A simplified theoretical model for a phenomenon of fast randomization of an electron gas which was investigated experimentally is presented. It is assumed that a certain region in constricted electrical discharges, called “plasma sac” can become the siege of trapped electroacoustic waves generated by a beam‐plasma interaction. The interaction between those waves and the electron gas is treated by a pseudo‐collisional method leading to a generalization of Boltzmann'sH‐theorem. The velocity distribution, which is essentially Maxwellian with a significant deficiency in the fast electron tail, is deduced.