The amount of energy out was more than in. fusion scientists have been trying to get energy gain for 70 years. At 1 a.m. on 5 December, researchers at the National Ignition Facility in California exploded a small capsule of fusion fuel with 2.05 megajoules of laser light.

Anne White is a physicist at the Massachusetts Institute of Technology who was not involved in the work.

Mark Herrmann is the program director for weapons physics and design at Lawrence Livermore National Laboratory.

The result, announced today by officials at the U.S. Department of Energy, represents a shot in the arm for fusion researchers. The promise of plentiful, carbon-free energy can be found in fusion. It takes temperatures of millions of degrees Celsius to get hydrogen ion to fusion into helium. It is possible, at least for a short time, according to the NIF result. It's a lot of energy. Steven Rose is a physicist at Imperial College London.

fusion power stations are still a long way from being a reality. NIF was never meant to be used for generating power. Its primary function is to create thermonuclear explosions and provide data to make sure the U.S. arsenal of nuclear weapons is safe. Many researchers think tokamaks are a better design for commercial power because they can last longer. The fuel and magnetic fields are trapped in a tokamak. The challenge is to make it easy to use.

The ITER reactor under construction in France is not simple. It will not reach breakeven until the late 17th century. Proponents of laser-based fusion will be looking for funding to see if they can compete with the tokamaks.

In 2010 the NIF began itsignition campaign. The building it is housed in is the size of three U.S. football fields. The beams are focused on the target, which is a gold can the size of a pencil. The diamond shell of the capsule is destroyed by the x-rays that come from the heated gold. The fuel is compressed and heated by the blasted diamond.

fusion reactions begin in a central hot spot if the compression of the fuel is symmetrical. After more than a decade of effort, NIF scientists declared they had achieved that milestone after a shot in August 2021. The threshold it passed last week was set by the National Nuclear Security Administration.

It was difficult to go that extra mile. The NIF team couldn't duplicate it after August 2021. They used a smooth diamond capsule and it was the most spherical they had made. It was necessary to learn how to make the capsule better. The thicker the capsule, the stronger the implosion, but it needed a longer, more powerful laser pulse. The laser was adjusted so that it could squeeze out more juice.

A shot in September showed the NIF researchers they were on the right track, but the symmetry was not good. They were able to get a more spherical implosion when they adjusted the energy of the laser. The physicists at the University of Rochester have demonstrated the physics phenomenon.

NIF fell short if it meant producing more energy than electricity. It takes hundreds of megajoules of electricity to produce the 2 MJ of laser light and 3MJ of fusion energy. The repetition rate would need to be raised from one shot per day to 10 per second. It would take one million capsules a day to clear away.

Betti says that the NIF scheme is inefficient. The x-rays that actually spark fusion are generated by the laser blast of the gold can. He says that only a small amount of the laser energy gets into the fuel. Laser beams fire directly onto a fuel capsule and deposit 5% of their energy, which is what he favors. Insturment fusion for power generation is not funded by the DOE. Betti and White co-authored a report with the agency's fusion energy sciences advisory committee in 2020. There is no clear way to do a new paradigm.

Researchers hope laser fusion will get more funding now that NIF has cracked the problem. Betti jokes that he wants to pass the baton. He says this is a very important step. We accomplished it so I can retire.