JPH08338394A - Molecular pump - Google Patents

Abstract

PURPOSE: To obtain a molecular pump which can exhaust a gas with a small molecular weight and a small viscosity coefficient such as a hydrogen isotope efficiently in a nuclear fusion reactor, and can bear to a high energy and a high dose of radial rays generated from the nuclear fusion reactor. CONSTITUTION: While all the coverage members of coils 2a, 3a, 4a, 5a, and 6a around a shaft B, and the wires of wirings, are made of ceramics, the material of a rotor C is made of a titannium alloy, and furthermore, a heater G and a cooling water jacket E are provided at the inner side and the outer side of a stator D, so as to make the temperature of the stator D regulatable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular pump required for a nuclear fusion reactor that uses hydrogen isotopes such as deuterium and tritium as fuel.

[0002]

2. Description of the Related Art A molecular pump such as a turbo molecular pump or a helical groove molecular pump, which utilizes an interaction between a rotor and a gas rotating at a high speed as a gas exhausting principle, is used as a molecular pump for a nuclear fusion device. Magnetic bearings are used for the bearings of these molecular pumps from the viewpoint of oil-free.

Here, the turbo molecular pump is a high vacuum pump having a structure similar to that of an axial compressor, and the helical groove molecular pump has a helical groove (thread groove) on either the outer surface of the rotor or the inner surface of the stator. A high vacuum pump in which the rotor rotates within the stator with a small gap.

In conventional turbo molecular pumps and helical groove molecular pumps, organic substances such as varnish, epoxy resin, and Teflon are used for electrical insulation of the coils and lead wires of the magnetic bearings, drive motors, etc. that make up them. The rotor was made of aluminum alloy.

Conventional turbo molecular pumps and helical groove molecular pumps are designed assuming nitrogen as an exhaust gas, but in a nuclear fusion device, hydrogen and hydrogen isotopes (deuterium, tritium) having a small molecular weight and a small viscosity coefficient are used. ) Or helium or other gas with a small molecular weight will be mainly exhausted.

[0006]

When the magnetic bearing type molecular pump according to the prior art is used for a fusion reactor, the following problems occur.

(1) High energy and high dose of radiation are generated in a fusion reactor, but the organic substances used for electrical insulation of conventional magnetic bearings and coils of drive motors are irradiated with the radiation. There is a possibility that the electromechanical properties are gradually deteriorated, the normal operation of the molecular pump becomes impossible, or the control unit of the molecular pump fails due to the deterioration of the electric insulation of the organic substance.

(2) The molecular pump needs to be subjected to high temperature baking in order to reduce the amount of tritium accumulated in the pump. However, the organic substances used for electrical insulation of conventional magnetic bearings and coils of drive motors cannot withstand baking for a long time at 100 ° C. or higher, and thus there is a problem that sufficient baking cannot be performed.

(3) The conventional helical groove molecular pump is designed on the assumption that a large flow rate of a gas such as nitrogen having a relatively large molecular weight and a relatively large viscosity coefficient is exhausted. Considering this, the gap between the rotor and the stator is set to be fairly wide. This is because when the operation reaches a steady state, the gap expands to an optimum value due to thermal expansion of the rotor, and a large compression ratio is obtained.

However, when a gas such as a hydrogen isotope having a small molecular weight and a small viscosity coefficient is exhausted, the compression ratio is lowered in principle, and since the heat generated by friction is small, the thermal expansion of the rotor is small, and therefore, The gap between the rotor and the stator becomes wider than that during steady operation of nitrogen gas. Generally, the compression ratio of the helical groove molecular pump decreases in inverse proportion to the square of the gap between the rotor and the stator, so that widening the gap has been a serious problem.

(4) Generally, the exhaust performance of a molecular pump improves in proportion to the rotational speed of the rotor. Therefore, it is desirable to set the rotational speed of the rotor as high as possible, but the centrifugal force generated in the rotor should be below the allowable stress of the rotor material. There is a need to.

The aluminum alloy rotor used in the conventional molecular pump has a problem that the operating temperature is limited to 120 ° C. because the allowable stress sharply decreases when the temperature exceeds 120 ° C. .

An object of the present invention is to solve these problems and to provide a molecular pump suitable for exhausting gas such as hydrogen isotope having a small molecular weight and a small viscosity coefficient.

[0014]

In order to achieve the above-mentioned object, the present invention is a molecular pump provided with a magnetic bearing and a driving motor, and the coating material of the electric wire used inside the molecular pump is made of ceramics. It is characterized by having done.

