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In the IR-T1 tokamak plasma, study of the MHD activities is presented by using the combination of singular value decomposition (SVD) and Hilbert-Huang transform (HHT). In this work, we have proposed the SVD+HHT method to study the MHD activity for mode number identification and time-frequency behavior. Also, we have used spatio-temporal structures of the Mirnov coil fluctuations in terms of correlation function to better identification of mode number and frequencies of dominant MHD modes. High correlation values of spatio-temporal wave-like structures in lifetime below 0.1 ms in the different poloidal separation were observed. It was shown that the main frequency rotation of the MHD activities is above 10 kHz. Spatio-temporal wave-like structures, with maximum value in poloidal separation 120 or 180 degrees, show that the wavelength of the MHD mode is related to m = 2 and m = 3. Also, there are small-scale structures, mostly contributed by high-frequency short wavelength fluctuating component in the bottom of the poloidal separation 90 degrees related to m = 4 or m = 5 mode numbers. These results have been compared with the SVD + HHT analysis results. In addition, amplitude modulation of Mirnov oscillations in IR-T1 tokamak plasma generates intra-wave frequency modulation. These amplitude variations of MHD oscillations cause a frequency fluctuation. Our results have indicated that in the Hilbert spectrum (HT) analysis, the intra-wave frequency modulation is small compared to the short-time Fourier transform (STFT) and wavelet transform (WT) spectrum.

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 experiment, the effect of magnetohydrodynamic (MHD) fluctuations in the hard X-ray radiation from the IR-T1 tokamak plasma is investigated. To reach this goal, the main parameters of plasma such as plasma current and loop voltage are measured. Also, the rake and poloidal Langmuir probes are used to calculate the radial and poloidal electric fields. To detect the hard X-ray radiation, a NaI-scintillator detector is used. To study on the MHD fluctuations, an array of 12 Mirnov coils is used. The obtained data are analyzed by using the singular value decomposition (SVD) algorithm. The wavelet spectrum of the dominant principal components of Mirnov coils is drawn. The results of wavelet and SVD analysis show that the hard X-ray radiation is increased with increasing the fluctuations of the dominant principal components (at the same time). It is also shown that the rate of hard X-ray radiation emitted from the tokamak plasma increased with increasing the MHD fluctuations. The energy of the system is wasted and reduced by these radiations. This an increase in the particle pressure of the plasma.

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.

Carbon nanotubes (CNTs) modified with semiconductor nanocrystalline particles may find wide applications due to their unique properties. Here Cadmium Sulfide (CdS) nanoparticles were successfully grown on Multi-Walled Carbon Nanotubes (MWNTs) via a magnetron sputtering method for the first time. The CdS/MWNTs sample was characterized with X-ray diffraction (XRD), Field Emission Scanning and High Resolution Transmission Electron Microscopies (SEM/TEM) and four point probe. The obtained images show clearly the decoration of the MWNTs by the CdS nanoparticles, and the XRD measurements indicate the CdS structure as hexagonal type. Moreover, the physical properties of the CdS/MWNTs were compared with the physical properties of the CdS nanoparticles grown on the silicon. Electrical measurements of CdS and CdS/MWNTs reveal that CdS/MWNTs has lower resistivity than the CdS sample which may be due to the higher carrier concentrations.

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.

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.Further, the corresponding author was not able to explain the reason for adding the author M. Ghoranneviss to the revised article.

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.

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 research, the IR-T1 Tokamak plasma effect on tungsten oxide (WO3) nano-sheets has been investigated. For this purpose we deposited WO3 on stainless steel 316L (S.S.316L) via hot filament chemical vapor deposition method with hot tungsten filament in temperature 1800 °C. So, S.S.316L and WO3 sample installed on IR-T1 chamber and exposed to 300 shots of hydrogen plasma with a total duration of 11 s. For investigation of hydrogen plasma effects on crystalline structure properties, the X-ray diffraction (XRD), atomic force microscope (AFM), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy analysis was performed. It observed the some small changes in the position and intensity of XRD peaks therefore the plasma can affect the crystalline structure properties of WO3. The comparison of FESEM images of WO3 sample and S.S.316L show that WO3 has the least morphology defect against plasma shots as we can observe a crack with length around 100 μm on S.S.316L surface while WO3 surface was smoothed and didn’t create any defect, significantly. Also, the AFM analysis of WO3 shows the least evolutions of surface roughness.

