Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here...Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here,we report the preliminary diagnostic measurements after relative sensitivity calibration.The measurement results show a much higher temporal resolution compared with conventional CXRS,benefiting from the usage of a prismcoupled,high-dispersion volume-phase holographic transmission grating and a high quantum efficiency,high-gain detector array.Utilizing the UF-CXRS diagnostic,the fast evolutions of the ion temperature and rotation velocity during a set of high-frequency small-amplitude edgelocalized modes(ELMs)are obtained on the EAST tokamak,which are then compared with the case of large-amplitude ELMs.展开更多
The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the supe...The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.展开更多
In 2021,EAST realized a steady-state long pulse with a duration over 100 s and a core electron temperature over 10 keV.This is an integrated operation that resolves several key issues,including active control of wall ...In 2021,EAST realized a steady-state long pulse with a duration over 100 s and a core electron temperature over 10 keV.This is an integrated operation that resolves several key issues,including active control of wall conditioning,long-lasting fully noninductive current and divertor heat/particle flux.The fully noninductive current is driven by pure radio frequency(RF)waves with a lower hybrid current drive power of 2.5 MW and electron cyclotron resonance heating of 1.4 MW.This is an excellent experimental platform on the timescale of hundreds of seconds for studying multiscale instabilities,electron-dominant transport and particle recycling(plasma-wall interactions)under weak collisionality.展开更多
The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak,including the blob detection rate Nb,sizeδb,lifetimeτb and radial velocity vr,b.The blob proper...The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak,including the blob detection rate Nb,sizeδb,lifetimeτb and radial velocity vr,b.The blob properties in L-mode and I-mode are similar,and those in ELM-free H-mode are different to them.The blob Nbis smaller whileτbis larger in H-mode.The experimental blob sizeδband velocity scalings vr,b-δb show a good agreement with the theoretical models.The variation in blob properties during the L-I and H-L transitions,and their relations to the scrape-off layer(SOL)density,edge and SOL turbulence,and SOL collisionality are discussed.The suppression of the edge(inside the last closed flux surface)turbulence is not reflected in the blob behavior,while the blob detection rate shows a correlation with the SOL density and its low-frequency(3–50 kH z)fluctuations.In addition,the blob detection rate is found to increase with the divertor collisionalityΛdiv,indicating a dependence of blob behavior onΛdiv.The differences in blob detection rates among the three operating regimes might be due to their different SOL densities and collisionalities.The investigation contributes to understanding the influences of edge and SOL plasma parameters on the blob behavior.展开更多
A helicon wave plasma source in a tube of ring permanent magnets(PMs)has been constructed to study the effect of the conflguration of the magnetic fleld with zero magnetic points on plasma parameters.This device also ...A helicon wave plasma source in a tube of ring permanent magnets(PMs)has been constructed to study the effect of the conflguration of the magnetic fleld with zero magnetic points on plasma parameters.This device also serves as an exploration platform for a simple,compact helicon wave plasma source adaptable to engineering applications.A small-diameter(26 mm)highdensity(~10^(18)m^(-3))blue core plasma is produced in~1 Pa argon by helicon RF(radiofrequency)discharge using a NagoyaⅢantenna under magnetic fleld(~2 k G)of compact ring PMs(length~204 mm).Operational parameters,i.e.RF power and neutral gas pressure are scanned and plasma density is measured by an RF compensated probe to explore the operating characteristics of the device.Iconic feature of a helicon discharge,such as blue core plasmas and E-H-W mode transitions are well observed in the device,despite the wavelength calculated using the conventional dispersion relation of a bounded whistler waves(Chen 1991 Plasma Phys.Control.Fusion 33339)is order of magnitudes longer than the length of the plasma in this device which seems to suggest that such helicon device is impossible.Surprisingly,the wavelength calculated by the unbounded whistle wave dispersion formula in turn suggests the occurrence of a half wavelength resonance.展开更多
Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a u...Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a uniform,quiescent multi-dipole confined hot cathode discharge with two operation scenarios:one in which the probe sweeping frequency fsweepis much lower than the ion plasma frequency fpi,another one where fsweepis much greater than fpi,respectively.This allows investigation into the effect of limited ion-motion on I–V traces.Serious distortions of I–V traces at high frequencies,previously claimed to be an ion-motion limitation effect,were not found unless shunt resistance is sufficiently high,despite a f;/f;ratio of~3.On the other hand,evidences of sheath capacitance on the I–V traces have been observed.Distortions of I–V traces qualitatively agree with predictions of sheath capacitance response to the sweeping voltage.Additionally,techniques in fast sweep Langmuir probe are briefly discussed.The comparison between the high-speed dual Langmuir probe(HDLP)and the single probe setup shows that the capacitive response can be removed via subtracting a leakage current for the single probe setup almost as effectively as using the HDLP setup,but the HDLP setup does remain advantageous in its facilitation of better recovery of weak current signal commonly in low density plasma.展开更多
