Radial identification of tearing modes in a Tokamak

The focus of the present research is the control of rotating magnetic islands of low helical mode numbers (m,n) in thermonuclear plasmas. These perturbations are associated with local distortions of the current profile that can be a serious cause of degradation of the plasma confinement. The islands are reduced in width or completely suppressed by restoring the unperturbed current profile. The current can be driven by the deposition of radio frequency power within the island. Traditionally magneto-hydrodynamic (MHD) instabilities are monitored by external magnetic signals that however give no information about the radial location of the perturbation within the plasma. Because temperature fluctuation is also associated with MHD instabilities, ECE (electron cyclotron emission) signals that give information about local electron temperature, are used to identify the islands position. Here, we describe the design of a real time diagnostics/control device using an original algorithm for an effective control action that involves identification of relevant state variables (radial location, island amplitude, frequency and phase) in "real time" and varies accordingly the control variables (wave beam power modulation and steering angles).