Instability of beams in plasma waveguides with diffuse boundaries

Dissipative instability of cylindrical and tubular low density electron beams interacting with a homogeneous plasma in the presence and absence of an external magnetic field is studied in quasi-linear approximation. The plasma is characterized by strong dissipation, caused both by collisions of plasma electrons with ions and neutral particles and by the presence of a nonuniform transition layer at plasma boundary, in which the energy of surface waves in absorbed. Practically, all the energy lost by the beam as a result of the dissipative instability is shown to be converted into the thermal energy of the plasma.