Study of an Attenuator Supporting Meander-Line Slow Wave Structure for Ka-Band TWT

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S11 of the ML is below −20 dB and S21 varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively.

Klynotron with using the open resonator and symmetric conical corrugated mirrors – goratron

А further development of the radial klynoorotron idea – klynotron with symmetric conical radial corrugated resonator mirrors, is presented in the article. Strong coupling volume and surface resonance fields in the double conical mirrors in such a device is formed due to which the synchronous harmonic field is in the entire intermirror space. All saying above makes it possible to use a wide electronic flow. The conical mirror geometry provides a klynotron effect. As a result, not only the permissible device power is increased, but also its efficiency in comparison with a conventional radial klynoorotron. The article presents the calculating results of the Goratron at b0 = 0.51. The solution of the two-dimensional boundary value problem for the potentialV(r, z) = rBj(r, z), which determines Goratron resonator axisymmetric oscillation Em01, was carried out by standard packages for solving general partial differential equations using finite elements. The distribution analysis Er(r, z), Ez(r, z), Bj(r, z) shows that the field periodic component exists in the entire space between the comb mirrors. Given feature allows to use a wide (up to l/4) electron flow. Goratron electron flow modelcontains 16 layers along z, the equations of motion were relativistic. The electronic efficiency averaged over all layers is more than 30 %, which is 1.5 times higher than that obtained in the radial klynotron efficiency calculations.

Multibeam spherotron

The article proposes two types of multibeam spherotron-diotron based on a two-spherical resonator (an early article suggested a spherotron-diotron with non-synchronous interaction on a bi-spherical resonator, where the electron beam in this generator passes along the resonator z axis from the outer sphere to the inner one and interacts with the longitudinal (axial) electric resonator field). The first spherotron type has electron beams going from outer to inner sphere with slope ϧ about the z-axis: ϧ=0, π/8, π/4. The electrons interact with the resonator field through the emergence of quadratic forces in the field increasing along the electron motion. The second type (inverted spherotron) has electron beams located in half arc of the equatorial resonator plane, and the electrons move from the inner sphere to the outside. The interaction in it is carried out due to the spatial electron phasing. Both spherotron types achieve efficiency of 30 % at ultra-high pulse power and tens of kuloampère of total beam currents. The data presented in the article indicate the prospects of broad application for the inverted spherotron by the following indicators: extreme ease of design; no precision gratings or combs are required with a step significantly shorter than the wavelength; no focusing magnetic systems are required; electronic efficiency from 26 to 45 % is ensured. Note that the spherotron is fundamentally a highpower device (10-100 MW in a 1-10ns pulse) for in order to maintain the efficiency of non-synchronous interaction, one needs a high strength of the electromagnetic field, which is achieved only with a high-power device.

Highly efficient X-band relativistic twistron

The paper proposes a new scheme of high-power microwave oscillator of twistron type using a moderately relativistic high-current electron beam. In numerical experiment using axisymmetric version of the completely electromagnetic PiC code KARAT, a 56% conversion efficiency of electron beam power to electromagnetic radiation was demonstrated. With 340 kV accelerating voltage, 3.3 kA electron beam current, and 2.2 T guiding magnetic field strength, the simulated microwave power was 630 MW at 9.7 GHz. The “electronic efficiency” of the source reaches 66%.