EP0250613B1 - Cryopump and method of operating this cryopump - Google Patents

Description

The invention relates to a method for operating a cryopump with a housing, with a gas inlet opening to which a recipient can be connected via a valve, with a vacuum pump connected to the housing via a valve, with a two-stage refrigerator in the housing as the cooling source, with pump surfaces on the two cooling heads of the refrigerator, which are equipped with an electric heater, with a sensor for controlling the pressure within the pump housing and with a control unit, in which the operation of the cryopump is monitored and with the help of the control unit and the signals supplied by the sensor is controlled for this purpose, based on the data supplied by the sensor, the pump capacity of the cryopump still present, and in the event of a pump capacity which is no longer sufficient, an automatically running regeneration process controlled by the control unit is initiated. Operation of the cryopump should be understood here to mean not only the pumping and evacuating operation, but also the regeneration operation. The invention also relates to a cryopump suitable for carrying out this method.

Cryopumps belong - such as B. also the ion getter pumps - to a type of pump that does not supply the gases removed from a recipient directly to the atmosphere, but initially accumulates on the pump surfaces. Once their pumping capacity has been reached, it is necessary to regenerate the pumping surfaces, ie to remove the gases on the pumping surfaces. This can for example, by switching off the refrigerator to the recipient after closing the valve and / or by flowing preferably heated gases through the pump. The warm gases are used to heat up the pump surfaces and to remove the gases that are released. In another regeneration process (German patent application P 35 12 614.0), the pump surfaces are connected to the by means of an electrical heater Pump surfaces heated. The gases released are pumped out with a backing pump connected to the pump housing.

Regeneration of cryopumps presents some difficulties. On the one hand, it is not always easy to determine when the maximum capacity of a cryopump is reached. It is particularly difficult to be able to determine whether a residual capacity that may still be available is sufficient for a subsequent pump cycle. This problem is present, for example, when using cryopumps in vapor deposition or sputtering systems. In systems of this type, a batch is placed in a recipient, which is then evacuated using the cryopump. Reactive gases and / or additional inert gases are then admitted into the recipient, up to a pressure at which the parts are coated. After the gas inlet has been interrupted, the remaining gases are removed in order to control the previous vapor deposition step. Then the recipient is separated from the cryopump and aerated for the subsequent batch change. It is difficult to determine whether the cryopump has sufficient capacity after the last evacuation. For safety reasons, a regeneration step is usually started long before the maximum capacity is reached. The operation of the system must be interrupted for this time.

Furthermore, it is difficult to recognize when a regeneration phase has ended, i.e. H. when the pump surfaces are completely free of the gases due to their heating. It is therefore customary to assume a maximum occupancy for safety reasons and to heat accordingly for a long time. However, this has the disadvantage that the cryopump fails for a relatively long time for the evacuation operation and thus the system to which the cryopump is connected often also stands idle for an unnecessarily long time.

A method of the type mentioned at the outset is known from WO-A-8 400 404. There are means in the disclosed cryopump provided with which it is possible to directly transfer thermal energy from the outside only to the pumping surfaces of the second (colder) stage of the refrigerator. This makes it possible to regenerate the pump surfaces of the second (colder) stage of the refrigerator independently of the pump surfaces of the first (warmer) stage of the refrigerator. Although a temperature sensor and also a pressure sensor are mentioned, the document mentioned does not disclose how it can be determined whether a pump in operation is in need of regeneration or not, ie whether or not the remaining pumping capacity is sufficient for the next pumping cycle.

-Messungen durchgeführt werden, und daß, wenn die noch vorhandene Pumpkapazität für den nächsten Pumpzyklus nicht mehr ausreicht, der Regeneriervorgang eingeleitet wird. Bei einer besonders zweckmäßigen Ausführungsform ist ein Mikroprozessor vorgesehen, der in Abhängigkeit der vom Sensor gelieferten Signale einen optimal kurzen Regeneriervorgang auslöst und steuert.The object of the present invention is to equip a cryopump of the type mentioned at the outset with monitoring and control devices in such a way that the time required for regeneration is minimized. According to the invention, this object is achieved in that suction capacity measurements are carried out to determine the pump capacity that is still present, either by repeatedly measuring the time it takes for the cryopump to reach a certain pressure value, or in the case of evacuation processes $\frac{\text{dp}}{\text{German}}$

-Measurements are carried out, and that when the pump capacity still available for the next pump cycle is no longer sufficient, the regeneration process is initiated. In a particularly expedient embodiment, a microprocessor is provided which, depending on the signals supplied by the sensor, triggers and controls an optimally short regeneration process.

