The control of plasma parameters to avoid high current disruptions in JET

Disruptions at high plasma current in the JET (Joint European Torus) are a serious operational problem because of thermal overloading of in-vessel components and mechanical stresses due to induced currents. The empirically determined operating space, which determines the operating conditions free of disruptions both for x-point and limiter configurations, has been mapped. In JET, there are three causes of disruption: MHD induced disruptions, density limit, and vertical instabilities. In order to avoid disruptions three operational diagrams which define operationally stable regions have been created. Gross MHD stability is described by a plasma internal inductance versus safety factor diagram. Density limit disruptions can be described by a Hugill diagram. A stability diagram for vertical instability in terms of plasma elongation versus plasma current has been developed. The JET operation space of parameters and the means to control the plasma parameters to stay within the boundaries are described