Link do seminarium: https://bit.ly/3gxxhAo

Abstract

Due to the predicted high opacity of the ITER SOL to neutrals, in ITER the plasma density will have to be controlled through injection of cryogenic pellets. This is different to the situation in present day machines, for which gas dosing has been traditionally used. In addition, ELM pacemaking with pellets is one of the techniques foreseen in ITER to control ELMs. Due to technical limitations pellet velocity is limited to 300 m/s. In combination with the high pedestal temperatures expected in ITER, this implies a pellet ablation depth which is comparable to the width of the edge transport barrier (ψpel ∼ 0.95). Due to its size, the JET tokamak is capable of reaching ITER-like pellet ablation depths. In addition, JET can reach smaller ratios of pellet to target plasma particle content compared to medium sized tokamaks. This together with the presence of Be/W-based first wall material mix (ITER-like Wall, or ILW), renders JET ideally suited for the study of pellet fuelling and pellet ELM pacing physics under ITER-relevant conditions.

In addition, thanks to the refurbishment of the JET pellet system in 2018, the pellet delivery reliability has been strongly improved. This has extended the use of pacing pellets at JET, which has become integral part of the high-performance scenarios developed for the JET Deuterium Tritium experiments. In particular for the baseline scenario, pacing pellets have proven beneficial not only for impurity control but also to access high fusion performance.

Dedicated experiments have been carried out on JET to study systematically the effect of cryogenic pellet fuelling and pellet ELM-pacemaking on type-I ELMy H-modes in the presence of an ITER-like Wall (ILW) and with ITER-like pellet ablation depths. The main aim of this work is to document and understand how shifting the radial particle source localisation from the plasma edge (gas dosing) to inside the H-mode transport barrier (pellets) impacts the boundary plasma as well as the structure and height of the pedestal under ITER-relevant conditions. The work will be presented in two parts. In part I (IPPLM Seminar Feb-2022), we will look into the changes in SOL and divertor conditions with pellets. In the next IPPLM Seminar (part-II), we will look into the changes to the pre-ELM pedestal height and structure and how the differences are linked to the previous SOL findings.