The first delivery of tritium has arrived at the Culham Centre for Fusion Energy (CCFE), home of the Joint European Torus (JET). Europe’s flagship research facility is preparing for another high-power deuterium-tritium (DT) campaign, the first since 1997 during which 16 megawatts of fusion power were produced. Deuterium-tritium operations are rare events and spark curiosity amongst the scientific community.

A question of licensing and safety

Usually, experiments at JET are fuelled by deuterium, sometimes supplemented by campaigns with hydrogen plasmas. While these plasmas behave in a similar way to the targeted DT plasmas, the nuclear fusion experiments carried out in 1997 showed that there are significant differences compared to DT. Since then, JET has undergone major changes, in particular, the vessel wall has been rebuilt using beryllium and tungsten making it more ITER-like with a considerable impact on plasma behaviour. For this reason, the ITER-like wall in JET now needs to be tested under conditions similar to those that the real ITER wall will have to face.

“For licensing reasons, only a limited amount of tritium may be transferred into the JET tritium storage facility at any one time. Additional batches will be delivered later in order to make up a total amount of 55 grams in addition to the approximately 5 grams still remaining from 1997. In this way, we will have the amount we need for the scheduled campaign”, states Tim Jones, CCFE Senior Manager for the JET Operating Contract. Realising a DT campaign at JET also means ensuring that the operating staff has been trained to safely work with radioactive tritium. Since JET is the only machine capable of operating with tritium, this training is a unique opportunity to prepare for ITER.

JET – invaluable for ITER

EUROfusion scientists are currently increasing their focus on the preparation of the upcoming DT campaign. This will be a major step towards achieving an understanding of ITER’s plasma. “We are now exploring the performance limits of deuterium plasmas. The goal of deuterium-tritium experiments is to prove that our findings can be applied to the fuel mixture that will be used in a fusion reactor”, says Lorne Horton, Head of the JET Exploitation Unit. “The results of the tritium experiments are invaluable for ITER, which must demonstrate the feasibility of fusion as an energy source.”

Extending the JET schedule

At present, JET experiments are scheduled to end in 2018, when Europe’s largest experiment on fusion will slowly close its massive torus hall doors. EUROfusion has already approached the European Commission concerning an extension of JET operation by two years, primarily for scientific reasons. This wish is supported by the recent outcome of a working group on the assessment
of the ‘D-T readiness’ of JET. Richard J. Hawryluk, professor at the Princeton Plasma Physics Laboratory (USA), led the ad hoc group, which carried out the results in the first half of 2015. Their conclusion: A DT campaign can only entirely accomplish its full objectives within the extended schedule.
Following the working group’s reasoning in early July, the EUROfusion members unanimously endorsed the proposed extension to 2020 during the General Assembly, the ultimate decision making body made up of representatives from all Research Units. “An extended schedule would give us additional time to prepare the experiments and exploit the ITER-like wall more intensively. We hope to receive an in principle agreement from the European Commission after summer, which will enable us to adjust the schedule accordingly. However, we are aware that the formal decision regarding the future of the EUROfusion programme beyond 2018 can only be made in 2017”, says Tony Donné, EUROfusion Programme Manager.

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