EP0126909B1 - Pompe cryostatique avec réfrigération rapide et stabilité de pression améliorée - Google Patents

Pompe cryostatique avec réfrigération rapide et stabilité de pression améliorée Download PDF

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Publication number
EP0126909B1
EP0126909B1 EP84103732A EP84103732A EP0126909B1 EP 0126909 B1 EP0126909 B1 EP 0126909B1 EP 84103732 A EP84103732 A EP 84103732A EP 84103732 A EP84103732 A EP 84103732A EP 0126909 B1 EP0126909 B1 EP 0126909B1
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EP
European Patent Office
Prior art keywords
stage
radiation shield
cryopump
temperature
heat load
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP84103732A
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German (de)
English (en)
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EP0126909A2 (fr
EP0126909A3 (en
Inventor
Michael J. Eacobacci
Donald A. Olsen
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Azenta Inc
Original Assignee
Helix Technology Corp
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Application filed by Helix Technology Corp filed Critical Helix Technology Corp
Publication of EP0126909A2 publication Critical patent/EP0126909A2/fr
Publication of EP0126909A3 publication Critical patent/EP0126909A3/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B37/00—Pumps having pertinent characteristics not provided for in, or of interest apart from, groups F04B25/00 - F04B35/00
    • F04B37/06—Pumps having pertinent characteristics not provided for in, or of interest apart from, groups F04B25/00 - F04B35/00 for evacuating by thermal means
    • F04B37/08—Pumps having pertinent characteristics not provided for in, or of interest apart from, groups F04B25/00 - F04B35/00 for evacuating by thermal means by condensing or freezing, e.g. cryogenic pumps

