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

Microwave tubes required to drive future 1-TeV linear colliders have challenging requirements, including 300-MW peak power at wavelengths near 3 cm. It is believed that gyrotrons have good potential for development into the high peak power, high gain, efficient amplifier required for this application. Presented here is the detailed design for a 3-cm gyroklystron amplifier at a peak power level of ~ 30 MW. This power level is approximately three orders of magnitude above the gyroklystron state of the art, and a 30-MW experimental study will be a crucial step toward achieving the 300-MW goal. Novel problems associated with a high-energy (? ~ 2) gyrotron beam are considered in detail. A new partially self-consistent nonlinear analysis is described and subsequently used to design the gyroklystron circuit. Based on the TE011 mode in cavities of circular cross section, stable operation is anticipated; the current is well below the threshold at which an unbunched electron beam would excite oscillations in the cavities and the drift spaces are designed to heavily load modes which are not cut off.

A 30-MW Gyroklystron-Amplifier Design for High-Energy Linear Accelerators

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

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†

The gyrotron is a microwave tube which employs the electron cyclotron maser interaction to produce high power output at millimeter wavelengths. It has important and growing applications for heating of plasmas in controlled thermonuclear fusion experiments. The Varian 60 GHz gyrotron has recently generated microwave power in excess of 200 kW during CW operation, with excellent dynamic range and operating stability. This is the highest average power ever produced by a microwave tube in the millimeter wave region. A description of the gyrotron design and test results are presented.

/pdf/first-200-kw-cw-operation-of-a-60-ghz-gyrotron-2tyc29aw53.pdf

First 200 kW CW operation of a 60 GHz gyrotron

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

The design features and initial test results of Varian 70 GHz and 140 GHz CW gyrotrons are presented. The first experimental 140 GHz tube has achieved an output power of 102 kW at 24% efficiency under pulsed conditions in the desired TE031 cavity mode. Further tests aimed at achieving the design goal of 100 kW CW are currently underway. The 70 GHz tube has achieved an output power of 200 kW under pulsed conditions and possesses a wide dynamic range for output power variations. 6 refs., 8 figs.

Recent operating experience with Varian 70 GHz and 140 GHz gyrotrons

A gyrotron oscillator capable of generating 100 kW of CW power is currently under development at Varian. The tube is being designed for operation in the TE 031 ocavity mode with the electron beam located at the second radial electric field maximum in the cavity. The electron beam will be produced by a magnetron injection gun and the 56 kG magnetic field required for 140 GHz operation will be provided by a superconducting magnet. Initial design calculations for the important elements of the tube are reported and the various technology issues of the tube design are discussed.

/pdf/design-considerations-for-a-100-kw-cw-140-ghz-gyrotron-jjcnsz8cbp.pdf

Design considerations for a 100 kW CW, 140 GHz gyrotron oscillator

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