Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with...Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with respect to time is a fraction. In this case, the Caputo fractional derivative relative to time is utilized, because it preserves the form of the initial conditions. A numerical calculation reveals that the fractional order of the temporal derivative α(α ∈(0, 1), sub-diffusive regime) controls the diffusion rate. The temporal fractional derivative is related to the fact that the evolution of a physical quantity is affected by its past history, depending on what are termed memory effects. The magnitude of α is a measure of such memory effects. When α decreases, so does the rate of particle diffusion due to memory effects. As a result,if a system initially has a density profile without a source, then the smaller the α is, the more slowly the density profile approaches zero. When a source is added, due to the balance of the diffusion and fueling processes, the system reaches a steady state and the density profile does not evolve. As α decreases, the time required for the system to reach a steady state increases. In magnetically confined plasmas, the temporal fractional transport model can be applied to off-axis heating processes. Moreover, it is found that the memory effects reduce the rate of energy conduction and hollow temperature profiles can be sustained for a longer time in sub-diffusion processes than in ordinary diffusion processes.展开更多
As an obstacle in high-performance discharge in future fusion devices,disruptions may do great damages to the reactors through causing strong electromagnetic forces,heat loads and so on.The drift waves in tokamak are ...As an obstacle in high-performance discharge in future fusion devices,disruptions may do great damages to the reactors through causing strong electromagnetic forces,heat loads and so on.The drift waves in tokamak are illustrated to play essential roles in the confinement performance as well.Depending on the plasma parameters and mode perpendicular wavelength,the mode phase velocity is either in the direction of electron diamagnetic velocity(namely,typical trapped electron mode)or in the direction of ion diamagnetic velocity(namely,the ubiquitous mode).Among them,the ubiquitous mode is directly investigated using gyro-fluid simulation associating with gyro-fluid equations for drift waves in tokamak plasmas.The ubiquitous mode is charactered by the short wavelength and propagates in ion diamagnetic direction.It is suggested that the density gradient is essential for the occurrence of the ubiquitous mode.However,the ubiquitous mode is also influenced by the temperature gradients and other plasma parameters including the magnetic shear and the fraction of trapped electrons.Furthermore,the ubiquitous mode may play essential roles in the turbulent transport.Meanwhile,the relevant parameters are scanned using a great number of electrostatic gyro-fluid simulations.The stability map is taken into consideration with the micro-instabilities contributing to the turbulent transport.The stability valley of the growth rates occurs with the assumption of the normalized temperature gradient equaling to the normalized density gradient.展开更多
Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC(MHD@Dalian Code).Based on a set of two-fluid fourfield equations,the bootstrap current,...Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC(MHD@Dalian Code).Based on a set of two-fluid fourfield equations,the bootstrap current,parallel,and perpendicular transport effects are included appropriately.Taking into account the bootstrap current,a mode penetration-like phenomenon is found,which is essentially different from the classical tearing mode model.To reveal the influence of the plasma flow on the mode penetration process,E×B drift flow and diamagnetic drift flow are separately applied to compare their effects.Numerical results show that a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode.Furthermore,an oscillation phenomenon of island width is discovered.By analyzing it in depth,it is found that this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island.This physical mechanism is verified again by key parameter scanning.展开更多
Alfvén resonance in high beta plasmas is studied with a five-field model based on the two-fluid theory.The mode conversion and low frequency oblique whistler wave generation are found in the resonance layer.Prope...Alfvén resonance in high beta plasmas is studied with a five-field model based on the two-fluid theory.The mode conversion and low frequency oblique whistler wave generation are found in the resonance layer.Properties of wave propagation,polarity,and interaction with charged particles are also investigated.展开更多
A single-legged coil behind the lower divertor and covering a 120° toroidal angle is utilized in a recent EAST discharge, for the purpose of increasing the wetted area of the divertor surface by locally modifying...A single-legged coil behind the lower divertor and covering a 120° toroidal angle is utilized in a recent EAST discharge, for the purpose of increasing the wetted area of the divertor surface by locally modifying the magnetic field near the X-point. The plasma response, in particular, the plasma boundary surface corrugation due to the single-legged coil current, is modeled by the updated MARS-F code, by computing the plasma displacement for all important toroidal harmonics(n?=?1, 2, 4 and 5) associated with the partial toroidal coverage by the coil. The plasma response produced by the single-legged coil is found to be non-local and is of the kinkpeeling type. For a reference EAST plasma with a lower single-null magnetic configuration, the plasma boundary corrugation near the X-point, produced by the upper single-legged coil, is about twice as large as that produced by the lower single-legged coil, despite the proximity of the latter to the X-point.展开更多
基金supported by the National Key R&D Program of China (Grant No. 2022YFE03090000)the National Natural Science Foundation of China (Grant No. 11925501)the Fundamental Research Fund for the Central Universities (Grant No. DUT22ZD215)。
文摘Anomalous transport in magnetically confined plasmas is investigated using temporal fractional transport equations.The use of temporal fractional transport equations means that the order of the partial derivative with respect to time is a fraction. In this case, the Caputo fractional derivative relative to time is utilized, because it preserves the form of the initial conditions. A numerical calculation reveals that the fractional order of the temporal derivative α(α ∈(0, 1), sub-diffusive regime) controls the diffusion rate. The temporal fractional derivative is related to the fact that the evolution of a physical quantity is affected by its past history, depending on what are termed memory effects. The magnitude of α is a measure of such memory effects. When α decreases, so does the rate of particle diffusion due to memory effects. As a result,if a system initially has a density profile without a source, then the smaller the α is, the more slowly the density profile approaches zero. When a source is added, due to the balance of the diffusion and fueling processes, the system reaches a steady state and the density profile does not evolve. As α decreases, the time required for the system to reach a steady state increases. In magnetically confined plasmas, the temporal fractional transport model can be applied to off-axis heating processes. Moreover, it is found that the memory effects reduce the rate of energy conduction and hollow temperature profiles can be sustained for a longer time in sub-diffusion processes than in ordinary diffusion processes.
