Excitation of the low-voltage CRM oscillations at the second harmonic of cyclotron frequency

Operation of the CRM at low accelerating voltages is of the great interest for such areas of science as spectroscopy and diagnostics of the various media where is no requirement for the high output power of the device, but remain high requirements for the stability of the operating frequency [1,2]. The using of the low accelerating voltages will allow to simplify and to reduce the dimensions of the device design and facilitate work with it. Also the generation on the second harmonic of the cyclotron frequency will allow to use more compact magnetic systems [3,4]. In this connection the coupling factor of electron beam with the RF field of the cavity is calculated in the paper. The calculations show that the coupling factor is strongly depended on the direction of the electrons rotation in the beam and the RF field in the cavity. Due to such factor dependencies it became possible to provide a couple of the beam with TE₀₁ mode of a cylindrical cavity with practically zero couple factor with the main TE₁₁ mode, without increasing the magnetic field. Computer simulation of the wave-particle interaction of low-voltage electron beam with high-frequency field of a cylindrical cavity shows the single-frequency generation at TE₀₁ mode at the second harmonic of the cyclotron frequency.