GB2638985A

GB2638985A - Cryopump

Info

Publication number: GB2638985A
Application number: GB2403151.0A
Authority: GB
Inventors: Eric Dalgetty Michael; Haddad Jinane; Francesco Salvetti Matteo; F Moran Peter
Original assignee: Edwards Vacuum LLC
Current assignee: Edwards Vacuum LLC
Priority date: 2024-03-05
Filing date: 2024-03-05
Publication date: 2025-09-10
Also published as: GB202403151D0; WO2025186650A1; WO2025186650A8

Abstract

A cryopump has one or more crypopanel structures 10, 20 providing pumping surfaces for the pump. The cryopanels are cooled by a refrigerator 30 and there is at least one heating element formed of a conductive track 44 that is mounted on a surface of at least one of the cryopanel structures. A method of providing a cryopump with a heating element comprises applying a non-conductive coating (43, fig 2) to a surface of a cryopanel structure and applying a conductive track onto the non-conductive coating to form a heating element. The conductive track may be formed from a conductive paint or epoxy. Applying the track may comprise printing the track using an ink jet printer, or placing a mask over the cryopanel structure to define the track and applying a conductive paint, or applying a conductive epoxy and coating the epoxy track with charcoal.

Description

CRYOPUMP

FIELD OF THE INVENTION

The field of the invention relates to cryopumps and to a method of applying a 5 heating element to a cryopump.

BACKGROUND

Cryopumps are capture type pumps, which have cooled surfaces or cryopanels on which gas molecules condense. As they are capture type pumps they need to io be regenerated from time to time to release the captured molecules. This has conventionally been done during a regeneration cycle, where the cryopump is heated to release the molecules. The heaters may be attached to the refrigeration unit and act to heat the refrigeration unit and cryopanels together. Once the temperature of the pump has risen sufficiently to release the condensed and adsorbed gases and the pump has been purged, the cryopump can then be cooled back to an operational temperature. Such a regeneration cycle takes time and provides a period during which the pump is not operational.

SUMMARY

A first aspect provides a cryopump comprising: at least one crypopanel structure comprising at least one pumping surface; a refrigerator for cooling said at least one cryopanel structure; and at least one heating element, said at least one heating element comprising a conductive track mounted on a surface of at least one of said at least one cryopanel structure.

As noted above the regeneration of cryopumps takes time, and this is time during which the cryopump cannot be used. The time taken is that required both to heat the cryopump to a temperature where the captured gas molecules are released and then to cool it back to an operational temperature. It was 3o recognised that it is the temperature of the cryopanels themselves that are important during regeneration. Thus, were one to direct any heating directly at the cryopanels, the heating might be able to be done more quickly and the heat -2 -capacity of the structure heated might be less, requiring less energy and allowing for a faster cool down time following regeneration. Providing the heaters as heating elements mounted on a surface of one or more cryopanel structures allows for direct and effective heating of the cryopanel structures. This increases the speed at which the crypanels heat up and reduces the heating of other components within the vacuum pump thereby saving energy and reducing subsequent cool down times. In effect by forming the heating elements as conductive tracks on the surfaces of the cryopanels the heat transfer can be high and targeted to the desired structure providing for a thoroughly efficient and effective way of supplying the heat.

In some embodiments, said conductive track is formed from a conductive paint or epoxy.

The conductive track may be formed in a number of ways but in some embodiments it is formed from a conductive paint or epoxy. A paint or epoxy may be easily applied as a conductive track to a cryopanel, in a cost effective way which does not unduly affect the basic design or build of the vacuum pump.

In some embodiments, a thickness of said conductive track is between 30 to 100 microns thick, in other embodiments it may be thicker, between 0.5 and 3mm thick. A conductive track that provides an effective heating element may be very thin, leading to very little change to the structure and providing a low heat capacity heater.

Although, the conductive paint and/or the epoxy may comprise different compounds provided they are conductive, in some embodiments the conductive paint comprises one of a carbon, nickel, silver-plated copper or copper paint.

3o In some embodiments, said cryopanel structure is conductive and said at least one surface mounting said conductive track comprises at least one of an -3 -electrically insulating layer and a thermal buffer layer between said conductive track and said cryopanel structure surface.

Cryopanels are conventionally conductive as this allows them to be effectively cooled and thus, applying a conductive heating track to such a surface may require an electrically insulating layer between the track and cryopanel. In some embodiments the electrically insulating layer forms a thermal expansion buffer between said cryopanel structure and said conductive track. In other embodiments there may be an expansion buffer layer in addition to the insulating io layer between the cryopanel surface and the conductive track.