[0015]

In the molecular pump according to claim 1, since the coating material of the electric wire inside the molecular pump is made of ceramics,
When the molecular pump is used in a fusion reactor, the insulation of the coating is not deteriorated by high-energy and high-dose radiation generated from the fusion reactor, and in order to reduce the amount of tritium retained, Even if the molecular pump is baked at 100 ° C. or higher, it can withstand this sufficiently.

In the molecular pump of claim 2, since the rotor material is made of titanium alloy or heat-resistant steel to improve the heat resistance, the maximum operating temperature of the molecular pump can be raised to about 300 ° C. The rotor speed can also be set high.

In the molecular pump of claim 3, since at least a part of the molecular pump is a helical groove molecular pump capable of actively controlling the gap between the rotor and the stator, the molecular weight and viscosity coefficient of hydrogen isotopes are small. A sufficient compression ratio can be obtained even when the gas is exhausted.

In the molecular pump of claim 4, since the temperature of the stator section can be adjusted by the heating section and the cooling section, the gap between the rotor and the stator is actively controlled by controlling the thermal expansion amount of the stator section. can do.

In the molecular pump according to the fifth aspect, since the elastic material is sandwiched between the outer casing and the inner stator, it is possible to absorb the radial extension when the stator is heated.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a longitudinal sectional view of a magnetic bearing type helical groove molecular pump, where A is a casing, B is a shaft, and C is a rotor of the helical groove molecular pump section.

The stator D of the helical groove molecular pump portion has a two-layer structure of the casing A and the inside and outside, and the elastic material F is sandwiched between the layers.

A cooling water jacket E is installed as a cooling unit in the casing A, and an electric heater G is embedded as a heating unit in the stator D.

A gap sensor 4 is provided on the stator D, and the gap between the rotor C and the stator D is detected to control the amount of water passing through the cooling water jacket E or the amount of electricity supplied to the heater G. Further, the rotor C is made of titanium alloy or heat-resistant steel, and has a higher heat resistance than the conventional one made of aluminum alloy.

The magnetic bearing device supporting the shaft B includes an upper radial displacement sensor 1, an upper radial bearing electromagnet 2, a lower radial bearing electromagnet 5, a lower radial displacement sensor 6,
The motor includes a thrust bearing electromagnet 7, a thrust displacement sensor 8, and the like. The motor stator 3 forms a motor together with a rotor (not shown) provided on the shaft B.

The electric wires such as the coils 2a, 3a, 5a and 7a used in these parts 1 to 8 are formed by plating a copper wire with nickel and coating the entire surface with a ceramic material. Al with good electrical insulation for the ceramic material
₂ O ₃ , SiO ₂ , BeO and various new ceramics are used.

As for the coating of the electric wire with the ceramic material, the coating with the woven cloth of fibrous ceramics is adopted in addition to the method of forming by sintering.

The operation of the magnetic bearing type helical groove molecular pump of the first embodiment will be described.

The molecular pump takes in air from the intake port X and exhausts it from the exhaust port Y by the high speed rotation of the rotor C. In this example, the helical groove of the pump is provided on the rotor C side, but it may be provided on the stator D side.

The rotor C is fixed to the shaft B, and the shaft B is supported by two sets of radial magnetic bearings and one set of thrust magnetic bearings, which enables operation without lubrication.

A method of controlling the gap between the rotor C and the stator D in this molecular pump will be described.

During operation of this molecular pump, the gap between the rotor C and the stator D is constantly measured by the gap sensor 4, and if the gap becomes larger than the target value, the energization amount of the heater G is reduced or the cooling water jacket E is cooled. Increase the water flow,
Automatic control is performed so that the temperature of the stator part D decreases.

When the gap becomes smaller than the target value, the amount of water passing through the cooling water jacket E is reduced or the amount of electricity supplied to the heater G is automatically controlled.

Thus, by controlling the amount of thermal expansion of the stator D by controlling the temperature of the stator D, the rotor C
And the gap between the stator D can be adjusted to keep the gap at the target value.

Further, the elastic material F between the stator D and the casing A absorbs the rapid radial expansion of the stator D when the temperature of the stator D is increased, and an unreasonable force is exerted on the stator D and the casing A during the operation of the molecular pump. It acts so as not to take it.

