Whistler modes with wave magnetic fields exceeding the ambient field

Area of Science:

• Plasma Physics
• Magnetohydrodynamics

Background:

• Whistler-mode waves are fundamental in plasma physics.
• High electron-beta plasmas present unique wave propagation characteristics.

Purpose of the Study:

• To investigate the excitation and properties of whistler-mode wave packets in a high electron-beta plasma.
• To explore wave packet topology and propagation dynamics.

Main Methods:

• Excitation of waves using a loop antenna with controlled dipole moment orientation.
• Observation of wave packet topology, including spheromak-like structures.
• Analysis of wave propagation characteristics and energy densities.

Main Results:

• Whistler-mode wave packets with fields exceeding the ambient dc magnetic field were successfully excited.
• Wave packets exhibited spheromak topology when the antenna's dipole moment was opposite to the dc field.
• Propagating wave packets demonstrated force-free electron magnetohydrodynamics fields with wave energy exceeding particle energy density.
• Stable propagation at subelectron thermal velocities was observed.

Conclusions:

• The study demonstrates controlled excitation of complex whistler-mode wave structures in high beta plasmas.
• Electron magnetohydrodynamics fields can be force-free and possess high wave energy density.
• Spheromak-like topologies can be generated and propagate in the whistler mode.