Fast ion-acoustic soliton stopbands in kappa-distributed two-electron-temperature plasmas

Electrostatic solitary waves (ESWs) are observed in abundance in space and in laboratory plasmas. These are localized forms presented as pulse-shaped electrostatic potential excitations generating characteristic stationary profile ambipolar electric field structures accompanied by copropagating density and electron/ion fluid speed disturbances. It is by now established that the existence condition for ESWs leads to a velocity range of values between the sound speed (lower bound) and the infinite compression limit (upper bound), among other possible constraints. The existence of stopbands, i.e. ranges in speed for which fast ion-acoustic solitons cannot propagate was reported for the very first time in a three-component plasma with cold ions, warm (adiabatic) ions and Boltzmann electrons and was later extended to various plasma configurations. Our study presented here extends the model presented in to a four–component plasma with two distinct electron populations which follow a non-Maxwellian (kappa) distribution, described by the respective spectral indices κc and κh, where indices c and h denote the cool and hot electron component(s), respectively. The analysis shows that the existence of stopbands is favoured for large values of κc and κh when the velocity distributions are close to Maxwellian. The effect of decreasing κc or κh widens the stopband region over the range of (values of the) cold-to-warm ion charge density ratio f until the stopbands disappear when the single valued warm ion density limiting curves are obtained for very small values of κc or κh. The stopbands are found to have infinite extent over f for some intermediate magnitudes of κc or κh. The effect of increasing temperature ratio of the hot-to-cool electrons manifests a similar behaviour, favouring the existence of stopbands for smaller values and their disappearance for large values. (author)