A major challenge facing the steady-state operation of tokamak fusion reactors is to develop a viable divertor solution with order-of-magnitude increase in power handling capability as compared with present experience...A major challenge facing the steady-state operation of tokamak fusion reactors is to develop a viable divertor solution with order-of-magnitude increase in power handling capability as compared with present experience.A recently developed divertor concept for this end has been tested recently on EAST tokamak through combining the effects of a closed divertor corner and E×B drifts.The E×B drifts in the divertor move particles towards the outer divertor corner area in the scrape-off layer for B×▽B directed away from the divertor,which can significantly enhance the particle concentration there,facilitating divertor detachment.In recent EAST experiments,the effects have been demonstrated where the lowest electron temperature at the divertor plate is obtained with strike point located close to the corner in the horizontal target and with B×▽B away from the divertor.These experimental results are in reasonable agreement with SOLPS-ITER simulations including drift effects,suggesting that the new divertor concept potentially provides a promising divertor solution for long-pulse operations of future tokamak fusion reactors with much higher power fluxes.展开更多
This paper reviews the current state of understanding of the L-H transition phenomenon in tokamak plasmas with a focus on two central issues： （a） the mechanism for turbulence quick suppression at the L-H transitio...This paper reviews the current state of understanding of the L-H transition phenomenon in tokamak plasmas with a focus on two central issues： （a） the mechanism for turbulence quick suppression at the L-H transition; （b） the mechanism for subsequent generation of sheared flow. We briefly review recent advances in the understanding of the fast suppression of edge turbulence across the L-H transition. We uncover a comprehensive physical picture of the L-H transition by piecing together a number of recent experimental observations and insights obtained from 1D and 2D simulation models. Different roles played by diamagnetic mean flow, neoclassical-driven mean flow, turbulence-driven mean flow, and turbulence-driven zonal flows are discussed and clarified. It is found that the L-H transition occurs spontaneously mediated by a shift in the radial wavenumber spectrum of edge turbulence, which provides a critical evidence for the theory of turbulence quench by the flow shear. Remaining questions and some key directions for future investigations are proposed.展开更多
An algorithm for automated fitting of the effective electron temperature from a planar Langmuir probe I-V trace taken in a plasma with multiple Maxwellian electron populations is developed through MATLAB coding.The co...An algorithm for automated fitting of the effective electron temperature from a planar Langmuir probe I-V trace taken in a plasma with multiple Maxwellian electron populations is developed through MATLAB coding.The code automatically finds a fitting range suitable for analyzing the temperatures of each of the electron populations.The algorithm is used to analyzeⅠ-Ⅴtraces from both the Institute of Plasma Physics Chinese Academy of Sciences's Diagnostic Test Source device and a similar multi-dipole chamber at the University of Wisconsin-Madison.Ⅰ-Ⅴtraces reconstructed from the parameters fitted by the algorithm not only agree with the measured I-V trace but also reveal physical properties consistent with those found in previous studies.Cylindrical probe traces are also analyzed with the algorithm and it is shown that the major source of error in such attempts is the disruption of the inflection point due to both decreased signal-to-noise ratio and greater sheath expansion.It is thus recommended to use planar probes with radii much greater than the plasma Debye length when signal-to-noise ratio is poor.展开更多
In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（E...In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（EIPT） has been developed.With the typical plasma parameters of the EAST tokamak,the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability,which indicates that the L-H transition can be caused by the stabilization of the edge instability through EIPT.The weak E？×？B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures,which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport.With the acceleration mechanism of E？×？B flow shear,fast L-H and H-L transitions are demonstrated under the control of the input heating power.Due to the simplified scrape-offlayer boundary condition applied,the ratio between the heating powers at the H-L and L-H transition respectively differs from the ratio by Nusselt number.The results of the modeling reveal a scaling of the power threshold of the L-H transition,P_（L-H）？∝？n^（0.76） B^（0.8） for deuterium plasma.It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.展开更多
Neon(Ne)seeding is used to cool the edge plasma by radiation to protect the divertor tungsten(W)target in the Experimental Advanced Superconducting Tokamak(EAST).The W sputtering in the outer divertor target with Ne s...Neon(Ne)seeding is used to cool the edge plasma by radiation to protect the divertor tungsten(W)target in the Experimental Advanced Superconducting Tokamak(EAST).The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system.It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature.After reaching a maximum around 25 eV,the W sputtering rate starts to decrease,presenting a suppression effect.The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed.The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering.Moreover,ELM suppression is observed when Ne and W impurities enter the core plasma,which could be correlated to the enhanced turbulence transport in the pedestal.展开更多
We find that the perturbed Lagrangian derived from the drift-kinetic equation in[Porcelli F et al 1994 Phys.Plasmas 1470]is inconsistent with the ordering for the low-frequency large-scale magnetohydrodynamic(MHD).Her...We find that the perturbed Lagrangian derived from the drift-kinetic equation in[Porcelli F et al 1994 Phys.Plasmas 1470]is inconsistent with the ordering for the low-frequency large-scale magnetohydrodynamic(MHD).Here,we rederive the expression for the perturbed Lagrangian within the framework of nonideal MHD using the ordering system for the low-frequency largescale MHD in a low-beta plasma.The obtained perturbed Lagrangian is consistent with Chen's gyrokinetic theory[Chen L and Zonca F 2016 Rev.Mod.Phys.88015008],where the terms related to the field curvature and gradient are small quantities of higher order and thus negligible.As the perturbed Lagrangian has been widely used in the literature to calculate the plasma nonadiabatic response in low-frequency MHD applications,this finding may have a significant impact on the understanding of the kinetic driving and dissipative mechanisms of MHD instabilities and the plasma response to electromagnetic perturbations in fusion plasmas.展开更多
