TY - JOUR
T1 - The role of temperature fluctuations in the dynamics of type-I and type-II edge localized modes at ASDEX Upgrade
AU - Classen, I.G.J.
AU - Boom, J.E.
AU - Bogomolov, A.
AU - Wolfrum, E.
AU - Maraschek, M.
AU - Suttrop, W.
AU - de Vries, P.C.
AU - Donné, A.J.H.
AU - Tobias, B.J.
AU - Domier, C.W.
AU - Luhmann, N.C.
PY - 2013
Y1 - 2013
N2 - Two-dimensional temperature measurements using the electron cyclotron emission imaging diagnostic at ASDEX Upgrade revealed a variety of temperature fluctuations associated with type-I and type-II edge localized modes (ELMs). The characteristics and dynamics of these modes, and their role in the ELM cycle, are presented. During type-I ELMs, different phases of distinct mode activity have been identified. At the onset of the ELM crash, a short lived mode is observed in the pedestal region. During the actual crash phase, multiple filamentary structures are observed just outside the separatrix. A third type of fluctuation, the inter-ELM mode, is often observed in between type-I crashes. The occurrence of this mode tends to lengthen the ELM period. During type-I ELM suppression with magnetic perturbation coils, smaller crash events become more frequent, replacing the large type-I crashes. In type-II ELMs, temperature crashes are absent altogether, and a continuous broadband fluctuation in the 20–60 kHz range, showing beat wave like behaviour, is observed. The similarities between the characteristics of this mode and the inter-ELM mode suggest that it is the same instability. In type-I ELMs it delays the next crash, in type-II ELMs it might be responsible for the complete absence of crash events.
AB - Two-dimensional temperature measurements using the electron cyclotron emission imaging diagnostic at ASDEX Upgrade revealed a variety of temperature fluctuations associated with type-I and type-II edge localized modes (ELMs). The characteristics and dynamics of these modes, and their role in the ELM cycle, are presented. During type-I ELMs, different phases of distinct mode activity have been identified. At the onset of the ELM crash, a short lived mode is observed in the pedestal region. During the actual crash phase, multiple filamentary structures are observed just outside the separatrix. A third type of fluctuation, the inter-ELM mode, is often observed in between type-I crashes. The occurrence of this mode tends to lengthen the ELM period. During type-I ELM suppression with magnetic perturbation coils, smaller crash events become more frequent, replacing the large type-I crashes. In type-II ELMs, temperature crashes are absent altogether, and a continuous broadband fluctuation in the 20–60 kHz range, showing beat wave like behaviour, is observed. The similarities between the characteristics of this mode and the inter-ELM mode suggest that it is the same instability. In type-I ELMs it delays the next crash, in type-II ELMs it might be responsible for the complete absence of crash events.
U2 - 10.1088/0029-5515/53/7/073005
DO - 10.1088/0029-5515/53/7/073005
M3 - Article
SN - 0029-5515
VL - 53
SP - 073005
JO - Nuclear Fusion
JF - Nuclear Fusion
IS - 7
M1 - 073005
ER -