Bump-on-Tail Instability in Cairns Distributed Plasma

The growing rate of bump-on-tail instability has been investigated in unmagnetized plasma with Cairns distribution. The growing rate depends significantly on the number density ratio n₁/n₂, temperature ratio T₁/T₂, and the nonthermal parameter α. The influence of these parameters on the maximum growing rate is analyzed numerically by using solar data. The higher α can enhance the growing rate of bump-on-tail instability. The maximum growth rate also will increase with the decrease of number density ratio n₁/n₂ and the increase of temperature ratio T₁/T₂. These interesting results will be helpful for understanding some phenomena in space plasma.