Role of edge poloidal density asymmetry in tokamak confinement

TL;DR

This paper demonstrates how edge poloidal density asymmetries influence tokamak confinement through a simple MHD model, offering insights into phenomena like the LH transition and implications for ITER fueling.

Contribution

It introduces a straightforward MHD equilibrium framework to explain the impact of edge density asymmetries on tokamak confinement, bypassing complex neoclassical physics.

Findings

Edge density asymmetries affect mass flows and electric fields in tokamaks.

The model explains the dependence of LH transition power threshold on magnetic topology.

Implications for ITER fueling port placement and power requirements.

Abstract

Mass flows and radial electric field driven by edge poloidal density asymmetries can be used as a highly effective control mechanism for the edge and thus global confinement in tokamaks. The underlying physics can be demonstrated entirely within a simple magnetohydrodynamic equilibrium model, without resorting to sophisticated and usually collisionality-dependent neoclassical physics arguments. As an example, strong dependence of the low to high (LH) transition power threshold on the magnetic topology, an experimental observation still poorly understood, can be easily explained within this framework. Similar arguments indicate that the ITER fueling ports above the midplane might lead to higher input power requirements.