Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

B. Vanovac, E. Wolfrum, M. Hoelzl, M. Willensdorfer, M. Cavedon, G.F. Harrer, F. Mink, S.S. Denk, S. Freethy, M. Dunne, P. Manz, N.C. Luhmann

Research output: Contribution to journalArticleAcademicpeer-review

2 Citations (Scopus)

Abstract

The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I edge localizes modes (ELMs). These modes are dominantly observed in electron cyclotron emission (ECE) and ECE imaging measurements as a modulation of radiation temperature (δTrad). In the radial magnetic field (r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km s-1 to 2.5 ± 0.5 km s-1 and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km s-1 or zero. The poloidal structure of the modes is found to agree with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence analysis. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.

Original languageEnglish
Article number112011
Number of pages10
JournalNuclear Fusion
Volume58
Issue number11
DOIs
Publication statusPublished - 3 Oct 2018

Fingerprint

low frequencies
cyclotrons
gradients
phase velocity
electrons
frequency ranges
modulation
heating
causes
radiation
magnetic fields

Keywords

  • bicoherence
  • ELMs
  • inter-ELM modes
  • pedestal
  • poloidal velocity

Cite this

Vanovac, B., Wolfrum, E., Hoelzl, M., Willensdorfer, M., Cavedon, M., Harrer, G. F., ... Luhmann, N. C. (2018). Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade. Nuclear Fusion, 58(11), [112011]. https://doi.org/10.1088/1741-4326/aada20
Vanovac, B. ; Wolfrum, E. ; Hoelzl, M. ; Willensdorfer, M. ; Cavedon, M. ; Harrer, G.F. ; Mink, F. ; Denk, S.S. ; Freethy, S. ; Dunne, M. ; Manz, P. ; Luhmann, N.C. / Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade. In: Nuclear Fusion. 2018 ; Vol. 58, No. 11.
@article{326e8470185c47809643c848fe7976df,
title = "Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade",
abstract = "The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I edge localizes modes (ELMs). These modes are dominantly observed in electron cyclotron emission (ECE) and ECE imaging measurements as a modulation of radiation temperature (δTrad). In the radial magnetic field (r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km s-1 to 2.5 ± 0.5 km s-1 and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km s-1 or zero. The poloidal structure of the modes is found to agree with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence analysis. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.",
keywords = "bicoherence, ELMs, inter-ELM modes, pedestal, poloidal velocity",
author = "B. Vanovac and E. Wolfrum and M. Hoelzl and M. Willensdorfer and M. Cavedon and G.F. Harrer and F. Mink and S.S. Denk and S. Freethy and M. Dunne and P. Manz and N.C. Luhmann",
year = "2018",
month = "10",
day = "3",
doi = "10.1088/1741-4326/aada20",
language = "English",
volume = "58",
journal = "Nuclear Fusion",
issn = "0029-5515",
publisher = "Institute of Physics",
number = "11",

}

Vanovac, B, Wolfrum, E, Hoelzl, M, Willensdorfer, M, Cavedon, M, Harrer, GF, Mink, F, Denk, SS, Freethy, S, Dunne, M, Manz, P & Luhmann, NC 2018, 'Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade', Nuclear Fusion, vol. 58, no. 11, 112011. https://doi.org/10.1088/1741-4326/aada20

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade. / Vanovac, B.; Wolfrum, E.; Hoelzl, M.; Willensdorfer, M.; Cavedon, M.; Harrer, G.F.; Mink, F.; Denk, S.S.; Freethy, S.; Dunne, M.; Manz, P.; Luhmann, N.C.

In: Nuclear Fusion, Vol. 58, No. 11, 112011, 03.10.2018.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

AU - Vanovac, B.

AU - Wolfrum, E.

AU - Hoelzl, M.

AU - Willensdorfer, M.

AU - Cavedon, M.

AU - Harrer, G.F.

AU - Mink, F.

AU - Denk, S.S.

AU - Freethy, S.

AU - Dunne, M.

AU - Manz, P.

AU - Luhmann, N.C.

PY - 2018/10/3

Y1 - 2018/10/3

N2 - The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I edge localizes modes (ELMs). These modes are dominantly observed in electron cyclotron emission (ECE) and ECE imaging measurements as a modulation of radiation temperature (δTrad). In the radial magnetic field (r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km s-1 to 2.5 ± 0.5 km s-1 and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km s-1 or zero. The poloidal structure of the modes is found to agree with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence analysis. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.

AB - The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I edge localizes modes (ELMs). These modes are dominantly observed in electron cyclotron emission (ECE) and ECE imaging measurements as a modulation of radiation temperature (δTrad). In the radial magnetic field (r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km s-1 to 2.5 ± 0.5 km s-1 and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km s-1 or zero. The poloidal structure of the modes is found to agree with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence analysis. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.

KW - bicoherence

KW - ELMs

KW - inter-ELM modes

KW - pedestal

KW - poloidal velocity

UR - http://www.scopus.com/inward/record.url?scp=85054710897&partnerID=8YFLogxK

U2 - 10.1088/1741-4326/aada20

DO - 10.1088/1741-4326/aada20

M3 - Article

AN - SCOPUS:85054710897

VL - 58

JO - Nuclear Fusion

JF - Nuclear Fusion

SN - 0029-5515

IS - 11

M1 - 112011

ER -

Vanovac B, Wolfrum E, Hoelzl M, Willensdorfer M, Cavedon M, Harrer GF et al. Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade. Nuclear Fusion. 2018 Oct 3;58(11). 112011. https://doi.org/10.1088/1741-4326/aada20