The basic feasibility of a proposal to simplify the conventional low energy rf electron linear accelerator (linac), is considered. The design suggested foresees replacement of the traditional high power systems of external rf generator and modulator by a more passive switched energy storage system. The proposed conception of a compact linac is based on known rf energy compression techniques and an efficient self‐excited oscillation in a special accelerating/oscillating linac structure. The principal relations, performance estimations, and one‐dimensional time‐dependent simulation results for such a linac are presented. The possibility of self‐excited oscillation by an unbunched low voltage beam in a waveguide linac section is proved and investigated experimentally. The common features and differences compared with a conventional backward‐wave tube are analyzed. An application of this effect is proposed for impedance and group velocity measurements in slow‐wave structures. Since the rf energy commutation may be one or two orders faster than the electric high voltage energy commutation (conventional modulator), combining the structure proposed and rf energy compression system can give high levels of the average beam power (10–100 kW). The linac facility would have considerably reduced weight and sizes (more than 2.5 times) as compared to similar industrial linacs. The power supply required is in 40–120 kV range dc source, and an estimated overall wall plug efficiency is a few percent. ©1995 American Institute of Physics.