JPH0319685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting magnet, and more particularly to a superconducting magnet with a highly uniform magnetic field.

Conventionally, there has been a device of this type as shown in FIG. In the figure, a superconducting magnet 1 is composed of a superconducting solenoid coil 2 and a superconducting cis-coil 3 fixedly attached to the superconducting solenoid coil 2. In the conventional superconducting magnet 1 having such a structure, when a DC current is passed through the superconducting solenoid coil 2, a DC magnetic field that does not change over time is generated inside the coil.
However, this DC magnetic field changes spatially because the superconducting solenoid coil 2 has a finite length. Therefore, a plurality of superconducting cis coils 3 are installed in order to create a highly uniform region in which the magnetic field hardly changes spatially in a certain finite space near the center of the superconducting solenoid coil 2. The superconducting cis-coil 3 is circular or hollow-shaped, and has a first-order error term and a second-order error term of the axial magnetic field of the superconducting solenoid coil 2.
This is to correct higher-order error terms of the order or higher order.
This superconducting shim coil group is a superconducting solenoid 2
However, they are usually installed in symmetrical positions.

However, since the conventional superconducting magnet 1 is configured as described above, in order to create a highly uniform magnetic field, it is necessary to attach a large number of superconducting shim coils 3 and operate each of these superconducting shim coils 3 independently. First, there was a drawback that the device became extremely complicated.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional solenoid coil, and by appropriately providing taps on the compensation coil winding of a superconducting solenoid coil with a compensation coil, non-uniformity that changes in the axial direction is eliminated. The object of the present invention is to provide a highly uniform superconducting magnet from which a magnetic field is removed.

Hereinafter, one embodiment of this invention shown in FIGS. 2 and 3 will be described. In FIG. 2, the superconducting magnet 11 is composed of a main superconducting coil 12 and a pair of compensation coils 13 attached to both ends of the main superconducting coil 12 in the axial direction. In such a configuration, the main superconducting coil 12 and the compensation coil 13 are subject to various factors such as changes in winding thickness, tension differences applied during winding, changes in winding density, and reverse winding pitch at the ends of the coil during manufacture. For some reason, the uniformity of the magnetic field is worse than that determined by ideal calculation. There is an upper limit to the precision of coil manufacturing depending on the machine tool and manufacturing method. Therefore, if it is desired to manufacture a magnet with very high magnetic field uniformity, a compensation system is required to increase the uniformity. Therefore, in the present invention, a tap is provided on the compensation coil 13 to enable proper compensation. That is, in FIG. 3, the end point of the superconducting wire 12a wound around the main superconducting coil 12 is connected to the compensation coil 13 via the crossover wire 14.
is connected to the superconducting wire 13a. A tap 15 for switching and connecting current leads is attached several turns above the end of the winding of the superconducting wire 13a.

Next, we will discuss the effects. If it becomes clear from actual measurements of the magnetic field that the magnetic field is not as homogeneous as designed, the main superconducting coil 1 can be removed by connecting a current lead to an appropriate tap 15.
The first and second order fluctuations of the magnetic field in the axial direction of the main superconducting coil 12 are corrected to create a highly uniform magnetic field region in a finite region at the center of the main superconducting coil 12. To describe this in more detail, if the center of the coordinate C shown in FIG. 2 is the center of the main superconducting coil 12, the coil is rotationally symmetric, so the Take. When the magnetic flux density in the z-axis direction changes linearly with the change in z, the number of turns of one of the compensation coils 13 attached to both ends of the main superconducting coil 12 is increased by operating the tap 15, and the compensation of the other is increased. The number of turns of the coil 13 is similarly reduced by operating the tap 15. When the magnetic flux density in the z-axis direction changes in proportion to the square of z, the number of turns of the compensation coils 13 at both ends is increased or decreased by the same number. Tap 15 is selected to decrease the number of turns when the magnetic flux density increases with z, and to increase the number of turns when it decreases with z. Furthermore, when a change in magnetic flux density occurs only on one side of the z-axis viewed from the coordinate origin, it is only necessary to increase or decrease the number of turns of the compensation coil 13 on the side where the change occurs.

Although a superconducting magnet has been described in the above embodiment, a normal conducting magnet may also be used, and the same effect can be obtained.

As described above, according to the present invention, the decrease in magnetic field uniformity due to dimensional errors during the manufacturing of the superconducting coil is compensated for by increasing or decreasing the number of turns of the compensation coil winding by changing the taps. There is no need to provide a superconducting coil with shims, making the device simpler and cheaper than conventional superconducting coils with shims. Also,
If the coil windings are made fine, changes in magnetic flux density due to switching between adjacent taps will be small, so even with the above-described discrete adjustment method, high magnetic field uniformity can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a conventional device, FIG. 2 is a vertical cross-sectional view of a main part of an embodiment of the present invention, and FIG. 3 is a partial wiring diagram. 11... superconducting magnet, 12... main superconducting coil, 12a... superconducting wire, 13... compensation coil, 13a... superconducting wire, 14... crossover wire, 15
...Tap.

Claims (1)

[Claims] 1. A main superconducting coil, a pair of compensation coils attached to both ends of the main superconducting coil in the axial direction and respectively connected to the main conducting coil, and a current lead provided connected to the compensation coil by switching and connecting the A superconducting magnet comprising a plurality of taps for compensating for a decrease in magnetic field uniformity of a main superconducting coil.