A nonlinear saturation mechanism for reversed shear Alfvén eigenmode(RSAE)is proposed and analyzed,and is shown to be of relevance to typical reactor parameter region.The saturation is achieved through the genera...A nonlinear saturation mechanism for reversed shear Alfvén eigenmode(RSAE)is proposed and analyzed,and is shown to be of relevance to typical reactor parameter region.The saturation is achieved through the generation of high-frequency quasi-mode due to nonlinear coupling of two RSAEs,which is then damped due to coupling with the shear Alfvén continuum,and leads to the nonlinear saturation of the primary RSAEs.An estimation of the nonlinear damping rate is also provided.展开更多
In a tokamak fusion reactor operated at steady state,the equilibrium magnetic field is likely to have reversed shear in the core region,as the noninductive bootstrap current profile generally peaks off-axis.The revers...In a tokamak fusion reactor operated at steady state,the equilibrium magnetic field is likely to have reversed shear in the core region,as the noninductive bootstrap current profile generally peaks off-axis.The reversed shear Alfvén eigenmode(RSAE)as a unique branch of the shear Alfvén wave in this equilibrium,can exist with a broad spectrum in wavenumber and frequency,and be resonantly driven unstable by energetic particles(EP).After briefly discussing the RSAE linear properties in burning plasma condition,we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels,and illustrate their potentially important role in reactor-scale fusion plasmas.By means of simplified hybrid MHD-kinetic simulations,the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP,as results of weak/vanishing magnetic shear and relatively low frequency.Through the route of wave-EP nonlinearity,the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure,and the resultant EP transport generally has a convective feature.The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations.Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory,and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE.Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode,which may effectively transfer the EP energy to fuel ions via collisionless Landau damping.Moreover,zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope,and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.展开更多
The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sag...The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sagdeev technique was employed,and an energy equation was derived.Our findings show that the proposed system reveals the existence of a double-layer solution,periodic,supersoliton,and superperiodic waves.The phase portrait and potential analysis related to these waves were investigated to study the main features of existing waves.It was also found that decreasing the electron temperature helps the superperiodic structure to be excited in our plasma model.Our results help interpret the nonlinear and supernonlinear features of the recorded Alfvén waves propagating in the ionosphere D-region.展开更多
The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclo...The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclotron instability driven by ion temperature anisotropy in a kappa plasma.By solving the kinetic linear dispersion equation,we explore the sensitivity of growth rates to the spectral indexκof a bi-kappa distribution under different plasma conditions,including a variety of plasma beta β_(hp) and temperature anisotropy A_(hp) values of hot protons.Furthermore,a concise,analytic scaling formula is derived that relates the dimensionless maximum growth rate to three independent variables:the spectral index and the plasma beta and temperature anisotropy of hot protons.Our results show that as theκ-value increases,the instability bandwidth narrows and the maximum growth rate increases significantly.For higherβ_(hp)and A_(hp)′the maximum instability undergoes a sharp increase as well.When our fits of dimensionless maximum growth rates are compared with solutions to kinetic linear dispersion theory,the results generally exhibit good agreement between them.Especially under the circumstances of largeκ-values and highβ_(hp)and A_(hp)′the scalings of maximum growth rates primarily accurately model the numerical solutions.Our analytic expressions can readily be used in large-scale models of the Earth’s magnetosphere to understand wave generation due to the Alfvén-cyclotron instability.展开更多
Nonlinear evolution of multiple toroidal Alfven eigenmodes(TAEs) driven by fast ions is self-consistently investigated by kinetic simulations in toroidal plasmas.To clearly identify the effect of nonlinear coupling on...Nonlinear evolution of multiple toroidal Alfven eigenmodes(TAEs) driven by fast ions is self-consistently investigated by kinetic simulations in toroidal plasmas.To clearly identify the effect of nonlinear coupling on the beam ion loss,simulations over single-n modes are also carried out and compared with those over multiple-n modes,and the wave-particle resonance and particle trajectory of lost ions in phase space are analyzed in detail.It is found that in the multiple-n case,the resonance overlap occurs so that the fast ion loss level is rather higher than the sum loss level that represents the summation of loss over all single-n modes in the single-n case.Moreover,increasing fast ion beta β_h can not only significantly increase the loss level in the multiple-n case but also significantly increase the loss level increment between the single-n and multiple-n cases.For example,the loss level in the multiple-n case for β_h=6.0% can even reach 13% of the beam ions and is 44% higher than the sum loss level calculated from all individual single-n modes in the single-n case.On the other hand,when the closely spaced resonance overlap occurs in the multiple-n case,the release of mode energy is increased so that the widely spaced resonances can also take place.In addition,phase space characterization is obtained in both single-n and multiple-n cases.展开更多
