[IGPP Everyone] TODAY: Plasma Seminar 10/14 1pm: "A stringent limit on the amplitude of Alfvénic perturbations in high-beta low-collisionality plasmas" (J. Squire, Caltech)

[Emmanuel V. Masongsong]

Dear all,

Just a reminder: We have a plasma seminar TODAY, Friday, October 14th at 
1PM in Room 4-330 of the Physics & Astronomy Building (PAB).  Coffee and 
cookies will be available in the room at 12:45.  Our speaker is Dr. 
Jonathan (Jono) Squire of Caltech, and his title and abstract are as 
follows:

"A stringent limit on the amplitude of Alfvénic perturbations in 
high-beta low-collisionality plasmas"

I will discuss and explore a stringent nonlinear limit on the amplitude 
of shear-Alfvén waves in low-collisionality plasmas.
In particular, the result states that collisionless plasmas cannot 
support linearly polarized shear-Alfvén fluctuations above the
critical amplitude $\delta B_{\perp}/B_{0} \sim \beta^{\,-1/2}$, where 
$\beta$ is the ratio of thermal to magnetic pressure.
Above this cutoff, a developing fluctuation will generate a pressure 
anisotropy that is
sufficient to destabilize itself through the parallel firehose 
instability. This causes the wave
frequency to approach zero, interrupting the fluctuation before any 
oscillation, and
the magnetic field lines relax into a sequence of angular zig-zag 
structures. I will conclude
by discussing a variety of interesting implications that stem from this 
restrictive amplitude maximum,
focusing in particular on our ongoing work on magnetized turbulence
and the solar wind around 1AU.

http://www.pa.ucla.edu/sites/default/files/plasma_Squire101416.pdf