Methods and systems for maintaining a high vacuum in a vacuum enclosure

Abstract

A system for maintaining a high vacuum in a vacuum enclosure such as cryostat, for example, is described. The system includes a high-vacuum pump having an input that is connected to the cryostat and an output. A vacuum vessel is connected to the output of the high-vacuum pump. A second vacuum pump is connectable to the vacuum vessel. The system is operated such that the high-vacuum pump maintains the cryostat at a high vacuum and the second vacuum pump is periodically operated to maintain the pressure of the vacuum vessel below a threshold pressure. The second vacuum pump may be either permanently connected to, or removable from, the vacuum vessel. The vacuum vessel acts to maintain the output of the high-vacuum pump within a suitable pressure range. This removes the need for the output of the high-vacuum pump to be connected to a continuously operating, second-stage vacuum pump. Furthermore, the second vacuum pump is only required to be operated periodically in order to maintain the pressure in the vacuum vessel below the threshold pressure.

Claims

1. A system for maintaining a high vacuum in a vacuum enclosure comprising: a rotary cryostat; a vacuum vessel; a high-vacuum pump having an input connected to the vacuum enclosure and an output connected to the vacuum vessel; and a second vacuum pump connectable to the vacuum vessel; wherein the high-vacuum pump is operated to maintain the cryostat at a high vacuum and the vacuum vessel is maintained below a threshold pressure by periodic operation of the second vacuum pump, and; wherein the high-vacuum pump and the vacuum vessel are mounted to rotate with the rotary cryostat.

2. The system of claim 1, wherein the second vacuum pump is only connected to the vacuum vessel when it is necessary to operate the second vacuum pump.

3. The system of claim 1, wherein the second vacuum pump is permanently connected to the vacuum vessel.

4. The system of claim 1, wherein the second vacuum pump is a low-vacuum pump.

5. The system of claim 4, wherein the second vacuum pump is a diaphragm pump.

6. The system of claim 1, further comprising a valve formed at a connection between the vacuum vessel and the second vacuum pump.

7. The system of claim 1, wherein the high-vacuum pump is a turbo-molecular pump.

8. The system of claim 1, wherein the input to the high vacuum pump comprises a valve.

9. The system of claim 1, wherein the high-vacuum pump is mounted on the rotary cryostat such that the rotary axis of the cryostat is coaxial with the rotary axis of the high-vacuum pump.

10. The system of claim 1, wherein the second vacuum pump is powered by the rotation of the rotary cryostat.

11. A method of maintaining a high vacuum in a rotary cryostat, the rotary cryostat being connected to an input of a high-vacuum pump and an output of the high-vacuum pump being connected to a vacuum vessel; the method comprising the steps of: operating the high-vacuum pump to maintain a high vacuum in the vacuum enclosure; and maintaining the pressure in the vacuum vessel below a threshold pressure by periodically operating a second vacuum pump to evacuate the vacuum vessel, the high-vacuum pump in the vacuum vessel being mounted to rotate with the rotary cryostat.

12. The method of claim 11, wherein the step of maintaining the pressure in the vacuum vessel by operating the second vacuum pump includes connecting the second vacuum pump to the vacuum vessel before each operation and disconnecting the second vacuum pump from the vacuum vessel after each operation.

13. The method of claim 11, wherein the second vacuum pump is permanently connected to the vacuum vessel.

14. The method of claim 11, wherein the second vacuum pump is a low-vacuum pump.

15. The method of claim 14, wherein the second vacuum pump (5) is a diaphragm pump.

16. The method of claim 11, wherein the high-vacuum pump is a turbo-molecular pump.

17. The method of claim 11, wherein the high-vacuum pump is mounted on the rotary cryostat such that the rotary axis of the cryostat is coaxial with the rotary axis of the high-vacuum pump.

18. The method of claim 11, wherein the operation of the second vacuum pump is powered by the rotation of the rotary cryostat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic drawing of an embodiment of a system according to the present invention that operates according to the method of the present invention.

