The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform

A. Salar Elahi - One of the best experts on this subject based on the ideXlab platform.

  • RETRACTED: A new perspective on hydrogen Plasma Equilibrium calculation along with the MHD potential energy
    International Journal of Hydrogen Energy, 2017
    Co-Authors: A. Salar Elahi, M. Ghoranneviss
    Abstract:

    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.

  • Prevention of Plasma–Surface Interactions by Control of Plasma Equilibrium in Large Aspect Ratio Tokamaks
    Journal of Inorganic and Organometallic Polymers and Materials, 2016
    Co-Authors: Z. Amerian, Mohammad Kazem Salem, Mahmood Ghoranneviss, A. Salar Elahi
    Abstract:

    In tokamak Plasma, impurities present a number of problems. One is the radiative power loss, principally due to line radiation from partially stripped ions. Another is fuel dilution. This arises because impurity atoms produce many electrons and, for a given Plasma pressure, these electrons lake the place of fuel particles. At high concentrations impurities prevent the Plasma being heated. This is particularly a problem during the Plasma start-up phase since impurities radiate most strongly at low temperatures before they become highly ionized. Impurities can also lead to disruptions as a result of edge cooling and consequent current profile modification. On the other hand, these problems can be prevented by control of Plasma Equilibrium (which is defined by Grad–Shafranov (GS) equation). Numerous methods exist to solve the GS equation, describing the Equilibrium of Plasma confined by an axisymmetric magnetic field. In this paper, we have proposed a new numerical solution to the GS equation of an axisymmetric, transformed in cylindrical coordinates solved with the Chebyshev collocation method, when the source term (current density function) on the right hand side is linear. The Chebyshev collocation method is a method for computing highly accurate numerical solutions of deferential equations. We describe a circular cross section of tokamak and present numerical result of magnetic surfaces on the IR-T1 tokamak and then compare the results with an analytical solution.

  • Magnetic Studies of Tokamak Plasma Equilibrium Based on Magnetic System Materials and Characteristics
    Journal of Inorganic and Organometallic Polymers and Materials, 2016
    Co-Authors: K. Mikaili Agah, M. Ghoraneviss, A. Salar Elahi
    Abstract:

    In this contribution, we have studied the magnetic system of ITER, and Plasma Equilibrium using the semi-empirical technique. Tokamak magnet systems consist of four main sub-systems: Toroidal field coils, Central solenoid coils, Poloidal field coils, and Correction coils. The Plasma horizontal position 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 Plasma column. The results are compared and discussed.

  • RETRACTED: Plasma Equilibrium reconstruction for the nuclear fusion of magnetically confined hydrogen isotopes
    International Journal of Hydrogen Energy, 2016
    Co-Authors: J. Habibian, A. Salar Elahi, M. Ghoranneviss, Mohammad Kazem Salem, S. Saviz
    Abstract:

    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.

  • Control of heat and mass transfer processes by Plasma Equilibrium reconstruction in toroidal magnetic confinement nuclear fusion devices
    International Journal of Thermal Sciences, 2016
    Co-Authors: Z. Amerian, A. Salar Elahi, Mahmood Ghoranneviss, Mohammad Kazem Salem, J. Izadiyan
    Abstract:

    Abstract Heat and mass transfers can be controlled by Plasma Equilibrium reconstruction in toroidal confinement nuclear fusion systems such as tokamaks. The Magnetohydrodynamic Equilibrium in axisymmetric Plasma is described by the Grad-Shafranov equation in terms of the magnetic flux. In this paper, we have proposed a new numerical solution to the Grad-Shafranov equation of an axisymmetric, transformed in quasi-cylindrical coordinates solved with the Chebyshev collocation method, when the source term (current density function) on the right hand side is quadratics as it is described by Atanasiu et al. The Chebyshev collocation method is a method for computing highly accurate numerical solutions differential equations. We have described a circular cross section of tokamak and presented numerical result of magnetic surfaces on the IR-T1 tokamak and compared the results with an analytical solution and then calculated the Shafranov shift using a minimization procedure based on the Newton method.