Definitions

  • This invention relates to a cryopump and a method of preventing crossover hang up in a cryopump having at least two refrigerator stages comprising providing a passive heat load to the first stage, the first stage being held at a temperature above about 50 K, the heat load being less at initial first stage temperatures, wherein the passive heat load is due to radiant heat flow resulting from a radiation shield.
  • a low temperature second stage array is the primary pumping surface. This surface is surrounded by a higher temperature cylinder, usually operated in the temperature range of 70 to 130 K, which provides radiation shielding to the lower temperature array.
  • the radiation shield generally comprises a housing which is closed except at a frontal array positioned between the primary pumping surface and the chamber to be evacuated. This higher temperature, first stage, frontal array serves as a pumping site for higher boiling point gases such as water vapor.
  • high boiling point gases such as water vapor are condensed on the frontal array.
  • Lower boiling point gases pass through that array and into the volume within the radiation shield and condense on the second stage array.
  • a surface coated with an adsorbent such as charcoal or a molecular sieve operating at or below the temperature of the second stage array may also be provided in this volume to remove the very low boiling point gases.
  • the cooler In systems cooled by closed cycle coolers, the cooler is typically a two stage refrigerator having a cold finger which extends through the rear of the radiation shield.
  • the cold end of the second, coldest stage of the cryocooler is at the tip of the cold finger.
  • the primary pumping surface, or cryopanel is connected to a heat sink at the coldest end of the second stage of the coldfinger.
  • This cryopanel may be a simple metal plate or an array of metal baffles arranged around and connected to the second stage heat sink.
  • This second stage cryopanel also supports the low temperature adsorbent.
  • the radiation shield is connected to a heat sink, or heat station at the coldest end of the first stage of the refrigerator.
  • the shield surrounds the first stage cryopanel in such a way as to protect it from radiant heat.
  • the frontal array is cooled by the first stage heat sink through the side shield or, as disclosed in U.S. Patent 4,356,701, through thermal struts.
  • Cross over is the processing step in which a valve between the work chamber and cryopump is opened to expose the very high vacuum cryopump to a lower vacuum work chamber. The pressure of the work chamber is then reduced by the cryopump. To bring the work chamber pressure to a vacuum of, for example, 1.3332 .10-' mbar (10-' torr), it is necessary that, in the case of argon, the gas be condensed on the cold, second stage array at a temperature of 28,6 K. Condensation of argon at higher temperatures results in a higher partial pressure of the argon and thus a higher pressure in the work chamber.
  • the argon does not condense on the first stage array but passes directly to the second stage array for proper condensation on that array.
  • the front array temperature can drop to as low as about 40 K.
  • argon does condense on the frontal array; and at that temperature the partial pressure resulting from the balanced evaporation of solid argon and condensation of argon molecules results in a partial pressure of only 1.3332.10-3 to 1.3332 10-4 mbar (10- 3 to 10- 4 torr). So long as any argon is in this state of sublimation on the frontal array, the pressure in the work chamber cannot be taken down to the desired 1.3332 ⁇ 10 -7 mbar (10- 7 torr).
  • the argon gas evaporates during sublimation, it eventually migrates to the colder second stage and is captured by that stage. However, the sublimation process is a slow one and until complete the pressure in the system "hangs up" at the higher pressure.
  • the first stage arrays be made warmer by introducing an electrical heat load onto the first stage to prevent excessive cooling of that stage.
  • a load on the stage generally increases cooldown time of the refrigerator. Minimizing cooldown time is a significant concern in designing cryopump systems.
  • electrical elements can present a hazard where the concentration of hydrogen is high.
  • GB-A-2 061 391 there is known a cryopump having at least two refrigerator stages comprising a passive heat load to the first stage, the first stage being held at a temperature above about 50 K, the heat load being less at initial first stage temperatures, wherein the passive heat load is due to radiant heat flow resulting from a radiation shield.
  • GB-A-2 061 391 states that the first stage of this cryopump is typically maintained at a temperature on the order of 50°K to 80°K there is no indication in this document that the above problem of cross over "hang up" has been realized.
  • cryopump systems Another problem associated with cryopump systems is that a pulsed thermal load can result in erratic pressure in the work chamber. For example, as a low emissivity valve door is opened to expose the frontal array to a higher emissivity radiating surface, the thermal load is increased, and the pressure may become unstable.
  • cross over hang up in a cryopump is avoided by blackening the outer surface of the radiation shield, thereby providing apassive heat loadtothe first stage to assure that the first stage is held at a temperature above about 50 K.
  • the passive heat load is substantially less than that at the final cooldown temperature condition, so that cooldown time is not substantially affected.
  • the effective emissivity between at least a portion of the radiation shield and the vacuum vessel is increased.
