Feedback control of the lower hybrid power deposition profile on Tore Supra

The Tore Supra facility is well suited to study ITER relevant topics such as the real-time control of plasma current and the sustaining of steady-state discharges. This work describes a tool that was recently developed and implemented on Tore Supra to control in real time, by means of the direct knowledge of the suprathermal electron local emission pro. le, the width of the lower hybrid power deposition pro. le. This quantity can be considered to some extent equivalent to the width of the plasma current density pro. le in case of fully non-inductive discharges. This system takes advantage of an accurate hard xray diagnostics, of an efficient lower hybrid additional heating and of a reliable real-time communication network. The successful experiments carried out to test the system employed, as actuators, the parallel refractive index n(//) and the total power P-LH. The control of the suprathermal electron local emission pro. le through n// was also integrated with the feedback control of the total plasma current IP with PLH and of the loop voltage V-loop with the central solenoid flux. These results demonstrate that the system is robust, reliable and able to counterbalance destabilizing events. This tool can be effectively used in the future in fully non-inductive discharges to improve the MHD stability and to maintain internal transport barriers or lower hybrid enhanced performance modes. The real-time control of the lower hybrid power deposition pro. le could also be used in conjunction with the electron-cyclotron radiofrequency heating for synergy studies.