JET is the central experiment of the European Fusion Programme. It is closest to ITER – in terms of size, of its inner reactor wall materials and of its capability to operate with tritium. As a joint European experiment, JET has always been managed along the strategy that is now forming the Fusion Roadmap. The main objectives of the JET Component of the 2014 Work Programme are the exploitation of the ITER-Like Wall and the preparation for planned experiments with deuterium-tritium fuel.

Exploiting the ITER-Like Wall

After having successfully demonstrated good plasma performance with a vessel wall that uses the same material mix (tungsten and beryllium) planned for ITER, JET will continue to widen the range of plasma operation to more challenging scenarios. It will further study high confinement modes and develop robust operation scenarios for ITER. Methods to predict and mitigate harmful plasma instabilities such as disruptions will be developed. Tungsten from the wall can accumulate in the plasma core. This is a critical issue for ITER and JET will therefore demonstrate an acceptable tungsten concentration for the foreseen ITER regimes. Following these experiments, JET will be shut down to re-install the “ITER-like Antenna” (an antenna which is expected to provide more central heating and efficient tungsten control), to relocate the High Frequency Pellet Injection so as to better combine its plasma fuelling and ELM control missions and to replace wall tiles, which are used to analyse how plasma interacts with the wall materials. (Ed. note: Edge Localised Modes or ELMs are instabilities that harm the plasma performance.) Important questions are, for example, how the vessel wall erodes, how this material migrates through the plasma and re-deposits on a different location of the wall, and how much dust is formed inside the vessel. In a similar manner, mirrors, which are used for optical measurements, are removed and analysed to determine their expected lifetime under ITER plasma conditions.

Preparing for a deuterium-tritium campaign

In order to achieve the best possible preparation for ITER, an experimental campaign with deuterium and tritium (D-T) is planned on JET (Ed. note: Deuterium-tritium fusion will be used in fusion power plants while fusion experiments normally use deuterium-deuterium reactions to avoid working with radioactive tritium.). In this way, the combination of ITER wall materials, highest possible plasma performance and actual fusion conditions will be simultaneously demonstrated. To support these experiments, a series of enhancements to JET’s measurement capabilities is presently being launched. D-T experiments at JET will also be used to provide unique technological input to ITER. This will include determining the effect of the fast fusion neutrons on the materials that comprise the reactor, assessing the radiation dose expected in areas of ITER where manned access is planned, and gaining experience on the handling of tritium and of tritiated waste. Together with Fusion for Energy and the ITER Organization, a number of projects have been developed, which will be carried out during the D-T experiments. One key project is the calibration of the JET neutron measurement equipment at the energy of D-T fusion neutrons, a process that is prototypical of what will be required at ITER.