Localized cyclotron mode driven by fast alpha particles under a nonuniform magnetic field

Area of Science:

• Plasma Physics
• Astrophysical Plasmas
• Particle Acceleration

Background:

• Resonance phenomena typically demand precise synchronization between waves and particles.
• Previous models assumed strict synchronism requirements for instabilities in magnetic fields.

Purpose of the Study:

• To investigate the survival of relativistic cyclotron instability under conditions of magnetic field nonuniformity.
• To reconcile simulation observations with analytical predictions for wave-particle interactions.

Main Methods:

• Hybrid particle-in-cell simulations were employed to model plasma behavior.
• Analytical theory was developed to include magnetic field profile and eigenvalue effects.
• Comparison of simulated wave profiles with theoretical predictions.

Main Results:

• Relativistic cyclotron instability was observed to persist even when magnetic field nonuniformity surpassed synchronism requirements.
• A localized eigenmode was identified and found consistent with analytical predictions.
• The wave profile exhibited significant spatial extent in regions of negative frequency mismatch, contrary to expectations.

Conclusions:

• The study demonstrates that relativistic cyclotron instability is more robust to magnetic field variations than previously thought.
• The findings necessitate a revision of the understanding of resonance conditions in magnetized plasmas.
• The observed phenomenon has implications for particle dynamics, particularly for alpha particles.