JP4210854B2 - Rotary joint for high frequency transmission - Google Patents

Description

  The present invention relates to a high-frequency transmission rotary joint used in a radiotherapy apparatus or the like.

  As a radiotherapy apparatus using a microwave generated by a magnetron or klystron, for example, [Patent Document 1] is disclosed. Further, the discharge in the high-pressure gas related to the present invention is described in [Non-Patent Document 1].

  As shown in FIG. 9, the radiotherapy apparatus of [Patent Document 1] has an irradiation head 51 having an electron gun, a linear accelerator, and a target, and a support movement for supporting and moving the irradiation head on a predetermined spherical coordinate. A mechanism 52; a microwave oscillator 53 installed on the floor; a waveguide section 54 having one end electromagnetically connected to the microwave oscillator and the other end electromagnetically connected to the linear accelerator; And an RF window provided in the waveguide portion located in the position.

Further, in such a radiotherapy apparatus, each waveguide section 54 is a metal hollow tube, so that a rotary joint is used to connect a plurality of waveguide sections rotatably and electromagnetically. It is done.
In this rotary joint (rotary RF coupler in Patent Document 1), as shown in FIG. 10, the waveguide of the waveguide 54 communicates with the rotary spaces 57a and 57b surrounded by the rotary member of the rotary joint 56. The microwave is guided in the in-pipe mode 2a (2b).
In this figure, 58 indicates a bearing and 59 indicates a λ / 4 wavelength choke. By such a combination of the rotary joint 56 and the waveguide section 54, the microwave for acceleration can be smoothly supplied to the irradiation head moving from the acceleration microwave source such as a klystron fixed to the floor or the like.

JP 2003-175117 A, "Radiotherapy apparatus"

Discharge Handbook, Electrical Society of Japan, Ohmsha, P197-205

In the above-described high-frequency propagation rotary joint, it is necessary to prevent discharge at a bearing portion or the like and material deterioration of a sealing material or the like due to high-frequency leakage to the rotation support portion. Therefore, the conventional high-frequency propagation rotary joint employs a choke structure such as the above-mentioned λ / 4 wavelength choke 59 to reduce high-frequency leakage to the rotation support portion side.
However, recent technological trends in high-frequency devices are moving toward smaller size with higher power, and devices capable of transmitting high-power and high-frequency are desired. In the case of such a rotary joint that transmits a large amount of power, the general choke structure as described above cannot sufficiently reduce high-frequency leakage to the rotation support side. There was a risk of causing this.

  The present invention has been made to solve such problems. That is, the object of the present invention is to reduce the high frequency leakage to the rotation support part side, avoid discharge and material deterioration on the rotation support part side, and transmit high power high frequency even if it is downsized. It is to provide a rotary joint.

According to the first aspect of the present invention, the end faces are connected in series with a certain gap therebetween, and can be relatively rotated around a concentric axis, and a hollow waveguide for high-frequency transmission is provided therein. A high-frequency transmission rotary joint comprising: a pair of waveguides having a rotation support portion that is provided outside the waveguide and supports the relative rotation and hermetically seals the gap. A choke structure having an internal space communicating from the gap to the rotation support portion, the choke structure having one end communicating with the gap to reduce the intrusion of the high frequency, and one end of the choke cavity having one end communication, the other end Ri is Do and a seal cavity which communicates to the rotation support portion, said choke cavity communicates with one end to the gap, extending in the axial direction of the waveguide and the other end of the high frequency from the gap At a position roughly equivalent to a quarter wavelength A hollow cylindrical first cavity, and the other end and one end of the first cavity communicate with each other, extend in the axial direction with a cylindrical partition wall outside the first cavity, and the other end is closed. There is provided a rotary joint for high-frequency transmission , wherein one end of the seal cavity is connected to the choke cavity at a position facing the tip of the partition wall .

According to the second invention of the present invention, the end faces are connected in series with a certain gap therebetween, and can be relatively rotated around a concentric axis, and a hollow waveguide for high-frequency transmission inside. A rotary joint for high frequency transmission provided with a pair of waveguides having a rotation support portion provided outside the waveguide and supporting the relative rotation and hermetically sealing the gap. And
The choke structure has an inner space communicating from the gap to the rotation support portion, the choke structure having one end communicating with the gap to reduce the intrusion of the high frequency, and one end in the choke cavity. A high-frequency transmission characterized by comprising: a seal cavity whose other end communicates with the rotation support portion; and an RF contact located in the seal cavity and electrically conducting between the pair of waveguides A rotary joint is provided.

