Edge stability analysis of JET Quiescent H-mode experiments.

The edge stability of JET QH-mode plasmas has been studied using the transport code JETTO coupled to a quasi-linear model for ballooning and peeling modes. Attempts on JET to access the Quiescent H-mode (QM-mode) regime with counter-NBI heating, produced plasmas with extended ELM-free phases up to 1.5 s duration. These were characterised by continuous edge n=1 MHD modes similar to the DIII-D ``edge harmonic oscillation.'' Some of the edge parameters, such as high edge pedestal temperatures (T$_{i,e }\sim $ 2-3 keV) and high current densities are similar to the ELM-free hot-ion H-mode regime previously studied at JET. The latter was also characterised by an n=1 mode, the outer mode, observed in co- and counter- NBI when the edge was kink unstable, but still below the unstable ballooning threshold. Here we explore the possibility that the edge n=1 mode observed in the QH-mode plasmas may be a saturated peeling/ external kink mode. Continuous peeling modes can be obtained at high edge temperature, because slow current redistribution maintains the edge current unstable for long periods$.$ Modelling assumptions have been verified using the MHD stability code MISHKA. Predictive simulations with current ramp-up and ramp-down will be presented.