Vacuum feedthrough and vacuum system

Abstract

Vacuum feedthrough in particular to provide an electrical connection from ambient pressure into a vacuum chamber, comprising a first wall to be at least partially connected to or part of the vacuum chamber, a second wall, wherein the first wall and the second wall are connected by one or more sidewalls, wherein by the first wall, the second wall and the one or more sidewalls an internal volume is created, a first electrical feedthrough arranged in the first wall providing one or more electrical connection through the first wall in a vacuum tight manner, a second electrical feedthrough arranged in the second wall providing one or more electrical connection through the second wall in a vacuum tight manner, wherein one or more of the electrical connections of the first electrical feedthrough are connected with respective electrical connections of the second electrical feedthrough, wherein, in use, the internal volume is maintained at a pressure below ambient pressure.

Description

[0001] VACUUM FEEDTHROUGH AND VACUUM SYSTEM

[0002] The present invention relates to a vacuum feedthrough and in particular to provide an electrical feedthrough from ambient pressure into a vacuum chamber. Preferably, the vacuum chamber contains a high vacuum such as high vacuum (HV), ultrahigh vacuum (UHV) or extremely high vacuum (XHV). In addition, the present invention relates to a vacuum system comprising such a vacuum feedthrough and a method for operating such a vacuum system.

[0003] Trapped-ion quantum computers and other applications may need to be operated in the XHV range, meaning a pressure of 10'12mbar and lower. The devices also require several electrical connections and therefore vacuum feedthroughs. In XHV the contribution of the leak rates of these feedthroughs to the total gas load of the vessel and hence achievable base pressure can become sizeable.

[0004] Reaching pressures around and below 10-12mbar is very important. Combined Ion Getter Pump (IGP)-Non Evaporable Getter (NEG) pumps are typically used in XHV applications with pumping speeds of the order of 1 ,000 l / s where the gas load is mainly hydrogen and carbon monoxide from outgassing and permeation. However, the pumping speed and capacity of atmospheric gases including the inert gases Ar and He of these combined pumps is lower than for hydrogen and therefore, if many feedthroughs are used, their combined leak rate can have a significant impact on the lowest pressure that can be achieved. More I bigger NEG pumps can be used but, in these applications, space is at a premium and also there are significant cost implications. Moreover, when NEG pumps become saturated by the major components of the atmosphere, they must be regenerated. Therefore, the equipment intervention life is shortened.

[0005] It is an object of the present invention to provide a vacuum feedthrough with an improved leak rate attributable to the electrical feedthroughs such that lower pressures can be achieved in the vacuum chamber. At the same time, longer operation of IGP and NEG connected to the vacuum chamber are achieved. The problem is solved by a vacuum feedthrough according to claim 1 , a vacuum system according to claim 12 and a method for operating such a vacuum system according to claim 13.

[0006] In an aspect of the present invention, a vacuum feedthrough is provided in order to provide an electrical connection from ambient pressure into the vacuum chamber. The vacuum feedthrough comprises a first wall to be at least partially connected to or part of the vacuum chamber. Therein, the first wall may be connected to a chamber wall of the vacuum chamber. Alternatively, the first wall is integrally built with a chamber wall of the vacuum chamber, i.e. the first wall and the chamber wall of the vacuum chamber are one piece continuously formed such that the chamber wall serves, first, as chamber wall of the vacuum chamber and, second, as first wall of the vacuum feedthrough.