According to a preferred embodiment of the present invention, the choke cavity has one end communicating with the gap, extending in the axial direction of the waveguide, and the other end substantially corresponding to a quarter wavelength of the high frequency from the gap. A hollow cylindrical first cavity located at
The other end and one end of the first cavity communicate with each other, and a hollow cylindrical second cavity that extends in the axial direction with a cylindrical partition wall outside the first cavity and has the other end closed.

According to a preferred embodiment of the first invention, one end of the seal cavity is located at or near the position where the magnetic field formed in the communication portion between the first cavity and the second cavity is the weakest.

  The gap between the waveguides is located at or near the position where the electric field formed in the waveguide is the weakest.

  The dimensions of the choke cavity and the seal cavity are set so that the magnetic field formed therein is sufficiently smaller than the discharge limit.

According to a preferred embodiment of the second invention, the RF contact is a conductive ring member that contacts the pair of waveguides and is centered on the axis of the waveguide.
The RF contact is a copper circular spring that has good conductivity and does not interfere with rotation.

Preferably, pressurized SF ₆ gas is enclosed in the waveguide. Further, the inside of the waveguide may be decompressed to a vacuum state.

  The high frequency is a high-power microwave having a frequency of 2 GHz or more.

According to the first invention, high-frequency leakage in the choke structure portion of the high-frequency transmission rotary joint is caused by induction of electromagnetic waves in the internal space (seal cavity) communicating with the rotation support portion. The induced electromagnetic wave is guided to the seal cavity by the strength of the magnetic field at the tip position of the seal cavity. Therefore, by placing the tip of the seal cavity at a position facing the tip of the cylindrical partition wall where the magnetic field formed in the choke cavity is the weakest, induction of electromagnetic waves to the rotation support portion can be drastically reduced. it can.

  By performing an electromagnetic field analysis inside the rotary joint, it is possible to identify the position where the magnetic field inside the choke structure is zero. Therefore, by positioning the tip of the seal cavity communicating with the rotation support at the position where the magnetic field is 0 (position where the electric field is concentrated), induction of electromagnetic waves into the seal cavity can be suppressed and transmitted. It is possible to drastically reduce the leakage of high-frequency rotating support parts, and even when transmitting high-power high-frequency waves, avoid discharge and material deterioration on the rotating support parts due to high-frequency leakage. Is possible.

  Further, according to the second invention, by providing the RF contact for electrically conducting between the waveguides in the seal cavity, the generation of the electric field of the portion is suppressed by the RF contact, and the electromagnetic field deeper than the RF contact is provided. Guidance can be deterred.

  In view of this, problems such as discharge and material deterioration have been achieved by providing copper round springs, etc., which have good conductivity and do not interfere with rotation, as RF contacts in the seal cavity and reduce high frequency leakage to the seals and bearings. It is possible to solve this problem.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a relationship diagram between a gap and an AC discharge voltage disclosed in Non-Patent Document 1. This figure shows the discharge characteristics during high pressure SF _6. SF ₆ (sulfur hexafluoride) is one of negative gases that easily become negative ions due to attachment of electrons, and is particularly suitable as a gas insulation type insulating medium. In addition, since it has a higher dielectric strength compared to atmospheric insulation, it has the feature that the device can be miniaturized.
However, as can be seen from FIG. 1, the dielectric strength (AC discharge voltage) of SF ₆ gas increases as the pressure is increased from atmospheric pressure. Therefore, it is preferable to use pressurized SF ₆ gas as the insulating medium. For example, the AC discharge voltage increases substantially in proportion to the gap under a pressure of 2 atm or more. Therefore, it can be seen that the smaller the gap, the lower the voltage.
The discharge limit voltage in 2 atm SF ₆ gas is about 14 MV / m, although it varies depending on the electric field format and the applied voltage mode. Therefore, it can be said that discharge can be avoided if it is 10 MV / m or less in consideration of the fluctuation range and the safety factor.

FIG. 2 is a schematic cross-sectional view of a conventional rotary joint. As shown in this figure, the conventional rotary joint 1 includes a pair of waveguides 12 and 14, a rotation support portion 20, and a choke structure portion 30.
The pair of waveguides 12 and 14 have end faces 12a and 14a connected in series with a certain gap 15 therebetween, and can be relatively rotated around a concentric axis ZZ, so that high-frequency transmission is performed inside. Hollow waveguides 12b and 14b.
The rotation support unit 20 includes a bearing 22 and a gas seal 24 provided outside the waveguides 12 and 14, supports the relative rotation by the bearing 22, and seals the gap hermetically with the gas seal 24. A pressurized SF ₆ gas is preferably sealed in the waveguides 12 and 14, and the gas seal 24 prevents this gas from leaking from the gap 15. Note that the inside of the waveguide may be decompressed to a vacuum state.
The choke structure portion 30 is configured so that the internal space communicates from the gap 35 to the rotation support portion 20 to reduce high-frequency penetration.

