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Intrinsic ELMing in ASDEX Upgrade and global control system-plasma self-entrainment

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Chapman, Sandra C., Lang, Peter Thomas, Dendy, R. O., Watkins, Nicholas W., Dunne, Mike G and Giannone, Louis (2018) Intrinsic ELMing in ASDEX Upgrade and global control system-plasma self-entrainment. Nuclear Fusion, 58 (12). 126003. doi:10.1088/1741-4326/aadd1c ISSN 1741-4326.

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Official URL: https://doi.org/10.1088/1741-4326/aadd1c

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Abstract

It is well established that edge localized modes can be entrained to the frequency of applied global magnetic perturbations. These perturbations are delivered to the plasma using the vertical control system field coil currents. These field coils are part of an active control system that is required to maintain the plasma in a steady state. We perform time domain timeseries analysis of natural ELMing when there are no applied perturbations in the ASDEX Upgrade tokamak. We find that the plasma can transition into a state in which the control system field coil currents continually oscillate and are synchronized with oscillations in characteristic plasma parameters such as plasma edge position and total MHD energy. These synchronous oscillations have a one-to-one correlation with the naturally occurring ELMs; the ELMs all occur when the control system coil current is around a specific temporal phase. Large and small ELMs may be distinguished by the amplitude of inward movement of the edge following an ELM. Large ELMs are then found to occur preferentially around a specific temporal phase of the vertical position control coil current. Small ELMs are most likely in antiphase to this. The large and small natural ELMs occur at the opposite extrema of the oscillations in the control system vertical position control coil current. The control system coil current phase may thus provide a useful parameter to order the observed ELM dynamics. We have identified a class of natural ELMing which is a self-entrained state, in which there is a continual non-linear feedback between the global plasma dynamics and the active control system that is intrinsic to the cyclic dynamics of naturally occurring ELMs. Control system-plasma feedback thus becomes an essential component for integration into future models of natural ELM dynamics.

Item Type: Journal Article
Subjects: Q Science > QC Physics
Divisions: Faculty of Science, Engineering and Medicine > Science > Physics
SWORD Depositor: Library Publications Router
Library of Congress Subject Headings (LCSH): Edge-localized modes, Synchronization, Tokamaks, Plasma confinement, Magnetohydrodynamic waves
Journal or Publication Title: Nuclear Fusion
Publisher: IOP Publishing
ISSN: 1741-4326
Official Date: 17 September 2018
Dates:
DateEvent
17 September 2018Published
28 August 2018Available
28 August 2018Accepted
Volume: 58
Number: 12
Article Number: 126003
DOI: 10.1088/1741-4326/aadd1c
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Open Access (Creative Commons)
Date of first compliant deposit: 18 September 2018
Date of first compliant Open Access: 18 September 2018
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
633053H2020 Euratomhttp://dx.doi.org/10.13039/100010687
EP/P012450/1[EPSRC] Engineering and Physical Sciences Research Councilhttp://dx.doi.org/10.13039/501100000266
Scholarship US-UK Fulbright Commissionhttp://dx.doi.org/10.13039/501100000592
FA9550-17-1-0054Air Force Office of Scientific Researchhttp://dx.doi.org/10.13039/100000181
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