Magnetic Field Amplification by Cosmic Rays Near Supernova Remnant Shocks

Mario Riquelme (Princeton) - Sept 21, 2009 at 12:10 pm

Cosmic ray (CR) acceleration in supernova remnants (SNRs) appears to be tightly related to a significant (factor of ~100) magnetic field amplification in the forward shock environment of these objects. We review the evidence supporting this magnetic growth, and use particle-in-cell plasma simulations to analyze the possible amplification mechanisms. First, we study the cosmic ray current-driven (CRCD) instability (Bell 2004), which is due to the electric current of positively charged CRs propagating parallel to the field in the upstream medium of SNR shocks. We show that this instability can potentially amplify the field to very non-linear values but, for the case of SNRs, it would only reach an amplification factor of ~10. Then we introduce a new mechanism, driven by CRs drifting perpendicular to the magnetic field direction in the field pre-amplified by the CRCD instability. We show that this perpendicular CR drift can naturally happen in regions close to SNR shocks, and lead to magnetic amplifications several times larger than the CRCD saturation limit.

The seminar will be held in 544 Campbell Hall.


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