MHD operational limits and disruption statistics in TCV ohmic plasmas

We describe the operational limits of ohmic plasmas in the elongated TCV tokamak. The latter is a flexible machine in which a wide variety of plasma configurations may be produced and in which plasmas with κ<2.1, -0.7<δ<0.9, Ip<0.81 MA have already been achieved. The vessel interior has 64% coverage of carbon protection tiles and is regularly boronised. The data include plasmas produced both before and after boronisation in limiter and diverted configurations and in both L- and H-mode confinement regimes. A database dedicated to the study of the plasma operational range and disruption probability statistics has been created, covering one and half years of operation. The experimental campaigns in TCV are exploratory by design, leading inevitably to a large variety of disruptions. This paper presents a first attempt to describe disruptions and the operational range in TCV. The essential diagnostics presently available and used for this study are: the equilibrium reconstruction code LIUQE based on magnetic measurements, a 5 channel interferometer, mhd probes, soft-X rays, and some spectroscopic lines. The quality of plasma performance so far achieved in these ohmic discharges is βN<2.0, HITER-89P<2.4. (author) 4 figs., 3 refs