In-Situ Measurements of the Secondary Electron Yield in an Accelerator Environment: Instrumentation and Methods

TL;DR

This paper presents an in-situ measurement system for secondary electron yield in an accelerator environment, enabling detailed studies of electron cloud effects and surface conditioning over time.

Contribution

It introduces a novel in-situ apparatus for measuring SEY in a working accelerator, allowing for real-time analysis of surface conditioning and mitigation strategies.

Findings

SEY measurements can be performed without venting the vacuum chamber.

Surface conditioning reduces SEY over time.

The system distinguishes between photon and electron-induced emissions.

Abstract

The performance of a particle accelerator can be limited by the build-up of an electron cloud (EC) in the vacuum chamber. Secondary electron emission from the chamber walls can contribute to EC growth. An apparatus for in-situ measurements of the secondary electron yield (SEY) in the Cornell Electron Storage Ring (CESR) was developed in connection with EC studies for the CESR Test Accelerator program. The CESR in-situ system, in operation since 2010, allows for SEY measurements as a function of incident electron energy and angle on samples that are exposed to the accelerator environment, typically 5.3 GeV counter-rotating beams of electrons and positrons. The system was designed for periodic measurements to observe beam conditioning of the SEY with discrimination between exposure to direct photons from synchrotron radiation versus scattered photons and cloud electrons. The samples can be exchanged without venting the CESR vacuum chamber. Measurements have been done on metal surfaces and EC-mitigation coatings. The in-situ SEY apparatus and improvements to the measurement tools and techniques are described.