It has been shown not long ago that in a non-equilibrium plasma that is near an unstable state, abnormally large, so-called "critical" fluctuations are possible. As is known, through fluctuation correlation operators one defines such plasma characteristics as the stopping power (energy losses of charged particles passing through a plasma) and also scattering coefficients of different types of oscillations and their transformation into oscillations of other types. Owing to the presence of oritioal fluctuations these plasma characteristics can be abnormally large if the plasma state approaches an unstable state.In the first section of this paper we investigate interaction between particles and a plasma consisting of cold ions and hot electrons that move with respect to the ions; in addition, we define the particle energy losses for the excitation of acoustic oscillations. If the projection of particle velocity is in the direction of electron motion, sound velocity and the directed electron velocity are near each other, and particle energy losses are abnormally large and can exceed energy losses due to twobody collisions. In the first section we also consider the question of interaction between a particle and shortwave (Langmuir ion) oscillations.In the second section we investigate interaction between a particle and a plasma through which a compensated beam of charged particles passes. Expressions have been deduced for the cross sections of a particle for scattering and for energy losses to the excitation of Langmuir oscillations. Energy losses of the particle are specially large if its velocity is near beam velocity in both value and direction.In the third and fourth sections of this paper we discuss transformation of transverse waves into longitudinal waves and scattering of longitudinal plasma waves with a directed electron motion. We investigate under what conditions the transformation and scattering coefficients that characterize increase of energy density of the secondary wave per unit time are abnormally large.