Mass spectrometry analysis of the impurity content in N2 seeded discharges in JET-ILW

Presented are the results of the first mass spectrometry study of impurities at JET with the ILW. Measurements are performed with the newly-installed RGA system that allows for data acquisition in all stages of machine operation. Impurities are predominantly found in the 16-20 AMU range, populated by water, methane and ammonia, and at 28 AMU (CO and N-2). The main contaminants in non-seeded discharges are deuterated methane and water, and nitrogen, which are present only in low amounts, and are likely produced by plasma-surface interaction. During N-2 seeded discharges, signals increase significantly at 28 AMU, but also in the 16-20 AMU range, indicating conversion of nitrogen to ammonia. In subsequent non-seeded discharges, impurity content is reduced by an order of magnitude, however it exhibits a 5-7 discharge-long legacy. (C) 2015 EURATOM. Published by Elsevier B.V. All rights reserved.