  The harmonics effect on ion-bulk (IBk) waves has been researched by Vlasov
simulation. The condition of excitation of a large-amplitude IBk waves is given
to explain the phenomenon of strong short-wavelength electrostatic activity in
solar wind. When $k$ is much lower than $k_{lor}/2$ ($k_{lor}$ is the wave
number at loss-of-resonance point), the IBk waves will not be excited to a
large amplitude, because a large part of energy will be spread to harmonics.
The nature of nonlinear IBk waves in the condition of $k<k_{lor}/2$ is undamped
Bernstein-Greene-Kruskal-like waves with harmonics superposition. Only when the
wave number $k$ of IBk waves satisfies $k_{lor}/2\lesssim k\leq k_{lor}$, can a
large-amplitude and mono-frequency IBk wave be excited. These results give a
guidance for a novel scattering mechanism related to IBk waves in the field of
laser plasma interaction.
