Effects of a kappa distribution function of electrons on incoherent scatter spectra

In usual incoherent scatter data analysis, the plasma distribution function is assumed to be Maxwellian. In space plasmas, however, distribution funct ions with a high energy tail which can be well modeled by a generalized Lor entzian distribution function with spectral index kappa (kappa distribution ) have been observed. We have theoretically calculated incoherent scatter s pectra for a plasma that consists of electrons with kappa distribution func tion and ions with Maxwellian neglecting the effects of the magnetic field and collisions. The ion line spectra have a double-humped shape similar to those from a Maxwellian plasma. The electron temperatures are underestimate d, however, by up to 40% when interpreted assuming Maxwellian distribution. Ion temperatures and electron densities are affected little. Accordingly, actual electron temperatures might be underestimated when an energy input m aintaining a high energy tail exists. We have also calculated plasma lines with the kappa distribution function. They are enhanced in total strength, and the peak frequencies appear to be slightly shifted to the transmitter f requency compared to the peak frequencies for a Maxwellian distribution. Th e damping rate depends on the electron temperature. For lower electron temp eratures, plasma lines for electrons with a re distribution function are mo re strongly damped than for a Maxwellian distribution. For higher electron temperatures, however, they have a relatively sharp peak.