EUROfusion’s flagship facility was literally jumping for joy. The Joint European Torus (JET), the only fusion device capable of operating deuterium-tritium, has just delivered the most successful experimental campaign of the last five years. The newest results prepare the ground properly for the deuterium-tritium (DT) campaign, scheduled for 2019.

The staff was all smiles

“I haven’t seen so many smiley faces in the Control Room for years. This is the best indicator that we, as the JET Operator, did well”, says a relieved Dragoslav Ciric, Tokamak Operations Manager at the Culham Centre for Fusion Energy (CCFE) and home to JET. What made this campaign so successful was the proof of high machine reliability, high heating power and good plasma diagnosis.

Photo taken during the last shift of this year´s JET experiments. The campaign has provided plenty of valid data for the scientists. Picture: © protected by United Kingdom Atomic Energy Authority

Photo taken during the last shift of this year´s JET experiments. The campaign has provided plenty of valid data for the scientists. Picture: © protected by United Kingdom Atomic Energy Authority

Achieving reliable high-power beams was one goal. The Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating (ICRH) delivered a machine performance of 23 to 26 MW as well as 4 to 6 MW with every JET pulse. NBI is a method of providing additional heating and current drive to the plasma using a beam of high velocity neutral atoms. In October 2016 alone, JET was able to achieve 68 high power NBI pulses. To put these numbers into perspective, this is more than the entire number of high power pulses obtained over the past five years!

Access to a new regime

Bringing the machine back on track was a tricky task since technical issues have hampered the tokamak for quite some time. The primary problem was related to the breakdowns (arcs) in the neutral beam high voltage transmission system. They were difficult to diagnose. The arcs were causing cross-talk between systems which had made the underlying cause difficult to find.  An ad-hoc task force with daily meetings had successfully analysed the problems. The experts deployed additional diagnostics on the transmission system, which rapidly brought JET back into operation, albeit with a maximum power limited to 28 MW. During the recent deuterium campaign, the system routinely functioned above 25 MW, providing access to a regime that has never been accessible on JET – with the new ITER-like wall, made of tungsten and beryllium, “We are now more confident of reaching high levels of fusion performance in JET with the ITER wall materials and of a rapid and successful push to high performance in ITER itself,” says JET’s Exploitation Manager Lorne Horton.

Pushing ITER to high performances

The results were presented during the 2016 Fusion Energy Conference. “Apart from JET’s technical reliability, we observed some very interesting and new physics,” says Xavier Litaudon, Head of EUROfusion’s ITER physics department. “For example, during the high-power deuterium campaign, we developed ITER operating scenarios that were much more stable than what we had achieved before,” he states.

Focussing on the DT campaign

With JET now in shutdown, EUROfusion will start with preparations for the next scientific programme. “We are going to analyse the results in detail, in order to prepare for the next campaigns, and draw some conclusions for ITER operation. The focus remains on the completion of the tritium-tritium operation in 2018 and deuterium-tritium in 2019-2020,” explains Xavier from EUROfusion. In the meantime, JET will receive upgraded components for the NBI system – in collaboration with ITER and US scientists and new Shattered Pellet Injector, which will allow the researchers to study disruption mitigation scenarios, and should also push JET up to its full power of 34 MW.