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Magnetic-field generation and amplification in an expanding plasma
K M Schoeffler1, N F Loureiro1, R A Fonseca2
1Instituto de Plasmas e Fusão Nuclear-Laboratório Associado, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal.
Physical Review Letters
|May 20, 2014
Summary
Particle-in-cell simulations reveal magnetic field generation in plasmas. The Weibel instability dominates over the Biermann battery effect for larger systems, with fields saturating at a fixed amplitude.
Area of Science:
- Plasma physics
- Astrophysics
- Computational physics
Background:
- Magnetic fields are crucial in astrophysical plasmas.
- Understanding their generation mechanisms is key to plasma dynamics.
- Previous studies suggested the Biermann battery effect.
Purpose of the Study:
- Investigate magnetic field generation in plasmas with perpendicular gradients.
- Compare the roles of the Biermann battery and Weibel instability.
- Analyze the scaling of magnetic fields with system size.
Main Methods:
- Particle-in-cell (PIC) simulations.
- Varying system sizes (L) relative to ion skin depth (d(i)).
- Analysis of magnetic field strength, saturation, and energy spectra.
Main Results:
- Biermann battery effect dominates for L ~ d(i).
- Weibel instability becomes dominant for large L/d(i), producing magnetic fields.
- Weibel-produced fields saturate at plasma beta ~ 100, independent of L.
- Magnetic energy spectra follow a power law with slope -16/3.
Conclusions:
- The Weibel instability is a primary driver of magnetic fields in large-scale plasmas.
- Magnetic field saturation is independent of system size for Weibel-dominated regimes.
- Simulation results align with theoretical predictions for magnetic energy spectra.
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