51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009;
Atlanta, Georgia
Session GI2: Micro and Low-temperature Plasmas
9:30 AM–12:30 PM,
Tuesday, November 3, 2009
Room: Centennial I
Chair: Martin Lampe, Naval Research Laboratory
Abstract ID: BAPS.2009.DPP.GI2.3
Abstract: GI2.00003 : Kinetic Theory of Instability-Enhanced Collisional Effects*
10:30 AM–11:00 AM
Preview Abstract
Abstract
Author:
Scott D. Baalrud
(Department of Engineering Physics, University of Wisconsin-Madison)
A generalization of the Lenard-Balescu collision operator is
derived which accounts for the scattering of particles by
instability amplified fluctuations that originate from the
thermal motion of discrete particles (in contrast to evoking a
fluctuation level externally, as is done in quasilinear kinetic
theory) [1]. Emphasis is placed on plasmas with convective
instabilities. It is shown that an instability-enhanced
collective response results which can be the primary mechanism
for scattering particles, being orders of magnitude more frequent
than conventional Coulomb collisions, even though the
fluctuations are in a linear growth phase. The resulting
collision operator is shown to obey conservation laws (energy,
momentum, and density), Galilean invariance, and the Boltzmann
${\mathcal{H}}$-theorem. It has the property that Maxwellian is
the unique equilibrium distribution function; again in contrast
to weak turbulence or quasilinear theories. Instability-enhanced
collisional effects can dominate particle scattering and cause
strong frictional forces. For example, this theory has been
applied to two outstanding problems: Langmuir's paradox [2] and
determining Bohm's criterion for plasmas with multiple ion
species [3]. Langmuir's paradox is a measurement of anomalous
electron scattering rapidly establishing a Maxwellian
distribution in gas discharges with low temperature and pressure.
This may be explained by instability-enhanced
scattering in the plasma-boundary transition region (presheath)
where convective ion-acoustic instabilities are excited. Bohm's
criterion for multiple ion species is a single condition that the
ion fluid speeds must obey at the sheath edge; but it is
insufficient to determine the speed of individual species. It is
shown that an instability-enhanced collisional friction, due to
streaming instabilities in the presheath, determines this
criterion.\\[4pt]
[1] S.D. Baalrud, J.D. Callen, and C.C. Hegna, Phys. Plasmas {\bf
15}, 092111 (2008).\\[0pt]
[2] S.D. Baalrud, J.D. Callen, and C.C. Hegna, Phys. Rev. Lett.
{\bf 102}, 245005 (2009).\\[0pt]
[3] S.D. Baalrud, C.C. Hegna, and J.D. Callen (submitted July
2009); preprint UW-CPTC 09-5 at www.cptc.wisc.edu.
*This material is based upon work supported under a NSF Graduate Research Fellowship and by U.S. DoE Grant No. DE-FG02-86ER53218. This work was done in collaboration with C.C. Hegna and J.D. Callen.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DPP.GI2.3