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Machine Learning Characterization of Alfvénic and Sub-Alfvénic Chirping and Correlation With Fast-Ion Loss at NSTX

Journal Article · · IEEE Transactions on Plasma Science

Abrupt large events in the Alfvenic and sub-Alfvenic frequency bands in tokamaks are typically correlated with increased fast ion loss. Here, machine learning is used to speed up the laborious process of characterizing the behaviour of magnetic perturbations from corresponding frequency spectrograms that are typically identified by humans. Analysis allows for comparison between different mode character (such as quiescent, fixedfrequency, chirping, avalanching) and plasma parameters obtained from the TRANSP code such as the ratio of the neutral beam injection (NBI) velocity and the Alfven velocity (vinj./vA), the q-profile, and the ratio of the neutral beam beta and the total plasma beta (βbeam,i/β). In agreement with previous work by Fredrickson et al., in this work, we find correlation between βbeam,i and mode character. In addition, previously unknown correlations are found between moments of the spectrograms and mode character. Character transition from quiescent to non-quiescent behaviour for magnetic fluctuations in the 50 - 200 kHz frequency band is observed along the boundary vΦ ≲ (1/4) (vinj. - 3vA) where vΦ is the rotation

Research Organization:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE; Biotechnology and Biological Sciences Research Council (BBSRC) Engineering and Physical Sciences Research Council (EPSRC); Euratom
Grant/Contract Number:
AC02-09CH11466
OSTI ID:
1643701
Journal Information:
IEEE Transactions on Plasma Science, Journal Name: IEEE Transactions on Plasma Science Journal Issue: 1 Vol. 48; ISSN 0093-3813; ISSN 1939-9375
Publisher:
IEEECopyright Statement
Country of Publication:
United States
Language:
English

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