Cryopump

Abstract

A cryopump (10) comprises: a housing (12) having an inlet (16) connected to a vacuum chamber (18); a cold head (20) arranged in the housing (12) for generating a temperature for condensation of the gas or steam; a cold plate (30) connected to the cold head (20); and a non-evaporable getter (NEG) element (36) connected to the cold plate (30).

Description

Technical Field

[0001] This invention relates to cryogenic pumps or deep cryogenic pumps that generate a vacuum by capturing gases and vapors through the condensation of gases and vapors on a cold surface. Background Technology

[0002] Traditional cryogenic pumps include a cold head extending into the pump housing. The housing includes an inlet, where the cryogenic pump inlet is connected to a vacuum chamber or vacuum apparatus. The cold head is typically cooled by liquid helium or liquid nitrogen. A cold plate is attached to the cold head to increase its surface area for the cryogenic condensation pumping process. The cold head cools the cold plate to temperatures typically below 20 K for pumping N2, Ar, O2 (other gases such as Xe, Kr, and CO are pumped at temperatures below 55 K at the cold plate; H2O vapor and CO2 are typically pumped at around 65 K).

[0003] Traditional cryogenic pumps are typically combined with a suction pump. Activated carbon (AC) is usually used as the adsorbent material and is coated onto a cold plate located inside the pump, which is cooled by a cold head. Gases such as H2, He, and Ne are adsorbed onto the cooled AC at low temperatures.

[0004] AC (Acoustic Acid) can be easily and irreversibly contaminated by hydrocarbons, including methane. Contaminated AC cannot be cleaned or reactivated and must be replaced. Replacing AC is very complex and expensive, and requires returning the pump to the manufacturer, potentially resulting in prolonged operational downtime. Furthermore, AC is typically bonded to cold plates with epoxy resin. However, epoxy resin can be degraded by radioactive materials such as tritium. Additionally, common epoxy resins can contaminate the pumping environment. Replacing the commonly used epoxy resin used to attach AC can be costly. Summary of the Invention

[0005] The purpose of this invention is to provide a cryogenic pump with improved pump performance and reliable operation.

[0006] This problem is solved by the cryogenic pump according to claim 1.

[0007] The cryogenic pump according to the invention includes a housing with an inlet that can be connected to a vacuum chamber. A cold head is disposed within the housing. The cold head is preferably configured to generate a temperature low enough to condense gas or vapor thereon. At least one cold plate is connected to the cold head. A non-evaporative getter element (NEG element) is connected to the cold plate or each cold plate.

[0008] Therefore, according to the present invention, the activated carbon (AC) used in the prior art is replaced by NEG elements. NEG elements have the advantage that they are not irreversibly contaminated by hydrocarbons. NEG elements can be reactivated by heating. Therefore, the cryogenic pump can operate more reliably and stably. Meanwhile, it has been shown that NEG elements operating at reduced temperatures can have improved pumping performance. Therefore, the low temperature generated by the cold head can improve the pumping performance of the NEG elements, or each NEG element, and thus improve the pumping performance of the cryogenic pump. In particular, compared to operating the NEG elements at room temperature, depending on the operating temperature, the pumping capacity can be increased by more than 10 times, preferably more than 100 times.

[0009] Preferably, the cryogenic pump comprises multiple cold plates, wherein the NEG element is connected to more than one cold plate and preferably to each cold plate. Thus, by providing multiple NEG elements, sufficient surface area of ​​the NEG material is provided for efficient pumping of the gas.

[0010] Preferably, the cold plate is formed as a baffle or plate. The NEG element is preferably attached to the surface of the baffle facing away from the inlet. Thus, the NEG element is protected by the shape of the baffle and is prevented from being blocked by condensed gas on the opposing surface of the baffle facing the inlet.

[0011] Preferably, the NEG element is cooled to a temperature below 20K, and more preferably below 10K. At these temperatures, cryogenic condensation in the cryogenic pump is possible. Simultaneously, the pumping performance of the NEG element is improved by more than 100 times compared to operation at room temperature.

