JP6413926B2 - Vacuum pump and mass spectrometer - Google Patents

Description

  The present invention relates to a vacuum pump and a mass spectrometer.

  Vacuum pumps such as turbo molecular pumps are used in various devices as pumps that can generate a clean high vacuum environment. For example, in a mass spectrometer, the degree of vacuum in a quadrupole rod or detector is set to be about 5 to 10 times higher than the degree of vacuum in an ion source. Therefore, a vacuum pump having a plurality of exhaust ports is known so that such a device can be handled with a single vacuum pump (see, for example, Patent Document 1).

  The vacuum pump described in Patent Document 1 includes first and second turbo molecular stages and a Holweck stage, a first air inlet that can flow into the first turbo molecular stage, a first turbo molecular stage, A second air inlet that can flow into the second turbo molecular stage and a third air inlet that can flow into the Holbeck stage are provided. A through hole communicating with the third intake port is formed on the stator side of the Holbeck stage.

JP 2003-129990 A

  By the way, a plurality of spiral grooves are formed in the stator of the Holbeck stage, and they have the same shape. However, in the vacuum pump described in Patent Document 1, since the through hole penetrates only a part of the spiral grooves, the gas flow rate is different for each spiral groove. As a result, the intake side pressure of the Holbeck stage is increased, and the exhaust performance of the entire pump is deteriorated.

The vacuum pump according to a preferred embodiment of the present invention is provided on the downstream side of the first pump stage and the first pump stage, and a plurality of screw grooves and screw threads are alternately formed in the circumferential direction of the inner peripheral surface. A cylindrical stator, a second pump stage having a cylindrical rotor provided on the inner peripheral side of the cylindrical stator, a first intake port provided upstream of the first pump stage, and the first A vacuum pump provided downstream of one pump stage and communicating with the second pump stage, wherein the cylindrical stator includes at least one of the second air inlet and one or more of the air inlets. A through hole communicating with the screw groove is formed so as to penetrate from the outer peripheral surface of the cylindrical stator to the inner peripheral surface, and the groove shape of the first screw groove in which the through hole is formed is formed as a through hole. It has not been Unlike the second screw groove of the groove shape it is set in a groove shape suitable for larger flow rates.
In a further preferred embodiment, the parameters representing the groove shape are a groove width, a groove angle, and a groove depth of a screw groove, and at least one of the groove width, the groove angle, and the groove depth of the first screw groove is The first screw groove is set to be suitable for a larger flow rate than the second screw groove.
In a further preferred embodiment, the groove shape of the second screw groove is set so that the flow rate becomes larger as the second screw groove arranged closer to the circumferential direction than the first screw groove. Yes.
In a further preferred embodiment, in the cylindrical stator, the groove shape of the first screw groove and the groove shape of the second screw groove are the same in a region upstream of the through hole in the stator axial direction. Yes, the groove shape of the first screw groove is different from the groove shape of the second screw groove in a region downstream of the through hole in the stator axial direction.
The vacuum pump according to a preferred embodiment of the present invention is provided on the downstream side of the first pump stage and the first pump stage, and a plurality of screw grooves and screw threads are alternately formed in the circumferential direction of the inner peripheral surface. A cylindrical stator, a second pump stage having a cylindrical rotor provided on the inner peripheral side of the cylindrical stator, a first intake port provided upstream of the first pump stage, and the first A vacuum pump provided downstream of one pump stage and communicating with the second pump stage, wherein the cylindrical stator includes the second air inlet and the plurality of screws. A through-hole communicating with the groove is formed so as to penetrate from the outer peripheral surface of the cylindrical stator to the inner peripheral surface, and the first screw groove in which the through-hole is formed is the first without the through-hole. 2 screws Screw Article number of the first and second screw groove is set to be suitable for high flow rates than.
In a more preferred embodiment, the number of threads of the first screw groove is set to be smaller than the number of threads of the second screw groove .
A mass spectrometer according to a preferred embodiment of the present invention includes the above-described vacuum pump, a first analysis unit, a second analysis unit that operates in a higher pressure region than the first analysis unit, and the first analysis unit. A first chamber having a first exhaust port to which an analysis unit is housed and to which a first air inlet of the vacuum pump is connected, and a second chamber to which the second analysis unit is housed and a second air inlet of the vacuum pump are connected. A second chamber having a second exhaust port.

