Power deposition behaviour on the neutralizer plates during detachment with the ergodic divertor on Tore Supra

The behaviour of the particle and of the power deposition on the neutralizer plates of the ergodic divertor (ED) of Tore Supra is reported for density ramp up experiments in deuterium. Both the particle flux and the power deposition are shown to be non-uniform when the plasma is attached while a uniform deposition is obtained when it is detached. A degree of detachment (DoD) is proposed, based on IR measurements using the ratio of the heat flux deposition from a ‘hot’ and a ‘cold’ area. This infrared degree of detachment (IR_DoD) is larger than 1 in the attached phase and decreases towards 1 when the plasma approaches detachment. A comparison between the classical DoD deduced from Langmuir probes and the IR_DoD deduced for IR data is given, showing a similar sensitivity when the density increases. Finally, since the IR_DoD does not require any modification of the IR system, it is an opportunity to optimize the ratio by a careful selection of the viewed area, free from major drifts and calibrations of the measurement system.