Properties of linear ion acoustic waves in negative ion plasmas

Summary form only given, as follows. It is now well known that there exist two modes of ion acoustic waves in plasmas including two ion species. This theory also holds when one of the two is a negative ion species, although characteristics of the modes are strongly changed by the negative ions. As in such negative ion plasmas, the two modes are customarily called the fast and the slow modes, after the properties of their velocities. On the other hand, the features of their Landau damping rates which had been uncovered by theoretical and experimental investigations were as follows: the slow mode always has much higher damping rate than the fast mode to be usually trivial physically, resulting in the domination of various ion wave phenomena by the fast mode. However, we have recently found that the slow mode can possess lower damping rate instead of the fast depending upon the mass ratio of the negative to the positive ion species and the temperature ratio of electron to ion. These parameters have respective critical values, below which the slow mode can be dominant. These values are calculated using kinetic approach. To confirm this novel wave phenomenon, we performed ion wave experiments.