Innovations in Applied Physics

The simulation technique of helical beam formation system of gyrotrons with typical axial symmetry distortion is presented. The simulation of the second harmonic magnetron-injection gun for 260 GHz band gyrotron with 0.5 mm beam axis displacement was made. It was shown that displacement of axis beam has a significant effect upon the angular distribution of pitch-factor.

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A secondary ion yield change from photoconducting semiconductors under influence of illumination has been established (secondary-ion photoeffect). The classification of this phenomenon is given: the normal and the anomalous secondary ion photoeffects are defined. The normal photoeffect is found in reducing of cadmium positive secondary ion yield from CdS-PbS sample under illumination as a result of electron work function decrease. The anomalous effect consists in increase of lead positive secondary ion yield from the same sample under illumination (up to 1200% about in dark).

An analytical Markov nonstationary model of electron emission is suggested. The model is determined by having limited life time of cathode. Some relations between probabilistic characteristics of emissivity and reliability of an emitter are obtained.

Methods of fullerene-coated tip field emitter creation were worked out and investigated. Basic rules and mechanisms of the microstructure origin on the fullerene surface during coverage formation and treatment (thermal and field) were determined. The emitters with fullerene coatings were made that secure stable currents from the single submicron tip up to 150 mA at static regime and up to 1.5–2 mA at pulsed one. Activation of the fullerene-coated field emitter by potassium atom and ion flows was studied.

The 3-mm band relativistic gyrotron excited by 250 keV electron beam with record output parameters (power 5–10 MW, efficiency 35–40%, microwave pulse duration 0.5–1 μs) was developed. The main design solutions of components, such as the electron-optical system forming helical electron beam, the interaction space and the electrodynamic system of microwave output, are presented.

The article presents the latest published in the literature data on the development and research of promising field emitters made from carbon nanotubes, graphene and semiconductors. The possibilities of obtaining high densities and currents of field emission, as well as opportunities to ensure long-term operation of emitters in high-voltage electron devices are analyzed.

Some results of the X-band magnetron research are presented. Its active conductivity and the reactive one are measured in dependence both on anode voltage and RF voltage of the oscillatory systems. Approximating formulas are built for these dependences. This is necessary for transient processes calculation in microwave systems of X-band electron accelerators. The comparison is carried out with the known relations for the S-band magnetron.

The results of first experiments and future trends in advancing to sub-THz and THz frequency ranges with self-oscillators working at high cyclotron harmonics and gyromultipliers are discussed. In both varieties of gyrotrons, selective excitation of high harmonics can be simplified by the use of electron beams describing helical trajectories whose centers are close to the cavity axis (the configuration of Large Orbit Gyrotron).