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Session BO3: Beams, Instabilities, and Turbulence

9:30 AM–12:30 PM, Monday, November 12, 2007
Rosen Centre Hotel Room: Salon 9/10

Chair: Gurudas Ganguli, Naval Research Laboratory

Abstract ID: BAPS.2007.DPP.BO3.12

Abstract: BO3.00012 : Instability of coherent whistlers propagating along field lines in the magnetosphere*

11:42 AM–11:54 AM

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Authors:

Martin Lampe
Gurudas Ganguli
(NRL Plasma Phys. Div.)

Glenn Joyce
Wallace Manheimer
(U. Maryland)

We report on analytic and simulation studies of nonlinear instability triggered by a whistler propagating along a geomagnetic field line. For simplicity of interpretation, the electron distribution is taken to be the highly unstable ring distribution f(\textbf{v})=$\delta $(v$_{\vert \vert }-$v$_{\vert \vert 0})\delta $(v$_{\bot }-$v$_{\bot 0})$. The variation (quadratic near the equator) of the geomagnetic field B(z) along a field line is important, even though $\lambda \quad \sim $ 1 km while the field gradient scale $\sim $1000 km. The instability is triggered by an initial wave pulse of finite duration $\tau _{p}$; the value of $\tau _{p}$ also plays an important role. Instability occurs initially at the resonant points where $\omega -$kv$_{\vert \vert }-\Omega $=0, but is carried backwards in the pulse by the stream of resonant electrons. The fresh flow of unperturbed electrons into the pulse plays an important role, and in the non-uniform B(z), phase-trapped electrons can continue to drive the nonlinear stage of the instability, which is characterized by both growth and strong spatio-temporal variations of the wave frequency.

*Supported by ONR

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.BO3.12