Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer...Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.展开更多
The Shanghai Synchrotron Radiation Facility (SSRF) is a proposed 3rd generation light source with 3.5 GeV in energy. It is composed of 20 DBA cells resulting in a ring that is about 10 nm(rad in emittance and 396 m in...The Shanghai Synchrotron Radiation Facility (SSRF) is a proposed 3rd generation light source with 3.5 GeV in energy. It is composed of 20 DBA cells resulting in a ring that is about 10 nm(rad in emittance and 396 m in circumference, and provides 10 straight sections of 7.24 m and other 10 straight sections of 5.0 m for the inclusion of insertion devices, injection components and RF cavities. The lattice has high flexibility, and the tunes and beta functions can be easily adjusted within a wide range to meet the requirements for different operation modes, including high beta mode and hybrid beta mode with and/or without dispersion in straight sections. In this paper, the results of linear optics design and dynamic aperture study are presented.展开更多
Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit：...Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit： nm） were nano-fabricated on the Si（100）/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography （EBL） and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance （TMR ＆ R） versus driving current （I） loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co6oFe2oB2o layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both I NR-MTJ＋1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.展开更多
In this paper, we calculate the low-lying spectra of a single-electron magnetic quantum ring with an offcenter Coulomb impurity, where the magnetic field is zero within the ring and constant elsewhere. The impurity, e...In this paper, we calculate the low-lying spectra of a single-electron magnetic quantum ring with an offcenter Coulomb impurity, where the magnetic field is zero within the ring and constant elsewhere. The impurity, either an acceptor or a donor, is located at a distance d as measured from the plane of the ring along the vertical z direction. The magnetic moments are found in order to get visible discontinuities at the points of the ground-state orbital angular momentum L transitions induced by magnetic fields.展开更多
The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However,we always observe a lar-ger ΔH at h...The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However,we always observe a lar-ger ΔH at higher latitude stations than lower ones,implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper,we analyze 11 intense magnetic storms from 2000 to 2004,and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δt≈13°―25° and latitude shift δs≈0°―21.8°. The ground disturbed field distribution should be improved as ΔHk = ΔHmaxcos(k-δ ),which agree well with the geomagnetic observations.展开更多
Axial magnetic field produced by an axial magnetized permanent ring was studied. For two permanent rings, if they are magnetized in the same directions, a nearly uniform axial field can be produced. If they are magnet...Axial magnetic field produced by an axial magnetized permanent ring was studied. For two permanent rings, if they are magnetized in the same directions, a nearly uniform axial field can be produced. If they are magnetized in opposite direction, an axial gradient magnetic field can be generated, with the field range changing from-Bo to Bo- A permanent magnet with a high axial gradient field was fabricated, the measured results agree with the PANDIRA calculation very well. For wider usage, it is desirable for the field gradient to be changed. Some methods to produce the variable gradient field are presented. These kinds of axial gradient magnetic field can also be used as a beam focusing for linear accelerator if the periodic field can be produced along the beam trajectory. The axial magnetic field is something like a solenoid, large stray field will leak to the outside environment if no method is taken to control them. In this paper, one method is illustrated to shield off the outside leakage field.展开更多
The effect of magnetic field on the tribological process of sleeve-ring pair lubricated by WRL lubricants was investigated by means of a NG-x wear tester and a PS5013 video microscope. The friction coefficient(f) and ...The effect of magnetic field on the tribological process of sleeve-ring pair lubricated by WRL lubricants was investigated by means of a NG-x wear tester and a PS5013 video microscope. The friction coefficient(f) and the wear weight(W) in lubricating test with WRL lubricant were decreased with the increase in the magnetic field vertical to the rubbing surface, and an almost zero wear lubricating situation was gained in a magnetic field of 1000A/m. The captured wear micro particles on the rubbing surface were observed in the testing process, and the theoretical analysis of magnetic effects was completed. It is indicated that the magnetic field has not only a capturing action of wear micro particles on the worn surface, but also a inducing polarization of magnetic anisotropy of lubricant molecular. The actions promote the absorption of WRL lubricant into the wear surface as well as wear micro-particles, so that a good tribological effect is obtained when both magnetic field and WRL present.展开更多
We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero p...We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spinorbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring.展开更多
Aharonov-Casher oscillasions of transmission through a mesoscopic ring with a magnetic impurity is investigated. Both spin-dependent transmission and reflection coefficients of spin-state electrons at zero-temperature...Aharonov-Casher oscillasions of transmission through a mesoscopic ring with a magnetic impurity is investigated. Both spin-dependent transmission and reflection coefficients of spin-state electrons at zero-temperature are calculated as a function of the textured electric fields and its title angle in the present of spin-flipper scattering. It is found that the spin-exchange interaction can destroy intermittently periodic oscillations of spin-up transmission and reflection coefficients within some small ranges in the adiabatic region of quantum phase. However spin-down transmission and reflection coefficients appear periodic AC oscillations. The calculated results manifest that spindown transmission and reflection coefficients have the same perfect oscillation patterns. In the nonadiabatic region, the behavior of the anomalous AC oscillations are depedent on the difference between the tilt angle of spin and that of texture electric field.展开更多
