Title: Vacuum pump

The present invention relates to a vacuum pump, such as a dry vacuum pump or a turbomolecular vacuum pump.

Dry or turbomolecular vacuum pumps may be used in methods using chemistries that generate reaction by-products which may be solid. This is the case, for example, with some methods for manufacturing semiconductors, photovoltaic screens, flat screens, or LEDs. These solid by-products may be drawn in by the vacuum pump and degrade its operation, notably by impeding the rotation of the rotor(s), or, in the worst case, even preventing such rotation entirely.

To avoid this, it is known to heat the stators of vacuum pumps using chip resistors mounted in contact with the stators. By heating the stator, the contaminating gas species can be kept in gaseous form, thus preventing their condensation or solidification into powder or sludge inside the vacuum pump.

However, the heating temperature is limited, usually being around 110°C in dry vacuum pumps or 120°C in turbomolecular vacuum pumps, since an excessively high temperature may run the risk of damaging the mechanical parts such as the bearings of a dry vacuum pump, or may cause creep of the rotor of a turbomolecular vacuum pump.

This limited heating may not be sufficient to prevent all deposition in the vacuum pump.

One of the aims of the present invention is to overcome at least one of the drawbacks of the prior art.

To this end, the invention proposes a dry vacuum pump comprising:

- a stator having at least one compression chamber into which the gases to be pumped are intended to flow,

- two rotors configured for rotating in the at least one compression chamber of the stator, to drive the gas to be pumped between a suction inlet and a delivery outlet of the stator, characterized in that the vacuum pump further comprises at least one magnet arranged in at least one rotor so as to face a surface, made of ferromagnetic material, of the stator on each rotation of the at least one rotor, so that the rotation of the at least one rotor causes heating of the surface of ferromagnetic material by magnetic induction.

The rotary movement of the rotors is used to generate additional heating of the stator by magnetic induction. The rotary movement of the magnets generates eddy currents in the surface of ferromagnetic material, which in turn generate heat by the Joule effect. Eddy currents are electric currents created by the variation of the magnetic field generated by the rotation of the magnets. This heating may enable the surface temperature of the stator to be increased locally, by 5°C to 30°C for example, which may enable the contaminating gas species to be kept in gaseous form. The magnetic field enabling this heating to be obtained is, for example, in the range from 0.3 T to 1.5 T. In this way, localized heating in the inner areas of the vacuum pump prone to deposition is obtained on the surface, and without contact with the stator. Localized surface heating makes it possible to avoid damaging the mechanical parts, such as the bearings, that could not be heated throughout beyond the temperature reached by conventional heating of the stator, and enables the problems of thermal expansion of the stator to be limited.

The dry vacuum pump may also have one or more of the characteristics described below, considered individually or in combination.

At least one magnet extends, axially for example, in a rotor element of the rotor, with a longitudinal direction parallel to the axis of rotation of the rotors, on a lateral edge surface of the rotor element configured for sweeping a lateral surface of the compression chamber.

At least one magnet extends, for example, in a rotor element of the rotor, with one face perpendicular to the axis of rotation of the rotors, on a transverse edge surface of the rotor element configured for sweeping a transverse surface of the compression chamber.

The transverse surface is, for example, that of the end of the compression chamber of the first or last pumping stage, the transverse surface being interposed between the compression chamber and a bearing support of the stator.

The dry vacuum pump comprises, for example, at least one magnet for each rotor element of at least one compression chamber, at least one magnet arranged on a lateral edge surface of the rotor element, and/or at least one magnet arranged on a transverse edge surface of the rotor element. The dry vacuum pump may comprise at least two magnets for each rotor element or for each rotor, the polarity of the magnets being inverted in the thickness or in the length or in each adjacent magnet or in each adjacent rotor element.

The dry vacuum pump is, for example, a multi-stage rough vacuum pump. A rough vacuum pump is a volumetric vacuum pump configured for using the two rotors to draw in, transfer and then deliver the gas to be pumped at atmospheric pressure. According to another example, the vacuum pump is of the Roots compressor type and comprises one to three pumping stages. Vacuum pumps of the Roots compressor type are mounted in series upstream of a rough vacuum pump.

The dry vacuum pump, whether of the rough or the Roots compressor type, may comprise at least three pumping stages arranged in series, the at least one magnet being arranged in a rotor element configured for rotating in the last and/or the penultimate pumping stage in the direction of flow of the gases.

