Oxford-based UK tech firm Tokamak Energy has reached a milestone in privately-funded fusion research after its ST-40 spherical tokamak reactor reached a temperature of 100 million °C (180 million °F), which it says is the threshold for commercial fusion energy.

For over 75 years, the promise of a practical fusion reactor has remained frustratingly out of reach, with the promise of one seemingly being just a couple of decades down the line for decades now. However, the implications of such a reactor technology and its ability to supply humanity with a practically unlimited supply of cheap, clean energy is such a game changer that scientists and engineers continue to pursue it.

The principle behind nuclear fusion is relatively simple. Just take hydrogen atoms and subject them to the kind of heat and pressures found inside the Sun long enough for them to fuse together to form heavier atoms and they release enormous amounts of energy in the process.

Unfortunately, this is a classic example of something like a violin, which is easy to play in theory, but incredibly hard to do in practice. Put simply, getting the three main factors (heat, pressure, and time) to balance out in order to produce fusion isn't that hard. In fact, during the 1964 New York World's Fair, an exhibit was staged where the public could watch a bench-top fusion reactor operate in real time for a fraction of a second. The hard part since then has been to come up with a reactor that can produce practical amounts of energy in a steady supply and in amounts greater than has to be put in to start the reaction.