Fusion

Human life is based on solar radiation. Its energy comes from the fusion of hydrogen into helium, a process that has been going on for 4.6 billion years. During fusion, two light atomic nuclei fuse to form a heavier nucleus, releasing enormous amounts of energy. This inexhaustible, climate-neutral energy source – available 24/7 – should be harnessed on Earth in the future. Research institutions, industrial companies and start-ups around the world are working round-the-clock on concepts and technology modules for nuclear fusion power plants.

In particular, the fusion of the hydrogen isotopes deuterium and tritium to form helium has proven to be feasible. In order to trigger fusion, the so-called ‘Coulomb wall’ – a strong repulsive force between the nuclei – must first be overcome. This requires temperatures of around 150 million degrees Celsius. Under these conditions, the nuclei come within a femtometer of each other and under the influence of an even stronger nuclear force, which causes the isotopes to fuse into helium nuclei, each with two protons and two neutrons. One neutron remains. In total, the deuterium and tritium isotopes are heavier than the helium nucleus. According to Albert Einstein's theory of the equivalence of mass and energy, fusion releases binding energy, which amounts to 17.6 megaelectronvolts (MeV) or 9.2 x 104 kWh per gram. To put this into perspective, 1 kg of this deuterium-tritium mixture contains as much energy as 55,000 barrels of diesel or 18,630 tons of brown coal.

Laser and magnetic fusion

Commercial power plants require technologies that reliably ignite fusion, keep it running and utilize the energy released, a challenging task. Several times, however, California's Lawrence Livermore National Laboratory at its National Ignition Facility (NIF) has demonstrated that it can ignite a fusion plasma that sustains itself. The NIF relies on laser inertial confinement fusion. In its system, a short laser pulse causes a small fuel pellet to implode very quickly, generating the required pressures and temperatures. Since December 2022, the California institute has repeatedly succeeded in igniting a deuterium-tritium plasma using the world's largest and highest energy laser, thereby creating a fusion plasma that burns sustainably and has a high net gain of energy.

In addition to laser inertial confinement fusion, magnetic fusion is also on the global research agenda. There are two concepts for this: first, the tokamak, a torus-shaped type of fusion chamber in which the magnetic confinement is created by superimposed magnetic fields. A transformer coil usually induces the plasma current. The second concept is called the stellarator, with a complex, non-rotationally symmetrical fusion chamber. In the stellarator, the magnetic confinement is generated by a single external coil system that carries the current.

This is not enough for the fusion power plants of the future. The design must change completely; among other things, the flash lamps must be replaced by laser diodes in favor of efficiency. Such a diode-pumped laser system would have to perform at least 50 times better than the best lasers available today. The number of beam paths would have to at least double. Instead of one shot per day, 10 to 20 ignitions per second are required. This requires new, heavy-duty optics, new reactor materials, target injectors and target concepts, interchangeable reactor modules and new concepts for heat dissipation and utilization. Since the successful fusion experiment in December 2022, a global race has begun to bring all of these technology components to market maturity. In this competition, Fraunhofer ILT and many other institutes of the Fraunhofer-Gesellschaft are technology partners sought-after internationally.