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The MDF technique for the analysis of tokamak edge plasma fluctuations

Published online by Cambridge University Press:  21 November 2013

M. Lafouti ,
M. Ghoranneviss ,
S. Meshkani  and
A. Salar Elahi
M. Lafouti
Affiliation:
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
M. Ghoranneviss
Affiliation:
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
S. Meshkani
Affiliation:
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
A. Salar Elahi*
Affiliation:
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
*
†Email address for correspondence: [email protected]
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Abstract

Tokamak edge plasma was analyzed by applying the multifractal detrend fluctuation analysis (MF-DFA) technique. This method has found wide application in the analysis of correlations and characterization of scaling behavior of the time-series data in physiology, finance, and natural sciences. The time evolution of the ion saturation current (Is), the floating potential fluctuation (Vf), the poloidal electric field (Ep), and the radial particle flux (Γr) has been measured by using a set of Langmuir probes consisting of four tips on the probe head. The generalized Hurst exponents (h(q)), local fluctuation function (Fq(s)), the Rényi exponents (τ(q)) as well as the multifractal spectrum f(αh) have been calculated by applying the MF-DFA method to Is, Vf, and the magnetohydrodynamic (MHD) fluctuation signal. Furthermore, we perform the shuffling and the phase randomization techniques to detect the sources of multifractality. The nonlinearity shape of τ(q) reveals a multifractal behavior of the time-series data. The results show that in the presence of biasing, Is, Vf, Ep, and Γr reduce about 25%, 90%, 70%, and 50%, respectively, compared with the situation with no biasing. Also, they reduce about 15%, 90%, 35%, and 25%, respectively, after resonant helical magnetic field (RHF) application. In the presence of biasing or RHF, the amplitude of the power spectrum of Is, Vf, Γr, and MHD activity reduce remarkably in all the ranges of frequency, while their h(q) increase. The values of h(q) have been restricted between 0.6 and 0.68. These results are evidence of the existence of long-range correlations in the plasma edge turbulence. They also show the self-similar nature of the plasma edge fluctuations. Biasing or RHF reduces the amount of Fq(s). The multifractal spectrum width of Is, Vf, and MHD fluctuation amplitude reduce about 60%, 70%, and 42%, respectively, by applying biasing. In the presence of RHF, their width reduces about 60%, 85%, and 75%, respectively. It means that biasing and RHF reduce the degree of multifractality.

Type
Papers
Information
Journal of Plasma Physics , Volume 80 , Issue 1 , February 2014 , pp. 43 - 58
Copyright
Copyright © Cambridge University Press 2013 

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