ELECTRON VELOCITY DISTRIBUTION FUNCTION IN A PLASMA WITH TEMPERATURE-GRADIENT AND IN THE PRESENCE OF SUPRATHERMAL ELECTRONS - APPLICATION TO INCOHERENT-SCATTER PLASMA LINES
P. Guio et al., ELECTRON VELOCITY DISTRIBUTION FUNCTION IN A PLASMA WITH TEMPERATURE-GRADIENT AND IN THE PRESENCE OF SUPRATHERMAL ELECTRONS - APPLICATION TO INCOHERENT-SCATTER PLASMA LINES, Annales geophysicae, 16(10), 1998, pp. 1226-1240
The plasma dispersion function and the reduced velocity distribution f
unction are calculated numerically For any arbitrary velocity distribu
tion function with cylindrical symmetry along the magnetic field. The
electron velocity distribution is separated into two distributions rep
resenting the distribution of the ambient electrons and the supratherm
al electrons. The velocity distribution function of the ambient electr
ons is modelled by a near-Maxwellian distribution function in presence
of a temperature gradient and a potential electric field. The velocit
y distribution function of the suprathermal electrons is derived from
a numerical model of the angular energy flux spectrum obtained by solv
ing the transport equation of electrons. The numerical method used to
calculate the plasma dispersion function and the reduced velocity dist
ribution is described. The numerical code is used with simulated data
to evaluate the Doppler frequency asymmetry between the up- and downsh
ifted plasma lines of the incoherent-scatter plasma lines at different
wave vectors. It is shown that the observed Doppler asymmetry is more
dependent on deviation from the Maxwellian through the thermal part f
or high-frequency radars, while for low-frequency radars the Doppler a
symmetry depends more on the presence of a suprathermal population. It
is also seen that the full evaluation of the plasma dispersion functi
on gives larger Doppler asymmetry than the heat how approximation for
Langmuir waves with phase velocity about three to six times the mean t
hermal velocity. For such waves the moment expansion of the dispersion
function is not fully valid and the full calculation of the dispersio
n function is needed.