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Vacuum ion-getter pump with cryogenically cooled cathodeVacuum ion-getter pump with cryogenically cooled cathode description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070286738, Vacuum ion-getter pump with cryogenically cooled cathode. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]This invention relates to vacuum pumps known as vacuum ion-getter pumps and, more particularly, to vacuum ion-getter pumps having cooled cathodes for improved performance. Vacuum ion-getter pumps are sometimes referred to as sputter ion pumps. BACKGROUND OF THE INVENTION [0002]The basic structure of a vacuum ion-getter pump includes an anode, a cathode, and a magnet. The anode includes one or more pump cells, which may be cylindrical. Cathode plates, typically titanium, are positioned on opposite ends of the pump cells. A magnet assembly produces a magnetic field oriented along the axis of the anode. A voltage, typically 3 kV to 9 kV, applied between the cathode plates and the anode, produces an electric field which causes electrons to be emitted from the cathode. The magnetic field produces long, more or less helical electron trajectories. The relatively long trajectories of the electrons before reaching the anode improves the chances of collision with gas molecules inside the pump cells. When an electron collides with a gas molecule, it tends to liberate another electron from the molecule, forming a positive ion. The positive ions travel to the cathode due to the action of the electric field. The collision with the solid surface produces a phenomenon called sputtering, i.e., ejection of titanium atoms from the cathode surface. Some of the ionized molecules or atoms impact the cathode surface with sufficient force to penetrate the solid and to remain buried. [0003]Prior art vacuum ion-getter pumps have generally satisfactory performance, but exhibit certain limitations. Such pumps have limited pumping capacity for light gases, such as hydrogen and helium. In addition, such pumps require a starting pressure on the order of 10.sup.-2 to 10.sup.-3 torr in order to begin operation. [0004]U.S. Pat. No. 5,357,760, issued Oct. 25, 1994 to Higham, discloses a so-called hybrid cryogenic vacuum pump wherein a separate cryopump and a separate ion-getter pump are positioned in one vacuum chamber. The disclosed vacuum pump does not overcome the limitations described above. [0005]Accordingly, there is a need for improved vacuum ion-getter pumps and methods for operating vacuum ion-getter pumps. SUMMARY OF THE INVENTION [0006]According to a first aspect of the invention, a vacuum ion-getter pump comprises a vacuum chamber having a pumping port, an anode positioned in the vacuum chamber, a cathode positioned in the vacuum chamber in proximity to the anode, a voltage source coupled between the anode and the cathode, a magnet assembly to produce a magnetic field in the vacuum chamber, and a cooling device thermally coupled to the cathode. [0007]The cooling device may be a cryogenic cooling device, such as a closed cycle refrigerator. The closed cycle refrigerator may have a cold head in the thermal contact with the cathode. The anode may be operated at room temperature or may be cooled. [0008]According to a second aspect of the invention, a method is provided for operating a vacuum ion-getter pump of the type including an anode and a cathode positioned in a vacuum chamber. The method comprises cooling the cathode. The cathode may be cryogenically cooled. The method may further comprise coupling the vacuum chamber to an enclosure to be evacuated, applying a voltage between the anode and the cathode and producing a magnetic field in the vacuum chamber. [0009]According to a third aspect of the invention, a vacuum ion-getter pump comprises a vacuum chamber having a pumping port, an anode positioned in the vacuum chamber, a cathode positioned in the vacuum chamber, and a cryogenic cooling device thermally coupled to the cathode. BRIEF DESCRIPTION OF THE DRAWINGS [0010]For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: [0011]FIG. 1 is a schematic diagram of a prior art ion pump cell; [0012]FIG. 2 is a schematic diagram of a prior art vacuum ion-getter pump; and [0013]FIG. 3 is a simplified schematic diagram of a vacuum ion-getter pump in accordance with an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION [0014]A schematic diagram of a prior art ion pump cell is shown in FIG. 1. A cylindrical anode cell 20 has a cell axis 22. Anode cell may be fabricated of stainless steel, for example. Cathode plates 24 and 26 are positioned at opposite ends of anode cell 20 and may be perpendicular to cell axis 22. A power supply 30 applies a voltage, typically 3 kV to 9 kV, between the cathode plates 24, 26 and the anode cell 20. A magnet assembly (not shown in FIG. 1) produces a magnetic field 32 in anode cell 20 parallel to cell axis 22. [0015]A schematic diagram of a prior art vacuum ion-getter pump having multiple anode cells is shown in FIG. 2. Like elements in FIGS. 1 and 2 have the same reference numerals. The ion-getter pump of FIG. 2 includes multiple anode cells 20a, 20b, . . . 20n located between cathode plates 24 and 26. Power supply 30 is connected between cathode plates 24, 26 and anode cells 20a, 20b, . . . 20n. [0016]A magnet assembly 40 includes magnets 42 and 44 located on opposite ends of anode cells 20a, 20b, . . . 20n. Magnet 42 may have a north pole facing anode cells 20a, 20b, . . . 20n, and magnet 44 may have a south pole facing anode cells 20a, 20b, . . . 20n. A magnet yoke 50 of magnetic material provides a return path for magnetic fields between magnets 42 and 44. In the configuration of FIG. 2, magnetic yoke 50 has a generally rectangular shape. In other prior art ion-getter pumps, the magnet yoke may be U-shaped, with an open side. Magnets 42 and 44 produce magnetic field 32 in the region of anode cells 20a, 20b, . . . 20n. The entire assembly shown in FIG. 2 may be enclosed in a vacuum chamber. [0017]The voltage between cathode plates 24, 26 and anode cells 20a, 20b, . . . 20n results in the generation of free electrons in the anode cell volume. These free electrons ionize gas molecules that enter the anode cells. The ionized gas molecules are accelerated to the cathode plates, usually made of titanium or tantalum, resulting in sputtering of the cathode material onto surfaces of the anode cells. The sputtered cathode material readily pumps gas molecules and is the primary pumping mechanism in the ion pump. Secondary electrons produced from the ionization process sustain the plasma in the anode cells so that the pumping action is continuous. The magnetic field axial to the anode cells is required to maintain a long electron path and to sustain a stable plasma in the anode cells. [0018]A simplified schematic diagram of a vacuum ion-getter pump in accordance with an embodiment of the invention is shown in FIG. 3. The pump includes an anode 120 and a cathode 122. Anode 120 includes anode cells 120a and 120b in the embodiment of FIG. 3. Cathode 122 includes cathode plates 124 and 126, and end plate 128 in the embodiment of FIG. 3. Anode cells 120a and 120b are located between and are spaced from cathode plates 124 and 126. End plate 128 is connected between cathode plates 124 and 126. The ion pump may include one or more anode cells. Each anode cell may have a cylindrical configuration and may be fabricated of stainless steel. The anode cells 120a, 120b, are oriented with their axes parallel to each other and perpendicular to cathode plates 124, 126. Cathode plates 124 and 126 and end plate 128 may be fabricated of titanium or tantalum, for example, or other suitable metals or alloys. [0019]A power supply 130 applies a voltage, typically 3 kV to 9 kV, between cathode 122 and anode 120, and more particularly between cathode plates 124, 126 and anode cells 120a, 120b. Cathode plates 124 and 126 are electrically connected together, and anode cells 120a and 120b are electrically connected together. Continue reading about Vacuum ion-getter pump with cryogenically cooled cathode... Full patent description for Vacuum ion-getter pump with cryogenically cooled cathode Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Vacuum ion-getter pump with cryogenically cooled cathode patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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