FIG. 3 is an enlarged view of the conventional choke structure shown in FIG. This figure shows a case where a high-power microwave having a frequency of about 11 GHz is transmitted. Each dimension in the figure is a specific example.
As shown in this figure, the conventional choke structure 30 includes a hollow cylindrical first cavity 32 and a second cavity 34, and a seal cavity 36 that communicates from the second cavity 34 to the rotary support 20.
One end of the hollow cylindrical first cavity 32 communicates with the gap 35 and extends in the axial direction of the waveguides 12 and 14. The hollow cylindrical second cavity 34 communicates with the other end of the first cavity 32 at one end, extends in the axial direction with a cylindrical partition wall 37 outside the first cavity 32, and is closed at the other end. One end of the seal cavity 36 communicates with the outer end of the second cavity 34, and communicates with the rotation support unit 20 (not shown).

FIG. 4 is a simulation result of an electromagnetic field in the conventional choke structure shown in FIG. Here, the curve represents an equipotential line, and the circle represents the strength of the magnetic field. The larger the circle, the stronger the magnetic field. The direction of the magnetic field is a direction in which a symbol obtained by superimposing a circle on a circle is directed toward the paper surface, and a circle is directed from the paper surface.
As shown in this figure, the electric fields at points A, B, C, and D are 10, 4.2, 8.3, and 0.7 MV / m, respectively.
The energy loss at the waveguide wall surface was 278 W, and the energy loss at the choke structure was 56 W. Compared to the wall loss of the entire waveguide, the energy loss in the choke structure portion reaches about 20%, and the maximum electric field of the choke structure portion reaches about 80% of the maximum electric field at the end face of the waveguide.
Therefore, it can be seen from the simulation results in FIG. 4 that the conventional choke structure has a large energy loss and a high maximum electric field.

FIG. 5 is a cross-sectional view of the rotary joint according to the first embodiment of the present invention. The rotary joint of the present invention is used to transmit a high frequency of about 11 GHz with high power (10 MW or more) generated by a magnetron or klystron.
As shown in this figure, the rotary joint 10 of the present invention includes a pair of waveguides 12 and 14, a rotation support portion 20, and a choke structure portion 40.
The pair of waveguides 12 and 14 have end faces 12a and 14a connected in series with a certain gap 15 therebetween, and can be relatively rotated around a concentric axis ZZ. It has hollow waveguides 12b and 14b for transmitting the high frequency generated by the klystron. The rotation support unit 20 includes a bearing 22 and a gas seal 24 provided outside the waveguides 12 and 14, supports the relative rotation by the bearing 22, and seals the gap hermetically with the gas seal 24. A pressurized SF ₆ gas is preferably sealed in the waveguides 12 and 14, and the gas seal 24 prevents this gas from leaking from the gap 15. Note that the inside of the waveguide may be decompressed to a vacuum state.
The choke structure portion 40 has an internal space communicating from the gap 35 to the rotation support portion 20 so as to reduce high-frequency penetration.

  FIG. 6 is an enlarged view of the choke structure shown in FIG. 5 and a simulation result of the electromagnetic field. The numbers other than the electric field in the figure are dimensions in mm. In this example, the dimensions of the choke cavity 41 and the seal cavity 46 are set so that the magnetic field formed therein is sufficiently smaller than the discharge limit.

As shown in this figure, in the present invention, the choke structure portion 40 includes a choke cavity 41 and a seal cavity 46. The gap 15 between the waveguides 12 and 14 is located at a position where the electric field formed in the waveguide is the least sparse and the magnetic field is the maximum.
One end of the choke cavity 41 communicates with the gap 15 and has a function of reducing high-frequency penetration. In the seal cavity 46, one end 46 a communicates with a position where the electric field formed in the choke cavity 41 is dense and the magnetic field is small, and the other end communicates with the rotation support unit 20.
The choke cavity 41 includes a hollow cylindrical first cavity 42 and a second cavity 44. The hollow cylindrical first cavity 42 has one end 42 a communicating with the gap 15, extending in the axial direction of the waveguides 12, 14, and the other end 42 b extending from the gap 15 with a ¼ wavelength (about 6.5 mm). It is located at a position approximately corresponding to. The hollow cylindrical second cavity 44 communicates with the other end 42b of the first cavity 42 and one end 44a, extends in the axial direction with a cylindrical partition wall 47 outside the first cavity 42, and closes the other end 44b. ing.
One end 46a of the seal cavity 46 is located at a position facing the tip of the partition wall 47 where the electric field formed in the communication portion between the first gap 42 and the second gap 44 is the most dense and the magnetic field is the smallest.

