MEASUREMENT OF THE EFFECTIVE PLASMA ION MASS IN LARGE TOKAMAKS USING GLOBAL ALFVEN EIGENMODES

There is not yet a straightforward method for determining the D-T rati o in the centre of a tokamak plasma. One of the simpler measurements p ut forward in the past is the interpretation of the MHD spectrum in th e frequency range of the global Alfven eigenmodes (GAE). However, the frequencies of these modes do not depend on the plasma mass alone, but are also quite strongly dependent on the details of the current and d ensity profiles; this creates a problem of deconvolution of the estima te of the plasma mass from an implicit relationship between several me asurable plasma parameters and the detected eigenmode frequencies; In view of the lack of competitive diagnostics, this method has been revi sited to assess its likely precision for the JET tokamak. Our results show that the low-n GAE modes are sometimes too close to the continuum edge to be detectable and that the interpretation of the GAE spectrum is therefore rendered less direct than had been hoped. However, infor mation on the effective plasma ion mass is still available in the dete ctable modes and we present a statistical study on the precision with which this quantity could be estimated from the GAE spectrum on JET, i ncluding other directly measured or simply available plasma parameters .