Investigation of a Miniaturized E-Band Cosine-Vane Folded Waveguide Traveling-Wave Tube for Wireless Communication

To realize the miniaturization of E-band traveling-wave tubes (TWTs), the size analysis and optimization design were carried out based on an improved cosine-vane folded waveguide (CV-FWG) slow-wave structure (SWS) that operates in a low voltage. In addition, a novel miniaturized T-shaped coupler was proposed to achieve a good voltage standing wave rate (VSWR) in a broad bandwidth. The coupler length was reduced by as much as 77% relative to an original design. With higher coupling impedance, the radius and length of the shortened SWS were optimized as 1.3 mm and 50 mm, respectively. Using microwave tube simulator suit (MTSS) and CST particle studio (PS), 3D beam–wave simulations at 9400 V, 20 mA predicted a gain of 20 dB and a saturated output power of 9 W. The simulation results for CV-FWG TWTs were compared with conventional FWG TWTs from 81 GHz to 86 GHz, showing significant performance advantages with excellent flatness for high-rate wireless communication in the future. The CV-FWG SWS circuit will be fabricated by 3D printing, and this work is underway.

Design and Experiments of the Sheet Electron Beam Transport with Periodic Cusped Magnetic Focusing for Terahertz Traveling-Wave Tubes

The successful transport of a sheet electron beam under the periodic cusped magnet (PCM) focusing at the terahertz frequencies is reported. The sheet beam with a current density of 285 A/cm2 is intended for the developing G-band sheet-beam traveling-wave tube (TWT) whose operating voltage is nominally 24.5 kV. A beamstick was developed to validate the design of the electron optics system, which is considered as the most challenging part for developing a sheet-beam device. A beam transmission ratio of 81% is achieved over a distance of 37.5 mm at a cathode voltage of −25.0 kV. The total current and the collector current were measured to be 125 and 102 mA, respectively. The experimental results are promising, demonstrating that the PCM scheme is capable of focusing a high-current-density sheet beam and hence can find use in the terahertz TWTs, offering the advantages of compact size and light weight.

Gyrotron: The most Suitable Millimeter-Wave Source for Heating of Plasma in Tokamak

In this chapter, brief outline is presented about gyro-devices. Gyro-devices comprise of a family of microwave devices and gyrotron is one among those. Various gyro devices, namely, gyrotron, gyro-klystron and gyro traveling-wave tubes (gyro-TWT) are discussed. Gyrotron is the only microwave source which can generate megawatt range of power at millimeter-wave and sub-millimeter-wave frequency. Gyrotron is the most suitable millimeter wave source for the heating of plasma in the Tokamak for the controlled thermoneuclear fusion reactors. This device is used both for the electron cyclotron resonance heating (ECRH) as well as for the electron cyclotron current drive (ECCD). In this chapter, the basic theory of gyrotron operation are presented with the explanation of various sub-systems of gyrotron. The applications of gyrotrons are also discussed. Also, the present state-of-the-art worldwide scenario of gyrotrons suitable for plasma heating applications are presented in details.

Traveling-wave tubes on looping waveguides with a potential jump

Using computer simulation, a study of the effect of a potential jump on the interaction processes in O-type traveling-wave tubes has been carried out. In these devices, the interaction of the electron beam with a slowed down electromagnetic wave is carried out. To slow down the electromagnetic wave, various electrodynamics systems are used: spiral, on chains of coupled resonators, etc. In this work, we have chosen a slowing down system in the form of a chain of looping rectangular waveguides. Its advantage is that it has a wide bandwidth and each link in such a chain is coordinated with the adjacent ones. To assess the effect of a potential jump on the interaction processes in O-type traveling-wave tubes, a mathematical model has been developed, which takes into account most fully all the factors influencing the interaction processes. These include: relativistic effects during the motion and interaction of electrons, sagging of fields in the gaps of the waveguide, losses in the walls of the waveguide, taking into account the space charge fields (taking into account the periodization of the fields). Based on the developed model, a program was compiled and calculations of various variants of TWT were carried out for accelerating voltages of 20–500 kV, electron beam currents of 0.3...160 A. When performing calculations, the gap with a potential jump was located in different places of the TWT slow-wave structure and its location was chosen where the maximum effect on the electron bunching processes is manifested. As the calculations have shown, the potential jump makes it possible to increase the output power of the TWT by 15–20 %. It can be noted for comparison that the use of a potential jump in multi-cavity klystrons [1] also leads to an increase in the output power by 15-25 %. This confirms the reliability of the mathematical models used in TWT and klystrons.