JPS60101455A - Method of controlling superfluid helium generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for controlling a cryogenic device, and in particular, a device for generating unsaturated superfluid helium as a coolant for a superconducting magnet device.

[Technical background of the invention and its problems]

As is well known, superconducting magnet devices use liquid helium as a refrigerant. Generally, a so-called superfluid helium generator is constructed as shown in FIG. That is, a helium tank 2 containing liquid helium 1 at a temperature of 4°2 and an unsaturated superfluid helium tank 3 are connected via a communication channel 4.

A saturated superfluid helium tank 5 for cooling the inside of the tank 3 is arranged in the unsaturated superfluid helium tank 3, and one end side of the helium tank 5 is connected to a Joule 1 to Mouson valve (hereinafter referred to as J).
It is abbreviated as T-valve. ) 6. Connect to the helium tank 2 through the primary side of the JT heat exchanger 7, and connect the other end to the JT heat exchanger 7.
It is connected to the suction port of the vacuum pump 8 via the secondary side of the heat exchanger 7. A discharge port of the vacuum pump 8 is connected to a refrigerator 10 via a compressor 9. and,
The inside of the helium tank 1 is cooled by the above-mentioned freezing MIO.

Therefore, this device makes the helium in the unsaturated superfluid helium tank 3 superfluid in the following manner. That is, while maintaining the inside of the unsaturated superfluid helium tank 3 at one pressure, the vacuum pump 8, compressor 9, and refrigeration t1
Operate 10. By the operation of the vacuum pump 8, a portion of the helium at 4°2 in the helium tank 2 is transferred to the primary side of the JT heat exchanger 7, the JT valve 6, and the saturated superfluid helium (No. 5, J
It flows through the secondary side path of the T heat exchanger 7. Assuming that the inside of the saturated superfluid helium tank 5 is evacuated by the vacuum pump 8 to a saturated vapor pressure corresponding to a temperature lower than the temperature Tb inside the unsaturated superfluid helium tank 3, the helium leaving the helium tank 2 is precooled to, for example, 2.2 K while passing through the primary side of the JT heat exchanger 7, and is then expanded by the JT valve 6 to become a gas and a liquid at a temperature TS. This liquid evaporates while passing through the saturated superfluid helium tank 5, and as a result,
The helium in the unsaturated superfluid helium tank 3 is cooled.

By the way, in such a device, there is a particular problem in how to control the JT valve 6 during initial freezing. That is, until now there has been no reliable guideline for adjusting the JT valve 6. For this reason, the reality is that adjustments are made based on so-called intuition.
Helium enters the JT heat exchanger 7 due to the excessive gap, which causes an unstable phenomenon in which the temperature on the upstream side of the JT valve 6 changes drastically. There was a problem.

(Object of the Invention) The present invention has been made in view of the above circumstances, and its purpose is to efficiently and stably reduce the temperature of an unsaturated superfluid helium tank to a target superfluid helium temperature. An object of the present invention is to provide a method for controlling a superfluid helium generator capable of initial freezing up to

[Summary of the invention]

In the present invention, a saturated superfluid helium tank for cooling the inside of the unsaturated superfluid helium tank is arranged, and cooling helium is passed through a Joule-Thomson valve into the saturated superfluid helium tank. In the superfluid helium generator configured to
During initial freezing from K to 2.17 below superfluid helium temperature, the temperature Tb of the unsaturated superfluid helium bath
and the temperature Ts of the saturated superfluid helium tank,
The TS is controlled by the Joule-Thomson valve so that the relationship between the Tb and the TS is the maximum refrigerating capacity, and the Ts is controlled so that the amount of heat input and the refrigerating capacity become equal when the target temperature is reached. It is characterized in that it is controlled by a Joule-Thomson valve to obtain an equilibrium state.

This will be explained in more detail as follows.

That is, let us now consider a steady state in which the mass flow peak in the JT valve and the exhaust mass flow peak p by the vacuum pump are equal. Assuming that the temperature at the outlet of the vacuum pump is 300K, as the temperature Ta increases, the temperature increases, i.e.,
Refrigeration capacity increases.

However, when the temperature Ts approaches <f% degrees Tb of an unsaturated superfluid helium bath, the refrigeration capacity Q becomes It decreases according to the formula Q=aKAcTb3 (Tb Ts). Here, AC is the heat transfer area of the saturated superfluid tank.
This is a coefficient when the TS resistance is hK=ah TS.

