JPH01205576A - Cryostat - Google Patents

Abstract

PURPOSE:To reduce an evaporation amount of liquid helium and to extend a usable term by arranging two or three sheets of 20K shields being provided with a multilayer heat insulator to be cooled by evaporation helium gas between an 80K shield and a liquid helium tank. CONSTITUTION:An 80K shield 2a to be cooled by liquid nitrogen and a liquid helium tank 1 are provided inside a vacuum heat-insulating tank 5 so as to form a cryostat. At this time, two to three sheets of 20K shields 2b, 2c and 2d provided with a multilayer heat-insulating material to be cooled by evaporation helium gas are inserted between 80K shield 2a and the liquid helium tank 1. Invasion heat entering the shields 2b, 2c and 2d due to radiant heat and conductive heat are removed by cooling capacity of evaporation helium gas. The temperature of the shield 2d nearest the helium tank 1 influencing an evaporation amount is suppressed low for reducing the evaporation amount of liquid helium. Thereby, a usable term is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Application in Industry-1-) The present invention relates to a low-heat-intrusion type fly Ostara h having a built-in superconducting coil.

(Conventional technology) Conventional cryostars y1~ will be explained using FIG. 5.

Fly Ostara 1- of conventional nuclear magnetic resonance imaging diagnostic equipment, etc.
is a liquid helium tank (10) containing a superconducting coil (10).
1) and a radiation shield placed around it■
and a heat insulating support device (2) that adiabatically supports the liquid helium tank O) and the radiation seal 1 (2) in the vacuum space (4), and a vacuum space O) are formed, and the liquid helium tank (1),
It consists of a vacuum insulation tank 0 that supports the radiation shield (2) and forms the outer shell of the device (i). The vacuum insulation tank (c) is kept at room temperature, and the radiation shield ■ is a shield at 80 K (absolute temperature) cooled with liquid nitrogen (12) and a shield at 20 cooled by another layer of gas helium 11. It is a combination. Liquid helium tank ■ is liquid helium (11)
is filled and maintained at a temperature of approximately 4.2°C at 1 atm to keep the coils contained therein in a superconducting state. A cylindrical room temperature space (6) is formed in the center of the device, and the magnetic field generated in this space is used for various purposes. 2 is a chimney connected to the liquid helium tank, which leads liquid helium injection, helium 11 gas discharge 1, current supply -I~, xi a+ wires, etc. to the outside. Since this chimney part ω becomes a heat inflow path between the room temperature part and 4.2, it is configured to have a small heat conduction cross section and a long insulation distance. The heat insulating support device ① also serves as a heat infiltration path, so use a strong metal or resin rod with low thermal conductivity.

With this configuration, maintenance is facilitated by reducing the consumption of expensive cryogen such as liquid helium.

On the other hand, in order to further reduce the consumption of liquid helium and liquid nitrogen, there is a means for cooling the radiation seal 1- and the helium tank using a small refrigerator (not shown). In this case, the refrigerator is installed by penetrating the wall of the vacuum insulation tank (c) and making thermal contact with a radiation shield or the like.

(Problems to be Solved by the Invention) In the conventional fly Ostara 1 described in -1-, a gas helium cooling seal 1 is inserted between the liquid helium gas and the radiation shield 80. Only a portion of the helium refrigerant's capacity is used; most of the refrigerant's capacity is released into the room-temperature space.

If the seal l' is cooled to 20°C with a small refrigerator, the amount of evaporation will be reduced, but the cooling capacity of the refrigerant is not enough to release all of it into the room temperature space, and the electric power of the small refrigerator is required.
It has the disadvantage that the overall amount of heat is not efficiently utilized.

The present invention solves the above eight problems and increases the cooling capacity of the refrigerant by 1-
The purpose of the present invention is to provide fried cod 1~ with low evaporation amount.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a fly ostar 1 having a shield (2a) and a liquid helium tank (1) at 80 which are cooled with liquid nitrogen in a vacuum insulation tank (c). (2
The fly Ostara 1- is constructed by inserting a shield into two or three sheets 20 having a multilayer insulation material cooled by evaporated helium gas between a) and a liquid helium tank (1).

