Fine scale structures in the RTP tokamak plasma, measured with high resolution Thomson scattering

The Rijnhuizen Tokamak RTP, closed in Sept.1998, was unique for its combination of domi nant 2nd harmonic ECH (4-7 times the Ohmic power, deposited within 10% of the minor radius) and highresolution electron diagnostics. By scanning the ECH deposition through the plasma, electron transporr barriers associated with the rational q-values l,4/3,3/2,2, 5/2, and 3 were experimentally demonstrated. Modulated ECH showed that the transport barriers are layers of strong inward convection. The ECH power is deposited just outside the barriers. A conceptual model was developed in which transporr barriers are linked to rational q-values. The model reproduces all of the essential features of the RTp data sets, and was also tested against data from JET and TEXTOR.