We have reviewed the synthesis of nanocomposite zinc oxide deposited carbon nanotube with two different methods. Initially the multi-walled carbon nanotubes (MWCNT) were prepared by the plasma enhanced chemical vapour deposition technique. Then By two different methods ZnO layers were coated on the tubes. RF sputtering was one of the ways to directly deposit ZnO thin layer on the MWCNTs. On the other hand, we used the thermally physical vapour deposition for making thin Zn film to oxidize it later. Scanning electron microscopy and also Raman spectroscopy measurements of the prepared samples confirmed the presence of ZnO nanolayers on the CNT bodies. By the field emission microscopy measurements we found that ZnO deposited CNTs have a more efficient emissivity than that of CNTs alone.

The graphene has several unique characteristics and many applications in all fields. Some of these characteristics are the quantum Hall effect at room temperature, the ambipolar field effect, the optical properties, the high electron mobility and the best electronic properties. The ability of fabricating large-area monolayer graphene is hindering its application. In this paper the effects of growth time on the quality of graphene synthesized by low-pressure chemical vapour deposition (LPCVD) has been investigated. Large-area monolayer graphene is synthesized on polycrystalline Cu foil (~1 cm2) by controlled experiment LPCVD at different growth times (30, 60, 120 and 150 s). The synthesized graphene was characterized using Raman spectroscopy and scanning electron microscopy (SEM). The Raman spectrum showed a I G /I 2D ~0.2 ratio which indicates that all samples are single-layer graphene and the SEM images demonstrate that the domain size increases when the growth time increases. The growth mechanism of LPCVD of graphene on Cu and the mechanisms governing the Raman scattering process in the films are also discussed. The control over the grain size of synthesized graphene by adjusting the growth time (achieved in this work), provides useful insights for understanding the growth mechanism of LPCVD of graphene and for optimization of the growth process to further improve the quality of graphene. Finally, with analyses of all investigations we found that the quality and the large-area of monolayer graphene improved by increasing the growth time and it is very important consequence for all those who do research on graphene.

We present a comprehensive study of the parameter for graphene growth by low pressure chemical vapor deposition on Cu foil. The growth of graphene was investigated in various conditions, changing the gas pressures, gas ratio, growth temperature and growth time. The synthesized graphene were characterized using Raman spectroscopy and Field Emission Scanning Electron Microscopy (FESEM). By varying the growth time it can be concluded that the domain size increases when the growth time increases. The absence of 2D band in this section suggest that the produced graphene-like films are not monolayer and graphite can be formed in this growth conditions. The FESEM images demonstrate that increasing growth temperature while holding other parameters constant yields in larger domains which may be due to a faster growth at the higher temperature. The Raman spectra also showed the recovery of the 2D peak by increasing the growth temperature, indicating the crystallization of the damaged graphene layer. Hence the quality of grown graphene-like films is highly correlated to the process temperature. We show that the methane-to-hydrogen ratio is critical parameters that affect the structural perfection of graphene like domains. The Raman studies denote graphene like carbon nature due to the appearance of significant G and 2D peaks. Also the 2D peak intensity increases by increasing the H2 concentration in gas mixture, indicating a low graphene layers. The resulting domain size and the nucleation density are maximum at maximum value of H2 concentration. We can conclude that by controlling the growth parameters, the morphology and structure of graphene can be changed. We suggest that graphene can be used for fusion reactor first wall due to its unique physical and chemical properties. Our results provide important guidance toward the synthesis of high quality and uniform graphene films.

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.

