Monday, November 19, 2018
Dr. Mark Koepke
West Virginia University
3:15 - 4:15 pm
SEH, B1220
Abstract
Each dust grain is a heavy charged particle. An electrostatic potential well, arising naturally in the plasma or applied externally, can confine or expel dust grains and the properties of this dusty plasma equilibrium and its dynamics can be studied. The dusty plasma is considered magnetized if the charge-to-mass ratio of the dust grain is sufficiently large that a significant fraction of the grains gyrate with gyro-radii much smaller than the dusty plasma’s dimensions perpendicular to the magnetic field and if the dust gyro-motion is not prevented by particle collisions. The guiding center drift of a magnetized-orbit dust grain in inhomogeneous plasma depends sensitively on the charging-rate details when the grain gyro-synchronously deviates from being fully charged at its in-situ equilibrium-charge state. Gyro-phase-resonant excursions into a region with inhomogeneity or anisotropy can cause periodic charge-state changes. When such charge-state changes are not instantaneous, a modification, known as gyro-phase drift, to the usual ExB drift, alters the grain’s diamagnetic drift vector in ways that may be significant in modeling planetary and lab dusty plasma.
Biography
Mark Koepke received his Ph.D. in Physics (1984) from Univ. Maryland, College Park. His PhD thesis was on bounce-resonant Landau damping of the loss-cone instability in a mirror trap. As a Research Associate and a Research Assistant Professor at the Univ. Washington (Seattle, WA), his research expanded into theta pinches, stellarators, high-beta physics, and high-beta plasma diagnostics.
Prof. Koepke started the West Virginia University plasma physics group in 1987, with the theme "space-related laboratory experiments". It has since grown to include space plasma physics theory as well as a multi-topical experimental program. He served as 2014 APS-DPP chair, 2013-2016 FESAC* chair, chair of DOE FESAC's 2014 strategic planning committee on 10-year priority assessment and budget scenarios, and 2017 GEC secretary.