Asymmetries in the divertor power loading in START

Langmuir probe measurements from the divertor strike points for a series of very similar, highly up-down magnetically symmetric double-null divertor discharges are presented. These show a strong in-out electron density (n(e)) asymmetry, as well as up-down asymmetries in the electron temperature (T-e), the power density scale length (lambda(q)) and n(e), on the inboard side.;These up-down asymmetries seem to be due to particle drift effects and not due to an imbalance in the magnetic X-points. It is estimated that only about 35% of the power that enters the scrape-off layer (SOL) reaches the divertor tiles. There is a high neutral density in the START SOL and it is conjectured that the bulk of this missing power is lost through charge exchange, or elastic collisions, of the ions with these neutrals as they flow towards the divertor tiles. The highest power density (q), of about 4-8 MW/m(2) is found to be at the upper outboard strike point, not the inboard, because the major radii of the inboard and outboard strike points is similar and n(e) is much higher on the outboard side. (C) 1999 Elsevier Science B.V. All rights reserved.