Nonlinear magnetoacoustic waves in plasma with isentropic thermal instability

Area of Science:

• Plasma Physics
• Wave Propagation
• Magnetohydrodynamics

Background:

• Magnetoacoustic (MA) waves exhibit complex dispersion in heat-releasing plasma due to temperature and density-dependent heating/cooling.
• Isentropic instability can lead to MA wave amplification, but linear equations are limited by this instability.
• Existing nonlinear models (KdV, Burgers) have limitations in describing wave evolution in such media.

Purpose of the Study:

• To analyze the evolution of magnetoacoustic waves in heat-releasing plasma.
• To derive a new nonlinear equation applicable to both fast and slow MA waves, accounting for non-adiabatic processes.
• To investigate the formation and stability of nonlinear wave structures, including shock waves and self-sustained pulses.

Main Methods:

• Analogy between nonequilibrium relaxing gas and heat-releasing plasma.
• Derivation of a nonlinear magnetoacoustic equation (NMAE) by including quadratic nonlinear terms.
• Analytical solutions for shock waves and self-sustained pulses, validated by numerical solutions of NMAE and MHD equations.

Main Results:

• A novel NMAE is derived, differing from existing models and applicable without wave spectrum restrictions.
• Analytical solutions reveal shock waves and self-sustained (autowave) pulses, whose stability is confirmed numerically.
• Self-sustained pulses demonstrate complete shape recovery after collision, a phenomenon unique to isentropic instability.

Conclusions:

• The derived NMAE accurately describes MA wave evolution in heat-releasing plasma, including non-adiabatic effects.
• The study confirms the existence and stability of self-sustained autowave pulses under isentropic instability.
• The findings provide a new framework for understanding nonlinear wave phenomena in complex plasma environments.