  • the radiation heat load on the first stage is great due to the fact that the heat flux is a function of the difference in temperatures to the fourth power.
  • the temperature differential between the radiation shield and the vacuum vessel is less and, due to the fact that the radiation heat flux is a function of the difference in temperatures, the load is substantially less.
  • the heat load is negligible.
  • the effective emissivity between the radiation shield and vacuum vessel is obtained by painting the outer surface of the radiation shield black. Painting of the inner surface of the vacuum vessel would also increase the effective emissivity, but might result in outgasing from the paint at the higher temperatures of the vacuum vessel.
  • a problem related to cross over "hang up” can occur as a result of condensation of gases on the side of the second stage refrigerator cylinder. This problem is particularly apparent where an open second stage array is used to provide for maximum flow to an adsorbent material on the back side of the array.
  • an open second stage array is used to provide for maximum flow to an adsorbent material on the back side of the array.
  • Argon and other gases can condense along a zone of the refrigerator cylinder which is at a temperature of less than 50 K. The temperature of that zone is determined by the system pressure.
  • the first stage temperature increases and shifts the 50 K zone along the length of the refrigerator cylinder.
  • a close fitting sleeve surrounds the refrigerator cylinder. That sleeve is in thermal contact with the second stage heat sink but is not in contact with the refrigerator cylinder. Most gas which passes the second stage array is condensed on the shield before it reaches the cylinder.
  • the narrow gap of about 2.54 mm (0.1 inch) or less between the shield and the cylinder assures that even gas which passes beneath the cylinder is quickly condensed on and thus captured by the cold shield.
  • the cryopump of Figs. 1 and 2 comprises a vacuum vessel 12 which is mounted to the wall of a work chamber along a flange 14.
  • a front opening 16 in the vessel 12 communicates with a circular opening in a work chamber.
  • a removable cover 17 is provided over the opening as shown in Fig. 2.
  • the cryopump assembly may protrude into the chamber and a vacuum seal be made at a rear flange.
  • a two stage cold finger 18 of a refrigerator protrudes into the vessel 12 through an opening 20.
  • the refrigerator is a Gifford-MacMahon refrigerator such as disclosed in U.S. Patent No. 3,218,815 to Chellis et al., but others may be used.
  • a two stage displacer in the cold finger 18 is driven by a motor 22. With each cycle, helium gas introduced into the cold finger under pressure through line 24 is expanded and thus cooled and then exhausted through line 26.
  • a first stage heat sink, or heat station, 28 is mounted at the cold end of the first stage 29 of the refrigerator.
  • a heat sink 30 is mounted to the cold end of the second stage 32.
  • a suitable temperature sensor element 34 is mounted to the rear of the heat sink 30.
  • the primary pumping surface is an array mounted to the heat sink 30.
  • This array comprises a disc 38 and a set of circular chevrons 40 arranged in a vertical array and mounted to disc 38 by thermal struts 41.
  • the struts 41 extend through the chevrons 40 and cylindrical spacers 43 between the chevrons, and nuts at the ends of the struts compress the chevrons and spacers into a tight stack.
  • a low temperature adsorbent such as charcoal particles is adhered to the lower backside surface area of the chevrons. Access to this adsorbent by low boiling point gases is through the open chevrons 40.
  • chevrons supported by struts, allows for simple assembly and also ready flow of gases past the front side of the chevrons 40 to the adsorbent.
  • the chevrons could be supported on an inner cylinder to which adsorbent could adhere.
  • a sleeve 52 is positioned over the second stage refrigerator cylinder 32.
  • the sleeve 52 is formed of two hemicylindrical elements 54 and 56 which are mounted to and extend downward from the second stage heat sink 30.
  • a small gap 55 is provided between the sleeve and the cylinder 32.
  • a cup shaped radiation shield 44 is mounted to the first stage, high temperature heat sink 28.
  • the second stage of the cold finger extends through an opening 45 in that radiation shield.
  • This radiation shield 44 surrounds the second stage array to the rear and sides to minimize heating of the array by radiation.
  • the temperature of this radiation shield is less than about 120 K.
  • a frontal cryopanel array 46 serves as both a radiation shield for the primary cryopanel and as a cryopumping surface for higher boiling temperature gases such as water vapor.
  • This array comprises louvers 48 joined by rim 50.
  • the frontal array 46 is mounted to the radiation shield 44, and the shield both supports the frontal array and serves as the thermal path from the heat sink 28 to that array.
  • the configuration of this array need not be confined to the arrangement shown but it should be an array of baffles so arranged as to act as a radiant heat shield and a higher temperature cryopumping panel while providing a path for lower boiling temperature gases to the second stage array.
  • the problem of cross over hang up results from argon and other gases freezing on the first stage frontal array rather than passing directly through to the second stage array.
  • hang up due to argon can be avoided by holding the temperature of the frontal array above 50 degrees. This in turn can be accomplished by providing a heat load to the first stage at low temperatures.
