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Superposition of Magnetohydrodynamic (MHD) modes in Tokamak leads to complications in finding these modes. In order to obtain plasma modes, energy levels and noise filtering powerful methods such as singular value decomposition (SVD) exist. The SVD method is very effective in separating spatial and temporal dependencies in a set of temporal series which may exist in different spaces. In this paper a new analysis method for finding poloidal modes (m) on Tokamak mirnov oscillations IR-T1 is presented. This approach is based on the frequency filtering and fitting of spatial structure of SVD analysis with the aid of simulation. In the following, momentary analysis of time series main components with the aid of wavelet transform method and also the effect of external electric and magnetic fields on MHD modes are studied.

In this contribution we have reviewed on remote magnetic techniques for determination of plasma displacement based on poloidal flux in large aspect ratio tokamaks. This instrument consists of a two semicircle loops which installed toroidally on inner and outer sides of tokamak chamber and connected with each other. Really, this instrument detects the difference of poloidal flux on the High Field Side (HFS) and Low Field Side (LFS) of tokamak chamber, which we needed in calculating of the Plasma displacement. Main benefit of our proposed instrument is its simplicity. Based on this technique we determined the plasma position, and to compare the result obtained using this technique, an array of four magnetic probes and two flux loops are also designed, constructed and installed on outer surface of the IR-T1 tokamak and plasma position obtained from them. Results are in good agreement with analytical solution of equilibrium problem.

Equilibrium reconstruction consists in identifying, from experimental measurements, a distribution of the plasma current density that satisfies the pressure balance constraint. Numerous methods exist to solve the Grad–Shafranov equation, describing the equilibrium of plasma confined by an axisymmetric magnetic field. In this research, we have reviewed six techniques for determination of the plasma position in IR-T1 tokamak and the effects of superconducting coils and chamber: an optical, flux loops, magnetic probes, multipole moments techniques, and two methods based on the vertical field coil characteristics and analytical solution of Grad–Shafranov equation. In the first method an image processing technique used for the output signal of CCD camera and plasma emission intensity profile and then plasma position obtained. To compare the plasma position obtained using this method, flux loop method, magnetic probe method, multipole moments method, analytical solution of Grad–Shafranov equation, and a sensor-less method based on vertical field coil characteristics are also experimented on the IR-T1 tokamak. Results were compared and discussed.

Magnetic field lines in plasmas can be regarded as trajectories of Hamiltonian systems. For the field line tracing two methods can be applied: i) integration of the trajectory and ii) mapping of the trajectory. The latter is a modern technique for the Hamiltonian system. It is more than an order of magnitude, faster than the integration. A properly chosen mapping procedure always conserves the main flux preserving property of the magnetic field, which is important for a correct reproduction of the long term behavior of field lines in stochastic regions. Simplistic maps form any Hamiltonian problems have been extensively used during the last four decades. This paper is devoted to the study of some mapping models for the study of magnetic configurations in tokamaks which exhibit non-axisymmetric MHD or RMP perturbations. The destruction of a transport barrier is described using the transmissivity between the chaotic zones situated of its both sides.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal).This article has been retracted at the request of the Editors-in-Chief.After a thorough investigation, the Editors have concluded that the acceptance of this article was based upon the positive advice of at least one illegitimate reviewer report. The report was submitted from an email account which was provided to the journal as a suggested reviewer during the submission of the article. Although purportedly a real reviewer account, the Editors have concluded that this was not of an appropriate, independent reviewer.This manipulation of the peer-review process represents a clear violation of the fundamentals of peer review, our publishing policies, and publishing ethics standards. Apologies are offered to the reviewers whose identities were assumed and to the readers of the journal that this deception was not detected during the submission process.

