"Another perennial threat to the company is regulation.  Where Airbnb has contributed to influxes of tourists that local communities struggle to cope with, governments have proposed curbs like tourist taxes and new rules on gaining permission for private holiday rentals.

"Mast Upgrade is one attempt to come up with a template for more compact, cheaper fusion reactors. It makes use of an innovative design known as a spherical tokamak to squeeze the fuel into a 4.4m-tall, 4m-wide space. By comparison, the containment vessel Iter will use to control its fusion reactions is 11.4m tall and 19.4m wide.

But Mast Upgrade's bijou dimensions come at a price: "You're making something that's hotter than the Sun... in a smaller volume. How you then get the heat out becomes a big challenge," said Prof Chapman.

The core of the plasma within the tokamak reaches temperatures of 100 million C. Without an exhaust system that can handle this unimaginable heat, materials in the design would have to be regularly replaced - significantly affecting the amount of time a power plant could operate for.

The new exhaust system being trialled at Culham is known as a Super-X divertor. This would allow components in future commercial tokamaks to last for much longer; greatly increasing the power plant's availability, improving its economic viability and reducing the cost of fusion electricity.

Tests at Mast Upgrade have shown at least a tenfold reduction in the heat on materials with the Super-X system.

Researchers said the results were a "game-changer" for the promise of fusion power plants that could provide affordable, efficient electricity. Against the background of climate change, fusion could offer a clean and virtually limitless source of energy.

Dr Andrew Kirk, lead scientist on Mast Upgrade, said the results were "the moment our team at UKAEA has been working towards for almost a decade".

"We built Mast Upgrade to solve the exhaust problem for compact fusion power plants, and the signs are that we've succeeded.

"Super-X reduces the heat on the exhaust system from a blowtorch level down to more like you'd find in a car engine. This could mean it would only have to be replaced once during the lifetime of a power plant."

The success of the exhaust system for Mast Upgrade delivers a boost to plans for a prototype fusion power plant in the UK called Step. It is expected to come online sometime in the 2040s.

The Mast Upgrade facility will have its official opening ceremony on Wednesday, where guest of honour, astronaut Tim Peake, will create his own artificial star by running a plasma test on the machine."