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 temperature, impurity density and plasma rotation. The reconstruction of synthetic line-of-sight-integrated PCX emission spectra is based on a modelled neutral density profile as derived from the FRANTIC code, local emission rates for D0(1s) and D0(2s) donor states and finally local impurity ion densities (C6+, He2+) from CX analysis. As a result of the PCX modelling the experimental errors in ion temperature values can be reduced and the range of accessible PCX spectra extended from magnetic axis to separatrix. A comparison between the modelled intensity of the synthetic spectra and experimental PCX data also allows a consistency check of neutral density and its radial distribution.