Helion Energy Inc., a startup working to develop commercial fusion reactors, today announced that it has closed a $425 million late-stage funding round.

The Series F deal included the participation of Lightspeed Venture Partners, SoftBank Vision Fund 2 and an unnamed university endowment. They were joined by several existing backers including Sam Altman, who invested $375 million in Helion four years ago. The company is now valued at $5.245 billion.

Nuclear reactors generate energy through a process called fission, which involves splitting atoms of a heavy element into lighter elements. Fusion uses the opposite process: It merges two light elements into a heavier one. This approach can theoretically produce significantly more power than fission. 

In practice, however, scientists have struggled to harness fusion for commercial energy generation. The reason is that the atoms a fusion reactor merges to generate power have an identical electric charge.

Particles with an identical charge repel one another. Merging atoms requires a fusion reactor to overcome this repulsion, which can only be done by generating enormous amounts of heat and pressure. Producing the necessary heat and pressure, in turn, requires far more electricity than current fusion reactors can generate, which makes the technology impractical for commercial use. 

Everett, Washington-based Helion is working to address the challenge. It’s developing reactors based on a technology dubbed magneto-inertial fusion. The company believes this technology could solve the technical challenges that currently make fusion power impractical. 

Helion’s reactor is a tubelike machine surrounded by magnets. The two opposite ends of the tube contain the reactor’s fuel: plasma made from deuterium and helium-3. The process that turns this fuel into power unfolds in multiple phases.

First, the reactor uses magnets to mix the deuterium and helium-3 plasma stored in the two ends of the tube. It then accelerates the fuel toward the center of the tube at a speed of 1 million miles per hour. Once at the center, another set of magnets compresses the fuel, a process that heats it to a temperature of 100 million degrees Celsius and leads to fusion.

The fusion reaction causes the reactor’s fuel to expand, which in turn changes the electric field of the surrounding magnets. This change is what produces electricity. The reactor mixes, accelerates and compresses the fuel in pulses that repeat several times per minute.

In 2021, Helion achieved a major research milestone with a prototype reactor called Trenta. The device was the first of its kind from a private company to reach 100 million degrees Celsius, the temperature necessary for commercial power generation. Helion has since built a newer prototype, Polaris, that it expects to be the first reactor to demonstrate fusion-based electricity generation.

“We are on the brink of delivering a transformative energy solution that can meet the world’s increasing electricity demands while preserving U.S. energy leadership,” said Helion co-founder and Chief Executive Officer David Kirtley.

According to TechCrunch, Helion will use its $425 million funding round to upgrade its manufacturing capabilities. The company currently relies on external suppliers to provide it with capacitors, a type of energy storage device. Helion hopes that moving capacitor manufacturing in-house will enable it to significantly speed up production.

The company will also use the capital to support the construction of a 50-megawatt fusion power plant Microsoft Corp. commissioned in 2023. The facility is expected to come online in 2028. Helion has also inked a deal to build a 500-megawatt power plant for Nucor Corp., a major steel producer that participated in the funding round. 

Photo: Helion