Phase-locking of a second-harmonic gyrotron oscillator using aquasi-optical circulator to separate injection and output signals

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in gyrotrons operating at the fundamental cyclotron frequency which may be attributed to the longer resonant cavity in the second harmonic gyrotron and the corresponding larger value of external quality factor. The measurements are roughly in agreement with predictions of Adler's phase-locking equation which is given for our system in terms of powers propagating in the output waveguide toward and away from the gyrotron cavity     

Integrated design of depressed collectors for gyrotrons

In order to obtain optimum collector efficiency and to control the electron trajectories in the collector region the design process for depressed collectors has to take into account several interlinked parameters. A flow diagram is presented for a systematic design procedure which integrates the various steps. A library of computer codes has been developed to assist in different stages of design. Among the key elements is a code that generates contours of effective potential and helps to define the regions of accessibility for electrons. These contours and the lines of magnetic flux can be drawn against the backdrop of the collector geometry. The different control parameters can be varied and their effect on the contours studied interactively. The search area for optimum parameters is thus considerably reduced. Additional codes make it possible to evaluate each design in terms of collector efficiency, division of beam current between different collectors, and the heat dissipation density profile. Using these codes, a design has been developed for a two-stage depressed collector for a 1-mW, 110-GHz gyrotron yielding a collector efficiency of 68%     

Experimental and numerical studies of sheet electron beampropagation through a planar wiggler magnet

Detailed experimental studies on sheet relativistic electron beam propagation through a long planar wiggler are reported and compared with numerical simulations. The planar wiggler has 56 periods with a period of 9.6 mm. Typically, the wiggler field peak amplitude is 5 kG. The experimental efforts are focused on controlling the deviation of the beam toward the side edge of the planar wiggler along the wide transverse direction. It is found that a suitably tapered magnetic field configuration at the wiggler entrance can considerably reduce the rate of deviation. The effects of the following techniques on beam transport efficiency are discussed: side focusing, beam transverse velocity tuning at the wiggler entrance, and beam spread limiting. High beam transport efficiency (almost 100%) of a 15-A beam is obtained in some cases     

Design of a multistage depressed collector system for 1-MW CWgyrotrons. I. Trajectory control of primary and secondary electrons in atwo-stage depressed collector

Part I of this paper presents the design of a two-stage depressed collector for a 110 GHz, 1 MW gyrotron, taking into account the trajectories of electrons backscattered from the electrode surfaces. The collector geometry and the magnetic circuit were adjusted in order to minimize the effect of backscattered electrons. A computer code was employed which is based on a new algorithm designed to give good representation to a variety of energy levels and angles of emergence of backscattered electrons. The collector efficiency estimated on the basis of primary electrons alone was 68%. The estimated collector efficiency which included also the effect of backscattered electrons was 60%. In the latter case the surface of the collectors was assumed to be that of polished copper. The techniques and codes used in the design are reviewed and results of trajectory tracing are presented for primaries and secondaries. Part II of the paper presents the system aspects, including the mechanical and thermal designs and the solid-state power supply design     

Performance characteristics of a high-power X-bandtwo-cavity gyroklystron

The operating characteristics of a two-cavity X-band gyroklystron experiment are reported. Beam voltages and currents up to 440 kV and 200 A, respectively, are generated in 1 μs pulses by a thermionic magnetron injection gun. Velocity ratios (ν_⊥ /ν_z) near one in the output cavity are used to achieve peak powers of 24 MW near 9.87 GHz. The maximum saturated efficiency of more than 33% occurs at a beam voltage of 425 kV and a current of 150 A. A large signal gain in excess of 34 dB is realized by operating the input cavity just below the start oscillation threshold. Details of tube stability and the dependence of amplification on magnetic field profile, input signal parameters, and various beam quantities are presented     

High-power X-band amplification from an overmodedthree-cavity gyroklystron with a tunable penultimate cavity

Experimental results for a 10 GHz TE₀₁ mode three-cavity gyroklystron with a tunable penultimate cavity are presented. The electron beam was produced by a pulse line modulator and a magnetron injection gun which operates to 433 kV and 225 A with 1 μs flat-top. Three-cavity circuits have produced a peak power of 27 MW with efficiency of 32% and pulse energy of 39 J. A maximum gain of 50 dB was achieved at a peak power of 20 MW, and a maximum efficiency of 37% was achieved at a peak power of 16 MW