D. King

On the challenge of plasma heating with the JET metallic wall

The major aspects linked to the use of the JET auxiliary heating systems: NBI, ICRF and LHCD, in the new JET ITER-like wall are presented. We show that although there were issues related to the operation of each system, efficient and safe plasma heating was obtained with room for higher power. For the NBI up to 25.7 MW was safely injected; issues that had to be tackled were mainly the beam shine-through and beam re-ionization before its entrance into the plasma. For the ICRF system, 5 MW were coupled in L-mode and 4 MW in H-mode; the main areas of concern were RF sheaths related heat loads and impurities production. For the LH, 2.5 MW were delivered without problems; arcing and generation of fast electron beams in front of the launcher that can lead to high heat loads were the keys issues. For each system, an overview will be given of: the main modifications implemented for safe use, their compatibility with the new metallic wall, the differences in behaviour compared with the previous carbon wall, with emphasis on heat loads and impurity content in the plasma.

Challenges in the extrapolation from DD to DT plasmas: experimental analysis and theory based predictions for JET-DT

A strong modelling program has been started in support of the future JET-DT campaign with the aim of guiding experiments in deuterium (D) towards maximizing fusion energy production in Deuterium–Tritium (DT). Some of the key elements have been identified by using several of the most updated and sophisticated models for predicting heat and particle transport, pedestal pressure and heating sources in an integrated modelling framework. For the high beta and low gas operational regime, the density plays a critical role and a trend towards higher fusion power is obtained at lower densities. Additionally, turbulence stabilization by E  ×  B flow shear is shown to generate an isotope effect leading to higher confinement for DT than DD and therefore plasmas with high torque are suitable for maximizing fusion performance. Future JET campaigns will benefit from this modelling activity by defining clear priorities on their scientific program.