Ion-acoustic waves in a plasma with negative ions

Propagation and damping of ion-acoustic waves have been investigated in a Q-machine plasma consisting of K+ positive ions, SF−6 negative ions, and electrons. The phase velocity of the ion-acoustic ‘‘fast’’ mode increases with increasing ε, the concentration of negative ions. The wave damping decreases with increasing ε, and nearly disappears, for the highest wave frequencies investigated, when ε≳0.9. Both results are in agreement with predictions from Vlasov theory.