Using the data of ULF/ELF electric and magnetic wave field measured on board AUREOL-3 satellite, by the high resolution spectral analyses, one obtained for the first time the spatial measurement on the evidence of ion...Using the data of ULF/ELF electric and magnetic wave field measured on board AUREOL-3 satellite, by the high resolution spectral analyses, one obtained for the first time the spatial measurement on the evidence of ionospheric alfvén resonator. The result of the measurement indicates that there are 7. 8 Hz for fundamental frequency, 14 Hz for second resonant frequency in the electric field component, and also the spectral resonance structure, but not in the magnetic vertical component for the magnetic field components.展开更多
Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency...Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency chirping down process can be completed within-1 ms,and the frequency shift can reach 30-50 kHz.The CMs propagate in ion diamagnetic drift directions poloidally.The toroidal mode number is confirmed to be n=1,2,3 and 4 for the f-35-65,55-90,70-120 and 100-150 kHz CMs,respectively.The CMs are more like to be energetic-particle continuum modes(EPMs),since the modes almost locate on the Alfven continuum.展开更多
As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanet...As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection （ICME） is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv@nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present an observation of Alfv@n waves in a magnetic cloud （MC） near 1 AU, in situ detected by WIND in February 17,-~20, 2011. The MC was generated by a CME accompanied with the first X-class flare in the 24th solar cycle. The slope of the power spectral densities of magnetic fluctuation in the MC, are similar to those modes in ambient solar wind, but more anisotropic. The results will also be helpful for studies of CME theories and ICME thermodynamics.展开更多
At the Earth＇s magnetopause, the electron transport due to kinetic Alfvén waves（KAWs） is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° ...At the Earth＇s magnetopause, the electron transport due to kinetic Alfvén waves（KAWs） is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves,as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.展开更多
The hybrid scenario is a projection for CFETR operation with high plasma current and density.Therefore, the energetic particles(EPs) generated by fusion reactions can destabilize Alfvén eigenmodes(AEs), which cou...The hybrid scenario is a projection for CFETR operation with high plasma current and density.Therefore, the energetic particles(EPs) generated by fusion reactions can destabilize Alfvén eigenmodes(AEs), which could result in significant EPs loss and redistribution. Both the eigenvalue code NOVA-K and the wrapped local stability code TGLFEP are used to analyze AE stability. The simulation indicates the beta-induced Alfvén eigenmodes with n?>?5 in the core region are the most unstable. The NOVA-K code is used to benchmark the critical density gradient calculated by TGLFEP. In addition, the EPtran code is employed to predict EP transport induced by unstable AEs and turbulence, which reduce EP density in the core and drive approximately 30% EP transport from the core to the edge, thus the EP density profile flattens and EPs with lower energy deposit near the edge.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
In the presence of energetic particles(EPs)from auxiliary heating and burning plasmas,fishbone instability and Alfvén modes can be excited and their transition can take place in certain overlapping regimes.Using ...In the presence of energetic particles(EPs)from auxiliary heating and burning plasmas,fishbone instability and Alfvén modes can be excited and their transition can take place in certain overlapping regimes.Using the hybrid kinetic-magnetohydrodynamic model in the NIMROD code,we have identified such a transition between the fishbone instability and theβ-induced Alfvén eigenmode(BAE)for the NBI heated plasmas on HL-2 A.When the safety factor at magnetic axis is well below one,typical kink-fishbone transition occurs as the EP fraction increases.When q0 is raised to approaching one,the fishbone mode is replaced with BAE for sufficient amount of EPs.When q0 is slightly above one,the toroidicity-induced Alfvén eigenmode dominates at lower EP pressure,whereas BAE dominates at higher EP pressure.展开更多
The kinetic excitation of ideal magnetohydrodynamic （MHD） Alfvén instabilities is investigated for operations at the EAST tokamak. The instabilities include α-induced toroidal Alfvén eigenmodes （αTAE; h...The kinetic excitation of ideal magnetohydrodynamic （MHD） Alfvén instabilities is investigated for operations at the EAST tokamak. The instabilities include α-induced toroidal Alfvén eigenmodes （αTAE; here, α =-q2 Rdβ/dr, with q being the safety factor, β the ratio between the plasma and magnetic pressures, R the major radius, and r the minor radius）, toroidicity-induced Alfvén eigenmodes （TAE）, and the energetic particle continuum mode （EPM）. The αTAE, trapped by α-induced potential wells along the magnetic field line, can be readily destabilized by energetic particles due to negligible continuum damping via wave energy tunneling. It is shown for the geometry and the parameters similar to those of the EAST equilibrium that αTAE is different not only from the EPM by the potential-well determined frequency, but also from the TAE by the broad frequency spectrum outside the toroidal frequency gap.展开更多
