  We study the electron-acoustic instabilities in plasmas with two
kappa-distributed electrons and stationary ions. The instabilities are driven
by the relative drift between two electron components. The suprathermal effects
of different species on growth rates and instability thresholds are analyzed
and compared by numerical calculations. The present study reveals that the
suprathermal electrons with slow most probable speed play more important roles
than the suprathermal ones with fast most probable speed. The former
significantly reduces the instabilities and raises the instability thresholds.
The parameters used in this study are inspired from the observations in Earth's
magnetopause.
