Quasi-optical Gyrotron Research Articles

First experiment of gyrotron tube with quasi-optical cavity of special configuration

A new kind of quasi-optical cavity—Axisymmetrical Quasi-Optical Cavity of Oblique Rotation (AQCOR) and the new scheme for quasi-optical gyrotron with AQCOR had been proposed in [1], and the experimental tube was built in our institute. Now the initial test results of the tube are reported in this paper.

On the design of open resonators for quasi-optical gyrotrons

In the design of a 120 GHz 200 kW quasi-optical gyrotron, we have analyzed the influence of the open resonator geometry (two circular mirrors facing one another) on the electronic efficiency, the ohmic losses, the output coupling and the multimode behavior. The method we have used to optimized the resonator design will be presented. Mode selectivity is improved by using a resonator formed by two mirrors each of which has a central step. Numerical simulations show that single mode operation can also be attained in the more favorable situation of a magnetic field having a positive taper over the interaction region.

Axisymmetric optical system for quasi-optical gyrotron

An analysis is carried out with a profile of hollow Gaussian radiation beam propagating in an optical system composed of coaxial annular curved mirrors. The result will be a useful tool in designing an axisymmetric quasi-optical gyrotron oscillator (ASQUOTRON).

Open resonator for quasi-optical gyrotrons: structure of the modes and their influence

Abstract The influence of the resonator geometry on the design of quasi-optical gyrotrons is presented. Basic equations and relevant properties of quasi-optical resonators are reviewed. Since confocal resonators radiate an equal amount of power from each mirror, non-confocal resonators have to be used in order to maximize the output-coupling on one side. Technical constraints on ohmic power losses and mirror diameter are discussed. Using numerical solutions of the quasi-optical resonator equations, the influence of the actual electromagnetic field profile on the electronic efficiency is calculated for several cases.

Quasi-optical gyro-peniotron at high cyclotron harmonics

Abstract This paper proposes a new kind of device operating at short millimetre wavelength, in which RF radiation generation is based on the interaction of a beam of sub-relativistic gyrating electrons and the RF standing-wave field of a quasi-optical resonator. This device can be called ‘quasi-optical gyro-peniotron’ because it is similar in electron-beam configuration, microwave circuitry and cyclotron resonance properties to the quasi-optical gyrotron and in its operational mechanism to the peniotron. Starting from relativistic equations of motion for the electrons, the calculation formulae are derived. Using computer simulation, a beam-wave interaction efficiency of 43% is obtained for the third cyclotron harmonic at frequency 100 GHz, beam voltage 80 kV and the applied magnetic field 13·3 kG, indicating that this tube will be potentially a high-efficiency high-power source not requiring a superconduction magnet system even within the 150 GHz band.

Experimental study of a single-mode quasi-optical gyrotron

Abstract The first experimental results of a high-power quasi-optical gyrotron are presented. The cavity was designed to eliminate all mode competition, longitudinal as well as radial. Powers to 80 kW and efficiencies to 11% were measured with indications that the actual electronic efficiency was at least a factor of 1·5 greater.

An analytical theory for comparing the efficiency of gyrotrons with various electrodynamic systems

Abstract An analytical theory is developed that permits one to analyse the influence of the transverse inhomogeneity of the interaction space on the efficiency of gyrotrons with various resonators. A number of different gyrotrons including the quasi-optical one are considered. The results obtained make it possible, in particular, to estimate the efficiency of quasi-optical gyrotrons for different values of the electron beam radius and the ellipticity of the resonator mirrors.

Generation of High-Frequency Radiation by Quasi-Optical Gyrotron at Harmonics of the Cyclotron Frequency

A quasi-optical gyrotron can operate, in principle, at high harmonics of the electron-cyclotron frequency, as well as at the fundamental. Lower harmonics are suppressed by exploiting their larger diffraction losses. The radiation-field amplitude is kept below the breakdown value by taking advantage of the focusing properties of the quasi-optical resonator. Cavity design parameters and starting currents are presented which characterize the operation of the quasi-optical gyrotron at the eighth harmonic of gyrofrequency.

