The wave guide properties of a tubular relativistic electron beam are analyzed for a wave guide with conducting walls, with consideration of the positive ions captured by the electrostatic field of the beam to form a background plasma. The partial neutralization of the electron charge by the ions is accompanied by an increase in the limit current of the relativistic electron beam for a specified injection energy. The system is unstable, and the development of the electron-ion mode leads to a significant nonlinear reduction in the phase velocity of the slow wave as a result of the relationship between the wave guide properties of the system (the limit current) and the amplitude of the oscillations.