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Title: Processes and properties of edge-localised instabilities in 2T 2MA plasmas in the Joint European Torus

During July 2012, 150 almost identical H-mode plasmas were consecutively created in the Joint European Torus, providing a combined total of approximately 8 minutes of steady-state plasma with 15 000 Edge Localised Modes (ELMs). In principle, each of those 15 000 ELMs are statistically equivalent. Here, the changes in edge density and plasma energy associated with those ELMs are explored, using the spikes in Beryllium II (527 nm) radiation as an indicator for the onset of an ELM. Clearly different timescales are observed during the ELM process. Edge temperature falls over a 2 ms timescale, edge density and pressure fall over a 5 ms timescale, and there is an additional 10 ms timescale that is consistent with a resistive relaxation of the plasma's edge. The statistical properties of the energy and density losses due to the ELMs are explored. For these plasmas the ELM energy (δE) is found to be approximately independent of the time between ELMs, despite the average ELM energy (〈δE〉) and average ELM frequency (f) being consistent with the scaling of 〈δE〉∝1/f. Instead, beyond the first 0.02 s of waiting time between ELMs, the energy losses due to individual ELMs are found to be statistically the same. Surprisingly no correlation is found betweenmore » the energies of consecutive ELMs either. A weak link is found between the density drop and the ELM waiting time. Consequences of these results for ELM control and modelling are discussed.« less
Authors:
;  [1] ;  [2]
  1. JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
22403264
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 11; Other Information: (c) 2014 EURATOM; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BERYLLIUM; DENSITY; EDGE LOCALIZED MODES; H-MODE PLASMA CONFINEMENT; JET TOKAMAK; PLASMA