The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are take...The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.展开更多
A pool cooled experimental magnet based on the copper stabilized NbTi supercon- ducting wire was designed, fabricated and tested, in order to evaluate the engineering design of the dipole superconducting magnet for th...A pool cooled experimental magnet based on the copper stabilized NbTi supercon- ducting wire was designed, fabricated and tested, in order to evaluate the engineering design of the dipole superconducting magnet for the collector ring （CR） of the facility for antiproton and ion research （FAIR） project. In this paper, the experimental setup including quench protection system was presented. Performance of the liquid helium pool cooled test was introduced. All of the results indicate both the performance of conductor and the experimental superconducting magnet under low temperature is stable, which suggests the engineering design are feasible for the formal magnet in CR of the FAIR project.展开更多
The ground state of a two-dimensional square superconducting πring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the ＇antiferromagnetic＇ arrangement wit...The ground state of a two-dimensional square superconducting πring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the ＇antiferromagnetic＇ arrangement with directions of the nearest-neighbouring currents circulating oppositely in the absence of an external magnetic field. It is found that the external magnetic field could destroy the anti-parallel configuration effectively. The external magnetic field needed to destroy the anti-parallel configuration is related to the superconducting π ring＇s inductance parameter β= 2πLIc/Ф0. For a small β the anti-parallel configuration, which is the lowest-energy ground state of the system, will be fully destroyed and changed to the configuration that the circulating currents have the same direction and parallel to the external magnetic field when the magnetic flux reaches Ф0/4 in each ring. Moreover, the magnetic field needed to destroy the anti-parallel configuration will be very small when β is large enough.展开更多
Existence of the magnetic field of Saturn and the temperature around 70 - 100 K nearby of it bring us to the idea of diamagnetism and superconductivity of the rings particles. The rings could emerge from the icy parti...Existence of the magnetic field of Saturn and the temperature around 70 - 100 K nearby of it bring us to the idea of diamagnetism and superconductivity of the rings particles. The rings could emerge from the icy particles moving on chaotic orbits around Saturn within protoplanetary cloud. After appearance of the magnetic field of Saturn all chaotic orbits of icy particles start to shift to the magnetic equator plane, where there is a minimum of the particles magnetic energy, due to diamagnetic force of expulsion like Meissner phenomenon. Each particle comes to the stable position preventing its own horizontal and vertical shift. Particles are locked within three-dimensional magnetic well due to Abrikosov quantum vortex phenomenon for superconductor. This mechanism is valid and it works even particles have a small fraction of superconductor. Final picture is similar to the picture of iron particles forms the same shape around a magnet on laboratory table. Any other phenomena like gravity resonances, dusty plasma and others may bring some peculiarities to the final picture of the rings. It follows that magnetic field of Saturn and low temperature around of it are the main reason for the rings origin and the rings is product of the early time of the magnetic field of Saturn appearance. Additional matter to the rings also may come from the frozen water particles generated from the Saturn sputniks geysers due to magnetic coupling between planet and satellites. The data of Cassini mission to Saturn rings are conforming suggested theory of their origin and existence.展开更多
The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure curren...The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.展开更多
Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets.Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precu...Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets.Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process.The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process.The resulting magnets possess many advantages such as near-net-shape,outstanding corrosion resistance,and ultrafine-grain structure.The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report.As a near-net-shape technique,the hot deformation process has notable advantages with regard to the production of irregular shapes,especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls.The difficulties associated with the fabrication of crack-free,homogeneous,and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters,and application of theoretical simulation.Considering the characteristics of hotdeformed magnets which include grain shape and size,anisotropic distribution of intergranular phases,etc.,investigation and improvement of the mechanical and electric properties,in addition to thermal stability,with the objective of improving the application of hot-deformed magnets or ring-shaped magnets,is of practical significance.展开更多
基金financially supported by the National High Technology Research and Development Program of China (No. 2011AA03A403)the National Natural Science Foundation of China (No. 51171122)the Sichuan Provence Science and Technology Support Program (Nos. 2011GZ0117 and 2013GZ0056)
文摘Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.
