Deuterated ammonia formation, transport and dissociation in Ohmically-heated and nitrogen-seeded JET plasmas with low-recycling conditions at the divertor targets

A new deuterated ammonia ( ) formation, transport and dissociation model implemented in the ERO2.0 Monte Carlo-code predicts a peak line-integrated deuterated imidogen radical (ND) band emission intensity 50% higher than measured by the vertically-viewing divertor spectrometer in low-recycling, Ohmically-heated and nitrogen-seeded Joint European Torus (JET) plasmas. By assuming a greater kinetic energy release (KER) of 10 eV instead of 1 eV upon the dissociation of and its radicals, the model predicts a peak line-integrated ND band emission intensity 25% lower than measured. Together these predictions support the assumption of thermal re-release of incident nitrogen atoms and ions from the divertor targets as nitrogen molecules ( ) and ND 3 in equal fractions. Band emission from the ND radical has previously been measured in nitrogen-seeded divertor plasmas in the JET and ASDEX Upgrade tokamaks. The proposed model makes use of the AMMONX database for electron-impact dissociation and ionization rates of molecules and its dissociation products, and recent computational estimates of the electron-impact excitation rates of the ND radical. The assumption of thermal re-release of incident nitrogen ions and atoms as and in equal fractions is also consistent with the maximum rates of ammonia production observed in measurements of tokamak divertor plasmas as well as with measurements performed in laboratory plasma devices with high surface fluxes of reactive hydrogen and nitrogen species. • A deuterated ammonia (ND3) formation, transport and dissociation model implemented in ERO2.0. • Nitrogen ions and atoms assumed to recycle as N2 and ND3 molecules in equal fractions. • Peak ND band emission intensity 50% above or 25% below JET measurements, depending on assumed kinetic energy release (KER) values.