JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2007 | Volume:1 | Issue:2|Papers Count:11

The neural network post-shot reconstruction analysis, as implemented on the START spherical tokamak at Culham, is described. This used a combination of magnetic and soft X-ray diagnostic inputs to evaluate selected plasma parameters as a function of time throughout the shot. An in-built “novelty detector “was used to detect inadequate database coverage associated with plasma configurations not represented in the database. The method is illustrated by results from the high beta campaign on START.

The following modified preprint of a chapter in the forthcoming book by Guillermo VelardePioneers on Inertial Confinement Fusion Energywith personal comments, is presented here as an example about the long years difficult developments towards the aim for producing unlimited, safe and clean nuclear energy in the same way as it is the energy source of the sun. There are arguments that the most recent developments with the plasma block ignition using petawatt-picosecond laser pulses may leas to a fusion power station with a highly simplified operation such that the cost of electricity may be three or more times lower than any energy source on earth, opening the golden age with dramatic consequences for human life and environment. Applied sciences in all fields, economics and politics may be stimulated just by considering these consequences though these new results on inertial fusion energy (IEE) need to be further examined and developed on a broad basis.

We review our results on the investigation of the breakpoint phenomena in the stacks with finite number of intrinsic Josephson junctions in high temperature superconductors. New ideas concerning the breakpoint region structure are discussed as well.

Numerous physical and chemical methods have been developed for the preparation of magnetic nanoparticles.Here we have discussed synthesis of cobalt nanoparticles by using inverse micelle technique at room temperature.Cobalt nanoparticles were prepared by the reverse micelle technique (NaBH4 reduction of cobalt chloride in a reversed micelle solution of didodecylammoniumbromide (DDAB) /Toluene and CTAB/Toluene). The size of cobalt nanoparticles could be easily controlled by changing the water contents and micelle concentrations. Super paramagnetic cobalt nanoparticles (4.3nm) have been obtained by this method where coercivity is 8.34 gauss.

A new mechanism for the acceleration and production of ions in Z-pinch discharges, especially plasma focus is presented. Previously, Yousefi et al. [Phys. Plasma 13, 114506 (2006)] studied the multiple compression and pinch mechanism; they reported that this event can be attributed to the (m=0) type instability, while the subsequent ion and neutron acceleration mechanism was not reported. C ontinuing from previous work, Mizuguchi et al. [Phys.Plasma 14, 032704 (2007)] studied the simulation of high-energy proton production, generated by shock waves in pinch plasma discharge, by use of a 2D relativistic and fully electromagnetic particle-in-cell code. It was found that protons trapped in the electrostatic potential produced near the shock front, can be accelerated to a few Mev by the surfatron acceleration mechanism. On the other hand, the ring-shape of ion bunches, which is in good agreement with the experimental results, were shown. Now we report another acceleration mechanism for subsequent ion production, which differs from the m=0 instabilities caused by the surfatron acceleration mechanism.

Using Boltzman distribution in a quark-gluon plasma sample it is possible to obtain all existing magic numbers and their extensions without applying the spin and spin-orbit couplings. In this model it is assumed that in quarkgluon thermodynamic plasma, quarks have no interactions and they are trying to form nucleons. Considering a lattice for a central quark and the surrounding quarks, using a statistical approach to find the maximum number of microstates, the origin of magic numbers is explained and new magic numbers are obtained.

Ti films of 66.8 nm were deposited, using resistive heat method and post-annealed at different temperatures with flow of oxygen. The nano-structures of the films were obtained using X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed an initial reduction of the grain size at 373 K annealing temperature and increase of the grain size at higher temperatures. The cause of this was due to the reaction of oxygen with Ti atoms which breaks up the Ti grains and hence needle–like features form. The increase of annealing temperature to 473 and 573 K enhances the activation processes, hence diffusion effect and results in larger grains. The resistivity of the film increased with annealing temperature, which is due to competition between increased diffusion rate and the increased reaction rate of oxygen with Ti atoms. The latter increases the resistivity of the thin film while the former decreases its the resistivity.

This research has studied the effect of N2/ (N2+Ar) flow rate ratio (F (N2)) on the microstructure and anticorrosive property of zirconium nitride (ZrN) films deposited on AISI stainless steel (SS) 304 substrates. ZrN films were deposited using ion beam sputtering technique and their corrosion resistance has been investigated via electrochemical test using 0.5 M H2SO4 solution. The thickness of the films decreased with increasing of N2 flow rate. Results of Xray diffraction (XRD) showed that all the films had a preferred crystalline orientation which changed from [220] axis at low F (N2) to [111] axis at high F (N2). The electrochemical test revealed that the corrosion resistance increased with increasing (111) preferred orientation. Furthermore, micrographs obtained by scanning electron microscopy (SEM) indicated that damages on the sample surface due to corrosive agent attacks, may reduce with increasing film thickness.

In this paper, we have studied a typical high voltage gas circuit breaker. The main goal of this study is to survey arc plasma and its behavior by use of generalized Mayr-type equation model that follows high voltage circuit breakers interruption according to a semi-empirical one, named conductance model. Here, we have tried to evaluate some arc parameters affecting interrupting ability by performing a numerical analysis so that our model defines recorded experimental results of an actual test.

In this work, self-consistent calculations were performed for the nitrides Cr4N, FeCr3N and CrFe3N (in the perovskite structure) to investigate the influence on the electronic and magnetic properties of Fe4N due to the substitution of Fe atoms by Cr atoms. These calculations were done also for the ordered FeCr3 and CrFe3 compounds (in the FCC structure) to investigate the effects of inclusion of nitrogen in such alloys. The calculations (with FPLAPW+lo method) were performed at several lattice parameters in order to obtain the equilibrium volumes of these compounds. We also studied the behavior of the magnetism of these materials with pressure. The present calculations show that while FeCr3 is nonmagnetic, CrFe3 exhibits a ferrimagnetic order. On the other hand based on our calculations, FeCr3N and Cr4N are nonmagnetic contrary to CrFe3N that is ferrimagnetic. The analysis of density of states at equilibrium volume for CrFe3N shows that charge transfers to Fe atoms.

Operation of a prism optical fiber sensor for liquid level detection is described. This sensor operates on light intensity modulation, where modulations result from alteration of total internal reflection into partial reflection at the interface. The modulated intensity has been measured by using a source light, a pair of plastic optical fibers (one transmitting and the second one acting as receiving fiber) and a glass prism providing the total and partial reflections. The performance of this sensor is tested with a laser source and the results are reported here. To analyze the operation of such a sensor theoretical formulation for the sensor operation is also given in this study. A comparison is made between the theoretical estimation and the experimental results.