A COMPUTATIONAL INVESTIGATION OF DIVERTOR PLASMA SCALING LAWS

Usually, tokamak core scaling laws sure written in terms of dimensionl ess geometrical quantities and parameters corresponding to Coulomb col lisionality, gyro-motion,and plasma beta. However, Lackner [K. Lackner , Comments Plasma Phys. Controlled Fusion 15, 359 (1994)] observed tha t the temperature profiles also must be the same to obtain the same at omic 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 impli citly retained only two body interactions. Subsequent work [P. J. Catt o 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 densit ies above 10(19) m(-3); the regime in which the ITER divertor must ope rate. In this reactor relevant regime, scaling law information must be obtained experimentally and by complex numerical simulations. To reta in and quantify non-two-body effects on scaling laws we employ numeric al simulations from a two dimensional box geometry version of the UEDG E code [D. A. Knoll et al., Phys. Plasmas 3, 293 (1996)] which include s a coupled plasma and neutral fluid description retaining non-two-bod y effects. Results are presented from a numerical investigation into t he upstream parallel heat flux divided by upstream pressure scaling, a s well as collisionality scaling, of the tokamak divertor target heat flux and ion saturation current. (C) 1998 American Institute of Physic s.