An iterative wavelet method for diagnosing the onset of turbulence in magnetized plasma

Recent simulations suggest that a majority of the energy dissipation on kinetic scales in turbulent magnetized plasmas may occur in thin current sheets and other localized structures (e.g. [1]). Wavelet bases naturally capture localized structures of different length scales and provide an alternative to Fourier-based methods, which are not well-suited for these purposes. Here, we apply an iterative wavelet technique, originally formulated for neutral fluid turbulence (e.g., [2]), to extract and characterize coherent features in the plasma current density in simulations of Kelvin-Helmholtz unstable flow-shear layers conducted using several models (fully kinetic, hybrid kinetic ion/fluid electron, and Hall MHD). The onset of turbulence is identified with the growth of a background of incoherent fluctuations spread across a range of scales. We compare and demonstrate advantages of this technique against widely used diagnostics of turbulence such as the appearance of non-Gaussian statistics and Fourier spectra, among others.

[1] Karimabadi et al., PoP 20, 012303 (2013) and 21, 062308 (2014)
[2] Schneider et al., Journal of Turbulence, 7, N44 (2006)