OBSERVATION OF A QUASI-COHERENT MODE IN THE TEXAS EXPERIMENTAL TOKAMAK

A quasicoherent feature localized near the magnetic flux surface having a safety factor q = 3 has been detected by Langmuir probe and heavy ion beam probe (HIBP) measurements in the edge plasma of the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)]. A mode is identified with relatively low poloidal wave number (m = 12) compared to the usual broadband turbulence with m in the range of 50 to 100. In contrast to the turbulent activity, this mode is collisional and does not produce a fluctuation-driven radial particle flux via the coupling between density and potential fluctuation. A comparison with the expectation of the drift-tearing activity indicates that the mode can be collisional drift-tearing unstable.