52nd Annual Meeting of the APS Division of Plasma Physics
Volume 55, Number 15
Monday–Friday, November 8–12, 2010;
Chicago, Illinois
Session AR1: Review: The Many Faces of the Shear Alfven Wave
8:00 AM–9:00 AM,
Monday, November 8, 2010
Room: Grand Ballroom CD/EF
Chair: Cary Forest, University of Wisconsin
Abstract ID: BAPS.2010.DPP.AR1.1
Abstract: AR1.00001 : The many faces of the Shear Alfv\'{e}n Wave*
8:00 AM–9:00 AM
Preview Abstract
Author:
Walter Gekelman
(UCLA Dept of Physics)
One of the fundamental waves in a magnetized plasma is the shear
Alfv\'{e}n
wave. This wave is responsible for rearranging current systems
and, in fact,
all low frequency currents ($f<$ $f_{ci}$) are shear waves. It has
become
apparent that Alfv\'{e}n waves are important in a wide variety of
physical
environments. They play a central role in the stability of magnetic
confinement devices, give rise to aurora formation in planets,
and are
thought to contribute to heating and ion acceleration in the
solar corona.
Shear waves of finite transverse scale have electric fields
parallel to the
local background magnetic field, which is key to understanding
current
systems, and they can also cause particle acceleration over
considerable
distances in interstellar space. One may also consider magnetic
flux ropes
as low frequency shear waves. Shear waves can become nonlinear
and in
astrophysical environments this is proposed to result in
turbulent cascades
and the generation of structures. Measurements on board the Polar
satellite
indicate that the power of earthward bound shear waves equals
that of the
auroral electron beam. Alfv\'{e}n waves have been directly
observed in the
solar wind, the auroral ionosphere and magnetotail, in the sun's
corona, and
in fusion devices. Currently there is much interest in the
properties of
toroidal Alfv\'{e}n eigenmodes in tokamaks because they can be
triggered by
resonant alpha particles and thus could negatively affect particle
confinement if they were to grow to large amplitudes. Shear waves
of various
forms have been a topic of experimental research for more than
fifteen years
in the Large Plasma Device (LAPD) at UCLA. The waves were first
studied in
both the kinetic and inertial regimes when excited by fluctuating
currents
with transverse dimension on the order of the collisionless skin
depth
$\frac{c}{\omega _{pe} }$. The three dimensional currents
associated with
the waves have been mapped and the ion motion which closes the
currents
across the magnetic field observed with laser induced
fluorescence. The
propagation in inhomogeneous magnetic fields and density
gradients has been
studied as well as effects of collisions and reflections from
boundaries.
Heating of the plasma electrons and ions has also been observed.
The waves
have been launched with antennas, but have also been generated by
secondary
processes such as mode conversion of microwaves at the upper
hybrid layer
followed by Cherenkov radiation by fast electrons. They are also
produced by
an exploding laser produced plasma in a background magnetoplasma.
Magnetic
field line reconnection has been observed when Alfv\'{e}nic
current systems
interact. Flux ropes as well as temperature filaments also
exhibit shear
wave phenomena. Three-dimensional data illustrating these
processes will be
presented along with relevant theory. Part of the presentation
will be in
3D!
*Work funded by NSF and DOE and performed at the Basic Plasma Science Facility
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.DPP.AR1.1