In this contribution we have presented two techniques for determination of plasma equilibrium position in IR-T1 tokamak: Relaxation and optical techniques. An analysis method of tokamak plasma equilibrium by a relaxation method with specified magnetic axis was presented. The degrees of freedom due to designated positions of the magnetic axis are possible by using poloidal field coil currents. Stable steady state tokamak plasma equilibria are calculated along with the Magnetohydrodynamic (MHD) potential energy. The plasma generates a plasma current which partially or fully cancels the magnetic field from the poloidal field coils. For low-temperature plasmas, the plasma current distribution is centrally peaked; for high-temperature plasmas, the plasma current has a hole. A centrally peaked current distribution in a low-temperature plasma is evolved into a current distribution with a hole by increasing the plasma pressure by Ohmic heating, RF heating, or by neutral beam injection heating. In the second technique, an image processing technique is used for the output signal of CCD camera. Then, plasma emission intensity profile and plasma position were obtained. Results were compared and discussed.

The one-atom-thick materials such as graphene, once thought to be impermeable, allow protons to pass through them. The result will be more efficient fuel cells and the simplification of the heretofore difficult process of separating hydrogen gas for use as fuel in fuel cells. In this research, a large scale graphene were synthesized by Low Pressure Chemical Vapor Deposition (LPCVD) technique. The effects of temperature growth on morphological features of the synthesized graphene on Cu foils were studied, using only Scanning Electron Microscopy (SEM) analysis. Raman spectrum was used to quantify defects and characteristics of synthesized graphene. Three peaks at ∼1350, ∼1580 and ∼2750 cm −1 related to the D band, G band and 2D band are shown from Raman analysis. The Mountains Map Premium software and the Gwyddion software were used for investigation on morphological features of synthesized graphene samples. The results show that the defects intensity in graphene decreased and the quality of synthesized graphene increased with increasing growth temperature. The grain size and producing the large area of graphene decreased and increased, respectively with the rise of temperature. At all temperatures growth, the multilayer graphene are grown on Cu substrates. The results of the motifs analysis shows that the synthesized graphene layers are made of oblong grains. On the surface of synthesized samples at 800 and 850 °C were dominant of valleys. Also, on the surface of synthesized samples at 900 and 1000 °C, the peaks were dominant. Thus, the surfaces of all synthesized samples were spiky and isotropic and have an oriented or periodical structure. All results of this work represent that the defects intensity, quality, grain size and uniformity of synthesized graphene could be controlled by only changing the temperature and keeping the other effective parameters constant.

The primary superconducting coils have a fundamental role in plasma magnetic confinement in tokamaks. The magnetic field which produced by primary coil leads to more magnetic field force and better magnetic confinement. In addition, the primary coil acts as a transformer. In this research we have compared the changes of magnetic field and magnetic flux density in distinct status through COMSOL Multiphysics software. The simulations which performed for air core status and three: 90°, 120°, 180° iron core in D cross section and circular cross section tokamaks, indicated that in both kind of tokamaks, the magnetic confinement occurs in a better status with iron core compared with air core, and 90° iron core is the best status for confinement. Also 25 coils designed in different K and δδ which are elongation and triangularity respectively were simulated. The simulation represented that toroidal coils with 1

Analytical solutions of electromagnetism driven Grad-Shafranov equation (GSE) can be used for theoretical studies of plasma equilibrium, transport and Magnetohydrodynamic stability of tokamaks. In this research, an extended analytic solution to the Grad-Shafranov equation was presented. The solution describes standard tokamaks configurations. It allows the simulation magnetic surfaces of plasmas with elongation and triangularity, with an independent choice of pressure and plasma current. We have determined equilibrium magnetic surfaces in IR-T1 tokamak. With applying these solutions to IR-T1 tokamak, a small, air core, low beta and large aspect ratio tokamak with a circular cross section, we have calculated poloidal magnetic flux. Due to the generality and high accuracy of the first exact solution for all of the magnetic configurations of interest, the result of this solution for IR-T1 tokamak is acceptable equilibrium compare to the second one for this tokamak. These analytical solutions can be used as an input of feedback control system.