As shown in FIG. 6, in the present invention, the maximum electric field of the choke structure is 6.9 MV / m, which is about 69% with respect to the maximum electric field in the waveguide, which is greatly reduced from the conventional about 80%. Has been. Further, the maximum electric field of the seal cavity 46 is about 0.03 MV / m, which is about 1/20 or less of the conventional 0.7 MV / m, which is significantly about 0.3% with respect to the maximum electric field in the waveguide. Has been reduced.
Therefore, it can be seen that the high frequency energy entering the rotation support portion 20 is very small (about 0.002%) with respect to the energy transmitted through the waveguide.

When FIG. 4 (conventional example) is compared with FIG. 6 (present invention), the following is further understood.
In the conventional example, it can be seen that even if the gap of the seal cavity 36 is very small (0.25 mm), high frequency leaks to the rotation support portion side. In principle, it is possible to reduce the amount of high-frequency leakage by further narrowing the gap. However, due to mechanical dimensional errors such as bearing and seal accuracy, processing accuracy, and concentricity, narrowing the gap causes local discharge.
On the other hand, in the present invention, since the seal cavity 46 connected to the rotation support portion 20 is disposed at the position where the electric field is strongest, the amount of high frequency leakage can be reduced even if the gap is wide. Therefore, the present invention has a very useful structure in that the gap between the seal cavities 46 is wide and the amount of high-frequency leakage leaking with respect to the size of the gap is not affected.

In the present invention, the right end (R portion) of the partition wall 47 is a place where the maximum electric field is generated in the choke cavity 41. Since there is a condition that the maximum electric field increases due to actual mechanical accuracy and frequency fluctuation, it is necessary to suppress the electric field generated in this part as much as possible.
When the frequency fluctuation is ± 5 MHz, the electromagnetic field intensity leaking to the rotation support portion side changes by ± 10%. Therefore, it is preferable to relax the electric field distribution state by increasing R at the right end of the partition wall 47.

  FIG. 7 is a cross-sectional view of the rotary joint according to the second embodiment of the present invention, and FIG. 8 is an enlarged view of the choke structure shown in FIG. In this figure, 13a is a seal fixing piece, 13b is a bearing nut, and 16 is a bearing fixing piece.

As shown in FIG. 8, in the present invention, the choke structure 40 includes a choke cavity 41, a seal cavity 46, and an RF contact 48.
One end of the choke cavity 41 communicates with the gap 15 and has a function of reducing high-frequency penetration. One end of the seal cavity 46 communicates with the choke cavity 41 and the other end communicates with the rotation support portion 20. The RF contact 48 is located in the seal cavity 46 and has a function of electrically conducting between the pair of waveguides 12 and 14.

  The choke cavity 41 includes a hollow cylindrical first cavity 42 and a second cavity 44. The hollow cylindrical first cavity 42 has one end communicating with the gap 15, extending in the axial direction of the waveguides 12 and 14, and the other end extending from the gap 15 to a ¼ wavelength (about 6.5 mm) of high frequency. Located in the corresponding position. The hollow cylindrical second cavity 44 has one end communicating with the other end of the first cavity 42, extending in the axial direction with a cylindrical partition wall 47 outside the first cavity 42, and the other end closed.

In the embodiment of FIG. 8, the RF contact 48 is a conductive ring member that contacts the pair of waveguides 12, 14 and is centered on the waveguide axis. This conductive ring member is, for example, a copper circular spring that has good conductivity and does not interfere with rotation.
The RF contact 48 is not limited as long as the pair of waveguides 12 and 14 can rotate relative to each other about the axis ZZ and electrically conduct between the waveguides 12 and 14. For example, it may be a metal O-ring or slip ring that is electrically conductive and slides smoothly with at least one of the waveguides.

  With the above-described configuration, the electric field generated by the high frequency between the waveguides 12 and 14 can be zeroed by the RF contact 48 at the conduction portion. The high-frequency leakage in the choke structure is caused by the induction of electromagnetic waves in the internal space (seal cavity) that communicates with the rotation support part. Therefore, RF that electrically conducts between the waveguides in the seal cavity. By providing the contact, it is possible to suppress the generation of the electric field at that portion by the RF contact, and to suppress the induction of the electromagnetic field to the back of the RF contact.