The thermal expansion buffer may be formed of a material with a coefficient of thermal expansion that is between the thermal expansion coefficient of the cryopanel material and that of the conductive track. In this way a thermal expansion buffer is formed that reduces forces between the conductive track and the cryopanel as the temperature changes.

In some embodiments said conductive track is covered by a protective layer.

In some embodiments said protective layer comprises a thermally conductive plastic. In some embodiments the thermally conductive plastic may comprise a coefficient of thermal expansion that is close to, say within 30% of, the coefficient of thermal expansion of the conductive paint.

In some embodiments, said refrigerator comprising a two stage refrigerator, and said at least one cryopanel structure comprises a first stage cryopanel structure and a second stage cryopanel structure, each of said first and said second stage cryopanel structures comprising a conductive track mounted on at least one surface of said respective cryopanel structure.

Cryopumps are often two-stage cryopumps with a first stage cryopanel being at a higher temperature than a second stage cryopanel, the first stage cryopanel -4 -pumping gasses, such as water vapour, that condense at higher temperatures while the lower temperature second stage cryopanel pumps gasses that condense or are adsorbed at much lower temperatures. The first stage cryopanel protects the second stage cryopanel from being overloaded with the often more common gasses, that condense at the higher temperature.

In some embodiments, said first stage cryopanel structure comprises a radiation shield within a vessel, said radiation shield comprising an open frontal area forming an inlet to said vessel, said conductive track being mounted on an outer io surface of said radiation shield and said inner surface of said radiation shield comprising a pumping surface.

If the heating element is mounted on the outer surface of the radiation shield then it does not interfere with the main pumping surface and yet is still able to apply heat very effectively to the cryopanel.

Alternatively and/or additionally the heating element may be mounted on an inner surface of the cryopanel structure. Mounting the heating element on the inner surface of the structure may allow the heat to be applied more directly to the surface that may have the most amount of gas condensed on it. In some cases heating elements may be on both the inner and outer surfaces, This may increase the speed that the structure can be heated to the desired temperature and thereby decrease the regeneration time.

In some embodiments, at least one pumping surface of said second stage cryopanel structure comprises an adsorbent material forming a layer on said at least one pumping surface.

In some embodiments, said absorbent layer comprises a carbon layer. -5 -

In some embodiments, said at least one heating element mounted on at least one of said surfaces of said second stage cryopanel structure is mounted on said surface not comprising said adsorbent material.

For the heating element mounted on the second stage cryopanel, again it may be advantageous if it is mounted not on the primary pumping surface, which may be the one comprising the adsorbent. Such a heater would still apply effective heating to the cryopanel owing to the conductive nature of the cryopanel.

io Alternatively and/or additionally, it may be mounted on the pumping surface underneath any absorbent layer where it will apply a direct heat to the absorbent layer.

In some embodiments, said second stage cryopanel structure comprises at least one surface facing an inlet for receiving a gas to be pumped and said at least one surface mounting said heating element comprises at least one of said at least one surfaces facing said inlet.

In some cases, the second stage cryopanel structure may have as a primary pumping surface the surface that does not face the inlet. Molecules that arrive on this surface will generally have been deflected by the first stage cryopanel. Molecules deflected by the radiation shield will be predominantly type II or type III gases as the radiation shield will capture the type I gases. For this reason, the surface not facing the inlet may be the primary pumping surface and again it may be advantageous to mount the heating element not on this surface but on the other surface that faces the inlet. The primary pumping surface may be the one comprising the adsorbent.

In some embodiments, the cryopump further comprises control circuitry 3o configured to independently control current supplied to heating elements on said first and said second cryopanel structures. -6 -

Having different heating elements on the first and second stage cryopanels allows the current supplied to each to be independently controlled. In this way they may be used to control a temperature difference between the two cryopanel structures. In this regard, where the cryopanel structures are cooled by a first and second stage refrigerator then the temperature difference between the two is set by the two stage refrigerator properties and is not controllable, providing independently controllable heating elements allows such control.

In some embodiments, said control circuitry is configured to initiate a io regeneration cycle by stopping said refrigerator from cooling said cryopump and initiating the current supply to said heating elements.

The control circuitry may also be in control of starting and stopping the regeneration cycle by controlling the flow of current to the heating element(s) and controlling operation of the refrigerator.