[0012] Preferably, the NEG element or each NEG element includes one or a combination of Zr, V, Ti, Fe, Al, and Ta.

[0013] Preferably, the cryogenic pump includes activated carbon connected to one of the cold plates. Therefore, the cryogenic pump may include a combination of AC and NEG elements to combine their advantages. Alternatively, the cryogenic pump may not include activated carbon.

[0014] Preferably, the cold plate, or each cold plate, includes a coating of NEG material. Therefore, since the NEG element is directly coated onto the cold plate, no additional adhesives or connecting elements are required. This prevents contamination of the NEG material due to the degradation of any adhesives or bonding agents. Because the NEG element can be reactivated, replacement is not required, and the NEG element can be permanently coated onto the cold plate.

[0015] Alternatively, preferably by means of radiation-resistant epoxy resin, at least one NEG element, more preferably more than one NEG element, and most preferably all NEG elements are bonded to their respective cold plates.

[0016] As an alternative, at least one NEG element, more preferably more than one NEG element, and most preferably all NEG elements are mechanically attached to their respective cold plates. This allows each NEG element to be constructed as a separate component and to be clamped or otherwise mechanically attached to the cold plate. Thus, the NEG elements can be replaced if needed.

[0017] Preferably, the NEG element has a diameter of 300 cm. 2 Or larger, more preferably 500 cm 2 Or larger, most preferably 600cm 2 The total surface area may be larger, depending on the size of the cryogenic pump in which the NEG elements are housed. Therefore, the combined surface area of ​​all NEG elements is large enough to provide sufficient pumping speed and capacity.

[0018] Preferably, at room temperature, the NEG element has a pumping capacity of more than 1000 liters / second for H2, and 1500 liters / second for a cryogenic pump with nominal N2. The NEG material increases the H2 pumping speed by at least 10 times below 20K. High pumping speeds can be achieved due to the combined effect of the large surface area and cryogenic temperature, which enhances the pumping performance of the NEG element.

[0019] Preferably, a common heating element is provided in the cryogenic pump to reactivate the cold plate and the NEG element. The heating element can be connected to the cold head. The temperature of both the cold plate and the NEG element can be increased by the heating element. This causes the condensed gas on the cold plate to evaporate and be removed, while simultaneously reactivating the NEG element. Preferably, the heating element is configured to heat the NEG element to a temperature above 100°C, preferably above 150°C, and most preferably above 250°C, so as to reactivate the NEG element preferably at a pressure below 1E-5 mbar. Therefore, NEG regeneration / reactivation may necessitate the use of a supported, preferably detachable pump, such as a turbomolecular pump. Attached Figure Description

[0020] The invention will now be described in detail with reference to the accompanying drawings.

[0021] Figure 1 An illustrative cryogenic pump according to the present invention is shown. Detailed Implementation

[0022] The cryogenic pump 10 includes a housing 12 defining a pump chamber 14 and an inlet 16. The inlet 16 is connected to a vacuum chamber 18 to remove gas from the vacuum chamber 18 using the cryogenic pump 10. The cryogenic pump 10 includes a cold head 20, which may be, for example, a two-stage Gifford-McMahon cryostat. The cold head 20 includes a first stage 22 and a second stage 24. The cold head 20 may be cooled by liquid helium. During operation, the first stage 22 may be at a temperature of approximately 80 Kelvin, while the second stage 24 may be at a temperature of less than 20 Kelvin, preferably less than 10 Kelvin. Specifically, during operation, the temperature of the second stage may be between 7 K and 9 K.

[0023] The cold head 20 is surrounded by a radiation shield 26 to reduce heat transfer to the cold head 20 via radiation. The radiation shield 26 is supplemented by an inlet baffle 28. During operation, the baffle 28 and the radiation shield 26 can be maintained at a temperature of approximately 100 Kelvin. Gas compounds with high condensation temperatures received from the vacuum chamber 18 will condense on the baffle. Similarly, those compounds will also condense on the inner surface of the radiation shield 26.

