Tri Alpha Energy, a company with $500 million in backing that has been working on nuclear fusion technology for nearly two decades, reached a major milestone last month.

On Monday, the company announced that it started up a new nuclear fusion reactor that can achieve the high temperatures needed to continue to validate its technology plans. The reactor, named Norman -- after the late company founder and professor, Norman Rostoker -- can operate at temperatures between 50 million and 70 million degrees centigrade, which is in the temperature range of the core of the sun.

Commercial-scale nuclear fusion will likely have to operate in the range of a billion degrees centigrade. So Norman, which is the company’s fifth reactor, is just a step along the way. But it will be an important proving point.

“This is huge for us,” said Tri Alpha Energy president and CTO Michl Binderbauer, a former student of Rostoker’s.

Over the years, the company has been working on proving two things: building a reactor that can hold plasma for “long enough” and at a “hot enough” temperature.

Two years ago, Tri Alpha Energy showed it could hold the plasma in a reactor for several milliseconds, which was a major feat. Now the Norman reactor is meant to answer the “hot enough” question.

Norman, which is 100 feet in length and 45 feet wide, is housed at the company’s Foot Hill Ranch facility in Southern California. It can consume a whopping 750 megawatts of power in a short burst when it’s holding the plasma that is needed to create a nuclear fusion reaction.

Because of the high energy needs, the facility has an array of batteries and flywheels on standby that store the needed energy to get the reactor running. Norman achieved what’s called “first plasma” (i.e., it generated plasma in its core) in June.

Nuclear fission, which splits atoms apart to generate energy, is used in today’s nuclear reactors. Nuclear fusion, on the other hand, smashes atomic nuclei together to release energy -- and it's not yet a commercialized technology. Fusion hasn’t been able to produce more energy than needed to start up the reaction.

The most well-known fusion technology is based on the donut-shaped rings of the tokamak. This technology turns hydrogen fuel into plasma under intense heat and pressure, and shaped by magnetic coils. At high heat, the plasma particles can fuse, and release fusion energy.

The largest and most mature of the tokamak designs is from an international coalition building ITER, or the International Thermonuclear Experimental Reactor project. That project, under construction in Southern France, is billions over budget and years behind schedule.

There are a handful of startups, like Tri Alpha Energy, that have turned to the private sector instead, and are trying to operate in a leaner, faster way to some day bring nuclear fusion to market.

Unlike the tokamak’s donuts, Tri Alpha Energy is using a design that shoots beams of plasma into a vessel where it’s held in place, spinning, by a magnetic field. The design shares some properties with particle accelerators.

Norman cost $100 million to build, and can fit five times more plasma in it than the previous reactor. At the same time, it can still be housed at the facility that held the previous reactor.

With Norman, Tri Alpha is looking to answer the question: “As we enter higher temperatures, will the same scaling behavior hold?” said Binderbauer.

If Norman operates as expected, Binderbauer said the company has high confidence that it will be able to build a bigger reactor that will be able to generate electrons for the power grid.

It might sound (and actually be) crazy, but the company has won over a lot of converts. Former Energy Secretary and physicist Ernie Moniz joined the company’s board of directors earlier this year. The $500 million in funding has come from investors like Microsoft co-founder Paul Allen, Goldman Sachs, Wellcome Trust, and Silicon Valley’s NEA and Venrock.

If Norman succeeds, the next reactor will move the company into a dramatically different stage of its existence. It will need to use superconducting magnets, which Tri Alpha Energy has been developing in conjunction with the fusion reactor tech.

The company will also need to raise more money, likely in the form of project financing, to build the next reactor. In addition, the next reactor will need a lot more sophisticated data monitoring and analysis control room.

“We’re going to have to develop other muscles to go to the next step,” said Binderbauer.