EP3867528A1

EP3867528A1 - Non-mechanical vacuum pumping system and analytical instrument

Info

Publication number: EP3867528A1
Application number: EP19787367.2A
Authority: EP
Inventors: Andrew David CHEW
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2018-10-18
Filing date: 2019-10-03
Publication date: 2021-08-25
Anticipated expiration: 2039-10-03
Also published as: GB2578138A; EP3867528B1; WO2020079396A1; GB201816978D0

Abstract

A mobile pumping system and analytical instrument are disclosed. The mobile pumping system comprises exclusively non-mechanical pumps for providing a vacuum, said system comprising: a vacuum chamber; a shock resistant non- mechanical intermediate vacuum pump configured to evacuate a chamber from a first pressure to a second intermediate pressure, said first pressure being a pressure between 10 mbar and 1 X 10-2 mbar; and an internal power supply for supplying power to said pump.

Description

NON-MECHANICAL VACUUM PUMPING SYSTEM AND ANALYTICAL

INSTRUMENT

FIELD OF THE INVENTION

The field of the invention relates to a mobile non-mechanical pumping system and an analytical instrument.

BACKGROUND

There are a range of vacuum pumps available providing different levels of vacuum, different vacuum pumps being suitable for different pressure regions.

Primary pumps such as Roots, Scroll and Northey-claw pumps are operable from atmospheric pressure to ~ 1 X 10 ² mbar. To reach pressures below 10 ² mbar a different type of vacuum pump is required and this has generally been provided by a turbomolecular pump. Turbomolecular pumps are able to evacuate from about 10 ¹ mbar to <10 ¹¹ mbar depending on their design and configuration.

Although turbomolecular pumps are designed to operate in these pressure regions they require a backing pump. Furthermore, owing to their high speed of rotation and close manufacturing tolerances, they are vulnerable to mechanical shocks. For higher vacuums getter pumps are often used. These pumps have a limited lifetime and operation at lower vacuums reduces this lifetime considerably.

Although a range of vacuum pumps has been developed for providing different levels of vacuum, there are advantages and drawbacks with the different pump types. In particular, turbomolecular pumps are sensitive to vibrations and shocks. Furthermore, all mechanical or rotating pumps generate some level of rotating electro-magnetic field and vibrations. Some analytical instruments may be sensitive to such things.

It would be desirable to be able to provide a pumping system and analytical instrument that are able to operate with pumping systems providing the required level of vacuum in a convenient manner. SUMMARY

A first aspect provides a mobile pumping system comprising exclusively non- mechanical pumps for providing a vacuum, said system comprising: a vacuum chamber; a shock resistant non-mechanical intermediate vacuum pump configured to evacuate a chamber from a first pressure to a second intermediate pressure, said first pressure being a pressure between 10 mbar and 1 X 10 ² mbar; and an internal power supply for supplying power to said pump.

The inventors of the present invention recognise that a drawback of

turbomolecular pumps which makes them unsuitable for mobile pumping systems, is related to their mechanical structure and the requirement to mount the rotor in a manner that allows a high rotational speed, and provides positioning and spacings to high tolerances. The speed of rotation and the closeness of the tolerances make the pumps very susceptible to shocks. Furthermore, such pumps are not able to pump down from atmospheric presssure and require backing pumps. These backing pumps themselves require power and can be bulky. The inventors recognised these drawbacks arise from the mechanical or rotational nature of the pumps and that providing exclusively non mechanical pumps in such a system would address these drawbacks.

Furthermore, non-mechanical pumps are available that pump in the vacuum regions conventionally pumped by turbomolecular pumps. As they do not require backing pumps and are non-mechanical their power consumption is considerably lower than those of a conventional system, comprising a turbomolecular and backing pump, again improving the mobility of the system and lengthening the lifetime of the system when operating from an internal power supply.