In this article,the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes(ADLPs).Recent...In this article,the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes(ADLPs).Recent theoretical and experimental studies have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications for satellite-based Langmuir probes.The effects predicted by the latest theory of the electron Bohm criterion were not experimentally observed and the experimental results remain supportive of a critical area ratio(A_(L)/A_(S))_(crit)=(m_(i)/(2.3m_(e)))^(1/2)between the probe area A_(S)and the satellite area A_L as conventionally believed.A satellite-based Langmuir probe must satisfy this criterion to physically act as a single Langmuir probe.However,experimental investigations also found that high-energy electrons adversely affect(A_(L)/A_(S))_(crit)and a Langmuir probe's signal quality by giving additional electron current to A_(L).Based on these results,a number of limitations of the maximum probe area are derived when designing satellite-based Langmuir probes,with consideration of both the aim of the satellite and the plasma where the satellite-based probe works.These proposed measures are expected to only partially alleviate the effect of the inadequate satellite surface area on the application of satellite-based Langmuir probes.Using a larger satellite to carry a Langmuir probe remains the most viable means to obtain precise space plasma parameters.展开更多
Detachment in helium(He)discharges has been achieved in the EAST superconducting tokamak equipped with an ITER-like tungsten divertor.This paper presents the experimental observations of divertor detachment achieved b...Detachment in helium(He)discharges has been achieved in the EAST superconducting tokamak equipped with an ITER-like tungsten divertor.This paper presents the experimental observations of divertor detachment achieved by increasing the plasma density in He discharges.During density ramp-up,the particle flux shows a clear rollover,while the electron temperature around the outer strike point is decreasing simultaneously.The divertor detachment also exhibits a significant difference from that observed in comparable deuterium(D)discharges.The density threshold of detachment in the He plasma is higher than that in the D plasma for the same heating power,and increases with the heating power.Moreover,detachment assisted with neon(Ne)seeding was also performed in L-and H-mode plasmas,pointing to the direction for reducing the density threshold of detachment in He operation.However,excessive Ne seeding causes confinement degradation during the divertor detachment phase.The precise feedback control of impurity seeding will be performed in EAST to improve the compatibility of core plasma performance with divertor detachment for future high heating power operations.展开更多
Lithium Beam Emission Spectroscopy systems in the outer midplane and divertor Langmuir probe arrays embedded in the divertor target plates,are utilized to investigate the scrape-off layer(SOL)blob transition and its r...Lithium Beam Emission Spectroscopy systems in the outer midplane and divertor Langmuir probe arrays embedded in the divertor target plates,are utilized to investigate the scrape-off layer(SOL)blob transition and its relation with divertor detachment on EAST.The blob transition in the near SOL is observed during the density ramp-up phase.When the plasma density,normalized to the Greenwald density limit,exceeds a threshold of f_(GW)~0.5,the blob size and lifetime increases by 2–3 times,while the blob detection rate decreases by about 2 times.In addition,a weak density shoulder is observed in the near SOL region at the same density threshold.Further analysis indicates that the divertor detachment is highly correlated with the blob transition,and the density threshold of blob transition is consistent with that of the access to the outer divertor detachment.The potential physical mechanisms are discussed.These results could be useful for the understanding of plasma-wall interaction issues in future devices that will operate under a detached divertor and high density conditions(over the blob transition threshold).展开更多
Accurate and stable measurements of edge density fluctuation with high spatio-temporal resolution have been achieved by the lithium beam emission spectroscopy(Li-BES)diagnostic on experimental and advanced superconduc...Accurate and stable measurements of edge density fluctuation with high spatio-temporal resolution have been achieved by the lithium beam emission spectroscopy(Li-BES)diagnostic on experimental and advanced superconducting tokamak(EAST).The new narrower band interference filter exhibits good ability to suppress background emission signal even under strong lithium coating of the tokamak.The raw data measured by channels at different spatial locations in avalanche photo diode camera with high chopping frequency show good consistency.Based on the detected experimental data,detailed information of density profile and fluctuation structures is obtained.A clear edge coherent mode in the auto-power spectrum is observed in pedestal region,which is regarded as the dominant factor for the strong pedestal density fluctuation amplitude.The cross-power spectrum analysis further excludes the additional effects of common-mode noises and non-local perturbation,demonstrating that the detected fluctuation is only caused by local density fluctuation.The normalized radial and poloidal wave-number spectra can specify the quantitative changes of radial wavenumber(k_(r))and poloidal wavenumber(k_(θ)) during the pedestal density fluctuation phase.This new Li-BES system,which can provide more accurate experimental data,allows further studies of edge density fluctuation and complex transport process on EAST.展开更多
The properties of grassy edge-localized modes(ELMs)in EAST in the favorable and unfavorable Btare statistically studied.Statistical analysis indicates that there is no systematical difference in the frequencies of gra...The properties of grassy edge-localized modes(ELMs)in EAST in the favorable and unfavorable Btare statistically studied.Statistical analysis indicates that there is no systematical difference in the frequencies of grassy ELMs under the two different magnetic configurations in the similar parameter spaces.The high-frequency grassy ELM(fELM>1 k Hz)in unfavorable Bt is dependent on the high poloidal betaβpand high triangularityδu,while the high-frequency grassy ELM(fELM>1k Hz)in favorable Btappears to rely on the high plasma density.A frequently occurring phenomenon in favorable Btdefined as‘clustered ELM’seems to be the most evident difference in ELM behavior between favorable and unfavorable Bt.Statistical analysis shows that larger plasma-wall outer gap,longer plasma elongation,lower low-hybrid wave heating power and electron cyclotron resonance heating power favor the occurrence of clustered grassy ELMs.Further studies indicate that the generation of clustered grassy ELMs could be correlated with the lower electron temperature in the bulk plasma.展开更多
