In this work it is shown that the refractive index and temperature distribution of atmospheric Dielectric Barrier Discharge (DBD) plasmas are measured by Moiré deflectometry. Fringe analysis is used to calculate Moiré deflection and to evaluate refractive index in different points of plasma. By Sa-Ha equation and considering the first ionization, the dependence of refractive index and temperature, electrons, ions and molecules number densities of DBD plasma is obtained. By knowing this relation between plasma parameters, the spatial distributions of the plasma refractive index and temperature are evaluated. The advantages of this method are: simplicity, non-contact, non-destructive measurement, low cost, high accuracy and direct measurement of refractive index gradient.
The experimental investigation of thermodynamic properties such heat and mass transfer of plasmas has many
applications in different industries. Laboratory atmospheric arc plasma is studied in this work. The refractive index of
the air around the plasma is changed because of convection phenomena. When the convection creates the air flowing
around the plasma, the density and consequently, the refractive index of air are distributed symmetrically.
Moiré deflectometry is a technique of wave front analysis which in both Talbot effect and moiré technique is applied
for measuring phase objects. Deflection of light beam passing through the inhomogeneous medium is utilized to obtain
the refractive index distribution. In experimental set-up, an expanded collimated He-Ne laser propagate through the arc
plasma and the around air. The temperature distribution is obtained by use of thermo-optic coefficient of air. To
calculate the thermo- optic coefficient and the refractive index of air for a given wavelength of light and given
atmospheric conditions (air temperature, pressure, and humidity), the Edlén equation is used. The convective heat
transfer coefficient is obtained by calculating the temperature gradient on the plasma border. This method is not
expensive, complicated and sensitive to environmental vibrations.
For two different pulse shapes, Gaussian and piecewise, the electron acceleration by a circularly polarized laser pulse is considered. First, with a piecewise shape similar to Gaussian, it is shown that the acceleration results for different pulse shapes coincide well, especially for strong self-generated magnetic field in the acceleration direction. Then the effect of extending the rising part or falling part of piecewise pulse shape on electron acceleration is examined. For falling part, no new result is obtained but spreading the rising part reduces the electron energy gain.
An experiment for increasing the relaation rate of the lower laser level in a CuBr-He laser has been carried out by applying a variable axial external magnetic field. A homemade CuBr-He was employed. The effect of an axial external magnetic field on the output power of the laser under different charging voltages and buffer gas pressures has been studied. The results show that the laser output power increases about 400 percent at 0.19 Tesla, 7 Torr of He gas pressure, 10 Kv charging voltage, and 14 KHz repetition rate frequency.