MHD spectroscopy in toroidal plasmas using various MHD instabilities

A possibility to MHD spectroscopy where information of MHD equilibrium is extracted by means of monitoring energetic ion driven MHD instabilities is discussed in toroidal plasmas such as stellarator/helical and tokamak plasmas. This technique is very important for a fusion reactor where sophisticated diagnostic systems for internal plasma measurements will be considerably limited, and only simpler diagnostics such as magnetic probe arrays and microwave diagnostics will be available. Some promising examples of MHD spectroscopy in the Large Helical Device are shown and are compared with those in tokamaks. (author)