Fusion energy startup Helion announced Friday that it has hit a key milestone in its quest for fusion power. Plasmas inside the company’s Polaris prototype reactor have reached 150 million degrees Celsius. This temperature is three-quarters of the way toward what the company believes it will need to operate a commercial fusion power plant.
Polaris is also operating using deuterium-tritium fuel, a mixture of two hydrogen isotopes. The company states this makes Helion the first fusion company to do so. The startup reported seeing the fusion power output increase dramatically in the form of heat as expected.
The Everett, Washington-based startup is in a race with several other companies seeking to commercialize fusion power, a potentially unlimited source of clean energy. That potential has investors rushing to bet on the technology. Recently, Inertia Enterprises announced a large funding round. In January, Type One Energy said it was raising a significant sum, while last summer Commonwealth Fusion Systems raised a major round from investors including Google and Nvidia. Helion itself raised a substantial amount last year from a group that included Sam Altman and several prominent investment firms.
While most other fusion startups are targeting the early 2030s to put electricity on the grid, Helion has a contract with Microsoft to sell it electricity starting in 2028. That power would come from a larger commercial reactor called Orion that the company is currently building, not from the Polaris prototype.
Every fusion startup has its own milestones based on its reactor design. Commonwealth Fusion Systems, for example, needs to heat its plasmas to more than 100 million degrees Celsius inside its tokamak device. Helion’s reactor is different, needing plasmas that are about twice as hot to function as intended. The company’s reactor design is called a field-reversed configuration.
The inside chamber looks like an hourglass. At the wide ends, fuel gets injected and turned into plasmas. Magnets then accelerate the plasmas toward each other. When they first merge, they are around 10 million to 20 million degrees Celsius. Powerful magnets then compress the merged ball further, raising the temperature to 150 million degrees Celsius. This entire process happens in less than a millisecond.
Instead of extracting energy from the fusion reactions in the form of heat, Helion uses the fusion reaction’s own magnetic field to generate electricity. Each pulse pushes back against the reactor’s own magnets, inducing an electrical current that can be harvested. By harvesting electricity directly, the company hopes to be more efficient than its competitors. Over the last year, Helion refined some circuits in the reactor to boost how much electricity they recover.
While the company uses deuterium-tritium fuel today, it plans to use deuterium-helium-3 in the future. Most fusion companies plan to use deuterium-tritium and extract energy as heat. Helion’s chosen fuel, deuterium-helium-3, produces more charged particles. These particles push forcefully against the magnetic fields, making this fuel better suited for Helion’s approach of generating electricity directly.
Helion’s ultimate goal is to produce plasmas that hit 200 million degrees Celsius, far higher than other companies’ targets. This is a function of its reactor design and fuel choice. The company believes that 200 million degrees is the optimal sweet spot for operating a power plant.
When asked whether Helion had reached scientific breakeven, the point where a fusion reaction generates more energy than it requires to start, the company’s CEO focused on the practical goal of making electricity rather than pure scientific milestones.
Helium-3 is common on the moon but not on Earth, so Helion must make its own fuel. To start, it will fuse deuterium nuclei to produce the first batches. In regular operation, while the main power source will be deuterium-helium-3 fusion, some reactions will still be deuterium-on-deuterium. These will produce helium-3 that the company will purify and reuse.
Work is already underway to refine this fuel cycle. The company reported that a lot of the related technology has been easier to develop than expected. Helion has been able to produce helium-3 at very high efficiencies in terms of both throughput and purity.
While Helion is currently the only fusion startup using helium-3 in its fuel, the company’s CEO believes others will in the future, hinting he would be open to selling it to them. He suggested that as other companies recognize the efficiency gains from direct electricity recovery, they will also want to use helium-3 fuel.
Alongside its experiments with Polaris, Helion is building Orion, a 50-megawatt fusion reactor needed to fulfill its Microsoft contract. The company’s ultimate goal is not to build and deliver Polaris, but to use it as a step along the way toward scaled power plants.