Why Is There a “Miniature Sun” Just Outside Oxford?
How the Joint European Torus harnesses fusion energy at the Culham laboratory
The Joint European Torus (JET) based at the Culham Centre for Fusion Energy (CCFE) in Oxfordshire in the UK is the world’s largest and most successful fusion experiment. JET is now the central point of the European fusion research program with more than 350 scientists and engineers from all over Europe working there, but choosing a site for JET in the 1970s was not a straightforward process.
The primary purpose of JET is to study fusion in conditions similar to those required for a power plant, in order to pave the way for fusion as a commercial source of energy. The process of nuclear fusion is a reaction that combines several atomic nuclei to produce one or more different nuclei and subatomic particles. The difference in mass between the products and reactants can lead to the release of very large amounts of energy. Fusion is the process that fuels main-sequence stars like the Sun.
Atomic nuclei must be held together long enough for fusion reactions to take place. In the Sun, this is a result of huge gravitational forces. Here on Earth, scientists attempt to hold nuclei together by instead using powerful magnetic fields, but this poses some big challenges for keeping the extremely hot matter from touching the walls of their container. Whereas the core of the Sun has a temperature of 15 million ºC, the interior of JET has reached in excess of 200 million ºC.
JET has a “tokamak” design, with magnets that confine plasma in the shape of a doughnut. Plasma is the fourth state of matter, a gas that is so hot that the charged particles that make up atoms can move independently of each other, allowing the plasma to be strongly influenced by electromagnetic forces. One method of heating the plasma is using neutral beam injection (NBI), where a beam of high-energy neutral particles transfers its energy through collisions with particles in the plasma.
The aim of JET is to achieve “breakeven”, where the energy produced is equal to the energy required to keep the plasma hot enough for fusion. JET uses a fuel mix of two forms of hydrogen, deuterium and tritium, to produce hydrogen and neutrons. This process is much cleaner than fission, with the waste products becoming relatively safe after a century. JET has set the current world record for fusion output, producing 16 MW for 24 MW of heating, but breakeven is still yet to be achieved. A new type of tokamak has been incorporated in the design for the International Experimental Reactor (ITER), which is currently under construction in the south of France, with plans to open in 2025. Recently, JET has been used to test aspects of the ITER design.
The first proposals for JET were completed in 1975, following the success of the Soviet T-3 tokamak in 1968. An agreement was reached to establish a “Joint Undertaking” status, whereby a JET Council would be formed in order to share power between the European Commission and the member states. However, the question of the site choice resulted in a large number of debates, with five different locations in Europe being proposed. This was narrowed down to the two sites that hosted a fusion research infrastructure at the time: Culham in the UK and Garching in Germany. Support for the Culham site stemmed from the academic and cultural appeal of Oxford as a location for multinational researchers, as well as a favourable infrastructure. Discussions to decide between them had lasted for nearly two years and remained in deadlock, with France, Denmark, Ireland, the Netherlands and the UK in support of Culham, and Germany and Luxemburg speaking in favour of Garching as the host.
Then, in the summer of 1977, a Frankfurt-bound Lufthansa aeroplane was taken hostage by terrorists and eventually landed in Somalia, where 86 passengers were held captive. The German chancellor, Helmut Schmidt, made the decision to storm the aeroplane, which was a successful operation, aided by intelligence and equipment from the British Special Air Service.
It is unclear the extent to which this event influenced the choice of site for JET, but, according to the German minutes, when British Prime Minister James Callaghan met with Schmidt five days later for a previously scheduled meeting, they were both friendly and respectful. Both agreed to not oppose the decision of the Council of Research Ministers and just a few days later, the Council reached their final decision to select the Culham site.
Following this tragic and dramatic turn of events, JET was constructed at a cost equivalent to 438 million US dollars, achieving its first plasma in 1983 and being opened in 1984 by Queen Elizabeth II. Despite concerns with regards to Brexit, which may result in the UK leaving Euratom (Europe’s nuclear agency which provides funding for JET), the European Commission and the UK Government agreed in March 2019 to extend JET operations until the end of 2020.