  The achievable beam current and beam quality 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 walls of the vacuum chamber can contribute
to the growth of the electron cloud. An apparatus for in-situ measurements of
the secondary electron yield (SEY) of samples in the vacuum chamber of the
Cornell Electron Storage Ring (CESR) has been developed in connection with EC
studies for the CESR Test Accelerator program (CesrTA). The CesrTA 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 SEY chambers can be isolated from the CESR beam pipe, allowing
us to exchange samples without venting the CESR vacuum chamber. Measurements so
far have been on metal surfaces and EC-mitigation coatings. The goal of the SEY
measurement program is to improve predictive models for EC build-up and
EC-induced beam effects. This report describes the CesrTA in-situ SEY
apparatus, the measurement tool and techniques, and iterative improvements
therein.