基金Project partially supported by the National Natural Science Foundation of China(Grant Nos.12205035 and 11925501)also partially by the National Key Research and Development Program of China(Grant Nos.2017YFE0301200 and 2017YFE0301201).
文摘As an obstacle in high-performance discharge in future fusion devices,disruptions may do great damages to the reactors through causing strong electromagnetic forces,heat loads and so on.The drift waves in tokamak are illustrated to play essential roles in the confinement performance as well.Depending on the plasma parameters and mode perpendicular wavelength,the mode phase velocity is either in the direction of electron diamagnetic velocity(namely,typical trapped electron mode)or in the direction of ion diamagnetic velocity(namely,the ubiquitous mode).Among them,the ubiquitous mode is directly investigated using gyro-fluid simulation associating with gyro-fluid equations for drift waves in tokamak plasmas.The ubiquitous mode is charactered by the short wavelength and propagates in ion diamagnetic direction.It is suggested that the density gradient is essential for the occurrence of the ubiquitous mode.However,the ubiquitous mode is also influenced by the temperature gradients and other plasma parameters including the magnetic shear and the fraction of trapped electrons.Furthermore,the ubiquitous mode may play essential roles in the turbulent transport.Meanwhile,the relevant parameters are scanned using a great number of electrostatic gyro-fluid simulations.The stability map is taken into consideration with the micro-instabilities contributing to the turbulent transport.The stability valley of the growth rates occurs with the assumption of the normalized temperature gradient equaling to the normalized density gradient.
基金supported by the National Key R&D Program of China(No.2022YFE03040001)National Natural Science Foundation of China(Nos.11925501 and 12075048)+1 种基金Chinese Academy of Sciences,Key Laboratory of Geospace Environment,University of Science&Technology of China(No.GE2019-01)Fundamental Research Funds for the Central Universities(No.DUT21GJ204)。
文摘Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC(MHD@Dalian Code).Based on a set of two-fluid fourfield equations,the bootstrap current,parallel,and perpendicular transport effects are included appropriately.Taking into account the bootstrap current,a mode penetration-like phenomenon is found,which is essentially different from the classical tearing mode model.To reveal the influence of the plasma flow on the mode penetration process,E×B drift flow and diamagnetic drift flow are separately applied to compare their effects.Numerical results show that a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode.Furthermore,an oscillation phenomenon of island width is discovered.By analyzing it in depth,it is found that this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island.This physical mechanism is verified again by key parameter scanning.
基金*Supported by the National Natural Science Foundation of China under Grant Nos 40731056,10975012 and 41104112ITER-CN Program under Grant Nos 2009GB105004 and 2010GB106002the National Undergraduate Innovation Programs.
文摘Alfvén resonance in high beta plasmas is studied with a five-field model based on the two-fluid theory.The mode conversion and low frequency oblique whistler wave generation are found in the resonance layer.Properties of wave propagation,polarity,and interaction with charged particles are also investigated.
基金funded by the Fundamental Research Funds for the Central Universities (No. 2232021G-10)National Natural Science Foundation of China (Nos. 12075053, 11505021 and 11975068)+1 种基金the National Key R&D Program of China (Nos. 2017YFE030052, 2017YFE0301100, 2017YFE0301104, 2017YFE0300500 and 2017YFE0300501)supported by the U.S. Do E Office of Science (Nos. DEFG02–95ER54309 and DEFC02–04ER54698)。
文摘A single-legged coil behind the lower divertor and covering a 120° toroidal angle is utilized in a recent EAST discharge, for the purpose of increasing the wetted area of the divertor surface by locally modifying the magnetic field near the X-point. The plasma response, in particular, the plasma boundary surface corrugation due to the single-legged coil current, is modeled by the updated MARS-F code, by computing the plasma displacement for all important toroidal harmonics(n?=?1, 2, 4 and 5) associated with the partial toroidal coverage by the coil. The plasma response produced by the single-legged coil is found to be non-local and is of the kinkpeeling type. For a reference EAST plasma with a lower single-null magnetic configuration, the plasma boundary corrugation near the X-point, produced by the upper single-legged coil, is about twice as large as that produced by the lower single-legged coil, despite the proximity of the latter to the X-point.