Additionally, the lack of requirement for a backing pump provides greater flexibility and the pumping system is not so vulnerable to a loss of vacuum allowing the system to be used in rougher environments. Thus, a mobile pumping system is provided that comprises exclusively non mechanical pumps and has at least one intermediate pump that is able to evacuate the chamber from a first pressure to a second intermediate pressure, the first pressure being between 10 mbar and 1 X 10² mbar. This pressure range is a pressure range that conventionally is served almost exclusively by

turbomolecular pumps and as such providing vacuums in this range has been difficult in a mobile system. The inventors have addressed this by recognising that a non-mechanical pump would have many advantages regarding mobile use and may be configured for operation in this range.

In some embodiments, the system further comprises a shock resistant non- mechanical high vacuum pump configured to evacuate said chamber from said second intermediate pressure to a third high vacuum pressure.

In addition to the intermediate vacuum pump there may be a high vacuum pump configured to evacuate the chamber from the intermediate pressure to a third high vacuum pressure.

There are not many pumps configured for operation in the vacuum ranges of operation of a turbomolecular pump. Where the target vacuum is a high vacuum, then it may be advantageous to have two pumps, one for pumping for a shorter period of time in the lower vacuum regions and the other for pumping at higher vacuums during the operational period of the system. In this regard non- mechanical pumps such as for example ion or Getter pumps, will be depleted quickly if operated at higher pressures. This is addressed by the use of an intermediate pump which operates in the region that conventionally a

turbomolecular pump would have operated in and which is only operational during pump down and thus, although its performance may deteriorate more quickly when operational than a pump operated at a lower pressure, as it is only used for shorter periods its overall lifetime is prolonged. Furthermore, by providing two pumps, one may be configured specifically for a higher pressure operation and thus, be more resistant to this deterioration. In some embodiments, the system comprises an external connecting port for connection to an external primary pump for evacuating said chamber to said first pressure during an initialisation phase.

As the non-mechanical intermediate vacuum pump is able to evacuate from a first pressure of between 10 mbar and 1 X 10 ² mbar, a primary pump may be used to provide this initial pressure. There may be an external connecting port for connection to this primary pump and during an initialisation phase the chamber may be evacuated to the pressure at which the intermediate vacuum pump can start operation. At this point the mobile pumping system may be disconnected from the primary pump using the external connection and the pump may be used in a mobile manner.

In some embodiments, the mobile pumping system further comprises an unmanned aerial vehicle configured to transport said mobile pumping system.

There are many applications of a mobile pumping system that exclusively comprise shock resistant non-mechanical vacuum pumps. One of these is within an unmanned aerial vehicle. There may be situations where the quality of a gas in a remote location is to be analysed. For example, where there has been a potential incident at a polluting entity such as a nuclear power station or where there is a conflict zone. Being able to access the gases locally to determine their composition and whether it may be safe to enter the zones is important in these cases. Many analytical instruments for analysing gases require vacuums to perform this analysis. Providing a mobile pumping system that is formed exclusively of non-mechanical pumps that are resistant to shocks allows them to be mounted on an unmanned aerial vehicle and allows analysis of these gases in these remote locations in a safe and accurate manner.

In other embodiments, the mobile pumping system comprises a portable container for carrying said mobile pumping system. As an alternative to the unmanned aerial vehicle the mobile pumping system may be mounted on a container allowing the mobile pumping system to be carried by a user. In some embodiments, the mobile pumping system comprises a vehicle for transporting said pumping system.

Alternatively and/or additionally the mobile pumping system may be mounted within a vehicle. This may allow it to reach a remote location. Where the location is such that it is not accessible by a vehicle, then providing a mobile pumping system that can be carried in a portable container allows access to even more remote locations. In some cases the portable pumping system may be

transported initially in a vehicle and then carried to the final destination by a user. In this regard the vehicle may have the primary pump within it and the system may be pumped down to an initial pressure of between 10 mbar and 1 X 10 ² mbar before the mobile system is disconnected from the primary pump and moved in the portable container to the point where it is to be used.

