Summary form only given, as follows. In this work, we study the space charge effects on thermionic emission via a self-consistent approach. The thermionic emission process is described by the Richardson-Dushman equation, corrected for the Schottky effect.
Summary form only given, as follows. The objective of this work is to develop a 2d3/spl nu/ computer program to simulate the electron cyclotron resonance (ECR) plasma source. This computer code incorporates a static magnetic field solver for the magnetic field produced by permanent magnets, particle-in-cell (PIC) plasma simulations, and Monte Carlo collisions. The collisional model includes not only collisions of plasma electrons with neutrals, but also electron-electron collisions. The simulation parameters of the ECR plasma source are: a plasma chamber with radius 7.7 cm and height 8.57 cm, 2.45-GHz axisymmetric TM or TE waves of different power levels, and helium or argon gas of a range of pressures. When the electron-neutral collision frequency is less than the wave frequency, simulation results show that the electron cyclotron resonance discharges will be set up. Simulations verify that the wave absorption occurs within the resonance layer and plasma is dominantly produced around the ECR zone. The dependence of some plasma parameters (e.g., average electron and ion energy, plasma density) on pressure, microwave power, mode structure, and magnetic field configuration for helium and argon discharges will be presented.
Manipulation of Smith-Purcell radiation (SPR) by electron-bunch excitation of localized surface plasmon (LSP) of gold (Au) disc arrays on Au substrate is investigated by FDTD simulation. When the wavelength of LSP mode is within the SPR emission band, SPR is locked and enhanced at the LSP wavelength. The emission angle of LSP-locked SPR still follows the wavelength-angle relation of traditional SPR. Furthermore, both the emission wavelength and angle increase as the radius and height of Au disc increase.
It has been previously shown that higher-power microwaves can be generated from vircators with an abrupt discontinuity in circular waveguides. In this paper the authors investigate the effects of the distance of the waveguide step from the anode on the microwave output and the dominant microwave frequency via the two-dimensional, relativistic, electromagnetic, particle-in-cell code. The parameters of the vircator in this simulation study are: a negative constant voltage of 270 kV applied to the cathode, a constant injection current of 7.3 kA at the cathode surface, 0.46 cm for the cathode to anode distance, 1.3 cm cathode radius, 12.5 cm for the drift tube length, and the radii of the front and the rear section of the drift tube are 4 and 5 cm, respectively. Simulation results show that the dominant microwave frequencies are concentrated in two bands centered roughly at 8.24 and 11 GHz. As the distance of the waveguide step from the anode increases from 0 to 7 cm, the dominant microwave frequency hops between lower- and higher-frequency bands. Among each band, the frequency gradually decreases with increasing distance of the waveguide step. They have demonstrated qualitatively, through time-domain analysis of open cavities containing no sources, the dependencemore » of the dominant microwave frequency on the distance of the waveguide step. The output powers observed in the simulation are greatly enhanced at the waveguide steps of, roughly, 0.8, 1.7, 3.7--4.3, and 7.0 cm from the anode with respective dominant-mode excitation of TM{sub 01}, TM{sub 02}, TM{sub 03}, and TM{sub 04}.« less
In this article, the field-emission properties of the one-dimensional nanostructure grown on doped silicon substrate have been studied via computer simulation. The classical transport equation is used to describe the carrier transport in the material and solved together with Poisson’s equation. The field emission at the emitter-vacuum interface is modeled by the Fowler-Nordheim equation. Our simulation results agree with the experimental results qualitatively. For narrow-band-gap material, the p-type Si substrate will limit the field-emission current in the high applied voltage region. This result can be ascribed to the formation of reverse-biased p-n junction. For wide-band-gap material, however, the p-type Si substrate will enhance the field-emission current, which is attributable to the lower carrier injection barrier height and the stronger driving force offered by the p-type substrate.
The operation characteristics of a newly proposed reflective-type carbon nanotube field emission display (CNT-FED) were studied experimentally and via computer simulation. Both the CNT emitter and the phosphor electrode are manufactured on the same lower plate. One advantage of the reflective CNT-FED is that the distance between the upper indium tin oxide (ITO) electrode and the lower plate is not a critical issue and can be as large as 1 mm, which overcomes the vacuum sealing problem during its manufacture. It is found from the experimental measurements and also the computer simulations that the display resolution varies with the negative upper ITO electrode bias. The magnitude of the upper ITO electrode bias needs to be larger than that for the CNT emitter in order to repel the emitted electrons back to the lower plate and strike only the nearest neighboring phosphor electrode in order to achieve a good display resolution. Under suitable operation conditions, the reflective CNT-FED can achieve good display resolution as well as brightness.
We propose an innovative active imaging device named gain-assisted hybrid-superlens hyperlens and examine its resolving power theoretically. This semi-cylindrical device consists of a core of semi-cylindrical super-lens and a half cylindrical outer shell of hyperlens. Both the superlens and hyperlens parts of the device are appropriately designed multi-layered metal-dielectric structures having indefinite eigenvalues of dielectric tensors. The dielectric layers of the hyperlens are doped with Coumarin, which play the role of gain medium. The gain medium is analyzed thoroughly using a generic four-level system model, and the permittivity of the gain medium is extracted from this analysis for simulating the imaging characteristics of the device. According to our simulation at wavelength of 365 nm, an excellent resolution power much better than the diffraction limit value can be achieved.
Several focusing field emission devices are simulated by the MAGIC particle-in-cell code program. The emission current, anode current, and focusing effect are compared and analyzed. The results show that the coaxial focusing structure has the smallest electron dispersion width, the coplanar focusing structure has good focusing effect and simplest fabrication process, and the ridge focusing structure has the largest anode current. The overall consideration reveals that the coplanar focusing structure is the better choice for display application.
The magnetically controlled planar hyperlens which consists of an InSb-PMMA multilayered structure is proposed and analyzed. The ability of the proposed hyperlens to resolve subwavelength structures at THz region is demonstrated by electromagnetic numerical simulation. The asymmetric field pattern in the hyperlens is caused by the surface magnetoplasmon (SMP) propagating in the InSb-PMMA waveguide. By using transfer matrix method and the effective medium approach of the investigated components, the role of SMP played in the super-resolution is elucidated. Furthermore, the super-resolution of the proposed device under various frequencies is accomplished by merely changing the value of external magnetic field. The proposed device would provide a practical route for multi-functional material, real-time super-resolution imaging, photolithography, and THz imaging.
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