-Messung (zeitliche Änderung des Druckes) läßt sich der Zustand der Pumpe ermitteln.A major advantage of the method according to the invention is that with the aid of the signals supplied by the pressure sensor and a suitably programmed microprocessor, relatively precise indications of the pump capacity still available can be obtained. If, for example, the time it takes for the cryopump to reach a certain pressure is measured during an evacuation process, conclusions can be drawn from the measured time about the pump capacity still available. If a certain time is exceeded, an automatically running regeneration process can be triggered, whereby the necessary measures are initiated by the control unit or by the microprocessor. Even from one $\frac{\text{dp}}{\text{German}}$

-Measurement (change in pressure over time) the condition of the pump can be determined.

From the knowledge of the capacity still available, the degree of occupancy of the pump surfaces with gases can further be concluded, so that maximum regeneration times do not necessarily have to be observed. Around to achieve an optimally short regeneration phase, however, it is advisable to provide additional sensors with which the release of a pump surface from the gases can be determined. Temperature sensors that are attached to the pump surfaces are useful for this purpose.

If a cryopump of the type according to the invention is operated in such a way that the pumping speed and thus the pump capacity of the cryopump that is still present is monitored on the basis of the data supplied by the sensor or sensors, and that in the event of a pump capacity that is no longer sufficient for the next pumping cycle, an automatically running regeneration process is initiated, then this cryopump can be operated optimally, i.e. with pumping phases as long as possible or pumping cycles as often as possible and with regeneration phases as short as possible. Downtimes of systems to which cryopumps of the type according to the invention are connected are therefore optimally short. The cryopump can be included in the automatic operation of a system. Operating personnel who are constantly present are no longer required. The pump or the associated system can also be operated overnight.

Further advantages and details of the invention will be explained with reference to an embodiment shown in the figure.

The figure shows a cryopump with a housing 1, which has an inlet opening 2 for the gases to be pumped out. The recipient 30 to be evacuated is connected to the flange 3, specifically via a shut-off device 31, so that the cryopump can be separated from the recipient 30 for start-up and regeneration.

A two-stage refrigerator 4 projects into the housing 1 from below. At the first cooling stage 5 of the refrigerator 4, a further, essentially pot-shaped, housing 7 is held in a heat-conducting manner, the opening 8 of which lies approximately parallel to the opening 2 of the housing 1 and is covered with the shielding metal strip forming a baffle 9. The walls of the housing 7 assume a temperature of approximately 60 to 100 K during pump operation (when the refrigerator 4 is switched on) and serve as pump surfaces for water vapor and carbon dioxide (by cryocondensation). In addition, the shape of the pot 7 is chosen so that the pot together with the baffle 9 optimally shields the components arranged therein from external heat rays.

The second stage 10 of the refrigerator 4 projects into the pot-shaped housing 7 and carries the pumping surfaces 12 at its cold end 11. These often consist of two flat sheet metal sections arranged parallel to one another. To enlarge the surface or to improve the pumping of light gases, the sheet metal sections are covered with the adsorption material 13 on their inner sides. It expediently consists of molecular sieve, activated carbon or zeolite. On the outside of the pump surfaces 11, the accumulation of gases (N₂, Ar, CO, methane or the like) takes place by cryocondensation or cryotrapping. Preferably, the light gases (H₂, He) reach the inside of the pump surfaces and are bound there by cryosorption.

Two further connecting pieces 14 and 15 are provided on the housing 1 of the cryopump shown. The forevacuum pump 18, preferably a rotary vane pump with a final pressure of approximately 10 -3 mbar, is connected to the connecting piece 14 via a valve 16 and an adsorption trap 17.

The connecting piece 15 is used to carry out power supply lines 21 and 22, via which heaters 23 and 24, which are arranged on the cooling stages 5 and 11 and are composed of heating wires, are supplied with current. The connecting piece 15 can also serve to hold a supply device 25 with a controller with which the maximum permitted temperature of the heaters 23 and 24 can be set and maintained or regulated. For this purpose, the housing of the device 25 has a blind flange 26 with a current feedthrough which is fastened to the flange 27 of the connector 15. This arrangement ensures that the user of the cryopump is not able to work without controlled heating. Removing the device from the housing means venting the pump so that it can no longer perform its function.