At least one magnet may be arranged in a shaft of the rotor to heat a surface, made of ferromagnetic material, of a shaft passage of the stator.

The at least one magnet is, for example, of the NdFeB or rare earth type. According to another example, the at least one magnet comprises a ferrite. Ferrite is inexpensive, but has the drawback of generating a weak magnetic field.

The at least one magnet may be nickel-coated to protect it from any corrosion or to allow its easy replacement by dismantling.

Preferably, the at least one magnet is arranged as closely as possible to the surface of the rotor, or is flush with the surface of the rotor. The at least one magnet is, for example, fastened to the body of the rotor, by adhesion for example, or is received in a cavity of the rotor body.

At least one surface layer of the stator having a surface of ferromagnetic material is, for example, made of a nickel-iron alloy, also called “mu-metal”, such as nickel-enriched cast iron, also called “Ni-resist”. This is because the magnetic permeability of mu-metals is greater than that of cast iron. Mu-metals also have the advantage of enabling a significant Joule effect to be generated. The stator body may be made of a first material, such as cast iron, and have a surface layer of ferromagnetic material; or the stator may be made throughout of ferromagnetic material, such as nickel-iron alloy. At least one surface of ferromagnetic material may have a nickel coating. The nickel coating enables greater surface heating to be obtained. This heating increases with the thickness of the coating. For example, a coating with a thickness of between 20pm and 2 cm is provided, notably for rotors rotating at between 60 and 250 Hz.

The invention also proposes a turbomolecular vacuum pump comprising: a stator having a compression chamber into which the gases to be pumped are intended to flow, a rotor configured for rotating in the compression chamber of the stator, to drive the gas to be pumped between a suction inlet and a delivery outlet of the stator, characterized in that the vacuum pump further comprises at least one magnet arranged in the stator so as to face a surface, made of ferromagnetic material, of the rotor on each rotation of the rotor, so that the rotation of the rotor causes heating of the surface of ferromagnetic material by magnetic induction.

The rotary movement of the rotor is used to generate additional heating of the rotor by magnetic induction. The rotary movement of the rotor facing the magnet(s) generates eddy currents in the surface of ferromagnetic material, which in turn generate heat by the Joule effect. Eddy currents are electric currents created by the rotation of the rotor in the magnetic field of the stator magnets. This heating may enable the surface temperature of the rotor to be increased locally, by 5°C to 30°C for example, enabling the contaminating gas species to be kept in gaseous form. The magnetic field enabling this heating to be obtained is, for example, in the range from 0.3 T to 1.5 T. In this way, localized heating in the inner areas of the vacuum pump prone to deposition is obtained on the surface, and without contact with the rotor. Localized surface heating makes it possible to avoid damaging the rotor, by avoiding heating it throughout its whole volume, and enables the problems of thermal expansion of the stator to be limited.

The turbomolecular vacuum pump may also have one or more of the characteristics described below, considered individually or in combination.

The turbomolecular vacuum pump may comprise a plurality of magnets arranged in the stator in an area facing the surface of ferromagnetic material of the rotor, the polarity of the adjacent magnets being inverted in the thickness or in the length or in each adjacent magnet. The rotor may have a Holweck skirt that supports the surface of ferromagnetic material.

The at least one magnet is, for example, arranged in a molecular stage of the vacuum pump, in an area of the stator surrounding the Holweck skirt or located under the Holweck skirt.

As before, the at least one magnet is, for example, of the NdFeB or rare earth or ferrite type. It may be nickel-coated to protect it from any corrosion or to allow its easy replacement by dismantling. Preferably, the at least one magnet is arranged as closely as possible to the surface of the stator, or is flush with the surface of the stator. The at least one magnet is, for example, fastened to the stator, by adhesion to the stator for example, or is received in a cavity of the stator.

At least one part of the rotor having a surface of ferromagnetic material is, for example, made of iron, nickel or cobalt.

The rotor may be made in one piece from ferromagnetic material.

The invention also proposes a turbomolecular vacuum pump comprising: a stator having a compression chamber into which the gases to be pumped are intended to flow, a rotor configured for rotating in the compression chamber of the stator, to drive the gas to be pumped between a suction inlet and a delivery outlet of the stator, characterized in that the vacuum pump further comprises a magnetized material arranged in the rotor so as to face a surface, made of ferromagnetic material, of the stator on each rotation of the rotor, so that the rotation of the rotor causes heating of the surface of ferromagnetic material by magnetic induction.

