JPS61115310A - Superconducting magnet - Google Patents

Abstract

PURPOSE:To enable the generation of a stable and uniform magnetic field, by incorporating magnetic flux holding coils serially in conventional superconductive compensation windings. CONSTITUTION:Magnetic flux holding coils 11 and 12 are provided at the opposite ends of a hollow cylinder of a superconducting main magnet. By this constitution, the ratio of the number of magnetic fluxes traversing superconducting compensation windings out of the magnetic fluxes generated in a constantly- conducting compensation winding 3 to the total sum of the magnetic fluxes traversing the superconducting compensation windings can be lessened sharply. The reason is that the total number of the magnetic fluxes traversing the superconducting compensation windings 2 and 2' is lessened sharply since the magnetic fluxes generated in the constantly-conducting compensation winding 3 scarcely traverse the magnetic flux holding coils 11 and 12. Accordingly, the rate of a change in the number of magnetic fluxes traversing the superconducting compensation windings 2 and 2', which is caused by a change in a current of the constantly-conducting compensation winding 3, is diminished in a large degree, and consequently a change in a current flowing through the superconducting compensation windings 2 and 2' is reduced.

Description

[Detailed description of the invention] (Industrial application field) The present invention provides superconducting magnets with I! 11'.

(Prior Art) A superconducting magnet is a device that generates a strong magnetic field with minimal electric power by utilizing the superconductivity phenomenon (the phenomenon in which the resistance value becomes 0) that occurs when a conductor is cooled to an extremely low temperature. This type of device is used, for example, as a magnetic field generating device for MHD power generation, a magnetic field generating device for a nuclear magnetic resonance apparatus, or a magnetic field generating device for other VL@.

FIG. 3 shows the components of an embodiment of a conventional device of this type. The figure shows a cross section at the center of the cylinder. In the figure, 1 is a superconducting main magnet that is wound into a cylindrical shape and generates a main magnetic flux when cooled to an extremely low temperature, and 2.2' is a superconducting main magnet that homogenizes the magnetic field created in the center of the cylinder by the superconducting main magnet 1. A superconducting compensation winding (
3 is a normal-conducting compensation winding (
room temperature shim).

In the superconducting magnet configured in this way, when the superconducting main magnet 1- is cooled with, for example, liquid helium and a current is applied,
A magnetic field is generated at the center of the cylinder in the direction of the cylinder axis (two axes in the figure). At the same time, by passing current through the superconducting compensation windings 2 and 2' and the normal conduction compensation windings 3, the magnetic field at the center of the cylinder can be made uniform. In this kind of highly homogeneous superconducting magnet,
The central region of the magnet (within a sphere of radius a shown in the figure, generally 865
Only the magnetic field (cm) is of concern. Moreover, the magnetic field distribution in the Z-axis direction is important. Therefore, the Z-axis direction magnetic field generated by the magnet is extracted and expressed by expanding it into a Taylor series.

B (Z)=Bo +Bt Z+B2 Z2+B! Z
'+...+Bn Z' However, Bo, al...3n are differential coefficients in the case of a highly homogeneous superconducting magnet, and the superconducting compensation sound 12°2' is especially the compensation that creates the first-order term in the above equation. Taking a winding as an example, it is placed at a position where the third-order term is O.

(Problems to be Solved by the Invention) By the way, when creating a desired magnetic field at the center of the cylinder, a high magnetic field is generated by the superconducting main magnet 1, and the magnetic field is converted into superconducting compensation sound 1112.2', normal conduction The compensation winding 3 is used in this order to cancel out non-uniform components such as primary and secondary terms of the main magnetic field, creating a highly homogeneous magnetic field.

However, when setting the current of the normal conduction compensation winding [13], the superconducting main magnet 1. The superconducting compensation winding 2゜2' is disconnected from the power source and is in persistent current mode, so when the current in the normal conducting winding 3 is changed, this I! Superconducting main magnet 1 and superconducting compensation sound 112.2' due to the magnetic flux created by the flow
The persistent current flowing in the center changes, making it impossible to control the central magnetic field to be uniform.

In the case of the conventional device, for example, when the third-order term of the normal conduction compensation winding 3 is changed, the first-order term current of the superconducting main magnet 1 changes. Therefore, we predicted the value in advance and obtained a superconducting compensation sound of $12.2'
It is conceivable to flow a primary term current through the normal conduction compensation winding 3 so as to cancel the magnetic field.

