In the recent experiment on HT-6M tokamak,an improved ohmic confinement phase has been observed after application of the edge multi-pulse turbulent heating,and variance of plasma currentΔI_(p)/I_(p) is about 14-20%;....In the recent experiment on HT-6M tokamak,an improved ohmic confinement phase has been observed after application of the edge multi-pulse turbulent heating,and variance of plasma currentΔI_(p)/I_(p) is about 14-20%;.The improved edge plasma confinement phase is characterized by(a)increased average electron density N_(e) and electron temperature T_(e);(b)reduced Hαradiation from the edge;(c)steeper density and temperature profiles at the edge;(d)a more negative radial electric field over a region of~5mm deep inside the limiter;(e)a deeper electrostatic potential well at the edge;(f)reduced magnetic fluctuations at the edge.展开更多
The ELMy H-mode plasmas realized with the supersonic molecular beam injection（SMBI） are studied in relation to the energy confinement and the heating power for the L–H transition（P_（L-H） ） in the HL-2A tokamak....The ELMy H-mode plasmas realized with the supersonic molecular beam injection（SMBI） are studied in relation to the energy confinement and the heating power for the L–H transition（P_（L-H） ） in the HL-2A tokamak. A database is assembled for this study based on the ELMy H-mode discharges during the experimental campaigns in the period 2009–2013at the HL-2A tokamak. The statistical results show that the SMBI is favourable for reaching the H-mode by reducing the heating power at the L–H transition and for the H-mode performance by improving the energy confinement compared with the ordinary gas puffing（GP）. The reduction of P_（L-H） is about 20% when the density is low, and the energy confinement enhancement factor of H_（H98y2）= τ_E/τ_（th,98y2） ≈ 1.5 is achieved with the SMBI. Note that in the database the density dependence of P_（L-H） is non-monotonic with the ˉne,min≈ 3×10^（19） m^（-3） at which the P_（L-H） is minimum. Most of P_（L-H） data are on the low density branch where the P_（L-H） increases with the decrease in density. The minimum of the P_（L-H） in HL-2A is comparable to the ITPA multi-machine threshold power scaling P_（thr_scal08）. The physics behind the reduction of the P_（L-H） with the SMBI is also investigated in relation to the change of the density gradient at the plasma edge, the gas fuelling efficiency, and the recycling.展开更多
The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta al...The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.展开更多
Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma.The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbu...Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma.The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbulent fluctuations.The measured fluctuation levels and wave action fluxes are in good agreement with model predictions by Mattor et al.,suggesting that drift wave propagation could be a source of edge turbulence.展开更多
The influence of m/n=2/1(m and n are poloidal and toroidal mode numbers)tearing modes on plasma perpendicular flows and micro-fluctuations has been investigated in HL-2A neutral beam injection heated L-mode plasmas.It...The influence of m/n=2/1(m and n are poloidal and toroidal mode numbers)tearing modes on plasma perpendicular flows and micro-fluctuations has been investigated in HL-2A neutral beam injection heated L-mode plasmas.It is found that the local perpendicular rotation velocity and turbulence energy are modulated by the alternation between the island X-point and O-point of the naturally rotating tearing modes.Cross-correlation analysis indicates that the modulation of density fluctuations by the tearing mode is not only limited to the island region,but also occurs in the edge region near the last closed flux surface.The turbulence exhibits distinct spectral characteristics inside and outside the island region.In addition,it is observed that the particle flux near the strike point is also significantly impacted by the tearing modes.The experimental evidence reveals that there are strong core-edge interactions between the core tearing modes and the edge transport.展开更多
Power spectrum and the probability distribution function(PDF)of the turbulence-induced particle fluxΓin the velocity shear layer of the HT-6M edge region have been measured and analysed.Three regions of frequency dep...Power spectrum and the probability distribution function(PDF)of the turbulence-induced particle fluxΓin the velocity shear layer of the HT-6M edge region have been measured and analysed.Three regions of frequency dependence(f0,f-1,f-4)have been observed in the spectrum of the flux.The PDF of the flux displays aΓ-1 scaling over one decade inΓ.Using the rescaled-range statistical technique,we find that the degree of the self-similarity(Hurst exponent)of the particle flux in the measured region ranges from 0.64 to 0.83.All of these results may mean that the plasma transport is in a state characterized by the self-organized criticality.展开更多