Detailed investigations on the filamentary structures associated with the type-I edge-localized modes（ELMs） should be helpful for protecting the materials of a plasma-facing wall on a future large device.Related exp...Detailed investigations on the filamentary structures associated with the type-I edge-localized modes（ELMs） should be helpful for protecting the materials of a plasma-facing wall on a future large device.Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak（EAST） using combined Langmuir-magnetic probes.The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 kms^（-1） in the far scrape-off layer（SOL） region.It is remarkable that the electron temperature of these filaments is detected to be ~50eV,corresponding to a fraction of 1/6 to the temperature near the pedestal top,while the density ~3×10^（19）m^（-3） of these filaments could be approximate to the line-averaged density.In addition,associated magnetic fluctuations have been clearly observed at the same time,which show good agreement with the density perturbations.A localized current on the order of ~100kA could be estimated within the filaments.展开更多
The microwave reflectometer is a popular non-intrusive plasma density diagnostic instrument on tokamaks that provides centimeter and millisecond level resolution.The ultrashort-pulse reflectometer(USPR)achieves plasma...The microwave reflectometer is a popular non-intrusive plasma density diagnostic instrument on tokamaks that provides centimeter and millisecond level resolution.The ultrashort-pulse reflectometer(USPR)achieves plasma density measurement by emitting a chirped wave containing a broadband signal and measuring the time of flight from different frequency components.A USPR system is currently being built on EAST(Experimental Advanced Superconducting Tokamak)to meet the needs of diagnostic of the pedestal density evolution,such as high-frequency small edge-localized modes.In order to predict the density reconstruction of the EAST USPR system,this work presents a numerical simulation study of the beam propagation of the chirped wave of extraordinary waves(X-mode)in the plasma based on Python.The electron density profile has been successfully reconstructed by the reflection signal interpretation.The small gap between the right-hand cut-off layer and the electron cyclotron resonance layer,due to the low plasma density on the plasma edge,causes unexpected leakage from the transmitting microwave beam to the pedestal and the core region.This kind of‘tunneling’effect will cause the reflected signal to have energy loss in the low-frequency band.The study also discusses the influence of the poloidal magnetic field on the reflected signal.The spatial variation of the poloidal magnetic field will lead to the conversion between extraordinary(X)waves and ordinary(O)waves,which leads to energy loss in the reflected signals.The simulation results show that the‘tunneling’effect and the O-X mode conversion effect have little effect on the EAST USPR system.Therefore,the currently designed transmit power meets the working requirements.展开更多
The essential role of zonal flow in the L-H transition and the suppression of turbulence have been studied with a long range correlation technique using Langmuir probe arrays in EAST tokamak.Two toroidally localized p...The essential role of zonal flow in the L-H transition and the suppression of turbulence have been studied with a long range correlation technique using Langmuir probe arrays in EAST tokamak.Two toroidally localized probe arrays are used to measure the zonal flow during L-H transition and H-L back transition.The energy ratio of the low frequency zonal flow to the total drift wave turbulence is calculated.During ELM-free H mode,the energy ratio is higher than that in L mode,which reveals the important role of zonal flows in regulating turbulence amplitude in L-H transition.展开更多
基金supported by the National Magnetic Confinement Fusion Science Program of China (No. 2019YFE 03030004)National Natural Science Foundation of China (Nos. 11535013 and 11975232)
文摘Ultrafast charge exchange recombination spectroscopy(UF-CXRS)has been developed on the EAST tokamak(Yingying Li et al 2019 Fusion Eng.Des.146522)to measure fast evolutions of ion temperature and toroidal velocity.Here,we report the preliminary diagnostic measurements after relative sensitivity calibration.The measurement results show a much higher temporal resolution compared with conventional CXRS,benefiting from the usage of a prismcoupled,high-dispersion volume-phase holographic transmission grating and a high quantum efficiency,high-gain detector array.Utilizing the UF-CXRS diagnostic,the fast evolutions of the ion temperature and rotation velocity during a set of high-frequency small-amplitude edgelocalized modes(ELMs)are obtained on the EAST tokamak,which are then compared with the case of large-amplitude ELMs.
基金provided by the National Natural Science Foundation of China Youth Found of China (No.41102169)the doctoral foundation of Henan Polytechnic University of China (No. B2014-056)
文摘The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.
基金the National Key R&D Program of China(No.2022YFE03010003)National Natural Science Foundation of China(No.12275309).
文摘In 2021,EAST realized a steady-state long pulse with a duration over 100 s and a core electron temperature over 10 keV.This is an integrated operation that resolves several key issues,including active control of wall conditioning,long-lasting fully noninductive current and divertor heat/particle flux.The fully noninductive current is driven by pure radio frequency(RF)waves with a lower hybrid current drive power of 2.5 MW and electron cyclotron resonance heating of 1.4 MW.This is an excellent experimental platform on the timescale of hundreds of seconds for studying multiscale instabilities,electron-dominant transport and particle recycling(plasma-wall interactions)under weak collisionality.
