Physics and Real Time Control of Tearing modes in TEXTOR

The transport in and around magnetic islands has been studied by measurement of the two dimensional propagation of heat pulses generated by modulated ECRH. Inside an island with a flat temperature profile, the electron heat transport is shown to be strongly reduced with respect to the surrounding plasma. The generalized Rutherford equation is analyzed to determine the relative merits of localized heating and current drive for the stabilization of tearing modes. It is shown that for TEXTOR conditions the heating effect dominates over the effect of current drive in agreement with the experimental observations. On ITER, both are expected to be of the same order of magnitude. An optimized track-and-suppress system for tearing modes by launching angle control on TEXTOR is under development. Introduction High power Electron Cyclotron (EC) waves are effective in suppressing magnetic islands [1-3] and controlling sawteeth [4]. This paper reports on recent progress in the field of tearing mode (TM) physics and their suppression using high power electron cyclotron waves. TEXTOR [5] (major radius R = 1.75 m, minor radius a = 0.46 m) features a unique combination of tools that makes it very suited for this work. An Electron Cyclotron Resonance Heating (ECRH) system (140 GHz, 800 kW, 10 s) [6] is used for localized heating and current drive in the vicinity of the island. High resolution 2D Electron Cyclotron Emission Imaging (ECE-I) [7] is used for the island dynamics and transport. The Dynamic Ergodic Divertor (DED) [8] is used to reproducibly excite tearing modes by Resonant Magnetic Perturbations . A system to measure the ECE along the same sightline as the ECRH (in-Line ECE) [9] has been installed. This simplifies the real time determination of the radial location and phase of the island in support of the Real Time Control (RTC) of the ECW-beam launching. Transport in and around magnetic islands The cross field transport in and around magnetic islands has an important impact on the stability and evolution of (neoclassical) tearing modes. It determines the critical island size below which