Stunning photo, I haven’t seen one of these in operation for years, often they are made in metal cans and you cannot see the discharge. Which brand is it? I wonder if it might have been designed by my grandfather. He used to be R&D engineer for hydrogen thyratrons and ignitrons at the valve department of BTH-AEI lamp factory in Leicester, later English Electric. I also worked in the same factory five decades later when it was Thorn / GE Lighting!

Thanks James, yeah, large ones are often ceramic and metal cans so not so interesting to look at. This one is made by EV" Technologies and reasonably new. Interesting about your grandfather I do have an old mercury Thyratron from BTH: http://www.tuopeek.com/image2/thyratron.jpg