基金supported by the National Key R&D Program of China(Nos.2022YFE03020004,2017YFE0301300,2018YFE0303104 and 2019YFE03030000)the Major Science and Technology Infrastructure Maintenance and Reconstruction Projects of the Chinese Academy of Sciences+3 种基金National Natural Science Foundation of China(Nos.12275313,11922513,12005004 and U19A20113)the Institute of Energy,Hefei Comprehensive National Science Center(No.GXXT-2020-004)the Anhui Provincial Natural Science Foundation(No.2008085QA38)the Users with Excellence Program of Hefei Science Center,Chinese Academy of Sciences(No.2020HSC-UE009)。
文摘The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak,including the blob detection rate Nb,sizeδb,lifetimeτb and radial velocity vr,b.The blob properties in L-mode and I-mode are similar,and those in ELM-free H-mode are different to them.The blob Nbis smaller whileτbis larger in H-mode.The experimental blob sizeδband velocity scalings vr,b-δb show a good agreement with the theoretical models.The variation in blob properties during the L-I and H-L transitions,and their relations to the scrape-off layer(SOL)density,edge and SOL turbulence,and SOL collisionality are discussed.The suppression of the edge(inside the last closed flux surface)turbulence is not reflected in the blob behavior,while the blob detection rate shows a correlation with the SOL density and its low-frequency(3–50 kH z)fluctuations.In addition,the blob detection rate is found to increase with the divertor collisionalityΛdiv,indicating a dependence of blob behavior onΛdiv.The differences in blob detection rates among the three operating regimes might be due to their different SOL densities and collisionalities.The investigation contributes to understanding the influences of edge and SOL plasma parameters on the blob behavior.
基金supported by National Natural Science Foundation of China(No.U19A20113)。
文摘A helicon wave plasma source in a tube of ring permanent magnets(PMs)has been constructed to study the effect of the conflguration of the magnetic fleld with zero magnetic points on plasma parameters.This device also serves as an exploration platform for a simple,compact helicon wave plasma source adaptable to engineering applications.A small-diameter(26 mm)highdensity(~10^(18)m^(-3))blue core plasma is produced in~1 Pa argon by helicon RF(radiofrequency)discharge using a NagoyaⅢantenna under magnetic fleld(~2 k G)of compact ring PMs(length~204 mm).Operational parameters,i.e.RF power and neutral gas pressure are scanned and plasma density is measured by an RF compensated probe to explore the operating characteristics of the device.Iconic feature of a helicon discharge,such as blue core plasmas and E-H-W mode transitions are well observed in the device,despite the wavelength calculated using the conventional dispersion relation of a bounded whistler waves(Chen 1991 Plasma Phys.Control.Fusion 33339)is order of magnitudes longer than the length of the plasma in this device which seems to suggest that such helicon device is impossible.Surprisingly,the wavelength calculated by the unbounded whistle wave dispersion formula in turn suggests the occurrence of a half wavelength resonance.
基金supported by National Natural Science Foundation of China(No.11875285)the CAS Key Research Program of Frontier Sciences(No.QYZDB-SSWSLH001)the Chinese Academy of Science Hundred Youth Talent Program。
文摘Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a uniform,quiescent multi-dipole confined hot cathode discharge with two operation scenarios:one in which the probe sweeping frequency fsweepis much lower than the ion plasma frequency fpi,another one where fsweepis much greater than fpi,respectively.This allows investigation into the effect of limited ion-motion on I–V traces.Serious distortions of I–V traces at high frequencies,previously claimed to be an ion-motion limitation effect,were not found unless shunt resistance is sufficiently high,despite a f;/f;ratio of~3.On the other hand,evidences of sheath capacitance on the I–V traces have been observed.Distortions of I–V traces qualitatively agree with predictions of sheath capacitance response to the sweeping voltage.Additionally,techniques in fast sweep Langmuir probe are briefly discussed.The comparison between the high-speed dual Langmuir probe(HDLP)and the single probe setup shows that the capacitive response can be removed via subtracting a leakage current for the single probe setup almost as effectively as using the HDLP setup,but the HDLP setup does remain advantageous in its facilitation of better recovery of weak current signal commonly in low density plasma.
基金funded by the National Magnetic Confinement Fusion Program of China(Nos.2019YFE03030000,2019YFE03080500 and 2022YFE03060004)National Natural Science Foundation of China(No.U19A20113)。
文摘A major challenge facing the steady-state operation of tokamak fusion reactors is to develop a viable divertor solution with order-of-magnitude increase in power handling capability as compared with present experience.A recently developed divertor concept for this end has been tested recently on EAST tokamak through combining the effects of a closed divertor corner and E×B drifts.The E×B drifts in the divertor move particles towards the outer divertor corner area in the scrape-off layer for B×▽B directed away from the divertor,which can significantly enhance the particle concentration there,facilitating divertor detachment.In recent EAST experiments,the effects have been demonstrated where the lowest electron temperature at the divertor plate is obtained with strike point located close to the corner in the horizontal target and with B×▽B away from the divertor.These experimental results are in reasonable agreement with SOLPS-ITER simulations including drift effects,suggesting that the new divertor concept potentially provides a promising divertor solution for long-pulse operations of future tokamak fusion reactors with much higher power fluxes.
