My friend and I were discussing particle accelerators (betatrons to be exact) and we began to argue about the size of the core magnets and vacuum chamber. He said that an average torodial vacuum chamber is 0.5m. I have seen old photos of them and said thats more likely to be the diameter. I have reviewed several patents on betatrons, read three books on particle accelerator physics, and havent managed to find out how large a vacuum chamber is. If anybody can give me a rough estimate or other parameters so i could figure it out, I would be very appreciative. Or for that matter, any parameters of a betatron would do the trick.