Chapman, Sandra C., Dendy, R. O., Lang, P. T., Watkins, Nicholas W., Calderon, F. A., Romanelli, M. and Todd, T. N. (2017) The global build-up to intrinsic ELM bursts and comparison with pellet triggered ELMs seen in JET. Nuclear Fusion, 57 (2). 022017. doi:10.1088/0029-5515/57/2/022017 ISSN 0029-5515.

PDF WRAP_chapelmnf2016.pdf - Published Version - Requires a PDF viewer. Available under License Creative Commons Attribution. Download (4013Kb)

Request Changes to record.

Abstract

We focus on JET plasmas in which ELMs are triggered by pellets in the presence of ELMs which occur naturally. We perform direct time domain analysis of signals from fast radial field coils and toroidal full flux azimuthal loops. These toroidally integrating signals provide simultaneous high time resolution measurements of global plasma dynamics and its coupling to the control system. We examine the time dynamics of these signals in plasmas where pellet injection is used to trigger ELMs in the presence of naturally occurring ELMs. Pellets whose size and speed are intended to provide maximum local perturbation for ELM triggering are launched at pre-programmed times, without correlation to the occurrence times of intrinsic ELMs. Pellet rates were sufficiently low to prevent sustained changes of the underlying plasma conditions and natural ELM behaviour. We find a global signature of the build-up to natural ELMs in the temporal analytic phase of both the full flux loops and fast radial field coil signals. Before a natural ELM, the signal phases align to the same value on a ∼2–5ms timescale. This global build up to a natural ELM occurs whilst the amplitude of the full flux loop and fast radial field coil signals are at their background value: it precedes the response seen in these signals to the onset of ELMing. In contrast these signals do not clearly phase align before the ELM for ELMs which are the first to occur following pellet injection. This provides a direct test that can distinguish when an ELM is triggered by a pellet as opposed to occurring naturally. It further supports the idea [1–4] of a global build up phase that precedes natural ELMs; pellets can trigger ELMs even when the signal phase is at a value when a natural ELM is unlikely to occur.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Edge-localized modes
Journal or Publication Title:	Nuclear Fusion
Publisher:	Institute of Physics Publishing Ltd.
ISSN:	0029-5515
Official Date:	February 2017
Dates:	Date Event February 2017 Published 30 September 2016 Available 2 August 2016 Accepted 28 January 2016 Submitted
Volume:	57
Number:	2
Article Number:	022017
DOI:	10.1088/0029-5515/57/2/022017
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	3 October 2016
Date of first compliant Open Access:	3 October 2016
Funder:	Engineering and Physical Sciences Research Council (EPSRC), European Commission (EC), United States. Office of Naval Research, London Mathematical Society (LMS)
Grant number:	Euratom research and training programme 2014–2018 grant No 633053 (EC), NICOP grant N62909-15-1-N143 (ONR)

Request changes or add full text files to a record

Repository staff actions (login required)

View Item

Downloads