In some embodiments, said control circuitry is configured to control said refrigerator to continue to cool said cryopanel structures and to supply current to said heating element mounted on said second stage cryopanel at a same time, to independently regenerate said second stage cryopanel structure, while keeping said cryopump at a low temperature.

As noted previously, the regeneration cycle takes a significant amount of time during which the cryopump cannot be used. Much of this time is spent both heating the cryopanel structures, purging the vacuum pump and then cooling the cryopanels structure again. It may be that the second stage cryopanel structures require regeneration more often than the first stage cryopanel structures and it therefore may be advantageous to be able to independently heat the second cryopanel structure while not stopping the refrigerator, such that the first stage 3o cryopanel structures remain cold and thus, both the heating and the cooling of the cryopump back to operational temperature can be done in a much shorter time period. -7 -

A second aspect provides a method of providing a cryopump with at least one heating element, said method comprising: applying a non-conductive coating to at least one surface of at least one cryopanel structure; applying a conductive track onto said non-conductive coating to form said at least one heating element.

In some embodiments, said step of applying said conductive track comprises placing a mask over said cryopanel structure, said mask defining said track and applying a conductive paint.

In other embodiments, said step of applying said conductive track comprises printing said track using an ink jet style printer and conductive ink.

In other embodiments, said conductive track comprises a conductive epoxy and said step of applying said conductive track comprises applying said conductive epoxy to form said track and then coating said conductive epoxy with charcoal.

The conductive epoxy may have adhesive properties and thus, the charcoal may be coated onto the conductive track, by simply dipping it into charcoal. In some embodiments said conductive track may be a tightly packed conductive track allowing when coated with charcoal for a significant surface area of adsorbent material.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, 3o it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. -8 -

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 schematically shows a cryopump according to an embodiment; 5 Figure 2 schematically shows a heater element mounted on a cryopanel according to an embodiment; and Figure 3 shows a flow diagram outlining steps in a method for mounting heating elements on a cryopanel according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.

Embodiments provide a method of applying a resistive heater onto cryopump arrays or cryopanels using a conductive ink, paint or epoxy. This allows direct heating of the cryopump arrays, leading to faster pump regeneration and as the heat is targeted to the required areas faster subsequent cooldown times.

Conventional cryopump technology may use two individual cylindrical heater cartridges thermally bonded to the 1st and 2nd stage heat stations on the cryopump's refrigerator. During a regeneration cycle, the cryopanel structures or arrays, which have collected condensable gases or adsorbed gases, should be raised to a higher temperature to remove these gases and allow a roughing pump to evacuate them. The warmup and cooldown cycle involves heating and cooling the entire refrigerator and cryopanel structures and takes a significant amount of time.

Embodiments seek to address this by providing a cryopump having a heating element mounted directly on at least a portion of the cryopanel structure or array.

3o This may be done by applying a thin layer of conductive paint to form a conductive track on the structure and then passing an electrical current through the paint. In this way heat is applied directly to the structure. In effect by passing -9 -electrical current through this conductive trace, the array will be heated by conduction over a high surface area and with very little thermal resistance. This will significantly reduce warm up time. Because the refrigerator is no longer required to reach above ambient temperatures, the cooldown time may also be significantly reduced.

Figure 1 shows a cryopump according to an embodiment. In this embodiment the cryopump is a two stage cryopump with a two-stage refrigerator 30, the first stage cooling to between 40 -130 K and being connected to a first stage cryopanel structure 10, which acts as a radiation shield and as a pumping surface for gases with a higher condensing temperature such as water vapour and a second stage cryopanel structure 20 cooled in the range of 4-25 K, and which may be coated with a capture material such as charcoal. This second stage cryopanel array acts as the primary pumping surface The radiation shield may be the pump housing or may be within the pump housing and is generally closed except for an inlet 50 which is positioned between the second stage cryopanel array 20 and the chamber to be evacuated. This inlet 50 is in this embodiment partially obscured by a first stage frontal cryopanel array 10 which forms part of and is thermally coupled to the radiation shield 10 and serves as a pumping site for high boiling point type I gases such as water vapour.

In operation, when gases pass through the inlet 50 into the pump vessel, at least some of the type I gases such as water vapour are condensed on the frontal array. The lower boiling point gases pass through the frontal array and into the volume within the radiation shield. Type II gases, such as nitrogen, condense on the second stage array 20, while type Ill gases, such as hydrogen, helium and neon which have appreciable vapour pressures at 4K are absorbed by an adsorbent such as activated carbon, zeolite or a molecular sieve that coats the lower surface of the second stage cryopanels 20.