[0007] Further, the vacuum feedthrough comprises a second wall which may be connected at least partially to the environment having ambient / atmospheric pressure. However, the second wall does not necessarily need to be connected to the environment as long as the second wall is in connection with a higher pressure than in the vacuum chamber. The first wall and the second wall are connected by one or more sidewalls such that by the first wall, the second wall and the one or more sidewalls an internal volume is created. Therein, the one or more sidewalls may be one sidewall in the case that the internal volume has a cylindric shape, i.e. a circular cross-section. Alternatively, the one or more sidewalls are four sidewalls in the case that the internal volume has a rectangular cross-section. Other configurations are possible as well. According to the invention, a first electrical feedthrough is arranged in the first wall providing one or more electrical connections through the first wall in a vacuum tight manner. Additionally, a second electrical feedthrough is arranged in the second wall providing one or more electrical connections through the second wall in a vacuum tight manner. Therein, the first electrical feedthrough and I or the second electrical feedthrough might be commercially available feedthroughs such as a “Hermetic D-sub Connector” of Douglas Electrical. However, the present invention is not limited to the specific shape, the number of electrical connections and the type of used electrical feedthroughs as first electrical feedthrough and second electrical feedthrough. According to the present invention, one or more of the electrical connections of the first electrical feedthrough are connected with respective electrical connections of the second electrical feedthrough. Thus, the electrical connections of the first electrical feedthrough may be electrically connected to the electrical connections of the second electrical feed- through. Therein, the number of electrical connections of the first electrical feedthrough may correspond to the number of electrical connections of the second electrical feedthrough, may be larger or may be smaller. In particular, there might be a one-to-one connection between respective electrical connections of the first electrical feedthrough and electrical connections of the second electrical feedthrough. Thus, an electrical connection from the environment at the second wall is provided into the vacuum chamber via the first wall. In particular, the electrical connections of the first electrical feedthrough are connected to the electrical connections of the second electrical feedthrough by wires. Alternatively or additionally, passive components such as resistors, diodes, capacitors or the like may be arranged between the electrical connections of the first electrical feedthrough and the electrical connections of the second electrical feedthrough within the internal volume of the vacuum feedthrough. Therein, in the internal volume is a vacuum. Thus, by the construction of the vacuum feedthrough, there is no direct leakage from the environment under ambient pressure through either the first electrical feedthrough or the second electrical feedthrough into the vacuum chamber. Instead due to the vacuum in the internal volume, leakage is first through the second electrical feedthrough from the environment into the internal volume. In addition, there might be leakage through the first electrical feedthrough from the vacuum of the internal volume into the vacuum chamber. Since leakage is determined by the pressure difference, leakage into the vacuum chamber can be greatly reduced by the vacuum in the internal volume. Hence, by the construction of the vacuum feedthrough of the present invention overall leakage into the vacuum chamber is reduced, resulting in reduced requirements regarding pump performance of a vacuum pump connected to the vacuum chamber in order to maintain the vacuum in the vacuum chamber. At the same time, due to reduced leakage via the vacuum feedthrough, lower pressures can be achieved in the vacuum chamber. Similarly, less air may enter the vacuum chamber, increasing the equipment intervention life.

[0008] Preferably, the volume of the internal volume is between 100 cm3and 1000 cm3and preferably between 300 cm3and 700 cm3. By the volume of the internal volume a vacuum buffer is created in order to compensate for leakage through the second electrical feedthrough from the ambient pressure into the vacuum of the internal volume. Upon a constant leak rate, the larger the volume of the internal volume, the smaller the pressure increase overtime. Hence, a beneficial pressure difference between the internal volume and the vacuum chamber can be maintained over a longer time providing longer stability of the vacuum in the vacuum chamber.

[0009] Preferably, the distance between the first wall and the second wall is between 5 cm and 20 cm, preferably between 5 cm and 15 cm.

[0010] Preferably, the area of the first wall and I or the second wall is between 20 cm2and 500 cm2, more preferably between 50 cm2and 100 cm2.

[0011] Preferably, the complete first wall is connected to the vacuum chamber or part of the vacuum chamber.

[0012] Preferably, the complete second wall is connected to the environment.

[0013] Preferably, the internal volume is independent from the vacuum chamber. In particular, the vacuum of the internal volume is independent from the vacuum in the vacuum chamber. No fluid or gas connection is present between the internal volume and vacuum chamber. In particular, the vacuum of the internal volume can be selected independently of the vacuum of the vacuum chamber. Hence, upon change of the vacuum in the internal volume, the vacuum of the vacuum chamber is less effected and can remain at lower pressures.

[0014] Preferably, the pressure in the vacuum chamber is below 10'11mbar and preferably below 10'12mbar. However, the present invention is also beneficial for reduction of leakage rate if higher pressures in the vacuum chamber are present.

[0015] Preferably, the pressure in the internal volume is higher than the pressure in the vacuum chamber. In other words, the vacuum in the internal volume is lower than the vacuum in the vacuum chamber. In particular, in order to reduce the leak rate from the internal volume into the vacuum chamber, no such high requirements to the pressure / vacuum in the internal volume are imposed. However, even if the pressure in the internal volume is higher than the pressure in the vacuum chamber, sufficient reduction of the leak rate can be achieved.