Nuclear fusion is a nuclear reaction in which two or more atomic nuclei (such as a deuterium–tritium) come very close and then collide at a very high speed and join to form a new high energy nucleus (Helium). Determination of accurate plasma horizontal position during plasma discharge is essential to transport it to a control system based on feedback. The solutions of Grad-Shafranov equation (GSE) analytically can be used for theoretical studies of plasma equilibrium, transport and magneto hydrodynamic stability. Here we have presented specific choices for source functions, kinetic pressure and poloidal plasma current, to be quadratic in poloidal magnetic flux and derive an analytical solution for Grad-Shafranov equation. With applying this solution to NSTX tokamak, we calculated poloidal magnetic flux, toroidal current density and normalized pressure profiles for this tokamak. Toroidal and poloidal flows can considerably change the equilibrium parameters of tokamak. These effects on the equilibrium of tokamak plasmas are numerically investigated using the code FLOW. As a comparative approach to equilibrium problem, the code is used to model equilibrium of NSTX tokamak for case pure toroidal flow. Comparison of the results of these two methods for NSTX tokamak shows good agreement between two and that our analytical solution can be served as good benchmark against the equilibrium code FLOW.

CNTs were produced on a silicon wafer by Plasma Enhanced Chemical Vapor Deposition (PECVD) using acetylene as a carbon source, cobalt as a catalyst and ammonia as a reactive gas. The DC-sputtering system was used to prepare cobalt thin films on Si substrates. A series of experiments was carried out to investigate the effects of reaction temperature and deposition time on the synthesis of the nanotubes. The deposition time was selected as 15 and 25 min for all growth temperatures. Energy Dispersive X-ray (EDX) measurements were used to investigate the elemental composition of the Co nanocatalyst deposited on Si substrates. Atomic Force Microscopy (AFM) was used to characterize the surface topography of the Co nanocatalyst deposited on Si substrates. The as-grown CNTs were characterized under Field Emission Scanning Electron Microscopy (FESEM) to study the morphological properties of CNTs. Also, the grown CNTs have been investigated by High Resolution Transmission Electron Microscopy (HRTEM) and Raman spectroscopy. The results demonstrated that increasing the temperature leads to increasing the diameter of CNTs.

In this paper, thin films of tungsten are coated on 304 type stainless steel substrates using a low energy (1.6 kJ) plasma focus device. 35 focus shots are applied each at 6, 8, 10 and 12 cm axial distances from the top of the anode and at 0° angular position with respect to anode axis to deposit the W films on SS-304 substrates. X-ray diffraction (XRD) patterns show that the degree of crystallinity of W films strongly depends on axial distances from the anode tip. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) results demonstrate that the sample deposited at 8 cm distance has a relatively smooth, uniform and homogeneous surface. Also, energy dispersive X-ray (EDX) analysis reveals the existence of the elemental composition of W in the exposed samples. The corrosion test of samples shows that the highest corrosion resistance belongs to the sample deposited at 8 cm distance. Moreover, in order to observe the effect of corrosion on the surface of samples, we have utilized SEM analysis after the corrosion test.

Zinc oxide (ZnO) thin films were deposited on LiNbO3 (LN) single crystals with 200 nm thicknesses by three different ways, where coating of zinc (Zn) film was followed by thermal oxidation for four, two, and one steps with 50, 100, and 200 nm thicknesses repeatedly. Sample, which was produced at 4-step of deposition and oxidation of Zn layer, showed high transmittance and low structural defect due to a lower photoluminescence intensity and Urbach energy. Average grain size in X-ray diffraction (XRD), scanning electron microscopy (SEM) micrograph, and atomic force microscopy (AFM) images for multilayer of ZnO was lower than monolayer of ZnO thin films. Applying multilayer coating technique leads to decrease of surface roughness and scattering on light on surface and fabrication of LiNbO3 waveguides with lower optical loss.

