Squeeze inside a fusion reactor with a Nat Geo photographer

Wearing a clean white lab suit complete with white shoes and gloves, National Geographic Explorer Paolo Verzone laid down and shimmied into an opening not much wider than himself. He was, as he says, “entering into a star.”  

Or, at least, it’s just about as close one can get to the experience on Earth. On this November day, Verzone was granted a rare exclusive look at the insides of the Wendelstein 7-X, an experimental fusion reactor at the Max Planck Institute for Plasma Physics in Greifswald, Germany, while it was undergoing maintenance.  

When Wendelstein 7-X is operational, the doughnut-shaped chamber where Verzone stands is filled with plasma, a type of hot, supercharged gas. The machine heats this plasma to tens of millions of degrees Celsius, and then contains it with superconducting magnets cooled to minus 269 degrees, a temperature close to absolute zero. 

That contrast means, when turned on, this facility is temporarily both the hottest and coldest place in our entire solar system. But more importantly, those extremes will make it possible to achieve nuclear fusion, where lightweight atoms like hydrogen join together under enormous heat and pressure, and in the process produce heavier atoms and a side of clean energy. It’s the same method by which our sun generates its heat and light. The hope is, one day, fusion reactors could provide our electric grids with near-limitless, emissions-free power.  

Fusion reactors come in a few configurations. Wendelstein 7-X is what’s known as a stellarator, which offers a rather sculptural solution to a problem fusion physicists wrestle with.  

Think of a toy car on a racetrack, says Josefine Proll, a physicist who works on the experiment. In this metaphor, the car is like the particles of plasma in the reactor. They need to do two things for fusion to happen: move fast, and stay on track (or else they'll careen and crash into the walls of the experiment). So “just as with your little [toy] race track,” Proll says, you need to gently bank the track around a turn so the car can “still stay in the lane.” 

Whereas other fusion experiments like the enormous ITER tokamak in France make these lane curves by creating an electrical current in the plasma, the stellarator does it with magnificently twisted magnetic coils surrounding the reaction chamber. The design choice has allowed for breakthroughs: The Wendelstein 7-X recently set a record for maintaining super-heated plasma for 43 seconds, surpassing what tokamaks have achieved. It also makes it a beautiful piece of engineering to crawl inside. About 8,000 graphite tiles and water-cooled steel plates adorn the helical walls to keep the experiment from overheating. 

For Verzone, this peek behind the scenes was close to a spiritual experience. “It's like you are entering into a crypt of a cathedral,” he says. A rarely visited sanctum where one can contemplate the sublime. “Imagine Einstein entering into the same place—he would have cried.” 

This reactor hasn’t achieved useable fusion power yet. The experiments conducted so far are mostly to test the design and stability of the plasma system. And even if the scientists can achieve a stable fusion reaction, which outputs more energy than it consumes, more engineering challenges remain. Like: How do you get the energy contained in the plasma out to power an electric grid? (Scientists are working on that too.)  

Despite the long road ahead, Proll is optimistic humanity will achieve fusion power in our lifetimes. “In the last decade, there have been such cool advancements,” Proll says. “And I think there is finally more momentum behind it.”