The roles of power loss and momentum-pressure loss in causing particle-detachment in tokamak divertors: I. A heuristic model analysis

Abstract

Particle-detachment is defined here based on Loarte’s Degree of Detachment, quantifier (1998 Nucl. Fusion 38 331). Specifically, particle-detachment is defined to be the edge plasma regime that sets in on an edge flux-tube when the plasma flux density onto the divertor target, starts to increase less than quadratically with nu, the plasma particle density in the flux tube upstream of the divertor. A simple heuristic model that includes volumetric loss of both pressure-momentum, ptotal, and parallel power flux density in the flux tube, q∣∣, is used to explicitly demonstrate that, generically, both types of volumetric loss are required for particle-detachment to occur. The principle conclusion of this paper is that it is the combination of momentum-loss and power-loss that is the cause of particle-detachment and that therefore any attribution of particle-detachment to just one of these volumetric loss processes, or any assignment of paramountcy to one type of loss over the other, as sometimes may appear to occur, would not be appropriate.