We have studied the electrical resistance of carbon nanotubes (CNTs) grown on sodalime glass using Cu as catalyst at 580°C temperature. The conductivity was measured at room temperature using four point probe technique. The Cu catalyst was coated on glass substrate by using dc magnetron sputtering system and etched by hydrogen (H2) gas in order to form nanometer sized catalytic particles. Mixture of C2H2/H2/Ar (20:80:100 standard centimeter cubic per minutes) gases were heated at 580°C for growth of CNTs on a glass substrate by using Thermal Chemical Vapor Deposition (TCVD). The temperature dependence of sheet resistance and current-voltage characteristics of the film were measured by a four point probes method. The morphology of the catalyst surface was probed by Atomic Force Microscopy (AFM), and the growth behavior of CNTs was investigated by scanning electron microscopy (SEM).

In this paper, electron beam (e-beam) reduction method is applied for the catalyst layer preparation in the growth of carbon nanotubes (CNTs). A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. This new method leads to reducing the diameter of particles via sputtering and evaporating the surface of catalyst. The growth of CNTs was performed on the Fe catalyst layer with SiO2 substrate in an environment of different mixed gases (H2, NH3 and C2H2) by thermal chemical vapor deposition (TCVD) system. The morphology of the electron beam reduced catalyst particles were probed by atomic force microscopy (AFM). All samples were analyzed by scanning electron microscopy (SEM) before and after growth of CNTs. SEM analyses clarified that the catalyst grains have been smaller under effect of electron beam bombardment.

In this contribution, we presented approaches for the determination of tokamak plasma column shift based on multipole moments and magnetic techniques. First, we presented analytical details for using this technique. Then, the principle of different models based on this technique for the design and fabrication of six coils will be presented: four modified Rogowski coils (two cosine coils and two sine coils) and two saddle coils (saddle sine coil and saddle cosine coil). Also, to compare the results, the flux loops technique is used. Because of continuous measurements of magnetic field distribution around the tokamak plasma using multipole coils, this technique gives us more reliable information about the plasma current displacement. Moreover, we deduced the plasma current and plasma boundary centers shift using the two semi-empirical techniques in the IR-T1 tokamak. First, the plasma current center is calculated from the vertical field coil characteristics. The calculation is made focusing on the vertical field coil current and voltage changes due to a horizontal displacement of the plasma column. Also, the plasma boundary center shift was measured from the external magnetic coils. The results from these two techniques are compared and discussed.

In this work the effects of Cold Biased Limiter (CBL) and Emissive Biased Limiter (EBL) have been individually investigated, in both positive and negative polarities, on the width and frequency of magnetic islands. The effects were examined using singular value decomposition and wavelet techniques on mirnov coil signals. The results show that the application of EBL with both positive and negative polarities has been more effective on plasma stability compared with CBL. Comparing different polarities of CBL and EBL revealed that the positive polarity was more effective on the width of magnetic islands than negative polarity. The greatest impact occurs during EBL with positive polarity, in which reduction is observed in both width of magnetic islands and emission of Hα radiation. Besides, intensity and frequency of magnetic islands are reduced from 50 to 25 kHz in around 1 ms after bias application. Meanwhile, the minimal effect on width and frequency of magnetic field occurs in CBL with negative polarity.

Edge plasma turbulence was investigated over a wide range of plasma and field parameters in the IR-T1 tokamak for the first time. Fluctuation levels and spectra were measured using two arrays of Langmuir probe in the region r/a = 0.75–1.2. Under almost all conditions the edge plasma was turbulently unstable, with a broadband fluctuation spectrum in the drift wave range of frequencies f = 10–1000 kHz. A stable state was observed only in the very cold, low-current discharge formed at unusually high neutral filling pressure. Otherwise, the relative fluctuation level as monitored by the ion saturation current was very high, in the range $$ {{\tilde{\rm J}^{ + } } \mathord{\left/ {\vphantom {{\tilde{\rm J}^{ + } } {\bar{\rm J}^{ + } }}} \right. \kern-0pt} {\bar{\rm J}^{ + } }} \cong 0.2{-}0.8 $$ , while the fluctuation power spectra were roughly invariant in shape. The relative fluctuation level was always highest near the wall and decreased monotonically toward the plasma centre.

