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Submitted for the DPP08 Meeting of The American Physical Society.

Experiments have been carried out on TCV using Electron Cyclotron Resonance Heating (ECRH) actuators to control the plasma current and elongation in real time. In fully non-inductive plasmas, the plasma current may be driven entirely by ECCD on TCV. By replacing the Ohmic coils with the gyrotron power supplies, we were able to control the plasma current in real time. In tokamak plasmas, the elongation is usually controlled by the quadrupole magnetic field from the poloidal field coils. Applying off-axis ECRH, the current profile is flattened reducing the plasma internal inductance, and at constant quadrupole field, the plasma elongates (κ ~ 2.4) [1]. This paper reports on experiments to control the plasma elongation using a real time elongation observer and the ECRH power actuator to control the current profile. As the plasma elongates, the ECRH deposition becomes more central. Therefore a deposition tracking control was developed which tracked the ECRH deposition at constant ρ by controlling the ECRH launcher mirror position.

The ability to control, in real time, the electron cyclotron heating & current drive systems for the control of MHD instabilities is particularly important for large tokamaks operating at high performance. Several algorithms have been developed and tested on TCV to explore possible control techniques, first in simple experiments to control the plasma current and elongation and subsequently in experiments to control the sawtooth instability and profile parameters. A summary of these experiments are presented in this paper together with the application of the break-in-slope technique as a possible real time calculation of the location of EC deposition.