Most protons in the solar wind belong to one of two different populations,the less dense beam protons and the denser core protons.The beam protons,with a velocity of(1-2)V_(A)(V_(A)is the local Alfvén speed),alwa...Most protons in the solar wind belong to one of two different populations,the less dense beam protons and the denser core protons.The beam protons,with a velocity of(1-2)V_(A)(V_(A)is the local Alfvén speed),always drift relative to the core protons;this kind of distribution is unstable and stimulates several kinds of wave mode.In this study,using a 2 D hybrid simulation model,we find that the original right-handed elliptically polarized Alfvén waves become linearly polarized,and eventually become right-handed and circularly polarized.Given that linearly polarized waves are a superposition of left-handed and right-handed waves,cyclotron resonance in the right-handed/left-handed component heats beam/core protons perpendicularly.The resonance between beam protons and right-handed polarized waves is stronger when the beam relative density is lower,resulting in more dramatic perpendicular heating of beam protons,whereas the situation is reversed when the beam relative density is larger.展开更多
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB0790000)the Collaborative Innovation Program of Hefei Science Center,CAS(No.2022HSC-CIP008)National Natural Science Foundation of China(Nos.12275236 and 12261131622)。
文摘A nonlinear saturation mechanism for reversed shear Alfvén eigenmode(RSAE)is proposed and analyzed,and is shown to be of relevance to typical reactor parameter region.The saturation is achieved through the generation of high-frequency quasi-mode due to nonlinear coupling of two RSAEs,which is then damped due to coupling with the shear Alfvén continuum,and leads to the nonlinear saturation of the primary RSAEs.An estimation of the nonlinear damping rate is also provided.
基金supported by National Natural Science Foundation of China (Nos. 12205251, 12275236 and 12261131622)Italian Ministry for Foreign Affairs and International Cooperation Project (No. CN23GR02)+2 种基金the National Key Research and Development Program of China (Nos. 2019YFE03020003 and 2017YFE0301900)Users of Excellence program of Hefei Science Center CAS (No. 2021HSC-UE016)funded by the European Union via the Euratom Research and Training Programme (No. 101052200–EUROfusion)
文摘In a tokamak fusion reactor operated at steady state,the equilibrium magnetic field is likely to have reversed shear in the core region,as the noninductive bootstrap current profile generally peaks off-axis.The reversed shear Alfvén eigenmode(RSAE)as a unique branch of the shear Alfvén wave in this equilibrium,can exist with a broad spectrum in wavenumber and frequency,and be resonantly driven unstable by energetic particles(EP).After briefly discussing the RSAE linear properties in burning plasma condition,we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels,and illustrate their potentially important role in reactor-scale fusion plasmas.By means of simplified hybrid MHD-kinetic simulations,the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP,as results of weak/vanishing magnetic shear and relatively low frequency.Through the route of wave-EP nonlinearity,the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure,and the resultant EP transport generally has a convective feature.The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations.Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory,and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE.Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode,which may effectively transfer the EP energy to fuel ions via collisionless Landau damping.Moreover,zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope,and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.
文摘The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sagdeev technique was employed,and an energy equation was derived.Our findings show that the proposed system reveals the existence of a double-layer solution,periodic,supersoliton,and superperiodic waves.The phase portrait and potential analysis related to these waves were investigated to study the main features of existing waves.It was also found that decreasing the electron temperature helps the superperiodic structure to be excited in our plasma model.Our results help interpret the nonlinear and supernonlinear features of the recorded Alfvén waves propagating in the ionosphere D-region.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.42204163,42188101,42025404,42241143,41774167,41774171,41974205,41804157,41904156,42130204,and 42241133)the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)+3 种基金the National Key R&D Program of China(Grant Nos.2022YFF0503700 and 2022YFF0503900)the pre-research projects on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administrationthe Macao Foundation,the Fundamental Research Funds for the Central Universities(Grant No.2042022kf1012the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001).TieLong Zhang was supported by the Chinese Academy of Sciences Center for Excellence in Comparative Planetology.
