Global Ion Heating during ST Merging Driven by High Guide Field Reconnection

Abstract

The physical processes of ion heating during high guide field (B_g/B_rec ∼ 6) reconnection is explored utilizing Doppler tomography measurement in the TS-6 ST (Spherical Tokamak) merging experiment. The newly developed 288CH extensive/high-resolution (Δr ∼ 1.5 cm; ΔZ = 1.0 cm) ion Doppler spectroscopy system has revealed the detailed characteristic of ion heating in the downstream region. In the high guide field regime,ion heating occurs not only around the diffusion region but also more globally in the downstream region. This was beyond the scope of the previous ion temperature measurement and hence we have confirmed a different heating mechanism which is attributed to strong in-plane electric field produced extensively in high guide field reconnection regime.