CN114743754B

CN114743754B - Low-power-consumption compact normal-temperature bit type strong magnet

Info

Publication number: CN114743754B
Application number: CN202210369516.8A
Authority: CN
Inventors: 鲁钝; 傅文杰; 韩梦; 鄢扬
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2022-04-08
Filing date: 2022-04-08
Publication date: 2023-04-25
Anticipated expiration: 2042-04-08
Also published as: CN114743754A

Abstract

The invention belongs to the technical field of strong magnetic fields, and particularly relates to a low-power-consumption compact normal-temperature Bitter type strong magnet. The low-power-consumption compact normal-temperature Bitter type strong magnet provided by the invention is based on the characteristic that the heat generation of a Bitter coil is in a descending trend from inside to outside. When each turn of coil is assembled, the inner radius of the cover plate is designed to be larger than that of the annular structure, so that the central area of the coil is not covered. After the magnet is assembled, the whole central area forms a hollow structure, so that a transverse heat dissipation channel is constructed, most of Joule heat is taken away, and the heat dissipation performance is improved, so that the magnet can continuously work. Compared with the mode of taking away the generated Joule heat by flowing the liquid in the holes aligned with the axial direction, the low-power-consumption compact normal-temperature Bitter type strong magnet provided by the invention can rapidly dissipate heat, and has the advantages of simple and compact structure, low power consumption and strong practicability.

Description

Low-power-consumption compact normal-temperature bit type strong magnet

Technical Field

The invention belongs to the technical field of strong magnetic fields, and particularly relates to a low-power-consumption compact normal-temperature Bitter type strong magnet which is particularly suitable for gyrotron and nuclear magnetic resonance imaging.

Background

Both gyrotron and nuclear magnetic resonance imaging require uniform strong magnetic fields, and currently commonly used strong magnetic field systems include permanent magnets, pulsed magnets, room temperature resistive magnets, and superconducting magnets. Permanent magnets are most convenient to use, but the volume and weight of the permanent magnets are remarkable, and the permanent magnets cannot be miniaturized. The superconducting magnet can generate an ultrahigh magnetic field to occupy absolute advantages under the application condition of the ultrahigh magnetic field, but the superconducting magnet is high in price and needs to work in a 3-4K ultralow temperature environment to require long refrigeration time, so that when the magnetic field intensity is in a range of 1-2T, the normal-temperature resistance magnet can be used immediately after being opened, the system is compact in structure, easy to miniaturize and lower in cost performance. The normal temperature resistance type magnet is also divided into a wire coil electromagnet and a perforated ring piece coil electromagnet, namely a Bitter type magnet, which is proposed by Francis Bitter of the national strong magnetic field laboratory.

The traditional normal temperature bit magnet adopts an axial via hole, the axial via hole is provided with a circular hole and an elongated hole, the sizes of all bit sheets are the same, and the generated Joule heat is taken away by liquid flowing in the holes aligned with the axial direction. However, when the current reaches hundreds of amperes or even thousands of amperes, a large amount of joule heat is generated, and the application system is difficult to continuously work only by an axial heat dissipation mode, so that the practical performance is still limited greatly.

Disclosure of Invention

The invention aims to provide a low-power-consumption compact normal-temperature bit type strong magnet, which solves the problems that the traditional normal-temperature bit type strong magnet cannot work continuously only by an axial heat dissipation mode and the practicability of an application system is affected.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a low-power compact normal-temperature bit type strong magnet comprises a magnet body and electric pure iron serving as a magnetic yoke;

the magnet body is formed by overlapping N turns of coils; each turn of coil consists of M annular sheets and a fixed ring; each annular sheet is provided with a plurality of through holes, and an insulating layer is arranged between two adjacent annular sheets; the insulating layers and the annular sheets have the same structural size, fan-shaped openings are formed in the same positions of all the insulating layers, and connecting pieces for connecting the upper annular sheet and the lower annular sheet are arranged at the openings; all the annular sheets and the insulating layers are overlapped together along the same axial direction to form an annular structure; the upper surface and the lower surface of the annular structure are covered with cover plates, and through holes are formed in the cover plates and are used for being matched with the fixing rings to assemble the annular structure together; the upper cover plate through hole, the lower cover plate through hole, the annular sheet through holes and the insulating layer through holes are vertically aligned after assembly to form a longitudinal heat dissipation channel; the radius of the outer circle of the cover plate is equal to that of the outer circle of the annular structure, and the radius of the inner circle is larger than that of the inner circle of the annular sheet, so that a transverse heat dissipation channel is formed in the central area of the annular sheet;

the electrical pure iron is loaded on the outer surface of the magnet body.

