# Intermittence

A signal is called intermittent when at irregularly spaced intervals, its standard deviation increases sharply. The time intervals with larger standard deviation are sometimes called 'bursts'.

The degree of intermittence can be quantified using various methods.
One traditional approach is through the Kurtosis of the signal ^{[1]}.
However, the Kurtosis is a quantifier of the shape of the distribution function, and does not really take the time-varying nature of intermittence into account.

A better quantifier is provided by a method from the field of Chaos theory, based on a box counting technique ^{[2]}^{[3]}.

It has been shown that the intermittence can be fruitfully exploited in the framework of fusion plasma physics: namely, it is found to decrease at locations where a single (helical, MHD) mode dominates, thus allowing to study the relation between turbulence and helical modes, and it was found to be affected by plasma flows (such as zonal flows) ^{[4]}^{[5]}^{[6]}^{[7]}^{[8]}.

## References

- ↑ Batchelor G K 1953 The Theory of Homogeneous Turbulence (Cambridge: Cambridge University Press), p. 183
- ↑ Carreras B A et al 2000 Intermittency of plasma edge fluctuation data: multifractal analysis, Phys. Plasmas
**7**3278 - ↑ B. van Milligen and R. Sánchez. Analysis of Turbulence in Fusion Plasmas. IOP Series in Plasma Physics. IOP Publishing, 2022. ISBN 978-0-7503-4854-6
- ↑ B. Carreras, L. García, J. Nicolau, B. van Milligen, U. Hoefel, M. Hirsch, and the TJ-II and W7-X Teams. Intermittence and turbulence in fusion devices. Plasma Phys. Control. Fusion, 62:025011, 2020
- ↑ B. P. van Milligen, B. Carreras, L. García, and C. Hidalgo. The localization of low order rational surfaces based on the intermittence parameter in the TJ-II stellarator. Nucl. Fusion, 60:056010, 2020
- ↑ B. van Milligen, A. Melnikov, B. Carreras, L. Garcia, A. Kozachek, C. Hidalgo, J. de Pablos, P. Khabanov, L. Eliseev, M. Drabinskij, A. Chmyga, L. Krupnik, the HIBP Team, and the TJ-II Team. Topology of 2-d turbulent structures based on intermittence in the TJ-II stellarator. Nucl. Fusion, 61(11):116063, 2021
- ↑ B. van Milligen, B. Carreras, I. Voldiner, U. Losada, C. Hidalgo, and the TJ-II Team. Causality, intermittence and crossphase evolution during confinement transitions in the TJ-II stellarator. Phys. Plasmas, 28:092302, 2021
- ↑ B. van Milligen, I. Voldiner, B. Carreras, L. García, M. Ochando, and the TJ-II Team. Rational surfaces, flows and radial structure in the TJ-II stellarator. Nucl. Fusion, 63:016027, 2023