Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall

The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal betw...

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Autores: Bowman, C., Dickinson, D., Horvath, L., Lunniss, A.E., Wilson, H.R., Jet Contributors, García Muñoz, Manuel
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2018
País:España
Institución:Universidad de Sevilla (US)
Repositorio:idUS. Depósito de Investigación de la Universidad de Sevilla
OAI Identifier:oai:idus.us.es:11441/99696
Acceso en línea:https://hdl.handle.net/11441/99696
https://doi.org/10.1088/1741-4326/aa90bc
Access Level:acceso abierto
Palabra clave:Pedestal
ELMs
JET
Stability
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spelling Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wallBowman, C.Dickinson, D.Horvath, L.Lunniss, A.E.Wilson, H.R.Jet ContributorsGarcía Muñoz, ManuelPedestalELMsJETStabilityThe pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, δ = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement—a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.EURATOM 633053EPSRC EP/K504178/1EPSRC EP/L01663X/1Plasma HEC Consortium EPSRCV EP/L000237/1IOP PublishingFísica Atómica, Molecular y NuclearRNM138: Física Nuclear Aplicada2018info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionapplication/pdfapplication/pdfhttps://hdl.handle.net/11441/99696https://doi.org/10.1088/1741-4326/aa90bcreponame:idUS. Depósito de Investigación de la Universidad de Sevillainstname:Universidad de Sevilla (US)InglésNuclear Fusion, 58 (1), 1-17.633053EP/K504178/1EP/L01663X/1EP/L000237/1https://doi.org/10.1088/1741-4326/aa90bcinfo:eu-repo/semantics/openAccessoai:idus.us.es:11441/996962026-06-17T12:51:07Z
dc.title.none.fl_str_mv Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
title Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
spellingShingle Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
Bowman, C.
Pedestal
ELMs
JET
Stability
title_short Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
title_full Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
title_fullStr Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
title_full_unstemmed Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
title_sort Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall
dc.creator.none.fl_str_mv Bowman, C.
Dickinson, D.
Horvath, L.
Lunniss, A.E.
Wilson, H.R.
Jet Contributors
García Muñoz, Manuel
author Bowman, C.
author_facet Bowman, C.
Dickinson, D.
Horvath, L.
Lunniss, A.E.
Wilson, H.R.
Jet Contributors
García Muñoz, Manuel
author_role author
author2 Dickinson, D.
Horvath, L.
Lunniss, A.E.
Wilson, H.R.
Jet Contributors
García Muñoz, Manuel
author2_role author
author
author
author
author
author
dc.contributor.none.fl_str_mv Física Atómica, Molecular y Nuclear
RNM138: Física Nuclear Aplicada
dc.subject.none.fl_str_mv Pedestal
ELMs
JET
Stability
topic Pedestal
ELMs
JET
Stability
description The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, δ = 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electronscale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement—a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.
publishDate 2018
dc.date.none.fl_str_mv 2018
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv https://hdl.handle.net/11441/99696
https://doi.org/10.1088/1741-4326/aa90bc
url https://hdl.handle.net/11441/99696
https://doi.org/10.1088/1741-4326/aa90bc
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv Nuclear Fusion, 58 (1), 1-17.
633053
EP/K504178/1
EP/L01663X/1
EP/L000237/1
https://doi.org/10.1088/1741-4326/aa90bc
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
application/pdf
dc.publisher.none.fl_str_mv IOP Publishing
publisher.none.fl_str_mv IOP Publishing
dc.source.none.fl_str_mv reponame:idUS. Depósito de Investigación de la Universidad de Sevilla
instname:Universidad de Sevilla (US)
instname_str Universidad de Sevilla (US)
reponame_str idUS. Depósito de Investigación de la Universidad de Sevilla
collection idUS. Depósito de Investigación de la Universidad de Sevilla
repository.name.fl_str_mv
repository.mail.fl_str_mv
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score 15,300724

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