[LINK] Commercially viable fusion reactors

[Stephen Loosley]

A Compact Fusion Reactor Barely 3 Feet Across Has Hit a Huge Milestone

01 June 2023 By DAVID NIELD  https://www.sciencealert.com/a-compact-fusion-reactor-barely-3-feet-across-has-hit-a-huge-milestone

New nuclear fusion reactor, the ST40 reactor. (Tokamak Energy)

“Ions inside a compact fusion reactor barely a meter (less than 3 feet) across have been heated to the magic figure of 100 million degrees Celsius (some 180 million degrees Fahrenheit) for the first time in a monumental step towards making nuclear fusion energy a practical reality.

In this case, a spherical tokamak called ST40 was used. Putting aside the machinery necessary for it to operate safely, the reactor itself is a mere 0.8 meters across, a mere fraction of the larger tokamaks that can stretch several meters in diameter.

Compared with larger fusion reactors, these smaller devices are cheaper to build, and potentially more efficient and more stable – all advantages if you want to make a technology commercially viable.

A number of optimizations were deployed by the researchers to reach the new temperature record, including the use of the ST itself, and the way the plasma was prepared in terms of how it was heated and its electron density.

Some techniques were borrowed from 'supershot' experiments carried out in the 1990s in the Tokamak Fusion Test Reactor, which is much larger than the ST40. Essentially, the approach involved a lot of heat being applied in a very short space of time.

Another optimization trick applied by the scientists was to heat up the positively charged ions more than the negatively charged electrons inside the plasma. Known as a hot-ion mode, it helps to increase the number of reactions and the tokamak performance.

"These temperatures were achieved in hot-ion mode scenarios, where the ion temperature exceeds that of the electrons, typically by a factor of two or greater," write the researchers.


While this breakthrough and others like it are certainly exciting, nuclear fusion is still very much in a test phase with multiple hurdles to yet clear before it could be considered as a practical source of power.

Not everyone believes that nuclear fusion power production is ultimately going to be possible, considering the technical challenges involved.

Those challenges are highlighted here too: the top temperature was reached for a mere 150 milliseconds. A fine achievement in the lab, but not much time to practically contribute anything to the energy grid.

Still, each discovery brings us closer to the ultimate goal – and this one is particularly notable, considering that spherical tokamaks are one of the most promising options for creating nuclear fusion reactions in a way that the necessary energy and economic equations end up making sense.

"These results demonstrate for the first time that ion temperatures relevant for commercial magnetic confinement fusion can be obtained in a compact high-field ST and bode well for fusion power plants based on the high-field ST," write the researchers.

The research has been published in Nuclear Fusion.