Investigation of pellet-driven magnetic perturbations in different tokamak scenarios

T. Szepesi, S. Kálvin, G. Kocsis, K. Lackner, P. T. Lang, M. Maraschek, G. Pokol, G. Pór

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Magnetic perturbations directly driven by pellets were studied in three different plasma scenarios in the ASDEX Upgrade tokamak to gain a deeper insight into the triggering process of type-I ELMs. In the type-I ELMy H-mode, promptly after the ELM, a mode with toroidal mode number n = -6 (the negative sign denoting the ion drift direction) was detected in the 100-150 kHz frequency range, for both spontaneous and triggered ELMs. For triggered ELMs with pellets ablating longer than the ELM crash, this mode was observed for a longer time - therefore this could be identified as the pellet-driven perturbation. However, pellets promptly trigger ELMs after entering the plasma, and the large-amplitude ELM footprint masks the pellet-driven perturbation at the instance of the trigger event, i.e. the pellet-driven mode can only be studied after the ELM in a type-I ELMy H-mode. In L-mode plasmas the pellet was observed to drive broadband Alfvén waves, detected in the 80-300 kHz frequency range with a toroidal mode number of n = -6, similar to the mode after type-I ELMs, confirming that the mode seen in the H-mode after ELMs is indeed the pellet-driven perturbation. The magnitude of the pellet-driven perturbation was observed to increase monotonically with pellet penetration, and showed an exponential decay after pellet burn-out. Similarities and differences are discussed for the type-III ELMy H-mode scenario, which resulted in the finding that the pellet only drives and/or triggers modes which can be naturally present in the target plasma. Concerning type-I ELM triggering, the pellet-driven magnetic perturbation is unlikely to be the trigger for ELMs, since the structure of the pellet-driven modes is completely different from that of the observed pre-ELM modes (coherent modes with toroidal mode number n = 3 and 4, similar to Washboard modes) or type-I ELMs themselves (also n = 3 and 4).

Original languageEnglish
Article number125002
JournalPlasma Physics and Controlled Fusion
Volume51
Issue number12
DOIs
Publication statusPublished - 2009

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pellets
Plasmas
perturbation
Masks
actuators
Ions
frequency ranges
crashes
footprints

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Nuclear Energy and Engineering

Cite this

Investigation of pellet-driven magnetic perturbations in different tokamak scenarios. / Szepesi, T.; Kálvin, S.; Kocsis, G.; Lackner, K.; Lang, P. T.; Maraschek, M.; Pokol, G.; Pór, G.

In: Plasma Physics and Controlled Fusion, Vol. 51, No. 12, 125002, 2009.

Research output: Contribution to journalArticle

Szepesi, T. ; Kálvin, S. ; Kocsis, G. ; Lackner, K. ; Lang, P. T. ; Maraschek, M. ; Pokol, G. ; Pór, G. / Investigation of pellet-driven magnetic perturbations in different tokamak scenarios. In: Plasma Physics and Controlled Fusion. 2009 ; Vol. 51, No. 12.
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abstract = "Magnetic perturbations directly driven by pellets were studied in three different plasma scenarios in the ASDEX Upgrade tokamak to gain a deeper insight into the triggering process of type-I ELMs. In the type-I ELMy H-mode, promptly after the ELM, a mode with toroidal mode number n = -6 (the negative sign denoting the ion drift direction) was detected in the 100-150 kHz frequency range, for both spontaneous and triggered ELMs. For triggered ELMs with pellets ablating longer than the ELM crash, this mode was observed for a longer time - therefore this could be identified as the pellet-driven perturbation. However, pellets promptly trigger ELMs after entering the plasma, and the large-amplitude ELM footprint masks the pellet-driven perturbation at the instance of the trigger event, i.e. the pellet-driven mode can only be studied after the ELM in a type-I ELMy H-mode. In L-mode plasmas the pellet was observed to drive broadband Alfv{\'e}n waves, detected in the 80-300 kHz frequency range with a toroidal mode number of n = -6, similar to the mode after type-I ELMs, confirming that the mode seen in the H-mode after ELMs is indeed the pellet-driven perturbation. The magnitude of the pellet-driven perturbation was observed to increase monotonically with pellet penetration, and showed an exponential decay after pellet burn-out. Similarities and differences are discussed for the type-III ELMy H-mode scenario, which resulted in the finding that the pellet only drives and/or triggers modes which can be naturally present in the target plasma. Concerning type-I ELM triggering, the pellet-driven magnetic perturbation is unlikely to be the trigger for ELMs, since the structure of the pellet-driven modes is completely different from that of the observed pre-ELM modes (coherent modes with toroidal mode number n = 3 and 4, similar to Washboard modes) or type-I ELMs themselves (also n = 3 and 4).",
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