Numerical and Experimental Study of the Trichel Pulses in Needle-plane Geometry

One of the unique aspects of the negative corona discharges in the air is the regular train of pulses that form the discharge current, called Trichel pulses. These pulses are the result of the combination of several phenomena such as the avalanche ionization of the neutral molecules by the impact of the energized electrons, formation of the cloud of positive ions close to the cathode, and formation of the cloud of negative ions at a farther distance from the corona electrode compared to their positive counterparts. In this thesis, the results of a detailed numerical investigation of the formation of Trichel pulses in a needle-plane negative corona discharge, as well as a simulation of the transition of the discharge from Trichel pulse regime to the glow discharge regime, is presented. All presented numerical models in this thesis were three-species models including the motion, generation, and dissipation of three charged species: electrons, positive ions, and negative ions. Also, all models were built using COMSOL multiphysics. Photoionization as the main mechanism for sustaining the positive corona discharge was included in the numerical analysis for both the positive and negative corona discharges using the three exponential approximation. A parametric study of the impact of different model coefficients on the characteristic of the Trichel pulses including the repetition frequency, average DC current and pulse rise time was investigated. The studied parameters include coefficients of the two ionization, and attachment reactions, the mobilities of the three charged species considered, electrons, positive ions, and negative ions, and the coefficient of the secondary electrons emitted from the needle. It was shown that two reactions, the recombination of positive and negative ions, and the recombination of electrons and positive ions play a minor role in the calculated characteristics of the Trichel pulses. Finally, an experimental study of the characteristics of the Trichel pulses in air at room temperature, pressure, and relative humidity has been conducted. The impact of different parameters: the needle voltage, needle-plane distance and the radius of curvature of the needle’s tip on the frequency, DC current, and the temporal characteristics of the pulses (rise time, fall time, and the pulse width) was studied. Four different needles with radii of curvature ranging from 19 to 55 microns were used. Applied voltage on the needle was varied from the onset voltage (-4 kV to -6 kV) to -10 kV. It was observed that the temporal characteristics of the pulses such as rise time, was not a function of needle tip radius of curvature, voltage level, or needle-plane distance. The experimental data were compared with the results of a numerical simulation. The experimental findings were in a good agreement with the results of the numerical model

Investigation on wave energy in Amirabad seaport of Caspian Sea using SWAN model results

In this study, SWAN numerical model used to modeling waves and obtain the significant wave height in range of Amirabad seaport of Caspian Sea. To do this, first, a general model to modeling the wave height in the entire Caspian Sea was built. Then the boundary conditions obtained from the general model, by using the NEST operation of SWAN model, modeling the local with higher magnification in the area Amirabad Seaport was used. The local models built in the Amirabad, was calibration and verification with waves profile data recorded by buoys deployed in that area. Comparison the results with data measured by the Amirabad buoy shows that modeling done in this area had a good accuracy. Then running the SWAN model for three years and Obtained significant wave height in the desired location. Finally the wave energy obtained from significant wave height

Enhanced frequency up-conversion in er3+-doped sodium lead tellurite glass containing silver nanoparticles.

A series of silver nanoparticle embedded in erbium-doped tellurite glasses were synthesized using a one step melt-quenching method. Density and refractive index of glasses were measured. Thermal and optical characterizations were performed and plasmon bands of elliptical nanoparticles were observed. An enhancement of green (525 and 550 nm) and red (632 nm) lines in luminescence spectra of Er3+-doped silver-embedded tellurite glass was recorded and explained by energy transfer mechanism from silver nanoparticles to erbium ion in addition to enhanced local field in vicinity of metallic nanoparticles in the glass. The presence of nanoparticles was confirmed by transmission electron microscopy imaging and reduction of silver ions to silver neutral particles discussed through the redox potential estimation in probable reactions. Silver-erbium co-doped tellurite glass exhibits strong novel optical properties which nominate it as the promising glass for laser, color displays, and photonic applications