On the existence of ion-acoustic double layers in negative-ion plasmas

It is well known that ion-acoustic double layers occur in plasmas containing two-temperature electron species and positive ions. It has been suggested that such structures can occur when there is only one electron species but both negative and positive ion species. A stationary modified Korteweg-de Vries equation was derived to support this deduction. The discrepancy is resolved by examining both approaches in the pseudo-potential formulation in more relevant detail. The implications of this study extend beyond the realm of the present subject. (author)