Spatio-temporal evolution of the electrostatic potential for different values of the spectral index of electrons and ions, i.e., κ_e and κ_i respectively. Panel a was plotted from run 2(i), panel b from run 3(vi), panel c from run 2(vi), and finally, panel d was plotted from run 4. The plasma parameters of these runs are given in Table 1. A comparison of panels a and d suggests that highly suprathermal electrons and/or ions (i.e., for lower values of κ) correspond to smaller amplitude DASW pulses, in comparison with weakly suprathermal (e.g., quasi-Maxwellian) electrons and/or ions.