IDGH-harmonic relativistic gyrotron as an alternative to FEL

In spite of a number of brilliant experimental results on the FELs their necessity for millimeter and submillimeter wavelength ranges is far from that which is convincingly proved. Moreover, it is obvious, that in some cases more “traditional” devices with a voltage significantly lower than that for the FEL are much simpler to be realized. Among such devices, no doubt, the gyrotron is one of the most attractive. Already at subrelativistic electron energies the gyrotron provides a giant radiation power up to 1 MW with a pulse duration of a few seconds at the short-millimeter waves [1], as well as about 100 kW of power with tens of microsecond pulse duration at the wavelengths shorter than 0.5 mm [2]. The subrelativistic gyrotron operating at the higher cyclotron harmonics is proved to be able to produce the radiation at the wavelengths as short as 0.4 mm [3] which makes it promising for many applications. Based on these results and the theory [4,5] we are trying to develop a gyrotron for submillimeter waves spectroscopy, operating at moderately relativistic electron energies 200–300 keV instead of 3–6 MeV for the FELs. Already at the mentioned comparatively low particle energies coupling of the electron beam, having a large pitch-factor, with cavity modes at higher harmonics is as strong as at the fundamental. Using high pulsed magnetic fields up to 20–30 T and providing selective excitation of the separate modes for the resonances up to the 5–7th harmonics it would be possible to obtain from a single device coherent radiation with broadband frequency step-tuning for all the submillimeter wavelength range.