A. V. Savilov

Moderately relativistic high-harmonic gyrotrons for millimeter/submillimeter wavelength band

A large orbit gyrotron with a 300 keV, 30 A, 20 ns electron beam has provided selective generation with radiation power from 1.5 MW at fundamental (wavelength of 14 mm) to 100 kW at the fifth cyclotron harmonic (wavelength of 4 mm). The next experiment with a unique electron beam (250 keV, 18 A, 10 /spl mu/s, 0.6 mm in diameter) is in progress.

Stimulated wave scattering in the Smith-Purcell FEL

Frequency multiplication in the Smith-Purcell free electron laser (FEL) as a way to obtain powerful millimeter/ sub-millimeter stimulated radiation from a high-current, moderately relativistic electron beam is studied. It is shown that the main mechanism that provided the multiplication is mutual scattering of low-frequency and high-frequency waves on the electron beam. The use of this mechanism can provide the power level of tens of megawatts and the possibility of a relatively broadband (few percent) frequency tuning.

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.

TO THE PROBLEM OF ENERGY RECUPERATION IN GYROTRONS

A relatively high level of the minimal electron energy at the gyrotron output even at very large spread in pitch factor is explained. An estimation of the recuperation efficiency, which can be obtained due to this effect, is given.

Dynamics of excitation of backward waves in long inhomogeneous systems

The spatio-temporal dynamics of excitation of a long backward-wave oscillator with a profiled resonant parameter is studied in detail. It is shown that the transition to multifrequency regimes of the rf generation occurs due to splitting the long oscillator into several shorter single-frequency oscillators with different eigenfrequencies. This fact can be useful, in particular, for an explanation of the dynamics of the intense cyclotron radiation, which is detected escaping from Earth in the kilometric wavelength range.

Experimental Realization of the High-Harmonic Gyrotron Oscillator With a Klystron-Like Sectioned Cavity

High-harmonic terahertz-frequency-range gyrotrons require long-length operating cavities due to both weak electron-wave coupling and relatively low electron currents. Since diffraction Q-factors of such cavities are very high, a great share of the radiated RF power is spent to ohmic losses. A sectioned klystron-like cavity was proposed as a way to combine a long electron-wave interaction region with a relatively low diffraction Q-factor. In this brief, results of the first experiment under the high-harmonic gyrotron with the klystron-like cavity are reported. In this experiment, selective operation of the gyrotron at the second (0.55 THz) and the third (0.74 THz) cyclotron harmonics has been observed.

A gyrodevice based on simultaneous excitation of opposite and forward waves (Gyrotron BWO-TWT)

A new method of significant efficiency enhancement, which is based on simultaneous interaction of electrons with an opposite wave at the second cyclotron harmonic, and a forward wave of the same frequency, at the fundamental cyclotron resonance, is proposed for the backward wave oscillator (gyro-BWO). Excitation of the forward wave results in significant efficiency enhancement, whereas the opposite wave provides a broadband feedback. This allows realizing a high-efficiency, frequency-tunable oscillator.