Formation of ammonia in nitrogen and nitrogen/noble gas seeded
hydrogen plasma in PSI-2
T. Dittmar, C. Brandt, S. Brezinsek, A. Kreter, A. Pospieszczyk,
T. Schlummer, I. A. Sorokina
Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik,
52425 Jülich, Germany
a National Research Nuclear University “MEPhI”, Moscow Kashirskoe sh. 31, 115409, Russia
[email protected]
Nitrogen seeding is an important procedure for controlling divertor plasma temperature
and power loads in present day experiments (e.g. ASDEX-UG, JET) and considered
an option for ITER. Seeding N2 into hydrogen plasma can lead to the formation of
ammonia (NH3 ). However, tritiated ammonia could significantly contribute to the tritium retention and has consequences for the tritium plant and the in vessel cryo-pump
systems. Therefore, understanding the physical mechanisms of the ammonia formation is crucial and different experiments in laboratory (e.g. [1], [2]) and tokamak scale
(e.g. [3]) were performed to study ammonia formation. However, many open questions regarding the influence of helium, expected as product of the D-T reaction in
fusion devices, remain. We present therefore the results from a dedicated study of NH3
formation in N2 and N2 /He seeded plasma in the linear plasma device PSI-2. Both
H2 or D2 (flow rates: 80. . .200 sccm) and impurity neutral gas seeding rates up to 20
% (N2 ) resp. 5% (He) were used. Typical plasma parameter for the discharges were
ne ' 2...6 ⇥ 1017 m 3 ,Te ' 5...20 eV. Diagnostics were spatially resolved UV-VIS
optical emission spectroscopy (OES), residual gas (RGA) and in-situ ion mass spectrometry (MSMP, [4]). The RGA data exhibit clear ammonia signals and preliminary
analysis results in N2 ! NH3 conversion factors in the range of 10...30%. The NH3
production increases linearly with the N2 seeding but is unchanged by adding He to the
plasma. The MSMP shows a broad feature indicating N+ - and NHx + -ions. By OES,
+
only N+
2 ,NH, and NH were visible nitrogen containing species and no indication of
NH2 or NH3 ions or neutrals were detectable for the used plasma conditions. Altogether, the data shows that small additions of He have no influence on the ammonia
production and supports the theory that ammonia is formed only on low-flux or non
plasma-wetted surfaces.
[1] M. Sode, et al., J. Appl. Phys. 117 (2015) 083303
[2] T. Dittmar, et al., Phys. Script. T145 (2011) 014009
[3] M. Oberkofler, et al., Fusion. Eng. Des., 98-99 (2015) 1371
[4] I. Sorokin, et al., this conference