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A study was presented to analyze the design of the depressed collector system and the scheme for high-voltage gyroklystron amplifiers. The net efficiency of the gyroklystron design was also analyzed. Results revealed that the design of the gyroklystron amplifiers can be improved from 41.1% to 54.8% by recovering 42.4% of the spent beam energy. In addition, energy recovery using the single-stage depressed collector can be utilized for a high-power, pulsed device.

We introduce a new broad-band amplifier configuration which contains elements of both linear and cyclotron resonance maser microwave tubes. A helix slow-wave structure is used to bunch a linearly streaming annular electron beam. A nonadiabatic magnetic transition, which is placed after a drift region at the point where the ac beam current is nearly maximized, converts much of the beam's axial momentum to rotational momentum. The beam then travels through a tapered right-circular waveguide, where microwave energy is extracted via the gyrotron interaction. The design of a proof-of-principle X-band amplifier is given, and the codes that are used in the simulation are described. The nominal beam voltage and current are 45 kV and 8 A, respectively. The tube is predicted to be stable, to possess a peak efficiency above 43%, and to have an instantaneous bandwidth of over 9%. Index Terms - Broad-band sources, microwave amplifiers, radar tubes.

We present the theoretical design of a second-harmonic small-orbit gyrotron amplifier which utilizes the interaction between a 35-kV 4-A beam and a [TE.sub.011] cavity to produce over 70 kW of amplified power at 9.9 GHz in a 1.83-kG magnetic field. One of the novel features of this device is that the electron gun produces an axially streaming annular beam which is velocity modulated by a short [TM.sub.0n0] input cavity. Perpendicular energy is imparted to the beam via a nonadiabatic magnetic transition at the end of a 13-cm drift region. An electronic efficiency of 53% is predicted with a large signal gain near 20 dB by a single particle code which takes into account nonideal effects associated with finite beam thickness and finite magnetic field transition widths.

Efficient 100-150 MW X- and Ku-band microwave sources with pulselengths of 1 [[micro]second] are being developed for driving future linear colliders. Two- and three-cavity co-axial designs of relativistic gyroklystron amplifiers are presented here which fulfill these requirements. Numerical simulations predict over 40% efficiency, 45-50 dB gain, and 100-160 MW power level for the gyroklystron designs operating at fundamental (8.568 GHz) and second harmonic (17.136 GHz). It is shown that introducing a penultimate (buncher) cavity significantly improves efficiency and gain of the second-harmonic amplifier.

The problem of mode competition in a high-power gyrotron oscillator is considered. The regions of parameter space in which a preexisting large-amplitude mode is able to suppress competing satellites are determined for cases in which the coupling coefficients and cavity quality factors for the operating and satellite modes are different. In addition, the effect of beam quality on the regimes of stable single-mode operation is investigated. Generally speaking, the requirement of stable operation favors devices whose interaction length measured by the parameter [Mu] defined in (17) is not too large. It is found that for [Mu] near 10 the operation is relatively stable and [Mu] near 17 is not.

1-MW continuous-wave (CW) gyrotrons operating at 140 GHz are being developed for heating fusion plasmas [1]. Energy recovery using a depressed collector is employed to improve total efficiency and reduce power supply voltage and voltage regulation requirements for various electron beam devices. This paper describes and compares three different types of single-stage, depressed-collector designs. The first design is a magnetically shielded, coaxial collector with fixed-current collector coils. The second and third designs use cylindrical collectors with an outer magnetic shield and collector coils with time-varying current values. The time-varying magnetic field produced by the collector coils sweeps the beam trajectories on the collector surface lowering the average power density. The second design employs axial beam sweeping using axisymmetric collector coils, whereas the third design employs transverse beam sweeping, making the instantaneous fields and electron trajectories nonaxisymmetric and three-dimensional (3-D). Relative advantages and disadvantages of these three schemes are discussed. Index Terms--Depressed collector, ECRH, gyrotron, high power microwave source.

Presents a study which described and compared some types of depressed-collector designs for the development of continuous-wave gyrotrons for heating fusion plasmas. Applications of gyrotrons and gyroklystrons; Summary.