Discrete Alfven eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes ...Discrete Alfven eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes are trapped by the s-induced potential wells along the magnetic field line. Here α = -q2Rdβ/dr with q being the safety factor, the ratio between plasma and magnetic pressures, and R the major radius, and r the minor radius. Due to negligible continuum damping via wave energy tunneling, these Alfven eigenmodes could be readily destabilized by energetic particles.展开更多
Realization of negative stiffness （NS） in damping low frequency acoustic and mechanical vibration is relevant in engineering applications. In this work, assemblage of two repelling magnets was used to produce negati...Realization of negative stiffness （NS） in damping low frequency acoustic and mechanical vibration is relevant in engineering applications. In this work, assemblage of two repelling magnets was used to produce negative magnetic spring （NMS）. A mass-spring system with NMS is experimented where the free and forced vibrations of the system are examined. The anti-phase movement is observed due to the presence of proposed NMS, confirming the analytical solution. We further showed the dynamics of the system containing NS spring could also be derived from Hamilton＇s principle.展开更多
In this paper, the electron temperature gradient （ETG） instability and corresponding turbulent transport in toroidal plasmas with negative magnetic shear is studied using the integral eigenvalue equations. The full ...In this paper, the electron temperature gradient （ETG） instability and corresponding turbulent transport in toroidal plasmas with negative magnetic shear is studied using the integral eigenvalue equations. The full electron kinetics is considered and the behaviours of the modes and the transport in the parameter regimes close to the instability threshold are emphasized. The fitting formulas of the critical gradient, for negative magnetic shear, are given.展开更多
It was found that there are multiplicity of low shear toroidicity-induced Alfv′en eigenmodes in a zero beta limit if the inverse aspect ratio is larger than the magnetic shear at the mode location(Candy 1996 Phys. Le...It was found that there are multiplicity of low shear toroidicity-induced Alfv′en eigenmodes in a zero beta limit if the inverse aspect ratio is larger than the magnetic shear at the mode location(Candy 1996 Phys. Lett. A 215 299). Because the reversed shear Alfv′en eigenmode(RSAE) and even the RSAE associated with the non-circular triangularity-induced Alfv′en eigenmode(NAE) gap(NAE–RSAE) usually reside near the shear-reversal point, the condition that the inverse aspect ratio is larger than the magnetic shear is naturally satisfied. For this reason, we numerically investigate the existence of multiplicity of core-localized NAE–RSAEs and mode characteristics in the present work. We firstly verify the existence of the multiplicity for zero beta plasma by using a D-shaped equilibrium. It is pointed out that, for a given toroidal mode number, the Alfv′en cascade spectrum accommodates down-sweeping and up-sweeping modes above and below the NAE range of frequencies. An analytical model for the existence of multiple RSAE modes is in good agreement with the simulation results. One notices that the triangularity has a greater effect on the odd-type modes than that on the even-type modes: the odd-type modes come into existence because of the plasma triangularity.展开更多
Heterostructures of van der Waals(vdW)ferromagnetic materials have become a focal point in research of lowdimensional spintronic devices.The current direction in spin valves is commonly perpendicular to the plane(CPP)...Heterostructures of van der Waals(vdW)ferromagnetic materials have become a focal point in research of lowdimensional spintronic devices.The current direction in spin valves is commonly perpendicular to the plane(CPP).However,the transport properties of the CPP mode remain largely unexplored.In this work,current-in-plane(CIP)mode and CPP mode for CrTe_(2) thin films are carefully studied.The temperature-dependent longitudinal resistance transitions from metallic(CIP)to semiconductor behavior(CPP),with the electrical resistivity of CPP increased by five orders of magnitude.More importantly,the transport properties of the CPP can be categorized into a single-gap tunneling-through model with the activation energy(Ea)of1.34 meV/gap at 300–150 K,the variable range hopping model with a linear negative magnetoresistance at 150–20 K,and weak localization region with a nonlinear magnetic resistance below 20 K.This study explores the vertical transport in CrTe_(2) materials for the first time,contributing to understand its unique properties and to pave the way for its potential in spin valve devices.展开更多
Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this targe...Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this target with its magnetic-frequency variation property,which reduces the magnetic reluctance of the fundamental component.However,this design cannot be applied to low-frequency transformers owing to the high loss caused by its limited self-inductance and quality factor.To solve this problem,a pole-wrapped negative equivalent magnetic reluctance(PNEMR)structure is presented.The proposed design employed a copper-based PNEMR structure wrapped around the magnetic poles to enhance the fundamental flux and suppress the DC component of flux.Accordingly,the magnetizing current is reduced,and the isolation transformer is less susceptible to the DC bias.The proposed design can simultaneously improve the anti-DC magnetic bias capability,efficiency,and power factor of the transformers.To verify the effectiveness of the proposed design,a 10 kW C-core PNEMR structure-based transformer for isolation-dependent applications was constructed and compared to the generalized structures and transformers with planar negative magnetic reluctance structures.Results indicate that the PNEMR-based transformer can enhance the efficiency and power factor from 96.1%and 0.87 to 96.6%and 0.93,respectively,under full load conditions.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.10675037)
文摘Discrete Alfven eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes are trapped by the s-induced potential wells along the magnetic field line. Here α = -q2Rdβ/dr with q being the safety factor, the ratio between plasma and magnetic pressures, and R the major radius, and r the minor radius. Due to negligible continuum damping via wave energy tunneling, these Alfven eigenmodes could be readily destabilized by energetic particles.
