S. V. Samsonov

GYROTRON TRAVELING WAVE AMPLIFIER WITH A HELICAL INTERACTION WAVEGUIDE

A new microwave system in the form of a cylindrical waveguide with a helical corrugation of the inner surface is proposed for a gyrotron traveling wave tube (gyro-TWT). The corrugation radically changes the wave dispersion in the region of small axial wave numbers. This allows significant reduction in the sensitivity of the amplifier to the electron velocity spread and an increase in its frequency bandwidth. An X-band gyro-TWT operating at the second cyclotron harmonic with a 200-keV, 25-A electron beam produced an output power of 1 MW, corresponding to a gain of 23 dB and an efficiency of 20%.

Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide

A gyrotron backward wave oscillator (gyro-BWO) with a helically corrugated interaction waveguide demonstrated its potential as a powerful microwave source with high efficiency and a wide frequency tuning range. This letter presents the theory describing the dispersion properties of such a waveguide and the linear beam-wave interaction. Numerical simulation results using the PIC code MAGIC were found to be in excellent agreement with the output measured from a gyro-BWO experiment.

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.

Cyclotron autoresonance masers: Recent experiments and projects

The cyclotron autoresonance maser (CARM) is one of the promising modifications of free-electron masers (FEM) operated at the millimeter and submillimeter waves. In this range CARM requires particle energies significantly lower than for the ubitron, and magnetic fields smaller than those for the gyrotron. The CARM is considered as a possible source of coherent millimeter wavelength radiation with large average (continuous) power for plasma heating in controlled fusion devices.

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.

Generation of 3 GW microwave pulses in X-band from a combination of a relativistic backward-wave oscillator and a helical-waveguide compressor

The phenomenon of passive compression of frequency-modulated (FM) pulses in a dispersive media (DM) was used to increase the peak microwave power up to the multigigawatt level. A helically corrugated waveguide was used as the DM, while a relativistic X-band backward-wave oscillator (RBWO) with a descending-during-the-pulse accelerating voltage served as a source of FM pulses. Compression of pulses down to a halfwidth of 2.2 ns accompanied by a 4.5-fold power increase up to a value of about 3.2 GW has been demonstrated.

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.

Experimental study of a high-current FEM with a broadband microwave system

Abstract The first stage of the experimental study of a frequency adjustable FEM-oscillator with a broadband microwave system based on the effect of microwave beams multiplication is presented. Operability of the key element of this system (wide-band reflector) was tested in the “hot” experiment. The 45 GHz FEM-oscillator with a microwave system of the new type was driven by a 500 keV, 120 A, 20 ns electron beam and generated 7 MW of radiation with a 12% efficiency. A new double-resonance operating regime of the FEM with combined - undulator and homogeneous guide - magnetic field, when both the undulator and the cyclotron resonance conditions are fulfilled simultaneously, was realized.

Comparative analysis of electron beam quality on the operation of a FEM with axial guide magnetic field and a CARM

Abstract A theoretical analysis of influence of electron beam quality on the operation of a Free-Electron Masers (FEM) with axial guide magnetic field and a Cyclotron Autoresonance Masers (CARM), is presented. For both FEM and CARM transverse velocity component achieved by transversely driving a rectilinear electron beam. The quality of electron beam depends on amplitude of initial random transverse oscillations of the particles. It is shown, that in a FEM operating in the regime far from cyclotron resonance (including the reversed-guide-field regime) the spread in the averaged axial particle velocities is equal to the spread in the initial beam and proportional to the square of the amplitude of parasitic initial oscillations. However, in a CARM this spread is linearly proportional to the initial transverse velocity and, thus, essentially exceeds the spread in the FEM for the same quality of electron beam. As a result, a drop in CARM efficiency with decline of beam quality is much more dramatic than in the FEM.

Experimental results on microwave pulse compression using helically corrugated waveguide

The paper presents new results on the development of a method to generate ultrahigh-power short-microwave pulses by using a known principle of compression (reduction in pulse duration accompanying with increase in pulse amplitude) of a frequency-swept wave packet propagating through a dispersive medium. An oversized circular waveguide with helical-corrugations of its inner surface ensures an eigenwave with strongly frequency dependent group velocity far from cutoff. These dispersive properties in conjunction with high rf breakdown strength and low Ohmic losses make a helically corrugated waveguide attractive for increasing microwave peak power. The experiments performed at kilowatt power levels, demonstrate that an X-band microwave pulse of 80 ns duration with a 5% frequency sweep can be compressed into a 1.5 ns pulse having 25 times higher peak power by optimizing the frequency modulation of the input wave packet.