Magnetic Field Design by Using Image Effect from Iron Shield

Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation at each coordinate angle ψ changes by =(n+1)ψ, where n is a positive or negative integer. For the uniformly magnetized case n=-1, the permanent ring produces no field in its bore, and the field is that of a dipole outside. When the ring is surrounded by a soft iron shield, its field becomes uniform in the bore, and zero outside the ring. The field can be varied continuously by moving the iron shield along the magnet axis. A small variable field device was constructed by using NdFeB permanent rings, which produced a field flux density of 0-0.5 T in the central region.

Build Axial Gradient Field by Using Axial Magnetized Permanent Rings

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.

A new veno-venous bypass type for ex-vivo liver resection in dogs

Ex-vivo liver resection is a procedure in which the liver is completely removed, perfused and after bench surgery, the liver is autotransplanted to the original site. Ex vivo liver resection is an important treatment for unresectable liver tumors. This surgical procedure requires long operation time, during which blood flow must be carefully maintained to avoid venous congestion. An effective veno-venous bypass (VVB) may meet this requirement. The present study was to test our new designed VVB device which comprised one heparinized polyvinylchloride tube and three magnetic rings The efficacy of this device was tested in five dogs. A VVB was established in 6-10 minutes. There was no leakage during the procedure. Hemodynamics was stable at anhepatic phase, which indicated that the bypass was successful. This newly-developed VVB device maintained circulation stability during ex-vivo liver resection in our dog model and thus, this VVB device significantly shortened the operation time.

Structural and magnetic properties of backward extruded Nd–Fe–B ring magnets made by different punch chamfer radius

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.

Rare earth permanent magnets prepared by hot deformation process

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.

Multi-impurity effects on the entanglement of anisotropic Heisenberg ring XXZ under a homogeneous magnetic field

The effects of multi-impurity on the entanglement of anisotropic Heisenberg ring XXZ under a homogeneous magnetic field are studied. The impurities make the equal pairwise entanglement in a ring compete with each other so that the pairwise entanglement exhibits oscillation. If the impurities are of larger couplings, both the critical temperature and pairwise entanglement can be improved.

Design and experimental study of a compact quasi-zero-stiffness isolator using wave springs

The quasi-zero-stiffness(QZS)vibration isolation has been proven to be an effective way to isolate low-frequency vibration.However,most of the existing QZS isolators are space-consuming,which could not be employed in the space-limited circumstances.In this paper,a quite compact QZS isolator is engineered by connecting a pair of mutually repulsive magnet rings and a space-saving wave spring in parallel,called WQZS isolator.The restoring force of the magnet ring is derived by the equivalent magnetic charge method,and an empirical formula for the restoring force of the wave spring is derived by the least squares method based on experimental data.The dynamic model of the WQZS vibration isolation system is built,and the vibration isolation performance is evaluated through transmissibility.Finally,an experimental prototype is fabricated,and the experimental tests on frequency sweep are carried out.The results show that compared with the linear counterpart,the vibration isolation frequency of the WQZS isolator is reduced by 48.89%,and the peak transmissibility is decreased by 59.33%.Most importantly,the space occupancy of the WQZS isolator designed in this paper is much lower than that of the traditional QZS isolators,and thus it should be a potential solution for low-frequency vibration isolation in the space-limited environment.

The magnet design for the HLS storage ring upgrade project

In order to improve the performance of the Hefei Light Source （HLS）,in particular to get higher brilliance synchrotron radiation and increase the number of straight section insertion devices,an upgrade project called HLSII will be launched soon.The storage ring lattice,which has a double bend achromatic structure with four periods,comprises eight dipoles,32 quadrupoles and 32 combined function sextupoles.The design and analysis of the magnets are shown in this paper,along with the optimization of the multipurpose combined function magnet,which consists of three magnets：skew quadrupole,horizontal dipole and vertical dipole,with the main sextupole magnet.This type of magnet is the first one that has been designed and used in China.The mechanical design and fabrication procedures for the magnets are also presented.

Design of a new compact THz source based on Smith-Purcell radiation

In recent years, people are dedicated to the research work of finding compact THz sources with high emission power. Smith-Purcell radiation is qualified for the possibility of coherent enhancement due to the effect of FEL mechanism. The compact experiment device is expected to produce hundreds mW level THz ray. The electron beam with good quality is provided under the optimized design of the electron gun. Besides, the grating is designed as an oscillator without any external feedbacks. While the beam passes through the grating surface, the beam bunching will be strong and the second harmonics enhancement will be evident, as is seen from the simulation results.