Intrinsic current driven by electromagnetic electron drift wave turbulence in the tokamak pedestal region

Abstract

The local intrinsic parallel current density driven by electron drift wave (DW) turbulence including electromagnetic (EM) effects is analytically studied. The scalings of the ratios of intrinsic current density driven by residual turbulent flux and by a turbulent source to the bootstrap (BS) current density with electron density and temperature are predicted to be and respectively. Based on the typical parameters in the DIII-D pedestal region, the local intrinsic current density driven by both the residual turbulent flux and the turbulent source is negligible. However, despite the negligible turbulent source driven current, the residual turbulent flux driven local intrinsic current density by EM DW turbulence can reach about 66% of the BS current density for International Thermonuclear Experimental Reactor (ITER) pedestal parameters due to much lower collisionality in ITER than in DIII-D. Moreover, the contributions from adiabatic ES parts, non-adiabatic ES parts, and non-adiabatic EM parts of the plasma response to EM fluctuations are analyzed. It is found that there is a strong cancellation between the non-adiabatic ES response and the non-adiabatic EM response for the ITER pedestal case, and thus the kinetic stress contributed by the adiabatic ES response of parallel electron pressure dominates the intrinsic current drive. This is different from the ES electron DW case. Therefore, the EM effects on turbulence driven intrinsic current density should be carefully considered in the future reactor with a high ratio of electron pressure to the magnetic pressure and steep pressure profile.