Coaxial Gyroklystron Research Articles

Design of a High-Gain K-Band Coaxial Gyroklystron

We present the design and simulation results of a high-power K-band coaxial frequency-doubling gyroklystron. The six-cavity gyroklystron tube has three cavities operating at the fundamental frequency and the last three cavities operating at twice the fundamental frequency at 22.848 GHz. Numerical simulations predict an efficiency of 37.2% and a gain of 78.3 dB at an average perpendicular-to-axial velocity ratio of 1.4. Start oscillation curves show that the tube is stable to self-oscillations up to an average velocity ratio of 1.4

On the frequency scaling of coaxial gyroklystrons

In this paper, we present scaling arguments for coaxial gyroklystron systems in order to assess their ultimate peak power capabilities as a function of output frequency. After reviewing the tradeoff equations for magnetron injection guns as they relate to frequency scaling, we present an analysis of the scaling properties and limitations of coaxial gyroklystron circuits. We then present concrete designs of both electron guns and microwave circuits to demonstrate the validity of the scaling arguments. The examples are derived from high-energy physics applications, where amplifiers with peak powers in excess of 100 MW are envisioned to be required in the millimeter wave range of frequencies. Concrete designs of coaxial systems predicted to produce about 100 MW in Ku-Band, Ka-Band, and W-Band are presented and compared. We demonstrate that there are a number of potential limitations to high-frequency operation.

Present status of a 17.1-GHz four-cavity frequency-doubling coaxial gyroklystron design

A design of a Ku-band 17.1-GHz four-cavity coaxial gyroklystron amplifier for driving future linear colliders is presented. The X-band input cavity operates in the TE/sub 0.11/ mode, whereas the remaining three cavities (buncher, penultimate, and output) operate in the TE/sub 021/ mode, doubling the frequency of the input signal. The electron beam parameters are the following: current of 540 A, voltage of 460 kV, perpendicular-to-parallel velocity ratio of 1.5, and a parallel velocity spread of 6.4%. The output cavity has been simulated as (1) zero-drive unstable with Q-factor of 320 and (2) zero-drive stable with Q-factor of 250. The simulations show that the maximum efficiency in the first case is 37.4%, and in the second one is 34.4%. In both cases, a high gain of 60 dB at a 100-MW output power level can be realized.

Design of a 34-GHz second-harmonic coaxial gyroklystron experiment for accelerator applications

Presents the complete design of a 34-GHz, four-cavity coaxial gyroklystron experiment. The 500-kV, 300-A beam is produced by a double anode magnetron injection gun (MIGc) with an average perpendicular-to-parallel velocity ratio of 1.5 and a parallel velocity spread of less than 5%. The microwave circuit has a first-harmonic TE/sub 011/ input cavity that is driven at 17.135 GHz. It has buncher, penultimate, and output cavities that operate In the TE/sub 021/-mode and are resonant near the second harmonic of the gyrofrequency. A peak power of 55 MW is obtained with a 47-46 gain and 36.5% efficiency. A complete description of the system is presented. We also present scaled circuit designs at 17 GHz and 91 GHz.

High-Power Operation of a Three-Cavity X-Band Coaxial Gyroklystron

Experimental studies of high-power amplification in a novel three-cavity X-band gyroklystron are reported. The electron gun produces a 520 A beam of 470 keV electrons. The voltage flat top is nearly $2\ensuremath{\mu}\mathrm{s}$ and the beam's average velocity ratio is about 1. All cavities are designed to operate in the ${\mathrm{TE}}_{011}$ coaxial mode near 8.6 GHz. Peak powers of 75--85 MW are measured. The resultant efficiency is near $32%$ and the gain is near 30 dB. This performance is in good agreement with simulations and represents nearly a threefold increase in the peak power capability of pulsed X-band gyroklystrons.

Gyro-amplifiers as candidate RF drivers for TeV linear colliders

The feasibility of future electron-positron colliders operating at energies >1 TeV will depend on both operating efficiency and cost of the microwave amplifiers that can be developed to drive the collider. To zeroth order, the required number of amplifiers depends inversely on the parameter A=P/sub p/T/sub p///spl lambda//sup 2/, where /spl lambda/ is the wavelength, and P/sub p/ and T/sub p/ are, respectively, the power and duration of the amplifier output pulses. Thus, one goal of amplifier research is to maximize A while keeping other parameter values within bounds so as not to excessively increase the cost of either the individual amplifier system or the collider structure (e.g., amplifier voltage V/spl lsim/500 kV, wavelength /spl lambda//spl gsim/1 cm). Operating within these bounds, gyro-amplifiers have demonstrated values of A=11/spl times/10/sup 4/ W s/m/sup 2/, which compares favorably with the best values of A achieved by klystrons. The gyro-amplifier program which led to this accomplishment is reviewed. Some 20 different gyro-amplifier configurations have been examined on our 450 kV gyro-amplifier test facility during the past several years. These tubes fall into five major categories: first-, second-, and third-harmonic gyroklystrons, as well as first- and second-harmonic gyrotwystrons. Peak powers in excess of 30 MW with pulse duration of 0.8 /spl mu/s have been achieved at 19.76 GHz in the TE/sub 02/ mode via a two-cavity second-harmonic gyroklystron with a first-harmonic drive cavity. The peak efficiency and gain were 28% and 27 dB, respectively. At present, there is ongoing construction of a new three-cavity second-harmonic coaxial gyroklystron, driven by a 500-kV 720-A beam, which is predicted to have an output power well above 100 MW at 17.136 GHz with an intrinsic efficiency in excess of 40%. With the use of a depressed collector, achievable overall amplifier efficiency, which is of very great importance in the collider application, could be in the range of 50-65%.