The magnetized material comprises, for example, fibres comprising cobalt or nanowires comprising cobalt embedded in a composite.

The rotor has, for example, a Holweck skirt, the magnetized material being arranged in the Holweck skirt.

Additionally, in all the embodiments of dry or turbomolecular vacuum pumps described above, at least one surface of ferromagnetic material of the rotor may have a nickel coating.

Description of the drawings Other characteristics and advantages of the invention will be apparent from the following description, provided by way of non-limiting example, with reference to the attached drawings, in which:

[Fig.1] Figure 1 shows a schematic perspective view of elements of a dry vacuum pump.

[Fig.2] Figure 2 shows a schematic cross-sectional side view of an example of a stator of the dry vacuum pump of Figure 1 with a rotor shown schematically in broken lines.

[Fig.3a] Figure 3a shows a perspective view of an example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.3b] Figure 3b shows a perspective view of another example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.3c] Figure 3c shows a face-on view and a top view of another example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.3d] Figure 3d shows a face-on view and a top view of another example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.4a] Figure 4a shows a face-on view and a top view of another example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.4b] Figure 4b shows a face-on view and a top view of another example of a rotor element of a rotor of the dry vacuum pump of Figure 1.

[Fig.5] Figure 5 shows schematically a portion of a stator seen in cross section at a surface of ferromagnetic material.

[Fig.6] Figure 6 shows schematically two rotors in a compression chamber of a dry vacuum pump according to a variant embodiment.

[Fig.7] Figure 7 shows a schematic sectional view of a first example of embodiment for a turbomolecular vacuum pump.

[Fig.8] Figure 8 shows a schematic sectional view of a second example of embodiment for a turbomolecular vacuum pump.

In these drawings, identical elements bear the same reference numerals. The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily signify that each reference relates to the same embodiment, or that the characteristics are solely applicable to a single embodiment. Simple characteristics of different embodiments may also be combined or interchanged to provide other embodiments.

“Upstream” is taken to mean an element which is placed before another with respect to the direction of flow of the gases to be pumped. Conversely, “downstream” is taken to mean an element placed after another with respect to the direction of flow of the gas to be pumped.

The axial direction is defined as the longitudinal direction of the vacuum pump, in which the axis or axes of rotation of the rotor or rotors extend.

Figures 1 and 2 show a first example of a vacuum pump 1.

The vacuum pump 1 is a dry vacuum pump.

The dry vacuum pump 1 comprises a stator 2 having at least one compression chamber 3, into which the gases to be pumped flow, and two rotors 4 configured for rotation in the at least one compression chamber 3 of the stator 2 to drive the gas to be pumped between a suction inlet 5 and a delivery outlet of the stator 2 (arrows G in Figure 1).

In this first example, the rotors 4 are configured for synchronized rotation in the inverse direction in the at least one compression chamber 3 of the stator 2, for driving the gas to be pumped G. The rotors 4 have respective rotor elements 6, notably at least two rotor elements 6 per rotor 4 in each compression chamber 3. The rotor elements 6 are, for example, lobes of identical profile, such as those of the Roots type. Each rotor 4 comprises, for example, two rotor elements 6 per compression chamber 3, as shown in the diagrams (with a cross section in the form of a figure of eight or a kidney bean), or more (three-lobe, four-lobe (see Figure 6) or five-lobe), or are of the “claw” type or based on another similar volumetric vacuum pump principle.

The shafts 7 of the rotors 4 are driven by a motor of a power system of the vacuum pump 1 (not shown), located at one end of the vacuum pump 1, at the same end as the delivery outlet or the suction inlet 5.

The dry vacuum pump 1 is, for example, a multi-stage rough vacuum pump. A rough vacuum pump is a volumetric vacuum pump configured for using the two rotors 4 to draw in, transfer and then deliver the gas to be pumped at atmospheric pressure. According to another example, the vacuum pump 1 is of the Roots compressor type and comprises one to three pumping stages. Vacuum pumps of the Roots compressor type are mounted in series upstream of a rough vacuum pump. In the illustrative example, the vacuum pump 1 comprises at least two pumping stages, for example between two and eight pumping stages, in this case five T1-T5. Each pumping stage T1-T5 of the stator 2 is formed by a compression chamber 3 receiving two interlinked rotors 4, the compression chambers 3 each comprising a respective inlet and outlet. The successive pumping stages T1-T5 are connected in series, one after another, by respective inter-stage channels 8 connecting the outlet (or delivery end) of the preceding pumping stage to the inlet (or intake) of the following stage (Figure 1). During rotation, the gas drawn in from the inlet is trapped in the volume formed by the rotors 4 and the stator 2, and is then driven by the rotors 4 towards the next stage.