Low temperature plasma (LTP) is nowadays an intensively investigated superficial treatment of wool. In this work we have investigated the effect of LTP on wool fabric under different conditions. The effect of the position of samples inside the reactor and the kind of gases used as discharge medium has been also investigated. The results show that not only the topography of the surface is modified but also the chemical composition of the surface. It is shown that the hydrophilicity of the samples and also their shrink resistance and anti-felting behavior have improved significantly under LTP treatment. The results show that the shrinkage of 30.1% for untreated samples has reduced to about 1.5% or even less depending on the sample position and the kind of gases used. Many analytical skills such as XRD, FTIR, and SEM were used to characterize the different aspects of the treated fabric. The details of the experiment are discussed in the text.

This research has studied the effect of N 2 /(N 2 + Ar) flow rate ratio (F (N 2 )) 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 H 2 SO 4 solution. The thickness of the films decreased with increase of N 2 flow rate. Results of X-ray diffraction (XRD) showed that all the films had a preferred crystalline orientation which changed from [220] axis at low F (N 2 ) to [111] axis at high F (N 2 ). 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.

Carbon nanotubes (CNTs) were directly grown on Ar ion bombarded AISI 304 stainless steel (SS) by chemical vapor deposition using H 2 , NH 3 and C 2 H 2 as gas precursors at 800 °C. Different ion doses and energies were used prior to pre-treatment with H 2 and NH 3 at 750 °C. The effects of the ion dose and energy on the growth of CNTs were investigated. It was found that the density of the grown CNTs strongly depends on the ion dose and energy, both of which are responsible for modifying the grain structure and increasing the roughness of the SS surface.

We discuss about the controlled self-assembled synthesis of metallic Cu nanoparticles on different substrates such as glass, Al 2 O 3 and SiO 2 at room temperature by the dc magnetron sputtering technique. Deposits have been made using Cu cylindrical target for a 2 m Torr Argon sputtering. After deposition, the films were annealed using oven at 400 °C for 10 min to induce the nucleation and growth of Cu nanoparticles. The average primary grain size of the materials thus synthesized could be controlled by proper choice of process parameters (the pressure of the sputtering gas, applied power, substrate material, annealing time and temperature). AFM and SEM/EDX were both applied to characterize the nanostructures of Cu nanoparticles in this study.

Carbon dioxide ions with 29 keV energy were implanted into (4 0 0) high-purity p-type silicon wafers at nearly room temperature and doses in the range between 1 × 10 16 and 3 × 10 18 ions/cm 2 . X-ray diffraction analysis (XRD) was used to characterize the formation of SiC in implanted Si substrate. The formation of SiC and its crystalline structure obtained from above mentioned technique. Topographical changes induced on silicon surface, grains and evaluation of them at different doses observed by atomic force microscopy (AFM). Infrared reflectance (IR) and Raman scattering measurements were used to reconfirm the formation of SiC in implanted Si substrate. The electrical properties of implanted samples measured by four point probe technique. The results show that implantation of carbon dioxide ions directly leads to formation of 15R-SiC. By increasing the implantation dose a significant changes were also observed on roughness and sheet resistivity properties.

Titanium films of 80 nm thickness were deposited on stainless steel type 304, and they were post-annealed under flow of oxygen at different temperatures. The prepared samples were corrosion tested in 1.0 M H 2 SO 4 solution using potentiodynamic and galvanometric polarization technique. The variation of corrosion resistance of these samples showed that the optimum annealing temperature is 473 K. The reduction of corrosion resistance of the sample with increasing the temperature above 473 K is attributed to the phenomena which are confirmed by AFM results: (a) increase of surface roughness, and (b) formation of larger grains with large grooves between them on the film surface. Hence larger effective surfaces for chemical reactions are provided. The films’ crystallographic and morphological structures were analysed using XRD and AFM, respectively before corrosion test and SEM after corrosion test. It is observed that the crystallographic structure of the film goes through a sudden change at 943 K annealing temperature and three phases of titanium oxide (i.e., rutile, anatase and brookite) are formed.

