A comparative study of modified Korteweg-de Vries (MKdV) and Korteweg-de Vries, (KdV) solitons in plasmas with, negative ions under the influence of electrons' drift motion

In the plasma under consideration, the existence of modified Korteweg-de Vries (MKdV) solitons has been established for different values of electrons' drift velocities nu'(e) and of Q' (= m(j)/m(i), negative to positive ion mass ratio). The amplitudes of the MKdV solitons are found to be much smaller (<1) than those of the corresponding amplitudes (<1) of the KdV solitons for Q' < 0.6 when nu'(e) = 10. Unlike the existence of both compressive and rarefactive KdV solitons with two unaccountable regions of nu'(e), there is found to exist only compressive MKdV solitons of small e amplitudes in the lower but entire range of nu'(e) for U = 1.09, 1.12, and 1.15 when Q' = 0.4. It is noteworthy to mention that, the width of the KdV soliton does not depend on Q', i. e., on the concentration of negative ions whereas that of the MKdV soliton depends on Q'. (C) 1998 American Institute of Physics. [S1070-664X(98)03409-0].