The inlet of the first pumping stage T 1 communicates with the suction inlet 5 of the vacuum pump 1. The outlet of the last pumping stage T5 communicates with the delivery outlet. The axial dimensions of the rotor elements 6 and of the compression chambers 3 are, for example, equal or decreasing in the order of arrangement of the pumping stages T1-T5 in the gas pumping direction, the pumping stage T1 located at the same end as the suction inlet 5 receiving the rotor elements 6 having the largest axial dimension.

The vacuum pump 1 is, notably, said to be “dry” because, in operation, the rotors 4 rotate inside the stator 2 without any mechanical contact between them or with the stator 2, making it unnecessary to use oil in the pumping stages T1-T5.

The vacuum pump 1 further comprises at least one magnet 9 arranged in at least one rotor 4 so as to face a surface of ferromagnetic material 10, 12, 16 of the stator 2 on each rotation of the at least one rotor 4, so that the rotation of the at least one rotor 4 causes heating of the surface of ferromagnetic material 10, 12, 16 by magnetic induction.

The rotary movement of the rotors 4 is used to generate additional heating of the stator 2 by magnetic induction. The rotary movement of the magnets 9 generates eddy currents in the surface of ferromagnetic material 10, 12, 16, which in turn generate heat by the Joule effect. Eddy currents are electric currents created by the variation of the magnetic field generated by the rotation of the magnets. This heating may enable the surface temperature of the stator 2 to be increased locally, by 5°C to 30°C for example, which may enable the contaminating gas species to be kept in gaseous form. In this way, localized heating in the inner areas of the vacuum pump 1 prone to deposition is obtained on the surface, and without contact with the stator 2. Localized surface heating makes it possible to avoid damaging the mechanical parts, such as the bearings, that could not be heated throughout beyond the temperature reached by conventional heating of the stator 2, and enables the problems of thermal expansion of the stator 2 to be limited.

The at least one magnet 9 has, for example, the form of a bar (elongate and parallelepipedal) or plate, less than three millimetres in size, for example.

According to an example of embodiment, as shown in Figures 3a, 3b, 3c and 3d, at least one magnet 9 extends axially in a rotor element 6 of the rotor 4, with a longitudinal direction parallel to the axis of rotation I of the rotors 4. The at least one magnet 9 extends on a lateral edge surface 6a of the rotor element 6 configured for sweeping (without contact) a lateral surface 10 of the compression chamber 3, in order to heat the lateral surface 10 of the compression chamber 3 of the stator 2.

In the illustrative example, the lateral surface 10 of the compression chamber 3 is a cylindrical surface, the shape of the compression chamber 3 being inscribed in two parallel cylindrical cavities which are also parallel to the axial direction, the cylindrical cavities overlapping transversely (Figures 1 and 2). The at least one magnet 9 arranged on a lateral edge surface 6a (on the “back” of the rotor element 6) thus allows “radial” heating of the compression chamber 3.

The vacuum pump 1 comprises, for example, at least one magnet 9 for each rotor element 6 in at least one compression chamber 3. There is, for example, a single magnet 9 for each lateral edge surface 6a of a rotor element 6, and this magnet covers, for example, the lateral edge surface 6a (Figure 3c), or there is a plurality of magnets 9, for example two, in the same surface 6a (Figures 3a, 3b, 3d).

According to another example of embodiment, as shown in Figures 4a and 4b, at least one magnet 9 extends in a rotor element 6 of the rotor 4, with a main face perpendicular to the axis of rotation I of the rotors 4 (Figures 4a, 4b), radially for example (Figure 4b). The at least one magnet 9 extends on a transverse edge surface 6b of the rotor element 6 configured for sweeping (without contact) a lateral surface 12 of the compression chamber 3, in order to heat the lateral surface 12 of the compression chamber 3 of the stator 2.