Al–Cu–N films have been deposited on steel substrate by DC magnetron sputtering. These samples were annealed at 200, 400, 600 and 800 °C under vacuum condition. The effects of annealing temperature on structure, morphology and optical properties of Al–Cu–N films were investigated. By means of X-ray diffraction (XRD) the phase composition was characterized. Atomic Force Microscopy (AFM) was used to evaluate and compare the surface roughness before and after annealing. Also UV–Vis–NIR spectrophotometer was used to investigate the optical properties of the samples. The results show that with increasing in the annealing temperature the intensity of the peaks gradually increased and the full width at half maximum (FWHM) of the peaks gradually decreased and also increasing in the grain size and the amount of the samples roughness during the annealing process are observed. It demonstrates that desirable reflectance and roughness of Al–Cu–N films deposited by DC reactive magnetron sputtering can be obtained by controlling the annealing temperature.

The surface modifications of Mo massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16–30 keV with a fluence of 1 × 10 18 N + cm −2 were implanted in molybdenum samples for 1600 s at different temperatures. XRD patterns clearly showed MoN (0 3 1) (hcp) very close to Mo (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from MoN (0 3 1) line, showed an increase with substrate temperature. AFM images showed the formation of grains on Mo samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in Mo studied by SIMS showed a minimum for N + density as well as a minimum for penetration depth of N + ions in Mo at certain temperatures, which are both consistent with XRD results (i.e., I Mo (2 0 0) / I Mo (2 1 1) ) for Mo (bcc). Hence, showing a correlation between XRD and SIMS results. This phenomenon is explained on the basis of residual gas, substrate temperature, dissociation of water in the chamber and the ion energy.

The chromium thin films were prepared using ion beam deposition on stainless steel 304. The chromium films were implanted by nitrogen ions after deposition at doses in the range of 4.5 × 1017 to 2.7 × 1018 N+/cm2 and energy of 30 keV. The formation of nitride phases and corrosion behavior after nitrogen implantation were characterized by XRD and corrosion test, respectively. The results show that corrosion resistance rise, reach to a maximum at dose of 1.8 × 1018, and then fall down at higher doses. In addition, the effect of corrosion tests was analyzed using scanning electron microscopy (SEM).

Depth and distribution of implanted ions play an important role in electrical and mechanical properties of implanted surfaces. In this study nitrogen implantation at 30 keV with different doses in the range of 1 x 10 17 -1 x 10 18 ions/cm 2 on AISI 304 stainless steel samples has been performed. The experimental and theoretical depth profiles of nitrogen-implanted samples are investigated. Experimental depth profile using secondary ion mass spectrometry (SIMS) is compared with theoretical analysis (TRIM simulation). By considering the presence of N 2 + in the implanting ion beam and sputtering effects, the TRIM and SIMS results were modified to good agreement. The proper ratio of N 2 + /N + is evaluated by a curve fitting procedure.

The production of p–n junctions and polar transistors in silicon to small scale lengths may be possible by plasma and electron beam techniques using the sub-threshold change of n-silicon into p-silicon by electron beam and its reversion at higher electron beam intensities. As a first step, in this study, experimental observation of the effect of electron beam on optical properties of n-type silicon samples is described. Electron bombardment with the energy of 20 keV and different doses in the range of 10 16 to 10 19 electron/cm 2 has been carried out. Use was made of a new design of an electron beam gun as described in details, using a helium obstructed discharge of a concave cold cathode. Optical properties of irradiated samples were determined by a UV–vis–NIR spectrophotometer. The results show an increase in the longer wave length than the fundamental band gap absorption with increasing electron dose. # 2004 Elsevier B.V. All rights reserved. PACS: 61.72.Tt; 78.68.+m