Direct observations of anomalous resistivity and diffusion in collisionless plasma

Area of Science:

• Space Physics
• Plasma Physics
• Astrophysical Plasmas

Background:

• Coulomb collisions are rare in low-density astrophysical plasmas, limiting traditional plasma resistivity and diffusion.
• Wave-particle interactions can induce anomalous resistivity, potentially crucial for processes like magnetic reconnection.
• Previous theories suggested waves might provide both diffusion and resistivity, supporting the reconnection electric field.

Purpose of the Study:

• To directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves.
• To determine the role of these wave-induced phenomena in supporting the magnetic reconnection electric field.
• To understand how wave-particle interactions modify plasma dynamics during magnetic reconnection.

Main Methods:

• Utilized in-situ measurements from the four Magnetospheric Multiscale (MMS) spacecraft.
• Directly quantified anomalous resistivity, viscosity, and cross-field electron diffusion.
• Analyzed data specifically associated with lower hybrid waves during magnetic reconnection events.

Main Results:

• Anomalous resistivity induced by lower hybrid waves is approximately balanced by anomalous viscosity.
• These waves do not directly contribute to sustaining the electric field driving magnetic reconnection.
• Waves generate anomalous electron drift and diffusion across the current layer, relaxing density gradients.

Conclusions:

• Lower hybrid waves do not provide the necessary resistivity to support the reconnection electric field.
• Wave-induced anomalous electron diffusion significantly modifies plasma density gradients on ion cyclotron timescales.
• These findings reveal a key mechanism by which wave-particle interactions alter magnetic reconnection processes in astrophysical plasmas.