The main thyratron inside a high voltage cabinet. The thyratron is a large vacuum tube with a high voltage input cap at the top of the tube via a small diameter tube. A thyratron is a very fast switch that can dump massive amounts of current, which goes into the Pulse Forming Network of the linear accelerator. Use of a grounding stick and cabinet interlocks keeps us safe while changing the very expensive and fragile thyratron.
https://media.mas.to/masto-public/media_attachments/files/111/420/240/197/073/510/original/60d19d674142086e.jpg