MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear...MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear density ramp experiment, interchange-like MHD modes whoserational surface is located very close to the last closed flux surface are strongly excited in acertain discharge condition and affect the plasma transport appreciably. In NBI-heated plasmasproduced at low toroidal field, various Alfven eigenmodes are often excited. Bursting toroidalAlfven egenmodes excited by the presence of energetic ions induce appreciable amount of energeticion loss, but also trigger the formation of internal and edge transport barriers.展开更多
Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were...Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago,and these plasma physical concepts have been central in discussions of substorm physics.A vast amount of research on reconnection,including both theoretical and computational studies,has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere.Still,however,we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection.While in the last twenty years,it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions,we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon.More than two decades ago it was suggested that the ballooning instability,the basic theory for which dates from the 1950s,may play an important role in substorms.Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning.However,it is also clear that kinetic effects introduce important modifications to the MHD stability criterion.It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part.Among the different types of simulations that have been applied to the substorm problem,global MHD codes are unique in that,in a sense, they represent the entire global substorm phenomenon,including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection,interchange,and ballooning.However,they have not yet progressed to the point where they can accurately represent the whole phenomenon,because grid-resolution problems limit the accuracy with which they can solve the equations of ideal MHD and the couphng to the ionosphere,and they cannot accurately represent small-scale processes that violate ideal MHD.展开更多
Stabilization of the axisymmetric magnetic mirror relies on the pressure-weighted magnetic field curvature.We report a new experiment by configuring a magnetic cusp structure to stabilize m=1 interchange mode in the K...Stabilization of the axisymmetric magnetic mirror relies on the pressure-weighted magnetic field curvature.We report a new experiment by configuring a magnetic cusp structure to stabilize m=1 interchange mode in the KMAX tandem mirror.The cusp configuration is formed by reversing currents in the two side cell coils,and a stronger cusp can lead to a more stable plasma once the null point of the cusp is less than 35–40 cm away from the device axis.The density fluctuations measured by four axial Langmuir probes are mitigated by 70%–80%.The stabilization effect is consistent with the prediction of a theoretical calculation.展开更多
Biogas from renewable sources and natural gas(NG) are both high-efficient and good-quality gaseous fuels on account of their enrichment in methane. Due to the dissimilar physical properties of biogas and NG, biogas ca...Biogas from renewable sources and natural gas(NG) are both high-efficient and good-quality gaseous fuels on account of their enrichment in methane. Due to the dissimilar physical properties of biogas and NG, biogas cannot substitute NG directly without treatment and is usually used on site due to the high cost of the transportation and distribution via exclusive pipeline system. Consequently, the injection of biogas into existing NG infrastructure was proposed to address the deficiency. In this paper, the Wobbe index (WI) as well as the combustion potential (CP) were introduced for analyzing the interchangeability of an NGbiogas mixture, and a mathematical framework was put forward for modeling and simulating NG grid with a decentralized biogas injection. Results show that the maximum admissible amount of biogas in mixture was 10.5% by volume. A medium pressure network was used to interrogate the comprehensive effect of distributed biogas injection, which showed an impact on both gas quality and hydraulic regime across the grid.展开更多
基金The project supported by the Core-University Program between Japan and China on Plasmas and Nuclear Fusion, and a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science
文摘MHD stability of the Large Helical Device (LHD) plasmas produced with intenseneutral beam injection is experimentally studied. When the steep pressure gradient near the edge isproduced through L-H transition or linear density ramp experiment, interchange-like MHD modes whoserational surface is located very close to the last closed flux surface are strongly excited in acertain discharge condition and affect the plasma transport appreciably. In NBI-heated plasmasproduced at low toroidal field, various Alfven eigenmodes are often excited. Bursting toroidalAlfven egenmodes excited by the presence of energetic ions induce appreciable amount of energeticion loss, but also trigger the formation of internal and edge transport barriers.
基金supported by the NASA Heliospheric Theory Program under grant NNX08AI55G
文摘Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago,and these plasma physical concepts have been central in discussions of substorm physics.A vast amount of research on reconnection,including both theoretical and computational studies,has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere.Still,however,we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection.While in the last twenty years,it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions,we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon.More than two decades ago it was suggested that the ballooning instability,the basic theory for which dates from the 1950s,may play an important role in substorms.Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning.However,it is also clear that kinetic effects introduce important modifications to the MHD stability criterion.It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part.Among the different types of simulations that have been applied to the substorm problem,global MHD codes are unique in that,in a sense, they represent the entire global substorm phenomenon,including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection,interchange,and ballooning.However,they have not yet progressed to the point where they can accurately represent the whole phenomenon,because grid-resolution problems limit the accuracy with which they can solve the equations of ideal MHD and the couphng to the ionosphere,and they cannot accurately represent small-scale processes that violate ideal MHD.
基金the National Key R&D Program of China(No.2017YFE0301802)National Natural Science Foundation of China(No.12175226).
文摘Stabilization of the axisymmetric magnetic mirror relies on the pressure-weighted magnetic field curvature.We report a new experiment by configuring a magnetic cusp structure to stabilize m=1 interchange mode in the KMAX tandem mirror.The cusp configuration is formed by reversing currents in the two side cell coils,and a stronger cusp can lead to a more stable plasma once the null point of the cusp is less than 35–40 cm away from the device axis.The density fluctuations measured by four axial Langmuir probes are mitigated by 70%–80%.The stabilization effect is consistent with the prediction of a theoretical calculation.
基金Funded by China 12th Five-year Plan Key R&D Program(2013BAJ11B05)
文摘Biogas from renewable sources and natural gas(NG) are both high-efficient and good-quality gaseous fuels on account of their enrichment in methane. Due to the dissimilar physical properties of biogas and NG, biogas cannot substitute NG directly without treatment and is usually used on site due to the high cost of the transportation and distribution via exclusive pipeline system. Consequently, the injection of biogas into existing NG infrastructure was proposed to address the deficiency. In this paper, the Wobbe index (WI) as well as the combustion potential (CP) were introduced for analyzing the interchangeability of an NGbiogas mixture, and a mathematical framework was put forward for modeling and simulating NG grid with a decentralized biogas injection. Results show that the maximum admissible amount of biogas in mixture was 10.5% by volume. A medium pressure network was used to interrogate the comprehensive effect of distributed biogas injection, which showed an impact on both gas quality and hydraulic regime across the grid.