High spatial resolution measurements of the electrostatic Reynolds stress,radial electric field and poloidal phase velocity of fluctuations in the edge region of the HT-6M tokamak are carried out.The Reynolds stress s...High spatial resolution measurements of the electrostatic Reynolds stress,radial electric field and poloidal phase velocity of fluctuations in the edge region of the HT-6M tokamak are carried out.The Reynolds stress shows a radial gradient in proximity to the poloidal velocity shear.A comparison of the profiles between the Reynolds stress gradient and the poloidal velocity damping reveals some similarity in their magnitude and radial structure.These facts suggest that the turbulence-induced Reynolds stress may play a significant role in generating the poloidal flow in the plasma edge region.展开更多
Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed.All the spectra have three distinct frequency regions with the...Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed.All the spectra have three distinct frequency regions with the spectral decay indices typical of self-organized criticality systems(0,-1 and-4)when Doppler shift effects induced by the plasma E x B flow velocity have been taken into account.These results are consistent with the predictions of the self-organized criticality models,which may be an indication of edge plasma turbulence in the HT-6M tokamak evolving into a critical state independent of local plasma parameters.展开更多
Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak.The measured...Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak.The measured ion mode wavenumber,scaling of the ion mode with chord-averaged density,and the estimatedηi value suggest that the observed ion mode may be the theoretically predictedηi mode driven by ion temperature gradient.展开更多
The impact of the mass isotope on plasma conflnement and transport properties has been investigated in Ohmically-heated hydrogen and deuterium plasmas in the HL-2 A tokamak.Experimental results show that under similar...The impact of the mass isotope on plasma conflnement and transport properties has been investigated in Ohmically-heated hydrogen and deuterium plasmas in the HL-2 A tokamak.Experimental results show that under similar discharge parameters the deuterium plasma has better conflnement and lower turbulent transport than the hydrogen one,and concomitantly,it is found that the magnitude of geodesic acoustic mode zonal flows,the tilting angle of the Reynolds stress tensor and the turbulence correlation lengths are all larger in the edge region of the deuterium plasma.The results provide direct experimental evidence on the importance of the nonlinear energy coupling between ambient turbulence and zonal flows for governing the isotope effects in fusion plasmas.展开更多
The characteristics of the energy transfer and nonlinear coupling among edge electromagnetic turbulence in thermal quench sub-period of the internal reconnection event （IRE） are studied at the sino-united spherical ...The characteristics of the energy transfer and nonlinear coupling among edge electromagnetic turbulence in thermal quench sub-period of the internal reconnection event （IRE） are studied at the sino-united spherical tokamak device using multiple Langmuir and magnetic probe arrays. The wavelet bispectral analysis and the modified Kim method are applied to investigate linear growth/damping and nonlinear energy transfer rates, along with multi-field turbulence interactions. The results show a multi-field nonlinear energy transfer from electrostatic to magnetic turbulence that results in two-mode coupling in magnetic turbulence, which may play a crucial role to trigger the IRE.展开更多
On HL-2A,two different injections（supersonic molecular beam injection（SMBI）and pellet injection（PI）） are used to mitigate edge localized mode（ELM）-filament convective transport.The changes of their characteris...On HL-2A,two different injections（supersonic molecular beam injection（SMBI）and pellet injection（PI）） are used to mitigate edge localized mode（ELM）-filament convective transport.The changes of their characteristics are studied in this paper.A high spatiotemporal resolution probe shows there are many similar phenomena,and the filament density amplitude and radial velocity are both suppressed.Our statistical results indicate that：the velocity suppression comes from the decrease of filament density and temperature;the transient particle and heat fluxes drop strongly;and long-range correlation along a magnetic flux surface also decreases,when the electron-ion collisionality increases significantly,which may have a role on the filament parallel current during ELM mitigation.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No,19675041.
文摘In the recent experiment on HT-6M tokamak,an improved ohmic confinement phase has been observed after application of the edge multi-pulse turbulent heating,and variance of plasma currentΔI_(p)/I_(p) is about 14-20%;.The improved edge plasma confinement phase is characterized by(a)increased average electron density N_(e) and electron temperature T_(e);(b)reduced Hαradiation from the edge;(c)steeper density and temperature profiles at the edge;(d)a more negative radial electric field over a region of~5mm deep inside the limiter;(e)a deeper electrostatic potential well at the edge;(f)reduced magnetic fluctuations at the edge.