In some embodiments, said first pressure comprises a pressure between 5 mbar and 1 X 10 ¹ mbar.

In some embodiments, the second intermediate pressure comprises a pressure between 10 ³ mbar and 10 ⁶ mbar.

The intermediate vacuum pump is configured to pump down from an initial relatively low vacuum of between 10 mbar and 10 ² mbar to a higher vacuum, which in some embodiments, where the system does not have a high vacuum pump, may be the operational point of the pumping system. In this regard although the pump may be configured for operation at the lower vacuums, this may be during an initial pump down phase that only lasts for a short time period, and the lifetime of the pump is extended as general operation is at the higher vacuums of the second intermediate pressure generally in the region of 10 ⁶ mbar. In some embodiments, said second intermediate pressure comprises a pressure between 5 X 10 ⁴ mbar and 5 X 10 ⁵ mbar.

In some embodiments, said third high vacuum pressure comprises a pressure below 10 ⁵ mbar, preferably said third high vacuum pressure comprises a pressure below 10 ^~7 mbar.

There are various types of non-mechanical pumps that may be used, including vapour and diffusion pumps, however in some embodiments the pumps comprise capture pumps and in some embodiments, said capture pumps comprise getter pumps, for example, ion getter, non-evaporable getter or Ti sublimation pumps..

Getter pumps do not have rotating parts and are non-mechanical and as such are shock resistant. Conventionally they have only been operable at high vacuums as operating at lower vacuums uses up the active sputtering surface and decreases the lifetime of the pump. This has been addressed by various design changes allowing these pumps to be used at lower vacuums and thus, making them suitable for mobile use.

Getter pumps, also commonly known as ion getter pumps or sputter ion pumps comprise an array of cylindrical anode tubes arranged between two cathode plates. An electrical potential is applied between the anode and cathode at the same time as magnets on opposite sides of the cathode plates generate a magnetic field aligned with the axes of the anode cylinders. The Getter pump operates by trapping electrons within the cylindrical anodes, gas molecule entering one of the anodes being struck by the trapped electrons causing the molecule to ionize. The resulting positively charged ion is accelerated by the electrical potential towards one of the cathode plates leaving the stripped electrons in the cylindrical anode to be used for further ionization of other gas molecules. The positivity charged ion is trapped at the oppositely charged electrode, an event in which it causes material from the cathode to be sputtered into the vacuum chamber of the pump. The sputtered material coats surfaces within the anode and acts to capture additional molecules moving within the pump. It is the sputtering effect that leads to a finite lifetime of the pump as the surface being sputtered will gradually be depleted. As can be understood operation at higher pressures with more molecules will increase the rate at which the active surface is used up. Operating at higher pressures for reduced amounts of time and using specially designed pumps that mitigate this depletion effect will enable a pump operating at these higher pressures to have an improved lifetime.

In particular, providing pulsed electric discharge in a Getter pump has been found to lengthen its life and allow higher pressure operation.

In some embodiments, said pumps comprise point of use pumps.

In addition to being shock resistant non-mechanical pumps can also be made in a miniaturised form allowing them to be particularly suitable for mobile use.

In some embodiments, said pumps comprise handheld pumps.

The pumps may be made to a size such that they are handheld pumps. Volumes of less than one litre are typical for such sizes of pumps. The intermediate pump may have a size of about 3 X 3 X 5 cm and comprise a pumping speed of 0.2 l/sec or less at 10⁶ mbar.

A second aspect provides a mobile mass spectrometer comprising a mobile pumping system according to a first aspect.

Mass spectrometers require relatively high vacuums and their use may be required at remote locations. Thus, the mobile pumping system of embodiments is particularly applicable for use with a mobile mass spectrometer allowing gases to be analysed at different locations in an effective and convenient manner. A third aspect provides an analytical instrument comprising a vacuum chamber for holding a sample, said analytical instrument comprising: a primary pump for evacuating said chamber to a first pressure; and a non-mechanical intermediate vacuum pump configured to evacuate said chamber from said first pressure to a second intermediate pressure, said first pressure being a pressure between 10 mbar and 1 X 10 ² mbar.