In addition, a control unit is shown schematically and designated 28. It contains known programmable control means (for example a microprocessor), which are able, depending on signals which are supplied by sensors to be described in detail, to emit control signals with which the operation of the cryopump can be controlled automatically.

The cryopump shown is also assigned means which allow gases (heated inert gases or air) to flow through the housing 1. These means include the gas supply 32, the heating device 33 and the valve 34, with which the supply of the gas through the pipe 35 can be controlled. The tube 35 passes through the housing wall of the pump and the cylinder 7, so that the inflowing gases strike the pump surfaces directly. The gas outlet is designated 36 and leads via the valve 38 either into the open or into a collecting container 37. This is only necessary if environmentally harmful gases must be removed from the pump surfaces. In this case, a receptacle 37ʹ is expediently also assigned to the outlet of the vacuum pump 18, which can be identical to the container 37, for example.

Finally, the pump is also associated with means which make it possible to admit a relatively small, certain amount of gas into the housing 1.
These means comprise, for example, two valves 39 and 40 which define the fixed gas volume between them and which are actuated in a corresponding sequence for the inlet of the gas. The volume between the valves 39 and 40 is fed from the supply volume 32ʹ.

In order to put the cryopump shown into operation, the shut-off device 31 between the housing 1 of the pump and the recipient 30 to be evacuated is first closed. Then the housing 1 of the pump is evacuated to a pressure of 10⁻² to 10⁻³ mbar using the vacuum pump 18. At the same time, the heaters 23 and 24 are switched on, so that the pump surfaces 7 and 12 heat up to the desired temperatures (70 ° C.). This condition is maintained until the pressure in the housing is 1 <10⁻² mbar. The refrigerator 4 can now be switched on. Thereafter, the heater 23 of the first cooling stage 5 of the refrigerator 4 is first switched off. As a result, the pump surface 7 cools and pumps the H₂O vapor that is still present. After this step, the heating 24 of the cooling stage 11 is switched off, so that the pump surfaces 12 also assume their operating temperature of approximately 12 K. Then the recipient 30 to be evacuated is connected to the cryopump, that is to say the shut-off device 31 is opened. These steps can run automatically if the microprocessor in the control unit is programmed accordingly. Since the sensors 41, 44 and 45 constantly provide signals about the state of the pump, the individual steps can be carried out be finished as soon as the desired state is reached. The pump can therefore be started up in an optimally short time.

In addition, this procedure has the advantage that in the first cooling phase, in which vapors are produced, it is prevented with certainty that they accumulate on the adsorption surfaces of the second stage and drastically reduce their capacity. The majority of the vapors therefore initially only accumulate on the pump surfaces 7. It is only when light gases, preferably helium, are to be pumped that the pump surfaces 12 are cooled to their operating temperature, so that the full pump capacity is available there.

In order to enable the cryopump to operate automatically with the aid of the control unit 28, it is necessary to feed it with information signals. Several sensors are provided for this. In detail, it is the pressure sensor 41, which delivers signals corresponding to the pressure in the pump housing 1 to the control unit 28 via the line 42. Temperature sensors 43, 44 and 45 are attached to the inner wall of the housing 1 and to the pump surfaces 7, 9 and 12, 13. They are connected to the control unit via lines 46, 47 and 48. The adsorption trap 17 can also be equipped with a temperature sensor 49 so that its operating state can be monitored during the possible heating process. All lines via which signals are supplied to the control unit 28 are shown in dash-dot lines.

Depending on the signals supplied, the control unit initiates the necessary measures. Depending on requirements, the refrigerator 4, the control valve 52, the valve 16, the control line 53, the valve 34 and the control valve 51 optionally existing heating device 33, via the control line 54 the valves 39 and 40, via the control line 55 the valve 31, via the control line 56 the backing pump and via the control line 57 the valve 38 to the collecting container 37. Finally, the control unit 28 is connected to the supply unit 25 for the cooling head heaters 23 and 24 via the control lines 58 and 59, so that the heaters can be started up separately or together. The control lines are shown with dashed lines.