[0016] Preferably, the maximum pressure in the internal volume is 100 mbar or higher and preferably 10 mbar or higher. Thus, even if the pressure in the internal volume is 100 mbar and preferably 10 mbar, this is sufficient in order to substantially reduce the leak rate via the first electrical feedthrough from the internal volume into the vacuum chamber by a factor of 10 or 100 respectively. Therein, it is noted, that the pressure inside the internal volume, if not continuously and actively pumped down, is subject to change and may increase over time due to a leak rate via the second electrical feedthrough from the environment into the internal volume and outgassing from the surfaces of the internal volume. Thus, increase of the pressure in the internal volume can be accepted up to a maximum pressure of 100 mbar or higher and preferably 10 mbar or higher which still ensures efficiently low leak rate into the vacuum chamber via the first electrical feedthrough to maintain the vacuum, i.e. UHV or even XHV, in the vacuum chamber. Thus, during operation the pressure in the internal volume might be below 100 mbar and in particular below 10 mbar. For example, the internal volume can be pumped down by a turbomolecular pump and IGP / NEG to 10’10mbar or lower and preferably 10-11and lower. Therein, the pressure in the internal volume might be limited by the leakage rate via the second electrical feedthrough which could be 1 x 10-9mbar l / s or higher if the vacuum pump is stopped, due to the leakage via the second electrical feedthrough from the environment into the internal volume, the pressure in the internal volume increases. However, as said before, as long as the pressure is below 100 mbar and preferably below 10 mbar, there is a sufficient reduction of the leak rate into the vacuum chamber.

[0017] Preferably, the leak rate from the internal volume into the vacuum chamber is less than 1 / 10, preferably less than 1 / 100 and more preferably less than 1 / 1000 of the leak rate of either the first electrical feedthrough or the second electrical feedthrough when they are arranged directly between ambient pressure and the vacuum chamber. Hence, by creating a vacuum in the internal volume the leak rate into the vacuum chamber can be reduced by a factor of 1 / 10, preferably 1 / 100 and more preferably 1 / 1000. At UHV conditions in the internal volume the leak-rate into the vacuum chamber can be reduced by a factor 1 / 1010 Preferably, the number of electrical connections of the first electrical feedthrough and I or the second electrical feedthrough is larger than 10 and preferably larger than 100. In particular, the first electrical feedthrough has the same number of electrical connections than the second electrical feedthrough.

[0018] Preferably, the first electrical feedthrough and the second electrical feedthrough are identically built. Alternatively, the first electrical feedthrough and the second electrical feed- through may differ.

[0019] Preferably, in the first electrical feedthrough and I or the second electrical feedthrough the connection elements are embedded in molten glass or molten ceramic. Thus, by the molten glass or molten ceramic, the electrical connections are sealed in order to reduce their intrinsic leak rate, respectively.

[0020] Preferably, in the internal volume an NEG pumping element is arranged. The NEG element comprises an NEG material. This could be an actual NEG pump. Alternatively, the NEG element may be one or more NEG pellets inside the volume. Hence, by the pumping effect of the NEG material, vacuum in the internal volume can be maintained even under outgassing loads and leakage via the second electrical feedthrough from the external environment into the internal volume. Hence, the internal volume can be kept at low pressure, high vacuum or ultra high vacuum over longer time maintaining the functionality of the vacuum feed- through over longer time, i.e. reducing the leak rate into the vacuum chamber.

[0021] Preferably, an inner surface of one or more of the first wall, the second wall and one or more of the sidewalls is covered or at least partially and preferably completely covered by an NEG material, for example an NEG thin film material. In particular, all inner surfaces of the first wall, the second wall and the sidewalls are covered by an NEG material. Hence, by the NEG material vacuum in the internal volume can be maintained even under leakage via the second electrical feedthrough from the environment into the internal volume. Hence, the internal volume can be kept at low pressure, high vacuum over longer time maintaining the functionality of the vacuum feedthrough over longer time, i.e. reducing the leak rate into the vacuum chamber. The internal volume is preferably connectable to a vacuum pump whereby, in use, the internal volume is maintained at a pressure below ambient pressure. Preferably, the internal volume is connected to a vacuum pump. Therein, the vacuum pump may be a turbomolec- ular pump in series with a mechanical pump to create an initial vacuum in the internal volume of 10'6mbar or lower.. However, the present invention is not limited to the specific type of vacuum pump and other vacuum pumps such as molecular drag pumps, screw pumps, scroll pump, roots pumps and claw pumps as well as capture (for examples a NEG pump, an ion pump or a combined NEG-ion pump), cryogenic pumps and diffusion pumps can also be used. Additionally, more than one pumps, and of different types, can be used. By the vacuum pump the vacuum in the internal volume is generated and maintained over longer time.

