A computational investigation of divertor plasma scaling laws

Abstract

Usually, tokamak core scaling laws are written in terms of dimensionless geometrical quantities and parameters corresponding to Coulomb collisionality, gyro-motion, and plasma beta. However, Lackner [K. Lackner, Comments Plasma Phys. Controlled Fusion 15, 359 (1994)] observed that the temperature profiles also must be the same to obtain the same atomic physics in the divertor region of similar discharges. He obtained a scaling indicating that none of the present tokamaks could be made similar to the International Thermonuclear Experimental Reactor (ITER) [G. Janeschitz et al., J. Nucl. Mater. 220–222, 73 (1995)], but implicitly retained only two body interactions. Subsequent work [P. J. Catto et al., Phys. Plasmas 3, 3191 (1996)] demonstrated that non-two-body effects (multistep radiation, excitation, and ionization processes as well as three body recombination) cannot be ignored for plasma densities above 1019 m−3; the regime in which the ITER divertor must operate. In this reactor relevant regime, scaling law information must be obtained experimentally and by complex numerical simulations. To retain and quantify non-two-body effects on scaling laws we employ numerical simulations from a two dimensional box geometry version of the UEDGE code [D. A. Knoll et al., Phys. Plasmas 3, 293 (1996)] which includes a coupled plasma and neutral fluid description retaining non-two-body effects. Results are presented from a numerical investigation into the upstream parallel heat flux divided by upstream pressure scaling, as well as collisionality scaling, of the tokamak divertor target heat flux and ion saturation current.