基金supported by the National Natural Science Foundation of China(Grant Nos.11375057 and 11175061)the National Magnetic Confinement Fusion Science Program,China(Grant Nos.2010GB102003 and 2014GB108003)
文摘The ELMy H-mode plasmas realized with the supersonic molecular beam injection（SMBI） are studied in relation to the energy confinement and the heating power for the L–H transition（P_（L-H） ） in the HL-2A tokamak. A database is assembled for this study based on the ELMy H-mode discharges during the experimental campaigns in the period 2009–2013at the HL-2A tokamak. The statistical results show that the SMBI is favourable for reaching the H-mode by reducing the heating power at the L–H transition and for the H-mode performance by improving the energy confinement compared with the ordinary gas puffing（GP）. The reduction of P_（L-H） is about 20% when the density is low, and the energy confinement enhancement factor of H_（H98y2）= τ_E/τ_（th,98y2） ≈ 1.5 is achieved with the SMBI. Note that in the database the density dependence of P_（L-H） is non-monotonic with the ˉne,min≈ 3×10^（19） m^（-3） at which the P_（L-H） is minimum. Most of P_（L-H） data are on the low density branch where the P_（L-H） increases with the decrease in density. The minimum of the P_（L-H） in HL-2A is comparable to the ITPA multi-machine threshold power scaling P_（thr_scal08）. The physics behind the reduction of the P_（L-H） with the SMBI is also investigated in relation to the change of the density gradient at the plasma edge, the gas fuelling efficiency, and the recycling.
基金supported by National Natural Science Foundation of China(No.11820101004)the National Key R&D Program of China(2017YFE0300100,2017YFE0301100)。
文摘The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.
基金Supported by the National Natural Science Foundation of China under Grant Nos.19675036,19635020the Doctoral Training Foundation of National Education Commission of China and Chinese Academy of Sciences.
文摘Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma.The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbulent fluctuations.The measured fluctuation levels and wave action fluxes are in good agreement with model predictions by Mattor et al.,suggesting that drift wave propagation could be a source of edge turbulence.
基金the National Key R&D Program of China(Nos.2017YFE0301201 and 2017YFE0301106)National Natural Science Foundation of China(Nos.11705051,11820101004,11875021 and 11775069)the Young Elite Scientists Sponsorship Program by CAST(No.2018QNRC001).
文摘The influence of m/n=2/1(m and n are poloidal and toroidal mode numbers)tearing modes on plasma perpendicular flows and micro-fluctuations has been investigated in HL-2A neutral beam injection heated L-mode plasmas.It is found that the local perpendicular rotation velocity and turbulence energy are modulated by the alternation between the island X-point and O-point of the naturally rotating tearing modes.Cross-correlation analysis indicates that the modulation of density fluctuations by the tearing mode is not only limited to the island region,but also occurs in the edge region near the last closed flux surface.The turbulence exhibits distinct spectral characteristics inside and outside the island region.In addition,it is observed that the particle flux near the strike point is also significantly impacted by the tearing modes.The experimental evidence reveals that there are strong core-edge interactions between the core tearing modes and the edge transport.
基金Supported by the National Natural Science Foundation of China under Grants Nos.19675036the Research Fund for the Doctoral Program of Higher Education(1999035809).
文摘Power spectrum and the probability distribution function(PDF)of the turbulence-induced particle fluxΓin the velocity shear layer of the HT-6M edge region have been measured and analysed.Three regions of frequency dependence(f0,f-1,f-4)have been observed in the spectrum of the flux.The PDF of the flux displays aΓ-1 scaling over one decade inΓ.Using the rescaled-range statistical technique,we find that the degree of the self-similarity(Hurst exponent)of the particle flux in the measured region ranges from 0.64 to 0.83.All of these results may mean that the plasma transport is in a state characterized by the self-organized criticality.
