Heat shield for a NEG pump

Abstract

Heat shield element for a non-evaporable getter (NEG) pump, comprising: a shielding element made from a sheet metal having a first end and an opposite second end, wherein the first end and the second end are connected by an upper edge and an opposite lower edge, wherein the shielding element comprises a plurality of openings, and connecting pins at the first end and / or the second end.

Description

[0001] The present invention relates to a heat shield element for a non-evaporable getter (NEG) pump. Further, the present invention relates to a heat shield com- prising such a heat shield element. Further, the present invention relates to a NEG pump comprising such a heat shield as well as a method of assembly of such a heat shield. Common NEG pumps are used in order to achieve ultra-high vacuum (UHV) or extremely high vacuum (XHV) in applications such as quantum computing, spectroscopy or layer deposition techniques. Therein, NEG pumps comprise NEG elements providing a pumping effect by the effect of sorption of gas molecules which are extracted from the vacuum volume and thereby reducing the pressure inside the volume. However, in order to activate such NEG elements (and also for re-activating after certain time of operation), the NEG elements need to be heated up above a certain heating temperature. Therefore, the NEG elements are connected to a heating element. In order to avoid adverse effects by heat radiation to other parts of the vacuum apparatus and in order to increase effi- ciency of the heating process, the NEG elements may be surrounded by a heat shield. Heat radiation generated by the heating element is then at least partially reflected by the heat shield. However, in common vacuum pumps, the heat shield is usually directly welded to or fastened to a component of the NEG pump, which reduces the ability to service the NEG pump. Further, the complete NEG pump must be handled during the welding process which increases complexity of the welding process. It is an object of the present invention to provide a heat shield and an NEG pump comprising such a heat shield, which can be easily assembled and re- moved for service without the need of additional fasteners. The problem is solved by a heat shield element according to claim 1, a heat shield according to claim 6, an NEG pump according to claim 9 and a method for assembly of a heat shield according to claim 13. In an aspect of the present invention a heat shield element for a non-evaporable getter (NEG) pump is provided. The heat shield element comprises a shielding element made from a sheet metal having a first end and an opposite second end, wherein the first end and the second end are connected by an upper edge and an opposite lower edge. Further, the shielding element comprises a plurality of openings in order to allow gas molecules to pass through the shielding ele- ment to reach NEG elements of the NEG pump. According to the present inven- tion, the shielding element comprises connecting pins at the first end, wherein the connecting pins may extend beyond the lower edge and the upper edge. Alternatively or additionally, connecting pins are also disposed at the second end which may extend beyond the lower edge and the upper edge. In particular, the connecting pins extend perpendicular to the lower edge and the upper edge. Thus, by the connecting pins, connection of the heat shield element to the NEG pump can be facilitated by inserting the connecting pins into a respective recess of the NEG pump by an axial motion along the axial axis or extension of the connecting pin. Alternatively, the connecting pins may not extend beyond the lower edge and / or the upper edge and may be inserted by a lateral motion substantially perpendicular to the axial axis of the pin, preferably by a snap fit as described below. The heat shield element is connected to the NEG pump by the connecting pins. This connection is releasable and does not require any welding. In particular, connecting the heat shield element to the NEG pump may be facilitated without additional tools. Thus, by fastening of the heat shield ele- ment to the NEG pump by the connecting pins of the heat shield element, the assembly process is simplified without the need of additional fasteners and the heat shield element is removable for service. In addition, the heat shield can be removed prior to packing / shipping the NEG cartridge. This allows the getter material to be directly supported by a vacuum-sealed bag or any other packing material during transport reducing rattling / vibrations / rubbing of the NEG mate- rial during transit. Preferably, the openings of the shielding element are round or oval, slotted or built as elongated holes or have any other shape. Preferably, the area of the openings is between 20% and 80% and preferably between 40% and 60% of the whole area of the shielding element. This means that 80%-20% and preferably 60%-40% of the shielding element are structured as closed surface, wherein consequently 20%-80% and preferably 40%-60% of the area of the shielding element are occupied by the openings. Thus, a good tradeoff between the shielding effect for the heat radiation by the heat shield element is provided, wherein at the same time conductance of the gas molecules from a vacuum volume towards the NEG elements of the NEG pump is suffi- ciently high. Preferably, the shielding element is curved