JPH0428210A - Cryogenic temperature device for superconducting coil - Google Patents

Abstract

PURPOSE:To obtain a water supply system requiring no forced circulation device for feeding of liquid nitrogen by a method wherein a cooling pipe arrangement, having the specific inside diameter, led out from a liquid nitrogen reservoir and provided by thermally connecting to a thermal shielding plate, is provided in a vacuum container. CONSTITUTION:Gravity is used as the driving force with which liquid nitrogen will be fet to a cooling pipe 4 in order to maintain a thermal shielding plate 3 at the temperature of liquid nitrogen. In this case, if the pipe has the inside diameter of about 15mm or more, the liquid nitrogen can be fed by the force of gravity without generation of vapor lock, and the thermal shielding plate 3 can be cooled sufficiently. Accordingly, a liquid nitrogen feeding system and a thermal shielding plate can be constituted with gravity as driving force using the pipe having the inside diameter of 15mm or more. Thus, the cooling piping is constituted in the pipe diameter of 15 to 20mm or thereabout so that the liquid nitrogen is sufficiently pervaded over the thermal shielding pipe and to accurately conduct the cooling of the thermal shielding plate, and as a result, the thermal shielding system can be constituted without occurrence of vapor lock and also without increase in size of the device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cooling a liquid nitrogen heat shield plate in a superconducting magnet.

[Prior Art] FIG. 5 shows an example of a superconducting magnet using a cryogenic device that has been manufactured so far. Figure 5 shows the literature (Institute of Electrical Engineers of Japan/Linear Drive Study Group Materials (1988-4-26) 2
This is a superconducting magnet for magnetic levitation railways published on page 7), and is a conventional example in which liquid nitrogen is forcibly supplied to cooling piping attached to a heat shield plate using a pump or pressurization in a liquid nitrogen tank. . In the figure, (2
) is the inner tank, which is a helium container containing the superconducting coil, (
3) is a heat shield plate, (7) is a persistent current switch to make the superconducting coil persistent current, (8) is an inner tank (2)
) for adiabatic support; <6) houses the components of the inner tank (2), heat shield plate (3), persistent current switch (7), and load support material (8). It is a vacuum container, that is, an outer tank. (4) is a liquid nitrogen supply pipe led from a liquid nitrogen tank (not shown).

Next, the operation of conventional magnets will be explained with a focus on heat rolling. A superconducting coil is housed in the inner tank 2), and liquid helium is also sealed therein to maintain the superconducting coil in a superconducting state. This superconducting coil is supplied with current by a power source (not shown), and is excited in persistent current mode by using a persistent current switch (7). To operate a superconducting coil in persistent current mode, a superconducting state must be maintained. For this purpose, it is necessary to reduce heat intrusion into the inner tank (2) from the outside as much as possible, and therefore, many measures are taken. Alternatively, for example, the use of heat insulating load supports (8) and the installation of heat shield plates 3) are possible.

The heat insulating load support material (8) is a measure to reduce heat intrusion due to heat conduction from the outer tank (6) to the inner tank (2), and the heat shield plate (3) similarly reduces heat intrusion due to heat radiation. This is a measure to ensure that This thermal silt plate (3) is normally cooled to liquid nitrogen temperature (77.3 lb. under 1 atm), but in this conventional example, it is maintained at the liquid nitrogen temperature by passing liquid nitrogen through the cooling pipe (4). method is adopted.

In other words, this cooling pipe (4) is led from a liquid nitrogen tank (not shown), which is used as a nitrogen reservoir in this device, and liquid nitrogen is forcedly circulated inside the cooling pipe (4) by a liquid nitrogen pump. The heat shield plate (3) is maintained at the liquid nitrogen temperature. Of course, the heat shield plate (
3) also has a large amount of heat radiation from the outer tank (6), but the basic idea when designing this type of superconducting magnet is to compensate for this with liquid nitrogen, which is cheaper than liquid helium.

[Problems to be Solved by the Invention] Conventional cryogenic devices for superconducting coils are configured and operated as described above, and therefore have the following problems. First, a forced circulation system for liquid nitrogen is required, which is by no means inexpensive. Also, since it has a drive unit, maintenance is required. In addition, if the circulation system malfunctions, it is customary to increase the internal pressure in the liquid nitrogen storage tank by 1 to supply liquid nitrogen at its own pressure, but this requires a separate device such as a valve.

The second invention was made to solve the above-mentioned problems, and aims to provide a liquid feeding system that does not require a forced circulation device for supplying liquid nitrogen.

[Means for Solving the Problems] The cryogenic device for superconducting coils according to the second invention includes: a superconducting coil; a helium container for storing the superconducting coil;
A heat shield plate is provided to reduce heat intrusion into the helium container from the outside, and a liquid nitrogen is supplied from a liquid nitrogen storage tank using gravity as a driving force to cool the heat shield plate. A vacuum vessel is provided with a cooling pipe having an inner diameter of 15 m+n or more and connected to a two-layer heat shield plate.

