Measurement of density and magnetic fluctuations in MST tokamak plasmas using an advanced interferometer-polarimeter*

Diagnosis of the internal MHD dynamics of tokamak plasma disruptions is needed for improved understanding of disruptions and for comparison with nonlinear MHD computational modeling. We have initiated measurements of both density and magnetic fluctuations in MST tokamak plasmas, before and during disruptions. The measurements are made with an advanced, far-infrared interferometer-polarimeter comprised of 11vertical chords spanning the plasma diameter. The diagnostic can detect fluctuations with several hundred kHz bandwidth. Initial analysis of interferometry data before the disruption reveals a ~6 kHz density fluctuation, as well as a ~30 kHz feature in the toroidal spectral coherence between core chords not visible in the density fluctuation spectrum. Analysis of polarimetry data reveals an ~18 kHz magnetic fluctuation leading up to the disruption. An increase in broadband fluctuations in both the density and magnetic fluctuation spectra are observed. Correlation of these fluctuations with MHD dynamics will be performed.