Bicoherence Analysis of Electrostatic Interchange Mode Coupling in a Turbulent Laboratory Magnetosphere*

Plasmas confined by a strong dipole field exhibit interchange turbulence, which previous experiments have shown respond locally to active feedback [1].  On the Collisionless Terrella Experiment (CTX), this turbulence is characterized by low frequency, low order, quasi-coherent modes with complex spectral dynamics.  We apply bicoherence analysis [2] to study nonlinear phase coupling in a variety of scenarios. First, we study the self-interaction of the naturally occurring interchange turbulence; this analysis is then expanded to include the effects of driven modes in the frequency range of the background turbulent oscillations.  Initial measurements of coupling coefficients are presented, as well as evidence for an inverse cascade. Future work is also discussed, including use of wavelet bicoherence analysis and applications to planetary magnetospheres.

[1]  Roberts, Mauel, and Worstell, Phys Plasmas (2015).

[2]  Grierson, Worstell, and Mauel, Phys Plasmas (2009).