[Function] In the cryogenic device for superconducting coils configured in this way,
In order to use gravity as the driving force, the liquid nitrogen tank is installed at a position higher than the highest point of the heat shield plate, and the cooling piping is sized (inner diameter) to ensure that nitrogen gas evaporated due to radiant heat can be removed by buoyancy. Because of this structure, there is no need for a forced circulation device for liquid nitrogen, and the phenomenon of absence of liquid nitrogen due to vaporization does not occur.Although it is an extremely simple device, it can reliably bring the heat shield plate to the liquid nitrogen temperature level. Can be retained.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In the figure, (1) is a superconducting coil, (2) is a helium container or inner tank, (3) is a thermal silt plate, and (4) is a helium container or inner tank.
) is the cooling pipe, (5) is the liquid nitrogen tank, and (6) is the vacuum container, that is, the outer tank. The persistent current switch 7) and load support member (8) shown in the conventional example of FIG. 5 are not shown for the sake of simplicity.

The basic operation of the superconducting magnet of the embodiment configured as described above is the same as that of the conventional example. In this embodiment, the driving force for supplying liquid nitrogen to the cooling pipe (4) is gravity in order to maintain the heat shield plate (3) at the liquid nitrogen temperature. The problem in this case is that the liquid nitrogen in the cooling pipe (4) evaporates depending on the heat load on the heat shield plate (3), so it is necessary to skillfully recover the gas component into the liquid nitrogen tank 5). . In other words, it is necessary to skillfully exchange the liquid component and the gas component in a countercurrent manner within the cooling pipe. When attempting to perform countercurrent exchange of gas-liquid components in a vertical pipe, a phenomenon called paper lock sometimes occurs in which evaporated gas prevents the liquid from falling.

Strictly speaking, this phenomenon is affected by the pipe diameter, heat load, fluid viscosity, condition of the pipe inner wall surface, etc., so it is not possible to describe its appearance or non-appearance generally, but it is very likely to occur when the pipe diameter is small. Become. Therefore, the thicker the cooling pipe (4), the better. However, the thicker the cooling pipe 4), the more dead space inside the outer tank (6), which increases the size of the superconducting magnet (outer tank) itself, which becomes a problem both economically and in terms of space. , there is a limit naturally. The present invention provides information on how much the pipe diameter should be set. Figure 2 is 800 rn long
The temperature at the lowest end was measured when a NL stainless steel tube was hung vertically in a liquid nitrogen tank (5) and a heat load was applied to the tube. In this figure, characteristic curves A, B,
C and D are cases where the inner diameter is 18, 14, and 10.6 mm, respectively. From these characteristic curves, it can be seen that there is no problem at all if the inner diameter is 18 mm. That is, this is the case of characteristic curve A.

In addition, even in the case of characteristic curve B with an inner diameter of 14 mm, the temperature rise is only a few and it cannot be said that there is a major problem, so if the pipe has an inner diameter of 15 mm or more, paper lock will occur. It can be said that it is possible to send liquid nitrogen by gravity without any friction, and it can be said that the thermal silt plate (3) can be sufficiently cooled. Therefore, by using a tube having an inner diameter of 15 mm or more, a liquid nitrogen liquid feeding system and a heat shield plate using gravity as a driving force can be constructed.

Regarding the embodiment shown in FIG. 1, specific examples of the shape and configuration when attaching the cooling pipe 4) to the heat shield plate (3) are shown in FIGS. 3 and 4. In short, it is sufficient that the structure is such as to avoid flat parts or midway storage parts where evaporated gas may remain in the pipe.

In this way, in order to ensure that liquid nitrogen is sufficiently distributed in the thermal silt piping that uses gravity to cool the heat shield plate, the cooling piping is installed at a distance of 15 to 20 m.
Since it is constructed with a tube diameter of approximately 1.5 m, a heat shield system can be constructed without causing paper lock and without significantly increasing the size of the device.

[Effects of the Invention] As described above, according to the present invention, there are provided a superconducting coil, a helium container housing the superconducting coil, a heat shield plate for reducing heat intrusion into the helium container from the outside, and In order to cool this heat shield plate, a cooling pipe with an inner diameter of 15 mm or more is guided from a liquid nitrogen storage tank and thermally connected to the heat shield plate to supply liquid nitrogen using gravity as a driving force. In preparation for
A forced circulation device for liquid nitrogen is not required, and the phenomenon of absence of liquid nitrogen due to paper lock does not occur, and although it is an extremely simple device, it has the effect of reliably maintaining the heat shield plate at the liquid nitrogen temperature level.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram schematically showing a cryogenic device for superconducting coils according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing temperature characteristics according to heat load of a vertical tube with its lower end closed. Third
FIGS. 0 and 94 are perspective views showing examples of installation of cooling piping according to an embodiment of the present invention, and FIG. 5 is a perspective view showing a conventional cryogenic device for superconducting coils. (1) is a superconducting coil, (2) is an inner tank, (3) is a heat shield plate, (4) is a cooling pipe, 5) is a liquid nitrogen tank, and (6) is an outer tank. Note that the same reference numerals in the figures do not indicate the same or corresponding parts. Agent Dai Iwa Masuo 1st Figure 1 Q M 2] ノ); んI ふ 1 く; ノシ ≧: 4 Honshaga 2 Unsurprisingly Fake Packer (W) th d Bad Labor ζ 1't'' Lrr, 'J日'＼ Fig. 4 Example Komao Hiroki Tank Here Fig. 5

Claims (1)

[Claims] A superconducting coil, a helium container that houses the superconducting coil, a heat shield plate to reduce heat intrusion into the helium container from the outside, and liquid nitrogen using gravity as the driving force to cool the heat shield plate. A cryogenic device for superconducting coils, comprising a cooling pipe having an inner diameter of 15 mm or more, which is led from a liquid nitrogen storage tank for supply and is thermally connected to the heat shield plate, in a vacuum container.