Tokamak edge plasma was analyzed by applying the multifractal detrend fluctuation analysis (MF-DFA) technique. This method has found wide application in the analysis of correlations and characterization of scaling behavior of the time-series data in physiology, finance, and natural sciences. The time evolution of the ion saturation current (Is), the floating potential fluctuation (Vf), the poloidal electric field (Ep), and the radial particle flux (Γr) has been measured by using a set of Langmuir probes consisting of four tips on the probe head. The generalized Hurst exponents (h(q)), local fluctuation function (Fq(s)), the Rényi exponents (τ(q)) as well as the multifractal spectrum f(αh) have been calculated by applying the MF-DFA method to Is, Vf, and the magnetohydrodynamic (MHD) fluctuation signal. Furthermore, we perform the shuffling and the phase randomization techniques to detect the sources of multifractality. The nonlinearity shape of τ(q) reveals a multifractal behavior of the time-series data. The results show that in the presence of biasing, Is, Vf, Ep, and Γr reduce about 25%, 90%, 70%, and 50%, respectively, compared with the situation with no biasing. Also, they reduce about 15%, 90%, 35%, and 25%, respectively, after resonant helical magnetic field (RHF) application. In the presence of biasing or RHF, the amplitude of the power spectrum of Is, Vf, Γr, and MHD activity reduce remarkably in all the ranges of frequency, while their h(q) increase. The values of h(q) have been restricted between 0.6 and 0.68. These results are evidence of the existence of long-range correlations in the plasma edge turbulence. They also show the self-similar nature of the plasma edge fluctuations. Biasing or RHF reduces the amount of Fq(s). The multifractal spectrum width of Is, Vf, and MHD fluctuation amplitude reduce about 60%, 70%, and 42%, respectively, by applying biasing. In the presence of RHF, their width reduces about 60%, 85%, and 75%, respectively. It means that biasing and RHF reduce the degree of multifractality.

In this paper, the effect of resonant helical magnetic field (RHF) and cold biased local limiter on plasma current, loop voltage, confinement time energy, poloidal beta, line emission intensity Hα, and magnetohydrodynamic (MHD) behavior based on Mirnov oscillations in the IR-T1 tokamak has been investigated. The experiments have been done in different regimes as cold biased local limiter, magnetic perturbation application, and both of these. At first the effect of the positive and negative bias voltage on plasma parameters and magnetic fluctuations detected by Mirnov coils has been investigated. Also, the effects of RHF on plasma parameters have been investigated in the edge region. Then the effects of applied biasing and RHF at the same time are analyzed. The bias voltage has been restricted to (−320 ≤ Vbias ≤ +320) and it has been applied with the limiter biasing that is fixed at r = 11.25 cm. These parameters have been measured using a diamagnetic loop, spectrometer, which is a visible light spectrometer for H-alpha, and Mirnov coils. The time-resolved frequency component analysis has been performed using short-time Fourier transforms. Fourier-based techniques and auto-correlation have been employed to analyze the frequency of MHD fluctuations. The results show that applied radial electric field at the plasma edge could control electromagnetic instabilities in the tokamak. In the positive biased regime, the amplitude of low-frequency Mirnov oscillations (

The high energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactor and reduce its life time. Therefore, finding a method to minimize runaway electron is much needed. Resonant helical field (RHF) is one of the methods for controlling the magnetohydrodynamic (MHD) activity. This paper attempts to examine the effect of RHF on the generation of runaway electrons. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, MHD oscillation, Hα radiation and MHD activity modes, in the presence and absence of RHF (L = 2 and L = 3), were measured. The results show that applying this system can change runaway electrons generation.