Analytical instruments that require vacuums may also benefit from non- mechanical pumps. Non-mechanical pumps are not only shock resistant, but they do not require backing pumps or rotors mounted on magnetic bearings. Furthermore, the lack of rotation means they do not generate vibrations. The inventors of the present invention recognised that for some analytical instruments that require a vacuum for operation and that are sensitive to one or more of vibrations and electro-magnetic fields, a non-mechanical pumping system and in particular, one where such pumps span the vacuum range generally serviced by turbomolecular pumps provide a good pumping solution.

In some embodiments, the analytical instrument further comprises a non- mechanical high vacuum pump configured to evacuate said chamber from said second intermediate pressure to a third high vacuum pressure.

In some embodiments, said analytical instrument comprises a surface science instrument.

In some embodiments, said analytical instrument comprises an electron microscope, said vacuum chamber comprising an electron gun region and a sample region, said non-mechanical intermediate vacuum pump being configured to evacuate said electron gun region, said electron microscope further comprising a non-mechanical high vacuum pump configured to evacuate said sample region to a third high vacuum pressure. ln some embodiments, said non-mechanical pumps comprise Getter pumps.

In some embodiments, said non-mechanical intermediate vacuum pump comprises a high pressure Getter pump configured for pulsed electric discharge.

In some embodiments, said second pressure comprises a pressure between 10 ³ mbar and 10 ⁶ mbar.

In some embodiments, said third high vacuum pressure comprises a pressure below 10 ⁵ mbar, preferably below 10 ⁷ mbar.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 provides a schematic diagram of typical operating pressure regions for different pumps;

Figure 2 shows a mobile pumping system according to an embodiment; and Figure 3 shows an analytical instrument according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide a modular mobile pumping system that is attachable to a primary mechanical vacuum pump (achieving low to medium vacuum) external to the mobile system for a first initialisation stage. Embodiments of the mobile system comprises an‘intermediate’ capture pump (operating in some

embodiments from 10 mbar and in others from 0.1/1 mbar to 10⁵ / 10⁶ mbar) and a high vacuum Ion Getter and/or Non evaporable getter pump to achieve and maintain high and ultra-high vacuum.

A benefit of embodiments is that after the initial evacuation using a mechanical pump, capture and Getter based technologies only are required. Kinetic turbomolecular pumps are thus unnecessary and the resulting unit is shock resistant, does not require a backing pump, and does not generate the same electro-mechanical fields that a rotating machine may generate. Furthermore, the pump is resistant to radiation which may be advantageous if used in a system sampling radioactive gas for example.

High and ultra-high vacuum pumping modules generally require a primary mechanical pump to achieve pressures where secondary pumps can be operated. Of the latter turbomolecular and diffusion pumps require the continued use of a supporting primary pump. Capture secondary pumps such as Getter pumps operate independently but conventionally require a turbomolecular pump to achieve their‘starting’ pressure.

Figure 1 schematically shows different vacuum pumps and their regions of operation.

Primary pumps denoted by P may comprise Roots blowers, scroll pumps, diaphragm pumps or other such pumps. These generally operate from

atmosphere down to 1 X 10² mbar. Turbomolecular pumps T operate in an intermediate region between 1 X 10^_1 mbar and 1 X 10 ¹¹ mbar. For higher vacuums other pumps may be used. These include standard Non-Evaporable Getter pumps denoted by N and operating between 1 X 10⁸ mbar and 1 X 10 ¹² mbar and Titanium Sublimation pumps denoted by TS and operating between 1 X 10⁸ mbar and1 X 10 ¹² mbar.

In addition to these more conventional pumps there have recently been

developed High Pressure Getter pumps denoted as HPG some of which may operate in the pressure region of between 10 mbar to 1 X 10⁶ mbar. Examples of pumps able to pump in these higher pressure regions are described in Russian patent application 2017126531 and US 2018/0068836 for example.

