Helion Energy, a 12-year-old fusion startup, has announced a $425 million Series F raise, pushing its valuation to $5.245 billion. This significant investment will accelerate the company's development of its commercial-scale power plant, which is expected to supply Microsoft with electricity by 2028.

The company's unorthodox approach to fusion power and relative secrecy have earned it both fans and critics. However, its investors, including Sam Altman, rumored to be in talks with OpenAI, remain confident in Helion's potential. The startup's latest prototype, Polaris, is expected to be the first fusion reactor to generate electricity.

Polaris, Helion's seventh prototype, is housed in a 27,000 square-foot building in Everett, Washington. The prototype took more than three years to build, which is relatively quick by fusion industry standards. To meet its ambitious 2028 deadline for Microsoft, the startup will need to move even faster on its commercial-scale power plant development.

One of the significant challenges Helion faces is the procurement of specialized components, such as large-scale, pulse-power semiconductors. CEO David Kirtley explained that the company had to order capacitors three years in advance, which set the timeline for the Polaris project. To overcome this hurdle, Helion plans to bring a significant amount of specialized manufacturing in-house, including capacitor production.

Kirtley remains optimistic that Helion can still deliver electrons to Microsoft in just a few years, despite having to build a supply chain from scratch. The company has already begun working on siting for the Microsoft facility, including permitting and grid interconnection, a process that can take years.

Helion's approach to fusion power differs from virtually every other startup in the sector. The company is building a field-reversed configuration reactor, which uses powerful magnets to guide and compress plasma throughout each reaction. This approach is expected to be more efficient than traditional magnetic confinement and inertial confinement methods.

The current design for a commercial-scale Helion reactor will pulse a few times per second, generating 50 megawatts of electricity. A single power plant could contain multiple reactors, making it a potentially significant source of clean energy.

The new funding round is smaller than the startup's previous fundraise of $500 million. New investors in the round include Lightspeed Venture Partners, SoftBank Vision Fund 2, and a major university endowment. Existing investors Sam Altman, Capricorn Investment Group, Mithril Capital, Dustin Moskovitz, and Nucor also participated.

Helion's progress in the fusion energy sector is significant, given the industry's challenges and the company's ambitious timeline. As the world continues to transition towards cleaner and more sustainable energy sources, Helion's innovative approach could play a crucial role in shaping the future of energy production.