JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2008 | Volume:2 | Issue:3|Papers Count:8

A joint experimental work on small tokamak, namely CASTOR of IPP Pragu, Czech Republic (2005), T-10 at PPC, Moscow, Russia (2006), ISTTOK at IST, Lisbon, Portugal (2007) and IR-T1 at PPRC, Tehran, Iran, was organized with the aim to diagonize and characterize the core and the edge plasma turbulence in a tokamak in order to investigate correlations between the occurrence of transport barriers, improved confinement, electric fields and electrostatic turbulence using advanced diagnostics with high spatial and temporal resolution. On CASTOR and ISTTOK, electric fields were generated by biasing an electrode inserted into the edge plasma and an improvement of the global particle confinement induced by the electrode positive biasing has been observed. Geodesic Acoustic Modes were studied using heavy ion beam diagnostics (HIBD) on T-10 and ISTTOK and correlation reflectometry on T-10.ISTTOK is equipped with gallium jet injector and the technical feasibility of gallium jets interacting with plasmas has been investigated in pulsed and AC operation. The effect of internal inductance on plasma position based on toroidal flux loop (diamagnetic loop) and magnetic probe was investigated on IR-T1 tokamak. The first JEs haveclearly demonstrated that small tokamaks are suitable for broad international cooperation to conduct dedicated joint research programmes. Other activities within the IAEA CRP on JRUST are also overviewed.

A standard relaxation theory known as the BPP theory is of common use in magnetic resonance spectroscopy. A typical phenomenon that can be briefly elucidated by the theory is a broadening of peaks in Fourier spectra due to a transverse relaxation of a spin magnetization. There are, however, drawbacks: this theory is a classical phenomenological theory and often claimed to be insufficient to describe small relaxation time. In addition, it cannot describe a motional narrowing without introducing a phenomenological approach. We introduce a simple model in which a system spin ½ is coupled with an environmental system localized around the system. The environmental system probabilistically dissipates into a thermal bath and a thermal environmental system migrates into the place instead. We show analytically that this model can describe a transverse relaxation and a motional narrowing simultaneously. We also show numerical simulations of decoherence in a spin system coupled with on-resonance bosonic modes. Our model will hopefully contribute to easier understanding of motional narrowing for a pedagogical purpose.

The effect of methane flow ratios F (CH4) in a mixture of Ar and N2 gases on the formation of zirconium carbonitride films deposited by single ion beam sputtering on AISI 304 stainless steel substrates have been investigated. To study this effect on the micro-structure of those films, scanning electron microscopy, X-ray diffraction analyses and Rutherford backscattering were performed. Surface hardness was also measured using a Vickers microhardness tester. The results show that an increase of methane flow ratio leads to a shift of ZrN crystalline phase toward ZrC crystalline phase through an intermediate phase ZrN1-xCx with 0£x£1. The increase of F (CH4) changes also the crystallographic texture from (111) to (220). A maximum hardness of 2520 Hv was obtained for x=0.57 which is in accordance with Cohen’s theoretical model.

The collision frequency should be taken into account in high-pressure (temperature) discharges. In this work by using forth order of Rung Kuta method, and two-fluid model, dependence of the Bohm velocity criterion to ion temperature is examined. The characteristics of a collisional DC plasma sheath, such as electric field, electric potential, ion and electron number density, and ion velocity, has been studied too. It will be shown in the constant cathode electric potential, the more the ion temperature, the more the thickness of sheath.

The main goal of this work was to examination the structural and compositional changes in the Polypropylene (PP) fabrics caused by ion irradiation. In this work, the PP fabric was irradiated with CO2 ions. The implantation conditions (i.e, exposure time, beam current, and discharge power) were changed to control the extent of surface modification. Dye ability of the untreated sample and treated sample under different conditions were investigated by using a 3% wt aqueous solution of a basic dyestuff.The obtained data show that, ion beam processing of PP fabrics allows an adjustable modification of their surface properties. The functional groups on the surface of samples were examined using FTIR spectrometer. Moreover, dyeing properties for treated fabrics has been tested. Significant increase in color strength has been achieved. Morphology of samples was examined by Scanning Electron Microscopy (SEM).

We investigate theoretically the optical properties of a 2D photonic band-gap crystal (square lattice of circular dielectric rods in air) through the plane-wave expansion method. We calculate the photonic band structure for both TE and TM polarizations for the 2D photonic structure. Band gaps exist only for TM polarization (E parallel to the rods). Also we study the effect of varying the dielectric constant of the rods and the rods radius-to-pitch ratio r/a on the first gap appeared in the photonic band structure for TM polarization.

Raman scattering was used to probe the electronic properties and hence derive the distribution of diameters of the Single-Walled Carbon Nanotubes (SWCNT) in high pressure carbon monoxide sample. Micro-Gravimetric nitrogen and hydrogen adsorption isotherms were measured at 77K and for gas pressures of up to 1 bar nitrogen and 10 bar hydrogen. In this paper we show that the majority of single-walled carbon nanotubes in Hipco sample which are excited by the two laser energies (2.41, 2 eV), are metallic with surface area of 646 m2/g and hydrogen capacity 1.12 wt%.

Soft X-ray (SXR) emissions in the spectral regime 8-17 A (730-1560 eV) from the neon plasma focus have been investigated. A 4-channel pinhole camera, 2 types of Ross filter for comparison and photoelectric effect x-ray detector (BPX65) were the diagnostics viewing the x-ray output of the pinched plasma region and a Rogowski current derivative coil was used to study the discharge characteristics of this plasma focus device. Aluminum and Mylar were applied to filter the outrange wavelength emissions. By varying the pressure from 2mbar to 9mbar and the voltage from 8 kV to 12 kV, at optimum condition (12 kV, 7 mbar) a total SXR yield of 77.5 J/shot and efficiency 3.88% of total input energy (2 kJ) at source into 4p steradians is observed. Also the linear relation between optimum pressures for highest efficiency in various output energies has been obtained.