The efficiency of the whole thing will very probably be below 50 %, so you could not expect more than 20 kW from your AC supply line. You're off by a factor of 50, at least.
The calculation has not taken into account the needed cooling and auxuíliary feeds.
Go have a look at a larger distribution transformer to have an idea of a 1 MW transformer. In the power grid it is not very large yet.
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.
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