In the illustrative example, the transverse surface 12 of the compression chamber 3 is a flat surface, like that of the transverse edge surface 6b, perpendicular to the axis of rotation I of the rotors 4. The at least one magnet 9 arranged on a transverse edge surface 6b (on a face of the rotor element 6) thus allows “axial” heating of the compression chamber 3.

The vacuum pump 1 comprises, for example, at least one magnet 9 for each rotor element 6 in at least one compression chamber 3. There is, for example, a single magnet 9 for each transverse edge surface 6b of a rotor element 6 (Figure 4a), or there is a plurality of magnets 9, for example two, in the same surface 6a (Figure 4b).

There is, for example, one or more magnets 9 on both transverse edge surfaces 6b of each rotor element 6 (Figure 4a).

There is, for example, at least one magnet 9 in at least one transverse edge surface 6b and at least one magnet 9 in a lateral edge surface 6a.

The transverse surface 12 of the compression chamber 3 is, for example, that of the end of the compression chamber 3 of the first or last pumping stage T1 or T5, the transverse surface 12 being interposed between the compression chamber 3 and a support 13 for bearings 14 of the stator 2 (Figure 2). Thus the transverse surface 12 of the end of the compression chamber 3 of the last or first pumping stage T5, T 1 can be heated in a highly localized way without any risk of damaging the bearings 14.

If the vacuum pump 1 comprises more than one magnet 9 for each rotor 4, it is advantageous to invert the polarity of the adjacent magnets 9 in order to optimize the generation of the eddy currents. The polarity inversions may be created in the thickness (Figure 3a) or in the length, that is to say in the axial direction (Figure 3b), or transversely, that is to say perpendicularly to the axial direction (Figures 3c, 3d, 4a and 4b), or in each adjacent magnet (Figure 3d, 4b) or in each adjacent rotor element 6, as described below.

More precisely, in Figure 3a where the polarity inversions are created in the thickness, each rotor element 6 received in the same compression chamber 3 is provided with two magnets 9, namely a magnet 9 whose surface facing the surface of ferromagnetic material 10 is polarized “south” and another magnet 9 whose surface facing the surface of ferromagnetic material 10 is polarized “north”.

In the case of Figure 3b, where the polarity inversions are created in the length, each rotor element 6 received in the same compression chamber 3 is provided with two magnets 9, namely a magnet 9 whose surface facing the surface of ferromagnetic material 10 is polarized “south” at a first axial end of the rotor element 6 and “north” at a second axial end, and another magnet 9 whose surface facing the surface of ferromagnetic material 10 is polarized “north” at the first axial end of the rotor element 6 and “south” at the second axial end.

In the case of a multi-stage vacuum pump 1, where the vacuum pump 1 comprises at least three pumping stages T1-T5, not all of the rotor elements 6 are necessarily provided with magnets. For example, it may be the rotor elements 6 configured for rotating in the last and/or the penultimate pumping stage T4, T5 in the direction of flow of the gases that are provided with magnets 9 (Figure 2). These are the pumping stages in which the pressures, and therefore the risks of deposition, are highest.

According to another example of embodiment shown in Figure 2, at least one magnet 9 is arranged in the shaft 7 of the rotor 4, for example between two compression chambers 3 in the case of a multi-stage vacuum pump 1 , for heating the surface 16 of a shaft passage of the stator 2.

The at least one magnet 9 is, for example, of the NdFeB or rare earth type. According to another example, the at least one magnet comprises a ferrite. Ferrite is inexpensive, but has the drawback of generating a weak magnetic field.

The at least one magnet 9 may be nickel-coated to protect it from any corrosion or to allow its easy replacement by dismantling. Preferably, the at least one magnet 9 is arranged as closely as possible to the surface of the rotor 4, or is flush with the surface of the rotor 4. The at least one magnet 9 is, for example, fastened to the body of the rotor 4, by adhesion for example, or is received in a cavity of the body of the rotor 4.

The body 2a of the stator 2 is, for example, made of cast iron.