[0022] Alternatively, the internal volume comprises a vacuum connection comprising a valve, wherein a vacuum pump is connectable to the vacuum connection. Therein, by the vacuum pump a vacuum can be created in the internal volume. Additionally, a bake-out of the vacuum chamber and / or the internal volume can be performed simultaneously to allow a lower base pressure to be attained. If a NEG element is present, for example as NEG coating or as separate NEG pump, this can also be activated. Afterwards, the valve can be closed in order to maintain the vacuum inside the internal volume. If the valve is closed, the vacuum pumps can be either removed or switched off. If the pumps are mechanical pump, this will eliminate their contribution to the chamber vibrations, which is important for many types of applications including electron microscopy, surface science, quantum computing, radio telescopes and others. The vacuum in the internal volume is sufficient in order to reduce the leak rate into the vacuum chamber over a longer time of 2 to 50 days and preferably 10 to 30 days. In one aspect the valve itself can have a vacuum similarly created in an internal volume at the inlet flange of the valve so as to minimise the leakage across the seat of the valve.

[0023] Preferably, the first wall and I or the second wall is connected to the one or more sidewalls by a flange. Preferably, the flange is a vacuum flange, such a KF / QF, ISO, CF, quick CF, Wheeler and ASA flange. Preferably the vacuum flange has a metal-to-metal seal or provided by an O-ring. Thus, the one or more sidewalls may be provided by a pipe having flanges at its first end and / or at its second end in order to be either connected to the vacuum chamber (by another flange connected to the vacuum chamber) and / or to the second wall. Therein, the second wall may be built as blank flange, wherein the second electrical feedthrough is arranged in this blank flange connected to the flange of the sidewalls.

[0024] Additionally or alternatively, the first wall may also be built as a blank flange, wherein the first electrical feedthrough is arranged in this blank flange, connected to main chamber via a flanged connection. The flange may be directly mounted on the wall of the vacuum chamber, or at the end of a pipe connected to the main chamber, via a flanged connection.

[0025] Additionally, the blank flange where the electrical feedthrough is arranged may also provide a flanged connection to the sidewalls. Thus, the blank flange forming the first wall or the second wall may also provide a flanged connection to the sidewalls. Therein, in particular, the blank flange of the first wall may be connected to a flange of the vacuum chamber and, at the same time, connected to a flange of the sidewalls. Alternatively, the first wall may be an integral part of the internal volume (i.e. welded to) formed by the sidewall and the second wall, which is then attached to the main chamber, preferably by a flanged connection.

[0026] Alternatively, the sidewall is connected preferably by a flange to a wall of the vacuum chamber, wherein the first wall is connected to a flange of the vacuum chamber separate of the connection between the sidewall and the vacuum chamber. Thus, there is only an indirect connection between the first wall and the sidewall vial a wall of the vacuum chamber.

[0027] Preferably, the second wall is connected to or part of a second vacuum feedthrough to further reduce the leakage rate into the vacuum chamber. Therein, the second vacuum feedthrough may comprise a third wall connected to the second wall by a second sidewall to create a second internal volume. Similar to the first vacuum feedthrough as described before, a third electrical feedthrough is arranged in the third wall and one or more electrical connections of the second electrical feedthrough are connected with respective electrical connections of the third electrical feedthrough. Therein, the pressure in the second internal volume might be higher than in the first internal volume. In particular, the second vacuum feedthrough might be built along the feature described before with respect to the first vacuum feedthrough. In another aspect, the vacuum system is provided comprising a vacuum chamber having a chamber wall and being connected to a first vacuum pump to create a vacuum in the vacuum chamber. Further, the vacuum system comprises a vacuum feedthrough as described before, wherein the first wall is connected to or integrally built with the chamber wall. Alternatively, the second wall may be connected to or integrally built with the chamber wall. In this case the internal volume may extend into the vacuum chamber and may be surrounded by the vacuum in the vacuum chamber.

[0028] Preferably, the vacuum system comprises a main vacuum pump connected to the vacuum chamber in order to generate and maintain a vacuum. In particular, the main vacuum pump is an NEG pump.

[0029] Further, the vacuum system is built along the features described in relation with the vacuum feedthrough before.

