A rectangular open tape helix is analysed for its dispersion characteristics by deriving the dispersion equations that restrict the fields within the tape helix region by incorporating a confinement function. The dispersion equations are derived by applying the accurate boundary conditions to one-quarter of the structure in axial and transverse directions owing to the symmetricity of the rectangular helical waveguide. The dispersion characteristics are numerically computed from an infinite number of simultaneous equations. The computed characteristics is compared with the theoretical model of sheath helix consisting of only the fundamental harmonics. Plotted dispersion characteristics reveals the potential usability of such devices as compact traveling wave tubes by miniaturization and can be printed.
Increasing the interaction current capacity and the interaction impedance is crucial to achieving high output power for traveling wave tubes (TWTs) in ${W}$ -band and terahertz (THz)-band. With the increased distance between the upper and lower metal walls of folded waveguide (FW), the slow wave structure (SWS) named dual-tunnel FW (DTFW) is formed. Benefiting from such a rational design, the electric field in the noninteracting region decreased and naturally formed dual electron beam tunnels. Meanwhile, the operating mode is cutoff at the beam tunnel, the electromagnetic wave in DTFW can be propagated along the path similar to FW and operate in the fundamental mode. Furthermore, compared with FW, due to its larger size, the DTFW has the same structural complexity and less manufacturing difficulty, which is significant for ${W}$ -band and THz-band. In this article, through the analysis of the high-frequency characteristics of the SWS using FW and DTFW, the physical mechanism of bandwidth and interaction impedance improvement of DTFW-SWS are revealed. Moreover, the particle-in-cell (PIC) simulation results reveal that, compared with a TWT using unprecedentedly excellent FW-SWS, the performance of TWT using DTFW-SWS has been significantly further improved in the aspects of saturated power, gain, and electron efficiency. Therefore, DTFW-SWS is a promising SWS for high-power and wide-bandwidth TWT in ${W}$ -band and THz-band.
Magnetically insulated line oscillators (MILOs) are crossed-field devices that generate high-power microwaves at the design frequencies without the use of external magnets. We present experimental data that demonstrates operation of a dual-frequency, Harmonic, Magnetically Insulated Line Oscillator (HMILO). This harmonic operation occurs in L-band (~1 GHz) and S-band (~2 GHz).
The report presents the results of a study of photo-cathodes based on phosphorus-doped nanocrystalline diamond films grown on conductive silicon substrates using the CVD method. The quantum efficiency of such cathodes was studied under the action of laser radiation with a wavelength of 266 nm and pulse duration of 15 ns. It has been found that the quantum efficiency increases with a decrease in the thickness of the diamond film, reaching a maximum at a thickness of 100 nm. In this case, the quantum efficiency was found to be 2.4 $\cdot 10^{-5}$ electrons per photon.
The mutual synchronization of two delay-coupled gyrotrons has attracted a considerable interest in recent years. In this paper, we study the effect of synchronization on the mode competition scenario in a multimode gyrotron. The possibility of controlling the processes of mode competition by increasing the power of the synchronizing signal is discussed. Synchronization of gyrotrons can contribute to the suppression of parasitic modes.
