Thomsen Scattering in the JET Edge Plasma

摘要

The behavior to the plasma edge temperature and density in H-mode plasmas with type I ELMs has been successfully described by the so-called edge operational diagram [1]. The edge diagram shows a clear boundary for the upper limit to the edge pressure. It is often assumed that the mechanism for this limitatio is the ballooning instability which has a critical edge pressure gradient. We have not in the past experimentally been able to fully test this hypothesis at JET because the spatial resolution of our measurements was not sufficient. Scaling experiments suggest that the scale length is determined by the ion poloidal larmor radius ofthe fast ions in neutral beam heated plasmas, making the scale length - 3 cm or less. A new attempt at determining edge density and temperature gradients using a LIDAR Thomson scattering system [2] is presented.