Published online by Cambridge University Press: 13 March 2009
The points raised by Schmidt (1979) are irrelevant and do not invalidate my paper (Hirose 1978). He has overlooked the beam deceleration and consequent obvious relationship, where V (t) is the beam drift velocity at arbitrary time, V(0) is the initial beam velocity, nb1, is the perturbed beam density and vb1 is the perturbed beam velocity. It is obvious that V(t) < V(0) due to beam deceleration caused by the instability as shown by Shapiro (1963) and also in the subject paper (Hirose 1978).