-Werten die noch vorhandene Kapazität der Pumpe festzustellen. Besonders zweckmäßig ist es, diese Möglichkeiten dann anzuwenden, wenn der Betrieb einer Anlage ohnehin wiederkehrende Evakuiervorgänge erfordert, die dann gleichzeitig der Zeit- oder der $\frac{\text{dp}}{\text{dt}}$

-Messung dienen können.The control unit 28 has, inter alia, the task of initiating the regeneration of the pump surfaces 7, 9, 12, 13 if this is desired or if the capacity of the pump surfaces is reached or almost reached. If the regeneration process is to be started automatically, it is first necessary for the control unit 28 to register the state of the need for regeneration. One possibility for this is the recurring measurement of the time in which the cryopump reaches a certain pressure after aeration or pressure increase in the recipient 30, for example a pressure of 5 x 10⁻⁷ mbar after 30 seconds. If this time is exceeded, then - with otherwise reasonable size ratios (size of the recipient, performance of the pump) - conclude that the capacity of the pumping surfaces has been reached. Another possibility is to relate pressure and time measurements in relation to recurring evacuation processes and to use those that can be calculated by the microprocessor $\frac{\text{dp}}{\text{German}}$

- Determine the remaining capacity of the pump. It is particularly expedient to use these options when the operation of a system requires recurring evacuation processes, which then take place at the same time or $\frac{\text{dp}}{\text{German}}$

-Measurement can serve.

In the case of cryopumps connected essentially continuously to a recipient, the occupancy of the pumping surfaces of the second stage can be determined by constantly registering the temperature of these pumping surfaces. For example, if the pump surface 12 of the second stage, which takes on a temperature of approximately 12 K when the pump is freshly regenerated, reaches 18 K, the regeneration process is started.

-Messungen vorzunehmen.Another possibility is to close the valve 31 between the recipient and the pump at intervals, to admit a known relatively small amount of gas into the pump housing by means of the valves 39, 40 and again the time or time described $\frac{\text{dp}}{\text{German}}$

-Make measurements.

• 1. Die Absperreinrichtung 31 zum Rezipienten 30 wird geschlossen;
• 2. der Refrigerator 4 wird abgeschaltet;
• 3. die Heizungen der ersten und zweiten werden eingeschaltet;
• 4. das Vorvakuumventil 16 wird geöffnet, wenn vom Sensor 41 ein Druck gemeldet wird, der z. B. etwas größer als 1 mbar ist;
• 5. die Heizungen werden so lange bei 70° C betrieben, bis sich ein Druck < 5 x 10⁻² mbar in der Pumpe eingestellt hat;
• 6. das Vorvakuumventil 16 wird geschlossen;
• 7. die Heizung der ersten Stufe wird ausgeschaltet;
• 8. der Refrigerator wird eingeschaltet, so daß sich die erste Stufe auf eine Temperatur < 160 K abkühlt;
• 9. die Heizung 24 der zweiten Stufe 10 wird abgeschaltet, so daß sich die zweite Stufe auf eine Temperatur < 20 K abkühlt;
• 10. die Absperreinrichtung 31 zum Rezipienten 30 wird geöffnet.

If the need for regeneration has been determined by the microprocessor in the control unit 28, the regeneration process is automatically initiated. This happens after the following steps:

• 1. The shut-off device 31 to the recipient 30 is closed;
• 2. the refrigerator 4 is switched off;
• 3. the heaters of the first and second are switched on;
• 4. the fore-vacuum valve 16 is opened when a pressure is reported by the sensor 41, which, for. B. is slightly larger than 1 mbar;
• 5. the heaters are operated at 70 ° C until a pressure <5 x 10⁻² mbar has been set in the pump;
• 6. the fore-vacuum valve 16 is closed;
• 7. the heating of the first stage is switched off;
• 8. The refrigerator is switched on so that the first stage cools down to a temperature <160 K;
• 9. the heater 24 of the second stage 10 is switched off, so that the second stage cools to a temperature <20 K;
• 10. the shut-off device 31 for the recipient 30 is opened.

The sensors 41, 44 and 45 concerned are constantly queried, so that the next step can be initiated immediately after the pressure and temperature values mentioned have been reached. The regeneration times are therefore optimally short. This also applies in the event that a pump that has not yet reached its maximum capacity is to be regenerated prematurely. The regeneration process must then be started manually on the control unit.