  According to the present invention, it is possible to improve the exhaust performance of a vacuum pump having a plurality of intake ports.

FIG. 1 is an external perspective view showing an embodiment of a vacuum pump according to the present invention. FIG. 2 is a sectional view of the vacuum pump. 3 is a cross-sectional view taken along line A1-A1 of FIG. FIG. 4 is a development view showing the structure of the inner peripheral surface side of the first screw stator. 5 is a diagram showing a cross section A2-A2 of FIG. FIG. 6 is a diagram illustrating an example of a mass spectrometer.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view showing an embodiment of a vacuum pump according to the present invention. The vacuum pump 1 includes a first housing 70 and a second housing 80. The first housing 70 is provided with a flange portion 75 in which a first air inlet 71, a second air inlet 72, and a third air inlet 73 are formed. Each of the intake ports 71, 72, 73 is formed with seal ring grooves 71a, 72a, 73a in which a seal ring is mounted. As will be described later, the second housing 80 is provided with a motor, and heat radiating fins 86 are formed on the surface of the second housing 80 (the bottom surface of the vacuum pump 1).

  FIG. 2 is a cross-sectional view of the vacuum pump 1 taken along the axial direction. FIG. 3 is a cross-sectional view taken along line A1-A1 of FIG. Inside the first housing 70, the shaft 10 to which the first turbine rotor 20, the second turbine rotor 30 and the motor rotor 90 are fixed is provided. The shaft 10 is supported by a magnetic bearing using permanent magnets 43 and 44 and a ball bearing 84. A motor stator 91 provided on the outer peripheral side of the motor rotor 90 is held by the second housing 80. The ball bearing 84 is held by a bearing holder 83 that is fixed to the second housing 80.

  The permanent magnet 44 is fixed in a recess formed at the right end of the shaft 10 in the figure. The permanent magnet 43 disposed inside the permanent magnet 44 is held by the magnet holder 40. The magnet holder 40 is fixed to the holder support portion 41, and the holder support portion 41 is fixed to the first housing 70. The magnet holder 40 is provided with a ball bearing 42. The ball bearing 42 functions as a regulating member that regulates the swing of the shaft 10 so that the permanent magnet 44 and the permanent magnet 43 do not come into contact with each other.

  The first turbine rotor 20 is formed with a plurality of first turbine blade stages 21 including a plurality of turbine blades in the axial direction. For the plurality of first turbine blade stages 21, first fixed blade stages 22 having a plurality of turbine blades are alternately arranged in the axial direction. These first turbine blade stage 21 and first fixed blade stage 22 constitute a first turbomolecular pump stage TP1.

  The second turbine rotor 30 is formed with a plurality of second turbine blade stages 31 including a plurality of turbine blades in the axial direction. For the plurality of second turbine blade stages 31, second fixed blade stages 32 having a plurality of turbine blades are alternately arranged in the axial direction. The second turbo blade stage 31 and the second fixed blade stage 32 constitute a second turbo molecular pump stage TP2. Positioning of the first fixed blade stage 22 and the second fixed blade stage 32 in the axial direction (left-right direction in the drawing) is performed by the spacers 23, 33, and 50.

  A disc portion 34 is formed on the pump downstream side (left side in the drawing) of the second turbine rotor 30 with respect to the second turbine blade stage 31. A first cylindrical rotor 62 and a second cylindrical rotor 63 are fixed to the disc portion 34. The second cylindrical rotor 63 is disposed on the inner peripheral side of the first cylindrical rotor 62. A first screw stator 60 is provided on the outer peripheral side of the first cylindrical rotor 62, and a second screw stator 61 is provided between the first cylindrical rotor 62 and the second cylindrical rotor 63. A through hole 60 a is formed in the first screw stator 60 at a position facing the third air inlet 73 of the first housing 70.

