A. G. Luchinin

A 670 GHz gyrotron with record power and efficiency

A 670 GHz gyrotron with record power and efficiency has been developed in joint experiments of the Institute of Applied Physics, Russian Academy of Sciences (Nizhny Novgord, Russia), and the University of Maryland (USA) teams. The magnetic field of 27–28 T required for operation at the 670 GHz at the fundamental cyclotron resonance is produced by a pulsed solenoid. The pulse duration of the magnetic field is several milliseconds. A gyrotron is driven by a 70 kV, 15 A electron beam, so the beam power is on the order of 1 MW in 10–20 ms pulses. The ratio of the orbital to axial electron velocity components is in the range of 1.2–1.3. The gyrotron is designed to operate in the TE31,8-mode. Operation in a so high-order mode results in relatively low ohmic losses (less than 10% of the radiated power). Achieved power of the outgoing radiation (210 kW) and corresponding efficiency (about 20%) represent record numbers for high-power sources of sub-THz radiation.

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.

A point-like source of extreme ultraviolet radiation based on a discharge in a non-uniform gas flow, sustained by powerful gyrotron radiation of terahertz frequency band

The possibility and prospects of extreme ultraviolet (UV) point-like source development are discussed in the present paper. The UV source is based on the discharge sustained by powerful gyrotron radiation of terahertz (THz) frequency band in non-uniform gas flow injected into vacuum volume through a nozzle with diameter less than 1 mm. Recent developments of THz-band gyrotrons with appropriate power level made such discharges possible. First experimental results on a point-like plasma creation by 100 kW radiation of 0.67 THz gyrotron are presented. The possibility of discharge localization within the area less than 1 mm is demonstrated. The discharge emission within the wavelength range from 112 nm to 650 nm was studied. The measured power of light emission in the range of 112–180 nm was measured to be up to 10 kW.

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).

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.

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.

Terahertz gyrotrons: State of the art and prospects

The state of the art for terahertz gyrotrons that are needed for various scientific research and practical applications is presented. Powers of 5 kW and 200 kW are obtained at frequencies of 1 and 0.7 THz using pulsed gyrotrons with pulse durations of tens of microseconds. A power of 100 W is demonstrated for cw gyrotrons at frequencies ranging from 0.2 to 0.5 THz.

Experimental investigation of technological gyrotrons

Powerful gyrotrons for technological applications, including material processing, are presented. 30 GHz gyrotrons at the second cyclotron harmonic TE/sub 02/ mode with oil-cooled solenoid were tested. On CW regime with output power 10 kW obtained efficiency 42% and output power 30 kW with efficiency 35%. The highest for the second harmonic gyrotrons efficiency 50% with 13 kW output power level was observed after modification of the tube. Experimental dependencies of output power and gyrotron efficiency before and after modification magnetic field profile are given. Conditions of high efficiency operation taking into account space-charge effects, velocity spread, RF field and static magnetic field profiles are discussed. Results of quality testing of cathodes and dependencies of the gyrotron efficiency on cathode emission inhomogeneity are presented.

Imaging the output field pattern of a 110-GHz gyrotron with pulsed magnetic field using recombination continuum emitted by a slab of the Cs-Xe dc discharge

It has been demonstrated that recombination continuum emitted by a slab of the positive column of the Cs-Xe discharge can be used successfully to image moderate-power pulsed millimeter waves. Using this technique, the output field patterns of a 110-GHz 10-kW gyrotron with a pulsed magnetic field have been imaged.

The Ka-band 10-kW continuous wave gyrotron with wide-band fast frequency sweep

The dual-frequency gyrotron with fast 2% frequency sweep at about 28 GHz is designed to power an electron cyclotron resonance ion source (ECRIS). Operation with an output power of up to 10 kW in CW mode and efficiency of 20% was demonstrated at both frequencies. Frequency manipulation has a characteristic time of about 1 ms and is based on magnetic field variation with an additional low-power coil. Fast frequency sweep will supposedly increase the ion current and the average ion charge of ECRIS. The possibility of 100% power modulation is demonstrated using the same control method.