In recent years, vacuum electronics technology has exhibited a trend toward moving to millimeter and submillimeter wavelength range. Use of traditional approaches to designing and constructing these elec tronic devices encounters considerable difficulties related, in particular, to small geometric dimensions of the main elements that generate and stabilize electro magnetic oscillations. Solution of this problem leads to the use of superdimensional (relative to wavelength) electrodynamic structures operating in multimodal regimes. The generation of electromagnetic oscilla tions with stable frequency is closely related to the excitation and selection of high order modes in these structures.The possibility of exciting weakly decaying oscilla tions in dielectric resonators with cylindrical and spherical surfaces using high order whispering gallery modes (WGMs) [1-5] accounts for their wide use in vacuum electronic devices for millimeter and submil limeter wavelength range, where the aforementioned technological problems can be solved. However, the output power level in radiation sources of traditional design sharply drops upon passage to submillimeter wavelengths [6]. Therefore, there arises a need for high energy oscillators excited by electron beams. It should be noted that the use of superdimensional elec trodynamic structures with electromagnetic oscilla tions excited by high current relativistic electron beams also eliminates the problem of electric break down.The present study was aimed at assessing the possi bility of creating electromagnetic radiation sources operating in the millimeter wavelength range, which would pose no limitations on passage to the terahertz frequency range. The approach to construction of the proposed source is based on the use of electrodynamic properties of a quasi optical cylindrical dielectric res onator (CDR) [2,7], which serves as the main element in the resonant auto oscillatory system.We have employed a fluoroplastic (Teflon) CDR with a radius of ρ 0 = 3.9 cm and length of L = 0.9 cm. Table 1 gives the values of eigenfrequencies /2π (p ≡ msl) and Q E for the E type modes with indices m = 36 (azimuthal), s =1 (radial), and l = 0, 1, 2 (axial). Cal culations were performed using formulas from [2,7]. The choice of CDR dimensions and working modes was determined by the desired frequency range of the auto oscillatory system described below and the mode type was determined by the method of resonator exci tation. Figure 1 shows the structures of fields of the E type eigenmodes of the CDR employed. As can be seen, the fields of weakly decaying WGMs are concentrated ω p ' Abstract-A new method of microwave generation in a system with high Q quasi optical cylindrical dielec tric resonator (CDR) excited by an azimuthal periodic electron beam current is proposed. Characteristic parameters of a cylindrical fluoroplastic CDR have been determined. Data on microwave generation in a sys tem based on a CDR with whispering gallery eigenmodes excited by a relativistic azimuthal periodic elec tron b...

No abstract

No abstract

No abstract

The aluminum and titanium plates were irradiated by the high-current electron beam with the electron energy around 0.35 MeV, impulse duration of 5 µs, beam current of 2 kA, and with the incident energy density up to 3.5 MJ/m 2. The cross-fractures were made in the modified and non-irradiated areas. The fracture surfaces were examined using a SEM JEOL JSM-840. The irradiation resulted in significant changes of the microstructure parameters (i.e. grain size, damage character). The fractal dimension of the grayscale SEM images of the fracture surfaces were statistically analyzed using the arithmetic, geometric and divisor step methods with the sliding square window of varying size. The calculated distributions of fractal dimensions helped to characterize the scaling behavior of the microstructures, which accompany a shift of the fracture mechanism into preferably brittle mode.