  As shown in FIG. 3, the inner peripheral surface of the first screw stator 60, the outer peripheral surface and the inner peripheral surface of the second screw stator 61, and the opposing surface of the second housing 80 facing the inner peripheral surface of the second cylindrical rotor 63. Each has a thread groove and a thread. The first and second cylindrical rotors 62 and 63, the first and second screw stators 60 and 61, and the screw grooves and the threads formed on the opposing surfaces of the second housing 80 constitute a Holweck pump stage HP. Is done.

  The gas flowing in from the first intake port 71 of FIG. 2 is exhausted to the downstream side of the first turbo molecular pump stage TP1 by the first turbo molecular pump stage TP1. Further, the gas flowing in from the second intake port 72 and the gas exhausted by the first turbo molecular pump stage TP1 are exhausted downstream of the second turbo molecular pump stage TP2 by the second turbo molecular pump stage TP2. . The gas exhausted by the second turbo molecular pump stage TP2 and the gas flowing in from the third intake port 73 are exhausted by the Holbeck pump stage HP. The gas exhausted by the Holbeck pump stage HP passes through exhaust passages 81 and 82 formed in the second housing 80 and is exhausted from the exhaust port 85. The pressure P at the intake ports 71, 72, 73 becomes higher toward the downstream side as P (71) <P (72) <P (73).

  FIG. 4 is a development view showing the structure on the inner peripheral surface side of the first screw stator 60. FIG. 5A shows the A2-A2 cross-sectional view of FIG. 4 is the intake side (pump upstream side) and the lower side is the exhaust side (pump downstream side). On the inner peripheral surface side of the first screw stator 60, a plurality of screw grooves and screw threads are alternately formed in the circumferential direction. In the example shown in FIG. 4, eight screw grooves 601a to 601h and eight screw threads 602a to 602h are alternately formed. The through hole 60a is formed over the three screw grooves 601c, 601d, and 601e. In the example shown in FIG. 4, the through hole 60a does not penetrate the threads 602d and 602e, but may be configured to penetrate.

  When the first cylindrical rotor 62 provided on the inner peripheral side of the first screw stator 60 rotates in the direction of the arrow, the gas flowing into the screw grooves 601a to 601h is exhausted to the pump downstream side (exhaust side). By the way, in the case of the screw stator in which the through hole 60a is not formed, the gas flowing in from the intake side flows into the screw grooves 601a to 601h almost uniformly. Therefore, the pressure state on the intake side is substantially the same in any of the thread grooves 601a to 601h.

  On the other hand, when the through hole 60a is formed like the first screw stator 60 and the gas from the third intake port 73 also flows from the through hole 60a, the flow rate R1 of the screw grooves 601c to 601e is different from that of the other screw grooves. It becomes larger than the flow rate R2 of 601a, 601b, 601f to 601h. Generally, the pressure P (73) of the third intake port 73 is 10 times or more the pressure P (72) of the second intake port 72. Therefore, the intake side pressure of the Holbeck pump stage HP is governed by the intake side pressure of the screw grooves 601c to 601e, and the intake side pressure of the Holbeck pump stage HP is higher than when the through hole 60a is not formed. .

  Therefore, in the present embodiment, as described below, the groove shapes of the screw grooves 601c to 601e in which the through hole 60a is formed are the same as those of the screw grooves 601a, 601b, and 601f to 601h in which the through hole 60a is not formed. Different from the groove shape, a groove shape suitable for a larger flow rate was set. By the way, the pressure on the exhaust side is almost determined by the vacuum system on the exhaust side, and the pressure on the exhaust side is almost the same in any of the screw grooves. The groove shape suitable for a larger flow rate is that the screw grooves 601c to 601e are larger than the screw grooves 601a, 601b, and 601f to 601h in terms of the flow rate of the exhaust gas, but the intake side pressure is almost the same. It means the groove shape set to be about. As a result, an increase in the intake side pressure of the Holbeck pump stage HP, that is, the pressure P (73) of the third intake port 73 can be prevented.

