The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as a function of generalized parameters for the second through fifth harmonics. The numerical results are valid for a wide range of operating conditions, including voltage, current, beam radius, cavity dimensions, and operating mode. Relatively high efficiencies are found even at high harmonics; the maximum transverse efficiencies for harmonics 2, 3, 4, and 5 are 0.72, 0.57, 0.45, and 0.36, respectively. The calculation of the efficiency in terms of generalized parameters allows the straightforward design and optimization of harmonic gyrotrons. The influence of the axial profile of the rf field in the gyrotron cavity on the efficiency is also investigated. Improved efficiency can be achieved with asymmetric field profiles. The implications of these results for the generation of millimeter and submillimeter wave radiation by harmonic emission are discussed.

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Generalized nonlinear harmonic gyrotron theory

250 GHz CW Gyrotron Oscillator for Dynamic Nuclear Polarization in Biological Solid State NMR

This paper proposes a new cyclotron fast-wave tube named the ‘gyro-peniotron’, which is promising as a highly efficient and powerful source of millimetre or sub-millimetre waves, and reports the analytical results of its operational characteristics using some computer simulations. The analytical results assuming two operating conditions of ω0;≃ ωc and ω0≃3ωc for the 35 GHz gyro-peniotron in the TE021 cavity mode predict a high efficiency of 63% and a quite high output power of 48 MW at a beam voltage of 80 kV and a magnetic field of 13 kG in the case of ω0≃ωc, and also, an efficiency of 48% and a power of 9 MW at a beam voltage of 60 kV and a magnetic field of 4·425 kG in the ease of ω0≃3ωc

Proposal of a high efficiency tube for high power millimetre or submillimetre wave generation: The gyro-peniotron

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.

Experimental study of a single-mode quasi-optical gyrotron

The operation of a gyrotron based upon a quasi-optical cavity is reported. The cavity mirrors were separated by 81 cm, allowing the use of mirrors large enough in diameter to be in principle compatible with CW operation. The pulse length in this experiment was 12 microseconds. The gyrotron operated between 113 GHz and 122 GHz, with a maximum output power of 50 kW. The highest efficiency observed was 7·3%. The observed powers and efficiencies were lower than originally anticipated, but when cavity losses and the actual performance of the electron gun was included, agreed well with theoretical predictions based on multimode simulations. The output spectra were measured, and were in good qualitative agreement with theory

Experimental-Study of a 115 Ghz Quasi-Optical Gyrotron with a Large Cavity

There are problems associated with the multimode character of oversize waveguides. This paper reports on a novel, direct way to identify modes in an oversize waveguide by looking at the field map on a liquid crystal sheet inserted in the waveguide. The local temperature change in the liquid crystal due to absorbed microwave energy is translated to a color change in such a way that a map of the Iocal power flow is observed on the sheet. Mode identification is very important in gyrotrons, for example, where the microwave energy generating device is subject to severe problems from mode competition.

A Technique to Identify Electromagnetic Modes in Oversize Waveguides (Short Papers)

In this paper, experimental results on a 35 GHz 250 kw gyrotron oscillator (TH 1501 A) are first summarized. The project of a 70 GHz oscillator operating on the second harmonic of the cyclotron resonance is then discussed, and first experimental results are described. Theoretical work on space charge effects in a single orbit cylindrical beam oscillator is also reported. Numerical results indicate typically a 15% decrease in logarithmic gain.

Development of gyrotrons at Thomson-CSF†

It is well known that different modes of electromagnetic waves in a waveguide have different attenuation for a waveguide of fixed size. For example, a TE8.1(Transverse Electric in circular guide mode has decreasing attentuation with increasing frequency. This property is shared by all TE0.n modes, and because of this , property some waves have received a good deal of attention for possible long distance propagation of en9r4ykl) and for low ohmic losses in rsonators of microwave and millimeter wave power sources such as gyrotrons.2) One of the major problems in the use of TEOn in circular waveguides arises because it is not the mode of lowest cutoff frequency, and therefore must always be used in a guide capable of propagating a number of modes (known as oversize guides). For the TEo.1 mode in a circular waveguide there are at least four other modes propagating if the TE mode is above cutoff T1,10.1, TE21). There are few ways to identify the mode of propagation 0.1 in an oversize waveguide, and even to measure the fractional power in each of them.

P. Boulanger

Papers

A Technique to Identify Electromagnetic Modes in Oversize Waveguides (Short Papers)

Development of gyrotrons at Thomson-CSF†

A Videography Technique To Identify Electromagnetic Modes In Oversize Waveguides