Transition between resistive ballooning mode and toroidal drift wave mode at the edge of tokamak plasmas

Abstract

The transition between the resistive ballooning mode (RBM) and toroidal drift wave (DW) mode is a possible physical mechanism triggering L-H transition in tokamaks. The two-fluid model [Rafiq et al., Phys. Plasmas 17, 082511 (2010)] developed by Rafiq et al. was improved by including ion diamagnetic effects in plasma polarization drift velocity. Based on the improved fluid model, the gyrokinetic results [Bourdelle et al., Nucl. Fusion 54, 022001 (2014)] about the transition between RBM and toroidal DW were recovered. It shows good agreement under a set of real experimental conditions. Hence the fluid theory is valid to investigate the physics of edge plasmas. A transition temperature Tmin about 80 eV, which RBM is dominant for plasma temperature Te < Tmin, but DW prevails for Te > Tmin, was found in gas puffing experiments of HL-2A tokamak. Employing the improved fluid model, we have simulated this phenomenon and the experimental result has been verified exactly.