Scientists test solutions for future fusion power plants

The Joint European Torus (JET) is a fusion experiment of the donut-shaped tokamak design located at Culham Centre for Fusion Energy in Oxfordshire, UK. The facility uses magnetic fields to keep the hot, ionised gas (plasma) away from the vessel's interior walls, enabling safe operation at 150 million degrees Celsius - ten times the temperature at the core of the Sun.

JET commenced operation in 1983 as a joint European project. Later, it underwent several enhancements to improve its performance. In 1991, JET became the world's first reactor to operate using a 50–50 mix of tritium and deuterium. The facility set numerous fusion records including a record Q-plasma (the ratio of the fusion power produced to the external power put in to heat the plasma) of 0.64 in 1997, and a fusion energy record output of 59 megajoules in a five-second pulse in December 2021. 

Built by Europe and used collaboratively by European researchers over its lifetime, JET became UKAEA property in October 2021, celebrated its 40th anniversary in June this year, and will cease operations at the end of 2023.

The experimental campaign at JET was conducted by over European 300 scientists participating in EUROfusion together with engineering and scientific technical staff at the United Kingdom Atomic Energy Authority (UKAEA). A group of Polish scientists from the Institute of Plasma Physics and Laser Microfusion in Warsaw took part in the campaign.

JET is the only existing facility in which a large number of thermonuclear reactions can be carried out. The high-performance deuterium-tritium fuel mix currently used there will be used in future fusion power plants. The goal of the completed experimental campaign was to develop the technologies and methodologies necessary for future fusion power plants.

Most fusion experiments use fuels like hydrogen or deuterium alone. Testing with deuterium-tritium mix is essential to get as close as possible to the conditions of a real fusion power plant.’

'The experiments at JET have optimized fusion reactions in deuterium-tritium and developed techniques to manage fuel retention, heat exhaust and materials evolution. This has generated crucial insights for the design and operation of future reactors like the international ITER experiment and the DEMO demonstration fusion power plant as well as for all other efforts worldwide to develop fusion power plants,’ the scientists report.

Explaining the importance of the experimental campaign, scientists combined the past and future in fusion research, saying: ‘The experimental campaign built on experiments at the end of 2021, enhancing our understanding of deuterium-tritium plasmas.’

The scientists tested new concepts (developed in smaller European tokamaks) in JET, initially with deuterium and then with a deuterium-tritium fuel mix. This research is key to help understand how processes observed in smaller devices will scale to larger future fusion projects.

According to the scientists, the campaign marks progress in working with tritium fuel. 'JET has made significant strides in managing the fuel component tritium, pioneering novel monitoring and cleaning technologies including laser-based diagnostic methods like LID-QMS (Laser Induced Desorption - Quadrupole Mass Spectrometry). These innovations are crucial for ITER's future operations, ensuring accurate tritium accountancy and enhancing operational safety,’ the EUROfusion consortium reports. 

It adds: ’A major success of the DTE3 campaign was its ability to replicate the high-fusion-energy experiments from 2021’s second deuterium-tritium experimental campaign (DTE2). This accomplishment highlights the reliability and maturity of JET's operational methodologies that are essential for the ITER project's future success.'

The campaign involved testing diverse operational scenarios to efficiently manage heat exhaust from the hot, ionised gas fuel (plasma). Researchers focused on dispersing energy at the plasma edge while maintaining high energy levels in the plasma core, a critical balance for reactor feasibility. This included minimizing or eliminating energy outbursts from plasma edge instabilities and implementing innovative heat load management techniques like feedback-controlled impurity gas injections to create a localised radiator plasma zone around the X-point. Additionally, the team demonstrated real-time control of the D-T fuel mix by injecting gas and frozen deuterium pellets, a key method for controlling fusion reactions. These advancements are instrumental for the successful operation of future fusion reactors.

The authors of the project also mention deepening knowledge about the effects of high-energy neutrons. 'Focusing on the impact of fusion-born 14.1 MeV neutrons that carry the energy from fusion reactions out of the plasma, the campaign provided insights into their effects on cooling systems and electronics, the latter in collaboration with CERN. This knowledge is essential for designing safe, more efficient future fusion reactors,’ they write.

The Polish Institute of Plasma Physics and Laser Microfusion, participating in the work with JET, represents the Polish scientific and research community in the EUROfusion consortium project and coordinates fusion research in Poland. For this purpose, the Scientific and Industrial Centre of New Energy Technologies (CeNTE) was established to combine the research potential of more than 20 Polish institutions, which include research institutes, universities, Polish Academy of Sciences institutes and industrial companies. (PAP)

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