Ion-acoustic super rogue waves in ultracold neutral plasmas with nonthermal electrons

The ion-acoustic rogue waves in ultracold neutral plasmas consisting of ion fluid and nonthermal electrons are reported. A reductive perturbation method is used to obtain a nonlinear Schrodinger equation for describing the system and the modulation instability of the ion-acoustic wave is analyzed. The critical wave number k(c), which indicates where the modulational instability sets in, has been determined. Moreover, the possible region for the ion-acoustic rogue waves to exist is defined precisely. The effects of the nonthermal parameter beta and the ions effective temperature ratio sigma(*) on the critical wave number k(c) are studied. It is found that there are two critical wave numbers in our plasma system. For low wave number, increasing beta would lead to cringe k(c) until beta approaches to its critical value beta(c), then further increase of beta beyond beta(c) would enhance the values of k(c). For large wave numbers, the increase of beta would lead to a decrease of k(c). However, increasing sigma(*) would lead to the reduction of k(c) for all values of the wave number. The dependence of the rogue waves profile on the plasma parameters is numerically examined. It is found that the rogue wave amplitudes have complex behavior with increasing beta. Furthermore, the enhancement of sigma(*) and the carrier wave number k reduces the rogue wave amplitude. It is noticed that near to the critical wave number, the rogue wave amplitude becomes high, but it shrinks whenever we stepped away from k(c). The implications of our results in laboratory ultracold neutral plasma experiments are briefly discussed. (C) 2013 AIP Publishing LLC.