[0030] In another aspect, a method for operating a vacuum system is provided. Therein, the vacuum system is built as described before. The method includes the steps of generating a vacuum in the internal volume of the vacuum feedthrough continuously or in intervals. Thus, in order to generate the vacuum in the internal volume, a vacuum pump can be connected to the internal volume and continuously pump down the internal volume to low pressures. Therein, the requirements regarding pump performance of this vacuum pump are small due to the small volume of the internal volume. Alternatively, the vacuum is generated / main- tained in intervals, wherein no active pumping is performed during these intervals. The intervals may have a fixed length or the length of the intervals may vary and depend on the pressure increase in the internal volume. For example, a pressure threshold can be set for the pressure in the internal volume. Upon exceeding the pressure threshold in the internal volume, the internal volume is pumped down again to lower pressures. Therein, the intervals are between 2 and 50 days and preferably between 10 and 30 days. Thus, due to the structure of the vacuum feedthrough according to the present invention, sufficient low vacuum can be maintained in the interval volume for a time of 2 to 50 days, in which no active action / pumping is required. In particular, the method is further built along the features described before in connection with the vacuum feedthrough and the vacuum system.

[0031] The present invention is described in more detail with reference to the accompanying figures.

[0032] The figures show:

[0033] Fig. 1 a first embodiment of the vacuum feedthrough according to the present invention,

[0034] Fig. 2 a vacuum system including the vacuum feedthrough of Fig. 1 ,

[0035] Fig. 3 another embodiment of the vacuum system according to the present invention,

[0036] Fig. 4 another embodiment of the vacuum feedthrough according to the present invention,

[0037] Fig. 5 another embodiment of the vacuum system according to the present invention and

[0038] Fig. 6 another embodiment of the vacuum feedthrough according to the present invention.

[0039] Throughout the following description of the figures, same or similar elements are denoted by the same reference number.

[0040] The vacuum feedthrough 10 of Fig. 1 has a first wall 12a and a second wall 12c which is connected by a sidewall 12b. By the first wall 12a, the second wall 12c and the sidewall 12b an internal volume 12 is created. In the first wall 12a, a first electrical feedthrough 14 is arranged. Similar, in the second wall 12c, a second electrical feedthrough 16 is arranged. The first electrical feedthrough 14 comprises electrical connections 24 extending from the internal volume 12 into a vacuum chamber 18. Similar, the second electrical feedthrough 16 may comprise electrical connections 26 extending from the environment 20 into the internal volume 12. The electrical connections of the first electrical feedthrough 14 and the second electrical feedthrough 16 are connected by wires 22 in order to provide an electrical connection from the environment 20 into the vacuum chamber 18. Therein, the first electrical feedthrough 14 and I or the second electrical feedthrough 16 might be commercially available feedthroughs such as a “Hermetic D-sub Connector” of Douglas Electrical. However, the present invention is not limited to the specific shape, the number of electrical connections and the type of used electrical feedthroughs as first electrical feedthrough and second electrical feedthrough.

[0041] Therein, a vacuum is present in the internal volume 12. Means for generating the vacuum are omitted for simplicity in Fig. 1. However, in Fig. 2 showing a similar vacuum feedthrough 10, a vacuum pump 34 is connected to the internal volume 12. Further, the first wall 12a is integrally built with a chamber wall 28 of a vacuum chamber 18. A main vacuum pump 30 is connected via a flange 32 to the vacuum chamber 18. In particular, the sidewall 12b may be welded to the chamber wall 28 in order to provide the internal volume of the vacuum feedthrough 10. Alternatively, as shown in Fig. 5, the sidewall 12b may be connected to the chamber wall 28 by a flange 38 as described below. In both cases, the chamber wall 28 at the same time serves as first wall of the vacuum feedthrough. In a third alternative, the first wall may be provided by a blank flange intermediately connected to a flange of the vacuum chamber 18 and a flange 38 of the sidewall 12b. In this way, the first wall is connected to the vacuum chamber 18 by the flange of the vacuum chamber and is separate of the chamber wall 28

[0042] The volume of the internal volume 12 may between 100 cm3and 2000 cm3and preferably between 300 cm3and 700 cm3. By the volume of the internal volume 12 a buffer is created in order to compensate for leakage through the second electrical feedthrough 16 from the ambient pressure into the vacuum of the internal volume 12. The larger the volume of the internal volume 12, the smaller the pressure increase overtime. Hence, a beneficial pressure difference between the internal volume 12 and the vacuum chamber 18 can be maintained over a longer time providing longer stability of the vacuum in the vacuum chamber 18. Preferably, the distance between the first wall 12a and the second wall 12c is between 5 cm and 20 cm, preferably between 5 cm and 15 cm. Preferably, the area of the first wall 12a and I or the second wall 12b is between 20 cm2and 100 cm2, more preferably between 50 cm2and 100 cm2.

