The JET ‘Trace Tritium Experiments’ (TTE) Campaign was completed successfully. It was the first use of tritium in JET experiments under the EFDA organisation.

On 1 November, the JET ‘Trace Tritium Experiments’ (TTE) Campaign was brought to a successful conclusion. This Campaign marked the first use of tritium in JET experiments under the EFDA organisation with the Association Euratom – UKAEA as Operator.

The Scientific Co-ordination for the experiments came from staff in nine of the EFDA Associations. The Campaign was led by teams from ENEA (Italy), VR (Sweden) and UKAEA. There were also experimental neutron detector devices installed by Russian visitors to detect the 14 MeV neutrons emitted by the plasma DT reactions. This was the first active participation by Russian physicists in JET campaigns, and more visits are planned.

The experiments in TTE used tritium injected into the plasma either via gas introduction system or in the form of high velocity neutrals from the Neutral Beam Injection (NBI) system. The fraction of tritium in the plasma was always kept at ‘trace’ levels, i.e. <1-2% of the deuterium majority fuel. Some 25 experimental proposals gathered data during the TTE.

In total, over 160 JET pulses were supplied with tritium and there were no significant faults on the tritium systems. The rate of DT fusion reactions is about two orders of magnitude larger than that of DD reactions, and the energy of the emitted neutrons is distinctive – 14 MeV. When the tritium ions fuse with the majority deuterium ions, the neutrons ‘tag’ the motions of the tritium particles. By observing them it is thus possible to follow particle transport of a fuel ion in the plasma, something that is otherwise remarkably difficult to do. Tritium transport has been studied in all the foreseen ITER operating scenarios, including plasmas with internal transport barriers, and with scans of key physics parameters such as the normalised Larmor radius or plasma collisionality.

The re-establishment of a ‘full quota’ of 14 MeV neutron diagnostics on JET was one of the most important side benefits of this Campaign.

The amounts of tritium injected into any one plasma during this month-long experimental campaign were minute – only up to 5 mg per shot. “Although the tritium is injected in such small quantities into the plasma, it is supplied to the machine in gram quantities then recovered and recycled within the system”, explained UKAEA’s Tim Jones, who led the team undertaking the technical preparations. “Establishing this tritium supply and reprocessing capability is nearly as demanding on the JET Operator as providing the fuelling for a 50:50 Deuterium-Tritium (D-T) plasma.”

Derek Stork, Leader of EFDA-JET Task Force DT, said:
“The use of tritium in this precise, diagnostic, manner will yield invaluable information on the way in which fuel will be confined and transported in a future reactor, and also the way in which high energy tritium can provide plasma heating.”