文摘This paper reviews the current state of understanding of the L-H transition phenomenon in tokamak plasmas with a focus on two central issues： （a） the mechanism for turbulence quick suppression at the L-H transition; （b） the mechanism for subsequent generation of sheared flow. We briefly review recent advances in the understanding of the fast suppression of edge turbulence across the L-H transition. We uncover a comprehensive physical picture of the L-H transition by piecing together a number of recent experimental observations and insights obtained from 1D and 2D simulation models. Different roles played by diamagnetic mean flow, neoclassical-driven mean flow, turbulence-driven mean flow, and turbulence-driven zonal flows are discussed and clarified. It is found that the L-H transition occurs spontaneously mediated by a shift in the radial wavenumber spectrum of edge turbulence, which provides a critical evidence for the theory of turbulence quench by the flow shear. Remaining questions and some key directions for future investigations are proposed.
基金This work is supported by the Chinese Academy of Science Hundred Youth Talent Program Start-up Funding,CAS Key Research Program of Frontier Sciences(No.QYZDB-SSW-SLH001)National Natural Science Foundation of China(Nos.11875285,11575248 and 11505220)well as US National Science Foundation Award(No.1804654).
文摘An algorithm for automated fitting of the effective electron temperature from a planar Langmuir probe I-V trace taken in a plasma with multiple Maxwellian electron populations is developed through MATLAB coding.The code automatically finds a fitting range suitable for analyzing the temperatures of each of the electron populations.The algorithm is used to analyzeⅠ-Ⅴtraces from both the Institute of Plasma Physics Chinese Academy of Sciences's Diagnostic Test Source device and a similar multi-dipole chamber at the University of Wisconsin-Madison.Ⅰ-Ⅴtraces reconstructed from the parameters fitted by the algorithm not only agree with the measured I-V trace but also reveal physical properties consistent with those found in previous studies.Cylindrical probe traces are also analyzed with the algorithm and it is shown that the major source of error in such attempts is the disruption of the inflection point due to both decreased signal-to-noise ratio and greater sheath expansion.It is thus recommended to use planar probes with radii much greater than the plasma Debye length when signal-to-noise ratio is poor.
基金supported by National Natural Science Foundation of China under Contract Nos.11575235 and 11422546China Postdoctoral Science Foundation under Contract No.2016M602043+2 种基金the National Magnetic Confinement Fusion Science Program of China under Contract No.2015GB101002Key Research Program of Frontier Sciences,CAS,Grant No.QYZDB-SSW-SLH001K C Wong Education Foundation
文摘In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（EIPT） has been developed.With the typical plasma parameters of the EAST tokamak,the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability,which indicates that the L-H transition can be caused by the stabilization of the edge instability through EIPT.The weak E？×？B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures,which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport.With the acceleration mechanism of E？×？B flow shear,fast L-H and H-L transitions are demonstrated under the control of the input heating power.Due to the simplified scrape-offlayer boundary condition applied,the ratio between the heating powers at the H-L and L-H transition respectively differs from the ratio by Nusselt number.The results of the modeling reveal a scaling of the power threshold of the L-H transition,P_（L-H）？∝？n^（0.76） B^（0.8） for deuterium plasma.It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.
基金supported by the National Key Research and Development Program of China(Grant Nos.2017YFE0301300,2017YFA0402500,and 2018YFE0303103)the National Natural Science Foundation of China(Grant Nos.12192283 and 12022511)+3 种基金the Users with Excellence Project of Hefei Science Center,CAS(Grant No.2018HSC-UE008)the CASHIPS Director’s Fund(Grant No.BJPY2019B01)the JSPS-CAS Bilateral Joint Research Project(Grant No.GJHZ201984)the Key Research Program of Frontier Sciences of CAS(Grant No.ZDBS-LY-SLH010)。
文摘Neon(Ne)seeding is used to cool the edge plasma by radiation to protect the divertor tungsten(W)target in the Experimental Advanced Superconducting Tokamak(EAST).The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system.It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature.After reaching a maximum around 25 eV,the W sputtering rate starts to decrease,presenting a suppression effect.The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed.The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering.Moreover,ELM suppression is observed when Ne and W impurities enter the core plasma,which could be correlated to the enhanced turbulence transport in the pedestal.
基金supported by the National Magnetic Confinement Fusion Energy Program of China(No.2019YFE03030000)National Natural Science Foundation of China(Nos.11905253 and U19A20113)。
文摘We find that the perturbed Lagrangian derived from the drift-kinetic equation in[Porcelli F et al 1994 Phys.Plasmas 1470]is inconsistent with the ordering for the low-frequency large-scale magnetohydrodynamic(MHD).Here,we rederive the expression for the perturbed Lagrangian within the framework of nonideal MHD using the ordering system for the low-frequency largescale MHD in a low-beta plasma.The obtained perturbed Lagrangian is consistent with Chen's gyrokinetic theory[Chen L and Zonca F 2016 Rev.Mod.Phys.88015008],where the terms related to the field curvature and gradient are small quantities of higher order and thus negligible.As the perturbed Lagrangian has been widely used in the literature to calculate the plasma nonadiabatic response in low-frequency MHD applications,this finding may have a significant impact on the understanding of the kinetic driving and dissipative mechanisms of MHD instabilities and the plasma response to electromagnetic perturbations in fusion plasmas.
