The JET Alfven Eigenmode Local Manager for the real-time detection and tracking of a frequency-degenerate spectrum of MHD instabilities

We present the real-time VME system used to detect and track MHD instabilities, and particularly Alfven Eigenmodes, on the JET tokamak [J.Wesson, Tokamaks, 3rd ed., Oxford Science Publication, Oxford, 2003, p.617]. This system runs on a 1 kHz clock cycle, and allows performing a real-time, unsupervised and blind detection, decomposition and tracking of the individual components in a frequency-degenerate, multi-harmonic spectrum, using a small number of input data which are unevenly sampled in the spatial domain. This makes it possible to follow in real-time the detected modes as the plasma background evolves, and measure in real-time their frequency, damping rate, toroidal mode-number and relative amplitude. The successful implementation of this system opens a clear path towards developing real-time control tools for electro-magnetic instabilities in future fusion devices aimed at achieving a net energy gain, such as ITER [J.Wesson, Tokamaks, 3rd ed., Oxford Science Publication, Oxford, 2003, p.711].