7 research outputs found
Collisional damping rates for plasma waves
The distinction between the plasma dynamics dominated by collisional
transport versus collective processes has never been rigorously addressed until
recently. A recent paper [Yoon et al., Phys. Rev. E 93, 033203 (2016)]
formulates for the first time, a unified kinetic theory in which collective
processes and collisional dynamics are systematically incorporated from first
principles. One of the outcomes of such a formalism is the rigorous derivation
of collisional damping rates for Langmuir and ion-acoustic waves, which can be
contrasted to the heuristic customary approach. However, the results are given
only in formal mathematical expressions. The present Brief Communication
numerically evaluates the rigorous collisional damping rates by considering the
case of plasma particles with Maxwellian velocity distribution function so as
to assess the consequence of the rigorous formalism in a quantitative manner.
Comparison with the heuristic ("Spitzer") formula shows that the accurate
damping rates are much lower in magnitude than the conventional expression,
which implies that the traditional approach over-estimates the importance of
attenuation of plasma waves by collisional relaxation process. Such a finding
may have a wide applicability ranging from laboratory to space and
astrophysical plasmas.Comment: 5 pages, 2 figures; Published in Physics of Plasmas, volume/Issue
23/6. Publisher: AIP Publishing LLC. Date: Jun 1, 2016. URL:
http://aip.scitation.org/doi/10.1063/1.4953802 Rights managed by AIP
Publishing LL
Ion Dynamics Across a Low Mach Number Bow Shock
A thorough understanding of collisionless shocks requires knowledge of how
different ion species are accelerated across the shock. We investigate a bow
shock crossing using the Magnetospheric Multiscale spacecraft after a coronal
mass ejection crossed Earth, which led to solar wind consisting of protons,
alpha particles, and singly charge helium ions. The low Mach number of the bow
shock enabled the ions to be distinguished upstream and sometimes downstream of
the shock. Some of the protons are specularly reflected and produce
quasi-periodic fine structures in the velocity distribution functions
downstream of the shock. Heavier ions are shown to transit the shock without
reflection. However, the gyromotion of the heavier ions partially obscures the
fine structure of proton distributions. Additionally, the calculated proton
moments are unreliable when the different ion species are not distinguished by
the particle detector. The need to high time-resolution mass-resolving ion
detectors when investigating collisionless shocks is discussed.Comment: 16 pages, 5 figure