  • the heat load of the first stage be minimized at higher temperatures in order to maintain high cooldown speeds.
  • a radiation heat load is applied to the first stage by painting the outside of the radiation shield 44 with flat black paint. This increases the emissivity of the shield and increases the radiant heat flow from the vacuum vessel to the shield. That radiant heat flow is a thermal load on the first stage refrigerator.
  • the thermal load on the first stage is due to the radiant heat flow Q to the radiation shield 44: where A is the surface area, a is a constant, Oeff is the effective emissivity, T H is the temperature of the vacuum vessel and T L is the temperature of the radiation shield.
  • the effective emissivity is a function of the emissivity e. of the outer surface of the radiation shield and the emissivity e, of the inner surface of the vacuum vessel: In the past, these surfaces have been polished to obtain very low emissivities of less than about 0.1 for an effective emissivity of less than about 0.05. That low effective emissivity minimizes radiant heat flow and the resultant load on the first stage. To provide a proper heat load to the first stage in accordance with this invention the effective emissivity should be at least about 0.10. This effective emissivity is obtained by an emissivity of the outer surface of the radiation shield 44 approaching one and the emissivity of the inner surface of the vacuum vessel 12 of about 0.1.
  • the high emissivity is provided on the radiation shield 44 and not on the frontal array 46.
  • the effective emissivity could vary greatly. As a valve door to the work chamber opens, the emissivity seen by the array would change from 0.1 to near one. With an emissivity on the array of near one, the effective emissivity would change from about 0.1 to about one. This would result in a change in thermal load of several watts.
  • the frontal array has an emissivity of about 0.1 so that as the valve opens the frontal effective emissivity only changes from about 0.05 to about 0.1.
  • the effective emissivity between the radiation shield and vacuum vessel remains at about 0.1 regardless of the valve position.
  • the first stage load remains much more constant at about one or two watts.
  • the radiation heat flow is a function of the difference in temperatures raised to the fourth power.
  • the heat flow increases. It has been found that by painting the radiation shield 44 black, which provides a shield emissivity of about 0.9, a significant heat load on the first stage due to radiant heat flow is obtained at low temperatures of the first stage. That heat load is sufficient to keep the temperature of the first stage, including the frontal array 46, above 50 K. However, at higher temperatures the radiant heat load is much less significant and thus does not appreciably hamper cooldown of the system.
  • the radiation heat load provides uniform loading of the second stage and does not result in any structural changes to the system. Radiation heat load avoids the need for an electrical heating element in the system, and provides greater thermal loading as the first stage temperature decreases.
  • the heat load provided by the increased radiation to the radiation shield 44 prevents the condensation of argon and other low condensing temperature gases on the frontal array, but it was found that a problem still existed with the condensation of argon on the second stage refrigerator cylinder 32. Even at normal operating temperatures with the first stage heat sink 28 at 77 K and the second stage heat 30 at 15 K, a temperature gradient exists between those heat sinks along the length of the cylinder 32.
  • the pressure of the chamber for example 1.3332.10-4 mbar (10- 4 torr), determines a limited temperature range less than 50 K at which argon gas condenses and evaporates in equilibrium.
  • Another result of the argon condensation on the cylinder 32 is pressure instability with changes in the thermal load on the first stage. For example, when a valve is opened to the work chamber, the first stage is subjected to a large thermal load which increases the temperature of the first stage heat sink 28. This in turn causes a rapid shift in the critical zone and unstable pressure in the chamber.
  • a closed cycle, two stage refrigerator is shown.
  • a cryopump cooled by an open cycle refrigerator such as liquid nitrogen, hydrogen or helium may also be used.
  • combinations of single and two stage closed cycle refrigerators may be used to provide the cooling.
  • the embodiment of a cryopump comprises first and second stage cryopumping surfaces in thermal contact with first and second refrigeration stages for respectively condensing predetermined high and low condensing. temperatures gases, and blackening of the outer surface of a radiation shield in thermal contact with the first refrigeration stage means for providing a passive heat load to the first refrigerator stage, the passive heat load being low during cooldown of the cryopump and substantially higher at low first stage temperatures to assure that the temperature of the first stage cryopumping surface remains above a temperature at which the gases to be condensed on the second stage cryopumping surface are able to condense. It is preferred that the emissivity of the radiation shield is greater than about 0.1.
  • the gases to be condensed on the second stage cryopumping surface include argon, nitrogen or oxygen.
  • a preferred modification of this cryopump comprises a condensing shield in thermal contact with the second stage heat sink and surrounding the refrigerator cylinder to preclude substantially all condensation of gas on the refrigerator cylinder.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Compressors, Vaccum Pumps And Other Relevant Systems (AREA)