文摘The Shanghai Synchrotron Radiation Facility (SSRF) is a proposed 3rd generation light source with 3.5 GeV in energy. It is composed of 20 DBA cells resulting in a ring that is about 10 nm(rad in emittance and 396 m in circumference, and provides 10 straight sections of 7.24 m and other 10 straight sections of 5.0 m for the inclusion of insertion devices, injection components and RF cavities. The lattice has high flexibility, and the tunes and beta functions can be easily adjusted within a wide range to meet the requirements for different operation modes, including high beta mode and hybrid beta mode with and/or without dispersion in straight sections. In this paper, the results of linear optics design and dynamic aperture study are presented.
基金the State Key Project of Fundamental Research of Ministry of Science and Technology （No. 2006CB932200） the National Natural Science Foundation of China （NSFC, No. 10574156）+2 种基金 the Knowledge Innovation Program of Chinese Aca.demy of Sciencesthe protial support of 0utstanding Young Researcher Foundation （Nos. 50325104 and 50528101） K.C.Wong Education Foundation, Hong Kong.
文摘Nano-ring-type magnetic tunnel junctions （NR-MTJs） with the layer structure of Ta（5）/Ir22Mn78（10）/ Co75Fe25（2）/Ru（0.75）/CoooFe20B20（3）/Al（0.6）-oxide/Co60Fe20B20（2.5）/Ta（3）/Ru（5） （thickness unit： nm） were nano-fabricated on the Si（100）/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography （EBL） and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance （TMR ＆ R） versus driving current （I） loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co6oFe2oB2o layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both I NR-MTJ＋1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.
基金The project supported by National Natural Science Foundation of China under Grant Nos. 50371058 and 90103028
文摘In this paper, we calculate the low-lying spectra of a single-electron magnetic quantum ring with an offcenter Coulomb impurity, where the magnetic field is zero within the ring and constant elsewhere. The impurity, either an acceptor or a donor, is located at a distance d as measured from the plane of the ring along the vertical z direction. The magnetic moments are found in order to get visible discontinuities at the points of the ground-state orbital angular momentum L transitions induced by magnetic fields.
基金Supported by National Natural Science Foundation of China (Grant No.40436016)KIP Pilot Project of the Chinese Academy of Sciences (Grant No.KZCX3-SW-144)National Basic Research Program of China (Grant No.2006CB806305)
文摘The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However,we always observe a lar-ger ΔH at higher latitude stations than lower ones,implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper,we analyze 11 intense magnetic storms from 2000 to 2004,and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δt≈13°―25° and latitude shift δs≈0°―21.8°. The ground disturbed field distribution should be improved as ΔHk = ΔHmaxcos(k-δ ),which agree well with the geomagnetic observations.
文摘Axial magnetic field produced by an axial magnetized permanent ring was studied. For two permanent rings, if they are magnetized in the same directions, a nearly uniform axial field can be produced. If they are magnetized in opposite direction, an axial gradient magnetic field can be generated, with the field range changing from-Bo to Bo- A permanent magnet with a high axial gradient field was fabricated, the measured results agree with the PANDIRA calculation very well. For wider usage, it is desirable for the field gradient to be changed. Some methods to produce the variable gradient field are presented. These kinds of axial gradient magnetic field can also be used as a beam focusing for linear accelerator if the periodic field can be produced along the beam trajectory. The axial magnetic field is something like a solenoid, large stray field will leak to the outside environment if no method is taken to control them. In this paper, one method is illustrated to shield off the outside leakage field.
文摘The effect of magnetic field on the tribological process of sleeve-ring pair lubricated by WRL lubricants was investigated by means of a NG-x wear tester and a PS5013 video microscope. The friction coefficient(f) and the wear weight(W) in lubricating test with WRL lubricant were decreased with the increase in the magnetic field vertical to the rubbing surface, and an almost zero wear lubricating situation was gained in a magnetic field of 1000A/m. The captured wear micro particles on the rubbing surface were observed in the testing process, and the theoretical analysis of magnetic effects was completed. It is indicated that the magnetic field has not only a capturing action of wear micro particles on the worn surface, but also a inducing polarization of magnetic anisotropy of lubricant molecular. The actions promote the absorption of WRL lubricant into the wear surface as well as wear micro-particles, so that a good tribological effect is obtained when both magnetic field and WRL present.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 110704032 and 110704033)the Natural Science Foundation of Jiangsu Province of China (Grant No. BK2010416)the National Basic Research Development Program of China (Grant No. 2009CB945504)
文摘We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spinorbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring.
