An Improvised Two-Dimensional Laser Surface Scanner for Diagnosis of RF Thermionic Electron Gun Problems

Abstract

The Advanced Photon Source circulates electrons in a ring 1,104 metres round, injected by radio-frequency thermionic electron guns whose heated cathodes boil off the electrons. In early 2010, several guns developed problems shortly after their ageing cathodes were replaced, and the Survey and Alignment Section was asked to measure the cathode surfaces to find out why. William Jansma describes the two-dimensional laser surface scanner improvised for the job – the word is his – and what it found.