Publication Date: 2022
IEEE Transactions on Plasma Science (00933813)50(6)pp. 1814-1822
Graphite samples, used in first-wall and divertor of nuclear fusion reactors like tokamaks, were irradiated using hydrogen and argon ions produced in an MTPF-2 plasma focus device in 20 shots to study radiation damages. Ion energy spectra are dNH (E H)/dEH E H-2.8 with a minimum energy of 120 keV to a maximum of 1 MeV for hydrogen ions and dN Ar (E Ar) dE Ar E Ar-3.5 with a minimum energy of 200 keV and a maximum energy of 2 MeV for argon ions. Based on the results of the SRIM code, the maximum destruction of hydrogen ions is at a depth of 900 nm, and a rate of 0.025 DPA/shot and highest hydrogen density is 0.5% at 920 nm. Conversely, the highest degradation of argon ions is at a depth of 120 nm and 0.23 DPA/shot, and the highest density of argon ions at a depth of 200 nm is 0.07%. Different maximum degradation locations and the maximum density of argon ions are due to their heavy mass compared to hydrogen. SEM micrographs show holes with high population density and some sublimated areas on hydrogen-irradiated surfaces. The predominant phenomenon due to argon ion irradiation is physical sputtering, leading to cavities with a depth of several micrometers. Based on the X-ray diffraction (XRD) spectrum, the location and intensity of peaks are changed, and irradiation reduces graphitization and increases the size of the graphite crystal. © 1973-2012 IEEE.
Publication Date: 2021
IEEE Transactions on Plasma Science (00933813)49(6)pp. 1871-1876
Kinetic particle-in-cell (PIC) method is a reliable technique for the laser-plasma interactions simulation based on particles' statistical behavior. This method can be applied in simulating physical phenomena involved in optical diagnostics tools, such as the interferometry-polarimetry (IP) system. IP is one of the significant laser diagnostic methods suggested in the large tokamaks, such as international thermonuclear experimental reactor (ITER), as to improve the accuracy of density and magnetic field measurements. In this article, two separate simulations of the poloidal IP system are run by applying a 2-D/3-V XOOPIC code to observe the phase-shift and Faraday effect in a magnetized plasma with input density and poloidal magnetic field of ne =3.00× 1019 m-3 and Bp=1.00 T, respectively. For this purpose, a gaseous (CO2) linear-polarized far-infrared laser beam of λ i=118μ m wavelength, and about 30W m2 intensity is passed through the plasma, parallel to the magnetic field. The density and poloidal magnetic field are computed from laser phase-shift and Faraday rotation theories, at ne, com=2.99× 1019 m-3 and Bp, com=0.99 T, which correspond to the input values of these simulations. The obtained results indicate the competence and potency of the PIC method in simulating role-playing phenomena in ITER diagnostic devices like the IP system. © 1973-2012 IEEE.
Publication Date: 2021
Nuclear Physics A (03759474)1008
The strong interaction between heavy and kaon mesons can consistently described by coupling constant in an effective lagrangian. Here, the improved strong coupling constants of gB and gB vertices in the framework of the three-point QCD sum rules are calculated. The coupling constants are calculated, when both the B1 and K states are off-shell. In this calculation, the contributions of the quark-quark, quark-gluon, and gluon-gluon condensates corrections are considered. By considering the SUf(3) symmetry, the comparison of results with existing predictions has also been made. © 2021 Elsevier B.V.