(3) FIG. 2 is an illustration of the cryostat, high vacuum pump, and vacuum vessel, illustrated in FIG. 3, configured in accordance with a rotating reference frame, according to the embodiments. 15

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) A system for maintaining a high vacuum according to the present invention is shown in FIG. 1. The system 1 comprises a stationary cryostat 2, a turbo-molecular pump 3 (or high-vacuum pump), a vacuum vessel 4 and a diaphragm pump 5 (or second vacuum pump). The turbo-molecular pump 3 has an inlet 6 that is connected to the cryostat 2. The inlet 6 of the turbo-molecular pump 3 includes a valve 7 that allows the inlet to be opened and sealed as required. The turbo-molecular pump 3 has an outlet 8 that is connected to the vacuum vessel 4. The diaphragm pump 5 has an inlet 9 that is connectable to the vacuum vessel 4 (shown to be operably connected in FIG. 1). The inlet 9 of the diaphragm pump has a valve 10 that allows the inlet to be opened and sealed as required when the diaphragm pump is connected to the vacuum vessel.

(5) The system 1 can be operated to maintain a high vacuum in the cryostat 2 in the following manner. During normal operation, the valve 7 of the inlet 6 of the turbo-molecular pump 3 is open and the turbo-molecular pump is continuously operated to maintain the pressure within the cryostat 2 within a high vacuum range in a conventional manner. The outlet 8 of the turbo-molecular pump 3 directs the exhaust of the turbo-molecular pump to the vacuum vessel 4. During normal operation, the valve 10 is closed and the diaphragm pump 5 is not operably connected to the vacuum vessel 4. The high-vacuum pump 3 is mounted on the rotary cryostat 2 such that a rotary axis 12 of the cryostat 2 is coaxial with the rotary axis 12 of the high-vacuum pump 3.

(6) Before initial operation, after the cryostat 2 has been evacuated to a high vacuum, the vacuum vessel 4 is evacuated using the diaphragm pump 5 such that it has a pressure suitable for the outlet 8 of the turbo-molecular pump 3. A suitable pressure for the vacuum vessel 4 will be a pressure that allows the turbo-molecular pump 3 to operate satisfactorily. In particular, the pressure of the vacuum vessel 4 must typically be low enough to prevent the turbo-molecular pump 3 from stalling. After evacuating the vacuum vessel 4, the valve 10 is closed and the diaphragm pump 5 is operably disconnected from the vacuum vessel 4. The turbo-molecular pump 3 is operated in a conventional manner to maintain the high vacuum within the cryostat 2.

(7) Over time, as the turbo-molecular pump 3 is operating, the pressure of the vacuum vessel 4 will rise due to the gas entering the vacuum vessel 4 from the exhaust of the turbo-molecular pump 3. When the pressure of the vacuum vessel 4 rises to a first pre-defined limit (i.e. a threshold pressure) the diaphragm pump 5 is operably connected to the vacuum vessel 4. The valve 10 of the inlet 9 of the diaphragm pump 5 is opened and the diaphragm pump 5 is operated to re-evacuate the vacuum vessel. When the action of the diaphragm pump 5 has reduced the pressure in the vacuum vessel 4 to a second pre-defined limit, the valve 10 of the inlet 9 of the diaphragm pump 5 is closed, the diaphragm pump is stopped, and the diaphragm pump is operably disconnected from the vacuum vessel 4. In this manner the pressure within the vacuum vessel 4 can be permanently maintained between the first pre-defined limit (which is equal to, or lower than, a threshold pressure) and the second pre-defined limit. During and after the operation of the diaphragm pump 5, the turbo-molecular pump 3 is operated to maintain the high vacuum within the cryostat 2. The diaphragm pump 5 can be physically removed from the vacuum vessel 4 if necessary.

(8) As will be readily appreciated, the precise values of the first and second pre-defined limits are dependent upon the requirements of the specific individual system. Generally, the second pre-defined limit will be the lowest pressure that can be reasonably achieved in the vacuum vessel by a diaphragm pump 5 or other conventional pumping means. The first pre-defined limit may be the upper limit of pressure at which outlet 8 of the turbo-molecular pump 3 may be maintained, i.e. the threshold pressure of the vacuum vessel.

(9) In FIG. 2, the high vacuum pump 3 and the vacuum vessel 4 are mounted to rotate with the rotary cryostat 2. That is, the rotary cryostat 2 in the vacuum vessel 4 are mounted to share a rotating reference frame (i.e., rotating about the axis 12).

(10) The cryostat can be a rotary cryostat.