Abstract.We present a method to obtain reliable edge proles of the electron temperature by forward modelling of the electron cyclotron radiation transport. While for the core of ASDEX Upgrade plasmas, straightforward analysis of electron cyclotron intensity measurements based on the optically thick plasma approximation is usually justied, reasonable analysis of the steep and optically thin plasma edge needs to consider broadened emission and absorption proles and radiation transport processes. This is done in the framework of integrated data analysis which applies Bayesian probability theory for joint analysis of the electron density and temperature with data of dierent interdependent and complementary diagnostics.By this means, electron cyclotron radiation intensity delivers highly spatially resolved electron temperature data for the plasma edge. In H-mode, the edge gradient of the electron temperature can be several times higher than the one of the radiation temperature. Furthermore, we are able to reproduce the`shine-through' peak the observation of increased radiation temperatures at frequencies resonant in the optically thin scrape-o layer. This phenomenon is caused by strongly down-shifted radiation of Maxwellian tail electrons located in the H-mode edge region and, therefore, contains valuable information about the electron temperature edge gradient.
Abstract. The ASDEX Upgrade tokamak is currently being enhanced with a set of invessel saddle coils for non-axisymmetric perturbations aiming at mitigation or suppression of Edge Localised Modes (ELMs). Results obtained during the first experimental campaign are reported. With n = 2 magnetic perturbations, it is observed that type-I ELMs can be replaced by benign small ELM activity with strongly reduced energy loss from the confined plasma and power load to the divertor. No density reduction due to ELM mitigation (density "pumpout") is observed. ELM mitigation has, so far, been observed in plasmas with different shape, heating powers between a factor of 2 − 8 above the H-mode threshold, different heating mixes and, therefore, different momentum input. The ELM mitigation regime can be accessed with resonant and non-resonant perturbation field configurations. The main threshold requirement appears to be a critical minimum plasma edge density which depends on plasma current. So far it is not possible to distinguish whether this is an edge collisionality threshold or a critical fraction of the Greenwald density limit.
We report the identification of a localized current structure inside the JET plasma. It is a field-aligned closed helical ribbon, carrying current in the same direction as the background current profile (cocurrent), rotating toroidally with the ion velocity (corotating). It appears to be located at a flat spot in the plasma pressure profile, at the top of the pedestal. The structure appears spontaneously in low density, high rotation plasmas, and can last up to 1.4 s, a time comparable to a local resistive time. It considerably delays the appearance of the first edge localized mode.
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