Publication Date: 2020
Nuclear Engineering and Technology (2234358X)52(11)pp. 2535-2542
To understand the fundamental parameters of Alvand tokamak, A Rogowski coil with an active integrator was designed and constructed. Considering the characteristics of the Alvand tokamak, the structural and electrical parameters affecting the sensor function, were designed. Calibration was performed directly in the presence of plasma. The sensor has a high resistance against interference of external magnetic fields. Plasma current was measured in various experiments. Based on the plasma current profile and loop voltage signal, the time evolution of plasma discharge was investigated and plasma behavior was analyzed. Alvand tokamak discharge was divided into several regions that represents different physical phenomena in the plasma. During the plasma discharge time, plasma had significant changes and its characteristic was not uniform. To understand the plasma behavior in each of the phases, the Rogowski sensor should have sufficient time resolution. The Rogowski sensor with a frequency up to 15 kHz was appropriate for this purpose. © 2020 Korean Nuclear Society
Moradi zamenjani f., ,
Asgarian, M.A.,
Mostajabodaavati m., M.,
Rasouli, C. Publication Date: 2020
Nuclear Engineering and Technology (2234358X)52(3)pp. 568-574
The feasibility of the particle-in-cell (PIC) method is assessed to simulate the non-collective phenomena like non-collective Thomson scattering (TS). The non-collective TS in the laser-plasma interaction, which is related to the single-particle behavior, is simulated through a 2D relativistic PIC code (XOOPIC). For this simulation, a non-collective TS is emitted from a 50-50 DT plasma with electron density and temperature of ne=3.00×1013cm−3 and Te=1000eV, typical for the edge plasma at ITER measured by ETS system, respectively. The wavelength, intensity, and FWHM of the laser applied in the ETS system are λi,0=1.064×10−4cm, Ii=2.24×1017erg/s⋅cm2, and 12.00ns, respectively. The electron density and temperature predicted by the PIC simulation, obtained from the TS scattered wave, are ne,TS=2.91×1013cm−3 and Te,TS=1089eV, respectively, which are in accordance with the input values of the simulated plasma. The obtained results indicate that the ambiguities rising due to the contradiction between the PIC statistical collective mechanism caused by the super-particle concept and the non-collective nature of TS are resolved. The ability and validity to use PIC method to study the non-collective regimes are verified. © 2020
Publication Date: 2020
Fusion Engineering and Design (09203796)160
Tungsten (W) surface damages due to high-energy irradiations of a plasma focus device, including pure Hydrogen (H) ions, pure Helium (He) ions, and 50−50 H +He mixture was assessed. W is one of the candidate materials for use in the first-wall of nuclear fusion reactors such as tokamaks. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) were utilized to analyze these damages. SEM images, in a good agreement with blister formation mechanisms proposed by large-scale atomic/molecular massively parallel simulator (LAMMPS) simulations, illustrated three different states. Due to the ability of He ions to increase the join probability of tiny blisters, the intermediate state of H+He mixture irradiation, including large individual blisters perches between two limit states of pure H and pure He irradiations, including tiny individual blisters and large clusters of blisters, respectively. AFM analyses confirm the role of He to provide the intermediate state based on values of roughness in these three states. XRD analyses show the considerable changes in the position and intensity of peaks. The shifted peak positions toward the higher angles present a mean value in the intermediate state of H+He mixture irradiation. Also, the medium peak intensity of the intermediate state clarifies the role of He in modulating the sharp behavior of H in the irradiation of W sample. The calculated compressive stresses show a moderate value for the irradiation with the H+He mixture. © 2020 Elsevier B.V.
Asgarian, M.A.,
Janbazi m., ,
Kazemi e., ,
Kamgar f., ,
Seyedhabashi m.r., M.M.R. Publication Date: 2020
Nuclear Physics A (03759474)1003
In this article, the three-point QCD sum rules are used to compute the strong coupling constants of vertices containing strange charmed mesons with the K⁎. The coupling constants are calculated when both charm and K⁎ states are off-shell. In this calculation, the contributions of the quark-quark, quark-gluon, and gluon-gluon condensates corrections are considered. Considering the SUf(3) symmetry, the coupling constant D0K⁎Ds0⁎ and D1K⁎Ds0⁎ vertices are calculated 7.25±0.76 and 9.69±0.85 GeV−1, respectively. © 2020 Elsevier B.V.
Publication Date: 2018
AIP Advances (21583226)8(4)
Electron Bernstein waves (EBW) consist of promising tools in driving localized off-axis current needed for sustained operation as well as effective selective heating scenarios in advanced over dense fusion plasmas like spherical tori and stellarators by applying high power radio frequency waves within the range of Megawatts. Here some serious non-linear effects like parametric decay modes are highly expect-able which have been extensively studied theoretically and experimentally. In general, the decay of an EBW depends on the ratio of the incident frequency and electron cyclotron frequency. At ratios less than two, parametric decay leads to a lower hybrid wave (or an ion Bernstein wave) and EBWs at a lower frequency. For ratios more than two, the daughter waves constitute either an electron cyclotron quasi-mode and another EBW or an ion wave and EBW. However, in contrast with these decay patterns, the excitation of an unusual up-shifted frequency decay channel for the ratio less than two is demonstrated in this study which is totally different as to its generation and persistence. It is shown that this mode varies from the conventional parametric decay channels which necessarily satisfy the matching conditions in frequency and wave-vector. Moreover, the excitation of some less-known local non-propagating quasi-modes (virtual modes) through weak-turbulence theory and their contributions to energy leakage from conversion process leading the reduction in conversion efficiency is assessed. © 2018 Author(s).
