A well-earned shutdown time for JET

Eurofusion 21st November 2016

JET is equipped with an ITER-like plasma facing wall, tungsten divertor and beryllium wall.

As EUROfusion’s flagship device JET went into shutdown on November 15, 2016, for the current year, JET researchers and engineers marked the 2015-2016 experimental campaign as one of the most successful in the long history of JET. JET was able to meet almost all of the goals set for the campaign.

Head of the JET Exploitation Unit, Lorne Horton, says that the campaign had three highlights: rehearsal of the procedures for future tritium-tritium and deuterium-tritium experiments, the hydrogen campaign during which physicists learned about the dependence of plasma parameters on the mass of the hydrogen fuel used, and the high-power deuterium campaign. And all these experiments achieved expected results.

This success means that JET is right on track for carrying out the tritium-tritium and deuterium-tritium experiments in upcoming campaigns – experiments that will be crucial foundations when ITER begins operations in the future to prove the feasibility of fusion energy.

Achieving reliable high-power Neutral Beam Injection (NBI) was one aspect of the above-mentioned goals. NBI is a method of providing additional heating and current drive to the plasma by using a beam of high velocity neutral atoms injected into the plasma. In October 2016 alone, JET was able to achieve 68 high power NBI pulses. To put the number in perspective, this is more than the entire number of high power pulses obtained over the past five years! Dragoslav Ciric, Tokamak Operations Manager, was delighted with recent operations. “I haven’t seen so many smiley faces in the JET Control Room for many years. This is the best indicator that we, as the JET Operator, did well in the last five weeks.”

Head of EUROfusion’s ITER physics department Xavier Litaudon presented the JET campaign results during the 2016 Fusion Energy Conference, and it was very well received by the community. “Apart from JET’s technical reliability, we were able to observe some very interesting and new physics,” he says. “For example, during the high-power deuterium campaign, we developed ITER operating scenarios that were much more stable than what we had before,” he states. Lorne is also excited about the high-power deuterium campaign which explored the performance limits of JET’s new ITER-like Wall. “We have extended operation greatly, reaching maximum performance levels of many parameters previously seen only with JET’s old carbon wall. 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,” he says.

Xavier also points out that the other important result was achieving the isotope scaling. “When we move from hydrogen plasma, to deuterium plasma and to tritium, we are changing the mass of the plasma, and we need to understand how the plasma properties and fusion performance change. New and fascinating results have been obtained during the recent JET hydrogen campaign that need to be understood for ITER extrapolation with our first principle modelling tools,” he explains.

With JET in shutdown now, EUROfusion will start with preparations for the next scientific programme. “Of course, we are going to analyse the results in detail, in order to prepare for the next experimental campaigns, and draw some conclusions for ITER operation. And, the focus will remain on the completion of the tritium-tritium operation in 2018 and the deuterium-tritium one in 2019-2020,” explains Xavier. The device is also going to get some sprucing up, starting with upgraded components of the NBI system and a new Shattered Pellet Injector technology, which will allow researchers to study disruption mitigation scenarios. So the shutdown looks likely to be as busy as the experimental sessions for researchers and engineers, but JET plasma operation will take a well-deserved break till it starts again next year.