Modelling of passive charge exchange emission and neutral background density deduction in JET

Passive charge exchange (PCX) emission between neutralized background ions entering the plasma from the walls, and fully ionized light impurities in a tokamak fusion plasma have been investigated. The incentive was to improve the evaluation of active charge exchange (ACX) spectra, leading to ion tem perature, impurity density and plasma rotation. The reconstruction of synth etic line-of-sight-integrated PCX emission spectra is based on a modelled n eutral density profile as derived from the FRANTIC code, local emission rat es for D-0(1s) and D-0(2s) donor states and finally local impurity ion dens ities (C6+, He2+) from CX analysis. As a result of the PCX modelling the ex perimental errors in ion temperature values can be reduced and the range of accessible PCX spectra extended from magnetic axis to separatrix. A compar ison between the modelled intensity of the synthetic spectra and experiment al PCX data also allows a consistency check of neutral density and its radi al distribution.