Spectroscopic observation of LT-3 tokamak plasma at disruptive instability

Chord observations of radiation from oxygen impurity ions (O III, O IV, and O V) in the LT-3 hydrogen plasma have been made simultaneously through a number of optical ports. These showed a spatially structured entry of oxygen into the plasma just before the disruption and, at the disruption, an expansion of the central plasma into the outer regions with velocities of 3-8 km/s. The plasma column appeared to be kinked with a stationary modal structure of m = n = 1 on which were superimposed a moving central m = 1 perturbation and, at larger radii, moving perturbations with m greater than 1.