“A milestone,” it is according to the US Department of Energy. It confirms that researchers in California have succeeded in producing 3.15 megajoules of energy with nuclear fusion by heating a capsule of fuel with 2.05 megajoules of laser energy. That’s not much in absolute terms – 1 MJ is about what it takes to boil a few liters of water – but it is the first time that a fusion reaction produces more energy than it costs. “That is an essential condition if we ever want to use nuclear fusion as an energy source,” says plasma physicist Dirk Van Eester (Royal Military School). “So this is an important achievement.”
In nuclear fusion, hydrogen nuclei fuse to form a helium nucleus, a process that releases an enormous amount of energy. To achieve this, the enormous repulsive forces between atomic nuclei must be overcome, and this is only possible at very high pressure and temperature. It is the process that underlies the energy produced by the sun and other stars. Because nuclear fusion produces no long-lived radioactive waste, and can produce a great deal of energy from a little abundant fuel, some say it is the ultimate energy source.
In the sun, the enormous gravity causes atomic nuclei to fuse. However, mimicking the conditions in the sun on Earth is no easy feat. And because it takes so much energy to create the right conditions for fusion, until recently it proved impossible to get more out of it than it took in. The Americans experimented with so-called ‘inertial fusion’, in which hydrogen nuclei are enclosed in a small capsule that is heated with lasers. In what follows, the capsule vaporizes and the fuel implodes, resulting in a fusion reaction lasting several billionths of a second.
“An important step forward on a lab scale”, says Vincent Massaut, affiliated with the nuclear study center SCK. “At the same time, electricity production with inertial nuclear fusion is still a long way off.” If only because we are talking about completely different orders of magnitude. “The researchers can now allow such a reaction to take place in their lab once a day, because the entire system has to be fine-tuned each time. While in a reactor with the power of Doel 3, a thousand capsules per second would have to be fired.”
An important side note is also that the experiment only yielded net energy if you look at the last step of the entire process. If you zoom out, the profit evaporates, because about 400 MJ of electrical energy was needed to produce the 2.05 MJ of laser energy. This is because the lasers are very inefficient. “And I don’t immediately see how they can solve that problem,” says Van Eester.
Eternal for within 30 years
If we ever want to cook and drive around on fusion-generated electricity, we may have to take a different approach. In a so-called tokamak, a doughnut-shaped reactor, hydrogen atoms are heated to a plasma, an electrically charged gas, in which fusion reactions take place. Strong magnetic fields keep that plasma in place. Earlier this year, scientists in the British-European pilot reactor JET (Joint European Torus) succeeded in producing 59 MJ of energy with a five-second fusion reaction at 150 million degrees. They would have needed three times as much energy to do that.
The ITER reactor that is being built in the south of France has the ambition to initiate a fusion reaction that will sustain itself for a longer period of time, without the need to add energy to the system. That should produce ten times more energy than was pumped into it.
Tokamaks face their own challenges. For example, a lot of electricity is needed to heat the plasma and generate the powerful magnetic fields that must keep the plasma under control. The reactor wall must withstand the extreme temperatures and neutron collisions that are released during the fusion reaction. “However, the technical hurdles seem less than the hurdles in scaling up inertial fusion,” says Van Eester.
In any case, ITER will not yet generate electricity with the energy produced. That will be the task of a next generation, even bigger demo actors. According to Eurofusion, the consortium of European nuclear fusion research institutes, if everything goes according to plan, they could be there around 2050. But nuclear fusion has always been ‘for within 30 years’, the critics sometimes joke. And will the technology still be on time at all? “We are definitely taking steps forward,” says Van Eester. “I think that a clean energy source, which takes up much less space than renewable energy, will always be able to make a valuable contribution.”
According to energy expert Pieter Fingerhoets, who recently investigated with colleagues at VITO/EnergyVille what the future energy system could look like, nuclear technology may still have a – limited – role in this. “An important question is then not only whether fusion will be able to generate net electricity, but also whether this can be done in a cost-effective manner,” says Fingerhoets. “We are still a long way from that.”