Further, since the electric wires of the coils 2a, 3a, 5a, 7a, etc. are all made of a ceramic coating, the electrical insulation of the coating is not deteriorated even by the high energy and high dose radiation generated from the fusion reactor.

Further, even when the molecular pump is baked at 100 ° C. or higher to reduce the amount of tritium retained, or when the stator D is heated by the heater G to adjust the gap between the rotor C and the stator D. Since the ceramic coating sufficiently withstands these heats, the insulation of the electric wire coating does not deteriorate.

A second embodiment of the present invention will be described with reference to FIG.

FIG. 2 is a longitudinal sectional view of a magnetic bearing type composite molecular pump, and a rotor J is composed of a rotor blade H of a turbo molecular pump section and a rotor C of a helical groove molecular pump section.

On the other hand, on the stator side, the stator blade I of the turbo molecular pump section and the stator D of the helical groove molecular pump section are also provided.
Consists of.

The rotor C is made of titanium alloy or heat-resistant steel,
The temperature-controllable cooling water jacket E, the heater G, and the elastic material F are all provided only on the outer circumference of the helical groove molecular pump portion.

The magnetic bearing and drive motor shown in FIG.
The electric wire such as a wire loop used in these parts 1 to 8 is also covered with a ceramic.

The operation of the magnetic bearing type composite molecular pump of the second embodiment will be described.

The molecular pump sucks air from the intake port X by the high speed rotation of the rotor J, and has a turbo molecular pump portion including a moving blade H and a stationary blade I, and a helical groove molecular pump portion including a rotor C and a stator D. Thus, the exhaust is performed from the exhaust port Y at a higher compression ratio than in the first embodiment.

The cooling water jacket E and the heater G are provided only in the helical groove molecular pump section. The helical groove molecular pump has a greater effect on the exhaust performance of the gap between the rotor and the stator, as compared with the turbo molecular pump. Because.

The cooling water jacket E and the heater G adjust the temperature of the stator D by the signal of the gap sensor 4 to control the gap between the rotor C and the stator D.

The function of the ceramic coating material for the electric wire is
Similar to the embodiment, it is particularly effective when the present composite molecular pump is used for exhausting hydrogen isotopes and the like from a fusion reactor.

[0048]

As described above, according to the present invention, when exhausting hydrogen isotopes and the like from a fusion reactor, it has durability against high energy and high dose radiation generated from the fusion reactor,
It is possible to provide a molecular pump capable of enduring high temperature baking for reducing the amount of retained tritium for a long time and having high exhaust performance even for a gas having a small molecular weight or a small viscosity coefficient.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a magnetic bearing type helical groove molecular pump according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a magnetic bearing type composite molecular pump according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 6 Displacement sensor 2, 5 Radial bearing Electromagnet 2a, 3a, 5a, 7a Coil 4 Gap sensor A Casing B Axis C Rotor D Stator E Cooling water jacket F Elastic material G Heater

Front page continuation (72) Inventor Yoshio Murakami 1-80-1, Mukaiyama, Naka-machi, Naka-gun, Naka-gun, Ibaraki Japan, Atomic Energy Research Institute Naka Research Institute, Japan (72) Junichi Nakamura 1-801, Mukaiyama, Naka-machi, Naka-gun, Ibaraki Prefecture Japan Naka Institute of Nuclear Research (72) Inventor Shoji Iguchi 3-2-25 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture

Claims (5)

[Claims] 1. A molecular pump comprising a magnetic bearing and a drive motor, wherein a coating material for an electric wire used inside the molecular pump is entirely made of ceramics. 2. The molecular pump according to claim 1, wherein a titanium alloy or heat-resistant steel is used for a rotor material of the molecular pump. 3. A structure in which at least a part of the molecular pump is a helical groove molecular pump, and a gap between a rotor and a stator of the helical groove molecular pump can be constantly and actively controlled. Alternatively, the molecular pump according to claim 2. 4. A heating unit and a cooling unit are provided in a stator section of the helical groove molecular pump, and a gap sensor for detecting the size of the gap is provided in the stator section, and a gap sensor is provided according to a detection signal from the gap sensor. The molecular pump according to claim 3, wherein the amount of heat applied to the heating unit and the cooling unit is controllable. 5. The stator portion is formed into a two-layer structure in a circumferential direction of an outer casing and an inner stator, a cooling portion is provided in the outer casing, and a heater is provided in the inner stator. The molecular pump according to claim 4, wherein an elastic material is sandwiched between the outer casing and the inner stator.