• 1. Die Absperreinrichtung 31 wird geschlossen;
• 2. die Heizung 24 der zweiten Stufe 10 wird bei laufendem Refrigerator eingeschaltet, und es wird so lange gewartet, bis sich bei einer Heiztemperatur von 70 K, überwacht vom Sensor 45, ein Druck von etwa 1 mbar (Sensor 41) im Gehäuse der Pumpe eingestellt hat;
• 3. Das Vorvakuumventil 16 wird geöffnet und die Heizung 24 der zweiten Stufe abgeschaltet, bis ein Druck von etwa 1 x 10⁻² mbar erreicht ist;
• 4. das Vorvakuumventil 16 wird geschlossen;
• 5. die Absperreinrichtung 31 zum Rezipienten 30 wird geöffnet, nachdem die Temperatur an der zweiten Kältestufe 20 K unterschritten hat.

Conditioning or regeneration of the cryopump after He and H₂ pumps follows the steps:

• 1. The shut-off device 31 is closed;
• 2. The heater 24 of the second stage 10 is switched on while the refrigerator is running, and it is waited until, at a heating temperature of 70 K, monitored by the sensor 45, a pressure of approximately 1 mbar (sensor 41) in the housing of the pump hired;
• 3. The fore-vacuum valve 16 is opened and the heater 24 of the second stage is switched off until a pressure of approximately 1 x 10⁻² mbar is reached;
• 4. the fore-vacuum valve 16 is closed;
• 5. The shut-off device 31 to the recipient 30 is opened after the temperature at the second cooling stage has fallen below 20 K.

Even with this partial regeneration, the sensors concerned continuously provide signals about the respective state to the control unit 28, so that the He and H₂ adsorbing surfaces are regenerated again after an optimally short time.

In this regeneration process, the possibility existing in two-stage refrigerators is used to keep the pump surfaces of the first stage at their operating temperature, while the pump surfaces of the second stage are heated. The reason for this is that the thermal conductivity between the cold stage 5 of the first stage and the cold stage 11 of the second stage of the refrigerator is very small, so that heating of the second stage has only an insignificant effect on the temperature in the region of the first stage.

By choosing a higher heating temperature (T> 120 K) at the second stage, the gases bound by cryocondensation or cryotrapping on the pumping surfaces 12 can also be removed independently of those on the pumping surfaces 7 of the first stage.

Another important advantage of using the programmable control unit 28 is that the regeneration process can be carried out in such a way that the condition in the pump housing is constantly monitored by the sensors in such a way that liquefaction of the condensed gases during the regeneration phase is avoided with certainty. This can be achieved, for example, by keeping the pressure in the pump slightly below the sublimation point. By controlling the heating output depending on the pressure or by metered inlet of regeneration gases, this condition can be met. The valve 34 must be designed as a metering valve with metered regeneration gas inlet.

If there is a risk that explosive gas mixtures can accumulate in the pump, the creation of an actual risk of explosion can be avoided with the help of the microprocessor. For example, the pressure in the pump can be kept at a level where the gas mixture is not is explosive. An H₂ / O₂ mixture, for example, is not explosive at a pressure below 14 mbar. If the regeneration of the cryopump is carried out in such a way that from about 10 mbar all current-carrying parts in the pump - such as heaters 23 and 24, ionization or heat conduction vacuum meters - are switched off, then any risk of explosion is also avoided.

Explosive gas mixtures can e.g. B. by admitting inert gas (Ar, N₂) from the bottle 32 via the heater 33, the valve 34 and the tube 7 are first diluted and then removed from the pump. The gas mixture is either pressed into the collecting container 37 with a slight overpressure via the valve 38 or conveyed into the container 37ʹ with the help of the backing pump 18 via the valve 16. The temperature sensors 44, 45 and 43 indicate when the gas inlet can be interrupted. After valve 34 is closed, valve 16 is opened in order to evacuate the cryopump to its starting pressure (<5 × 10 -2 mbar).

• 1. Schließen von Ventil 31,
• 2. Abschalten des Refrigerators 4,
• 3. Gaseinlaß über Ventil 34 (offen) aus dem Gasvorrat 32,
• 4. bei p≈1050 mbar Öffnen des Ventils 38 und Einspeisung des Gasgemisches in 37,
• 5. Unterbrechung des Gaseinlasses, wenn Sensor 45 eine ausreichend hohe Temperatur anzeigt;
  (T≈70 K bei H₂-Regenerierung;
  T≈150 K bei CH₂-Regenerierung)
• 6. Evakuieren der Pumpe mit der Vorpumpe auf p<5 x 10⁻² mbar.