or bend and in particular comprises a semi-circular shape. Thus, as described in more detail below, a combination of two or more heat shield elements may form a complete heat shield providing a closed cylindrical shell or hull preferably completely surrounding the NEG ele- ments. Preferably, the heat shield element comprises more than one, two, three, four or more than four pins. In particular, the heat shield element comprises exactly 4 pins, preferably two pins at the first end (one pin at the lower edge and one pin at the upper edge) and two at the second end (one pin at the lower edge and one pin at the upper edge). Preferably, the connecting pins are connected to the shielding element by weld- ing. Welding of the connecting pins to the shielding element can be done separate from the NEG pump components such that adverse effects by the weld- ing cannot affect the NEG pump. Preferably, the pins at the first end are built combinedly by a first post extending from the lower edge to the upper edge. Thus, the pins at the first end are inte- grally built by the first post which may extend beyond the upper edge and the lower edge of the shielding element. Alternatively, or additionally the pins at the second end are built combinedly by a second post extending from the lower edge to the upper edge. Thus, the pins at the second end are integrally built by the second post which may extend beyond the upper edge and the lower edge of the shielding element. The one or more posts have a length which may exceed the length of the first end and the second end by the amount of the respective pins, respectively. In particular, in combination with welding of the connecting pins, the post can be welded to the first end / or the second end of the shielding element thereby at the same time providing the pins at the upper edge and the lower edge. Thus, the pins at the first end are easy to manufacture and attached at once to the sheet metal of the shielding element in a reliable way. Similar, the pins at the second end are easy to manufacture and attached at once to the sheet metal of the shielding element in a reliable way. In addition, enough con- tact surface between the post and the shielding element is provided in order to securely attach the posts to the shielding element. Preferably, the shielding element is wound around a part of the connecting pin and preferably around the post at the first end and / or the second end in order to connect the respective pins to the shielding element. Preferably, the pins at the upper edge and the lower edge of the first end and / or the second end are combinedly constructed with the shielding element by rolling the first end and / or second end into a cylindrical shape to form the respective pins. The pins are integrally built with the shielding element, or, in other words, the pins are built by the shielding element itself. Thus, the rolled end of the shielding element has a small diameter to form the respective pins. The bottom and top edge of the rolled first and second ends may or may not extend past the upper lower edges of the shielding element. Preferably, the pins extend beyond the lower edge and / or the upper edge by 0.2-5mm, preferably 0.8-2.5mm and more preferably 1-2mm. Preferably, the diameter of one or more of the pins is between 0.5mm and 4mm, preferably between 1mm and 3mm and more preferably between 1.2mm and 2mm. Therein, all pins can extend by the same amount beyond the lower edge and / or the upper edge. Alternatively, the pins at the lower edge (at the first end and the second end) may extend a different amount than one of the pins at the upper edge. Alternatively, or additionally the pins at the first end may extend beyond the lower edge and / or the upper edge by a different amount than the pins at the second end. Thus, by the specific length and diameter of the pins, a compact and sufficiently strong fixturing of the heat shield element to the NEG pump is provided. In an aspect of the present invention a heat shield for a NEG pump is provided. Therein, the heat shield comprises a first heat shield element as described be- fore. In particular the heat shield may surround an NEG element of the NEG pump at least partially and preferably completely. Preferably, the heat shield comprises one or more second heat shield elements, which are also built as described before. In particular the heat shield may sur- round an NEG element of the NEG pump at least partially and preferably com- pletely by the first heat shield element and the one or more second heat shield elements combinedly. Preferably, the first heat shield element and at least one of the second heat shield elements are different. Thus, the heat shield can be customized and tai- lored to the respective application by selecting different heat shield elements. Alternatively, the first heat shield element and all second heat shield elements are identical. Preferably, the first heat shield element and one or more second heat shield elements are bend or curved to form together a cylindrical shell or hull in order to enclose and preferably completely enclose the NEG elements of the NEG pump. Thereby, by the heat shield an outer surface is provided reflecting heat radiation and at the same time protecting the brittle NEG elements from me- chanical impairment during handling of the NEG pump. Preferably, the heat shield provides a closed outer surface and maybe open at the