Google and Chevron are part of a $250 million funding raise announced Tuesday for TAE Technologies, a nuclear fusion startup with an unconventional strategy that has now raised a total of $1.2 billion.

Nuclear fusion is often referred to as the holy grail of clean energy because of its promise of generating nearly unlimited emission-free energy without the equivalent harmful, long-lasting radioactive waste that nuclear fission produces.

Nuclear fission is the process by way conventional nuclear power plants generate energy in which a larger atom is split into two smaller atoms, thereby releasing energy. Nuclear fusion reverses that process, with energy produced when two larger atoms slam together to form one larger atom.

Fusion is the elemental process that powers stars and the sun, but has proven fiendishly difficult to sustain in a controlled reaction on Earth, despite decades of effort.

“TAE — and fusion technology as a whole — has the potential to be a scalable source of no-carbon energy generation and a key enabler of grid stability as renewables become a greater portion of the energy mix,” said Jim Gable, president of Chevron Technology Ventures, the energy company’s corporate venture capital arm, in a statement announcing Tuesday’s funding round.

Google, the search giant owned by parent company Alphabet, has partnered with TAE since 2014, providing the fusion startup with artificial intelligence and computational power. But Tuesday marks Google’s first cash investment in TAE.

A Japanese investment company, Sumitomo Corporation of Americas, also participated in the round, and will help TAE bring its fusion technology to the Asia-Pacific region.

The investment follows an announcement in October that TAE partnered with Japan’s National Institute for Fusion Science. Japan currently gets the majority of its energy from coal, oil and natural gas, according to the International Energy Association. Its geography makes its clean energy goals particularly challenging.

“Unlike many other countries, Japan does not have an abundance of renewable energy resources and its high population density, mountainous terrain, and steep shorelines represent serious barriers to scaling up the ones it does have, particularly as many of its few flatlands are already heavily covered by solar panels,” Fatih Birol, executive director at the international industry organization, International Energy Agency, wrote about the country’s energy landscape in 2021. That means Japan needs to focus on energy efficiency and nuclear power, among other sources, Birol said.  

Also on Tuesday, TAE announced a technical milestone: It achieved temperatures greater than 75 million degrees Celsius with its current fusion reactor machine, nicknamed Norman. (A photo essay of how Norman works can be found here.)

The money TAE announced Tuesday will go towards building its next generation fusion machine, which it will call Copernicus and which it says it will have completed by 2025. TAE was founded in 1998 and aims to have a commercial scale fusion reactor delivering energy to the grid in the early 2030s.

The most common machine being built to achieve fusion on earth is a tokamak, which is a donut-shaped device and is the method being developed at ITER, the multi-national collaborative fusion project being constructed in France and pictured below:

TAE is instead using a linear machine, a long thin structure known as a beam-driven field-reversed configuration.

Plasma — the most energetic state of matter, beyond gas — is generated at both ends of the TAE fusion machine and then shot towards the middle, where the plasmas slam together and ignite the fusion reaction.

Another key differentiator of TAE’s fusion approach is the fuel it uses. The most common source of fuel for fusion reactions is with deuterium and tritium, which are both forms of hydrogen, the most abundant element in the universe. Deuterium is naturally occurring but tritium has to be produced. (A team at the Idaho National Lab is working on researching supply chains for tritium.)

But TAE’s fusion process uses hydrogen-boron (also known as proton-boron or p-B11) as a fuel. Hydrogen-boron does not need to have a tritium processing supply chain, which TAE counts as a benefit. The challenge, however, is that a hydrogen-boron fuel source requires much higher temperatures than a deuterium-tritium fuel source.

“Proton-boron11 fusion is indeed much more difficult than deuterium-tritium fusion for several reasons,” Nat Fisch, a professor of astrophysical sciences at Princeton University, told CNBC. Because the the cross-section for the pB11 fusion reaction is so small, it has to be confined longer for the fusion process to start. “At the same time, the temperatures required to reach even this smaller cross section are much larger,” Fisch told CNBC. This means it takes a lot of energy to ignite the fusion reaction and hold it, and the plasma where the reaction is happening, in place without contaminating the reaction.

“Taken together, this is a really, really hard problem — and it requires a very new learning curve. But the TAE team is really smart, and really fast moving, so if anyone is going to solve this problem, the TAE team is well positioned to be the one to do it,” Fisch said.