We conducted 2-D particle-in-cell simulations to investigate the impact of boundary conditions on the evolution of magnetic reconnection. The results demonstrate that the boundary conditions are crucial to this evolut...We conducted 2-D particle-in-cell simulations to investigate the impact of boundary conditions on the evolution of magnetic reconnection. The results demonstrate that the boundary conditions are crucial to this evolution. Specifically, in the cases of traditional periodic boundary(PB) and fully-opened boundary(OB) conditions, the evolutions are quite similar before the system achieves the fastest reconnection rate. However, differences emerge between the two cases afterward. In the PB case, the reconnection electric field experiences a rapid decline and even becomes negative, indicating a reversal of the reconnection process. In contrast, the system maintains a fast reconnection stage in the OB case. Suprathermal electrons are generated near the separatrix and in the exhaust region of both simulation cases. In the electron density depletion layer and the dipolarization front region, a larger proportion of suprathermal electrons are produced in the OB case. Medium-energy electrons are mainly located in the vicinity of the X-line and downstream of the reconnection site in both cases. However, in the OB case, they can also be generated in the electron holes along the separatrix. Before the reverse reconnection stage, no high-energy electrons are present in the PB case. In contrast, about 20% of the electrons in the thin and elongated electron current layer are high-energy in the OB case.展开更多
The kinetics of plasma during the process of Petschek mode magnetic reconnection is studied based on a two-dimensional hybrid code. It has been found that the acceleration of particles inside the reconnection layer is...The kinetics of plasma during the process of Petschek mode magnetic reconnection is studied based on a two-dimensional hybrid code. It has been found that the acceleration of particles inside the reconnection layer is highly anisotropy. Few particles are accelerated along field lines to a very high energy, while the bulk of the plasma remains in a relatively low velocity. We have pointed out that such a new picture of energy distribution in particles can be used to explain the formation of highly energized particle beams observed in space.展开更多
Single-photon flux is one of the crucial properties of nitrogen vacancy （NV） centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the singl...Single-photon flux is one of the crucial properties of nitrogen vacancy （NV） centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the single-photon count rate. Through the interaction between tightly confined optical mode in nanowires and NV centers, the single-photon lifetime is much shortened and the collection efficiency is enhanced. As a result, the detected single-photon rate can be at 564 kcps, and the total detection coefficient can be 0.8%, which is much higher than that in bulk diamond. Such a nanowire single-photon device with high photon flux can be applied to improve the fidelity of quantum computation and the precision of quantum sensors.展开更多
火星感应磁层边界的等离子体不稳定性,如边界层处速度剪切激发的Kelvin-Helmholtz(K-H)不稳定性,对火星感应磁层结构和磁层离子输运过程具有重要的影响.本文利用Mars Atmosphere and Volatile EvolutioN(MAVEN)卫星搭载的Magnetometer(M...火星感应磁层边界的等离子体不稳定性,如边界层处速度剪切激发的Kelvin-Helmholtz(K-H)不稳定性,对火星感应磁层结构和磁层离子输运过程具有重要的影响.本文利用Mars Atmosphere and Volatile EvolutioN(MAVEN)卫星搭载的Magnetometer(MAG)和Super Thermal and Thermal Ion Composition(STATIC)仪器所提供的磁场和等离子数据,分析了2018年5月21日火星感应磁层边界处观测到的K-H不稳定性事件,发现在磁场、重离子通量、离子成分与密度、和离子速度上存在五个连续的准周期变化,估算K-H波的周期为~100 s,同时在其中两个K-H涡旋内发现了磁通量绳结构.磁通量绳的轴向方向与边界层法向准垂直,且其中的离子成分与涡旋内电离层等离子体成分接近,表明此处的磁通量绳有可能是在K-H波的发展过程中形成.磁通量绳的整体速度也远大于此处的离子逃逸速度,这可能导致重离子O^(+)和O_(2)^(+)从火星大气中快速逃逸.展开更多
基金the support from the Key Research Program of the Chinese Academy of Sciences(No.ZDBSSSW-TLC00105)the National Key R&D Program of China(No.2022YFF0503200)+1 种基金National Natural Science Foundation of China(Nos.41974173 and 42274224)the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.2019066)。
文摘We conducted 2-D particle-in-cell simulations to investigate the impact of boundary conditions on the evolution of magnetic reconnection. The results demonstrate that the boundary conditions are crucial to this evolution. Specifically, in the cases of traditional periodic boundary(PB) and fully-opened boundary(OB) conditions, the evolutions are quite similar before the system achieves the fastest reconnection rate. However, differences emerge between the two cases afterward. In the PB case, the reconnection electric field experiences a rapid decline and even becomes negative, indicating a reversal of the reconnection process. In contrast, the system maintains a fast reconnection stage in the OB case. Suprathermal electrons are generated near the separatrix and in the exhaust region of both simulation cases. In the electron density depletion layer and the dipolarization front region, a larger proportion of suprathermal electrons are produced in the OB case. Medium-energy electrons are mainly located in the vicinity of the X-line and downstream of the reconnection site in both cases. However, in the OB case, they can also be generated in the electron holes along the separatrix. Before the reverse reconnection stage, no high-energy electrons are present in the PB case. In contrast, about 20% of the electrons in the thin and elongated electron current layer are high-energy in the OB case.
文摘The kinetics of plasma during the process of Petschek mode magnetic reconnection is studied based on a two-dimensional hybrid code. It has been found that the acceleration of particles inside the reconnection layer is highly anisotropy. Few particles are accelerated along field lines to a very high energy, while the bulk of the plasma remains in a relatively low velocity. We have pointed out that such a new picture of energy distribution in particles can be used to explain the formation of highly energized particle beams observed in space.
基金Supported by the National Key Research and Development Program of China under Grant No 2017YFA0304504the National Natural Science Foundation of China under Grant Nos 11374290,61522508,91536219 and 11504363
文摘Single-photon flux is one of the crucial properties of nitrogen vacancy （NV） centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the single-photon count rate. Through the interaction between tightly confined optical mode in nanowires and NV centers, the single-photon lifetime is much shortened and the collection efficiency is enhanced. As a result, the detected single-photon rate can be at 564 kcps, and the total detection coefficient can be 0.8%, which is much higher than that in bulk diamond. Such a nanowire single-photon device with high photon flux can be applied to improve the fidelity of quantum computation and the precision of quantum sensors.
文摘火星感应磁层边界的等离子体不稳定性,如边界层处速度剪切激发的Kelvin-Helmholtz(K-H)不稳定性,对火星感应磁层结构和磁层离子输运过程具有重要的影响.本文利用Mars Atmosphere and Volatile EvolutioN(MAVEN)卫星搭载的Magnetometer(MAG)和Super Thermal and Thermal Ion Composition(STATIC)仪器所提供的磁场和等离子数据,分析了2018年5月21日火星感应磁层边界处观测到的K-H不稳定性事件,发现在磁场、重离子通量、离子成分与密度、和离子速度上存在五个连续的准周期变化,估算K-H波的周期为~100 s,同时在其中两个K-H涡旋内发现了磁通量绳结构.磁通量绳的轴向方向与边界层法向准垂直,且其中的离子成分与涡旋内电离层等离子体成分接近,表明此处的磁通量绳有可能是在K-H波的发展过程中形成.磁通量绳的整体速度也远大于此处的离子逃逸速度,这可能导致重离子O^(+)和O_(2)^(+)从火星大气中快速逃逸.
