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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