Well, 1 MW = 1000 W, or roughly 1000 KVA, so it would be the size of a fairly big pad-mount transformer.
1000 KVA at 240 V = 4167 Amps, so probably not! And, a 1 MVA load on single phase would get the power company out hunting you with hooks. You'd really need a SERIOUS 3-phase supply, probably at 14.4 KV for this. The National Superconducting Cyclotron Lab at MSU runs their RF system off 18 KV (DC) at 46 A, so that is close to your 1 MVA. I think their mains transformer is a 14.4 KV - 14.4 KV Delta-Wye transformer.
Oh, yeah, you have to think about the cooling for the tubes, too! You'll probably need to mount a several ton cooling tower on the roof. If the anodes are directly cooled (most likely) you'll need an ultra low conductivity water system and a water-water heat exchanger to keep it clean.