Mark Henderson works at ITER, a reactor based on a tokamak design, in which a powerful magnetic field confines the plasma in a toroidal shape. ITER is poised to become the biggest fusion reactor in the world, and its goal is to demonstrate that fusion at the power-plant scale is feasible. At ITER, Henderson is in charge of the systems heating the plasma.

Eric Lerner develops a fusion concept called dense plasma focus, in which large electrical currents run through the plasma, harnessing its natural instabilities to confine and compress it; this type of reactor has the advantage of being much smaller and cheaper than other designs, but technologically is not as advanced. “The first error of the governments in the 1970s was to put all their eggs in the tokamak basket”, he comments. “But actually we still don’t know which route will lead to practical and economical fusion: you should invest not in ideas you think will work, but in all ideas you can’t prove won’t work”.

Michel Laberge is the founder of General Fusion, a private company developing a fusion power device that, instead of employing magnetic fields, uses pistons to compress liquid metal surrounding the plasma to create fusion conditions. “It’s pistons and its’ rings, it’s metal and pipes, it’s plumbing,” he explains. “Turning that into a power plant would actually be not that complicated. I have a saying, I tell my engineers: if you can’t find it at Home Depot it doesn’t go in the machine.”

Finally, Sibylle Gunter is the scientific director of Wendelstein 7-X, an experimental reactor in Germany that is the largest stellarator device in the world. Stellarators, which have worst plasma confinement than tokamaks but can run continuously — an important advantage for future power plants — are based on complicated coils optimized to generate a specific magnetic field configuration. Although stellarators are technologically behind tokamaks, some believe it is stellarators that will eventually deliver fusion on the grid.

The documentary takes the audience right at the beginning of the history of fusion, to the time when, in 1939, Hans Bethe understood the proton–proton reaction that powers stars. A decade later, in the USSR, a self-educated Red Army sergeant posted to a remote island suggested a concept that would become the tokamak; physicist Andrei Sakharov completed the projects for the first reactor in 1950. That same year, the claim (then proven fraudulent) that fusion had been achieved in Argentina inspired Lyman Spitzer, an American physicist, to develop the stellarator. The importance of international collaboration to achieve fusion was recognized already during the cold war (it helped that fusion has no military applications), and in 1985 Gorbachev and Reagan agreed to start a collaborative international project to develop fusion energy, laying the basis for the ITER project.

Among scientists, a period of tremendous enthusiasm in the 1960s was followed by a decade of doubt and skepticism when it was realized that the problem was more complex than initially thought. In the 1980s, on the wake of a new wave of enthusiasm, it was believed that fusion would be on the grid within 50 years, and indeed until 2000 advances were fast. But to take the next step a new machine was needed, bigger, more complex: ITER, which is likely the most complex machine ever built.  “I know I will be retired by the time ITER is successful” says Henderson, “so I’m like the guy building a cathedral, who knows he is gonna […] spend his entire career putting bricks together, but he will never see the end piece.”

Indeed, ITER is more than a decade behind schedule — first plasma was originally planned for 2016 — and several billion dollars over budget. In a management assessment back in 2013 the problem was pinned down as poor management, ill-defined decision-making processes and poor communications within the project. In 2015 a new Director General was appointed, Bernard Bigot. ITER now has a new date for first plasma, Christmas 2025. “I think ITER will probably work; it will demonstrate that fusion is doable,” says Laberge. “They are gonna blow their budget and their schedule big time, it will burn money at twice the rate you need to, but it will get built and it will work, and this will give a big shot in the arm of fusion.”

One point everybody seems to agree on is that more funding is needed to develop fusion. “The more money you put in, the faster the return. And we have really being putting in peanuts,” comments Henderson. “Fusion is about 20 billions for 20 years. One billion a year. One fancy bridge a year. Peanuts! Let’s do it!” says Laberge. “How long it will take to achieve fusion? At current levels of financing, it will take approximately the age of the universe,” concludes Lerner.

With its beautiful images, helpful animations and an engaging soundtrack, the documentary, which is all narrated through interviews and original clips, is informative and enjoyable. It does not shy away from the challenges and doubts about the feasibility of a complex project such as ITER, but keeps a positive outlook.  It is a welcome reminder that achieving fusion is an extremely important goal, and all potential avenues need to be explored. Whether expert on fusion or curious onlooker, in “Let there be light” there is something for everyone.