Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. IV. Drift-tearing mode

Here, the drift-tearing instability due to diamagnetic drift effects is verified using the Gyrokinetic Toroidal Code (GTC). First, the classical (2,1) resistive tearing mode is verified in a cylindrical geometry with a fluid model. The dependence of the growth rate of the resistive tearing mode on the beta value of the plasma is obtained and is found to qualitatively agree with the theoretical prediction. A drift-tearing mode is subsequently generated when the equilibrium pressure gradient is significant. In this mode, diamagnetic drift effects result in a reduced growth rate and a real frequency equal to the electron diamagnetic frequency. The scaling relation between the diamagnetic frequency and the growth rate of the drift-tearing mode has been calculated. Lastly, this relation shows good agreement with the theoretical prediction for a relatively small resistivity; however, an obvious deviation arises when the resistivity is large.