Fusion startup Helion faces extreme temperatures as it heads toward a 2028 deadline

Everett, Washington-based fusion energy startup Helion announced Friday that it has achieved a major milestone in its pursuit of nuclear fusion power. The plasma temperature inside the company’s Polaris prototype reactor has reached 150 million degrees Celsius, three-quarters of the way toward what the company believes it would need to operate a commercial fusion power plant.

“We’re obviously very excited to be able to get to this place,” Helion co-founder and CEO David Kirtley told TechCrunch.

Polaris also operates with deuterium and tritium fuel — a mixture of two hydrogen isotopes — which Kirtley said makes Helion the first fusion company to do so. “We were able to see a significant increase in fusion energy production as expected in the form of heat,” he said.

The startup is in a race with several other companies seeking to commercialize nuclear fusion energy, which has the potential to be an unlimited source of clean energy.

This potential has investors rushing to bet on the technology. This week, Inertia Enterprises announced a $450 million Series A round that included Bessemer and GV. In January, Type One Energy told TechCrunch that it was in the midst of raising $250 million, while last summer Commonwealth Fusion Systems raised $863 million from investors including Google and Nvidia. Helion itself raised $425 million last year from a group that included Sam Altman, Mithril, Lightspeed and SoftBank.

While most other fusion startups are targeting the early 2030s to bring electricity to the grid, Helion has a contract with Microsoft to sell it electricity starting in 2028, though that power will come from a larger commercial reactor called Orion that the company is currently building, not Polaris.

Each nuclear fusion startup has its own parameters based on its reactor design. For example, Commonwealth Fusion Systems needs to heat its plasma to more than 100 million degrees Celsius inside a tokamak, a donut-shaped device that uses powerful magnets to contain the plasma.

The Helion reactor is different, as it requires plasma about twice as hot to operate as intended.

The company’s reactor design is what is called a reverse field configuration. The inner chamber resembles an hourglass, and at the wide ends fuel is injected and converted into plasma. The magnets then accelerate the plasma toward each other. When they first fuse, their temperature is about 10 to 20 million degrees Celsius. Powerful magnets then compress the fused ball further, raising the temperature to 150 million degrees Celsius. It all happens in less than a millisecond.

Instead of extracting energy from fusion reactions in the form of heat, asparagus uses the magnetic field of the fusion reaction to generate electricity. Each pulse will push against the reactor’s magnets, generating an electrical current that can be harvested. By harvesting electricity directly from fusion reactions, the company hopes to be more efficient than its competitors.

Over the past year, Kirtley said Helion has improved some of the circuits in the reactor to increase the amount of electricity it recovers.

While the company uses deuterium-tritium fuel today, in the future it plans to use deuterium-helium-3 fuel. Most fusion companies plan to use deuterium and tritium and extract the energy as heat. Helion’s fuel choice, deuterium-helium-3, produces more charged particles, which push harder against the magnetic fields that confine the plasma, making it more suitable for Helion’s approach to generating electricity directly.

Helion’s ultimate goal is to produce plasma with a temperature of 200 million degrees Celsius, much higher than other companies’ goals, and is a function of its reactor design and fuel selection. “We think at 200 million degrees, that’s where you reach the sweet spot where you want to run a power plant,” Kirtley said.

When asked whether Helion had reached the scientific break-even point—the point at which the fusion reaction generates more energy than it takes to start the reaction—Kirtley demurred. “We focus on the electricity piece, the electricity industry, rather than the purely scientific milestones.”

Helium-3 is common on the Moon, but not here on Earth, so helium must make its own fuel. To start, the deuterium nuclei will be combined to produce the first batches. In regular operation, while the main source of energy will be the fusion of deuterium with helium-3, some of the reactions will still be deuterium on deuterium, which will produce helium-3 that the company will purify and reuse.

Work is already underway to improve the fuel cycle. “It was a pleasant surprise because implementing a lot of this technology was easier than we expected,” Kirtley said. He added that Helion is able to produce helium-3 “with very high efficiencies in terms of productivity and purity.”

While Helion is currently the only fusion startup using helium-3 in its fuel, Kirtley said he believes other companies will do so in the future, hinting that he would be open to selling it to them. “Other people — when they realize they want to take this approach of direct electricity recovery and see the efficiency gains from it — will want to use helium-3 fuel as well,” he said.

Besides its experiments with Polaris, Helion is also building Orion, a 50-megawatt fusion reactor it needs to fulfill its contract with Microsoft. “Our ultimate goal is not to build and deliver Polaris,” Kirtley said. “It is a step on the way towards creating large-scale power plants.”