Speaker
Aleksander Drenik
(EUROfusion Consortium)
Description
After the transition to full metal wall configurations at AUG and subsequently at JET, impurity seeding became necessary to maintain the divertor heat loads below material limits in H-mode discharges. Among the studied impurities, nitrogen (N) was found to be the most favourable option. However, it was also found that N2-seeding leads to formation of ammonia (NH3). Nitrogen and NH3 retained in surfaces can lead to increased tritium (T) retention. The presence of NH3 in the pump exhaust requires special arrangements for the operation of cryo-pumps and T recycling plant. Therefore, the quantification of NH3 production in N2-seeded discharges will also have direct implications on the design of the ITER tritium recycling plant.
Past experiments at AUG and JET revealed a N-to-NH3 conversion fraction of 7 % and 2 % respectively, however the amount of detected NH3 in a series of identical dis-charges was found to continuously increase, suggesting that the steady state production at ITER with 100 s long pulses might be higher than expected from present data.
The recent analysis of N2 seeded discharges at AUG and JET shows that the N2 seeding rate is the main discharge parameter determining NH3 production. However, NH3 also exhibits a significant legacy effect, which is visible as a gradually increasing level of detected NH3 in N2 seeded discharges, as well as an elevated level of released NH3 in subsequent non-seeded discharges. The release of retained NH3 was attributed both to plasma-wall interaction and flushing by gas injections, indicating that in-vessel surfaces can act as temporary pump for NH3, and that N2 seeding at ITER may lead to formation of a significant NH3 inventory in the vessel.
Co-authors
Aleksander Drenik
(EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom;Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany;Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia)
Alfonso De Castro
(Laboratorio Nacional de Fusión, CIEMAT, Avda Complutense 40, 28040 Madrid, Spain)
Antti Hakola
(VTT Technical Research Centre of Finland, P. O. Box 1000 (Otakaari 3K), FI-02044, Finland)
Daniel Alegre
(Departamento de Ingeniería Energética, UNED, C/ Juan del Rosal 12, 28040 Madrid, Spain;Laboratorio Nacional de Fusión, CIEMAT, Avda Complutense 40, 28040 Madrid, Spain)
Gerd Meisl
(Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany)
Gregor Primc
(Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia)
Gregory De Temmerman
(ITER Organization, St Paul Lez Durance, France)
Karl Krieger
(Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany)
Martin Oberkofler
(Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany)
Matjaz Panjan
(Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia)
Miran Mozetic
(Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia)
Misha Beldishevski
(Culham Centre for Fusion Energy, Abingdon, Oxon, OX14 3DB, United Kingdom)
Peter J.L. Heesterman
(Culham Centre for Fusion Energy, Abingdon, Oxon, OX14 3DB, United Kingdom)
Richard Pitts
(ITER Organization, St Paul Lez Durance, France)
Rok Zaplotnik
(Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia)
Rudolf Neu
(Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany)
Sebastijan Brezinsek
(IEK - Plasmaphysik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany)
Thierry Loarer
(CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France)
Timo Dittmar
(IEK - Plasmaphysik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany)
Uron Kruezi
(Culham Centre for Fusion Energy, Abingdon, Oxon, OX14 3DB, United Kingdom)
Volker Rohde
(Max-Planck-Institut für Plasmaphysik, Garching bei München, Germany)
and JET contributors the ASDEX-Upgrade team
(See the Appendix of F. Romanelli et al., Proceedings of the 25th IAEA Fusion Energy Conference 2014, Saint Petersburg, Russian Federation)
