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When the average electron density in a tokamak plasma is rising and approaching the density limit, regions of strong radiation may develop at the plasma boundary. The plasma is called detached when the radiating zone is poloidally symmetric. Very often poloidally asymmetric radiation, predominantly located at the high field side, is observed in tokamaks. These radiating zones, which extend to about 10%-30% of the poloidal circumference, are called MARFEs. It is generally agreed that both phenomena, detachment and MARFEs, are based on the specific radiation characteristics of impurities at the plasma boundary. In most cases the MARFE formation precedes a major disruption, whereas detached plasmas can be quasi-stationary. In order to use the advantages of a detached plasma, MARFE formation must be avoided. For many years only detached plasmas and no MARFEs have been observed in TEXTOR. When, due to technical reasons, the measurement of the horizontal plasma position for the feedback control was switched from interferometric to magnetic methods, MARFEs were frequently detected in TEXTOR. The possibility to apply the magnetic or interferometric measurements alternately from shot to shot for position control was used to show that the interferometric method could be a means for suppressing MARFEs.

Additional information

Authors: SAMM U, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE);KOSLOWSKI H R, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE);SOLTWISCH H, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Article: 18th European Conference on Controlled Fusion and Plasma Physics, Vol. III (1991) pp. 137-140
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