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, three-quarters of the way toward what the company thinks it will need to operate a commercial fusion power plant.

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

Polaris is also operating using deuterium-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 the fusion power output increase dramatically as expected in the form of heat,” he said.

The Everett, Washington-based startup is locked in a race with several other companies that are seeking to commercialize fusion power, a potentially unlimited source of clean energy.

That 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 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 put electricity on the grid, Helion has a contract with Microsoft to sell it electricity starting in 2028, though that power would come from a larger commercial reactor called Orion that the company is currently building, not Polaris.

Every fusion startup has its own milestones based on the design of its reactor.

Commonwealth Fusion Systems, for example, needs to heat its plasmas to more than 100 million degrees C inside of its tokamak, a doughnut-shaped device that uses powerful magnets to contain the plasma.

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Boston, MA | REGISTER NOW Helion’s reactor is different, needing plasmas that are about twice as hot to function as intended.

The company’s reactor design is what’s called a field-reversed configuration.

The inside chamber looks like an hourglass, and at the wide ends, fuel gets injected and turned into plasmas.

Magnets then accelerate the plasmas toward each other.

When they first merge, they’re around 10 million to 20 million degrees C. Powerful magnets then compress the merged ball further, raising the temperature to 150 million degrees C. It all 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 will push back against the reactor’s own magnets, inducing electrical current that can be harvested.

By harvesting electricity directly from the fusion reactions, the company hopes to be more efficient than its competitors.

Over the last year, Kirtley said that Helion had refined some of the circuits in the reactor to boost how much electricity they recover.

While the company uses deuterium-tritium fuel today, down the road it plans to use deuterium-helium-3.

Most fusion companies plan to use deuterium-tritium and extract energy as heat.

Helion’s fuel choice, deuterium-helium-3, produces more charged particles, which push forcefully against the magnetic fields that confine the plasma, making it better suited for Helion’s approach of generating electricity directly.

Helion’s ultimate goal is to produce plasmas that hit 200 million degrees C, far higher than other companies’ targets, a function of its reactor design and fuel choice.

“We believe that at 200 million degrees, that’s where you get into that optimal sweet spot of where you want to operate a power plant,” Kirtley said.

When asked whether Helion had reached scientific breakeven — the point where a fusion reaction generates more energy than it requires to start it — Kirtley demurred.

“We focus on the electricity piece, making electricity, rather than the pure scientific milestones.

” Helium-3 is common on the moon, but not here on Earth, so Helion must make its own fuel.

To start, it’ll fuse deuterium nuclei to produce the first batches.

In regular operation, while the main source of power will be deuterium-helium-3 fusion, 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 refine the fuel cycle.

“It’s been a pleasant surprise in that a lot of that technology has been easier to do than maybe we expected,” Kirtley said.

Helion has been able to produce helium-3 “at very high efficiencies in terms of both throughput and purity,” he added.

While Helion is currently the only fusion startup using helium-3 in its fuel, Kirtley said he thinks other companies will in the future, hinting that he’d be open to selling it to them.

“Other folks — as they come along and recognize that they want to do this approach of direct electricity recovery and see the efficiency gains from it — will want to be using helium-3 fuel as well,” he said.

Alongside its experiments with Polaris, Helion is also building Orion, a 50-megawatt fusion reactor it needs to fulfill its Microsoft contract.

“Our ultimate goal is not to build and deliver Polaris,” Kirtley said.

“That’s a step along the way towards scaled power plants

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