  The screw grooves 601a to 601h in FIG. 4 will be described. The screw grooves 601a to 601h are constituted by screw groove portions 601aa to 601ha on the intake side (pump upstream side) from the alternate long and short dash line L1, and screw groove portions 601ab to 601hb on the exhaust side (downstream of the pump) from the alternate long and short dash line L1. ing. An alternate long and short dash line L1 is a straight line that passes through the pump downstream end of the through hole 60a and extends in a direction orthogonal to the axial direction of the first screw stator 60.

  A part of the gas flowing into the screw grooves 601c to 601e from the through hole 60a flows backward to the intake side, but most of the gas is exhausted to the exhaust side in the screw groove. Therefore, the exhaust performance with respect to the inflowing gas is almost determined by the shape of the thread groove on the downstream side of the through hole 60a. Moreover, in this Embodiment, since the groove shape of the screw grooves 601c-601e is made into the shape suitable for a large flow volume as mentioned above, the back flow to the pump upstream side is suppressed rather than the through-hole 60a. As a result, on the upstream side of the through hole 60a, the exhaust conditions in the thread grooves 601a to 601h are substantially the same. Therefore, the setting (groove shape) of the screw grooves 601a to 601h can be made substantially the same on the upstream side of the through hole 60a.

  In the example shown in FIG. 4, the screw grooves 601a to 601h are spiral grooves having a constant groove angle and groove depth. The groove shapes of the screw groove portions 601aa to 601ha closer to the intake side than the one-dot chain line L1 are set to be the same. That is, the groove width Wa, the groove depth h (see FIG. 5), and the groove angle θa are the same. On the other hand, the groove shapes of the screw groove portions 601ab to 601hb on the exhaust side with respect to the alternate long and short dash line L1 are varied according to the flow rate.

  The screw groove 601d has the largest opening area in each screw groove 601c to 601e of the through hole 60a, and the screw grooves 601c and 601e are substantially the same area and smaller than the screw groove 601d. For this reason, the flow rate Qd of the screw groove 601db is the largest on the exhaust side from the one-dot chain line L1, and then the flow rates Qc and Qe (Qc≈Qe) of the screw grooves 601cb and 6001eb are large. On the other hand, the gas in the screw groove leaks into the adjacent screw groove through a minute gap (gap between the screw thread and the first cylindrical rotor 62) in the screw thread portion. Therefore, the flow rates Qa, Qb, and Qf to Qh of the screw groove portions 601ab, 601bb, and 601fb to 601hb are considered to be larger as the screw groove portions are closer to the screw groove portions 601cb and 601eb. That is, Qb≈Qf> Qa≈Qg> Qh.

  Therefore, in this embodiment, as an example, the groove angles of the screw groove portions 601ab to 601hb are set as shown in FIG. The groove angles θ1 to θ5 shown in FIG. 4 are set as θ1 <θ2 <θ3 <θ4 <θ5 according to the flow rate of each screw groove. The groove width Wb and the groove depth are the same for all the screw groove portions 601ab to 601hb. Here, the groove angles θ1 to θ5 are set based on the idea that the smaller the groove angle, the larger the flow rate and the higher the compression ratio. By setting in this way, the thread grooves 601c to 601e have a groove shape suitable for a large flow rate, and the intake side pressure of the Holbeck pump stage HP can be improved.

  In the example shown in FIG. 4, the screw grooves 601 c to 601 e through which the through hole 60 a passes and the screw grooves 601 a, 601 b, 601 f to 601 h that do not pass through are made to have different screw groove angles. The grooves 601c to 601e have a groove shape suitable for a large flow rate. However, not only the groove angle but also any one of the groove width, groove depth, and number of screw threads can be adjusted to make the screw grooves 601c to 601e into a groove shape suitable for a large flow rate. For example, the flow rate can be increased by increasing the groove width or groove depth or by reducing the number of screw threads, but in practice, combinations of these conditions can be set as appropriate. The same idea as described above can also be applied to variable grooves in which the shape of the thread groove (at least one of groove angle, groove width, and groove depth) changes along the axial direction.