基金supported by National Natural Science Foundation of China(Nos.12275305 and 12205334)the Chinese Academy of Science Hundred Youth Talent Program+1 种基金China Postdoctoral Science Foundation(No.2022M713188)the Director’s Fund of Hefei Institutes of Physical Science,Chinese Academy of Sciences(No.YZJJ2022QN19)。
文摘In this article,the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes(ADLPs).Recent theoretical and experimental studies have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications for satellite-based Langmuir probes.The effects predicted by the latest theory of the electron Bohm criterion were not experimentally observed and the experimental results remain supportive of a critical area ratio(A_(L)/A_(S))_(crit)=(m_(i)/(2.3m_(e)))^(1/2)between the probe area A_(S)and the satellite area A_L as conventionally believed.A satellite-based Langmuir probe must satisfy this criterion to physically act as a single Langmuir probe.However,experimental investigations also found that high-energy electrons adversely affect(A_(L)/A_(S))_(crit)and a Langmuir probe's signal quality by giving additional electron current to A_(L).Based on these results,a number of limitations of the maximum probe area are derived when designing satellite-based Langmuir probes,with consideration of both the aim of the satellite and the plasma where the satellite-based probe works.These proposed measures are expected to only partially alleviate the effect of the inadequate satellite surface area on the application of satellite-based Langmuir probes.Using a larger satellite to carry a Langmuir probe remains the most viable means to obtain precise space plasma parameters.
基金supported by the National Key Research and Development Program of China(Nos.2017YFA0301300,2017YFE0402500 and 2019YFE03030000)National Natural Science Foundation of China(Nos.11905255,12005004,12022511,U1867222 and U19A20113)+3 种基金the Institute of Energy,Hefei Comprehensive National Science Center(No.GXXT-2020-004)AHNSF(No.2008085QA38)the CASHIPS Director’s Fund(No.BJPY2019B01)the Key Research Program of Frontier Sciences of CAS(No.ZDBS-LY-SLH010)。
文摘Detachment in helium(He)discharges has been achieved in the EAST superconducting tokamak equipped with an ITER-like tungsten divertor.This paper presents the experimental observations of divertor detachment achieved by increasing the plasma density in He discharges.During density ramp-up,the particle flux shows a clear rollover,while the electron temperature around the outer strike point is decreasing simultaneously.The divertor detachment also exhibits a significant difference from that observed in comparable deuterium(D)discharges.The density threshold of detachment in the He plasma is higher than that in the D plasma for the same heating power,and increases with the heating power.Moreover,detachment assisted with neon(Ne)seeding was also performed in L-and H-mode plasmas,pointing to the direction for reducing the density threshold of detachment in He operation.However,excessive Ne seeding causes confinement degradation during the divertor detachment phase.The precise feedback control of impurity seeding will be performed in EAST to improve the compatibility of core plasma performance with divertor detachment for future high heating power operations.
基金supported by the National Key R&D Program of China(Nos.2017YFE0301300,2017YFA0402500,2019YFE03030000)Institute of Energy,Hefei Comprehensive National Science Center(Nos.GXXT2020004,12105187)+2 种基金National Natural Science Foundation of China(Nos.11922513,U19A20113,11905255,12005004)Anhui Provincial Natural Science Foundation(No.2008085QA38)China Postdoctoral Science Foundation(No.2021M702245)。
文摘Lithium Beam Emission Spectroscopy systems in the outer midplane and divertor Langmuir probe arrays embedded in the divertor target plates,are utilized to investigate the scrape-off layer(SOL)blob transition and its relation with divertor detachment on EAST.The blob transition in the near SOL is observed during the density ramp-up phase.When the plasma density,normalized to the Greenwald density limit,exceeds a threshold of f_(GW)~0.5,the blob size and lifetime increases by 2–3 times,while the blob detection rate decreases by about 2 times.In addition,a weak density shoulder is observed in the near SOL region at the same density threshold.Further analysis indicates that the divertor detachment is highly correlated with the blob transition,and the density threshold of blob transition is consistent with that of the access to the outer divertor detachment.The potential physical mechanisms are discussed.These results could be useful for the understanding of plasma-wall interaction issues in future devices that will operate under a detached divertor and high density conditions(over the blob transition threshold).
基金supported by the National Key R&D Program of China(Nos.2017YFA0301300,2019YFE03030000)National Natural Science Foundation of China(Nos.11805238,11775264,11922513,U19A20113,11905255,12005004)+1 种基金Anhui Provincial Natural Science Foundation(No.2008085QA38)Institute of Energy,Hefei Comprehensive National Science Center(No.GXXT-2020-004)。
文摘Accurate and stable measurements of edge density fluctuation with high spatio-temporal resolution have been achieved by the lithium beam emission spectroscopy(Li-BES)diagnostic on experimental and advanced superconducting tokamak(EAST).The new narrower band interference filter exhibits good ability to suppress background emission signal even under strong lithium coating of the tokamak.The raw data measured by channels at different spatial locations in avalanche photo diode camera with high chopping frequency show good consistency.Based on the detected experimental data,detailed information of density profile and fluctuation structures is obtained.A clear edge coherent mode in the auto-power spectrum is observed in pedestal region,which is regarded as the dominant factor for the strong pedestal density fluctuation amplitude.The cross-power spectrum analysis further excludes the additional effects of common-mode noises and non-local perturbation,demonstrating that the detected fluctuation is only caused by local density fluctuation.The normalized radial and poloidal wave-number spectra can specify the quantitative changes of radial wavenumber(k_(r))and poloidal wavenumber(k_(θ)) during the pedestal density fluctuation phase.This new Li-BES system,which can provide more accurate experimental data,allows further studies of edge density fluctuation and complex transport process on EAST.