基金Supported by the National Natural Science Foundation of China under Grant Nos.19675036 and 19635020the Research Fund for the Doctoral Program of Higher Education。
文摘High spatial resolution measurements of the electrostatic Reynolds stress,radial electric field and poloidal phase velocity of fluctuations in the edge region of the HT-6M tokamak are carried out.The Reynolds stress shows a radial gradient in proximity to the poloidal velocity shear.A comparison of the profiles between the Reynolds stress gradient and the poloidal velocity damping reveals some similarity in their magnitude and radial structure.These facts suggest that the turbulence-induced Reynolds stress may play a significant role in generating the poloidal flow in the plasma edge region.
基金Sponsored by the National Natural Science Foundation of China under Grant Nos.19675036 and 19635020the Research Fund for the Doctoral Programme of Higher Education under Grant No.1999035809the Chinese Academy of China.
文摘Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed.All the spectra have three distinct frequency regions with the spectral decay indices typical of self-organized criticality systems(0,-1 and-4)when Doppler shift effects induced by the plasma E x B flow velocity have been taken into account.These results are consistent with the predictions of the self-organized criticality models,which may be an indication of edge plasma turbulence in the HT-6M tokamak evolving into a critical state independent of local plasma parameters.
基金Supported by the National Natural Science Foundation of China under Grant No.19275041the Doctoral Training Foundation of National Education Commission of China,and the Chinese Academy of Sciences.
文摘Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak.The measured ion mode wavenumber,scaling of the ion mode with chord-averaged density,and the estimatedηi value suggest that the observed ion mode may be the theoretically predictedηi mode driven by ion temperature gradient.
基金partially supported by National Natural Science Foundation of China(Nos.11820101004,11875017,12075079 and 51821005)partially supported by the National Key R&D Program of China(No.2019YFE03020000)+2 种基金the National Magnetic Conflnement Fusion Science Program of China(No.2018YFE0310300)the Science and Technology Plan Project in Sichuan Province of China(No.2020YFSY0047)Sichuan International Science and Technology Innovation Cooperation Project(No.2021YFH0066)。
文摘The impact of the mass isotope on plasma conflnement and transport properties has been investigated in Ohmically-heated hydrogen and deuterium plasmas in the HL-2 A tokamak.Experimental results show that under similar discharge parameters the deuterium plasma has better conflnement and lower turbulent transport than the hydrogen one,and concomitantly,it is found that the magnitude of geodesic acoustic mode zonal flows,the tilting angle of the Reynolds stress tensor and the turbulence correlation lengths are all larger in the edge region of the deuterium plasma.The results provide direct experimental evidence on the importance of the nonlinear energy coupling between ambient turbulence and zonal flows for governing the isotope effects in fusion plasmas.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11261140327,11325524,11475102 and11575057the Chinese National Fusion Project for ITER under Grant Nos 2013GB112001,2013GB107001 and 2014GB108000+1 种基金the Tsinghua University Initiative Scientific Research Programthe 221 Program
文摘The characteristics of the energy transfer and nonlinear coupling among edge electromagnetic turbulence in thermal quench sub-period of the internal reconnection event （IRE） are studied at the sino-united spherical tokamak device using multiple Langmuir and magnetic probe arrays. The wavelet bispectral analysis and the modified Kim method are applied to investigate linear growth/damping and nonlinear energy transfer rates, along with multi-field turbulence interactions. The results show a multi-field nonlinear energy transfer from electrostatic to magnetic turbulence that results in two-mode coupling in magnetic turbulence, which may play a crucial role to trigger the IRE.
基金supported by National Natural Science Foundation of China(Nos.11075046,10975049,11375054,11275060)the National Magnetic Confinement Fusion Science Program of China(Nos.2013GB112008,2013GB107000,2013GB104002,2014GB107000,2014GB108000)the China-Korean Joint Research Program(No.2012DFG02230)
文摘On HL-2A,two different injections（supersonic molecular beam injection（SMBI）and pellet injection（PI）） are used to mitigate edge localized mode（ELM）-filament convective transport.The changes of their characteristics are studied in this paper.A high spatiotemporal resolution probe shows there are many similar phenomena,and the filament density amplitude and radial velocity are both suppressed.Our statistical results indicate that：the velocity suppression comes from the decrease of filament density and temperature;the transient particle and heat fluxes drop strongly;and long-range correlation along a magnetic flux surface also decreases,when the electron-ion collisionality increases significantly,which may have a role on the filament parallel current during ELM mitigation.
