7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Characterization of fluctuation and transport in KSTAR edge plasmas using theinformation-theoretic methodology
Minjun J. Choi1, Jae-Min Kwon1, Juhyung Kim1, Tongnyeol Rhee1, Jun-Gyo Bak1, Giwook Shin1,Hyun-Seok Kim1, Hogun Jhang1, Kimin Kim1, Gunsu S. Yun2, Minwoo Kim1, SangKyeun Kim3,
Helen H. Kaang1, Jong-Kyu Park4, Hyung Ho Lee1, Yongkyoon In5, Jaehyun Lee1, Minho Kim1,Byoung-Ho Park1
1Korea Institute of Fusion EnergyPohang University of Science and Technology
3Princeton University
4Seoul National University
5
Ulsan National Institute of Science and Technology
2e-mail (speaker): mjchoi@kfe.re.kr
Significant turbulent fluctuations are frequently
measured in tokamak edge plasmas in various conditions
such as the L-mode phase, the H-mode inter edge
localized mode (ELM) phase, the natural ELM freephase, and the resonant magnetic perturbation (RMP)
driven ELM suppression phase. We present that an
information-theoretical methodology such as theComplexity Entropy analysis can extract valuable
information from the measured turbulent fluctuation andparticle flux signals [1].
Based on the probability distribution of amplitude
orders in a given signal, the Complexity Entropy analysis[2] was proven to tell whether it is deterministicallychaotic (e.g., generated by the logistic map) or stochastic(e.g., generated by the fractional Brownian motion).
Here, Entropy and Complexity are information theoretic
terminologies having specific meaning. Entropy means ameasure of missing (unknown) information of the given
probability distribution. The equiprobable distribution
has the maximum Entropy because almost nothing canbe learned from the equiprobable distribution.
Complexity was suggested as the product ofDisequilibrium and Entropy to capture the intuitive
notion about a complex system [3]. Disequilibrium isanother information theoretic terminology, meaning ameasure of distance from the equiprobable distribution.
The idea of Complexity can be understood byconsidering two systems (a perfect crystal and an idealgas) regarded as simple [3]. A perfect crystal, represented
by a peaked probability distribution of states, would havelarge Disequilibrium but very small Entropy, so theirproduct Complexity would remain small. On the otherhand, an ideal gas, represented by the equiprobabledistribution of states, has large Entropy but very small
Disequilibrium, so again Complexity would remainsmall. The location of a given signal in the Complexity
and Entropy plane tells whether it is chaotic or
stochastic.

The analysis result on fluctuation signals shows thatthe pedestal top temperature fluctuation during the RMP
ELM suppression phase is stochastic, distinguished fromthe chaotic temperature fluctuation during the natural
ELM free phase. Also, the analysis of the ion saturation
current measurement around the major outer striking
point on the divertor also shows that it becomes morestochastic as the RMP field increases toward thesuppression level. Using the Complexity-Entropy
analysis, the dynamical behavior of edge turbulent
fluctuation and flux can be identified, supporting astochastic model for the pedestal dynamics especiallywhen a strong field penetration is applied. In addition,
the origin of the stochastic fluctuation in the narrowlayer on the pedestal top and the mechanism of the RMP
ELM suppression were discussed based on additional
spectral analyses and results of the recent numerical [4]and theoretical [5, 6] studies.

References[1] M. J. Choi et al., Phys. Plasmas 29, 122504 (2022)[2] O. A. Rosso et al., Phys. Rev. Lett. 99, 154102 (2007)[3] R. López-Ruiz et al., Phys. Lett. A 209, 321 (1995)[4] Q. M. Hu et al., Nucl. Fusion 60, 076001 (2020)[5] F. L. Waelbroeck et al., Phys. Rev. Lett. 87, 215003(2001)[6] M. Cao et al., Plasma Phys. Control. Fusion 64,035016 (2022)