-10 -Looking at Figure 1 the cryopump has a two-stage refrigerator 30 with a first stage 34 and a second stage 32, the second stage 32 cooling to the lower temperature. The first stage of the refrigerator 34 is coupled to the first stage cryopanels 10 comprising the radiation shield around the interior of the vacuum vessel and the frontal array 10 across the inlet 50. The second stage cryopanels are thermally conductively coupled with the second stage refrigerator 32 and are shielded by the radiation shield of the first stage cryopanels 10. The lower surfaces of the second stage cryopanels 20 have an adsorbent material 22 on them while the upper surfaces of at least some of them have a heating element formed by a conductive track 44. There is also a heating element formed by a conductive track 42 on the first stage radiation shield cryopanels and in this embodiment they are on the outer surface of the radiation shield that is within the vacuum vessel. There is control circuitry 40 for controlling the refrigerator 30 and for controlling the heating elements 42 and 44.

Control circuitry 40 may control the heating elements 42 and 44 independently and in this way may be able to control a difference in temperature between the two cryopanel structures during operation of the pump. Control circuitry 40 may also control the heaters 42, 44 during a regeneration cycle.

During the regeneration cycle the circuitry may control the refrigerator 30 to suspend cooling and may control both heating elements 42 and 44 to heat each of the cryopanel structures to free any gasses captured by the panels. Once the gases are freed and the vacuum vessel has been purged then the control circuitry 40 may control the refrigerator 30 to once again cool the cryopanels while no longer supplying current sent to the heaters 42, 44.

In some embodiments the control circuitry may be configured to perform a regeneration of just the second stage cryopanels. In this case, the control circuitry 40 may supply current to the heater 44 to heat the second stage 3o cryopanels. The refrigerator may continue to operate and the cryopump temperature may remain low. This will allow the cryopump to be cooled down to operating temperature much more quickly once the second stage cryopanels have been regenerated.

Figure 2 shows a cryopanel 20 comprising a heating element 44 in the form of a conductive track according to an embodiment. The face2l of the cryopanel 20 not comprising an adsorbent material has been coated with a silicone conformal insulator 43 that may have been sprayed or pointed onto the cryopanel prior to the conductive carbon paint track 44 being painted on to it. In this case the track is painted by spraying using a mask to define the shape of the track. Power io leads 24 may be attached with a conductive epoxy. In this embodiment, the cryopanel is a cryopanel of the second stage array and it is the side of the second stage array panel 20 that does not have the charcoal that has the conductive track on it. In other embodiments it may be the side having the charcoal layer that has the heating element and the heating element may be placed underneath the charcoal layer. In some embodiments the conductive track may be formed of a conductive epoxy and the charcoal may coat the conductive track. In some embodiments this may be achieved by dipping the cryopanel into the charcoal before the epoxy has set.

Figure 3 shows a flow diagram illustrating steps in a method of applying a heating element to a cryopump according to an embodiment. In a first step S10 a nonconductive coating is applied to at least one surface of one or more of the cryopanel structures of the pump. This coating may be a silicone conformal coating, or similar polymer which can withstand the low temperatures involved. It may be selected from materials that have a coefficient of thermal expansion that is between that of the cryopanel material and that of the conductive track, thereby providing both an electrically non-conductive layer and a thermal expansion buffer.

3o In a second step S20 a conductive track is applied onto the non-conductive coating to form a heating element. This may be done, once the non-conductive coating has dried, by placing a pre-cut vinyl mask onto the non-conductive coating, and applying a layer of conductive paint. In some embodiments this conductive paint may be applied through a dispensing nozzle and excess paint squeegeed off, this way a repeatable, uniform layer is created. In other embodiments, the conductive track may be printed onto the cryopanel using an ink-jet printer and conductive ink. In still other embodiments a conductive epoxy may be used to form the track. In some cases, the conductive epoxy may be coated with charcoal to form an adsorbent layer on the cryopanel covering the heating element. The step of coating may be performed by dipping the cryopanel in charcoal before the epoxy has set.

In embodiments where there is no adsorbent layer covering the conductive track, a further protective layer may be placed to cover the conductive track and to protect it from damage due perhaps to the harsh chemicals being pumped.

