Multiple port vacuum pump system

Abstract

A vacuum pump system for evacuating at least five volumes comprising a turbomolecular pump and a forevacuum pump arranged to pump an output of the turbomolecular pump arrangement to atmosphere. The turbomolecular pump has at least five pumping stages separated by rotor blades. Not more than three pumping stages have pumping speeds in excess of ⅓ of the highest pumping speed when under vacuum and/or a pumping port cross section in excess of ⅓ of the highest pumping port cross section, and at least two pumping stages have pumping speeds less than ¼ of the highest pumping speed when under vacuum and/or a pumping port cross section of less than ¼ of the biggest pumping port cross section. The ratio of pressures between the pumping stage with the highest pressure and the pumping stage with the lowest pressure is at least 100000:1 when under vacuum.

Claims

1. A mass spectrometer system comprising: an ion source; a mass analyzer; an ion optical arrangement for transporting ions from the ion source to the mass analyzer; and a vacuum pump system for evacuating at least 5 volumes of the mass spectrometer, the vacuum pump system comprising a forevacuum pump and a turbomolecular pump arrangement, the system arranged so that the forevacuum pump pumps an output of the turbomolecular pump arrangement to atmosphere, and wherein the turbomolecular pump arrangement comprises multiple pumping ports corresponding to different pumping stages and is configured so that: there are at least 5 pumping stages, each connected to a respective volume; each pumping stage is separated by at least one set of rotor blades and at least one set of stator blades; not more than 3 pumping stages have pumping speeds in excess of ⅓ of the highest pumping speed of a pumping stage when under vacuum and/or a pumping port cross section in excess of ⅓ of the biggest pumping port cross section; at least 2 pumping stages have pumping speeds less than ¼ of the highest pumping speed of a pumping stage when under vacuum and/or a pumping port cross section of less than ¼ of the biggest pumping port cross section; wherein when under vacuum the total range of pressures across all volumes pumped by the turbomolecular pump arrangement spans at least 8 orders of magnitude and the volume at the lowest pressure is maintained below 1×10.sup.−9 mbar.

2. The mass spectrometer system of claim 1, wherein at least one pumping stage of the turbomolecular pump arrangement contains a molecular drag pump.

3. The mass spectrometer system of claim 2, wherein the molecular drag pump is a Holweck pump with a helical pump channel.

4. The mass spectrometer system of claim 1, wherein not more than 3 pumping stages have pumping speed in excess of 50 ls.sup.−1 when under the vacuum; at least 2 pumping stages have pumping speeds less that 30 ls.sup.−1 when under vacuum; and wherein the forevacuum pump when in use maintains the output of the turbomolecular pump arrangement at a pressure of 1 mbar or more.

5. The mass spectrometer system of claim 1, wherein when in use at working gas loads the ratio of pressures between any two adjacent pumping stages of the turbomolecular pump arrangement is between 10 and 1000.

6. The mass spectrometer system of claim 1, wherein the greatest distance between any two pumping stages of the molecular pump arrangement is less than 400 mm.

7. The mass spectrometer system of claim 1, wherein the pumping stage connected to the volume at the lowest pressure has the highest pumping speed when under vacuum and/or the biggest pumping port cross section.

8. The mass spectrometer system of claim 1, wherein at least the volume at the lowest pressure is equipped with a heating arrangement for heating the volume, and wherein preferably the sealing of the volume at the lowest pressure does not contain elastomer seals.

9. The mass spectrometer system of claim 1, wherein at least one pumping port surrounds a second pumping port such that the second pumping port seals against pressure within the first pumping port and not against atmosphere, or wherein at least the volume of a first pumping stage surrounds the volume of a second pumping stage such that the volume of the second pumping stage seals against pressure within the first pumping stage and not against atmosphere.

10. The mass spectrometer system of claim 1, wherein the volume with the lowest pressure when under vacuum contains the mass analyzer.

11. The mass spectrometer system of claim 10, wherein the mass analyzer is a multi-reflection/multi deflection time of flight or electrostatic trap type mass analyzer of orbitrap type mass analyzer.

12. The mass spectrometer system of claim 1, wherein the ion optical arrangement comprises at least one mass filter and/or at least one ion trap and/or at least one collision cell.

13. The mass spectrometer system of claim 1, wherein at least one first volume pumped by a pumping stage of the turbomolecular pump arrangement surrounds the volume with the lowest pressure when under vacuum, such that the volume at the lowest pressure seals against pressure within the first volume and not against atmosphere, and wherein the volume at the lowest pressure is equipped with metallic seals and with a heating arrangement for heating the volume.

14. The mass spectrometer system of claim 1, wherein the turbomolecular pump arrangement spans 8 to 10 orders of magnitude.

