Electromagnetic instabilities in unmagnetized plasmas

Area of Science:

• Plasma Physics
• Astrophysical Plasmas
• Magnetohydrodynamics

Background:

• Nonuniform, unmagnetized plasmas exhibit complex behaviors under local perturbations.
• Understanding electromagnetic field generation is crucial for astrophysical phenomena and laboratory plasmas.

Purpose of the Study:

• To investigate the generation of electromagnetic fields in nonuniform unmagnetized plasmas.
• To analyze the role of plasma vorticity, compressibility, and density gradients in instability development.
• To determine the conditions under which ion acoustic waves become electromagnetic.

Main Methods:

• Theoretical analysis of plasma perturbations, focusing on electron and ion time scales.
• Examination of coupling between plasma vorticity and compressibility in inhomogeneous plasmas.
• Inclusion of electron-ion plasma dynamics and thermal fluctuations in a collisionless model.

Main Results:

• Linearly growing electromagnetic fields are generated on both electron and ion time scales.
• Instabilities with mixed transverse and longitudinal characteristics arise in electron and electron-ion plasmas.
• Ion acoustic waves can become electromagnetic in the presence of steep density gradients, leading to megagauss magnetic fields.

Conclusions:

• Plasma density inhomogeneity couples vorticity and compressibility, driving electromagnetic instabilities.
• Ion dynamics are crucial for magnetic field instability in the low-frequency limit (omega << omega(pe)).
• The electron-ion plasma model successfully predicts megagauss magnetic field magnitudes, consistent with observations.