I witnessed the operation of one of the first two operating fusion reactors, the twin tokamaks at UCLA and Princeton. The one at UCLA took roughly six months to prep for a millisecond shot. It was triggered by eight Litton Radarange microwave ovens with their magnetron tubes pumped by a massive (size of a semi truck) Lincoln welding supply - Huge 4 gauge cables ran into and out of the backs of the ovens. There were 4-8 Commodore c64 computers hooked up to sensors in and around the tokamak, and they had cheap color TV's for monitors. When the tokamak was fired, the monitors were gaussed beyond all rescue, and gallons of liquefied teflon ran out of the tokamak (The teflon had been big machined hunks used as dielectric insulation between the walls of the tokamak).
UCLA had previously built a small tokamak that was a twin of one built in Russia - the designed proved to be optimistically undersized and neither was completed, but it could be seen hidden behind some fences and tarps in the machine shop area of Boelter Hall until the mid eighties.
Anyway, as you can see from the vast scale of the Japanese reactor, a *portable* fusion reactor like the Gundam would use would be quite a leap.