The magnetic chamber of a plasma fusion reactor. MIT/PSFC Using the same physics that light up the sun, fusion reactors promise to generate almost infinite energy on Earth.

Physicists' favorite type of fusion reactor uses plasma. These machines heat up a gas until it's so hot and its atoms are moving so fast that the particles slam together and combine to release an extraordinary amount of energy — often hundreds of millions of degrees hotter than the sun.

The ultimate goal is to capture that energy and convert it to electricity. And, as Tech Insider learned during a recent tour of a futuristic reactor at the Massachusetts Institute of Technology, fusing atoms make a loud and eerie sound.

Getting fusion energy to work is easier said than done. Physicists have tried to crack the problem for decades, but we have yet to build a machine that can sustain a reaction, generate more energy than it consumes, and scale up to meet the energy demands of towns and cities.

One place that's still trying to figure out how to harness fusion energy is MIT's Plasma Science and Fusion Center in Cambridge, Massachusetts. The facility hosts a test plasma fusion reactor, called Alcator C-Mod, which is a cylindrical, truck-sized machine.

C-Mod is a "tokamak" style reactor. This means it uses a hollow, doughnut-shaped chamber of powerful magnets to confine and help fuse searing-hot plasma — without melting its walls into a puddle of liquid metal. The chamber is under a vacuum, so atmospheric air doesn't mess with the special gas that MIT physicists inject inside, but there's a window that can show the orange-hot glow of fusing matter.

Theodore Golfinopoulos, a physicist at MIT who toured us around the reactor facility, recently took a video of a two-second blast of fusion inside the machine through the window.

"I set my point-and-shoot camera here, but didn't hang around. Because that would have been dangerous," Golfinopoulos told our tour group outside C-Mod.

The bright blast of fusion energy seen through the port is shocking enough, but what really caught our attention was the noise of combining atoms. It sounds a lot like a child screaming bloody murder at the top of his or her lungs.

Watch Golfinopoulos' video of plasma fusion below, but make sure your volume is under control.