Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas
The properties of the edge ion-scale turbulence are studied using the beam emission spectroscopy (BES) diagnostic on MAST. Evidence of the formation of large-scale high-amplitude coherent structures, filamentary density blobs and holes, 2–4 cm inside the plasma separatrix is presented. Measurements...
| Main Authors: | , , , , , |
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| Other Authors: | |
| Format: | Journal article |
| Language: | English |
| Published: |
Cambridge University Press
2023
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| _version_ | 1826312803754967040 |
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| author | Sladkomedova, A Cziegler, I Field, AR Schekochihin, AA Dunai, D Ivanov, PG |
| author2 | MAST-U Team |
| author_facet | MAST-U Team Sladkomedova, A Cziegler, I Field, AR Schekochihin, AA Dunai, D Ivanov, PG |
| author_sort | Sladkomedova, A |
| collection | OXFORD |
| description | The properties of the edge ion-scale turbulence are studied using the beam emission spectroscopy (BES) diagnostic on MAST. Evidence of the formation of large-scale high-amplitude coherent structures, filamentary density blobs and holes, 2–4 cm inside the plasma separatrix is presented. Measurements of radial velocity and skewness of the density fluctuations indicate that density holes propagate radially inwards, with the skewness profile peaking at 7–10 cm inside the separatrix. Poloidal velocities of the density fluctuations measured using cross-correlation time delay estimation (CCTDE) are found to exhibit an intermittent behaviour. Zonal-flow analysis reveals the presence of poloidally symmetric coherent oscillations – low-frequency (LF) zonal flows and geodesic acoustic modes (GAM). Shearing rates of the observed zonal flows are found to be comparable to the turbulence decorrelation rate. The observed bursts in density-fluctuation power are followed by quiescent periods with a transient increase in the power of sheared flows. Three-wave interactions between broadband turbulence and a GAM are illustrated using the autobispectral technique. It is shown that the zonal flows and the density-fluctuation field are nonlinearly coupled and LF zonal flows mediate the energy transfer from high- to low-frequency density fluctuations. |
| first_indexed | 2024-04-23T08:27:14Z |
| format | Journal article |
| id | oxford-uuid:cc198215-8cfa-45e3-8277-827678f6f63c |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-04-23T08:27:14Z |
| publishDate | 2023 |
| publisher | Cambridge University Press |
| record_format | dspace |
| spelling | oxford-uuid:cc198215-8cfa-45e3-8277-827678f6f63c2024-04-19T12:35:28ZIntermittency of density fluctuations and zonal-flow generation in MAST edge plasmasJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:cc198215-8cfa-45e3-8277-827678f6f63cEnglishSymplectic ElementsCambridge University Press2023Sladkomedova, ACziegler, IField, ARSchekochihin, AADunai, DIvanov, PGMAST-U TeamEUROfusion MST1 TeamThe properties of the edge ion-scale turbulence are studied using the beam emission spectroscopy (BES) diagnostic on MAST. Evidence of the formation of large-scale high-amplitude coherent structures, filamentary density blobs and holes, 2–4 cm inside the plasma separatrix is presented. Measurements of radial velocity and skewness of the density fluctuations indicate that density holes propagate radially inwards, with the skewness profile peaking at 7–10 cm inside the separatrix. Poloidal velocities of the density fluctuations measured using cross-correlation time delay estimation (CCTDE) are found to exhibit an intermittent behaviour. Zonal-flow analysis reveals the presence of poloidally symmetric coherent oscillations – low-frequency (LF) zonal flows and geodesic acoustic modes (GAM). Shearing rates of the observed zonal flows are found to be comparable to the turbulence decorrelation rate. The observed bursts in density-fluctuation power are followed by quiescent periods with a transient increase in the power of sheared flows. Three-wave interactions between broadband turbulence and a GAM are illustrated using the autobispectral technique. It is shown that the zonal flows and the density-fluctuation field are nonlinearly coupled and LF zonal flows mediate the energy transfer from high- to low-frequency density fluctuations. |
| spellingShingle | Sladkomedova, A Cziegler, I Field, AR Schekochihin, AA Dunai, D Ivanov, PG Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title | Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title_full | Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title_fullStr | Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title_full_unstemmed | Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title_short | Intermittency of density fluctuations and zonal-flow generation in MAST edge plasmas |
| title_sort | intermittency of density fluctuations and zonal flow generation in mast edge plasmas |
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