Automatic Detection and Control of MHD Activity in FTU Tokamak by ECE and ECH/ECCD

Active control of MHD instabilities is important in order to improve tokamak performance. This paper describes experimental work done on FTU tokamak in this field, in particular for the automatic suppression of Tearing Modes (TM) via simultaneous detection and tracking of island position, sawteeth inversion radius and Electron Cyclotron Heating (ECH) power deposition. Effective control in real time is achieved through the implementation of a system for automatic detection of TM onset, and stabilizing reaction with ECH/ECCD. The system is composed by a particular arrangement of the 140 GHz, 4×0.5 MW ECH set-up, and a DSP-based (Digital Signal Processor) unit for the analysis of ECE and Mirnov data, and for the control of gyrotron power supplies. Main emphasis is given to the intrinsic capability of the arrangement for a fast reaction to an early warning of the TM appearance. In order to improve ECH power deposition identification by synchronous detection of ECE oscillations and ECH power modulation, special techniques based on non-periodic pulse sequences have been implemented.