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Control of power deposition onto plasma facing components in tokamaks is a determining factor for future thermonuclear fusion reactors. Plasma surface interaction can be performed using limiters or divertors. The ergodic divertor installed on Tore Supra is an atypical example of a magnetic divertor. It consists in applying a magnetic perturbation, which establishes a particular topology of the plasma in contact with the wall (edge plasma).
Dedicated experiments were carried out in order to study parallel heat flux, which strike the divertor neutralizers. This quantitative and qualitative analysis of heat flux as a function of experimental conditions allows determining the profiles of power deposition along the neutralizers. The influence of plasma electron density, additional heating, impurities and injected gas was established. An experimental study of the sheath heat transmission factor gamma was carried out by correlating measurements made with Langmuir probes and infrared imaging. This study gave rise to a major conclusion: for ohmic discharges with deuterium injection and most of the time with helium, it was experimentally confirmed that gamma=7 in agreement with classical sheath theory. However, an increase of this factor with additional power has been shown.
Detached plasma, which is an attractive regime in order to reduce the power deposition, requires an optimized control. A new measurement of the detachment onset has been developed. It is based on the variation of heat flux onto the plates derived from infrared measurements. A detachment cartography with the determination of a new 2D IR degree of detachment was carried out allowing to locate the zone where the detachment starts. We can apply this concept to other tokamaks such as JET and ITER.
A comparison between the axisymmetric divertor and the ergodic divertor is also presented concerning the power deposition in the two configurations. Low heat flux with the ergodic divertor is a major advantage ge

Additional information

Authors: COSTANZO L, Université de Provence, Aix, Marseille (FR)
Bibliographic Reference: Report: EUR-CEA-FC-1718 (2001), pp.200
Record Number: 200114119 / Last updated on: 2001-12-14
Original language: fr
Available languages: fr
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