An analysis of two experimental observations of Langmuir wave collapse
is performed. The corresponding experimental data are shown as evidence against
the occurrence of collapses. The physical reason preventing the collapses is found
to be the nonresonant electron diffusion in momentum. In this process, plasma
thermal electrons are efficiently heated at the expense of wave energy, therefore
intense collisionless wave dissipation takes place. The basic reason for the
underestimation of nonresonant electron diffusion in the traditional theory is shown to be
the substitution of a real plasma by a plasma probabilistic ensemble.
A study of nonresonant electron diffusion refraining from ensemble substitution
is performed. It is shown that its intensity is sufficient for suppression of Zakharov's
short-wavelength modulational plasma instability [Zakharov, V. E., Sov.
Phys. JETP35, 908 (1972)]. This explains the nonoccurrence of Zakharov's Langmuir
wave collapse in experiments.