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Planar periodic surface lattice (PSL) structures based on thin, subwavelength substrates have been studied experimentally and numerically. Coupled eigenmode resonances composed of partial volume and surface modes are observed for PSLs with lattice periodicities of 1.50 mm and 1.62 mm etched onto thin copper-backed, substrates. We show that the copper backing is essential for mode-selection in a multi-moded...
Experimental results from the operation of an electron beam driven, mm-wave, vacuum electronic source are reported. The aim of this work is to create improved electron-beam-driven, vacuum electronic mm-wave and sub-THz sources by exploiting dispersion-engineering. Dispersion-engineered structures can be manufactured by several techniques and in this work additive manufacturing has proven to be quick,...
To rapidly prototype novel mm-wave and THz sources there is a requirement to create intricate structures to produce and radiate electromagnetic fields. The motivation for this work is to create improved electron-beam-driven, vacuum electronic mm-wave and sub-THz sources by exploiting dispersion engineering. Although such structures can be manufactured by other techniques, additive manufacturing has...
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.
The pseudospark discharge is a form of low-pressure gas discharge capable of generating extremely high currents with short rise times by means of a unique hollow cathode structure [1-6]. A high-quality electron beam is generated during the later phases of the discharge process, which possesses high current density and brightness, as well as the ability to self-focus via ion channel focusing. This...
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...
Structures based on a periodic surface lattice (PSL) of planar geometry have been studied. It is shown that volume and surface fields can couple to form a cavity eigenmode, demonstrating the potential for novel mm-wave sources when combined in appropriate configurations with an electron beam.
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...
Studies are presented of a series of computer simulations, using CST (Microwave Studio), of novel waveguide components for a mm-wave gyro-TWA. Each component has a range of operation that can be optimised through observations of the S-parameters and the phase data, while altering geometric parameters in the simulations. This approach allows optimum performance of mm-wave gyro-TWAs.
Cyclotron coupling between electrons and waves is thought to occur in both polar and equatorial regions of the Earth's magnetosphere. The cyclotron emissions from an electron beam moving into a waveguide with an increasing magnetic field have been investigated in an experiment1, scaled to microwave frequencies, supported by numerical simulation2,3 and theoretical analysis, to reproduce aspects of...
Results are presented of recent numerical simulations of a high frequency, gyrotron oscillator based on the principle of frequency multiplication, where the high frequency waves are excited as a consequence of a strong non-linear interaction at a lower harmonic. The model strongly supports 1D non-linear predictions of the system's performance.
A two-dimensional (2D) periodic surface lattice (PSL) can be obtained by creating shallow periodic perturbations on a metal surface. When the individual lattice elements are synchronised by coupled volume and surface fields eigenmodes can be formed. Cavities based on a PSL of cylindrical topology have been studied and an analytical description of the dispersive properties of the cavity is presented...
Studies are presented of a series of computer simulations, using CST (Microwave Studio), of waveguide components for a Ka-band gyro-TWA. Each component has a range of operation that can be optimised through observations of the S-parameters and the phase data, while altering geometric parameters in the simulations. This approach allows optimum performance of mm-wave gyro-TWAs.
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...
Cavities based on a periodic-surface-lattice (PSL) of cylindrical topology have been studied. The lattice perturbations have an amplitude much smaller than the operating wavelength of the structure, allowing the PSL to be described as an effective metadielectric or high impedance surface. Dispersive plots describing the electromagnetic (EM) properties of the PSL are presented and the potential for...
The pseudospark discharge is a form of low-pressure gas discharge, capable of generating extremely high currents within short rise times by means of a unique hollow cathode structure [1–2]. A high-quality electron beam is generated during the later phases of the discharge process, which possesses high current density and brightness as well as the ability to self-focus via ion channel focusing. This...
A multitude of astrophysical plasma environments exist where a combination of particle acceleration, convergent magnetic fields and a sufficiently large ratio of electron cyclotron frequency to plasma frequency are present to support electron cyclotron-maser emission [1]. The resultant radiation signatures typically comprise of well-defined spectral components (around the relativistic electron cyclotron...
A multitude of astrophysical plasma environments exist where a combination of particle acceleration, convergent magnetic fields and a sufficiently large ratio of electron cyclotron frequency to plasma frequency are present to support electron cyclotron-maser emission [1–6]. The resultant radiation signatures typically comprise of well-defined spectral components (around the relativistic electron cyclotron...
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