Resonant-like behaviour during edge-localised mode cycles in the Joint European Torus
2015 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 8, 082501Article in journal (Refereed) Published
A unique sequence of 120 almost identical plasmas in the Joint European Torus (JET) recently provided two orders of magnitude more statistically equivalent data than ever previously available. The purpose was to study movement of eroded plasma-facing material from JET's new Beryllium wall, but it has allowed the statistical detection of otherwise unobservable phenomenon. This includes a sequence of resonant-like waiting times between edge-localised plasma instabilities (ELMs), instabilities that must be mitigated or avoided in large magnetically confined plasmas such as those planned for ITER. Here, we investigate the cause of this phenomenon, using the unprecedented quantity of data to produce a detailed picture of the plasma's behaviour. After combining the data, oscillations are clearly observable in the plasma's vertical position, in edge losses of ions, and in Beryllium II (527 nm) light emissions. The oscillations are unexpected, are not obvious in data from a single pulse alone, and are all clearly correlated with each other. They are likely to be caused by a small vertical oscillation that the plasma control system is not reacting to prevent, but a more complex explanation is possible. The clearly observable but unexpected link between small changes in the plasma's position and changes to edge-plasma transport and stability suggest that these characteristics cannot always be studied in isolation. It also suggests new opportunities for ELM mitigation and control that may exist.
Place, publisher, year, edition, pages
Culham Sci Ctr, JET EFDA, Abingdon OX14 3DB, Oxon, England. [Webster, A. J.; Morris, J.; Todd, T. N.; Coad, P.] Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England. [Brezinsek, S.] Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany. [Likonen, J.] VTT, Assoc Euratom Tekes, FI-02044 Espoo, Finland. [Rubel, M.] Royal Inst Technol KTH, Assoc EURATOM VR, Sch Elect Engn, Alfven Lab, Stockholm, Sweden., 2015. Vol. 22, no 8, 082501
IdentifiersURN: urn:nbn:se:kth:diva-173989DOI: 10.1063/1.4927755ISI: 000360647600040ScopusID: 2-s2.0-84938848922OAI: oai:DiVA.org:kth-173989DiVA: diva2:858308
QC 201510012015-10-012015-09-242015-10-01Bibliographically approved