基金supported by the National Natural Science Foundation of China(11472044,11221202,11632003,11521062)the 111 Project(B160030)
文摘Realization of negative stiffness （NS） in damping low frequency acoustic and mechanical vibration is relevant in engineering applications. In this work, assemblage of two repelling magnets was used to produce negative magnetic spring （NMS）. A mass-spring system with NMS is experimented where the free and forced vibrations of the system are examined. The anti-phase movement is observed due to the presence of proposed NMS, confirming the analytical solution. We further showed the dynamics of the system containing NS spring could also be derived from Hamilton＇s principle.
基金Supported by the National Natural Science Foundation of China（10135020）
文摘In this paper, the electron temperature gradient （ETG） instability and corresponding turbulent transport in toroidal plasmas with negative magnetic shear is studied using the integral eigenvalue equations. The full electron kinetics is considered and the behaviours of the modes and the transport in the parameter regimes close to the instability threshold are emphasized. The fitting formulas of the critical gradient, for negative magnetic shear, are given.
基金Project supported by the National Natural Science Foundation of China(Grant No.11675222)
文摘It was found that there are multiplicity of low shear toroidicity-induced Alfv′en eigenmodes in a zero beta limit if the inverse aspect ratio is larger than the magnetic shear at the mode location(Candy 1996 Phys. Lett. A 215 299). Because the reversed shear Alfv′en eigenmode(RSAE) and even the RSAE associated with the non-circular triangularity-induced Alfv′en eigenmode(NAE) gap(NAE–RSAE) usually reside near the shear-reversal point, the condition that the inverse aspect ratio is larger than the magnetic shear is naturally satisfied. For this reason, we numerically investigate the existence of multiplicity of core-localized NAE–RSAEs and mode characteristics in the present work. We firstly verify the existence of the multiplicity for zero beta plasma by using a D-shaped equilibrium. It is pointed out that, for a given toroidal mode number, the Alfv′en cascade spectrum accommodates down-sweeping and up-sweeping modes above and below the NAE range of frequencies. An analytical model for the existence of multiple RSAE modes is in good agreement with the simulation results. One notices that the triangularity has a greater effect on the odd-type modes than that on the even-type modes: the odd-type modes come into existence because of the plasma triangularity.
基金the National Natural Science Foundation of China(Grant Nos.12241403 and 61974061)the Natural Science Foundation of Jiangsu Province of China(Grant No.BK20140054).
文摘Heterostructures of van der Waals(vdW)ferromagnetic materials have become a focal point in research of lowdimensional spintronic devices.The current direction in spin valves is commonly perpendicular to the plane(CPP).However,the transport properties of the CPP mode remain largely unexplored.In this work,current-in-plane(CIP)mode and CPP mode for CrTe_(2) thin films are carefully studied.The temperature-dependent longitudinal resistance transitions from metallic(CIP)to semiconductor behavior(CPP),with the electrical resistivity of CPP increased by five orders of magnitude.More importantly,the transport properties of the CPP can be categorized into a single-gap tunneling-through model with the activation energy(Ea)of1.34 meV/gap at 300–150 K,the variable range hopping model with a linear negative magnetoresistance at 150–20 K,and weak localization region with a nonlinear magnetic resistance below 20 K.This study explores the vertical transport in CrTe_(2) materials for the first time,contributing to understand its unique properties and to pave the way for its potential in spin valve devices.
基金Supported by the Research Grant Council of the Hong Kong SAR Government under projects PolyU PolyU152180/19E.
文摘Isolation-dependent applications require a transformer with high efficiency,low magnetizing current,and anti-DC bias capability.The kilohertz planar negative magnetic reluctance structure is used to achieve this target with its magnetic-frequency variation property,which reduces the magnetic reluctance of the fundamental component.However,this design cannot be applied to low-frequency transformers owing to the high loss caused by its limited self-inductance and quality factor.To solve this problem,a pole-wrapped negative equivalent magnetic reluctance(PNEMR)structure is presented.The proposed design employed a copper-based PNEMR structure wrapped around the magnetic poles to enhance the fundamental flux and suppress the DC component of flux.Accordingly,the magnetizing current is reduced,and the isolation transformer is less susceptible to the DC bias.The proposed design can simultaneously improve the anti-DC magnetic bias capability,efficiency,and power factor of the transformers.To verify the effectiveness of the proposed design,a 10 kW C-core PNEMR structure-based transformer for isolation-dependent applications was constructed and compared to the generalized structures and transformers with planar negative magnetic reluctance structures.Results indicate that the PNEMR-based transformer can enhance the efficiency and power factor from 96.1%and 0.87 to 96.6%and 0.93,respectively,under full load conditions.
