English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Several analysis methods for nonstationary fluctuations are described andapplied to the edge localized mode (ELM) instabilities of limiter H-modeplasmas. The microwave scattering diagnostic observes poloidal $k_{\theta}$values of 3.3 cm$^{-1}$, averaged over a 20 cm region at the plasma edge.Ashort autoregressive filter enhances the nonstationary component of the plasmafluctuations by removing much of the background level of stationaryfluctuations. Between ELMs, the spectrum predominantly consists of broad-banded300-700 kHz fluctuations propagating in the electron diamagnetic driftdirection, indicating the presence of a negative electric field near the plasmaedge. The time-frequency spectrogram is computed with the multiple tapertechnique. By using the singular value decomposition of the spectrogram, it isshown that the spectrum during the ELM is broader and more symmetric than thatof the stationary spectrum. The ELM period and the evolution of the spectrumbetween ELMs varies from discharge to discharge. For the discharge underconsideration which has distinct ELMs with a 1 msec period, the spectrum has amaximum in the electron drift direction which relaxes to a near constant value%its characteristic shape in the first half millisecond after the end of theELM and then grows slowly. In contrast, the level of the fluctuations in theion drift direction increases exponentially by a factor of eight in the fivemilliseconds~after the ELM. High frequency precursors are found which occur onemillisecond before the ELMs and propagate in the ion drift direction. Theseprecursors are very short ($\sim 10 \mu$secs), coherent bursts, and theypredict the occurrence of an ELM with a high success rate.

Spectral Estimation of Plasma Fluctuations II: Nonstationary Analysis of ELM Spectra