Density limit disruption studies in the TCA tokamak

This paper describes density limit plasma disruptions that take place during the density increase in the plasma current flat top of TCA. In TCA, such disruptions have been observed to occur at two different densities, depending on discharge programming. An efficient method of achieving high density is to introduce a strong influx of neutral gas to the plasma, which was found to allow the plasma density to cross a range of densities that was otherwise unstable. In this kind of operation the disruption was observed to be approached from high to low plasma inductance in contrast to a slower density rise where the inductance is increasing. The study of the plasma temperature and density profiles as the disruption is approached, together with the characterisation of the mode and sawtooth activity, gives further insights into the physics of plasma disruptions. (author) 32 figs., 3 tabs., 30 refs