文摘The particle velocity distribution in space plasma usually exhibits a non-Maxwellian high-energy tail that can be well modeled by kappa distributions.In this study,we focus on the growth rates of the Alfvén-cyclotron instability driven by ion temperature anisotropy in a kappa plasma.By solving the kinetic linear dispersion equation,we explore the sensitivity of growth rates to the spectral indexκof a bi-kappa distribution under different plasma conditions,including a variety of plasma beta β_(hp) and temperature anisotropy A_(hp) values of hot protons.Furthermore,a concise,analytic scaling formula is derived that relates the dimensionless maximum growth rate to three independent variables:the spectral index and the plasma beta and temperature anisotropy of hot protons.Our results show that as theκ-value increases,the instability bandwidth narrows and the maximum growth rate increases significantly.For higherβ_(hp)and A_(hp)′the maximum instability undergoes a sharp increase as well.When our fits of dimensionless maximum growth rates are compared with solutions to kinetic linear dispersion theory,the results generally exhibit good agreement between them.Especially under the circumstances of largeκ-values and highβ_(hp)and A_(hp)′the scalings of maximum growth rates primarily accurately model the numerical solutions.Our analytic expressions can readily be used in large-scale models of the Earth’s magnetosphere to understand wave generation due to the Alfvén-cyclotron instability.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFE0301900)the National Natural Science Foundation of China(Grant No.11675083)the Fundamental Research Funds for the Central Universities of China(Grant No.DUT18ZD101).
文摘Nonlinear evolution of multiple toroidal Alfven eigenmodes(TAEs) driven by fast ions is self-consistently investigated by kinetic simulations in toroidal plasmas.To clearly identify the effect of nonlinear coupling on the beam ion loss,simulations over single-n modes are also carried out and compared with those over multiple-n modes,and the wave-particle resonance and particle trajectory of lost ions in phase space are analyzed in detail.It is found that in the multiple-n case,the resonance overlap occurs so that the fast ion loss level is rather higher than the sum loss level that represents the summation of loss over all single-n modes in the single-n case.Moreover,increasing fast ion beta β_h can not only significantly increase the loss level in the multiple-n case but also significantly increase the loss level increment between the single-n and multiple-n cases.For example,the loss level in the multiple-n case for β_h=6.0% can even reach 13% of the beam ions and is 44% higher than the sum loss level calculated from all individual single-n modes in the single-n case.On the other hand,when the closely spaced resonance overlap occurs in the multiple-n case,the release of mode energy is increased so that the widely spaced resonances can also take place.In addition,phase space characterization is obtained in both single-n and multiple-n cases.
文摘Using the data of ULF/ELF electric and magnetic wave field measured on board AUREOL-3 satellite, by the high resolution spectral analyses, one obtained for the first time the spatial measurement on the evidence of ionospheric alfvén resonator. The result of the measurement indicates that there are 7. 8 Hz for fundamental frequency, 14 Hz for second resonant frequency in the electric field component, and also the spectral resonance structure, but not in the magnetic vertical component for the magnetic field components.
基金Supported by the National Key R&D Program of China (Grant Nos.2018YFE0304102,2019YFE03020000 and 2017YFE0301202)the National Natural Science Foundation of China (Grant Nos.11875024,11875021,11835010 and 12005054)the Sichuan Provincial Science and Technology Project (Grant Nos.2020YFSY0047 and 2020JDJQ0070)。
文摘Multiple broadband Alfvenic chirping modes(CMs),with frequencies in the wide range of f-35-150 kHz and chirping down rapidly,are found in HL-2A neutral beam injection plasmas,and the CMs can even coexist.The frequency chirping down process can be completed within-1 ms,and the frequency shift can reach 30-50 kHz.The CMs propagate in ion diamagnetic drift directions poloidally.The toroidal mode number is confirmed to be n=1,2,3 and 4 for the f-35-65,55-90,70-120 and 100-150 kHz CMs,respectively.The CMs are more like to be energetic-particle continuum modes(EPMs),since the modes almost locate on the Alfven continuum.
基金supported by National Natural Science Foundation of China (Nos.40974104,40731056,and 10975012)Doctoral Fund of Ministry of Education of China (20090001110012)National Key Basic Research Science Foundation of China (2011CB811400,2009GB105004)
文摘As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection （ICME） is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv@nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present an observation of Alfv@n waves in a magnetic cloud （MC） near 1 AU, in situ detected by WIND in February 17,-~20, 2011. The MC was generated by a CME accompanied with the first X-class flare in the 24th solar cycle. The slope of the power spectral densities of magnetic fluctuation in the MC, are similar to those modes in ambient solar wind, but more anisotropic. The results will also be helpful for studies of CME theories and ICME thermodynamics.