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China(No.2017YFE0301300)National Natural Science Foundation of China(Nos.12005257 and 11905143)+1 种基金the Key Research Program of Frontier Sciences,the CASHIPS Director’s Fund(No.YZJJ2020QN13)Special Research Assistant Funding of CAS and China Postdoctoral Science Foundation(No.2020M671913)。
文摘The properties of grassy edge-localized modes(ELMs)in EAST in the favorable and unfavorable Btare statistically studied.Statistical analysis indicates that there is no systematical difference in the frequencies of grassy ELMs under the two different magnetic configurations in the similar parameter spaces.The high-frequency grassy ELM(fELM>1 k Hz)in unfavorable Bt is dependent on the high poloidal betaβpand high triangularityδu,while the high-frequency grassy ELM(fELM>1k Hz)in favorable Btappears to rely on the high plasma density.A frequently occurring phenomenon in favorable Btdefined as‘clustered ELM’seems to be the most evident difference in ELM behavior between favorable and unfavorable Bt.Statistical analysis shows that larger plasma-wall outer gap,longer plasma elongation,lower low-hybrid wave heating power and electron cyclotron resonance heating power favor the occurrence of clustered grassy ELMs.Further studies indicate that the generation of clustered grassy ELMs could be correlated with the lower electron temperature in the bulk plasma.
基金supported by National Natural Science Foundation of China under Contracts Nos.11275047,11705128,11422546,11575235,11575236 and 11505222Key Research Program of Frontier Sciences,CAS,Grant No.QYZDB-SSWSLH001National Magnetic Confinement Fusion Science Program of China under Contract Nos.2015GB101000 and 2013GB107003
文摘Detailed investigations on the filamentary structures associated with the type-I edge-localized modes（ELMs） should be helpful for protecting the materials of a plasma-facing wall on a future large device.Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak（EAST） using combined Langmuir-magnetic probes.The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 kms^（-1） in the far scrape-off layer（SOL） region.It is remarkable that the electron temperature of these filaments is detected to be ~50eV,corresponding to a fraction of 1/6 to the temperature near the pedestal top,while the density ~3×10^（19）m^（-3） of these filaments could be approximate to the line-averaged density.In addition,associated magnetic fluctuations have been clearly observed at the same time,which show good agreement with the density perturbations.A localized current on the order of ~100kA could be estimated within the filaments.
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China(No.2019YFE03030004)National Natural Science Foundation of China(No.12005144)。
文摘The microwave reflectometer is a popular non-intrusive plasma density diagnostic instrument on tokamaks that provides centimeter and millisecond level resolution.The ultrashort-pulse reflectometer(USPR)achieves plasma density measurement by emitting a chirped wave containing a broadband signal and measuring the time of flight from different frequency components.A USPR system is currently being built on EAST(Experimental Advanced Superconducting Tokamak)to meet the needs of diagnostic of the pedestal density evolution,such as high-frequency small edge-localized modes.In order to predict the density reconstruction of the EAST USPR system,this work presents a numerical simulation study of the beam propagation of the chirped wave of extraordinary waves(X-mode)in the plasma based on Python.The electron density profile has been successfully reconstructed by the reflection signal interpretation.The small gap between the right-hand cut-off layer and the electron cyclotron resonance layer,due to the low plasma density on the plasma edge,causes unexpected leakage from the transmitting microwave beam to the pedestal and the core region.This kind of‘tunneling’effect will cause the reflected signal to have energy loss in the low-frequency band.The study also discusses the influence of the poloidal magnetic field on the reflected signal.The spatial variation of the poloidal magnetic field will lead to the conversion between extraordinary(X)waves and ordinary(O)waves,which leads to energy loss in the reflected signals.The simulation results show that the‘tunneling’effect and the O-X mode conversion effect have little effect on the EAST USPR system.Therefore,the currently designed transmit power meets the working requirements.
基金the EAST team for their support during the experimentssupported by the National Natural Science Foundation of China with Grant Nos.10990210,10990211,11375188,11105144,and 11375053+1 种基金the National Magnetic Confinement Fusion Science Program of China under Contracts Nos.2013GB106002, 2013GB106003the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology with Grant No.2014FXCX003
文摘The essential role of zonal flow in the L-H transition and the suppression of turbulence have been studied with a long range correlation technique using Langmuir probe arrays in EAST tokamak.Two toroidally localized probe arrays are used to measure the zonal flow during L-H transition and H-L back transition.The energy ratio of the low frequency zonal flow to the total drift wave turbulence is calculated.During ELM-free H mode,the energy ratio is higher than that in L mode,which reveals the important role of zonal flows in regulating turbulence amplitude in L-H transition.
