Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

Localized electron heating of magnetic reconnection was studied under strong guide-field (typically $B_t \sim 15B_p$) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term $E_t \cdot j_t$. When we include a guide-field effect term $B_t/(B_p+\alpha B_t)$ for $E_t \cdot j_t$ where $\alpha = \sqrt{(v_{in}^2+v_{out}^2)/{v_{\parallel}^2}}$, the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point.