The design of a compact <inline-formula> <tex-math notation="LaTeX">{E} </tex-math></inline-formula>-band (71-76 GHz) sheet beam (SB) folded waveguide (FWG) traveling wave tube (TWT) for high data ...rate communications is presented in this article. The round beam tunnel for a pencil FWG slow wave structure (SWS) has been redesigned with a rectangular beam tunnel to be suitable for the SB with increased beam current. A novel periodic permanent magnet (PPM)-periodic quadrupolar magnet (PQM) focusing system has been developed to reduce the beam ripple and improve the transmission ratio. A multistep side-out coupler is designed to import and extract the RF power from the SWSs and be compatible with the planar periodic magnetic focusing system. Particle-in-cell (PIC) simulations are employed to evaluate the performance of the high-frequency circuit. Driven by a 1 W signal, the 30-period circuit is estimated to produce more than 100 W power and achieve a 21 dB gain with a less than 0.4 dB variation over 71-76 GHz. Moreover, phase and linearity analysis show a less than 6° in-band phase distortion and <inline-formula> <tex-math notation="LaTeX">\sim </tex-math></inline-formula>30 dB third-order intermodulation distortion (C/3IM) at 30 W of output power, meeting the requirements of a communications-focused TWT. Over 5% circuit efficiency and 40% overall efficiency when equipped with a single-stage collector can be achieved by the compact TWT over the target band.
In this article, a novel coaxial double staggered grating (CDSG) slow wave structure (SWS) evolving from the double staggered grating (DSG) SWS is proposed to develop a high-power, miniaturized ...vacuum power source for plasma diagnostics systems over the terahertz (THz) band. Conformal to the hollow electron beam, the ring-shaped beam tunnel of this novel SWS can mitigate the kinking and filamentation instability, thereby facilitating the high-density beam transport and use of a uniform magnetic field. Ridges have been added to the CDSG imposing the operation mode polarization direction and suppressing lower order competing modes. Compared with the DSG high-frequency circuit, the ridge-loaded CDSG one can support a higher beam current without causing a beam-wall interception, thereby improving the output power of the devices. A compact coupler has been designed to transfer the high-order operation mode into the TE10 waveguide mode and export the RF power. The particle-in-cell (PIC) simulation results of the demonstration novel ridge-loaded CDSG backward wave oscillator (BWO) predict a stable operation and 120-W peak power near 0.2 THz.
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfvén eigenmode structures obtained by ...numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.
PDF