A typical procedure without the help of the backing pump 18 is the following:

• 1. closing valve 31,
• 2. switching off the refrigerator 4,
• 3. gas inlet via valve 34 (open) from the gas supply 32,
• 4. at p≈1050 mbar opening valve 38 and feeding the gas mixture into 37,
• 5. Interruption of gas inlet when sensor 45 indicates a sufficiently high temperature;
  (T≈70 K with H₂ regeneration;
  T≈150 K with CH₂ regeneration)
• 6. Evacuate the pump with the backing pump to p <5 x 10⁻² mbar.

• 7ʹ. Starten des Refrigerators 4 (bei geschlossenem Ventil 16),
• 8ʹ. Öffnen des Ventils 31 bei T 20 K (Sensor 45) an der zweiten Kältestufe.

If only H₂ or CH₄ is removed, the pump can be put into operation again by the following steps:

• 7ʹ. Starting the refrigerator 4 (with the valve 16 closed)
• 8th. Open valve 31 at T 20 K (sensor 45) on the second cold stage.

• 7ʺ. Regenerierheizungen ein,
• 8ʺ. Aufheizen der Pumpenteile bis T 300 K (Sensoren 43, 44, 45). Bei p 8 x 10⁻² mbar sollte das Ventil 16 offen, bei p 5 x 10⁻³ mbar geschlossen sein.
• 9ʺ. Heizungen aus und Refrigerator starten.

If the pump is completely regenerated, then the following steps follow:

• 7ʺ. Regeneration heaters,
• 8th. Heating up the pump parts up to T 300 K (sensors 43, 44, 45). With p 8 x 10⁻² mbar, valve 16 should be open, with p 5 x 10⁻³ mbar closed.
• 9ʺ. Heaters off and refrigerator started.

Instead of step 9ʺ, steps 7 to 10 described on pages 10 and 11 can also be carried out.

The procedure described is expedient for the removal of explosive or toxic gases which, for example, are collected in the container 37 diluted by the regeneration gas. The corrosive gases do not get into the backing pump.

• 1. Schließen von Ventil 31,
• 2. Abschalten des Refrigerators 4,
• 3. Gaseinlaß über Ventil 34 (offen) aus dem Gasvorrat 32,
• 4. Ventil 16 öffnen bei etwa 8 x 10⁻² mbar.

If this precautionary measure is not necessary, the backing pump can also be used during the regeneration and can, for example, proceed as follows:

• 1. closing valve 31,
• 2. switching off the refrigerator 4,
• 3. gas inlet via valve 34 (open) from the gas supply 32,
• 4. Open valve 16 at about 8 x 10⁻² mbar.

• 5ʹ. Unterbrechung des Gaseinlasses, wenn Sensor 45 eine ausreichend hohe Temperatur meldet (T≈70 K für die H₂-Regenerierung; T≈150 K für die CH₄-Regenerierung),
• 6ʹ. Schließen des Ventils 16,
• 7ʹ. Refrigerator ein,
• 8ʹ. Öffnen des Ventils 31 bei T 20 K.

In the event that only H₂ or CH₄ should be removed:

• 5ʹ. Interruption of the gas inlet when sensor 45 reports a sufficiently high temperature (T≈70 K for H₂ regeneration; T≈150 K for CH₄ regeneration),
• 6ʹ. Closing the valve 16,
• 7ʹ. Refrigerator on,
• 8th. Opening valve 31 at T 20 K.

• 5ʺ. Regenerierheizungen ein. Daran schließen sich zweckmäßigerweise die auf Seiten 10 und 11 beschriebenen Schritte 5 bis 10 an.

In the event that the pump is to be completely regenerated:

• 5ʺ. Regeneration heaters. This is conveniently followed by steps 5 to 10 described on pages 10 and 11.

