Proton core heating and beam formation via parametrically unstable Alfvén-cyclotron waves

Area of Science:

• Space plasma physics
• Plasma astrophysics
• Kinetic theory

Background:

• The solar wind exhibits complex proton velocity distributions, particularly in the fast solar wind.
• Understanding the underlying plasma processes driving these distributions is crucial for solar wind modeling.

Purpose of the Study:

• To investigate the impact of compressible fluctuations from parametric instabilities on proton velocity distributions.
• To determine the role of kinetic effects in solar wind plasma dynamics.

Main Methods:

• Utilizing Vlasov theory to analyze plasma behavior.
• Employing one-dimensional hybrid simulations to model wave-particle interactions.

Main Results:

• Parametric instabilities drive Alfvén-cyclotron waves, leading to the generation of field-aligned proton beams.
• Proton beams exhibit drift speeds exceeding the Alfvén speed.
• Phase mixing causes the main proton distribution to become anisotropic, consistent with solar wind observations.

Conclusions:

• Kinetic effects significantly influence proton velocity distributions, even in regimes where fluid approximations might seem sufficient.
• The study identifies key instabilities responsible for observed solar wind features.