  In addition, this invention is not limited to the Example and embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a related figure of the clearance gap disclosed by the nonpatent literature 1, and alternating current discharge voltage. It is typical sectional drawing of the conventional rotary joint. It is an enlarged view of the conventional chalk structure part. It is a simulation result of the electromagnetic field in the conventional choke structure part. It is sectional drawing of the rotary joint of 1st Embodiment of this invention. It is the enlarged view of the choke structure part of this invention, and the simulation result of an electromagnetic field. It is sectional drawing of the rotary joint of 2nd Embodiment of this invention. It is an enlarged view of the chalk structure part of this invention. 1 is an overall schematic diagram of a “radiation therapy apparatus” in Patent Document 1. FIG. 10 is an explanatory diagram of a “rotary RF coupler” in Patent Document 1. FIG.

Explanation of symbols

1 Rotary joint, 12, 14 Waveguide,
12a, 14a end face, 12b, 14b waveguide,
15 clearance, 20 rotation support, 22 bearing, 24 gas seal,
30 choke structure, 32 first cavity, 34 second cavity,
36 seal cavity, 37 partition,
40 choke structure, 41 choke cavity, 42 first cavity,
42a one end, 42b the other end,
44 second cavity, 44a one end, 44b other end,
46 seal cavity, 46a one end, 47 partition,
48 RF contact

Claims (11)

A pair of waveguides whose end faces are connected in series with a certain gap, are rotatable relative to each other about a concentric axis, and have hollow waveguides for high-frequency transmission inside;
A rotary support for high-frequency transmission provided with a rotation support provided outside the waveguide and supporting the relative rotation and hermetically sealing the gap,
Has a choke structure section inner space to the rotating support is communicated through the gap, the choke structure includes a choke cavity end to the gap to reduce the penetration of the high frequency communication, one end of said choke cavity communicating and, Ri Do from the seal cavity and the other end communicates to the rotating support,
The choke cavity is
A hollow cylindrical first cavity having one end communicating with the gap, extending in the axial direction of the waveguide, and the other end being located at a position substantially corresponding to a quarter wavelength of the high frequency from the gap;
The other end and one end of the first cavity communicate with each other, a hollow cylindrical second cavity that extends in the axial direction with a cylindrical partition wall outside the first cavity and has the other end closed,
One end of the seal cavity is connected to the choke cavity at a position facing the tip of the partition wall . A pair of waveguides whose end faces are connected in series with a certain gap, are rotatable relative to each other about a concentric axis, and have hollow waveguides for high-frequency transmission inside;
A rotary support for high-frequency transmission provided with a rotation support provided outside the waveguide and supporting the relative rotation and hermetically sealing the gap,
It has a choke structure portion in which an internal space communicates from the gap to the rotation support portion,
A choke cavity that communicates at one end with the gap and reduces the penetration of the high frequency;
A seal cavity having one end communicating with the choke cavity and the other end communicating with the rotation support portion;
A rotary joint for high-frequency transmission, characterized by comprising an RF contact located in the seal cavity and electrically conducting between the pair of waveguides. The choke cavity has a hollow cylindrical first cavity in which one end communicates with the gap, extends in the axial direction of the waveguide, and the other end is located at a position substantially corresponding to a quarter wavelength of the high frequency from the gap. When,
The other end and one end of the first cavity communicate with each other, and a hollow cylindrical second cavity that extends in the axial direction with a cylindrical partition wall outside the first cavity and has the other end closed. The rotary joint for high frequency transmission according to claim 2 . 4. The rotary joint for high frequency transmission according to claim 3, wherein one end of the seal cavity is located at a position where the magnetic field formed in the communication portion between the first cavity and the second cavity is the weakest or in the vicinity thereof.   The high-frequency transmission rotary joint according to claim 1, wherein the gap between the waveguides is located at or near a position where an electric field formed in the waveguide is the weakest.   The rotary joint for high-frequency transmission according to claim 1, wherein the choke cavity and the seal cavity are dimensioned so that a magnetic field formed therein is sufficiently smaller than a discharge limit.   The high-frequency transmission rotary joint according to claim 2, wherein the RF contact is a conductive ring member that contacts the pair of waveguides and is centered on an axis of the waveguide.   The high-frequency transmission rotary joint according to claim 2, wherein the RF contact is a copper circular spring that has good conductivity and does not interfere with rotation.   The rotary joint for high frequency transmission according to claim 1 or 2, wherein a pressurized SF6 gas is sealed in the waveguide.   The rotary joint for high-frequency transmission according to claim 1 or 2, wherein the inside of the waveguide is decompressed to a vacuum state.   The rotary joint for high frequency transmission according to claim 1, wherein the high frequency is a high power microwave having a frequency of 2 GHz or more.

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