Further, in the N-turn coil, the outer diameter of each turn of coil is different, so that the magnetic field is more uniform.

Furthermore, the insulating layer, the fixing ring and the cover plate are all made of epoxy resin.

Further, the annular sheet is a copper sheet; the connecting piece arranged at the opening is a fan-shaped copper sheet, and the size of the fan-shaped copper sheet is the same as that of the opening.

Further, N is more than or equal to 5, and M is more than or equal to 5.

The low-power-consumption compact normal-temperature Bitter type strong magnet provided by the invention is based on the characteristic that the heat generation of a Bitter coil is in a descending trend from inside to outside. When each turn of coil assembly is assembled, the inner radius of the cover plate is designed to be larger than that of the annular structure, so that the central area of the coil is not covered. After the magnet is assembled, the whole central area forms a hollow structure, so that a transverse heat dissipation channel is constructed, most of Joule heat is taken away, and the heat dissipation performance is improved, so that the magnet can continuously work. Compared with the mode of taking away the generated Joule heat by flowing the liquid in the holes aligned with the axial direction, the low-power-consumption compact normal-temperature Bitter type strong magnet provided by the invention can rapidly dissipate heat, and has the advantages of simple and compact structure, low power consumption and strong practicability.

Drawings

FIG. 1 is a schematic diagram of a stack of coils per turn and a schematic diagram of a formed stack of coils per turn;

FIG. 2 is a schematic molding view of each turn of coil plus a fixing epoxy clamp block and cover plate;

FIG. 3 is a schematic diagram of a 2 turn coil, upper and lower pole pieces, and terminal connection;

FIG. 4 is a schematic illustration of a 16 turn diameter coil and connection;

FIG. 5 is a schematic diagram of a complete clamp block and insulating cover plate 16 turn coil; FIG. 6 is a schematic diagram of an example 1.1T high intensity magnetic field 16 turn coil assembly;

FIG. 6 is a schematic diagram of an example 1.1T high intensity magnetic field 16 turn coil assembly;

FIG. 7 is a graph showing the distribution of magnetic fields generated by the magnets of FIG. 6;

reference numerals:

1. a ring structure; 2. an annular copper sheet; 3. fixing an epoxy resin ring; 4. a cover plate; 5. an insulating layer; 6. a connecting piece; 7. a lateral heat dissipation channel; 8. a single turn coil; 9. a longitudinal heat dissipation channel; 10. electrician pure iron; 11. copper joints.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples.

The invention provides a low-power-consumption compact normal-temperature bit type strong magnet, which has a structure shown as 6 and comprises a magnet body and an electrical pure iron 10 serving as a magnetic yoke. The magnet body structure is shown in fig. 4 and 5, and is formed by stacking 16 turns of coaxial coils with the same inner diameter and different outer diameters. As is clear from the following magnetic field equation and ohmic loss equation, when the inner diameter is the same, the larger the outer diameter, the smaller the resulting magnetic induction intensity, and the smaller the power consumption. The combination of different outer diameters reduces the power consumption required to obtain a longer field homogeneity region while at the same time obtaining such a homogeneity region length.

