Impact of the magnetic shear on plasma equilibrium and turbulent transport in the vicinity of an X-point in TORPEX

Understanding cross field heat and particle transport is crucial in tokamaks, especially in the X-point and divertor regions. However, the complex magnetic field geometry and the associated turbulent and drift phenomena lead to large heat fluxes, rendering the experimental study of cross field heat and particle transport particularly challenging in tokamaks. In this work, plasmas are produced in an X-point magnetic field configuration in the low-temperature plasma device TORPEX. The effect of the magnetic shear s on the plasma is studied with the extensive set of in situ diagnostics, by investigating the evolution of typical plasma characteristics such as density and plasma potential profiles, dominant modes and instabilities, cross field turbulent transport, and heat flux. The E × B velocity remains constant over all s while the main mode frequency and wavenumber continuously decrease with s. A noticeable abrupt change is identified between two specific values of s in the average density, the horizontal turbulent transport, and the heat flux at the X-point position. The analyses suggest that this change is related to a modification in the nature of the dominant instability. The same abrupt change is observed in the correlation between cross field turbulent transport and heat flux, suggesting a strong effect of the increase in s on transport across the X-point.