Criticality and turbulence in a resistive magnetohydrodynamic current sheet

Area of Science:

• Plasma Physics
• Astrophysical Plasmas
• Space Physics

Background:

• Current sheets in plasmas are crucial for magnetic reconnection.
• Understanding their dynamics is key to explaining phenomena in space and astrophysics.
• Previous models often simplified the complex interplay of forces within current sheets.

Purpose of the Study:

• To investigate the scaling properties of a 2D plasma current-sheet simulation.
• To identify if the observed dynamics align with self-organized criticality (SOC) principles.
• To explore the relationship between SOC and intermittent turbulence (IT) in driven plasma systems.

Main Methods:

• Simulated a 2D plasma current sheet using full magnetohydrodynamic (MHD) equations.
• Incorporated current-dependent resistivity into the model.
• Analyzed spatiotemporal avalanches, power-law statistics, and scaling laws (critical susceptibility, finite-size scaling, geometric exponents).
• Examined multiscale correlations in the velocity field.

Main Results:

• The simulation demonstrated spatiotemporal avalanches with power-law statistics for lifetimes and sizes.
• Identified dynamics consistent with self-organized criticality (SOC) by verifying scaling laws.
• Obtained critical exponents indicating a slowly driven SOC state, comparable to directed stochastic sandpile models.
• Found velocity field correlations numerically indistinguishable from intermittent turbulence (IT) theories.

Conclusions:

• The findings suggest that driven current sheets in plasmas can exhibit self-organized criticality (SOC).
• SOC and intermittent turbulence (IT) may coexist in these systems.
• Provides insights into the physical conditions favoring SOC in various plasma systems with instabilities.