Kink Instabilities in High-Beta JET Advanced Scenarios
Stability of high-beta plasmas is studied on discharges from a series of JET experiments on steadystate and hybrid advanced scenarios, with a wide range of q-profiles and a range of normalized beta extending to bN = 4. Bursting and continuous forms of global n = 1 instabilities limit the achievable bN or degrade confinement. Stability boundaries in terms of qmin and pressure peaking are determined. For relatively broad pressure profiles the limit decreases from bN = 4 at qmin = 1 to bN = 2 at qmin = 3, while at fixed qmin it decreases with increasing pressure peaking. Triggering mechanisms and the internal structure of continuous n = 1 instabilities are analysed. A new form of instability that grows on typical resistive time-scales but has internal kink structure is identified.