Generation of energetic electrons during spherical tokamak merging in UTST

Abstract

Bursts of bremsstrahlung soft X-ray (SXR) emission ( > 200 eV) were observed during spherical tokamak merging in the University of Tokyo Spherical Tokamak (UTST) experiment. SXR signal waveforms coincided well with the time evolution of a reconnection electric field, and their intensity shows a clear dependence on the strength of a toroidal magnetic field. This result suggests that electrons near the X-point are effectively accelerated in the toroidal direction by a parallel electric field during plasma merging in the presence of a strong toroidal magnetic field.