Claims (15)

1. Method of operating a cryopump with a casing (1), a gas inlet opening (8), to which a container (30) can be connected via a valve (31), a vacuum pump (18), which is connected via a valve (16) to the casing, a two-stage refrigerator (4), which is disposed in the casing, as a cold source, pump faces (7, 12, 13) at the two cooling heads (5, 11) of the refrigerator, which heads are provided with an electric heating unit (23, 24), a sensor (41) for controlling the pressure inside the pump casing (1) and a control unit (28), with the operation of the cryopump being monitored and controlled by means of the control unit (28) and the signals supplied by the sensor (41), for which purpose the available pumping capacity of the cryopump is determined on the basis of the data supplied by the sensor (41), and an automatic regeneration process, which is controlled by the control unit (28), is initiated if the pumping capacity is no longer sufficient, characterised in that displacement capacity measurements are carried out in order to determine the available pumping capacity by either repeatedly measuring the time which the cryopump requires to reach a certain pressure value or carrying out dp/dt measurements during evacuation processes, and that the regeneration process is initiated if the available pumping capacity is no longer sufficient for the next pump cycle.
2. Method according to claim 1, characterised in that a certain gas quantity is introduced into the cryopump, which is closed towards the backing pump (18) and the container (30), and the time or dp/dt measurements are subsequently carried out in order to determine the pumping capacity.
3. Method according to claim 1, characterised in that the temperature of the pump faces of the second stage is monitored in order to determine the pumping capacity.
4. Method according to one of claims 1 to 3, characterised in that a partial regeneration process is carried out by heating the pump face(s) (13) and/or (12) while the refrigerator (4) is operating to a temperature of approximately 70 K (to remove He and H₂) or approximately 150 K (to remove N₂, Ar, etc.).
5. Method according to one of claims 1 to 4, characterised in that the pressure in the cryopump is maintained below the sublimation point of condensable gases present in the pump during the regeneration processes.
6. Method according to one of claims 1 to 4, characterised in that, if explosive gases or gas mixtures are present, the pressure p in the cryopump is maintained below the pressure at which a danger of explosion commences during the regeneration processes.
7. Method according to claim 5 or 6, characterised in that the pressure in the cryopump is maintained during the regeneration processes either by controlling the heating power or by a metered admission of regenerative gases.
8. Method according to one of claims 1 to 4, characterised in that, if explosive gases or gas mixtures are present, the pressure p in the cryopump is monitored during the regeneration processes, and that all the live parts disposed in the pump are turned off before the pressure at which a danger of explosion commences is reached.
9. Method according to one of the preceding claims, characterised in that the cryopump is regenerated by heating the pump faces, by a regenerative gas admission or by a combination of these two steps.
10. Cryopump for carrying out the method according to claim 1, with a casing (1), a gas inlet opening (8), to which a container (30) can be connected via a valve (31), a vacuum pump (18), which is connected via a valve (16) to the casing, a two-stage refrigerator (4), which is disposed in the casing, as a cold source, pump faces (7, 12, 13) at the two cooling heads (5, 11) of the refrigerator, which heads are provided with an electric heating unit (23, 24), a sensor (41) for controlling the pressure inside the pump casing (1), means (32, 33, 34) for admitting regenerative gases and a control unit (28), by means of which the operation of the cryopump is monitored and controlled in accordance with the signals supplied by the sensor, characterised in that it is provided with means (32', 39, 40) for admitting a small gas quantity of a certain volume, which means comprise at least two valves (39, 40) which are connected to the control unit (28).
11. Cryopump according to claim 10, characterised in that the vacuum pump (18) is connected via a valve (16) to the casing (1) of the cryopump, that the valve (16) is connected via a control line (52) to the control unit (28), and that an adsorption trap, which is also provided with a sensor (49), is arranged between the valve (16) and the vacuum pump (18).
12. Cryopump according to claim 10 or 11, characterised in that the control unit (28) is connected via a control line (53) to a valve (34) for admitting the regenerative gas.
13. Cryopump according to claim 12, characterised in that a collecting vessel (37, 37') is provided for the regenerative gases leaving the cryopump.
14. Cryopump according to claim 13, characterised in that the collecting vessel (37') is connected to the outlet of the vacuum pump (16) and/or to the actual pump casing via a valve (38), and that the valve (38) is connected via a control line (57) to the control unit (28).
15. Cryopump according to one of claims 10 to 14, characterised in that further sensors (43, 44, 45) are provided to monitor the temperature of the pump faces of the first and/or second stages(s) of the refrigerator.

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