V. N. Manuilov

Review of Subterahertz and Terahertz Gyrodevices at IAP RAS and FIR FU

The maximal frequency of radiation higher than 1 THz has been recently obtained in pulse gyrotrons both at IAP (Nizhny Novgorod, Russia) and FIR (Fukui, Japan). CW generation at a 2.2-kW power level is radiated from a 300-GHz gyrotron and used for technological applications. New gyrotrons demonstrate single-mode operation at the second cyclotron harmonic with a frequency of 395 GHz in the CW regime with a power of 100 W and at the third harmonic with frequencies of 371-414 GHz in 10-mus pulses with power of 10-20 kW. Methods of selective excitation of higher cyclotron harmonics, frequency multiplication, and smooth frequency tuning in terahertz gyrotrons are also discussed in the review.

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.

Numerical Simulation Models of Forming Systems of Intense Gyrotron Helical Electron Beams

Potentialities of different numerical models for calculation of helical electron beams parameters are analyzed. The most simple and economical with respect to the calculation time static mono-velocity model, as well as the model considering initial velocities of electrons and the dynamic model based on the PIC-method and on the quasi-static concept of the electric field are described. The main physical results obtained on the basis if each model mentioned above are given.

Generation of high power sub-terahertz radiation from a gyrotron with second harmonic oscillation

New power records of second harmonic gyrotron oscillation have been demonstrated in the sub-THz band. The first step gyrotron of demountable type had succeeded in oscillation with power more than 50 kW at 350 GHz and nearly 40 kW at 390 GHz [T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009)]. Then, the second step gyrotron of sealed-off type was manufactured. A cavity mode was carefully selected to avoid mode competition with a neighboring fundamental harmonic mode. Matching of the selected mode with the electron gun was also circumspectly considered. The second step gyrotron has attained higher power radiation than the first gyrotron. The maximum single mode power was 62 kW at 388 GHz. Then, the electron gun was modified for use of a different cavity mode with a higher coupling coefficient than that for the 62 kW mode. The new mode proved single mode oscillation power of 83 kW at about 389 GHz. These results are new second-harmonic-oscillation power records for sub-THz gyrotrons. The present study constitutes foundations of development of high power second harmonic sub-THz gyrotron for application to collective Thomson scattering measurement on fusion plasmas, especially on high-density plasmas such as those produced in LHD [N. Ohyabu et al., Phys. Rev. Lett. 97, 055002 (2006)]. This paper reports the design consideration to realize high power single mode gyrotron oscillation at second harmonic and the examination of oscillation characteristics of the gyrotron.

Advanced Numerical and Experimental Investigation for Gyrotrons Helical Electron Beams

The paper presents a modern approach to studies of characteristics of intense helical electron beams (HEBs) for gyrotrons. The essence of the method consists in finding functions of electron distribution with respect to oscillatory velocities in the beam both by numerical simulation and experimentally. Experimental and calculated data for beams with different topologies were compared in different frequency ranges. Evolution of the electron oscillatory velocities distribution function as the beam current grows has been traced. Influence of the reflected electrons on beam parameters has been simulated numerically.

Experimental tests of a 263 GHz gyrotron for spectroscopic applications and diagnostics of various media

A 263 GHz continuous-wave (CW) gyrotron was developed at the IAP RAS for future applications as a microwave power source in Dynamic Nuclear Polarization / Nuclear magnetic resonance (DNP/NMR) spectrometers. A new experimental facility with a computerized control was built to test this and subsequent gyrotrons. We obtained the maximum CW power up to 1 kW in the 15 kV/0.4 A operation regime. The power about 10 W, which is sufficient for many spectroscopic applications, was realized in the low current 14 kV/0.02 A regime. The possibility of frequency tuning by variation of the coolant temperature about 4 MHz/1 °C was demonstrated. The spectral width of the gyrotron radiation was about 10(-6).

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...

Design of a Subterahertz, Third-Harmonic, Continuous-Wave Gyrotron

The design of a 400-GHz gyrotron operating at the third cyclotron harmonic is presented. The gyrotron is designed to operate at the TE6!4-mode, which allows one to produce about 1 kW of output power with the density of ohmic losses acceptable for continuous operation. The dependence of performance characteristics on various gyrotron parameters (beam voltage, current, pitch-ratio, and velocity spread) is analyzed. It is shown that the desired mode is significantly distinct from competing modes. Special attention is given to the effect of imperfections in resonator fabrication on gyrotron performance. It is found that to keep the gyrotron performance close to the designed data obtained for an ideal resonator shape, the resonator should be fabricated with tolerance of about 1 mum. In view of the recent experimental data, such fabrication seems feasible. Therefore, the development of 1 kW, continuous-wave gyrotrons operating at the third harmonic in this frequency range looks possible.

Theory of helical electron beams in gyrotrons

Helical electron beams (HEB) with disturbed axial symmetry of currents density and HEB with locking electrons in magnetic trap are described. The theory of magnetron injection gun (MIG) in space-charge limited current is developed. Systems on permanent magnets forming HEB are considered.

Recent test results on broad-band gyro-TWT and gyro-BWO with helically grooved operating wave-guides

The paper presents recent test results on low relativistic (20-80 kV) gyro-TWT and gyro-BWO based on a microwave system in the form of a waveguide with helical surface. In particular, in experiments the Ka-band gyro-TWT showed the following output parameters: pulse power up to 180 kW, gain 25-30 dB, instant frequency band 10%, efficiency at second harmonic operation 27%. The gyro-BWO was designed for CW operation with output power of 5-7 kW at frequencies around 24 GHz. Smooth frequency tuning in the band of 10% was demonstrated.