Helion Achieves 150M°C Plasma Temperature Milestone in Race to Commercial Fusion Power by 2028
Everett, Washington-based fusion energy startup Helion announced on Friday that it has achieved a critical milestone in its pursuit of commercial fusion power generation. Plasma temperatures inside the company's Polaris prototype reactor have reached 150 million degrees Celsius, representing approximately 75% of the temperature threshold required for commercial fusion power plant operations.
"We're obviously really excited to be able to get to this place," stated David Kirtley, Helion's co-founder and CEO. Polaris is currently operating with deuterium-tritium fuel—a mixture of two hydrogen isotopes—making Helion the first fusion company to achieve this operational configuration. "We were able to see the fusion power output increase dramatically as expected in the form of heat," Kirtley explained.
The startup is engaged in intense competition with several other companies racing to commercialize fusion power, a potentially unlimited source of clean energy. This potential has attracted significant investor interest across the sector. Recent funding activity includes:
• Inertia Enterprises secured a $450 million Series A round featuring Bessemer and GV
• Type One Energy is raising $250 million in its Series B round
• Commonwealth Fusion Systems raised $863 million from investors including Google and Nvidia
• Helion itself raised $425 million last year from investors including Sam Altman, Mithril, Lightspeed, and SoftBank
While most fusion startups are targeting the early 2030s for grid electricity delivery, Helion has established a contract with Microsoft to supply electricity beginning in 2028. This power would be generated from a larger commercial reactor called Orion, currently under construction, rather than from the Polaris prototype.
Reactor Design and Technical Approach
Each fusion startup pursues distinct milestones based on their reactor architecture. Commonwealth Fusion Systems, for instance, must heat plasmas to over 100 million degrees Celsius within its tokamak—a toroidal device utilizing powerful magnets for plasma containment.
Helion's reactor employs a different architecture requiring plasmas approximately twice as hot. The company's design utilizes a field-reversed configuration. The internal chamber features an hourglass geometry where fuel is injected at the wide ends and converted to plasma. Magnetic systems then accelerate the plasmas toward each other. Upon initial merging, temperatures reach 10-20 million degrees Celsius. Powerful magnets subsequently compress the merged plasma ball, elevating the temperature to 150 million degrees Celsius—all within less than a millisecond.
Rather than extracting energy from fusion reactions as thermal energy, Helion leverages the fusion reaction's intrinsic magnetic field to generate electricity directly. Each pulse creates back-pressure against the reactor's magnets, inducing electrical current that can be harvested. By capturing electricity directly from fusion reactions, the company aims to achieve superior efficiency compared to competitors.
Over the past year, Kirtley reported that Helion has optimized reactor circuitry to enhance electrical recovery efficiency.
Fuel Strategy and Future Goals
While the company currently utilizes deuterium-tritium fuel, future operations will transition to deuterium-helium-3. Most fusion companies plan to use deuterium-tritium and extract energy thermally. Helion's fuel selection of deuterium-helium-3 produces more charged particles, which exert stronger forces against the magnetic fields confining the plasma, making it more suitable for Helion's direct electricity generation approach.
Helion's ultimate objective is to produce plasmas reaching 200 million degrees Celsius—significantly higher than other companies' targets, driven by 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 stated.
When questioned about achieving scientific breakeven—the point where fusion reactions generate more energy than required to initiate them—Kirtley declined to provide specifics. "We focus on the electricity piece, making electricity, rather than the pure scientific milestones."
Helium-3 is abundant on the Moon but rare on Earth, necessitating that Helion produce its own fuel. Initially, the company will fuse deuterium nuclei to generate the first batches. During regular operations, while deuterium-helium-3 fusion will be the primary power source, some deuterium-on-deuterium reactions will occur, producing helium-3 that the company will purify and recycle.
Development of the fuel cycle is already progressing. "It's been a pleasant surprise in that a lot of that technology has been easier to do than maybe we expected," Kirtley noted. Helion has successfully produced helium-3 "at very high efficiencies in terms of both throughput and purity," he added.
While Helion currently stands as the only fusion startup utilizing helium-3 in its fuel mix, Kirtley suggested other companies may follow suit, hinting at potential commercial opportunities. "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.
Concurrent with Polaris experiments, Helion is constructing Orion, a 50-megawatt fusion reactor required to fulfill its Microsoft contract. "Our ultimate goal is not to build and deliver Polaris," Kirtley emphasized. "That's a step along the way towards scaled power plants."