15. A method of evacuating at least 5 volumes of a mass spectrometer system comprising an on source, a mass analyzer and an on optical arrangement for transporting ions from the ion source to the mass analyzer, the method comprising: pumping an output of a turbomolecular pump arrangement to atmosphere with a forevacuum pump; and pumping each volume via a respective one of at least 5 pumping stages of the turbomolecular pump arrangement; wherein each pumping stage is separated by at least one set of rotor blades and at least one set of stator blades; not more than 3 pumping stages have pumping speeds in excess of ⅓ of the highest pumping speed when under vacuum; at least 2 pumping stages have pumping speeds less than ¼ of the highest pumping speed when under vacuum; wherein when pumping at working gas loads the total range of pressures across all volumes pumped by the turbomolecular pump arrangement spans at least 8 orders of magnitude and the volume at the lowest pressure is maintained below 1×10−9 mbar.

16. The method of claim 15, wherein the at least 5 volumes comprise chambers connected by apertures and/or elongated flow restrictors, which chambers house ion optical components of a mass spectrometer, and wherein the ion optical components comprise at least one ion trap and/or at least one collision cell and/or at least one mass filter.

17. The method of claim 15, wherein the turbomolecular pump arrangement spans 8 to 10 orders of magnitude.

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 is a schematic cross sectional diagram depicting an embodiment of a pumping system of the present invention in which a cartridge split-flow pump and a concentric pumping arrangement is utilised.

DETAILED DESCRIPTION

(2) FIG. 1 is a schematic cross sectional diagram depicting a pumping system of the present invention in which a cartridge split-flow turbomolecular pump is utilised. A vacuum system 10 comprises a housing 12 for ion optical components (not shown) and a housing 14 for accommodating a cartridge split-flow pump 15. The cartridge split-flow pump 15 is inserted into housing 14 and mates with flange 16.

(3) An atmospheric pressure ion source (not shown) is located outside the vacuum system. The ion source is advantageously based on the ESI (ElectroSpray Ionization) or DART (Direct Analysis in Real Time) technique for creating ions.

(4) Housing 13 encloses a first stage of ion optics which is in a volume 1, which is adjacent to the ion source. Housing 12 encloses all other components of the mass spectrometer. At working gas loads housing 13 is maintained at a pressure 1.5 to 2.5 mbar and is evacuated using a forepump 90 in gas communication with port 60, the forepump operating at 15 l.Math.s.sup.−1 pumping speed and conducting a gas flow rate of 23-37 mbar.Math.l.Math.s.sup.−1. In a typical mass spectrometer, volume 1 within housing 13 contains an RF device such as an ion funnel, Step-Wave™ collision guide, S-lens, RF carpet, or other ion optical device for transporting an ion beam at low vacuum. The forepump is in pumping communication with the exhaust of the split flow pump as well as being connected to housing 13 which encloses the first stage of ion optics. Hence the forepump both backs the turbomolecular pump arrangement (the splitflow pump) and the first stage of the ion optics which is located within a first volume 1, and advantageously only two pumps (the forepump and and turbomolecular pump) are needed to evacuate the entire scientific instrument.

(5) Cartridge split-flow pump 15 and housing 14 comprise 6 pumping stages, pumping ports 20, 22, 24, 26, 28 and 30 conducting gas from the remainder of the ion optics and the mass analyser. Each of the stages is connected to volumes within housing 12 via pumping ports.

(6) A molecular drag stage of the split-flow pump is aligned with pumping port 20, evacuating port 20 to a pressure of 0.1 mbar under a gas flow rate of 2 mbar.Math.l.Math.s.sup.−1 with 20 l.Math.s.sup.−1 pumping speed. In a typical mass spectrometer, volume 2 connected to this port contains an RF-only transport device such as a multipole or ion tunnel. Depending on the ion source, a gas flow rate of 3-4 mbar.Math.l.Math.s.sup.−1 can also occur; in principle, a molecular drag stage of a higher pumping speed can be used. The ion source may in particular be of the type described in US 2012/0043460 A1 or US 2012/0153141 A1, and a gas flow rate of up to 8 mbar.Math.l.Math.s.sup.−1 may occur.

(7) Pumping port 22 is aligned with pumping elements further along the split-flow pump and pumping port 22 is evacuated to 10.sup.−3 mbar with a pumping speed of 150 l.Math.s.sup.−1 at an incoming gas flow rate of 0.15 mbar.Math.l.Math.s.sup.−1. In a typical mass spectrometer, volume 3 connected to this port contains an ion cooling multipole or ion tunnel, though a mass selecting means, in particular a linear quadrupole mass filter, could also be located there. Depending on the ion source, a gas flow rate of 0.3-0.6 mbar.Math.l.Math.s.sup.−1 can also occur.

(8) Pumping port 24 is evacuated to 3×10.sup.−5 mbar with a pumping speed of 150 l.Math.s.sup.−1 at an incoming gas flow rate of 4×10.sup.−3 mbar.Math.l.Math.s.sup.−1. In a typical mass spectrometer, volume 4 connected to this port contains a mass selector such as a quadrupole mass filter, a linear ion trap, or a time-of-flight mass analyzer and also may include a collision cell, the collision cell containing a locally relatively high pressure of gas, some of which escapes the cell and is pumped through pumping port 24. Volume 4 also could contain an RF-only gas-filled storage device such as a C-trap, used for containing ions and ejecting them to a mass analyzer such as an Orbitrap™ or a multi-reflection time-of-flight analyzer.

