PALO ALTO — Helion Energy, the nuclear fusion startup backed by Sam Altman and a constellation of technology investors, announced on Wednesday that it has closed a $1.2 billion Series F funding round led by a consortium of sovereign wealth funds from Norway, Singapore, and the UAE, with participation from Microsoft's climate investment vehicle and a major Japanese industrial conglomerate.
The funding will finance construction of Helion's Polaris demonstration plant in Everett, Washington, which the company says will be the first privately built fusion facility to achieve net energy gain — producing more electricity than it consumes — with a target operational date of 2028.
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Helion's approach differs from most fusion programmes in using a pulsed, field-reversed configuration rather than the tokamak design pursued by ITER and most national programmes. The company argues that pulsed systems can be built at a fraction of the cost and scaled to commercially viable sizes more rapidly than the giant tokamak approach.
The company has achieved plasma temperatures of 100 million degrees Celsius in its seventh-generation prototype — hot enough for fusion — but has not yet demonstrated net energy gain. CEO David Kirtley said the Polaris plant will incorporate improvements to magnetic compression technology that he described as "the key unlock."
Microsoft, which signed a power purchase agreement with Helion in 2023, said it remained confident in the technology timeline and that the deal remained active.