The dependence of the H-mode edge transport barrier width on normalized ion gyroradius (ρ * = ρ/a) in discharges with type I ELMs was examined in experiments combining data for the JET and DIII-D tokamaks. The plasma configuration as well as the local normalized pressure (β), collisionality (ν * ), Mach number and the ratio of ion and electron temperature at the pedestal top were kept constant, while ρ * was varied by a factor of four. The width of the steep gradient region of the electron temperature (T e ) and density (n e ) pedestals

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A major upgrade to the charge exchange recombination spectroscopy system on MAST has recently been implemented. The new system consists of a high-throughput spectrometer coupled to a total of 224 spatial channels, including toroidal and poloidal views of both neutral heating beams on MAST. Radial resolution is ∼1cm, comparable to the ion Larmor radius. The toroidal views are configured with 64 channels per beam, while the poloidal views have 32 channels per beam. Background channels for both poloidal and toroidal views are also provided. A large transmission grating is at the heart of the new spectrometer, with high quality single lens reflex lenses providing excellent imaging performance and permitting the full exploitation of the available etendue of the camera sensor. The charge-coupled device camera chosen has four-tap readout at a maximum aggregate speed of 8.8MHz, and it is capable of reading out the full set of 224 channels in less than 4ms. The system normally operates at 529nm, viewing the C5+ emission line, but can operate at any wavelength in the range of 400–700nm. Results from operating the system on MAST are shown, including impurity ion temperature and velocity profiles. The system’s excellent spatial resolution is ideal for the study of transport barrier phenomena on MAST, an activity which has already been advanced significantly by data from the new diagnostic.

A new edge Thomson scattering diagnostic has been implemented at MAST to complement an existing high spatial resolution ruby laser system and the high time sampling core Nd:YAG system. The Nd:YAG system comprises of four independently controllable lasers. Scattered light from these lasers is viewed at large scattering angle (153°) by a special optical arrangement in the new edge system. The Nd:YAG lasers are viewed at 16 contiguous spatial locations separated by ∼1cm each, located at the plasma outboard pedestal and scrape-off layer region. Here the use of a low f-number lens for the collection of a large solid angle of scattered light is particularly beneficial due to low plasma density (ne). The spectrum of scattered light is significantly broader at large scattering angles, allowing diagnosis of lower plasma temperatures (Te) while using the same spectrometer design as the core system. The four Nd:YAG lasers follow two separate slightly offset (<1∕3 of a spatial channel) optical paths through the vessel. This is useful when the lasers are used in burst mode for detailed edge studies of fast events such as ELMs. Polychromators have been designed to allow for both Raman and Rayleigh calibration. First results from this diagnostic are presented showing H-mode pedestal behavior. A novel spectral fitting technique has been devised and is applied to edge pedestal fitting.