The history of gyrotron development, the principles of gyrotron operation, and possible ways to enhance the power level to increase the operating frequency of gyrotrons are outlined. The state of the art of gyrotrons, their present and possible applications, and perspectives on gyrotrons are considered. >

http://ieeexplore.ieee.org/iel1/5/247/00004454.pdf

Gyrotron oscillators

A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%.

A 35-GHz low-voltage third-harmonic gyrotron with a permanent magnet system

The operating characteristics of a 140 GHz pulsed gyrotron are reported. Total efficiencies of 36% and output powers of 175 kW have been obtained in single-mode operation. Measurements of power and efficiency have been made for a variety of modes between 120 and 160 GHz, and these results are in good agreement with predictions based on non-linear theory. The best results have been obtained with isolated asymmetric modes, such as the TE4, 2, 1 (127·3 GHz), TE2, 3, 1,(136·7 GHz) and TE3, 3, 1(155·6 GHz). Although mode competition was found to prevent the TE0, 3, 1, mode (139·5 GHz) from reaching the optimum operating conditions, an output power of 138 kW and total efficiency of 29% were achieved with this mode. A variety of new and highly accurate diagnostic techniques that have been developed to measure the power, frequency and mode content of the output radiation are reviewed. In addition, the operating characteristics of both laminar and non-laminar magnetron injection guns are compared. The hig...

/pdf/high-efficiency-operation-of-a-140-ghz-pulsed-gyrotron-42pynn6fic.pdf

High efficiency operation of a 140 GHz pulsed gyrotron

Gyrotron oscillators have served as effective sources for electron cyclotron heating (ECH) applications in the area of magnetic confinement fusion Successful development programs at frequencies at 28 GHz, 60 GHz, and 140 GHZ, have led to the availability of wide-range gyrotron sources with high-average-power capabilities Since 1975, over 100 pulsed and CW gyrotrons with typical power levels of 200 kW at frequencies ranging from 28–106 GHz have been used by various fusion laboratories Present development activity is aimed at providing sources that will generate power levels up to 1 MW CW at frequencies in the range 100–140 GHz for the ECH experiments that are currently being planned Initial experimental efforts in this area have verified many of the concepts to be employed in forthcoming 1-MW CW test vehicles Source requirements, that are even more formidable, are foreseen for the next generation magnetic fusion facilities Frequencies ranging from 200–300 GHz with power generation capabilities of 1–2 MW CW per tube are being considered for these future applications To this end, various gyrotron designs have been conceived that address these demanding specifications

Gyrotrons for ECH applications

A Ka‐ band gyrotron oscillator powered by a 600 kV pulse‐line accelerator has produced approximately 100 MW at 35 GHz in a circular TE62 mode. It has also demonstrated frequency tuning over the range 28 to 49 GHz by operating in a family of TEm2 modes, with the azimuthal index m ranging from 4 to 10, by variation of the guide magnetic field. Operation is in general agreement with the predictions of theory.

High peak power Ka‐band gyrotron oscillator experiment

For the first time, a Varian 60 GHz gyrotron designed specifically to generate microwaves in a single output mode has been operated at power levels up to 200 kW CW. Using mode-specific directional couplers, measurements of the output mode content indicated that greater than 95% of the microwave output was in the desired TE02 mode with only small percentages in the neighbouring TE01 and TE03 circular electric modes. High output-mode purity is required for the efficient utilization of gyrotrons as high-power microwave sources for electron cyclotron resonance heating (ECRH) in magnetic fusion plasmas.

A 60 GHz, 200 kW CW gyrotron with a pure output mode†

A Varian 60 GHz, CW gyrotron has recently been operated at power levels up to 200 kW CW. The tube employs a TE 011 /TE 021 complex interaction cavity which inhibits mode competition by the TE 221 mode with the desired TE 021 mode. The output mode of the cavity is nominally in the TE 02 circular waveguide mode in overmoded waveguide. Since the output waveguide also serves as the gyrotron collector, mode conversion occurs in the taper sections and gaps incorporated into the collector. Measurements of the mode conversion on a 60 GHz, 200 kw, 100 ms pulse tube, have been made and compared with similar measurements on the 60 GHz, 200 kW, CW gyrotron. These measurements indicated that the CW tube had significantly more conversion of the TE 02 mode into other TE on modes than did the pulse tube. Current design work is aimed at reducing the mode conversion of the CW design to the same levels as the pulse design (≲10% mode conversion).

/pdf/analysis-of-the-output-mode-from-60-ghz-200-kw-pulsed-and-cw-505akqahsr.pdf

Analysis of the output mode from 60 GHz, 200 kW pulsed and CW gyrotrons

For the first time, a Varian 60 GHz gyrotron, designed specifically to generate microwaves in a single output mode, has been operated at power levels up to 200 kW CW. High output mode purity is required for the efficient utilization of gyrotrons as high power microwave sources for electron cyclotron resonance heating (ECRH) in magnetic fusion plasmas. Using mode-specific directional couplers, measurements of the output mode content indicated that greater than 95% of the microwave output was in the desired TE 02 mode, with only small percentages in the neighboring TE 01 and TE 03 circular electric modes. The pure mode CW design uses a 2.5-inch diameter collector. The collector has a magnetic field arrangment which capably avoids excessive heating by distributing the 640 kW CW beam over a sufficient collector area. With pure mode operation, window temperatures are 10°C to 15°C higher than with mixed mode operation.

A 60 GHz 200 kW CW gyrotron with high output mode purity

/pdf/a-60-ghz-200-kw-cw-gyrotron-with-high-output-mode-purity-30uqw1nxm4.pdf

A 60 GHz, 200 kW CW gyrotron with high output mode purity

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A 60 GHz, 200 kW CW gyrotron with a pure output mode†

Analysis of the output mode from 60 GHz, 200 kW pulsed and CW gyrotrons

A 60 GHz 200 kW CW gyrotron with high output mode purity

A 60 GHz, 200 kW CW gyrotron with high output mode purity