Low frequency m = 1 modes during standard and improved confinement scenarios in W7-X

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F61389021%3A_____%2F25%3A00647938" target="_blank" >RIV/61389021:_____/25:00647938 - isvavai.cz</a>

Výsledek na webu

<a href="https://iopscience.iop.org/article/10.1088/1741-4326/adbb7e" target="_blank" >https://iopscience.iop.org/article/10.1088/1741-4326/adbb7e</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1088/1741-4326/adbb7e" target="_blank" >10.1088/1741-4326/adbb7e</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Low frequency m = 1 modes during standard and improved confinement scenarios in W7-X

Popis výsledku v původním jazyce

In the Wendelstein 7-X stellarator (W7-X), two related global low-frequency electromagnetic oscillations are observed on many diagnostic systems (e.g. plasma stored energy, Mirnov coils, Langmuir probes, etc). The activity is related to the presence of magnetic islands at certain radii. However, in contrast to initial analyses in earlier works, the mode activity is not localized at the magnetic islands, but rather of an m = 1 type in the plasma outer-core. We observe a strong cross-correlation between electron temperature fluctuations in the confined plasma region, measured with electron cyclotron emission radiometer, and scrape-off layer fluctuations measured with electric probes. Two limiting cases of the mode activity can be observed based on magnetic configuration. A quasi-continuous (QC) mode case, with frequencies of typically some 100 Hz , is found in configurations that have a 5 / 5 magnetic island chain at the last closed flux surface (LCFS). The mode frequency is found to increase linearly with the core electron temperature and decrease with increasing electron density. In contrast, for magnetic configurations with the 5 / 5 magnetic island chain just inside the LCFS, the mode activity becomes bursty and intermittent, exhibiting a crash-event like signature. Although these intermittent events are less frequent, more plasma stored energy is lost per event compared to a period of the QC oscillations. The intermittent oscillations are observable as a broadband modulation in turbulence spectra on most diagnostic systems. The presence of these intermittent bursts goes along with an improved energy confinement in the plasma, superficially resembling H-mode and Edge Localized Modes in tokamaks. A self-limiting process is proposed as an explanation of the intermittent oscillations based on observed ejection of particles during each crash event, which leads to steepening of density profiles and temporary suppression of ion temperature gradient turbulence and in turn suppression of turbulence driven m = 1 mode causing the crash.

Název v anglickém jazyce

Low frequency m = 1 modes during standard and improved confinement scenarios in W7-X

Popis výsledku anglicky

In the Wendelstein 7-X stellarator (W7-X), two related global low-frequency electromagnetic oscillations are observed on many diagnostic systems (e.g. plasma stored energy, Mirnov coils, Langmuir probes, etc). The activity is related to the presence of magnetic islands at certain radii. However, in contrast to initial analyses in earlier works, the mode activity is not localized at the magnetic islands, but rather of an m = 1 type in the plasma outer-core. We observe a strong cross-correlation between electron temperature fluctuations in the confined plasma region, measured with electron cyclotron emission radiometer, and scrape-off layer fluctuations measured with electric probes. Two limiting cases of the mode activity can be observed based on magnetic configuration. A quasi-continuous (QC) mode case, with frequencies of typically some 100 Hz , is found in configurations that have a 5 / 5 magnetic island chain at the last closed flux surface (LCFS). The mode frequency is found to increase linearly with the core electron temperature and decrease with increasing electron density. In contrast, for magnetic configurations with the 5 / 5 magnetic island chain just inside the LCFS, the mode activity becomes bursty and intermittent, exhibiting a crash-event like signature. Although these intermittent events are less frequent, more plasma stored energy is lost per event compared to a period of the QC oscillations. The intermittent oscillations are observable as a broadband modulation in turbulence spectra on most diagnostic systems. The presence of these intermittent bursts goes along with an improved energy confinement in the plasma, superficially resembling H-mode and Edge Localized Modes in tokamaks. A self-limiting process is proposed as an explanation of the intermittent oscillations based on observed ejection of particles during each crash event, which leads to steepening of density profiles and temporary suppression of ion temperature gradient turbulence and in turn suppression of turbulence driven m = 1 mode causing the crash.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10305 - Fluids and plasma physics (including surface physics)

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2025

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Nuclear Fusion

ISSN

0029-5515

e-ISSN

1741-4326

Svazek periodika

65

Číslo periodika v rámci svazku

4

Stát vydavatele periodika

US - Spojené státy americké

Počet stran výsledku

16

Strana od-do

046010

Kód UT WoS článku

001442133100001

EID výsledku v databázi Scopus

2-s2.0-105000246524