Influence of In-plane Electrostatic Potential on the Ion Heating Characteristic during ST Merging

The characteristic quadrupole electrostatic potential structure has been confirmed in the guide field magnetic reconnection during ST merging experiment in TS-6. The key question is how this electrostatic potential structure is formed and to what extent potential well accelerates particles. During ST merging startup, the reconnection electric field is aligned with the magnetic field, significantly accelerating electrons which are detected as energetic electrons around X-point and in the inboard-side downstream by a soft x-ray fast imaging system. The electrostatic potential profile develops synchronized with the increase of reconnection electric field and soft x-ray, indicating that the accelerated electrons have a crucial role in potential structure formation. Furthermore, we have first demonstrated that the amplitude of potential linearly increases both with reconnecting magnetic field B_rec and guide field B_g . We will discuss this electrostatic potential dependence on magnetic field and derive the ion outflow, which mainly consists of E×B flow where in-plane electrostatic field is stronger than reconnection electric field, scales mainly with reconnecting magnetic field. This result ultimately explains the ion heating scaling during ST merging startup, that is, △T_i ∝ B²_rec.