[0024] Multiple cold plates 30 are connected to the second stage 24 of the cold head 20. Each cold plate 30 has a first surface 32 facing the inlet 16 and an opposing second surface 34 facing away from the inlet 16. In particular, the cold plate 30 can be shaped as a baffle. During use, gas molecules may condense on the first surface 32. Thus, during use, the first surface 32 will be covered by frozen gas. A NEG element 36 is attached to the second surface 34 of the cold plate 30. The attachment of the NEG element 36 to the cold plate 30 can be achieved by coating the second surface 34 with NEG material. This is possible because it is not necessary to replace the NEG element 36. Alternatively, the NEG element 36 can be glued or otherwise mechanically attached to the cold plate 30. Due to the shape of the cold plate 30, the coverage of the NEG element 36 by frozen or condensed gas compounds is minimized, thereby maintaining the pumping action of the NEG element 36 over a longer operating period.

[0025] Due to the connection between the NEG element 36 and the cold head 20, the NEG element 36 is maintained at the same low temperature as the cold plate 30. Because of this low temperature, it has been surprisingly shown that the pumping performance of the NEG element 36 is improved by more than 10 times, and in particular by more than 100 times, compared to operation at room temperature. Simultaneously, the NEG element is not contaminated by hydrocarbons such as methane, unlike the use of activated carbon (AC) in the prior art. By directly coating the NEG element onto the second surface 34 of the cold plate 30, the degradation of any adhesives used in the prior art to attach AC to the cold plate can be avoided.

[0026] Since it has been found that the pumping performance of NEG materials improves at low temperatures, this invention provides a beneficial combination of a cryogenic pump and at least one NEG element, thereby avoiding the disadvantages of using activated carbon in the prior art. Therefore, the cryogenic pump can be operated for a longer period of time, resulting in increased pumping performance. Reactivation of the NEG element 36 is then possible without replacing it.

[0027] List of reference numerals in the attached diagram: 10 Cryogenic Pumps 12 shells 14 Pump Room 16 entrances 18 vacuum chambers 20mm water block 22 Level 1 24 Level 2 26 Radiation shielding components 28 baffles 30 cold-rolled steel plate 32 First Surface 34 Second Surface 36 NEG components.

Claims

1. A cryogenic pump, comprising: A housing having an inlet that can be connected to a vacuum chamber; The cold head is housed within the casing; At least one cold plate is connected to the cold head; as well as One or more non-evaporative getter (NEG) elements are connected to the at least one cold plate.

2. The cryogenic pump of claim 1, comprising a plurality of cold plates, wherein a corresponding NEG element is connected to each cold plate.

3. The cryogenic pump according to claim 1 or 2, comprising a common heating element for reactivating the cold plate and its corresponding NEG element.

4. The cryogenic pump according to any one of the preceding claims, wherein, The cold plate, or each cold plate, is in the form of a baffle, the baffle having NEG elements attached to its surface facing away from the inlet.

5. The cryogenic pump according to any one of the preceding claims, wherein, The cold plate is arranged to cool the NEG element or each NEG element to a temperature below 20K, preferably below 10K.

6. The cryogenic pump according to any one of the preceding claims, wherein, The NEG element or each NEG element includes one or a combination of Zr, V, Ti, Fe, Al, and Ta.

7. The cryogenic pump according to any one of the preceding claims, wherein, Activated carbon is attached to the cold plate or each cold plate.

8. The cryogenic pump according to any one of the preceding claims, wherein, The at least one cold plate is coated with NEG material.

9. The cryogenic pump according to any one of claims 1 to 7, wherein, The corresponding NEG components are bonded or mechanically attached to the cold plate or each cold plate.

10. The cryogenic pump according to any one of the preceding claims, wherein, The one or more NEG elements have a minimum of 300 cm 2 Preferably at least 500 cm 2 More preferably at least 600 cm 2 Surface area.

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