文摘Aharonov-Casher oscillasions of transmission through a mesoscopic ring with a magnetic impurity is investigated. Both spin-dependent transmission and reflection coefficients of spin-state electrons at zero-temperature are calculated as a function of the textured electric fields and its title angle in the present of spin-flipper scattering. It is found that the spin-exchange interaction can destroy intermittently periodic oscillations of spin-up transmission and reflection coefficients within some small ranges in the adiabatic region of quantum phase. However spin-down transmission and reflection coefficients appear periodic AC oscillations. The calculated results manifest that spindown transmission and reflection coefficients have the same perfect oscillation patterns. In the nonadiabatic region, the behavior of the anomalous AC oscillations are depedent on the difference between the tilt angle of spin and that of texture electric field.
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2009AA03Z405)the National Natural Science Foundation of China (Grant Nos. 60908028 and 60971068)the Fundamental Research Funds for the Central Universities (Grant No. BUPT2009RC0411)
文摘The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.
基金supported by Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) (MOU GSI ACC 2005 01)
文摘A pool cooled experimental magnet based on the copper stabilized NbTi supercon- ducting wire was designed, fabricated and tested, in order to evaluate the engineering design of the dipole superconducting magnet for the collector ring （CR） of the facility for antiproton and ion research （FAIR） project. In this paper, the experimental setup including quench protection system was presented. Performance of the liquid helium pool cooled test was introduced. All of the results indicate both the performance of conductor and the experimental superconducting magnet under low temperature is stable, which suggests the engineering design are feasible for the formal magnet in CR of the FAIR project.
文摘The ground state of a two-dimensional square superconducting πring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the ＇antiferromagnetic＇ arrangement with directions of the nearest-neighbouring currents circulating oppositely in the absence of an external magnetic field. It is found that the external magnetic field could destroy the anti-parallel configuration effectively. The external magnetic field needed to destroy the anti-parallel configuration is related to the superconducting π ring＇s inductance parameter β= 2πLIc/Ф0. For a small β the anti-parallel configuration, which is the lowest-energy ground state of the system, will be fully destroyed and changed to the configuration that the circulating currents have the same direction and parallel to the external magnetic field when the magnetic flux reaches Ф0/4 in each ring. Moreover, the magnetic field needed to destroy the anti-parallel configuration will be very small when β is large enough.
文摘Existence of the magnetic field of Saturn and the temperature around 70 - 100 K nearby of it bring us to the idea of diamagnetism and superconductivity of the rings particles. The rings could emerge from the icy particles moving on chaotic orbits around Saturn within protoplanetary cloud. After appearance of the magnetic field of Saturn all chaotic orbits of icy particles start to shift to the magnetic equator plane, where there is a minimum of the particles magnetic energy, due to diamagnetic force of expulsion like Meissner phenomenon. Each particle comes to the stable position preventing its own horizontal and vertical shift. Particles are locked within three-dimensional magnetic well due to Abrikosov quantum vortex phenomenon for superconductor. This mechanism is valid and it works even particles have a small fraction of superconductor. Final picture is similar to the picture of iron particles forms the same shape around a magnet on laboratory table. Any other phenomena like gravity resonances, dusty plasma and others may bring some peculiarities to the final picture of the rings. It follows that magnetic field of Saturn and low temperature around of it are the main reason for the rings origin and the rings is product of the early time of the magnetic field of Saturn appearance. Additional matter to the rings also may come from the frozen water particles generated from the Saturn sputniks geysers due to magnetic coupling between planet and satellites. The data of Cassini mission to Saturn rings are conforming suggested theory of their origin and existence.
文摘The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0700902)the National Natural Science Foundation of China(Grant Nos.51671207,51601207,and 51501213)
文摘Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets.Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process.The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process.The resulting magnets possess many advantages such as near-net-shape,outstanding corrosion resistance,and ultrafine-grain structure.The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report.As a near-net-shape technique,the hot deformation process has notable advantages with regard to the production of irregular shapes,especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls.The difficulties associated with the fabrication of crack-free,homogeneous,and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters,and application of theoretical simulation.Considering the characteristics of hotdeformed magnets which include grain shape and size,anisotropic distribution of intergranular phases,etc.,investigation and improvement of the mechanical and electric properties,in addition to thermal stability,with the objective of improving the application of hot-deformed magnets or ring-shaped magnets,is of practical significance.
