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Periodic surface lattice (PSL) structures have been fabricated and measured. When the required conditions are met, volume and surface waves can couple to form a cavity eigenmode at a frequency determined by the PSL's parameters. The formation of such eigenmodes is relevant to the realization of high-power mm-wave and THz coherent sources.
Periodic structures used for high power millimetre and sub-millimetre sources that implement relativistic beam — wave interactions have historically involved the implantation of a dielectric layer around the inner wall of the interaction region or a periodic corrugated structure that serves to reduce the velocity of an internal electromagnetic wave. Moving towards the THz regime, the physical dimensions...
Theoretical and modelling studies of periodic surface lattice (PSL) structures have been complemented by experiments. A cavity eigenmode can be formed, as a result of volume and surface wave coupling under certain conditions. The formation of such eigenmodes is relevant to the realization of high-power mm-wave and THz coherent sources.
Numerical finite difference time domain and Particle-In-Cell simulations have demonstrated an electron wave interaction in a Cherenkov maser utilizing a cylindrical two-dimensional (2D) Periodic Surface Lattice (PSL) as a mode selective cavity [1-8]. Optimization of this structure's physical properties resulted in the design of a cavity with 16 longitudinal periods of 1.6 mm length, 7 azimuthal variations...
Latest development and experimental study of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With an input seed signal from an 1.5 W, 90–96 GHz solid state source a gain of 27 dB was measured from the experiment. The bandwidth of the gyro-TWA was measured to be at least 5 GHz.
Numerical FDTD and PiC simulations demonstrate the successful electron wave interaction in a Cherenkov maser utilizing a cylindrical 2D PSL as a mode selective cavity. Optimization of this structure's physical properties results in the design of a cavity with 16 longitudinal periods of 1.6 mm length, 7 azimuthal variations and an unperturbed inner radius of 4 mm. In numerical simulations this design...
Numerical 3D PIC code simulations show that Slow-Wave-Structures SWSs demonstrate excellent potential as a virtual dielectric in a Cherenkov based Backward Wave Oscillator (BWO). CST Microwave Studio confirms internal mode coupling between a volume TM0,6 and surface HE20,1 modes resulting in the creation of a high-Q cavity, necessary for the Cherenkov mechanism to be exploited. MAGIC 3D demonstrates...
Micro-reentrant square cavities operating at high order modes have been demonstrated to be a viable solution for the realization of millimeter wave klystrons. However, the excitation of the required high order mode is a challenging task. The realization and measurement of a novel coupler for high order mode cavities is proposed.
Using a cavity based on a periodic-surface-lattice (PSL) the concept of a high-power, 200GHz Cherenkov source is developed. If the PSL satisfies certain defined conditions single mode operation is observed.
Results from numerical simulations have demonstrated the principle of a co-harmonic gyrotron, operating with a novel cavity. Such a cavity is capable of generating coherent radiation at both the 2nd and 4th harmonics of the electron cyclotron frequency simultaneously, at frequencies of 37.5 GHz and 75 GHz. Further results are presented here, including refinements to the output section of the cavity,...
A 390 GHz harmonic gyrotron based on a cusp electron gun was designed to operate on a TE71 mode and the 7th cyclotron harmonic of a large orbit electron beam. This beam is produced by a cusp electron gun with a voltage of 40 keV, a current of 1.5 A and an adjustable velocity ratio from 1 to 3. Smooth cylindrical waveguide was studied and built as the interaction cavity. The relationship between the...
A Ka-band cavity based on a two-dimensional periodic lattice is studied. The apparatus designed to excite the cavity is discussed. Coupling between the surface and volume fields is demonstrated and pulse propagation through the cavity is investigated. The measurements agree well with simulations.
A small-scale pseudospark discharge is being investigated as the electron beam source for a klystron operating at a frequency of 94 GHz and single-gap discharge experiments have been carried out. The klystron has been designed using the particle-in-cell (PiC) code MAGIC-2D and simulated output looks promising.
Summary form only given. Masers capable of producing high-power output radiation in the spectral range from 100's of GHz to low-THz, to address a range of user needs will be presented. Future applications include remote sensing and biological/medical imaging (to reduce the exposure time during large area mapping). Compact masers that are capable of producing the required output power at these frequencies...
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