(9) Pumping port 26 is evacuated to 5×10.sup.−7 mbar with a pumping speed of 20 l.Math.s.sup.−1 at an incoming gas flow rate of 5×10.sup.−6 mbar.Math.l.Math.s.sup.−1. The first part of a high-voltage lens system may be located within volume 5 connected to pumping port 26. Higher pumping speed here is not needed because the function of ion optics within volume 5 is to separate ions from the effusive gas jet emanating from the C-trap device and then guide them to the next pumped volume. The port 26 is substantially slot shaped.

(10) Pumping port 28 is evacuated to 2×10.sup.−8 mbar with a pumping speed of 10 l.Math.s.sup.−1 at an incoming gas flow rate of 1×10.sup.−7 mbar.Math.l.Math.s.sup.−1. Lenses preceding a high-resolution analyzer are located within volume 6 connected to pumping port 28. Here high pumping speed is also not needed because the length of the ion optical path within volume 6 needs to be minimized and therefore higher pumping speed barely affects the actual pressure along the ion axis. The port 28 is substantially slot shaped. Channel 85 is also pumped by pumping port 28, as will be further described.

(11) The ports 26, 28 being substantially slot shaped are smaller than the remaining ports 22, 24 and 30. The slot shaped ports have associated pumping speeds less than 30 l.Math.s.sup.−1. The larger ports 22, 24 and 30 have associated pumping speeds more than 50 l.Math.s.sup.−1. The pumping system generally may have one or more, preferably two or more, substantially slot shaped ports, which may be associated with respective stages of pumping having pumping speeds less than 30 l.Math.s.sup.−1.

(12) Pumping port 30 is adjacent the ultimate vacuum region of the turbomolecular pump arrangement and a pressure of <2×10.sup.−10 mbar is achieved at working gas loads. Pumping port 30 evacuates volume 7 containing the mass analyzer, and conducts a gas flow rate of 1×10.sup.−9 mbar. l.Math.s.sup.−1 at a pumping speed of 200 l.Math.s.sup.−1. The pressure in the final pumping stage is measured by vacuum pressure gauge 50. The mass analyzer is preferably of the Orbitrap™ or multi-reflection/multi-deflection time-of-flight or electrostatic trap types. A mass analyzer of the orbitrap type is for example disclosed in U.S. Pat. No. 5,886,346. Ultra-high vacuum is essential for correct operation of such analyzers because it ensures survival of labile multiply-charged proteins up to the end of mass analysis process in spite of their high kinetic energy (corresponding to 1 to 30 kV of acceleration).

(13) Split-flow turbomolecular pump 15 comprises a motor 70, a drag pumping stage 72, and five stages of rotor and stator blades, 74, 75, 76, 77, 78.

(14) Housing 14 is sealed to housing 12 in regions adjacent the pumping ports. Elastomer seals 80 provide gas-tight seals around pumping ports 20, 22 and 24. Metal to metal seals 81 are utilised around pumping ports 26, 28 and 30. FIG. 1 depicts a preferred embodiment in which pumping port 28 surrounds pumping port 30 such that pumping port 30 seals against pressure within pumping port 28 and not against atmosphere. This is facilitated by channel 85 which is pumped by pumping port 28 and which surrounds pumping port 30. By this means, regions of housings 12 and 14 adjacent pumping port 30 need not contain elastomer seals but may use a metal to metal seal of a type which does not cause plastic deformation of the metallic sealing material, whilst providing UHV at the pumping port. Similar seals are used to seal pumping ports 26 and 28, and this concentric pumping arrangement eliminates the difficulties found when attempting leak-tight sealing using plastic deformation of multiple seals in parallel.

(15) While the turbomolecular pump of FIG. 1 has its own housing 14, it is also possible to eliminate multiple O-rings 80 by making it of a cartridge type. In this case stators are encapsulated in a metal cage which slides into housing 12 and makes leaks between pumping stages negligible mainly by tight tolerances of the fit (though in some cases Viton™ or V-shaped soft metal rings could be used).

(16) As used herein, including in the claims, unless the context indicates otherwise, singular forms of the terms herein are to be construed as including the plural form and vice versa.

(17) Throughout the description and claims of this specification, the words “comprise”, “including”, “having” and “contain” and variations of the words, for example “comprising” and “comprises” etc, mean “including but not limited to”, and are not intended to (and do not) exclude other components.

(18) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(19) The use of any and all examples, or exemplary language (“for instance”, “such as”, “for example” and like language) provided herein, is intended merely to better illustrate the invention and does not indicate a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(20) All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).