Farnsworth Fusor

The team then turned to the AEC, then in charge of fusion research funding, and provided them with a demonstration device mounted on a serving cart that produced more fusion than any existing "classical" device. The observers were startled, but the timing was bad; Hirsch himself had recently revealed the great progress being made by the Soviets using the tokamak. In response to this surprising development, the AEC decided to concentrate funding on large tokamak projects, and reduce backing for alternative concepts

This is a precursor to the Polywell.   There is no controversy about the ability here to bring about fusion in a table top device.  This device is actually being commercially made today as a source of neutrons.  The neutrons that the device produces is evidence of fusion taking place.

This should be evidence enough that you don't need an office sized building in order to produce fusion.  To the contrary, hobbyists can reproduce the effect for

In the fusor, the ions are accelerated to several keV by the electrodes, so heating as such is not necessary (as long as the ions fuse before losing their energy by any process). Whereas 45 megakelvins is a very high temperature by any standard, the corresponding voltage is only 4 kV, a level commonly found in such devices as neon lights and televisions.

 A tremendous of energy is not necessary, provided that you can come up with a suitable confinement strategy that will make fusion possible.   In my opinion, there is a possibility that this could occur in a random setting and this could be why "cold fusion" can't be easily reproduced.