R. Yoshino - One of the best experts on this subject based on the ideXlab platform.

  • Plasma Equilibrium response modelling and validation on JT-60U
    Nuclear Fusion, 2002
    Co-Authors: J.b. Lister, Ati S. Sharma, David J. N. Limebeer, Y. Nakamura, J.p. Wainwright, R. Yoshino
    Abstract:

    A systematic procedure to identify the Plasma Equilibrium response to the poloidal field coil voltages has been applied to the JT-60U tokamak. The required response was predicted with a high accuracy by a state-space model derived from first principles. The ab initio derivation of linearized Plasma Equilibrium response models is re-examined using an approach standard in analytical mechanics. A symmetric formulation is naturally obtained, removing a previous weakness in such models. RZIP, a rigid current distribution model, is re-derived using this approach and is compared with the new experimental Plasma Equilibrium response data obtained from Ohmic and neutral beam injection discharges in the JT-60U tokamak. In order to remove any bias from the comparison between modelled and measured Plasma responses, the electromagnetic response model without Plasma was first carefully tuned against experimental data, using a parametric approach, for which different cost functions for quantifying model agreement were explored. This approach additionally provides new indications of the accuracy to which various Plasma parameters are known, and to the ordering of physical effects. Having taken these precautions when tuning the Plasmaless model, an empirical estimate of the Plasma self-inductance, the Plasma resistance and its radial derivative could be established and compared with initial assumptions. Off-line tuning of the JT-60U controller is presented as an example of the improvements which might be obtained by using such a model of the Plasma Equilibrium response.

  • Linear and Non-linear Plasma Equilibrium Responses on the JT-60U and TCV Tokamaks
    2001
    Co-Authors: J.b. Lister, Ati S. Sharma, Y. Nakamura, J.p. Wainwright, R.r. Khayrutdinov, V.e. Lukash, D.j.n. Limebeer, Fabio Villone, R. Yoshino
    Abstract:

    Although linear response models are useful for feedback controller design, their linear time-invariant properties cannot simulate the evolution of a full Plasma discharge. A suitable code for this purpose is DINA, which has now been benchmarked against a complete set of experimental data from TCV control experiments in both the time and frequency domains. Experimental measurements of the Plasma Equilibrium dynamic response to poloidal field coil voltage variations have recently been performed on the JT-60U tokamak. These results have been compared with the RZIP rigid current displacement model, previously validated on TCV, but enhanced for the work described.

  • Linear and non-linear Plasma Equilibrium responses on the JT-60U and TCV tokamaks
    Fusion Engineering and Design, 2001
    Co-Authors: J.b. Lister, Y. Nakamura, J.p. Wainwright, D.j.n. Limebeer, Fabio Villone, R Khayrutdinov, V Lukash, A Sharma, R. Yoshino
    Abstract:

    Although linear response models are useful for feedback controller design, their linear time-invariant properties cannot simulate the evolution of a full Plasma discharge. A suitable code for this purpose is DINA, which has now been benchmarked against a complete set of experimental data from TCV control experiments in both the time and frequency domains. Experimental measurements of the Plasma Equilibrium dynamic response to poloidal field coil voltage variations have recently been performed on the JT-60U tokamak. These results have been compared with the RZIP rigid current displacement model, previously validated on TCV, but enhanced for the work described. © 2001 Elsevier Science B.V. All rights reserved

  • Plasma Equilibrium control during slow Plasma current quench with avoidance of Plasma-wall interaction in JT-60U
    Nuclear Fusion, 1997
    Co-Authors: R. Yoshino, Y. Nakamura, Y. Neyatani
    Abstract:

    In JT-60U a vertical displacement event (VDE) is observed during slow Plasma current quench (Ip quench) for a vertically elongated divertor Plasma with a single null. The VDE is generated by an error in the feedback control of the vertical position of the Plasma current centre (ZJ). It has been perfectly avoided by improving the accuracy of the ZJ measurement in real time. Furthermore, Plasma-wall interaction has been avoided successfully during slow Ip quench owing to the good performance of the Plasma Equilibrium control system

J.p. Wainwright - One of the best experts on this subject based on the ideXlab platform.