Publication Date: 2016
European Physical Journal D (14346060)70(3)
The electron Bernstein wave (EBW) is typically the only wave in the electron cyclotron (EC) range that can be applied in spherical tokamaks for heating and current drive (H&CD). Spherical tokamaks (STs) operate generally in high-β regimes, in which the usual EC ordinary (O) and extraordinary (X) modes are cut off. As it was recently investigated the existence of EBWs at nonlinear regime thus the next step would be the probable nonlinear phenomena study which are predicted to be occurred within the high levels of injected power. In this regard, parametric instabilities are considered as the major channels for losses at the X-B conversion. Hence, we have to consider their effects at the UHR region which can reduce the X-B conversion efficiency. In the case of EBW heating (EBH) at high power density, the nonlinear effects can arise. Particularly at the UHR position, the group velocity is strongly reduced, which creates a high energy density and subsequently a high amplitude electric field. Therefore, a part of the input wave can decay into daughter waves via parametric instability (PI). Thus, via the present research, the excitations of ion Bernstein waves as the dominant decay channels are investigated and also an estimate for the threshold power in terms of experimental parameters related to the fundamental mode of instability is proposed. © 2016 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Physics of Plasmas (1070664X)22(6)
Ever increasing needs and capabilities in high power radio frequency waves heating and current drive scenarios of present and future magnetic confined fusion plasmas motivate expansion of understanding for vast variety of ever upcoming nonlinearities in such levels of power. Among many motivating experiments, one of the most relevant and actively studied in the regime for electron Bernstein wave (EBW) heating is high-β National Spherical Torus Experiment. A very special type of large amplitude electron plasma oscillations known as localized upper hybrid (UH) mode is demonstrated. It is shown that the mutual synergetic interaction of EBW and the localized UH mode can significantly shift the resonance layer about a3 x ∼ 0.9 mm compared to the prediction of linear theory and consequently can explain the considerable reduction of conversion value around 35% observed in our modelling. This reduction is due to scale up of density scale length, L n, at the new UH resonance (UHR) location followed by the increase of Budden parameter, η, which varies from 0.18 predicted by linear aspect to 0.40 in new position of UHR layer obtained by our modelling. Moreover, the parametric instabilities in the form of ion decays and dispersion of localized UH mode, approximately 7 mm due to the finite electron temperature account, are also observed which have an important contribution in reduction of conversion efficiency. © 2015 AIP Publishing LLC.
Publication Date: 2014
Physics of Plasmas (1070664X)21(9)
Electron Bernstein wave (EBW) can be effective for heating and driving currents in spherical tokamak plasmas. Power can be coupled to EBW via mode conversion of the extraordinary (X) mode wave. The most common and successful approach to study the conditions for optimized mode conversion to EBW was evaluated analytically and numerically using a cold plasma model and an approximate kinetic model. The major drawback in using radio frequency waves was the lack of continuous wave sources at very high frequencies (above the electron plasma frequency), which has been addressed. A future milestone is to approach high power regime, where the nonlinear effects become significant, exceeding the limits of validity for present linear theory. Therefore, one appropriate tool would be particle in cell (PIC) simulation. The PIC method retains most of the nonlinear physics without approximations. In this work, we study the direct X-B mode conversion process stages using PIC method for incident wave frequency f0 = 15 GHz, and maximum amplitude E0 = 105V/m in the national spherical torus experiment (NSTX). The modelling shows a considerable reduction in X-B mode conversion efficiency, Cmodelling = 0.43, due to the presence of nonlinearities. Comparison of system properties to the linear state reveals predominant nonlinear effects; EBW wavelength and group velocity in comparison with linear regime exhibit an increment around ∼36% and 17%, respectively. © 2014 AIP Publishing LLC.
Publication Date: 2013
Physics of Plasmas (1070664X)20(10)
One scheme for heating a dense magnetized plasma core, such as in a tokamak, involves launching an ordinary (O) electromagnetic wave at the low density edge. It is converted to a reflected extraordinary (X) electromagnetic wave under certain conditions, and then transformed into an electron Bernstein wave able to reach high density regions inaccessible to most other waves. The O-X mode conversion is important in heating and diagnostic processes in different devices such as tokamaks, stellarators, and some types of pinches. The goal of this study has been to demonstrate that the kinetic particle-in-cell (PIC) scheme is suitable for modeling the O-X conversion process as the first step toward a more complete simulation of O-X-B heating. The O-X process is considered and simulated with a kinetic particle model for parameters of the TJ-II stellarator using the PIC code, XOOPIC. This code is able to model the non-monotonic density and the magnetic profile of the TJ-II stellarator. It can also statistically represent the self-consistent distribution function of the plasma, which has not been possible in previous fluid models. By considering the electric and magnetic components of launched and reflected waves, the O-mode and X-mode waves can be detected, and the O-X conversion can be demonstrated. In this work, the optimum angle for conversion efficiency, as predicted by the previous theory and experimentally confirmed, is used. Via considering the power of the launched O-mode wave and the converted X-mode wave, the efficiency of 63% for O-X conversion for the optimum theoretical launch angle of 47 ° is obtained, which is in good agreement with efficiencies computed via full-wave simulations. © 2013 AIP Publishing LLC.
