LAUSR

Abstract Impurity seeding will be mandatory for ITER to protect the divertor tiles from excessive heat loads. Nitrogen seems to be a possible candidate due to its good radiation properties. The N content in the divertor plasma is crucial for cooling by radiation but is difficult to characterize. To assess the nitrogen fluence from the divertor plasma in nitrogen seeded discharges of ASDEX Upgrade (AUG), the concentration of two nitrogen containing molecules, ammonia and molecular nitrogen (N2) was measured. The N2 measurements were strongly affected by local effects which indicates that a significant fraction of the puffed N2 did not enter the plasma. In contrast, the measured ammonia fluence is proportional to the integrated nitrogen core density. This leads to the possibility of gaining the nitrogen fluence of the plasma, with the help of the created ammonia, for nitrogen seeded discharges. In discharges where the wall inventory was the only source of nitrogen in the plasma, 50% of the nitrogen was converted to ammonia, in the inner divertor. This allowed for the assessment of the nitrogen atom fluence from the plasma based on the detected ammonia in N2-seeded discharges.