Electron and ion heating characteristics during magnetic reconnection in MAST

TL;DR

This study reveals localized electron and ion heating during magnetic reconnection in MAST, showing how guide field strength influences heating profiles and their spatial distribution, using advanced diagnostics.

Contribution

First detailed 2D measurements of electron and ion heating profiles during reconnection in a spherical tokamak, highlighting guide field effects.

Findings

Localized electron heating at the X point increases with guide field.

Bulk downstream ion heating remains unaffected by guide field changes.

Heating profiles form a triple peak structure after energy relaxation.

Abstract

Local electron and ion heating characteristics during merging reconnection startup on the MAST spherical tokamak have been revealed for the first time using a 130 channel YAG-TS system and a new 32 chord ion Doppler tomography diagnostic. 2D local profile measurement of $T_e$, $n_e$ and $T_i$ detect highly localized electron heating at the X point and bulk ion heating downstream. For the push merging experiment under high guide field condition, thick layer of closed flux surface formed by reconnected field sustains the heating profile for more than electron and ion energy relaxation time $\tau^E_{ei}\sim4-10$ms, both heating profiles finally form triple peak structure at the X point and downstream. Toroidal guide field mostly contributes the formation of peaked electron heating profile at the X point. The localized heating increases with higher guide field, while bulk downstream ion heating is unaffected by the change in the guide field under MAST conditions ($B_t>3B_{rec}$).