Fusion power – Opportunities, challenges, timeframes
Munich, 25 January 2024
Nuclear fusion is a dream of humanity, as it holds the prospect of being able to tap into the same source of energy that powers the sun. The technical challenges are enormous – but around one year ago, plasma ignition was achieved for the first time in the US. This marked the moment when it became less a question of whether humanity’s dream of nuclear fusion will become reality and more a question of when and how. Experts and interested parties discussed these questions in an online edition of acatech am Dienstag on 16 January.
In his welcome address, acatech President Jan Wörner gave the around 160 guests an introduction to the fundamental physics and technical basics of fusion. He gave an initial overview of the two basic approaches to fusion: magnetic fusion and laser-based fusion. Experts then went into these approaches in detail.
Different concepts of nuclear fusion
Sibylle Günter, Scientific Director of the Max Planck Institute for Plasma Physics and acatech member, explained the fundamentals of and the experimental facilities for fusion research and magnetic fusion. The simplest process involves the fusion of deuterium and tritium to form helium and neutrons, said Sibylle Günter. In fusion, mass is converted into energy, producing approximately a million times more energy than in combustion. The global availability of the two fuels required is good. For fusion “ignition”, the deuterium-tritium plasma must be heated to 200 million degrees Celsius. No containment material could withstand such temperatures, plus the plasma would instantly cool on contact. For that reason, magnetism must be used to stabilise the plasma in a vacuum. An alternative is inertial fusion, where a millimetre-sized pellet of fusion material is very quickly brought up to temperature by laser bombardment. There are thus essentially two different approaches to nuclear fusion: magnetic fusion and inertial (or laser) fusion.
The two concepts of magnetic fusion – tokamak and stellarator:
- In a tokamak, the magnetic confinement area is created by external coils and a current driven through the plasma. It therefore only operates in pulsed mode. However, a pulse can last several hours.
- In a stellarator, the magnetic field cage is formed by a single coil system – unlike with a tokamak, there is no plasma current and hence no transformer. For that reason, stellarators are suitable for continuous operation.
Fusion power plants use the energy generated by fusion reactions (fusion of atomic nuclei). However, the majority of the energy produced by fusion in the form of energetic neutrons is absorbed by the walls of the reactor and converted into heat. A fusion power plant uses this thermal energy to create steam. This steam drives turbines which then generate electricity as in a conventional power plant.
There is a tokamak experimental facility in Garching near Munich and a stellarator research centre in Greifswald. Sibylle Günter and her team are testing these two concepts to find out which is more suitable. Research is already well advanced: in an ambitious scenario, the construction of a functional fusion power plant in Germany could be achieved in approximately 20 years.
In the alternative method of inertial fusion, a tiny pellet is heated until it explodes. The pressure is similar to that in the sun’s core. What is important is that irradiation is uniform, said Sibylle Günter. In 2022, during a laser fusion experiment in the Lawrence Livermore National Laboratory in the US, approximately one per cent of the energy expended on heating the pellet was transformed into fusion energy. This was a breakthrough: for the first time, more heat was produced by fusion than by external heating.
Nuclear fusion, said Sibylle Günter, has major advantages over nuclear fission in terms of safety: uncontrolled nuclear chain reactions, which are an eventuality in the case of nuclear power plants, are a physical impossibility with fusion reactors. The number of fusion reactions between hydrogen and tritium is externally determined by the input of fuel. Once the fuel runs out, the reaction stops. In addition, nuclear fusion does not produce highly radioactive waste which has to be put into long-term storage in underground repositories.
Laser fusion
Constantin Häfner, Representative for Fusion Research at the Fraunhofer-Gesellschaft and head of the BMBF expert commission on laser inertial fusion, began his talk with a look at the origins of laser fusion. Just one year after laser technology was invented, in 1961, US physicist John Nuckolls proposed the use of a laser to focus energy on a target with pinpoint accuracy to trigger a fusion reaction. However, sufficiently powerful lasers did not exist at that time. It was decades before lasers were able to heat up the fusion material sufficiently rapidly and to the required temperature. In 2009, the National Ignition Facility (NIF) was built at the Lawrence Livermore National Laboratory (LLNL) in California (USA). In this scientific research centre, laser fusion experiments have been taking place since 2011. In August 2021, 1.35 megajoules (MJ) were produced: 1.9 MJ of laser energy was input into the chamber to yield this 1.35 MJ. At the beginning of December 2022, output was increased to 3.15 MJ. This result attracted worldwide attention. The NIF is the world’s largest and most energetic laser and is the size of three football fields. The focus of experiments is fusion plasma research, not energy production.
Markus Roth, Professor of Laser and Plasma Physics at TU Darmstadt and Chief Science Officer of Focused Energy, a start-up he co-founded, represented the latter at acatech am Dienstag. The object of this German-US company is to bring laser-based nuclear fusion to market maturity. According to Markus Roth, the strengths of laser fusion are modularity and the physical separation of laser driver and reactor. The lasers are in a separate building and can be serviced or replaced during operation. The design and internal structure of the reactor can be kept very simple, as its only purpose is to absorb the energy and re-release the fusion energy in the form of heat. Markus Roth regards direct drive and fast ignition to be the most promising and robust approach to laser fusion.
The final speaker was Tony Donné, who until recently was Programme Manager with EUROfusion. Mr Donné highlighted the European perspective. In Europe, remarkable results have already been achieved with magnetic confinement in the Joint European Torus, setting a new world record for fusion energy. He described the ongoing importance of the International Thermonuclear Reactor ITER and concentrated on the European DEMOnstration power plant, DEMO, whose long-term goal is to produce electricity from fusion energy. DEMO, like ITER, is based on the tokamak principle and is set to be the first facility to test nuclear fusion on an industrial scale.
Multifaceted discussion
The discussion moderated by Marc-Denis Weitze, acatech Office, concerned the raw materials such as deuterium and tritium and focussed on the end products. During the discussion, Sibylle Günter reiterated that fusion only results in short-lived radioactive products that do not require final disposal. The tritium that is released has a half-life of 12 years, so deep geological storage is not required.
Political debate on fusion energy is in full swing. The Federal Ministry of Education and Research (BMBF) has set up an international expert commission which has prepared a memorandum on the status of and the steps required in research and development. The BMBF’s subsequent position paper outlines the framework for the required research in the areas of magnetic and laser fusion and forms the basis for the BMBF’s funding programme, which is in the pipeline.
Markus Roth emphasised that the funding and development of fusion energy certainly will not render investment in renewable energy obsolete: clean fusion energy will not supply power to the energy system to any appreciable extent until after the middle of this century. However, if we mastered the key technologies here, they could become a European export. An industrial ecosystem now needs to be created. Also, political leaders must develop a suitable, reliable legal framework.
The final subject of discussion was whether there should be parallel investment in the competing technologies and if so, for how long? Will one of them come out on top in a few years’ time or will it take decades? In the case of the two concepts of magnetic fusion presented, Sibylle Günter estimates that we could have a decision in a matter of years. Constantin Häfner stated that from today’s perspective both the principles of magnetic and laser fusion could ultimately be used in a fusion power plant. The crucial task now is to systematically continue advancing the research in Germany, actively involving industry and paving the way for a fusion power plant. Whichever one wins out in the end, the key is to get from basic research to a fusion power plant.
Closing the event, Jan Wörner advised against favouring one technology over another too soon – experience has shown that it is necessary to pursue different approaches to find the best solution or solutions.
Further information
Position paper on fusion research (in German)
Memorandum Laser Inertial Fusion Energy – Federal Ministry of Education and Research