At step S30 conductive wires are attached to either end of the conductive track and are attached to a power supply that is controlled by control circuitry. These power leads may be directly bonded to the conductive trace using a conductive, low temperature tolerant, epoxy. For increased durability, the power leads could be passed through stamped holes in the array and epoxied on the other side of the hole, similar to a through-hole soldered component. The shape of the trace and lead placement may be any shape which achieves the necessary resistance of the heater and provides a convenient location for the power leads. It is recommended that the power leads be strain relieved elsewhere in the pump.

In summary embodiments may provide one or more of the following advantages.

Heating cryopanels using conductive traces as heating elements allow for the heater manufacture to be very simple, indeed it may be as simple as applying a conductive paint over a mask.

-13 -Furthermore, by directly heating arrays rather than another component of the cryopump such as the refrigerator, warmup and cooldown times during regeneration and pumpdown will be reduced.

Furthermore where there are multiple arrays each array can be warmed individually, further reducing the need to heat the entire pump above ambient temperatures.

A further advantage of this means of heating the cryopanel structure(s) is that the io Wattage of these heating elements may also be significantly higher than the current heater cartridge design, due to the very high surface area of contact between the heater and the array. Higher powers will further improve warmup times.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

-14 -

REFERENCE SIGNS

first stage cryopanels second stage cryopanels 21 array side without adsorbent 22 charcoal layer 24 power leads refrigerator 32 first stage refrigerator unit io 34 second stage refrigerator unit control circuitry 42 first stage cryopanel heating element 43 silicone conformal coating 44 second stage cryopanel heating element 50 inlet

Claims

-15 -CLAIMS1. A cryopump comprising: at least one crypopanel structure comprising at least one pumping surface; a refrigerator for cooling said at least one cryopanel structure; and at least one heating element, said at least one heating element comprising a conductive track mounted on a surface of at least one of said at least one cryopanel structure.
2. A cryopump according to claim 1, wherein said conductive track is formed from a conductive paint or epoxy.
3. A cryopump according to claim 2, wherein said conductive paint comprises one of a carbon, nickel, silver-plated copper and copper paint.
4. A cryopump according to any preceding claim, wherein said cryopanel is conductive and said at least one surface mounting said conductive track comprises at least one layer between said conductive track and said cryopanel surface, said at least one layer comprises at least one of an insulating layer and a thermal expansion buffer layer.
5. A cryopump according to any preceding claim, said cryopump further comprising a protective layer covering said conductive track. 25
6. A cryopump according to any preceding claim, wherein said refrigerator comprising a two stage refrigerator, and said at least one cryopanel structure comprises a first stage cryopanel structure and a second stage cryopanel structure, each of said first and said second stage cryopanel structures comprising a conductive track mounted on at least one surface of said respective cryopanel structure.-16 -
7. A cryopump according to any claim 6, wherein said first stage cryopanel structure comprises a radiation shield within a vessel, said radiation shield comprising an open frontal area forming an inlet to said vessel, said conductive track being mounted on an outer surface of said radiation shield and said inner surface of said radiation shield comprising a pumping surface.
8. A cryopump according to claim 6 or 7, wherein at least one pumping surface of said second stage cryopanel structure comprises an adsorbent material forming a layer on said at least one pumping surface.
9. A cryopump according to claim 7 or 8, wherein said adsorbent material layer comprises a carbon layer.
10. A cryopump according to claim 8 or 9, wherein said at least one heating element mounted on at least one of said surfaces of said second stage cryopanel structure is mounted on said surface not comprising said adsorbent material.
11. A cryopump according to any one of claims 6 to 10, wherein said second stage cryopanel structure comprises at least one surface facing an inlet for receiving a gas to be pumped and said at least one surface mounting said heating element comprises at least one of said at least one surfaces facing said inlet.
12. A cryopump according to any one of claims 6 to 11, further comprising control circuitry configured to independently control current supplied to heating elements on said first and said second cryopanel structures.
13. A cryopump according to claim 12, said control circuitry being configured to control a temperature difference between said first and second stage 3o cryopanel structures, by said independent control of said current supplied to said heating elements.-17 -
14. A method of providing a cryopump with at least one heating element, said method comprising: applying a non-conductive coating to at least one surface of at least one cryopanel structure; applying a conductive track onto said non-conductive coating to form said at least one heating element.
15. A method according to claim 14, wherein said step of applying said conductive track comprises one of: io printing said conductive track using an ink jet printer; or placing a mask over said cryopanel structure, said mask defining said track and applying a conductive paint.
16. A method according to claim 14, wherein said step of applying said conductive track comprises applying a conductive epoxy to form said track, said method comprising a further step of coating said epoxy track with charcoal.