I. V. Bandurkin

High-harmonic gyrotron with sectioned cavity

High-harmonic large-orbit gyrotrons require long-length operating cavities because of both a weak electron-wave coupling and relatively low electron currents. Since diffraction Q factors of such cavities are very high, a large fraction of the radiated power is dissipated in Ohmic losses. A sectioned klystronlike cavity can be a way to combine a long electron-wave interaction region with a relatively low diffraction Q factor. In this paper, a design of a third-harmonic terahertz gyrotron is studied in detail and discussed. As compared to a regular cavity, the use of a sectioned microwave system provides an enhancement of the output rf power by several times along with the halving of the Ohmic losses.

Experimental study of a fourth-harmonic gyromultiplier

Simultaneous generation at the second and fourth cyclotron harmonics has been obtained from a single-cavity self-excited gyromultiplier. Output power of the short-wavelength radiation amounts to 100 W at a frequency of 75 GHz. The proposed scheme seems to be promising for the terahertz frequency range.

Sources of Coherent Terahertz Radiation

New results in the field of high‐frequency gyrotrons, gyro‐multipliers and orotrons allow one to consider these electron devices as promising candidates for the realization of powerful and available sources in Terahertz range. Electron beams with a very high compression of up to a factor of 4,400 have been obtained and selective generation at the 1st–5th cyclotron harmonics have been demonstrated in Large Orbit Gyrotrons (LOGs) at millimeter and submillimeter wavelengths at operating voltages from 50 to 250 kV. When operating at the third cyclotron harmonic (TE3,8 and TE3,9 modes in the first oscillator; TE3,5 mode in the second oscillator) output power levels of 10–20 kW have been obtained in the frequency range of 0.37–0.41 THz. Gyro‐multipliers with self‐exciting low‐frequency sections are proposed and studied theoretically. Low‐voltage orotrons have been demonstrated in the frequency range of 0.1–0.4 THz with output powers of 1.0–0.1 W and typical electrical‐mechanical frequency tunability within an o...

Klystron-like cavity with mode transformation for high-harmonic terahertz gyrotrons

A novel cavity scheme of a gyrotron is proposed and investigated. As it provides low Ohmic losses and high mode selectivity, it can be especially prospective for realization in gyrotrons operating in the THz frequency range. Numerical simulations show that it allows three-fold increase in the efficiency of the low-relativistic 500 GHz fourth-harmonic gyrotron as compared to conventional two-section scheme with modes transformation.

Negative-mass mitigation of Coulomb repulsion for terahertz undulator radiation of electron bunches

It is proposed to utilize the effect of negative mass for stabilization of the effective axial size of very dense and short electron bunches produced by photo-injector guns by using combined undulator and strong uniform magnetic fields. It has been shown that in the “abnormal” regime, an increase in the electron energy leads to a decrease in the axial velocity of the electron; due to the negative-mass effect, the Coulomb repulsion of electrons leads to their attraction and formation of a fairly stable and compact bunch “nucleus.” An undulator with a strong uniform magnetic field providing the negative-mass effect is designed for an experimental source of terahertz radiation. The use of the negative-mass regime in this experiment should result in a long-pulse coherent spontaneous undulator emission from a short dense moderately relativistic (5.5 MeV) photo-injector electron bunch with a high (up to 20%) efficiency and a narrow frequency spectrum.

Gyrotron with a sectioned cavity based on excitation of a far-from-cutoff operating mode

A typical problem of weakly relativistic low-power gyrotrons (especially in the case of operation at high cyclotron harmonics) is the use of long cavities ensuring extremely high diffraction Q-factors for the operating near-cutoff waves. As a result, a great share of the rf power radiated by electrons is spent in Ohmic losses. In this paper, we propose to use a sectioned cavity with π-shifts of the wave phase between sections. In such a cavity, a far-from-cutoff axial mode of the operating cavity having a decreased diffraction Q-factor is excited by the electron beam in a gyrotron-like regime.

Frequency multiplication in gyrotron autooscillators

A new scheme of the gyrotron autooscillator capable of simultaneously generating at the fundamental cyclotron frequency and one of the higher harmonics in the same electrodynamic system is proposed. Operating without an external drive signal, the multiplying gyrotrons of this type can be effective sources of coherent radiation in the submillimeter wavelength range.

Regime of non-resonant trapping in an FEM-amplifier

Abstract The regime of non-resonant electron trapping is studied for a moderately relativistic mm-wave FEM-amplifier with helical undulator and “reversed” guiding magnetic field. A possibility to provide simultaneously a very high (60–70%) electron efficiency, an ultra-broadband (over 30%) frequency tuning, and very weak sensitivity to the electron-beam quality is demonstrated.

Super-radiant effects in electron oscillators with near-cutoff operating waves

Super-radiant regimes in electron oscillators can be attractive for applications requiring powerful and relatively short pulses of microwave radiation, since the peak power of the super-radiant pulse can exceed the power of the operating electron beam. In this paper, possibilities for realization of the super-radiant regimes are studied in various schemes of electron oscillators based on excitation of near-cutoff operating waves (gyrotron and orotron).

Gyromultiplier with sectioned cavity

A novel scheme of a self-exciting single-cavity terahertz gyromultiplier is proposed and theoretically investigated. Simulations predict a possibility to obtain a power of 75 W at the frequency of 1.3 THz from the 80 kV/0.7 A electron beam when operating at the fourth cyclotron harmonic at the relatively low magnetic field of 14 T.