Tearing modes in plasma termination on JET: the role of temperature hollowing and edge cooling

Tearing modes in plasma termination on JET: the role of temperature hollowing and edge cooling

Tearing modes in plasma termination on JET: the role of temperature hollowing and edge cooling 150 150 amit lakhani
UKAEA-CCFE-PR(20)118

Tearing modes in plasma termination on JET: the role of temperature hollowing and edge cooling

In this work the mechanisms that can lead to disruptive MHD instabilities in the termination phase of plasma pulses on JET are investigated. It is shown that the broadening or the shrinking of the current density profile, as a consequence of a core hollowing or a edge cooling of the electron temperature profile, can lead to the destabilization of a 2/1 tearing mode, in agreement with the experimental observations. Two parameters are introduced to highlight changes in the shape of the temperature profile that can lead to MHD instabilities and an empirical stability diagram is introduced into the space of the two new parameters. A large data-set of pulses carried out in the high-current scenario at JET with ITER-like wall is analyzed and criteria for the development of disruption alerts based on the two risk indicators for MHD instabilities are discussed, taking into account the different dynamics of the observed phenomena leading to the onset of 2/1 tearing modes.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP (Institute of Physics)