  In a laser-irradiated plasma, the Langdon effect makes the electron energy
distribution function (EEDF) tend to a super-Gaussian distribution, which has
important influences on laser plasma instabilities. In this work, the
influences of a super-Gaussian EEDF on the convective stimulated backward Raman
scattering (SRS) and stimulated backward Brillouin scattering (SBS) are studied
systematically for a wide range of typical plasma parameters in the inertial
confinement fusion (ICF). Distinct behaviors are found for SRS and SBS in the
variation trend of the peak spatial growth rate and the corresponding
wavelength of the scattered light. Especially, the Langdon effect on the SBS in
plasmas with different ion species and isotopes is analyzed in detail, and the
parameter boundary for judging the variation trend of the peak spatial growth
rate of SBS with the superGaussian exponent is presented for the first time. In
certain plasma parameter region, it is found that the Langdon effect could
enhance SBS in mixed plasma, which may attenuate the improvement in suppressing
SBS by mixing low-Z ions into the high-Z plasma. These comprehension of Langdon
effect on LPIs would contribute to a better understanding of SRS and SBS in
experiments.