(Function) In the Fly Ostara 1~ having the shield configured according to the present invention, the intrusion heat entering the seal 1~ into the seal 20 through radiant heat and conduction heat is removed by the cooling ability of the evaporated helium gas, the shield temperature is dispersed, and the evaporation amount is directly reduced. Since the temperature of the shield closest to the liquid helium tank, which affects the temperature of the liquid helium, is kept low, the amount of evaporation of liquid helium is reduced. Also, as shown in Figure 4, one 20 with a shield on two and three 20's.
The amount of evaporation is reduced to 1/2 and 1/3 compared to the case of a shield, respectively, and even if more than 3 shields are inserted, the amount of evaporation is reduced compared to the proportion that the space for insertion increases. The reduction rate becomes smaller.

(Example) (Configuration of Example) FIG. 1 shows the configuration of an example of the present invention in which three shields are used. Furthermore, FIG. 2 shows an enlarged detail of the part marked ``■'' in FIG. 1.

In Figure 1, the cryostat consists of a vacuum insulation tank 0, a shield (2a) 80 with multi-layer insulation +4 cooled by liquid nitrogen inside the tank 0, and a multi-layer insulation cooled with evaporated helium gas inside the tank 80. It consists of three shields 20 (2b), (2C), (2b) and a helium tank (13) containing the innermost superconducting coil.The flow of evaporated helium gas (13) As shown in FIG. 3, the shields are connected by pipes or the like so that the cooling is sequentially carried out starting from the innermost shield (2d).

(Function of the embodiment) The Fly Ostara 1- configured in this embodiment uses the cooling ability of the evaporated helium gas to remove the amount of heat that enters the shield due to radiant heat and conduction heat, disperses the shield temperature, In order to keep the temperature of the inner layer of the shield low, the evaporation of the liquid helium 11 is reduced as shown in FIG.

Further, as shown in FIG. 4, when three 201<shields are inserted, the value decreases to one 20 and 173 in the case of a shield. However, even if three or more shields are inserted, the rate of reduction in evaporation is small compared to the rate of increase in the space required for insertion, and three shields is almost optimal.

(Effects of Example) Due to the above effects, the amount of evaporation of liquid helium is reduced, and since liquid helium is expensive, it is possible to significantly reduce costs. Furthermore, since a small refrigerator is not required, reliability as a cryostat is improved.

Furthermore, since the amount of evaporation is reduced, if the same amount of liquid helium is stored, the usable period is extended, the maintenance interval for re-souring etc. becomes longer, and maintenance becomes easier.

〔Effect of the invention〕

In the fly Ostara 1 to 1 of the present invention, the amount of evaporation of the liquid helium 11 is reduced because shields are inserted into two or three sheets 20 that are cooled with evaporated helium gas. Also, no.”
Since it does not require a type 1 refrigerator, it does not require a power source, improving reliability.

Furthermore, since the amount of evaporation is reduced, if the same amount of liquid helium is contained in one container, the usable period is extended, and maintenance intervals such as re-salting become longer, making maintenance easier.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the Fly Ostara 1- of the present invention, Fig. 2 is a detailed view of the part ■ in Fig. 1, Fig. 3 is a cooling flow diagram of the radiation shield in the above embodiment, Fig. 4 The figure is a graph showing the shielding effect, and FIG. 5 is a diagram showing the conventional fly Ostara l-. 1 ・Liquid helium tank 2-Radiation shield 2a -8
0K Shield Shield 3 on 2b, 2c, 2d-20
・Heat insulation support device 4-Vacuum space 5-Vacuum insulation tank 6 Room temperature space 7・Tsubo protrusion 10 Superconducting coil 11・Liquid helium 1112・Liquid nitrogen 13・Flow agent of evaporated helium gas Patent attorney Nori Chika Ken Yudo Daiko Ken Maru - 8 ~ Toru No. 12 inserted in Figure 2 (Text Figure 4 Self-17)

Claims (1)

[Claims] In a cryostat that has an 80K shield cooled with liquid nitrogen and a liquid helium tank inside a vacuum insulation tank,
2 to 3 sheets of 20K with multilayer insulation cooled by evaporated helium gas between the 80K shield and the liquid helium tank
A cryostat characterized by a shield.