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

Result code in 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>

Result on the web

<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>

Result language

angličtina

Original language name

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

Original language description

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.

Czech name

—

Czech description

—

Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10305 - Fluids and plasma physics (including surface physics)

Project

—

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2025

Confidentiality

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

Name of the periodical

Nuclear Fusion

ISSN

0029-5515

e-ISSN

1741-4326

Volume of the periodical

65

Issue of the periodical within the volume

4

Country of publishing house

US - UNITED STATES

Number of pages

16

Pages from-to

046010

UT code for WoS article

001442133100001

EID of the result in the Scopus database

2-s2.0-105000246524