EFDA-JET-CP(03)01/31

Edge Gradient and Pedestal Measurements of ELMy H-mode Plasmas at JET

For the study of ELM physics, localised measurements of the edge pressure and edge current density profile are essential. So far, at JET a direct comparison of measurements of these parameters with theory on peeling and ballooning limits has not been possible due to lack of spatial resolution of edge diagnostics. From the spring 2002 campaign up to the spring 2003 campaign dedicated experiments have been performed on JET to improve the edge pedestal density, temperature and pressure measurements. For this purpose a Diagnostic Optimised plasma Configuration (DOC-U) has been designed. This is a configuration with a high X-point position and the last closed flux surface aligned to the edge LIDAR Thomson scattering line of sight. It is close to the optimum shape for edge gradient measurements. It should be noted that in general different edge diagnostics are positioned at different locations on the machine and have different penetrations. To be able to compare the measurements they are mapped onto the plasma flux surfaces derived from the EFIT equilibrium code. For the edge LIDAR system this mapping improves the effective spatial resolution from 12 cm along the laser line of sight to ~2cm across the flux surfaces. So now it is possible to resolve the edge plasma parameters. By producing a large database of edge LIDAR data (density and plasma current scan), we aim to study the general behaviour of the JET Tokamak ELMy H-mode plasmas and use this database for comparison with other Tokamaks such as DIII-D and JT60-U.
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EFDC030131 909.97 Kb