Application of Tomographic Ion Doppler Spectroscopy to Merging Plasma Startup in the MAST Spherical Tokamak

Abstract

This paper describes recent advances in merging/reconnection experiments in MAST, namely tomographic ion Doppler spectroscopy capability from 2013 which solves the problem of the absence of ion temperature profile measurement during the solenoid-less startup. Providing 32 channel line-integrated spectra from 0.25 m < r_tangential < 1.1 m are connected to a grating spectrometer with the focal length of 1.0 m and grating frequency of 1800 L/mm, and tomographic reconstruction is applied to measure local ion temperature profile. This system successfully contributes to the study of ion heating during merging/reconnection startup and revealed that magnetic reconnection mostly heats ions in the downstream region of outflow jet and also found its contribution to bulk electron heating as well as the localized heating at X point with the time scale of energy relaxation between ions and electrons.