The last 12 months has seen scientists and engineers work around the clock to achieve high performance at Europe’s flagship fusion device, the Joint European Torus (JET) at Culham – despite the ongoing challenges posed by the global pandemic.
Early on in 2020 – prior to the pandemic – UKAEA completed a number of engineering upgrades on JET. They included replacing the machine hall’s 50-metre-long door seal – a not insignificant task, considering the door itself weighs 400 tonnes.
Work then followed on JET plasma experiments – with the focus on preparing for key tests planned for 2021 using deuterium and tritium, the fuel mix for delivering fusion power – until they were halted because of England’s first Covid lockdown. When work on JET did restart – along with a newly-configured control room layout and a number of other protection measures to ensure social distancing – it was with the good news that months of painstaking work on JET’s new Exhaust Detritiation System (EDS) had been successfully completed. The EDS is a safety system which removes tritium from JET’s exhaust gases, and is required for upcoming tritium experiments.
This major achievement meant that the system was now connected to JET’s Active Gas Handling System (AGHS) – the plant that enables tritium to be recovered from the plasma exhaust, processed, measured and stored for re-injection; crucial to allow scientists to experiment with tritium.
Heating records broken
Further uplifting news followed as the experiments posted record plasma performance and heating power. European fusion scientists were able to call upon the required 30 megawatts of Neutral Beam Injection heating power from the very first day of experiments after the outage earlier in the year (unprecedented in the history of JET). This meant records for the total heating power into JET were quickly broken – another accomplishment to celebrate.
Another key success of these tests was demonstration that JET’s newly-installed Shattered Pellet Injector could be an effective part of the protection systems for the ITER international fusion project being built in France. In particular, it can mitigate disruptions (very high electromagnetic loads on the tokamak) and runaway electrons which can significantly damage internal structures if not suitably controlled. ITER have subsequently thanked the team for the major results achieved with the JET experiments this past year.
On course for tritium operations
The next significant step was completion of commissioning AGHS, thus meeting a major milestone – that of being ready to expand the ‘tritium boundary’. Essentially this ensures tritium can be moved from the AGHS to the torus and to the neutral beam injection heating system. Before actually expanding the tritium boundary, the scientific team on JET completed the rehearsal phase – a point at which systems and procedures for moving tritium to the torus are tested and trialled.
In September, new JET plasma tests achieved deuterium fusion power (measured by the production of ‘DD’ deuterium-deuterium fusion neutrons) comparable with the best previously reported for deuterium plasmas in JET. The previous DD fusion record had stood for many years and these latest results were the first time that such high performance had been achieved with a metal (beryllium and tungsten) first wall – the same materials that will be used in ITER.
Earlier this month, JET was then able to start to experiment with tritium-tritium pulses in the machine. This is the first time since 1997 that significant quantities of tritium have been used in JET plasmas – and a crucial step towards 2021’s eagerly anticipated deuterium-tritium experiments on JET
Joe Milnes, JET Operating Contract Senior Manager at UKAEA, said: “Achieving these very challenging milestones while figuring out how to remotely operate the biggest and most complicated tokamak in the world, and doing this safely with less than a tenth of the JET workforce based on site, is something the team should be immensely proud of.”