There’s a new, mysterious entry in the race to master nuclear fusion. Tri Alpha Energy, a privately funded company operating out of an unlabeled industrial building in the suburbs of Los Angeles, has just made a breakthrough in containing the hot plasma that results from fusion reactions.

Nuclear fusion — essentially the slamming together of two hydrogen atoms to release energy — has long been considered the Holy Grail of clean, endless power. But figuring out what to do with the leftover plasma, a 10-million-degree-Celsius cloud of electrons and ions, has stumped scientists for decades.

Last week, a mini fusion reactor from MIT made headlines when it managed to contain super-hot plasma using circular, superconductive barium copper oxide magnets. They demonstrated that a strong enough magnetic field can hold the plasma in place.

Tri Alpha Energy’s strategy is slightly different: Instead of using external magnets to contain the plasma, their plasma creates its own magnetic field, allowing it to contain itself. This approach, known as field-reversed configuration, the unique flow of particles in the plasma, determined by the reactor design, allows it to be held in a cigar shape. Still, the unwieldy cylinder resists being confined, normally falling apart after about 0.3 milliseconds.

To help keep it together, the Tri Alpha reactor fires angled beams of high-energy particles at the plasma, forming a “cage.” With this technique, they’ve succeeded in holding the plasma for 5 milliseconds, which is a massive improvement — and proof that holding the plasma in a steady state is possible.

Tri Alpha hasn’t produced energy yet — they’ll need to scale up their reactor to achieve longer containment times and higher temperatures to do so — but their successes in holding plasma together are a big step toward figuring out nuclear fusion once and for all. On a day full of economic news, this may be the most important story of all.