Finding ways to make the plasma fuel in fusion reactors hot and dense enough to generate significant fusion power has been a goal of fusion researchers for decades. Now, using data from previous experiments with the Alcator C-Mod tokamak nuclear fusion device at MIT’s PSFC, the MIT researchers along with colleagues in Belgium and the UK, have found a new method of heating fusion plasmas in tokamaks.
The Alcator C-Mod tokamak, which completed its final run in September 2016, had achieved the highest yet magnetic field strength and highest plasma pressure. Now, say the researchers, a new approach has resulted in raising trace amounts of ions to megaelectronvolt (MeV) energies — an order of magnitude greater than previously achieved.
“These higher energy ranges are in the same range as activated fusion products,” says PSFC research scientist John C. Wright. “To be able to create such energetic ions in a non-activated device — not doing a huge amount of fusion — is beneficial, because we can study how ions with energies comparable to fusion reaction products behave, how well they would be confined.”
The new method uses a fuel composed of three ion species, whereas typically plasma used for fusion research is composed of two ion species, deuterium and hydrogen or deuterium and helium-3, with deuterium dominating the mixture by up to 95 percent. In experiments, researchers focus RF energy on the minority species, which heats up to much higher energies owing to its smaller fraction of the total density.
The new three-species fuel used by the MIT researchers comprises hydrogen, deuterium, and trace amounts – less than one percent – of helium-3. In this case, all of the RF energy is absorbed by just a trace amount of helium-3 and the ion energy is boosted even more — to the range of activated fusion products.
The MIT researchers’ results were replicated by researchers at the Joint European Torus – the largest fusion device in Europe. The results have the potential to not only advance nuclear fusion research, but, the researchers note, also provide insights into the understanding of helium-3-rich solar flares.
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