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**Evolution of Electron Beam Instabilities in the Auroral Region**

*C. T. Dum*
The evolution of the electron-beam distribution and of instabilities
in the magnetized plasma of the auroral region are closely coupled. Aside
from the Langmuir wave instability, the excitation of the highly obliquely
propagating lower hybrid instability is of particular interest, because
of the potential of ion heating perpendicular to the ambient magnetic field
(ion conic generation). Nonlinear turbulence effects, flattening of the
beam distribution by the initially dominant Langmuir instability and propagation
effects have been invoked for a significant excitation of lower hybrid
waves. In order to differentiate these effects, an analysis of wave growth
for the actual evolving distribution function is necessary. A code which
can evaluate the dispersion relation of a magnetized plasma for actual
(usually strongly non-Maxwellian) distribution functions obtained from
observation or simulation has been developed and applied to simulation
studies.

The figure shows
the modification of the electron distribution by the Langmuir and lower
hybrid instability. The latter can be excited by the anomalous Doppler
effect, even after the initially Maxwellian beam (at speed vpar=1) has
been completely flattened.