This report is devoted to the non-linear theory of symmetrical potential surface waves (SWs) excitation by low-density tubular beam in cylindrical waveguide structure ‘plasma - vacuum - metal’. The system of non-linear equations describing the temporary dynamics of plasma - beam interaction is obtained. The influence of beam and waveguide structure parameters on saturation amplitude and SW excitation is investigated both analytically and numerically. The process of beam thermalization in SW field is considered.