AbstractThe effect of negative ions on the density, temperature, and potential of plasma in a direct current discharge regime has been studied experimentally. Nitrogen as an electronegative gas was used to produce negative ions in the plasma. Langmuir probe was employed to measure plasma parameters. Discharge was performed in an evacuated glass tube, with circular disk electrodes at different pressures. To obtain the spatial variation of plasma characters, measurements were done at different points on the axis of discharge tube. Argon and nitrogen gases were used as the working gas, and plasma current was kept constant at 5 mA during the experiments. Discharge voltage decreased sharply with increasing pressure for both argon and nitrogen plasmas; however, to sustain the discharge at constant current in nitrogen plasma, higher voltage was required in comparison with argon plasma. The plasma electron density was decreased from cathode to anode during the discharge process, while electron temperature was increased. Results confirm that nitrogen plasma contains negative ions, and discharge process is influenced by them noticeably. تفاصيل المقالة

Abstract Effects of low power direct current nitrogen plasma on linear and nonlinear optical properties of red BS dye-doped poly(methyl methacrylate) (PMMA) film are studied employing different optical techniques. From spectrometry data, it is shown that applying plasma in such a low range of power does not affect the linear absorption coefficient, linear refractive index, and optical bandgap of this dye-doped polymer; however, nonlinear parameters are changed. Experiments are performed using the second harmonic of a continuous Nd-Yag laser beam at a 532-nm wavelength and 20-mW power. The effect of nonlinear refractive index of red BS dye-doped PMMA film in broadening the laser beam is observed. The optical bleaching behavior is investigated by measurement of the intensity of laser beam through the sample. Its third-order nonlinearity is measured using close and open Z-scan data. Nonlinear absorption coefficient and refractive index, as well as real and imaginary parts of the third-order nonlinear optical susceptibility χ3, are changed significantly due to plasma treatment. PACS: 42.65.-k: 42.65.An: 42.70.Jk: 61.41. + e: 71.35.Cc. تفاصيل المقالة

AbstractOptical properties of carbon nanostructures produced by laser ablation method in different liquid environments have been studied experimentally. In this work we used a 7 ns fundamental wavelength of pulsed Nd:YAG laser at 1064 nm and 10 Hz repetition rate to produce carbon nanostructures including graphene in distilled water, acetone, alcohol, and CTAB. Structure and morphology of carbon nanostructures were studied using their UV–Vis-NIR spectrum, TEM images, and Raman scattering spectrum. Results show that in our experimental condition distilled water was the most capable medium for producing graphene. Color of suspensions varied with the amount of carbon nanoparticles in the suspension while the bandgap energy of samples decreases with increasing the amount of graphene. تفاصيل المقالة

AbstractAn analytical model for the interaction of charged particle beams and plasma for a wakefield generation in a parabolic plasma channel is presented. In the suggested model, the plasma density profile has a minimum value on the propagation axis. A Gaussian proton beam is employed to excite the plasma wakefield in the channel. While previous works investigated on the simulation results and on the perturbation techniques in case of laser wakefield accelerations for a parabolic channel, we have carried out an analytical model and solved the accelerating field equation for proton beam in a parabolic plasma channel. The solution is expressed by Whittaker (hypergeometric) functions. Effects of plasma channel radius, proton bunch parameters and plasma parameters on the accelerating processes of proton driven plasma wakefield acceleration are studied. Results show that the higher accelerating fields could be generated in the PWFA scheme with modest reductions in the bunch size. Also, the modest increment in plasma channel radius is needed to obtain maximum accelerating gradient. In addition, the simulations of longitudinal and total radial wakefield in parabolic plasma channel are presented using LCODE. It is observed that the longitudinal wakefield generated by the bunch decreases with the distance behind the bunch while total radial wakefield increases with the distance behind the bunch. تفاصيل المقالة

AbstractEffect of aging on the properties of titanium dioxide nanoparticles produced by laser ablation process in water is investigated experimentally. The fundamental wavelength of a Q-switched Nd:YAG laser was employed to irradiate a high-purity Ti plate in distilled water at temperatures of 20, 35, 50 and 65 °C. Produced nanoparticles were diagnosed by UV–Vis–NIR spectroscopy, X-ray diffraction method, and dynamic light scattering device immediately after production and 1 week after. Bandgap energy of samples was extracted using Tauc method. Size of nanoparticles was increased after a week and their bandgap energy was decreased. Results show that the phase of TiO2 nanoparticles was transited from brookite to rutile after 1 week. تفاصيل المقالة

AbstractIn this study, the effects of gliding arc (G Arc) plasma system on the treatment of water have been investigated experimentally. An AC power supply of 15 kV potential difference at 50 Hz frequency was employed to generate plasma. Plasma density and temperature were measured using spectroscopic method. The water was contaminated with staphylococcus aureus (Gram-positive) and salmonella bacteria (Gram-negative), and Penicillium (mold fungus) individually. pH, hydrogen peroxide, and nitride contents of treated water were measured after plasma treatment. Decontamination of treated water was determined using colony counting method. Results indicate that G Arc plasma is a powerful and green tool to decontaminate water without producing any byproducts. تفاصيل المقالة