  • Plasma Equilibrium response modelling and validation on JT-60U
    Nuclear Fusion, 2002
    Co-Authors: J.b. Lister, Ati S. Sharma, David J. N. Limebeer, Y. Nakamura, J.p. Wainwright, R. Yoshino
    Abstract:

    A systematic procedure to identify the Plasma Equilibrium response to the poloidal field coil voltages has been applied to the JT-60U tokamak. The required response was predicted with a high accuracy by a state-space model derived from first principles. The ab initio derivation of linearized Plasma Equilibrium response models is re-examined using an approach standard in analytical mechanics. A symmetric formulation is naturally obtained, removing a previous weakness in such models. RZIP, a rigid current distribution model, is re-derived using this approach and is compared with the new experimental Plasma Equilibrium response data obtained from Ohmic and neutral beam injection discharges in the JT-60U tokamak. In order to remove any bias from the comparison between modelled and measured Plasma responses, the electromagnetic response model without Plasma was first carefully tuned against experimental data, using a parametric approach, for which different cost functions for quantifying model agreement were explored. This approach additionally provides new indications of the accuracy to which various Plasma parameters are known, and to the ordering of physical effects. Having taken these precautions when tuning the Plasmaless model, an empirical estimate of the Plasma self-inductance, the Plasma resistance and its radial derivative could be established and compared with initial assumptions. Off-line tuning of the JT-60U controller is presented as an example of the improvements which might be obtained by using such a model of the Plasma Equilibrium response.

  • Linear and Non-linear Plasma Equilibrium Responses on the JT-60U and TCV Tokamaks
    2001
    Co-Authors: J.b. Lister, Ati S. Sharma, Y. Nakamura, J.p. Wainwright, R.r. Khayrutdinov, V.e. Lukash, D.j.n. Limebeer, Fabio Villone, R. Yoshino
    Abstract:

    Although linear response models are useful for feedback controller design, their linear time-invariant properties cannot simulate the evolution of a full Plasma discharge. A suitable code for this purpose is DINA, which has now been benchmarked against a complete set of experimental data from TCV control experiments in both the time and frequency domains. Experimental measurements of the Plasma Equilibrium dynamic response to poloidal field coil voltage variations have recently been performed on the JT-60U tokamak. These results have been compared with the RZIP rigid current displacement model, previously validated on TCV, but enhanced for the work described.

  • Comparing DINA code simulations with TCV experimental Plasma Equilibrium responses
    Plasma Physics and Controlled Fusion, 2001
    Co-Authors: R.r. Khayrutdinov, J.b. Lister, V.e. Lukash, J.p. Wainwright
    Abstract:

    The DINA nonlinear time-dependent simulation code has been validated against an extensive set of Plasma Equilibrium response experiments carried out on the TCV tokamak. Limited and diverted Plasmas are found to be well modelled during the Plasma current flat top. In some simulations the application of the poloidal field coil voltage stimulation pulse sufficiently changed the Plasma Equilibrium that the vertical position feedback control loop became unstable. This behaviour was also found in the experimental work, and cannot be reproduced using linear time-independent models. A single null diverted Plasma discharge was also simulated from start-up to shut-down and the results were found to accurately reproduce their experimental equivalents. The most significant difference noted was the penetration time of the poloidal flux, leading to a delayed onset of sawtoothing in the DINA simulation. The complete set of frequency stimulation experiments used to measure the open-loop tokamak Plasma Equilibrium response was also simulated using DINA and the results were analysed in an identical fashion to the experimental data. The frequency response of the DINA simulations agrees with the experimental results. Comparisons with linear models are also discussed in order to identify areas of good and only occasionally less good agreement.