Axisymmetric quasi-optical gyrotron oscillator

An axisymmetric quasi-optical gyrotron (ASQUOTRON) is considered to realize a 10 MW, 150 GHz, CW oscillator required for an electron cyclotron resonance heating of a fusion plasma. The gyrotron has an axisymmetric mirror to be used as its optical cavity. It is shown that the axisymmetric mirror of relatively small radius (∼20 cm) can be used in producing the 10 MW continuous wave with a tolerable mirror heat load (∼0.5 kW/cm2). Considerations are also made on wave transmissions through the mirror and to a target.

Cavity design for quasi-optical gyrotron and gyroklystron operation at harmonics of the cyclotron frequency

A quasi-optical cavity is designed for harmonic operation of gyrotrons and gyroklystrons. Lower harmonics are suppressed by exploiting their larger diffraction losses and field amplitude is kept below the breakdown value by taking advantage of the focusing properties of the radiation in the resonator.

Engineering Design of the Quasi-Optical ECRH Injection System for the Mirror Advanced Reactor (MARS)

The engineering design of two high-power steadystate ECRH injection systems is presented for the MARS tandem mirror reactor. With a design power of 57 MW, System I is comprised of 1 MW cavity-mode gyrotrons coupled to a novel quasioptical launching system for the combination and transmission of the ECRH power to the plasma. System II has a design power of 84 MW and comprises 2.5 MW quasi-optical gyrotron units coupled to a quasi-optical launching system similar in principle to System I but displaying minimal space requirements. Potential operating conditions, parameters and constraints are presented for multi-MW gyrotrons and quasi-optical launching systems, and key ECRH development and technology needs for commercial tandem mirror reactors are defined.

Theory of quasioptical gyrotrons and gyroklystrons operating at higher harmonics of the cyclotron frequency

A multimode, non-linear, time-dependent formulation of the theory of quasioptical electron cyclotron masers operating at high gyrofrequency harmonics is presented. Linear calculations of the starting current and numerical analyses of the efficiency of the devices are performed. It is shown that with suitable contouring of the DC magnetic field, a stable single mode operation at the second harmonic is possible. To improve the efficiency, an alternative configuration, the quasioptical gyroklystron, is also analysed using single mode and multimode dynamics simulations. The gyroklystron operating at the second harmonic is shown to lead to a significant increase in efficiency (approximately 30%).

Multimode, time-dependent analysis of quasi-optical gyrotrons and gyroklystrons

A multimode, time-dependent analysis is carried out for the quasi-optical gyrotron to assess its promise as a high-power millimeter wave generator. It is shown that both relatively high efficiences and single mode operation are possible. An alternate device configuration, the quasi-optical gyroklystron, is also analyzed and is found to increase efficiency while decreasing the requirement on high-frequency field amplitude necessary for efficient operation.

Multimode theory and simulation of quasioptical gyrotrons and gyroklystrons

Very high power sources for millimeter wavelength radiation are desired for cyclotron heating of magnetic fusion devices. To meet this goal a quasioptical gyrotron has recently been proposed and analysed using a single mode approach. In this work, a more realistic analysis of the quasioptical gyrotron is carried out using multimode time-dependent simulations to study mode competition in a highly overmoded cavity. It is shown that with suitable contouring of the DC magnetic field, single mode operation at 30% or greater efficiency is possible. To further improve on efficiency, an alternative configuration, the quasioptical gyroklystron, is also analysed using multimode dynamic simulations. The gyroklystron is shown to lead to a significant increasing in efficiency (≈ 45%), particularly at moderate values for the high frequency electric field. Similar analyses of the quasioptical gyrotron and gyroklystron operating on the second harmonic have shown promising results ; efficiencies ≈ 30% have been obtained f...

Operation of the quasi-optical gyrotron at harmonics of the gyrofrequency

This paper investigates the performance of a quasioptical gyrotron, when the electron beam interacts with the radiation fields at harmonics of the gyrofrequency. The nonlinear equations of motion are obtained in the slow-timescale. The expression for the linear gain is derived and the conditions for excitation are given (frequency threshold, optimal operating point, bean current and resonator quality thresholds). In the nonlinear regime, it is shown that maximum efficiencies comparable to those at the fundemental (∼50%) are possible, albeit at a prohitively high radiation field amplitude, while realistically feasible field amplitudes can give somewhat smaller, but nevertheless still high efficiencies (∼15%). Finally, the results are suplemented by empirical scaling laws, useful for experimental designs.