Reflection of Solitons at Critical Density of Negative Ions: Contribution of Thermal and Gyratory Motions of Ions

On the basis of appropriate modified Korteweg-deVries (mKdV) equation derived for three cases of n_n0 < n_e0, n_n0 = n_e0, and n_n0 > n_e0 together with n_n0 < n_e0 as the density of negative ions (electrons), we observe that compressive and rarefactive mKdV solitons propagate in an inhomogeneous magnetized plasma having negative ions at their critical density. Two types of modes (fast and slow) separately evolve as the compressive and rarefactive solitons. However, only the solitons corresponding to the fast mode get reflected, if the obliqueness of the magnetic field lies under certain critical angle PsiCR which gets larger under higher thermal motions of the ions and shows stronger dependence on it when less number of negative ions are present in the plasma. There is a possibility of the change of polarities after the reflection of the solitons. The solitons suffer stronger reflection under the effect of larger ion thermal motions and smaller obliqueness of the magnetic field. The compressive solitons are found to downshift, whereas the rarefactive solitons are upshifted after the reflection, and these shifts get higher for the increasing concentration of the negative ions and lower obliqueness of the magnetic field. The compressive (rarefactive) solitons shift less (more) in the plasmas with ions of higher thermal energy; however, the upshift shows opposite behavior for the case of n_n0 > n_e0.