Linear technique to understand non-normal turbulence applied to a magnetized plasma

Area of Science:

• Plasma Physics
• Fluid Dynamics
• Nonlinear Dynamics

Background:

• Linear nonmodal analysis is superior to normal mode analysis for predicting turbulent properties in systems with nonorthogonal eigenvectors.
• The complex temporal evolution of nonmodal structures hinders quantitative analysis and prediction of turbulence.

Purpose of the Study:

• To develop a technique for modeling the impact of advective nonlinearities on spatial turbulent structures.
• To enhance the quantitative understanding and prediction of turbulence in nonlinear dynamical systems.

Main Methods:

• Modeling nonlinearities as a periodic randomizing force with a time scale aligned with critical balance arguments.
• Applying the technique to a model of drift wave turbulence in the Large Plasma Device.
• Comparing resulting growth rate spectra with those from nonlinear simulations.

Main Results:

• The developed technique provides a method to analyze the influence of nonlinearities on turbulent structures.
• Qualitative agreement was achieved between the predicted growth rate spectra and those from nonlinear simulations.
• The results showed particular improvement in comparison to eigenmode growth rate spectra.

Conclusions:

• The new technique effectively models the impact of nonlinearities on spatial turbulent structures.
• This approach offers improved predictions for turbulence, especially in systems dominated by nonmodal effects like drift wave turbulence.
• The findings contribute to a better understanding of turbulent phenomena in nonlinear dynamical systems and plasma devices.