upper edge and the lower edge. The heat shield may provide a circular outer surface in particular if the individual heat shield elements are curved or semi- circular. Alternatively, the cylindrical shell may have a square shaped outer sur- face or any other shape to receive the NEG elements of the NEG pump. In an aspect of the present invention an NEG pump is provided comprising a base element and a heating element extending from the base element. By the heating element heat can be generated. In particular, the heating element is a resistive heating element in order to generate heat for activating or re-activating a plurality of NEG elements arranged around the heating element. Further, the NEG pump comprises a top element arranged at the side of the NEG elements opposite to the base element. Thus, the NEG elements are held in place between the base element and the top element. In particular, the top element is con- nected to the base element by posts or set screws connecting the base element to the top element and providing mechanical stability to the NEG pump. Further, according to the present invention, the NEG pump comprises a heat shield as described before extending between the base element and the top element. Preferably, the base element may be connected to a flange or is integrally built with a flange such that the NEG pump can be fully inserted into a vacuum ap- paratus or vacuum chamber. Preferably, the shape of the base element and / or the top element corresponds to the shape of the heat shield. In particular, the heat shield flushes with the base element and / or the top element. For example, if the base element and the top element have a circular shape, the heat shield consisting of two or more heat shield elements approximate or are equal to the shape of the base element and the top element. Preferably, the heat shield is directly connected to the base element and / or the top element. Preferably, one, preferably more than one and more preferably all pins at the upper edge of the heat shield extend into respective recesses of the top element. Thus, the heat shield is directly connected with its upper edge to the top element of the NEG pump. Preferably, one, preferably more than one and more preferably all pins at the lower edge of the heat shield extend into respective recesses of the base ele- ment. Thus, the lower edge of the heat shield is directly connected with its lower edge to the base element of the NEG pump. Preferably, one or more of the recesses are open in a direction perpendicular to the extension of the pin and comprising an undercut such that the pin can be snap fitted into the respective recess. In particular, the pin can be inserted into the respective recess by a lateral movement, i.e. a movement perpendicular to the extension of the pin. Thus, by the snap fit connection between the pin and the top element or the base element, respectively, assembly of the heat shield can be tool free and reversible. Therein, in particular, the recesses at the top element may provide a snap fit, such that the pins at the lower edge of the heat shield can be inserted (e.g. in an axial movement along the length of the pins) into the recesses of the base element and afterwards the pins of the upper edge can be snap fitted into the recesses of the top element. Alternatively, the re- cesses at the base element may provide a snap fit, such that the pins at the upper edge of the heat shield can be inserted (e.g. in a movement along the length or extension of the pins) into the recesses of the top element and after- wards the pins of the lower edge can be snap fitted into the recesses of the base element. Alternatively, the recesses at the top element as well as the base ele- ment both provide lateral openings such that pins at the upper edge as well as pins at the lower edge can be snap fitted into the respective recesses. Preferably, adjacent recesses at the base element and / or the top element are combined such that a common recess is provided for the pins of adjacent heat shield elements. In an aspect of the present invention a method for assembly of a heat shield to an NEG pump is provided. In particular, the NEG pump is as described before. The method including: Providing a base element; Connecting a heating element to the base element and disposing a plu- rality of NEG elements around the heating element; Assembly of a top element disposed on a side of the plurality of NEG elements opposite to the base element; Assembly of a heat shield as described before. Preferably, the method includes inserting the pins of one of the heat shield ele- ments into respective recesses of the base element or the top element and sub- sequently inserting the pins of the heat shield elements subsequently into re- spective recesses in the other one of the base element or the top element. Preferably, inserting the pins of the heat shield element into the respective re- cess is performed by a snap fit. Preferably, the method is further specified by the features described above with respect to the heat shield element, the heat shield and the NEG pump. In the following, the present invention is described in more detail with reference to the accompanying figures. The figures show: Figure 1 a heat shield element according to the present invention, Figure 2 a sectional view of the NEG pump according to the pre- sent invention and Figure 3 a perspective view of the NEG pump