Helion builds pulsed fusion generators intended to sell electricity into the grid. The company has closed its upsized Series G at $500 million, adding $35 million to the $465 million initial close announced in June as it develops its Orion power plant in Washington for Microsoft.
The company’s machines form two rings of plasma from deuterium and helium-3 fuel, accelerate them toward one another and compress the merged plasma with magnetic fields until fusion occurs. Helion says the expanding plasma then pushes against those fields, inducing current that can be recovered directly as electricity instead of first producing steam for a turbine.
Microsoft is Helion’s first announced power customer under an agreement for at least 50 megawatts from Orion, while Constellation will market the power and manage transmission. That arrangement makes Helion’s proposed business model concrete: sell electricity from a fusion plant under a power purchase agreement. Orion is under construction in Chelan County, Washington.
Thrive Capital led the June close, which valued Helion at $15.5 billion after the investment. Chief Executive David Kirtley said the final close added crossover, pension and sovereign-wealth investors; the company said it capped the round despite additional interest. The financing is intended to support commercial deployment and expanded manufacturing capacity.
Helion says it has built and tested seven fusion prototypes. Its latest large machine, Polaris, has operated with deuterium-tritium fuel and reached plasma temperatures above 150 million degrees Celsius, according to the company. A smaller testbed called Tiny Merge is intended to examine plasma formation and merging more quickly before the final Orion designs are locked.
The commercial schedule remains a substantial execution risk. Helion’s current Orion page says initial operations will begin in 2028, while Axios reported that a company executive said full output would not arrive before 2029 or 2030. The same report said the Microsoft contract requires Orion to connect to the grid and begin operating by the end of 2028, although it remains unclear how much electricity that milestone requires.
The additional capital can fund construction, testing and manufacturing, but it does not resolve the central commercial question: whether Orion can repeat Helion’s fusion process efficiently enough to deliver usable grid electricity while commissioning the plant on Microsoft’s schedule.