H-mode pedestal physics studies in local dimensionless identity experiments

The characteristics of the H-mode density pedestal are determined by a balance between two competing processes ­ plasma transport across the region and neutral particle fuelling of the edge plasma. Identifying the relative role of plasma physics vs atomic physics of neutral fuelling is important for advancing our understanding of H-mode pedestal. A dimensionless identity technique can be used for this purpose, which is based on the fundamental fact that conservation of dimensionless plasma parameters (collisionality n*, normalized plasma pressure b, and normalized gyroradius n*) leads to invariance of plasma physics with respect to changes of dimensional parameters (plasma density ne and temperature Te). A first experiment applying this technique to tokamak pedestal studies was carried out on the Alcator C-Mod and DIII-D tokamaks. In this paper we compare the results of that experiment with the results of another experiment on JET and C-Mod and present a preliminary analysis of neutral fuelling in the discharges under consideration on all three tokamaks with the one-dimensional kinetic neutral transport code KN1D.