The structure of the single turn coil 8 is shown in fig. 1-3: the epoxy resin composite material consists of 13 annular copper sheets 2 and a fixed epoxy resin ring 3; each annular copper sheet 2 is provided with a plurality of through holes, the thickness of each annular copper sheet 2 is 0.4mm, and an insulating layer 3 is arranged between every two adjacent annular copper sheets. The insulating layer 3 has the same structural dimensions as the annular sheet and is made of epoxy resin with a thickness of 0.1mm. All insulating layers are provided with fan-shaped openings at the same position, connecting pieces 6 for connecting upper and lower annular copper sheets in series are arranged at the openings, the size of each connecting piece 6 is the same as that of each opening, and the fan-shaped copper sheets with the thickness of 0.1mm are adopted as the connecting pieces in the embodiment; all the annular copper sheets 2 and the insulating layers 3 are overlapped together along the same axial direction to form an annular structure 1; the upper surface and the lower surface of the annular structure 1 are covered with cover plates 4 made of epoxy resin, and the cover plates 4 are provided with through holes for being matched with and fixed with the epoxy resin ring 2 to assemble the annular structure together; the upper cover plate 4 through holes, the lower cover plate 4 through holes, the copper sheet through holes and the insulating layer 2 through holes are vertically aligned after assembly to form a longitudinal heat dissipation channel 9; the radius of the outer circle of the cover plate 4 is equal to that of the annular structure, and the radius of the inner circle is larger than that of the annular sheet, so that the central area of the annular sheet forms a transverse heat dissipation channel 7. The overall height of the single turn coil fabricated in accordance with the above structure was 7.4mm. The common Bitter type magnet only has the axial channel for heat dissipation, has very high requirements on long-time work and a water cooling system, and can better take away the dissipated heat by adding the transverse heat dissipation channel 7, so that the system works more stably.

The electrical pure iron 10 is loaded on the outer surface of the magnet body. In this embodiment, the electrical pure iron is selected to be DT4C, and a copper connector 11 is provided on the electrical pure iron for connection to a dc current source.

By adopting the structure, the current conduction directions of the annular copper sheets 2 in each single-turn coil are kept consistent, and the axial magnetic fields generated by the single copper sheets are kept consistent, so that the magnetic field and the ohmic loss of the single-turn coil can be obtained by the Biot-Savart Law.

The axial magnetic field formula generated by the single copper sheet is as follows:

wherein B (z) represents the axial magnetic induction intensity, mu ₀ Is free space permeability, J is current density, R _in And R is _out Is the inside and outside radius of the single turn coil, h is the thickness of the conductor, and I is the magnitude of the current passing through.

The ohmic loss of a single piece of copper sheet can be expressed by the formula:

where ρ is the conductivity of the conductor.

Based on the magnetic field formula and the axial magnetic field operation formula, the magnetic field distribution in a uniform region of 100mm can be achieved by only 16 circles, and the total height is 147.4mm, so that the Bitter type strong magnet has more compactness. FIG. 7 shows the axial magnetic field distribution of the Bitter type strong magnet of the present embodiment, which has a uniform region distance of 100mm and a magnetic field strength of 1.1T and is continuously operated when the current 520A is operated. The resistance is 37.5 milliohms, the working current is 520 ampere hours, the power consumption is 10.14 kilowatts, and the power consumption is more than 20 kilowatts when the common solenoid magnet generates the same magnetic field intensity and uniform area length.

In summary, the low-power-consumption compact normal-temperature bit type strong magnet provided by the invention has the advantages that the uniformity of a magnetic field is improved through the arrangement of different outer diameters of each turn of coils, and the low-power-consumption compact normal-temperature bit type strong magnet can still continuously work in a strong current state after a transverse heat dissipation channel is added.

The foregoing is merely illustrative of the present invention and not restrictive, and other modifications and equivalents thereof may occur to those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. A low-power compact normal-temperature bit type strong magnet comprises a magnet body and electric pure iron serving as a magnetic yoke; the method is characterized in that:

the electrical pure iron is loaded on the outer surface of the magnet body.

2. The low-power compact room temperature Bitter type ferromagnetic body as defined in claim 1, wherein: in the N-turn coils, the outer diameter of each turn of coil is different, so that the magnetic field is more uniform.

3. The low-power compact room temperature Bitter type ferromagnetic body as defined in claim 1, wherein: the insulating layer, the fixing ring and the cover plate are all made of epoxy resin.

4. The low-power compact room temperature Bitter type ferromagnetic body as defined in claim 1, wherein: the annular sheet is a copper sheet; the connecting piece arranged at the opening is a fan-shaped copper sheet, and the size of the fan-shaped copper sheet is the same as that of the opening.