Ion Acoustic Shocks Formed in a Collisionless Plasma with Negative Ions

Ion acoustic shocks are formed in a plasma with negative ions, where $T_e\ge T_{+}\gg T_{-}$ ( $T_e$, $T_{+}$, $T_{-}$: temperatures of electrons, positive ions, and negative ions, respectively). Depending on the ratio $\varepsilon$ of negative to positive density, a steepening of positive or negative density jumps is observed. For $\varepsilon <{\varepsilon }_c$ ( $\approx 0.65$, critical value), positive density jumps evolve into compressive shocks. For $\varepsilon >{\varepsilon }_c$, however, negative density jumps evolve into rarefactive shocks. The ratio ${\varepsilon }_c$ observed is well explained on the basis of Korteweg–de Vries equation.