Claims (8)

1. Cryopumpe ayant au moins deux étages de réfrigérateur (29, 32) comportant une charge de chaleur passive sur le premier étage (29), le premier étage (29) étant maintenu à une température supérieure à 50 K environ, la charge de chaleur étant moindre aux températures initiales du premier étage, la charge de chaleur passive étant due à un flux de chaleur de rayonnement provenant d'un écran de rayonnement (44), caractérisé en ce que la surface extérieure de l'écran de rayonnement (44) est noircie.
2. Cryopompe suivant la revendication 1, caractérisée en ce que la surface extérieure de l'écran de rayonnement (44) est peinte en noir.
3. Cryopompe suivant la revendication 1 ou 2, caractérisée en ce que l'émissivité effective de l'écran de rayonnement (44) est supérieure à 0,1 environ.
4. Cryopompe suivant la revendication 3, caractérisée en ce que l'émissivité de la surface extérieure de l'écran de rayonnement (44) est voisine de 1 et l'émissivité de la surface intérieure d'une cuve sous vide (12) entourant l'écran de rayonnement (44) est de 0,1 environ.
5. Cryopumpe suivant l'une quelconque des revendications 1 à 4, caractérisée en ce que l'argon, l'azote et l'oxygène gazeux dans le système sont empêchés de se condenser sur la surface de cryopompage de premier étage (48, 50).
6. Cryopompe suivant l'une quelconque des revendications 1 à 5, caractérisée en ce que ledit écran de rayonnement (44) entoure la surface de cryopompage de deuxième étage (30, 40, 41, 43) qui est en contact thermique avec au moins un évacuateur de chaleur (30) sur le deuxième étage de réfrigérateur (32) pour condenser les gaz à faible température de condensation.
7. Procédé pour empêcher l'accrochage de croisement dans une cryopompe ayant au moins deux étages de réfrigérateur (29, 32) comportant la fourniture d'une charge de chaleur passive au premier étage (29), le premier étage (29) étant maintenu à une température supérieure à 50 K environ, la charge de chaleur étant moindre aux températures initiales du premier étage, la charge de chaleur passive étant due à un flux de chaleur de rayonnement provenant d'un écran de rayonnement (44), caractérisé par le noircissement de la surface extérieure de l'écran de rayonnement (44).
8. Procédé suivant la revendication 7, caractérisé en ce que l'émissivité effective de l'écran de rayonnement (44) est rendue supérieure à 0,1 environ.
EP84103732A 1983-04-04 1984-04-04 Pompe cryostatique avec réfrigération rapide et stabilité de pression améliorée Expired EP0126909B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US48178383A 1983-04-04 1983-04-04
US481783 1983-04-04

Publications (3)

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EP0126909A2 EP0126909A2 (fr) 1984-12-05
EP0126909A3 EP0126909A3 (en) 1985-01-23
EP0126909B1 true EP0126909B1 (fr) 1987-07-22

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ID=23913381

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EP84103732A Expired EP0126909B1 (fr) 1983-04-04 1984-04-04 Pompe cryostatique avec réfrigération rapide et stabilité de pression améliorée

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EP (1) EP0126909B1 (fr)
JP (1) JPS59218372A (fr)
CA (1) CA1220948A (fr)
DE (1) DE3464948D1 (fr)
IL (1) IL71403A (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4555907A (en) * 1984-05-18 1985-12-03 Helix Technology Corporation Cryopump with improved second stage array
JPS63501585A (ja) * 1985-10-31 1988-06-16 ヘリツクス　テクノロジ−　コ−ポレ−シヨン 迅速吸着クライオポンプ
US4718241A (en) * 1985-10-31 1988-01-12 Helix Technology Corporation Cryopump with quicker adsorption
EP0338113B1 (fr) * 1988-04-22 1992-01-29 Leybold Aktiengesellschaft Procédé pour adapter une cryopompe à deux étages à un gaz défini
JP2009250148A (ja) * 2008-04-08 2009-10-29 Sumitomo Heavy Ind Ltd クライオポンプおよび冷凍機
CN112815563B (zh) 2015-12-04 2022-11-01 皇家飞利浦有限公司 具有依赖于温度的热分流器的低温冷却系统
CN118517395A (zh) * 2023-12-05 2024-08-20 上海优尊真空设备有限公司 一种真空稳定性优异的低温真空泵

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4150549A (en) * 1977-05-16 1979-04-24 Air Products And Chemicals, Inc. Cryopumping method and apparatus
US4295338A (en) * 1979-10-18 1981-10-20 Varian Associates, Inc. Cryogenic pumping apparatus with replaceable pumping surface elements
US4311018A (en) * 1979-12-17 1982-01-19 Varian Associates, Inc. Cryogenic pump
JPS57176372A (en) * 1981-04-21 1982-10-29 Osaka Oxgen Ind Ltd Low temperature heat transmitter
US4356701A (en) * 1981-05-22 1982-11-02 Helix Technology Corporation Cryopump

Also Published As

Publication number Publication date
IL71403A (en) 1991-01-31
JPS59218372A (ja) 1984-12-08
EP0126909A2 (fr) 1984-12-05
EP0126909A3 (en) 1985-01-23
JPH0549826B2 (fr) 1993-07-27
DE3464948D1 (en) 1987-08-27
CA1220948A (fr) 1987-04-28
IL71403A0 (en) 1984-06-29

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