[0043] Preferably, the internal volume 12 is independent from the vacuum chamber 18. In particular, the vacuum of the internal volume 12 is independent from the vacuum in the vacuum chamber 18. No fluid or gas connection is present between the internal volume 12 and vacuum chamber 18. In particular, the vacuum of the internal volume 12 can be selected independently of the vacuum of the vacuum chamber 18. Hence, upon change of the vacuum in the internal volume 12, the vacuum of the vacuum chamber 18 is less effected and can remain at lower pressures. Therein, the pressure in the vacuum chamber 18 may be 10-11mbar or below and preferably below 10-12mbar. The pressure in the internal volume 12 can be higher than the pressure in the vacuum chamber 18. In other words, the vacuum in the internal volume 12 can be lower than the vacuum in the vacuum chamber 18. In particular, in order to reduce the leak rate from the internal volume 12 into the vacuum chamber 18, no such high requirements to the pressure I vacuum in the internal volume 12 are imposed. However, even if the pressure in the internal volume 12 is higher than the pressure in the vacuum chamber 18, sufficient reduction of the leak rate can be achieved.

[0044] In the following an example is provided, elaborating the benefits of the present invention. However, it shall be understood, that the example cannot be construed as limiting the present invention. Specific numbers of the example are only given for illustrative purposes.

[0045] The leak rate from 1 electrical connector 24, 26 may be in the order of 10-9mbar l / s of Helium or higher when using for example “Hermetic D-Sub Connectors” by Douglas Electrical.

[0046] If 10 of these are used, the total leak rate is in the order of 10-8mbar l / s, creating an air gas load in the order of 10-8mbar l / s / 71 / 2= 3.8 x 10-9mbar l / s.

[0047] If the pumping speed for air of an NEG pump as main pump 30 of the vacuum chamber 18 is 500 l / s, the gas load generates a pressure rise in the chamber in the order of 7.6 x 10'12mbar. When there is additional gas load from outgassing and permeation in the chamber, it means that it is not possible to achieve pressures below 10-11mbar. Therein it is further noted, the situation becomes worse in the case of more electrical connections needed. In a specific application of quantum computing several tenth or even hundreds of electrical connections are necessary further increasing the leak rate and increasing the minimum possible pressure in the vacuum chamber 18.

[0048] If the internal volume 12 of the vacuum feedthrough 10 is pumped down with even a small pumping speed of 1 l / s, the pressure from leaks into the internal volume 12 will be in the order of 3.8 10'9mbar - this will practically eliminate the leak into the vacuum chamber.

[0049] A pressure as high as 10 mbar in the internal volume 12 can be sufficient to reduce the air leak rate in the vacuum chamber 18 by a factor of 100, and this would reduce the pressure rise due to the electrical connectors to 7.6 x 10-14mbar.

[0050] Therefore, very little pumping action is required.

[0051] It is referred to Fig. 3 showing a similar embodiment compared to Fig. 2. However, in the embodiment of Fig. 3, after initial pump down with the vacuum pump 34, the valve 36 can be closed and the vacuum pump 34 can be shut off. Due to the vacuum in the internal volume 12, leak rate into the vacuum chamber 18 is still reduced. Thus, the internal volume 12 could be pumped down at the beginning, for example by a TMP and then left until the pressure rises to 10 mbar for example. The time this takes depends on the leak rate of valve 36 (<10'8mbar- l / s) and the outgassing load from the internal volume. For a volume of 0.5 litres and a surface area of order 350 cm2then with a 1 hour outgassing rate of <1e-8 mbar- l / s / cm2, the total gas load would be < 10'5mbar l / s. Consequently, after about 20 days the pressure would rise to 10 mbar. Thus, the internal volume 12 can be left without further pumping for about 20 days while still providing the desired effect of reduced leak rate into the vacuum chamber 18.