Plasma-surface interaction experiments on TiN coated stainless steel 316L (S.S.316L) using a plasma focus (PF) device have been performed in an attempt to investigate whether we can use the hardness property of TiN against erosion to increase the lifetime of the mirrors used in plasma diagnostics equipment. Firstly, two similar S.S.316L samples were chosen for this purpose. One of the samples was coated with TiN by using a PF device, while the other was kept intact as a reference for investigating the effect of TiN coating. Then, in order to study the coating effects, these samples were exposed to 200 shots of hydrogen plasma with a total duration of 7 s in a tokamak. Before and after exposure, samples were analyzed by using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and a spectrophotometer. It was found that the uncoated sample was severely damaged, its reflection dropped significantly, and it developed some cracks and lines, while no significant change was observed on the surface characteristic of the coated sample. Moreover the weight loss of the uncoated sample was higher in comparison to the coated one. Therefore the results of this experiment showed that the coating of S.S.316L by TiN using a PF device is a useful method to strengthen it against plasma erosion and with further optimization it could possibly be used in preparing plasma diagnostics mirrors.

We calculated the internal inductance and the poloidal beta in a circular cross section Tokamak using Solov’ev assumption in the solution of Grad–Shafranov equation (GSE). GSE is solved by considering linear source functions and fixed boundary conditions. This solution has the three quantities (plasma current I p , plasma minor radius r p and $$ \beta_{p} + l_{i} /2 $$ ) that they are as input data. In two different discharges on IR-T1 Tokamak with this solution, we have shown that the internal inductance at a low value is required to extend the duration of Tokamak plasma discharge that it is consistence with other method.

The new candidates for laser fusion energy with minimized radioactivity were presented. The possibility of side-on laser ignition of H–11B with negligible radioactivity encouraged to study the fusion of solid state H–7Li fuel which again turns out to be only about ten times more difficult than the side-on ignition of solid deuterium–tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included. In other words, the specific approach discussed here involves inducing a fusion burn wave without radioactivity by laser-driven impact of a relatively large block of plasma on the outside of a solid density H–11B and H–7Li targets.

The new possibility of side-on laser ignition of p-11B with negligible radioactivity encouraged to study the fusion of solid state p-7Li fuel that again turns out to be only about 10 times more difficult than the side-on ignition of solid deuterium-tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included.

In addition to the matured “laser inertial fusion energy” with spherical compression and thermal ignition of deuterium-tritium (DT), a very new alternative for the fast ignition scheme may have now been opened by using side-on block ignition aiming beyond the DT-fusion with igniting the neutron-free reaction of proton-boron-11 (p-11B). Measurements with laser pulses of terawatt power and ps duration led to the discovery of an anomaly of interaction, if the prepulses are cut off by a factor 108(contrast ratio) to avoid relativistic self focusing in agreement with preceding computations. Applying this to petawatt (PW) pulses for Bobin-Chu conditions of side-on ignition of solid fusion fuel results after several improvements in energy gains of 10,000. This is in contrast to the impossible laser-ignition of p-11B by the usual spherical compression and thermal ignition. The side-on ignition is less than ten times only more difficult than for DT ignition. This is essentially based on the instant and direct conversion the optical laser energy by the nonlinear force into extremely high plasma acceleration. Genuine two-fluid hydrodynamic computations for DT are presented showing details how ps laser pulses generate a fusion flame in solid state density with an increase of the density in the thin flame region. Densities four times higher are produced automatically confirming a Rankine-Hugoniot shock wave process with an increasing thickness of the shock up to the nanosecond range and a shock velocity of 1500 km/s which is characteristic for these reactions.

Synthesis and growth of carbon nanotubes (CNTs) from C2H2 by thermal chemical vapour deposition (TCVD) using a mixture of different gases were investigated. A thin film of nickel was coated as catalyst on silicon substrates by ion beam sputtering technique. Various parameters such as thickness of oxide layer and time, as well as reduction temperature were investigated in view of obtaining the best conditions for CNTs growth. C2H2 was very effective as carbon feedstock and NH3 pretreatments were crucial steps towards obtaining a high density of nucleation sites for CNTs growth by inhibiting amorphous carbon generation in the initial stage of the synthesis. The substrate oxide layer was analysed by secondary ion mass spectrometry. The prepared CNTs were confirmed by Raman spectroscopy and were further characterised using scanning electron microscopy and transmission electron microscopy.