At least one surface layer 2b of the stator 2 having a surface 10 of ferromagnetic material is, for example, made of nickel-iron alloy, also called “mumetal”, such as nickel-enriched cast iron, also called “Ni-resist” (Figure 5). This is because the magnetic permeability of mu-metals is greater than that of cast iron. Mumetals also have the advantage of enabling a significant Joule effect to be generated. The body 2a of the stator 2 may be made of a first material, such as cast iron, and may have a surface layer 2b of ferromagnetic material; or the stator 2 (the body 2a and the surface layer 2b) may be made throughout of ferromagnetic material, such as nickeliron alloy. Additionally, at least one surface 10 of ferromagnetic material of the stator 2 may have a nickel coating 28. The nickel coating 28 enables greater surface heating to be obtained. This heating increases with the thickness of the coating 28. For example, a coating 28 with a thickness of between 20 pm and 2 cm is provided, notably for rotors 4 rotating at between 60 and 250 Hz.

Thus, according to an example of embodiment of the surface 10 of ferromagnetic material shown in Figure 5, the body 2a of the stator 2 is made of cast iron, and a surface layer 2b of the stator 2 is made of nickel-iron alloy and has a coating 28 of nickel.

The stator 2 is, for example, composed of stator elements assembled to each other, and only the stator element bearing the surface 10 of ferromagnetic material may have a surface layer 2b of nickel-coated mu-metal, in order to limit costs.

Although Figures 1 to 4b show an example of a rotor 4 of the two-lobe type, for which the rotor 4 comprises two rotor elements 6 offset by 180° for each compression chamber 3, other embodiments are evidently feasible.

Figure 6 shows another example, for which the rotor 4 is of the four-lobe type, that is to say comprising four rotor elements 6 offset by 90° for each compression chamber 3, each rotor element 6 being provided with a single magnet 9. In order to optimize current generation, provision may be made to invert the polarity of the magnets 9 in each adjacent rotor element 6, as shown in Figure 6 in the case of rotors 4 having an even number of rotor elements 6.

Figure 7 shows a second example of a vacuum pump 100.

The vacuum pump 100 is a turbomolecular vacuum pump.

It comprises a stator 2 having at least one compression chamber 3, into which the gases to be pumped are intended to flow, and a rotor 4 configured for rotation in the compression chamber 3 of the stator 2 to drive the gas to be pumped between a suction inlet 5 and a delivery outlet 17 of the stator 2 (arrows G in Figure 7).

According to an example of embodiment, the vacuum pump 100 comprises a turbomolecular stage 18 and a molecular stage 19 located downstream of the turbomolecular stage 18 in the direction of flow of the gases. The pumped gases enter through the suction inlet 5, passing through the turbomolecular stage 18 initially, then the molecular stage 19, then the delivery end, and are then discharged through the delivery outlet 17 of the vacuum pump 100. In operation, the delivery outlet 17 is connected to a rough vacuum pump.

In the turbomolecular stage 18, the rotor 4 comprises at least two stages of blades 20, and the stator 2 comprises at least one stage of fins 21. The blade stages 20 and the fin stage 21 follow each other axially along the axis of rotation I of the rotor 4 in the turbomolecular stage 18. The rotor 4 comprises, for example, more than four blade stages 20, for example between four and eight stages of blades 20 (six in the example shown in Figure 7).

Each stage of blades 20 of the rotor 4 comprises inclined blades which extend in a substantially radial direction from a hub of the rotor 4 fastened to a shaft 7 of the turbomolecular vacuum pump 100. The blades 20 are distributed regularly on the periphery of the hub.

Each stage of fins 21 of the stator 2 comprises a ring from which inclined fins, distributed regularly on the inside periphery of the ring, extend in a substantially radial direction. The fins of a stage of fins 21 of the stator 2 are engaged between the blades of two successive stages of blades 20 of the rotor 4. The blades of the rotor 4 and the fins of the stator 2 are inclined so as to guide the pumped gas molecules towards the molecular stage 19.

According to an example of embodiment, the rotor 4 comprises a Holweck skirt 22 in the molecular stage 19, formed by a smooth cylinder which rotates facing helical grooves in the stator 2. The helical grooves enable the pumped gases to be compressed and guided towards the delivery end.

The rotor 4 is fastened to a shaft 7 configured to be driven in rotation at a high speed in axial rotation in the stator 2, rotating for example at more than twenty thousand revolutions per minute, by means of a motor 23 of the turbomolecular vacuum pump 100. The motor 23 is, for example, arranged under a bell-shaped casing of the stator 2, which is itself arranged under the Holweck skirt 22 of the rotor 4. The rotor 4 is guided laterally and axially by magnetic or mechanical bearings 24. The vacuum pump 100 may also comprise emergency bearings 25.

