dc-Magnetic-field generation in unmagnetized shear flows

Area of Science:

• Plasma Physics
• Astrophysical Plasmas
• Space Physics

Background:

• Electron-ion shear flows are common in astrophysical and laboratory plasmas.
• The generation of magnetic fields in such flows is crucial for understanding plasma dynamics.
• Previous models often simplified the kinetic effects governing these interactions.

Purpose of the Study:

• To investigate the mechanisms responsible for generating direct current (dc) magnetic fields in unmagnetized electron-ion shear flows.
• To describe the growth and saturation of these dc magnetic fields using a kinetic model.
• To validate theoretical predictions with advanced numerical simulations.

Main Methods:

• Development of a kinetic model to describe magnetic field generation.
• Utilizing multidimensional particle-in-cell (PIC) simulations.
• Analysis of scenarios with both initial thermal effects and electron-scale shear instabilities.

Main Results:

• DC magnetic fields are generated by initial thermal effects or electron-scale shear instabilities, particularly the cold Kelvin-Helmholtz instability.
• The kinetic model accurately predicts the growth and saturation of dc magnetic fields.
• PIC simulations confirm the formation of long-lived magnetic fields (t~100s ω(pi)(-1)) within the shear layer, with specific transverse widths and magnitudes dependent on initial conditions.

Conclusions:

• Electron-scale shear gradients are fundamental to dc magnetic field generation in these flows.
• The study provides a comprehensive kinetic description and simulation-based evidence for magnetic field formation.
• The findings have implications for understanding magnetic field dynamics in various plasma environments.