Intrinsic current drive by electromagnetic electron temperature gradient turbulence in tokamak plasmas

TL;DR

This paper investigates how electromagnetic electron temperature gradient turbulence can intrinsically generate current in tokamak plasmas, potentially affecting current profiles in high-beta_e devices like ITER.

Contribution

It introduces a new understanding of intrinsic current drive mechanisms caused by EM ETG turbulence, emphasizing the role of residual turbulent flux.

Findings

Residual turbulent flux can drive up to 80% of the bootstrap current locally in ITER core.

Intrinsic current driven by residual turbulent source is negligible compared to flux-driven current.

No net intrinsic current exists on a global scale in the studied scenarios.

Abstract

The mean parallel current density evolution equation is presented using electromagnetic (EM) gyrokinetic equation. There exist two types of intrinsic current driving mechanisms resulted from EM electron temperature gradient (ETG) turbulence. The first type is the divergence of residual turbulent flux including a residual stress-like term and a kinetic stress-like term. The second type is named as residual turbulent source, which is driven by the correlation between density and parallel electric field fluctuations. The intrinsic current density driven by the residual turbulent source is negligible as compared to that driven by the residual turbulent flux. The ratio of intrinsic current density driven by EM ETG turbulence to the background bootstrap current density is estimated. The local intrinsic current density driven by the residual turbulent flux for mesoscale variation of turbulent flux can reach about 80% of the bootstrap current density in the core region of ITER standard scenario, but there is no net intrinsic current on a global scale. Based on this, the local intrinsic current driven by EM micro-turbulence and its effects on local modification of the profile of safety factor may be needed to be carefully taken into account in the future device with high beta_e which is the ratio between electron pressure to the magnetic pressure.