Generation of radial electric field induced by collisionless internal kink mode with density gradient

Abstract

Effects of density gradient on the collisionless m=1 (m/n=1/1) internal kink mode in a cylindrical tokamak plasma are studied by the gyrokinetic particle simulations. When the density gradient is not large enough to change the full reconnection process, the phenomena after the full reconnection, such as the secondary reconnection and the evolution of the safety factor profile, are changed considerably due to the self-generated radial electric field, i.e., the m/n=0/0 mode. The growing mechanism is explained by the difference of E×B drift motion between ions and electrons, which is caused by the fast parallel motion of electron. Once the radial electric field is triggered by the symmetrical flow induced by the 1/1 mode, the 0/0 mode grows up to the same level as the 1/1 mode, and drives an E×B plasma rotation in the ion diamagnetic direction, which breaks the symmetrical plasma flow induced by the 1/1 mode. The density and current distributions, and therefore minimum safety factor qmin after the full reconnection, are found to be affected by the asymmetrical flow driven by the 1/1 and 0/0 modes.