Analysis of energy flux deposition and sheath transmission factors during ergodic divertor operation on Tore Supra

Abstract

The magnetic deflection of field lines to dedicated wall components in the ergodic divertor of Tore Supra generates complex patterns of power deposition. In this paper, we analyze the energy flux deposition on neutralizer plates as measured by infrared cameras and Langmuir probes. Three important features will be discussed: (1) The energy deposition during helium shots is as much as twice that for deuterium shots, for a given input power level. (2) The sheath heat transmission factor, deduced experimentally by comparison between probes and infrared measurements, increases with input power independently of the working gas from ∼7.5 (P TOT =1 MW) to ∼10–11 for P TOT =5 MW) . In ohmic discharges, the standard value of 7 is recovered except specific cases in helium where γ can decrease to 2 or 3. (3) These anomalous values put in doubt the validity of edge temperature measurements by Langmuir probes in detached plasmas and have led to the development of a promising `infrared' degree of detachment (Dod).