US-based fusion startup Acceleron Fusion has closed a $24m Series A funding round co-led by Lowercarbon Capital and Collaborative Fund. Acceleron says the funding will support efforts to advance its low-temperature muon-catalysed fusion technology – sometimes described as a form of cold fusion. According to Acceleron, this technology uses subatomic muons to achieve deuterium-tritium (DT) fusion reactions at temperatures below 1,000°C, rather than the 100m degrees C required by traditional plasmas.

Soviet physicist Andrei Sakharov and British physicist Sir Frederick Frank first predicted the phenomenon of muon-catalysed fusion on theoretical grounds in the 1940s. Soviet physicist Yakov Borisovich Zeldovich discussed the phenomenon in 1954 and Canadian-American physicist John David Jackson published one of the first comprehensive theoretical studies in 1957.

In most cases, the muon is released following a fusion reaction and will catalyse additional fusions, but 1% of the time it sticks to a resulting alpha particle and is removed from the catalytic cycle. This effect has hindered efforts to design a reactor based on muon-catalysed fusion. In the mid-1980s, several groups worldwide demonstrated more than 100 fusion reactions per muon. However, muons are unstable, decaying in 2.2 micro-seconds. Even if muons were absolutely stable, each one could catalyse, on average, only about 100 DT fusions before sticking to an alpha particle.

Moreover, obtaining muons requires far more energy than can be produced by the resulting fusion reactions. To create useful room-temperature muon-catalysed fusion, reactors would need a cheap, efficient muon source and/or a way for each individual muon to catalyse many more fusion reactions.

Acceleron says it is developing an intense, high-efficiency muon source to produce beams of muons using less energy than current facilities, and a high-density fusion cell to allow each of these muons to catalyse larger numbers of fusion reactions. In October, the company ran its machine with highly compressed DT fuel, capturing data on 28 hours of continuous fusion after more than 100 hours of testing with deuterium. The team is using the High Intensity Proton Accelerator and Swiss Muon Source at the Paul Scherrer Institute in Switzerland.

“We are thrilled to have the support of Lowercarbon Capital and Collaborative Fund, whose deep experience in the fusion space makes them ideal partners as we push the boundaries of what’s possible with muon-catalyzed fusion,” said Ara Knaian, CEO and cofounder of Acceleron Fusion. “This investment will allow us to accelerate our R&D, grow our team, and bring us closer to demonstrating a viable commercial prototype.”