  • Linear and non-linear Plasma Equilibrium responses on the JT-60U and TCV tokamaks
    Fusion Engineering and Design, 2001
    Co-Authors: J.b. Lister, Y. Nakamura, J.p. Wainwright, D.j.n. Limebeer, Fabio Villone, R Khayrutdinov, V Lukash, A Sharma, R. Yoshino
    Abstract:

    Although linear response models are useful for feedback controller design, their linear time-invariant properties cannot simulate the evolution of a full Plasma discharge. A suitable code for this purpose is DINA, which has now been benchmarked against a complete set of experimental data from TCV control experiments in both the time and frequency domains. Experimental measurements of the Plasma Equilibrium dynamic response to poloidal field coil voltage variations have recently been performed on the JT-60U tokamak. These results have been compared with the RZIP rigid current displacement model, previously validated on TCV, but enhanced for the work described. © 2001 Elsevier Science B.V. All rights reserved

V.d. Pustovitov - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic pressure effects on Plasma Equilibrium in toroidal systems
    Plasma Physics and Controlled Fusion, 2010
    Co-Authors: V.d. Pustovitov
    Abstract:

    General properties of anisotropic Plasma Equilibrium in tokamaks and stellarators are considered within the approach allowing explicit analytical evaluation of the Equilibrium Plasma currents and the related integral quantities. This is done to provide a link to the conventional Equilibrium theory for isotropic Plasma, to find the rules for possible extensions of its results to configurations with anisotropic pressure and to unify the knowledge obtained in separate numerical studies. Expressions for the diamagnetic signal and, mainly, the Pfirsch–Schluter current in stellarators are considered. Ultimately this leads to a theoretical justification of the method of experimental evaluation of the pressure anisotropy in the Large Helical Device proposed by Yamaguchi et al (2005 Nucl. Fusion 45 L33). The conditions of its applicability are clarified and possible limitations are elucidated. Combined effects of the pressure anisotropy and inward–outward shift of the Plasma on the Pfirsch–Schluter current in stellarators are discussed.

  • Plasma Equilibrium with barriers
    Plasma Physics Reports, 2003
    Co-Authors: V.d. Pustovitov
    Abstract:

    The recently proposed concept of the transport barrier formation in a tokamak Plasma as a bifurcation of the Equilibrium state with a change in the toroidal magnetic field over the entire Plasma column, including the Plasma edge, is analyzed. The analysis is performed in the cylindrical approximation. It is shown that, in the framework of the discussed concept, all of the Equilibrium solutions are continuous functions of the parameters involved, bifurcations are absent, and the result is determined by the model assumptions that are necessary in order to make the task self-contained. Removing even part of these restrictive assumptions can substantially change the result. Under typical conditions, the effect of the Plasma rotation on the Plasma Equilibrium is negligibly small. Besides, from the viewpoint of the formal analysis of the force balance, the rotation does not facilitate but, in contrast, hampers the formation of a positive pressure jump.

  • Theoretical Principles of the Plasma-Equilibrium Control in Stellarators
    Reviews of Plasma Physics, 2000
    Co-Authors: V.d. Pustovitov
    Abstract:

    This review is devoted to the theory of Plasma Equilibrium in conventional stellarators with a plane circular axis and helical magnetic fields. Its primary objectives are the analysis of the conditions of finite-pressure Plasma Equilibrium in stellarators and the search for ways of increasing the achievable β (ratio of kinetic to magnetic pressures).

Ryan Fries - One of the best experts on this subject based on the ideXlab platform.

  • Plasma and tissue angiotensin converting enzyme 2 activity and Plasma Equilibrium concentrations of angiotensin peptides in dogs with heart disease
    Journal of Veterinary Internal Medicine, 2019
    Co-Authors: Eva Larouchelebel, Kerry A. Loughran, Mark A. Oyama, Phil F. Solter, Danielle Laughlin, Melissa D. Sánchez, Charles Antoine Assenmacher, Philip R. Fox, Ryan Fries
    Abstract:

    BACKGROUND Angiotensin-converting enzyme 2 (ACE2) is a homologue of angiotensin-converting enzyme (ACE) and produces angiotensin peptides (APs), such as angiotensin 1-9 and 1-7 that are vasodilatory and natriuretic, and act to counterbalance angiotensin II. HYPOTHESIS Evidence of ACE2 can be found in tissues and Plasma of dogs. Equilibrium concentrations of renin angiotensin aldosterone system (RAAS) APs differ in dogs with heart disease compared to healthy dogs and recombinant human ACE2 (rhACE2) alters relative concentrations of APs. ANIMALS Forty-nine dogs with and 34 dogs without heart disease. METHODS Immunohistochemistry and assays for tissue and Plasma ACE2 activity and Equilibrium concentrations of Plasma RAAS APs were performed. RESULTS Immunolabeling for ACE2 was present in kidney and myocardial tissue. Median Plasma ACE2 activity was significantly increased in dogs with congestive heart failure (CHF; 6.9 mU/mg; interquartile range [IQR], 5.1-12.1) as compared to control (2.2 mU/mg; IQR, 1.8-3.0; P = .0003). Plasma Equilibrium analysis of RAAS APs identified significant increases in the median concentrations of beneficial APs, such as angiotensin 1-7, in dogs with CHF (486.7 pg/mL; IQR, 214.2-1168) as compared to those with preclinical disease (41.0 pg/mL; IQR, 27.4-45.1; P < .0001) or control (11.4 pg/mL; IQR, 7.1-25.3; P = .01). Incubation of Plasma samples from dogs with CHF with rhACE2 increased beneficial APs, such as angiotensin 1-9 (preincubation, 10.3 pg/mL; IQR, 4.4-37.2; postincubation, 2431 pg/mL; IQR, 1355-3037; P = .02), while simultaneously decreasing maladaptive APs, such as angiotensin II (preincubation, 53.4 pg/mL; IQR, 28.6-226.4; postincubation, 2.4 pg/mL; IQR, 0.50-5.8; P = .02). CONCLUSIONS AND CLINICAL IMPORTANCE Recognition of the ACE2 system expands the conventional view of the RAAS in the dog and represents an important potential therapeutic target.

  • Plasma and tissue angiotensin-converting enzyme 2 activity and Plasma Equilibrium concentrations of angiotensin peptides in dogs with heart disease.
    Journal of veterinary internal medicine, 2019
    Co-Authors: Éva Larouche-lebel, Kerry A. Loughran, Mark A. Oyama, Phil F. Solter, Danielle Laughlin, Melissa D. Sánchez, Charles Antoine Assenmacher, Philip R. Fox, Ryan Fries
    Abstract:

    BACKGROUND Angiotensin-converting enzyme 2 (ACE2) is a homologue of angiotensin-converting enzyme (ACE) and produces angiotensin peptides (APs), such as angiotensin 1-9 and 1-7 that are vasodilatory and natriuretic, and act to counterbalance angiotensin II. HYPOTHESIS Evidence of ACE2 can be found in tissues and Plasma of dogs. Equilibrium concentrations of renin angiotensin aldosterone system (RAAS) APs differ in dogs with heart disease compared to healthy dogs and recombinant human ACE2 (rhACE2) alters relative concentrations of APs. ANIMALS Forty-nine dogs with and 34 dogs without heart disease. METHODS Immunohistochemistry and assays for tissue and Plasma ACE2 activity and Equilibrium concentrations of Plasma RAAS APs were performed. RESULTS Immunolabeling for ACE2 was present in kidney and myocardial tissue. Median Plasma ACE2 activity was significantly increased in dogs with congestive heart failure (CHF; 6.9 mU/mg; interquartile range [IQR], 5.1-12.1) as compared to control (2.2 mU/mg; IQR, 1.8-3.0; P = .0003). Plasma Equilibrium analysis of RAAS APs identified significant increases in the median concentrations of beneficial APs, such as angiotensin 1-7, in dogs with CHF (486.7 pg/mL; IQR, 214.2-1168) as compared to those with preclinical disease (41.0 pg/mL; IQR, 27.4-45.1; P