Now, the exhaust capacity of the vacuum pump is 70001/'min,
Tb=2. OK, aK Ac =200WK →
Fig. 2 shows the calculation of the refrigerating capacity Q in the case of . As can be seen from this figure, the amount of heat input Q
There are two equilibrium points, A and B, for ir+. State B cannot be a steady state because the liquid volume in the saturated superfluid helium tank is increasing. On the other hand, in state A, all of the helium that expanded and liquefied JT evaporates, and its latent heat balances the amount of heat input. Here, the temperature range between temperature Tm and temperature Tb where the maximum refrigerating capacity is obtained is an unstable range where liquid may enter the JT heat exchanger. Therefore, in order to perform initial freezing at the maximum refrigerating capacity, it is sufficient to always operate with the temperature Ts set close to Tm, which is lower than the temperature Tb. This relationship is expressed in terms of temperature Ts and temperature Tb as shown in FIG. 3.

In FIG. 3, the shaded area is the area where the effective refrigerating capacity is positive. The refrigerating capacity is maximum at the solid line portion.

Moreover, the dotted line portion is a state of stable equilibrium.

The control method according to the present invention skillfully utilizes such a relationship. First, in the initial freezing from 4.2K, the opening degree of the JT valve is adjusted while monitoring the temperatures Tb and Ts, and the temperature Control is performed so that Ts is within the shaded area in FIG. 3 and as close as possible to the solid line where the maximum refrigerating capacity is obtained.

Then, in response to the temperature drop in the unsaturated superfluid helium tank, the JT valve is throttled to prevent it from entering the unstable region. Furthermore, when the target temperature is reached, the JT valve is further narrowed down to control the temperature TS so that the refrigerating capacity is commensurate with the amount of heat input, thereby shifting to a stable equilibrium state.

〔Effect of the invention〕

With such a control method, it is possible to reliably prevent the above-mentioned problems caused by over-throttling or opening the JT valve, and it is possible to efficiently perform initial freezing to a target temperature.

[Embodiments of the invention]

The present invention will be explained in detail below.

FIG. 4 shows an example of an apparatus for implementing the control method according to the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals. Therefore, the explanation of the overlapping parts will be omitted.

In the figure, 21 is the temperature T of the saturated superfluid helium tank 5.
22 is a temperature sensor that detects the temperature Tb of the unsaturated superfluid helium bath 3. The outputs of these furniture sensors 2L 22 are input to the controller 25 via interface circuits 23 and 24, respectively. On the other hand, the drive shaft of the JT valve 6 is connected to a stepping motor 26. Further, the stepping motor 26 is controlled by the controller 25.

The controller 25 is composed mainly of, for example, a computer, and stores information in an internal storage device based on the heat transfer area of the saturated superfluid helium tank 5 and the amount of heat intrusion into the unsaturated superfluid helium tank 3. A cooling diagram as shown in FIG. 3 is stored in advance. Then, the temperatures TS and Tb are read at predetermined time intervals, and from the relationship between these temperatures Ts and Tb and the stored cooling diagram, the temperature TS
The opening degree of the JT valve 6 is controlled via the stepping motor 26 so that the opening is within the shaded area in FIG. 3 and in a direction that increases the refrigerating capacity. That is, temperature T
The opening degree of the JT valve 6 is controlled so that S gradually decreases as shown by the solid line Z in FIG. By repeating such control, when the temperature Tb drops to the target temperature, the JT valve 6 is throttled down to control the temperature TS so that it reaches exactly the dotted line in FIG. 3. Therefore, it is possible to initially freeze to the target temperature, that is, the target superfluid helium temperature, without causing any instability phenomena, and to stabilize it in that state, resulting in the above-mentioned effect being obtained. become.

It should be noted that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the spirit of the invention.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the superfluid helium generator, Figure 2
3 and 3 are diagrams for explaining the principle of the control method of the present invention, and FIG. 4 is a schematic configuration diagram of an apparatus implementing the control method of the present invention. 2... Helium tank, 3... Unsaturated superfluid helium tank, 5... Saturated superfluid helium tank, 6... Joule 1
~ Musson valve LJT valve), 7... JT heat exchanger, 8...
・Vacuum pump, 21.22...Temperature sensor, 25・
...Roller to controller 1, 26...Stepping motor. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Tb (on)

Claims (1)

[Claims] A saturated superfluid helium tank for cooling the inside of the unsaturated superfluid helium tank was placed inside the unsaturated superfluid helium tank, and helium for cooling was made to flow through the saturated superfluid helium tank through a Joule-Thomson valve. In the superfluid helium generator, the inside of the unsaturated superfluid helium tank is heated from 4.2K to 2.0K.
In step 17, during initial freezing to the following superfluid helium temperature, the temperature Tb of the unsaturated superfluid helium tank and the temperature TS of the saturated superfluid helium tank are monitored, and the relationship between the above Tb and TS is determined by freezing. The above-mentioned TS is controlled by the Joule-Thomson valve so that the capacity is maximized, and the above-mentioned T is controlled so that the amount of heat input becomes equal to the refrigerating capacity when the target temperature is reached.
A method for controlling a superfluid helium generator, characterized in that S is controlled by a Joule-Thomson valve to obtain an equilibrium state.