according to the present invention. The heat shield element 10 according to the present invention for a non-evap- orable getter (NEG) pump comprises a shielding element 12. The shielding ele- ment 12 is made from a sheet metal and comprising a plurality of openings 20. In the example of Figure 1 the openings 20 are shaped as elongated holes. Other shapes of the openings 20 can also be implemented and used for the heat shield element 12. In particular, the size of the openings 20 and the spacing between the openings 20 provide a tradeoff between conductance for gas molecules to enter the volume of the NEG pump and at the same time sufficient shielding of radiated heat generated during activation or re-activation of the NEG pump. In particular, the area of the openings 20 includes 20%-80% of the area of the shielding element 12 and preferably between 40%-60% of the area of the shielding element 12. The shielding element 12 comprises a first end 12a and an opposite second end 12b. The first end 12a and the second end 12b are connected by an upper edge 12c and a lower edge 12d. At the first end 12a and the second end 12b posts 14 are attached preferably by spot welding. The posts 14 extend beyond the upper edge 12c as well as the lower edge 12d. By the extension of the posts 14 beyond the upper edge 12c, pins 16 at the upper edge 12c are provided extend- ing substantially perpendicular to the upper edge 12c. Similarly, pins 18 at the lower edge 12d are provided by the extension of the posts 14 extending sub- stantially perpendicular to the lower edge 12d. By the pins 16, 18 the heat shield element 10 can be connected to the NEG pump 11. As exemplified in Figure 1, the shielding element 12 is curved and has a semi- circular shape. Thus, by combining the heat shield element 10 of Figure 1 with another heat shield element 10’ (see Fig. 3), which is built similar or identical and may also comprise semicircular shape, a cylindrical shell or hull is provided by the heat shield elements 10, 10’ which at least partially and preferably com- pletely surrounding NEG elements 26 (see Figure 2) of the NEG pump 11. Referring to Figure 2 showing an NEG pump 11 according to the present inven- tion. The NEG pump 11 comprises a base element 30 and a heating element 21 extending from the base element 30. The heating element 21 comprises heating wires 22 along the axial length of the heating element 21, wherein the heating wires 22 are connected to an electrical connector 24 at the base element 30. NEG elements 26 are placed around the heating element 21 such that heat gen- erated by the heating element 21 is applied to the NEG elements 26 in order to activate or re-activate the NEG elements 26. Therein, the NEG elements 26 may be disc shaped and have a round or circular shape. At a side of the NEG elements 26 opposite to the base element 30, a top element 28 is provided. Therein, the top element 28 may be connected to the base element by posts 36 (see Fig. 3) or set screws in order to provide mechanical stability of the NEG pump 11. In the base element 30 recesses 34 are provided, which receive the pins 18 of the lower edge 12d of the heat shield element 10. Similar, in the top element 28 recesses 32 are provided in order to receive the pins 16 at the upper edge 12c of the heat shield element 10. Referring to Figure 3, a first heat shield element 10 and a second heat shield element 10' which is in the example of Figure 3 identically built to the first heat shield element 10, is used in order to fully surround the NEG elements 26. Through the openings 20 gas molecules can enter the active volume of the NEG pump 11 Due to the semi-circular shape of the first heat shield element 10 and the semi-circular shape of the second heat shield element 10' a cylindrical shell or hull is provided by the heat shield, reflecting heat radiation generated by the heating element 21 during activation or re-activation of the NEG elements 26. As seen in Figure 3 the recesses 34 in the base element 30 are laterally open, i. e. open in a direction perpendicular to the extension of the pins. Further, the recesses 34 provide an undercut such that the pins 18 at the lower edge 12d of the heat shield 10 can be snap fitted into the respective recesses 34 of the base element 30. Alternatively, the situation can be reversed in that the recesses 34 in the top element 28 are laterally open to provide a snap fit. In alternative embodiments, neither the recesses at the top element 28 and the base element 30 are laterally open to provide a snap fit. Alternatively, the recesses of the base element 30 as well as the recesses of the top element 28 are laterally open and provide a snap fit to pins 16,18 of the heat shield. A method for assembly of the heat shield may include the steps: Providing a base element; Connecting a heating element to the base element and disposing a plu- rality of NEG elements around the heating element; Assembly of a top element disposed on a side of the plurality of NEG elements opposite to the base element; Assembly of a heat shield. Therein, in the example of Figure 3 first the pins 16 at the upper edge 12c of the heat shield element 10 is inserted into respective recesses 32 of the top element 28. Subsequently, the pins 18 and the lower edge 12d of the heat shield element 10 is snap fitted into the recesses 34. Subsequently, the second heat shield element 10' is assembled in the same manner.

