge dose of the samples exhibit a universal dependence on the energy of the primary impinging electrons. State-of-the-art models can successfully be used to describe the spectroscopic data. The supplied spectral dependence of electron emission and integrated electron yield as well as the derived parametrization can serve as a basis for forthcoming simulations of electron cloud formation and multipacting.

Highlights

The emission of secondary electrons (SE) from a surface induced by electron irradiation is a common effect used in electron multipliers and detectors [1,2] as well as a specific contrast mechanism in scanning electron microscopes [3,4,5]
In the analysis presented here we have refrained from adding further parameters to model the obtained experimental results because a numerical representation of the experimentally observed SE and reflected electrons (RE) energy dependence can be directly implemented into electron cloud simulation codes
In order to correlate the spectral dependence of electron emission with standard energy-integrated SE measurements, which are commonly used to qualify surfaces for electron cloud mitigation capabilities, secondary electron yield (SEY) (δ) measurements were performed for Ep < 1800 eV using identical twin samples at CERN

Summary

INTRODUCTION

The emission of secondary electrons (SE) from a surface induced by electron irradiation is a common effect used in electron multipliers and detectors [1,2] as well as a specific contrast mechanism in scanning electron microscopes [3,4,5] In some applications, this process creates undesirable phenomena such as charge build-up at the surface of spacecrafts and satellites [6,7] or the formation of an electron cloud in particle accelerators [8,9,10,11,12]. In the work presented here, special attention was paid to exposing the samples to a minimum of charge dose during the measurements that enabled the characterization of asreceived surfaces To this end, an RFA combined with lockin amplification was used. The studies explored whether SE emission of low-SEY surfaces can be described by universal models or materialspecific properties play a role

Apparatus

Samples

Energy distribution of secondary electrons

Secondary-electron yield

CONCLUSION