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 greater than or equal to T+ much greater than T- (T-e, T+, T-: temperatures of electrons, positive ions, and negative ions, respectively). Depending on the ratio epsilon of negative to positive density, a steepening of positive or negative density jumps is observed. For epsilon < epsilon(c) (approximate to 0.65, critical value), positive density jumps evolve into compressive shocks. For epsilon > epsilon(c), however, negative density jumps evolve into rarefactive shocks. The ratio epsilon(c) observed is well explained on the basis of Korteweg-de Vries equation.