  Further, for the screw grooves 601a, 601b, 601f to 601h through which the through hole 60a does not pass, the flow rate of the screw grooves closer to the screw grooves 601c, 601e is larger as Qb≈Qf> Qa≈Qg> Qh. Although the groove shape is set, it may be set to the same groove shape. Further, the screw grooves 601c to 601e may be set to the same groove shape.

  In the example shown in FIG. 4, the axial direction region of the screw groove portions 601ab to 601hb is set to the lower end portion of the through hole 60a, but may be the upper end portion of the through hole 60a. In any case, the groove shapes of the screw groove portions 601aa to 601ha are the same in the region upstream of the through hole 60a, and the groove shape and the screw of the screw groove portions 601cb to 601eb in the region downstream of the through hole 60a. The groove shapes of the groove portions 601ab, 601bb, 601fb to 601hb are different.

  In the example shown in FIG. 4, the groove shape changes discontinuously above and below the alternate long and short dash line L1. Therefore, in consideration of ease of manufacture, the first screw stator 60 may be divided into two parts, a part upstream from the one-dot chain line L1 and a part downstream from the one-dot chain line L1.

  FIG. 6 is a diagram illustrating an example of the mass spectrometer 100 on which the vacuum pump 1 including the three intake ports 71 to 73 is mounted. FIG. 6 is a schematic diagram showing a schematic configuration of a liquid chromatograph mass spectrometer using electrospray ionization (ESI). The mass spectrometer 100 includes an ionization chamber 150 and a mass analyzer 110. In the mass spectrometer 110, the first intermediate chamber 113 adjacent to the ionization chamber 150, the second intermediate chamber 114 adjacent to the first intermediate chamber, and the analysis chamber 115 adjacent to the second intermediate chamber 114 each have a partition wall. Is provided.

  The first intake port 71 of the vacuum pump 1 is connected to the exhaust port 131 of the analysis chamber 115. The second intake port 72 of the vacuum pump 1 is connected to the exhaust port 132 of the second intermediate chamber 114. The third intake port 73 of the vacuum pump 1 is connected to the exhaust port 133 of the first intermediate chamber 113. In this way, three spaces (first intermediate chamber 113, second intermediate chamber 114, and analysis chamber 115) having different pressure regions are evacuated by one vacuum pump 1.

  An ionization spray 151 is provided in the ionization chamber 150. The liquid sample separated by the liquid chromatograph LC is supplied to the ionization spray 151 through the pipe 152. Although not shown, nebulization gas is supplied to the ionization spray 151, and the liquid sample is sprayed by the ionization spray 151. A high voltage is applied to the tip of the ionization spray 151 and is ionized during spraying. A heater block 112 is provided between the first intermediate chamber 113 and the ionization chamber 150, and a desolvation pipe 120 that connects the ionization chamber 150 and the first intermediate chamber 113 is provided in the heater block 112. . The desolvation tube 120 has a function of promoting desolvation and ionization when ions generated in the ionization chamber 150 and sample droplets pass through.

  A first ion lens 121 is provided in the first intermediate chamber 113. The second intermediate chamber 114 is provided with an octopole 123 and a focus lens 124. In the partition wall between the second intermediate chamber 114 and the analysis chamber 115, an entrance lens 125 having pores is provided. In the analysis chamber 115, a first quadrupole rod 126, a second quadrupole rod 127, and a detector 128 are provided.

  The ions generated in the ionization chamber 150 sequentially pass through the desolvation tube 120, the first ion lens 121 in the first intermediate chamber 113, the skimmer 122, the octopole 123 in the second intermediate chamber 114, the focus lens 124, and the entrance lens 125. Unnecessary ions are sent to the analysis chamber 115 and discharged by the quadrupole rods 126 and 127, and only specific ions reaching the detector 128 are detected.