[0052] Referring to Fig. 4, the vacuum feedthrough 10 of Fig. 4 shows a first flange 38 and a second flange 40. The sidewall 12b might be built as pipe having the first flange 38 and the second flange 40. With the first flange 38, the vacuum feedthrough 10 may be connected to the chamber wall 28 either directly to a flange of the chamber wall 28 or to a pipe of the vacuum chamber 18 having a flange. This is depicted in Fig. 5. The second wall 12c is connected to the second flange 40. Thus, the vacuum feedthrough 10 comprises a simple structure which can be built from readily available components. Referring to Fig. 6 showing the vacuum feedthrough 10. Therein, the inner surfaces in the internal volume 12 are covered by an NEG material 42 in order to maintain the vacuum within the internal volume 12. Due to the NEG material 42, low pressure can be maintained in the internal volume over longer time thereby officially reducing the leak rate into the vacuum chamber 18. Therein, the NEG material may provide a pumping action of 1 l / s or more.

[0053] In addition, embodiments of the individual figures can be freely combined with each other. For example, fixturing the vacuum feedthrough to the vacuum chamber 18 by a flange can be without difficulty combined with different types of vacuum pumps 34, a valve 36 and / or any type of NEG material disposed in the internal volume 12.

[0054] Reference list:

[0055] 10 vacuum feedthrough

[0056] 12 internal volume

[0057] 12a first wall

[0058] 12b sidewall

[0059] 12c second wall

[0060] 14 first electrical feedthrough

[0061] 16 second electrical feedthrough

[0062] 18 vacuum chamber

[0063] 20 external environment

[0064] 22 wires

[0065] 24 electrical connection

[0066] 26 electrical connection

[0067] 28 chamber wall

[0068] 30 main vacuum pump

[0069] 34 vacuum pump

[0070] 36 valve

[0071] 38 first flange

[0072] 40 second flange

[0073] 42 NEG material

Claims

CLAIMS1. Vacuum feedthrough in particular to provide an electrical connection from ambient pressure into a vacuum chamber, comprising a first wall to be at least partially connected to or part of the vacuum chamber, a second wall, wherein the first wall and the second wall are connected by one or more sidewalls, wherein by the first wall, the second wall and the one or more sidewalls an internal volume is created, a first electrical feedthrough arranged in the first wall providing one or more electrical connection through the first wall in a vacuum tight manner, and a second electrical feedthrough arranged in the second wall providing one or more electrical connection through the second wall in a vacuum tight manner, wherein one or more of the electrical connections of the first electrical feedthrough are connected with respective electrical connections of the second electrical feed- through, wherein, in use, the internal volume is maintained at a pressure below ambient pressure.

2. Vacuum feedthrough according to claim 1 , wherein the volume of internal volume is between 100cm3and 2000cm3and preferably between 300cm3and 700cm3.

3. Vacuum feedthrough according to claim 1 or 2, wherein the internal volume is independent from the vacuum chamber.

4. Vacuum feedthrough according to any of claims 1 to 3, wherein the pressure in the internal volume is higher than in the vacuum chamber.

5. Vacuum feedthrough according to any of claims 1 to 4, wherein a maximum pressure in the internal volume is 100mbar or higher and preferably 10mbar or higher.

6. Vacuum feedthrough according to any of claims 1 to 5, wherein in the first electrical feedthrough and / or the second electrical feedthrough are connecting elements embedded in molten glass or ceramic.

7. Vacuum feedthrough according to any of claims 1 to 6, wherein an inner surface of one or more of the first wall, the second wall and one or more of the sidewalls is covered by an NEG material.

8. Vacuum feedthrough according to any of claims 1 to 7, wherein an NEG material is disposed in the internal volume.

9. Vacuum feedthrough according to any of claims 1 to 8, wherein the internal volume is connected to a vacuum pump.

10. Vacuum feedthrough according to any of claims 1 to 8, wherein the internal volume comprises a vacuum connection comprising a valve, wherein the vacuum pump is connectable to the vacuum connection.

11. Vacuum feedthrough according to any of claims 1 to 10, wherein the first wall and / or the second wall is connected to the one or more sidewalls by a flange.

12. Vacuum system comprising a vacuum chamber having a chamber wall and being connected to a first vacuum pump to create a vacuum in the vacuum chamber, and a vacuum feedthrough according to any of claims 1 to 11 , wherein the first wall or the second wall is connected to or integral with the chamber wall.

13. Method for operating a vacuum system according to claim 12 including the steps of: generating a vacuum in the internal volume of the vacuum feedthrough continuously or in intervals.

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