ICRF Power Feedback Regulation of the Plasma Diamagnetic Energy Content of the Tokamak TEXTOR

A real time control of the plasma diamagnetic energy content of the tokamak TEXTOR has been realised. The different signals necessary to the computation of the diamagnetic energy are acquired by a 80286 based PC-AT micro computer equipped with a data acquisition board AT-MIO16 of National Instruments. The computed diamagnetic energy content of the plasma is compared to a time-dependent reference signal pre-programmed on the ICRF main control computer and the difference is used to compute the generator output power signal by numerically implemented PID type regulator algorithm. This signal is clipped to a pre-set maximum power level and is output to the generators by the data acquisition board. The acquisition-computation-control cycle is completed in 2 ms. Simulations of the system using a simple energy confinement model showed that a 2 ms cycle time was sufficient to achieve a stable and reliable control of the diamagnetic energy using a continuously control parameter such as the ICRF power. Results so far on TEXTOR show that it is possible to reliably operate in conjunction with radiative edge cooling and to reach operation regimes not to far from the beta- and Greenwald limit in a stable way, with the possible enhancement of some confinement parameters.