The vacuum pump 100 further comprises at least one magnet 9 arranged in the stator 2 so as to face a surface of ferromagnetic material 27 of the rotor 4 on each rotation of the at least one rotor 4, so that the rotation of the rotor 4 causes heating of the surface of ferromagnetic material 27 by magnetic induction. The rotary movement of the rotor 4 is used to generate additional heating of the rotor 4 by magnetic induction. The rotary movement of the rotor 4 facing the magnet(s) 9 generates eddy currents in the surface of ferromagnetic material 27, which in turn generate heat by the Joule effect. Eddy currents are electric currents created by the rotation of the rotor 4 in the magnetic field of the magnets 9 of the stator 2. This heating may enable the surface temperature of the rotor 4 to be increased locally, by 5°C to 30°C for example, enabling the contaminating gas species to be kept in gaseous form. In this way, localized heating in the inner areas of the vacuum pump 1 prone to deposition is obtained on the surface, and without contact with the rotor 4. Localized surface heating makes it possible to avoid damaging the rotor 4, by avoiding heating it throughout its whole volume, and enables the problems of thermal expansion of the stator 2 to be limited.

The at least one magnet 9 is, for example, arranged in the molecular stage 19 of the vacuum pump 100, in an area of the stator 2 surrounding the rotor 4, for example by surrounding the Holweck skirt 22 or, as shown in Figure 7, by being located under the Holweck skirt 22. The surface 27 of ferromagnetic material is, for example, the Holweck skirt 22.

The vacuum pump 100 comprises, for example, a plurality of magnets 9, regularly distributed for example, the polarity of the adjacent magnets 9 being inverted in the thickness or in the length or between adjacent magnets.

As before, the at least one magnet 9 is, for example, of the NdFeB or rare earth or ferrite type. It may be nickel-coated to protect it from any corrosion or to allow its easy replacement by dismantling. Preferably, the at least one magnet 9 is arranged as closely as possible to the surface of the stator 2, or is flush with the surface of the stator 2. The at least one magnet 9 is, for example, fastened to the stator 2, by adhesion for example, or is received in a cavity of the stator 2.

At least one part of the rotor 4 having a surface 27 of ferromagnetic material is, for example, made of iron, nickel or cobalt.

The rotor 4 may be made in one piece from ferromagnetic material.

Additionally, at least one surface 27 of ferromagnetic material of the rotor 4 may have a nickel coating 28.

Figure 8 shows another example of a turbomolecular vacuum pump 200. This vacuum pump 200 differs from the previous one in that, in this case, a magnetic material 29 is arranged in the rotor 4 so as to face a surface of ferromagnetic material 27 of the stator 2 on each rotation of the rotor 4, so that the rotation of the rotor 4 causes heating of the surface 27 of ferromagnetic material by magnetic induction.

The magnetic material 29 is, for example, arranged in the Holweck skirt 22 of the rotor 4. The surface 27 of ferromagnetic material is the surface of the stator 2 facing the Holweck skirt 22.

For this purpose, for example, the magnetized material comprises fibres or nanowires comprising cobalt, such as cobalt or AINiCo, embedded in a composite. This makes it possible to achieve fields of 0.6 T for the rotation speeds of the rotor 4 in the turbomolecular vacuum pump 200.

Cobalt nanowires may be produced in a polyol medium, by a conventional thermal method or by microwaves, for example. The alignment of the cobalt nanowires is produced by drying in a very high magnetic field (several T).

The nanowires or fibres comprising cobalt may be embedded in a polymer composite, such as PI (polyimide) or PPS (polyphenylene sulphide) or PEI (polyetherimide) or PEEK (polyether ether ketone). Additives such as glass fibres may be incorporated in the composite to improve the mechanical strength.

The initial orientation of the fibres or nanowires determines the polarity. The polarity is, for example, regularly inverted to provide an alternation of the magnetic north and south fields on the periphery of the Holweck skirt 22.

The rotor 4 may be made in one piece, and only the Holweck skirt 22 is, for example, magnetized. Additionally, at least one surface 27 of ferromagnetic material of the rotor 4 may have a nickel coating 28.

At least one part of the stator 2 having a surface 27 of ferromagnetic material is, for example, made of iron, nickel or cobalt.