Evolution of nitrogen concentration and ammonia production in N 2 -seeded H-mode discharges at ASDEX Upgrade

Ammonia formation was studied in a series of dedicated nitrogen seeded H-mode discharges at ASDEX Upgrade. The evolution of ammonia formation was investigated with a reference phase before the seeding, and a long, stable flat-top nitrogen-seeded phase. It was monitored with divertor spectroscopy and analysis of the exhaust gas. The amount of the detected ammonia increased continuously over the course of five discharges with the same nitrogen seeding rate. The same trend was observed in the nitrogen density in the core plasma, as measured by charge exchange recombination spectroscopy and other signals, linked to the effects of nitrogen seeding. The results show that the rate of ammonia forma…