High and ultra-high vacuum pumping modules generally require a primary mechanical pump to achieve pressures where secondary pumps can be operated. Of the latter turbo-molecular and diffusion pumps require the continued use of a supporting primary pump. Capture secondary pumps operate

independently but require a turbomolecular pump to achieve their‘starting’ pressure.

Embodiments exploit such high pressure operating getter HPG pumps, or equivalent technologies to nullify the need for a TMP in this intermediate pressure range and to allow secondary pumps to be operated from a preferred vacuum level. Additionally no mechanical primary/backing pump is required after initial system evacuation.

Figure 2 shows a mobile pumping system 5 according to an embodiment. Mobile pumping system 5 comprises a vacuum chamber 10 to be evacuated. The vacuum chamber may have an inlet (not shown) in the form of an orifice or capillary for receiving sample gases to be analysed. The mobile pumping system comprises an external connection 15 configured to connect to an external primary pump for evacuating the vacuum chamber 10 to an initial vacuum of between 10 mbar and 10^-2 mbar during an initialisation phase. This connection 15 is connected via valve system 12 to vacuum chamber 10. Vacuum chamber 10 is evacuated to a first pressure, valve system 12 is closed and the primary pump is disconnected. The mobile system can then be moved to a site where it is to be used. At this point valve system 12 can connect intermediate pump 20, which is a high pressure getter pump, to the vacuum chamber and the vacuum chamber can be evacuated to a second intermediate pressure of about 10⁶ mbar. At this point high vacuum pump 30 can be started and can evacuate the chamber to the operational pressure of perhaps 10⁷ mbar. The time of operation of the high pressure getter pump at the lower vacuums is limited which increases its lifetime.

In some embodiments, the vacuum chamber is only evacuated to pressures in the region of 10⁶ mbar and in this case there may not be a high vacuum pump 30 in the mobile system.

The valve and pumps are controlled by control circuitry 50 and are powered by internal power supply 55. This may have the form of a battery or of a super capacitor.

Figure 3 shows an analytical instrument according to an embodiment. Analytical instrument is in this case an electron microscope shown schematically as 40.

The electron microscope has an electron gun region that is evacuated by a high pressure ion getter pump 20 and a sample region evacuated to a higher vacuum by high vacuum pump 30. The high pressure ion getter pump does not have a motor and does not generate a rotating electro-magnetic field and requires less or no shielding from the electron microscope. Furthermore as it is a non- mechanical pump it does not generate vibrations and does not interfere with the operation of the instrument.

In summary mobile pumping systems are provided where the module is resistant to motion, shocks and acceleration making them suitable for Point of Use systems and aeronautical use (e.g. UAV). Additionally no backing pump is required in contrast to current TMP/mechanical backing pump devices for PoU (including miniaturised pumps) Analytical instruments which include electron microscopes and surface science instruments suffer from sensitivity to vibrations from mechanical TMPs which limit final resolution and necessitate expensive vibration isolating devices.

Embodiments provide a system where no backing pumps are required thus preventing the need for the incorporation of vacuum reservoirs (which are used to allow the TMP to operate with the backing pump turned off); hence also overcoming the fixed operational/scanning time available before the backing line to the TMP has to be re-evacuated. The exclusion of TMPs also excludes their electromagnetic interference thus improving image magnification.

In summary there is provided systems with

- reduced power, space and cooling requirements

- increased pumping speed efficiency (close location of HPG to vacuum)

- increased lifetime of HV/UHV performance of the IGP/NEG

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modification s can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

5 mobile pumping system

10 vacuum chamber

12 valve system

15 external connection

20 high Pressure Getter pump

30 high Vacuum pump

40 electron microscope

50 control circuitry

55 internal power supply

Claims

1. A mobile pumping system comprising exclusively non-mechanical pumps for providing a vacuum, said system comprising:

a vacuum chamber;

a shock resistant non-mechanical intermediate vacuum pump configured to evacuate a chamber from a first pressure to a second intermediate pressure, said first pressure being a pressure between 10 mbar and 1 X 10² mbar; and an internal power supply for supplying power to said pump.