The growth behavior of carbon nanotubes (CNTs) grown on electron bombarded catalyst layer has been investigated in this paper. A hot cathodic electron beam facility was employed to electron bombarding of catalyst layer before stage of CNTs growth. The growth of carbon nanotubes was performed on the Fe catalyst layer with sio2 substrate in an environment of different mixed gases (H2, NH3 and C2H2) by Thermal Chemical Vapor Deposition (TCVD) system. The pretreated substrates were probed by Atomic Force Microscopy (AFM) and CNTs grown was confirmed by Raman spectroscopy. Moreover, all samples were analyzed by Scanning Electron Microscopy (SEM) before and after growth of CNTs. SEM analyzes clarified that the catalyst grains has been smaller under effect of electron beam bombardment.

An anomalously strong increase of nuclear fusion gains for laser driven compression and thermal ignition of hydrogen-boron11 has been discovered from computations by using the latest results of Newins and Swain about details of a resonance maximum of the astrophysical S-function at 148 keV for the reaction cross-sections. Extensive computations based on volume ignition showed some usual improvements of the fusion gains. However, for a very narrow range of parameters, the increase of the gain was found to be higher by more than a factor 6. This is very unusual in all similar computations and is related to retrograde properties which were known for other parameter values. On top it is most important that the anomalous range is in the practically very interesting range for incorporation of laser pulse energies of few megajoules. The gains of up to 20 may be of interest for power generation in future by the high density fusion scheme.

This work concentrates on the growth of carbon nanowalls (CNWs) using the thermal chemical vapour deposition (T-CVD) technique on a glass substrate coated with Fe nanocatalyst. A combination of CH4/NH3/H2 and C2H2/NH3/H2 renders the growth of carbon nanostructures such as diamond nanocrystals, carbon nanowalls and carbon nanotubes at atmospheric pressure. Parameters affecting the growth of the CNWs such as C2H2 flow ratio, deposition time and temperature are investigated. Low temperature plasma is applied for deposition of the Fe nanocatalyst on the glass substrate. Surface morphology of the substrate is observed using the atomic force microscopy (AFM) technique, while the thicknesses were measured by means of Rutherford back scattering (RBS) technique. The samples utilized are characterized by the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy techniques. One of the important conclusions in this work is that increasing the hydrocarbon gas flow rate and t...

Langmuir probes (LP) are the most common diagnostics for the local measurement of very important plasma parameters such as plasma density, electron temperature, plasma potential and the electron energy distribution function (EEDF). In this paper the applicability of the first derivative Langmuir probe method in processing the electron part of the current-voltage (I–V) characteristics in IR-T1 Tokamak is reported. The EEDF at different radial positions in the edge region and Scrape off Layer (SOL) are derived and the values of the plasma potential, electron temperature and electron density are estimated. Results comparison between the first derivative method and Stangeby method shows a satisfactory agreement.

In contrast to the usual laser fusion scheme with spherical irradiation and very high compression and ignition of fuel, the alternative scheme with side-on ignition of uncompressed solid density of fuel (Chu) may lead to a solution by using the now available picosecond laser pulses with higher than petawatt power. A necessary condition is to use clean laser pulses with better than 108contrast ratio for suppression of relativistic self-focusing. When updating the analysis of Chu for fusion of deuterium-tritium and proton-11B, one problem is that the correct use of the stopping power of the alpha particles had to be solved. Discrepancies are evaluated in view of the stopping power at the low temperature range of the plasmas where the change of the emitted bremsstrahlung is involved.

One of the best ways to get information about plasma and interactions within it, is the study on visible light emitted from plasma. Detection of the emission spectrum from plasma leads to identify the spectral lines of ions and impurities inside the plasma and measurement of all related parameters to ion flux such as velocity and temperature. The first measurement of impurities into the IR-T1 tokamak plasma is done by spectroscopic technique. The CCD-based spectrometer device with the wavelength range of 400-550 nm is used to detection the spectrum emitted from the plasma. The impurities into the plasma in the intended wavelength range are identified. Furthermore, the Doppler broadening of the most intense peaks of impurities and their temperatures are measured. The methods in this paper can be used on all fusion devices.