Mikhail Medvedev

Quasicollisional magneto-optic effects in turbulent plasmas

Mikhail Medvedev

University of Kansas

Friday, February 24, 2017



PSFC Seminars

Abstract: High-amplitude turbulent electromagnetic fluctuations are ubiquitous in laboratory and astrophysical plasmas, where they can be excited by kinetic plasma instabilities at small (even sub-Larmor) scales. Particles moving through such electromagnetic fields undergo small-angle stochastic deflections of their pitch-angles, thus establishing diffusive transport on long time-scales. This behavior can be equivalent to Coulomb collisions when the magnetic moment invariant is not conserved. The pitch-angle diffusion coefficient plays a role of an effective collision frequency. We show that such "quasicollisionality" may substantially change the expected radiative transport properties of plasmas (e.g., absorption, transmission, reflection, etc.). We demonstrate that quasicollisionality can be an important player in laboratory high-energy density laser plasmas, where Weibel turbulence is naturally produced. Another particularly interesting case is that of the Faraday effect -- the magnetically-induced birefringence in plasmas causing rotation of the polarization plane of a linearly polarized electromagnetic wave -- which is the common and useful probe of cosmic magnetic fields. We will discuss the observed puzzling anomaly in the Faraday rotation measurements in the Cygnus region as being due to a thin "blanket" of highly turbulent plasma at the front of an interstellar bubble/shock. Overall, the modified magneto-optic effects in plasmas can provide a novel radiative diagnostic tool of small-scale magnetic turbulence.

Bio: undergrad: MIPT (Moscow  Institute for Physics and Technology; sometimes called Physical-Technical Institute)
MS: 1993 @MIPT and Kurchatov Inst. with Kadomtsev and Pogutse
PhD: 1996 UCSD with Pat Diamond
postdocs: Harvard, Astro Dept & CITA (canadian inst for theor astrophys, toronto univ)
faculty: since 2002 U.Kansas,
IAS member in 2010,
long-term visiting prof: Nield Bohr Intl. Academy, Copenhagen 2009-2010 & ITC Harvard 2013, 2017