(1) As described above, the vacuum pump 1 includes a plurality of intake ports (first intake port 71, second intake port 72, and third intake port 73) as shown in FIG. The first screw stator 60 is formed with a through hole 60a communicating with the second air inlet 72 and the three screw grooves 601c, 601d, 601e so as to penetrate from the outer peripheral surface of the first screw stator 60 to the inner peripheral surface. The groove shapes of the screw grooves 601c, 601d, and 601e in which the holes 60a are formed are different from the groove shapes of the other screw grooves 601a, 601b, and 601f to 601h in which the through holes 60a are not formed, and are grooves suitable for a larger flow rate. The shape is set.

  Thus, since the flow rate of the screw grooves 601c, 601d, and 601e in which the through hole 60a is formed is larger than the flow rate of the screw grooves 601a, 601b, and 601f to 601h in which the through hole 60a is not formed, from the through hole 60a. Even if gas flows into the screw grooves 601c, 601d, and 601e, the influence on the pressure on the upstream side of the screw grooves 601c, 601d, and 601e can be suppressed. As a result, a pressure drop at the third air inlet 73 can be achieved.

(2) The parameters representing the groove shape are the groove width, groove angle, groove depth, and number of screw threads of the screw groove, and the groove width, groove angle, groove depth, and screw number of the screw grooves 601c, 601d, and 601e. At least one of the number of strips is set so that the flow rates of the screw grooves 601c, 601d, and 601e are larger than the flow rates of the screw grooves 601a, 601b, and 601f to 601h.

  For example, in the case of the first screw stator 60 shown in FIG. 4, the groove angle which is a parameter of the groove shape is different. That is, on the downstream side of the alternate long and short dash line L1, the groove angles θ1 and θ2 of the screw grooves 601c, 601d, and 601e are set smaller than the groove angles θ3 to θ5 of the screw grooves 601a, 601b, and 601f to 601h. Therefore, the flow rates of the screw grooves 601c, 601d, and 601e are larger than the flow rates of the screw grooves 601a, 601b, and 601f to 601h.

(3) Further, as shown in FIG. 4, regarding the groove shapes of the screw grooves 601a, 601b, 601f to 601h, the flow rate of the screw grooves arranged closer to the circumferential direction with respect to the screw grooves 601c, 601d, 601e is higher. It is preferable to set so as to increase. As described above, the gas in the screw groove leaks into the adjacent screw groove through a minute gap in the thread portion, so the screw groove closer to the screw grooves 601c, 601d, and 601e having a larger flow rate has a higher flow rate. . Therefore, not only the screw grooves 601c, 601d, and 601e but also the screw grooves 601a, 601e, 601e, With regard to 601b and 601f to 601h, the groove shape can be optimized. As a result, it is possible to further reduce the pressure at the third air inlet 73.

(4) Further, as shown in FIG. 4, in the region downstream of the through hole 60a, the groove shapes of the screw grooves 601c, 601d, 601e are set to the groove shapes suitable for a large flow rate as described above. , Backflow to the upstream side is suppressed. Therefore, in the region upstream of the through hole 60a, the groove shapes of the screw grooves 601c, 601d, and 601e may be the same as the groove shapes 601a, 601b, and 601f to 601h of the screw grooves.

(5) In the mass spectrometer of the present embodiment, for example, as shown in FIG. 6, the exhaust port 132 of the second intermediate chamber 114 in which the octopole 123 and the focus lens 124 as the first analysis unit are housed. The vacuum pump 1 is connected to the exhaust port 133 of the first intermediate chamber 113 where the second ion inlet 72 of the vacuum pump 1 is connected and the first ion lens 121 operating in a higher pressure region than the first analysis unit is accommodated. The third intake port is connected. Therefore, a plurality of chambers can be evacuated by one vacuum pump 1, and the cost of the mass spectrometer 100 can be reduced.

  Note that the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired. For example, in the embodiment, a vacuum pump having three intake ports has been described as an example. However, the present invention does not include the second turbo molecular pump stage TP2 and the second intake port 72, and the first intake port 71 and the third intake port. The present invention can also be applied to a vacuum pump having only 73.