[0002] List of references 10 heat shield element 11 NEG pump 12 shielding element 12a first end 12b second end 12c upper edge 12d lower edge 14 post 16 pin 18 pin 20 opening 21 heating element 22 heating wire 24 connector 26 heating element 28 top element 30 base element 32 recess 34 recess 36 post

Claims

CLAIMS 1. Heat shield element for a non-evaporable getter (NEG) pump, compris- ing: a shielding element made from a sheet metal having a first end and an opposite second end, wherein the first end and the second end are con- nected by an upper edge and an opposite lower edge, wherein the shield- ing element comprises a plurality of openings; and connecting pins at the first end and / or the second end.

2. Heat shield element according to claim 1, wherein the shielding element is curved or bent and preferably semicircular.

3. Heat shield element according to claims 1 or 2, wherein the connecting pins are connected to the shielding element by welding.

4. Heat shield element according to any of claims 1 to 3, wherein the pins at the first end and / or the second end are built combinedly by a post extending from the lower edge to the upper edge, respectively.

5. Heat shield element according to any of claims 1 to 4, wherein the pins of the first end and / or the second end are combinedly provided by rolling the respective end into a cylindrical shape to form the pin.

6. Heat shield for a non-evaporable getter (NEG) pump, comprising a first heat shield element according to any of claims 1 to 5 and preferably one or more second heat shield elements according to any of claims 1 to 5.

7. Heat shield according to claim 6, wherein the first heat shield element and the one or more second heat shield element are bent or curved to form together a cylindrical shell.

8. Heat shield according to claims 6 or 7, wherein the first heat shield ele- ment and at least one of the second heat shield element are different or the first heat shield element and the one or more second heat shield el- ements are identical.

9. NEG pump comprising a base element; a heating element extending from the base element; a plurality of NEG elements arranged around the heating element; a top element arranged at a side of the NEG elements opposite to the base element; and a heat shield according to any of claims 6 to 8 extending between the base element and the top element.

10. NEG pump according to claim 9, wherein one or more pins at the upper edge of the heat shield extend into respective recesses of the top ele- ment.

11. NEG pump according to claim 9 or 10, wherein one or more pins at the lower edge of the heat shield extend into respective recesses of the base element.

12. NEG pump according to claim 10 or 11, wherein one or more of the re- cesses are open in a direction perpendicular to the extension of the pin and comprising an undercut such that the pins can be snap-fitted into the respective recess.

13. Method for assembly of a heat shield according to any of claims 6 to 8 to an NEG pump, including: Providing a base element; Connecting a heating element to the base element and disposing a plu- rality of NEG elements around the heating element; Assembly of a top element disposed on a side of the plurality of NEG elements opposite to the base element; Assembly of a heat shield according to any of claims 6 to 8.

14. Method according to claim 13, including: Inserting the pins of one of the heat shield elements into respective re- cesses at the base element or the top element; and Inserting the pins of the same heat shield element subsequently into re- spective recesses in the other one of the base element or the top element.

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