The Fusion and Astrophysical Plasma Physics Group within the Physics Department and the Center for Astrophysics and Space Sciences at the University of California, San Diego is led by Professor Patrick H. Diamond, Distinguished Professor of Physics, and consists of two research scientists-- Mikhail Malkov, Fred Hinton, one Postdoctoral Scholar and two graduate student researchers-- and is managed by an administrative assistant.
Plus Charge Prevalence in Cosmic Rays: Room for Dark Matter in the Positron Spectrum
M.A. Malkov, P.H. Diamond and R.Z. Sagdeev
The unexpected energy spectrum of the positron/electron ratio is interpreted astrophysically, with a possible exception of the 100-300 GeV range. The data indicate that this ratio, after a decline between 0:5 -8 GeV, rises steadily with a trend towards saturation at 200-400GeV. These observations (except for the trend) appear to be in conflict with the diffusive shock acceleration (DSA) mechanism, operating in a single supernova remnant (SNR) shock. We argue that e+=e- ratio can still be explained by the DSA if positrons are accelerated in a subset of SNR shocks which: (i) propagate in clumpy gas media, and (ii) are modified by accelerated CR protons. The protons penetrate into the dense gas clumps upstream to produce positrons and, charge the clumps positively. The induced electric field expels positrons into the upstream plasma where they are shock-accelerated. Since the shock is modified, these positrons develop a harder spectrum than that of the CR electrons accelerated in other SNRs. Mixing these populations explains the increase in the e+=e- ratio at E > 8 GeV. It decreases at E < 8 GeV because of a subshock weakening which also results from the shock modification. Contrary to the expelled positrons, most of the antiprotons, electrons, and heavier nuclei, are left unaccelerated inside the clumps. Scenarios for the 100-300 GeV AMS-02 fraction exceeding the model prediction, including, but not limited to, possible dark matter contribution, are also discussed. Submitted to arXiv.org
To the memory of Professor Marshall N. Rosenbluth - an American plasma physicist and member of the National Academy of Sciences - who passed away on September 23, 2003.
We are working primarily on the theory of fusion plasma including: