Fluidization of collisionless plasma turbulence

Area of Science:

• Plasma Physics
• Astrophysics
• Fluid Dynamics

Background:

• Collisionless plasmas exhibit phase mixing, leading to Landau damping of compressive fluctuations.
• Observed broad power-law spectra in turbulent astrophysical plasmas, like the solar wind, contradict Landau damping predictions.

Purpose of the Study:

• Investigate the nature of compressive fluctuations in turbulent collisionless plasmas.
• Explain the discrepancy between theoretical predictions and observations of plasma turbulence.
• Re-evaluate the role of Landau damping in kinetic plasma turbulence.

Main Methods:

• Direct numerical simulations of magnetized plasma.
• Theoretical analysis using nonlinear advection and stochastic echoes.
• Comparison with fluid turbulence models.

Main Results:

• Turbulence in collisionless plasmas shows broad power-law spectra, similar to collisional fluids.
• Phase mixing is suppressed by stochastic echoes arising from nonlinear advection.
• Collisionless plasmas behave effectively as dissipationless except at very small scales.

Conclusions:

• Turbulence in collisionless plasmas resembles fluid turbulence, resolving the solar wind fluctuation puzzle.
• The concept of Landau damping as a primary dissipation mechanism in such systems needs revision.
• Fluid turbulence physics is applicable even to kinetic, collisionless systems.