  DESCRIPTION OF SYMBOLS 1 ... Vacuum pump, 10 ... Shaft, 20 ... 1st turbine rotor, 21 ... 1st turbine blade stage, 22 ... 1st fixed blade stage, 60a ... Through-hole, 30 ... 2nd turbine rotor, 31 ... 2nd turbine blade Steps 32, second fixed blade stages 60, first screw stator 61, second screw stator 62, first cylindrical rotor 63, second cylindrical rotor 70, first housing 71, first intake port 72 2nd intake port, 73 ... 3rd intake port, 75 ... Flange, 80 ... 2nd housing, 81, 82 ... Exhaust passage, 601a-601h ... Screw groove, 602a-602h ... Screw thread, 100 ... Mass spectrometer , 110 ... Mass spectrometer, 113 ... First intermediate chamber, 114 ... Second intermediate chamber, 115 ... Analysis chamber, 121 ... First ion lens, 123 ... Octopole, 124 ... Focus lens, 131, 132, 13 ... exhaust port, 150 ... ionization chamber, HP ... Holweck (Holweck) pump stage, TP1 ... first turbomolecular pump stage, TP2 ... second turbomolecular pump stage

Claims (7)

A first pump stage;
A cylindrical stator provided downstream of the first pump stage and having a plurality of screw grooves and screw threads formed alternately in the circumferential direction of the inner circumferential surface; and provided on the inner circumferential side of the cylindrical stator. A second pump stage having a closed cylindrical rotor;
A first air inlet provided upstream of the first pump stage;
A vacuum pump provided on the downstream side of the first pump stage and having a second intake port communicating with the second pump stage,
In the cylindrical stator, a through hole that communicates the second intake port and the one or more screw grooves is formed so as to penetrate from the outer peripheral surface of the cylindrical stator to the inner peripheral surface,
Groove shape of the first thread groove of the through hole is formed is different from the groove shape of the second screw groove through hole is not formed, is set in a groove shape suitable for larger flow rates, Vacuum pump. The vacuum pump according to claim 1, wherein
The parameters representing the groove shape are the groove width, groove angle and groove depth of the screw groove,
At least one of the groove width, groove angle, and groove depth of the first screw groove is set so that the first screw groove is more suitable for a larger flow rate than the second screw groove. . The vacuum pump according to claim 1 or 2,
The vacuum shape of the groove shape of the second screw groove is set such that the flow rate of the second screw groove disposed closer to the first screw groove is larger in the circumferential direction. The vacuum pump according to any one of claims 1 to 3,
The cylindrical stator is
In the region upstream of the through hole in the stator axial direction, the groove shape of the first screw groove and the groove shape of the second screw groove are the same,
The vacuum pump, wherein a groove shape of the first screw groove is different from a groove shape of the second screw groove in a region downstream of the through hole in the stator axial direction.   A first pump stage;
  A cylindrical stator provided downstream of the first pump stage and having a plurality of screw grooves and screw threads formed alternately in the circumferential direction of the inner circumferential surface; and provided on the inner circumferential side of the cylindrical stator. A second pump stage having a closed cylindrical rotor;
  A first air inlet provided upstream of the first pump stage;
  A vacuum pump provided on the downstream side of the first pump stage and having a second intake port communicating with the second pump stage,
  In the cylindrical stator, a through hole that communicates the second intake port and the plurality of screw grooves is formed so as to penetrate from the outer peripheral surface of the cylindrical stator to the inner peripheral surface,
  The number of threads of the first and second screw grooves is set so that the first screw groove in which the through hole is formed is suitable for a larger flow rate than the second screw groove in which the through hole is not formed. A vacuum pump.   The vacuum pump according to claim 5,
  The vacuum pump, wherein the number of threads of the first thread groove is set to be smaller than the number of threads of the second thread groove. A vacuum pump according to any one of claims 1 to 6 ,
A first analysis unit;
A second analysis unit operating in a higher pressure region than the first analysis unit;
A first chamber containing the first analysis unit and having a first exhaust port to which a first intake port of the vacuum pump is connected;
A mass spectrometer comprising: a second chamber that houses the second analysis unit and has a second exhaust port to which a second intake port of the vacuum pump is connected.

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