Neutral particle fueling at the midplane of DIII-D

Data from an array of eight tangential D-alpha viewchords, located at the outer midplane of DIII-D, are inverted to obtain atomic neutral density profiles across the separatrix and are compared to results of B2.5 and DEGAS simulations. In H-mode and (low density) L-mode plasma conditions, charge-exchange neutrals reflected and desorbed from the outer midplane region of the vacuum vessel wall can account for the midplane neutral density that is deduced from the D-alpha data, making it unnecessary to invoke main chamber ion recycling, The midplane measurements and DEGAS calculations are used to validate a slab-model of neutrals in the edge. In this model, cold neutrals from the wall fuel the edge and are attenuated by charge-exchange and ionization, and the results are in agreement with measured neutral profiles. (C) 2003 Elsevier Science B.V. All rights reserved.