2. A mobile pumping system according to claim 1 , said system further comprising:

a shock resistant non-mechanical high vacuum pump configured to evacuate said chamber from said second intermediate pressure to a third high vacuum pressure.

3. A mobile pumping system according to claim 1 or 2, comprising an external connecting port for connection to an external primary pump for evacuating said chamber to said first pressure during an initialisation phase.

4. A mobile pumping system according to any one of claims 1 to 3, further comprising an unmanned aerial vehicle configured to transport said mobile pumping system.

5. A mobile pumping system according to any preceding claim, comprising a portable container for carrying said mobile pumping system.

6. A mobile pumping system according to any one of claims 1 to 3 or 5, comprising a vehicle for transporting said pumping system.

7. A mobile pumping system according to any preceding claim, wherein said first pressure comprises a pressure between 5 mbar and 1 X 10 ¹ mbar.

8. A mobile pumping system according to any preceding claim, wherein said second intermediate pressure comprises a pressure between 10³ mbar and 10⁶ mbar.

9. A mobile pumping system according to claim 8, wherein said second intermediate pressure comprises a pressure between 5 X 10⁴ mbar and 5 X 10⁵ mbar.

10. A mobile pumping system according to any preceding claim, wherein said third high vacuum pressure comprises a pressure below 10⁵ mbar.

11. A mobile pumping system according to claim 10, wherein said third high vacuum pressure comprises a pressure below 10 ^~7 mbar.

12. A mobile pumping system according to any preceding claim, wherein said non-mechanical pumps comprise capture pumps.

13. A mobile pumping system according to claim 12, wherein said capture pumps comprise Getter pumps.

14. A mobile pumping system according to claim 12 or 13, wherein said shock resistant non-mechanical intermediate vacuum pump comprises a high pressure Getter pump configured for pulsed electric discharge.

15. A mobile pumping system according to any preceding claim, wherein said pumps comprise point of use pumps.

16. A mobile pumping system according to claim 15, wherein said pumps comprises handheld pumps.

17. A mobile mass spectrometer comprising a mobile pumping system according to any preceding claim.

18. An analytical instrument comprising a vacuum chamber for holding a sample, said analytical instrument comprising:

a primary pump for evacuating said chamber to a first pressure; and a non-mechanical intermediate vacuum pump configured to evacuate said chamber from said first pressure to a second intermediate pressure, said first pressure being a pressure between 10mbar and 1 X 10² mbar

19. An analytical instrument according to claim 18,

further comprising a non-mechanical high vacuum pump configured to evacuate said chamber from said second intermediate pressure to a third high vacuum pressure;

wherein said analytical instrument comprises a surface science analytical instrument.

20. An analytical instrument according to claim 18, wherein said analytical instrument comprises an electron microscope, said vacuum chamber comprising an electron gun region and a sample region, said non-mechanical intermediate vacuum pump being configured to evacuate said electron gun region, said electron microscope further comprising a non-mechanical high vacuum pump configured to evacuate said sample region to a third high vacuum pressure.

21. An analytical instrument according to any one of claims 18 to 20, wherein said non-mechanical pumps comprise Getter pumps.

22. An analytical instrument according to any one of claims 18 to 21 , wherein said non-mechanical intermediate vacuum pump comprises a high pressure Getter pump configured for pulsed electric discharge.

23. An analytical instrument according to any one of claims 18 to 22, wherein said second pressure comprises a pressure between 10³ mbar and 10⁶ mbar.

24. An analytical instrument according to any one of claims 18 to 23, wherein said third high vacuum pressure comprises a pressure below 10⁵ mbar, preferably below 10⁷ mbar.