However, in such a method, the load on the normal conduction compensation winding 3 becomes large, and a large amount of current needs to flow. As a result, the normal conduction compensation winding 3 itself generates heat, and in some cases, the superconducting compensation winding 2 generates magnetic fields such as third-order and fifth-order terms, making the design of the normal conduction compensation winding extremely complicated and difficult. turn into. The present invention has been made in view of these points, and its purpose is to realize a superconducting magnet that can generate a stable uniform magnetic field.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, uses a superconducting main magnet wound in a cylindrical shape and equalizes the 1fiji that can be generated at the center of the cylinder by the superconducting main magnet. Therefore, in a superconducting magnet composed of a superconducting compensation winding wound around the outer circumference of a superconducting main magnet and a normal-conducting compensation winding arranged at the center of the cylinder, there is a superconducting It is characterized by providing a magnetic flux holding coil connected in series with the compensation winding.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of the present invention. Third
Components that are the same as those in the figures are indicated by the same numbers. In the figure, 11 is a first magnetic flux holding coil connected in series with the superconducting compensation winding 2, and 12 is a second magnetic flux holding coil also connected in series with the superconducting compensation winding 12'. These magnetic flux holding coils 11, 12 are coils with a large number of turns wound around the outer circumference of the superconducting main magnet 1 as far away from the center as possible.

FIG. 2 is an equivalent circuit diagram of the device shown in FIG. The flux-holding coil 11.12 is connected in series with the superconducting compensation winding 2.2' as shown. SW is a changeover switch for flowing persistent current. That is, first, a current is caused to flow from an external power source, and after the superconducting state is achieved, the external power source is disconnected, and the contact of the switch SW is turned on to short-circuit the circuit, thereby allowing a persistent current to flow.

The operation of the circuit configured in this way will be explained below.

In the case of the conventional device, the superconducting compensation sound 12.2' is strongly influenced by the magnetic flux generated by passing a current through the normal-conducting compensation winding 3, as described above.

As a result, in an attempt to keep the number of magnetic fluxes crossing its own coil constant, the current changes significantly, distorting the magnetic field distribution in the central region. Therefore, magnetic flux holding coils 11 and 12 are provided at both ends of the superconducting main magnet cylinder as in the device of the present invention.

In this way, the ratio of the number of magnetic fluxes that cross the superconducting compensation winding among the magnetic flux generated in the normal-conducting compensation winding 3 to the total magnetic flux that crosses the superconducting compensated wire can be significantly reduced. The reason for this is that the magnetic flux generated by the normal-conducting compensator winding 3 hardly crosses the flux retaining coil 11.12, so the total number of magnetic fluxes that cross the superconducting compensator 1i12.2' is significantly reduced. It is from.

Therefore, the rate of change in the number of magnetic fluxes across the superconducting compensator $62.2' due to current changes in the normal-conducting compensation winding 3 is greatly reduced, and the current change in the superconducting compensating winding 2.2' is reduced. That is, according to the present invention, the disturbance of the magnetic field due to the interaction between the normal conduction compensating winding 3 and the superconducting compensator 1i12.2' can be reduced to a negligible extent.

In the above description, the case where the magnetic flux holding coil is wound around both ends of the superconducting main magnet cylinder is taken as an example, but it is not necessarily necessary to provide it at both ends, and it is sufficient to wind it around at least one end. Also, in the above description, the primary shim in the Z-axis direction has been considered, but a similar method can be applied to all superconducting compensation windings.

(Invention Nori J Song) As explained in detail above, according to the present invention, by incorporating a magnetic flux holding coil in series with the conventional superconducting compensation winding, it is possible to easily control the magnetic field in the central region. Therefore, a stable and uniform magnetic field can be generated. Further, since it is not necessary to apply an excessive load to the normal conduction compensation winding, the design of the normal conduction compensation winding becomes easy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing an example of a conventional device. 1... Superconducting main magnet 2.2'... Superconducting compensation winding 3... Normal conduction compensation winding 11.12... Magnetic flux holding coil SW... Switch patent applicant JEOL Ltd. Representative Patent Attorney: Fuji Ijima (1 person) Figure 1 Figure 2

Claims (1)

[Claims] A superconducting main magnet wound into a cylindrical shape, a superconducting compensating winding wound around the outer circumference of the superconducting main magnet in order to equalize the magnetic field generated in the center of the cylinder by the superconducting main magnet, and the center of the cylinder. A superconducting magnet comprising a normal-conducting compensation winding arranged in Conduction magnet.