Speaker
Description
In a tokamak plasma, impurities can diffuse depending on their atomic mass. One of the main (unwanted) source of impurities is erosion or sputtering of the first wall and of the divertor. The presence of different kind of impurities can modify the plasma dynamics, trigger instabilities, and dissipate energy through radiation.
In the past years, JET-ILW (ILW is for ITER-Like-Wall composed by a Berillium wall and a Tungsten divertor) performed two campaigns in D-T (DTE2 and DTE3) and completed its operations in 2023. JET-ILW demonstrated the possibility of sustaining high performances D-T discharges for long time (~5s) with a metallic wall differently from the former DTE1 campaign (in 1998) when it was operating with a Carbon Wall. One of the main problem faced during JET-ILW operations was the erosion and the ingress of high Z impurities in the plasma, coming from the erosion on the W divertor. This problem has been critical in the high-performance Baseline scenario [1], in particular at high plasma current. Long and stable operations for ~5s achievable with the available additional heating power in DTE3 campaign were limited to a maximum plasma current of 3MA [2].
In this scenario, a poloidally asymmetric distribution of the radiation is often seen, caused by W impurities accumulating off-axis with respect to the plasma center at mid radius in the Low Field Side (LFS). In this work we analyze a large number of experiments (>300 pulses) previously performed in the D campaigns [1,3] at different levels of plasma current, toroidal magnetic field, density, additional heating power.
The aim is firstly to show how much the asymmetric radiation distribution (ARP, Asymmetric Radiation Profile) is related with the possibility of destabilize the plasma and then lead to a disruption. The ARP level is here evaluated as the ratio between the measurements from two vertical bolometric cords, one crossing the plasma in the HFS (High Field Side) and the other in the LFS. JET discharges showing excessive ARP levels can undergo to early soft-stop termination because of high radiation. Alternatively, high ARP leads to a disruption because of core high Z impurity accumulation or because the triggering of 2/1 disruptive modes [4] for excessive radiation on the plasma edge.
Secondly, we will report about the relationship among ARP, plasma current and heating power attempting to determine the likelihood of destabilizing phenomena limiting the development of high performance scenarios.
Acknowledgements
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.
[1] L. Garzotti et al. 2025 Plasma Phys. Control. Fusion 67 075011
[2] A. Kappatou et al. 2025 Plasma Phys. Control. Fusion 67 045039
[3] J. Mailloux et al 2022 Nucl. Fusion 62 042026
[4] G. Pucella et al 2021 Nucl. Fusion 61 046020