基金Supported by the National Natural Science Foundation of China under Grant Nos 41474145,41574159,41731070 and 41504114the Frontier Science Foundation of the Chinese Academy of Sciences under Grant No QYZDJ-SSW-JSC028+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDA15052500the Specialized Research Fund for State Key Laboratories of China
文摘At the Earth＇s magnetopause, the electron transport due to kinetic Alfvén waves（KAWs） is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves,as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.
基金supported by National Natural Science Foundation of China (Grant No. 11535013)the National Key Research and Development Program of China (Grant Nos. 2017YFA0402500 and 2018YFE0302101)
文摘The hybrid scenario is a projection for CFETR operation with high plasma current and density.Therefore, the energetic particles(EPs) generated by fusion reactions can destabilize Alfvén eigenmodes(AEs), which could result in significant EPs loss and redistribution. Both the eigenvalue code NOVA-K and the wrapped local stability code TGLFEP are used to analyze AE stability. The simulation indicates the beta-induced Alfvén eigenmodes with n?>?5 in the core region are the most unstable. The NOVA-K code is used to benchmark the critical density gradient calculated by TGLFEP. In addition, the EPtran code is employed to predict EP transport induced by unstable AEs and turbulence, which reduce EP density in the core and drive approximately 30% EP transport from the core to the edge, thus the EP density profile flattens and EPs with lower energy deposit near the edge.
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supported by the National Magnetic Confinement Fusion Science Program of China(No.2019YFE03050004)National Natural Science Foundation of China(Nos.11875253,11775221,51821005)+3 种基金the Fundamental Research Funds for the Central Universities at University of Science and Technology of China(No.WK3420000004)Huazhong University of Science and Technology(No.2019kfy XJJS193)the Collaborative Innovation Program of Hefei Science Center,CAS(No.2019HSC-CIP015)the U.S.Department of Energy(Nos.DE-FG02-86ER53218 and DE-SC0018001)。
文摘In the presence of energetic particles(EPs)from auxiliary heating and burning plasmas,fishbone instability and Alfvén modes can be excited and their transition can take place in certain overlapping regimes.Using the hybrid kinetic-magnetohydrodynamic model in the NIMROD code,we have identified such a transition between the fishbone instability and theβ-induced Alfvén eigenmode(BAE)for the NBI heated plasmas on HL-2 A.When the safety factor at magnetic axis is well below one,typical kink-fishbone transition occurs as the EP fraction increases.When q0 is raised to approaching one,the fishbone mode is replaced with BAE for sufficient amount of EPs.When q0 is slightly above one,the toroidicity-induced Alfvén eigenmode dominates at lower EP pressure,whereas BAE dominates at higher EP pressure.
基金supported by National Natural Science Foundation of China(Nos.10975039,10975160,11175211)
文摘The kinetic excitation of ideal magnetohydrodynamic （MHD） Alfvén instabilities is investigated for operations at the EAST tokamak. The instabilities include α-induced toroidal Alfvén eigenmodes （αTAE; here, α =-q2 Rdβ/dr, with q being the safety factor, β the ratio between the plasma and magnetic pressures, R the major radius, and r the minor radius）, toroidicity-induced Alfvén eigenmodes （TAE）, and the energetic particle continuum mode （EPM）. The αTAE, trapped by α-induced potential wells along the magnetic field line, can be readily destabilized by energetic particles due to negligible continuum damping via wave energy tunneling. It is shown for the geometry and the parameters similar to those of the EAST equilibrium that αTAE is different not only from the EPM by the potential-well determined frequency, but also from the TAE by the broad frequency spectrum outside the toroidal frequency gap.
基金supported by National Natural Science Foundation of China(Nos.11822401,41674177 and 41874208).
文摘Most protons in the solar wind belong to one of two different populations,the less dense beam protons and the denser core protons.The beam protons,with a velocity of(1-2)V_(A)(V_(A)is the local Alfvén speed),always drift relative to the core protons;this kind of distribution is unstable and stimulates several kinds of wave mode.In this study,using a 2 D hybrid simulation model,we find that the original right-handed elliptically polarized Alfvén waves become linearly polarized,and eventually become right-handed and circularly polarized.Given that linearly polarized waves are a superposition of left-handed and right-handed waves,cyclotron resonance in the right-handed/left-handed component heats beam/core protons perpendicularly.The resonance between beam protons and right-handed polarized waves is stronger when the beam relative density is lower,resulting in more dramatic perpendicular heating of beam protons,whereas the situation is reversed when the beam relative density is larger.
