Superconducting accelerating cavity and electropolishing method for superconducting accelerating cavity

Provided is a superconducting accelerating cavity 30 including: a cavity main body 10 formed of a superconducting material into a cylindrical shape; and a refrigerant tank 20 installed around the cavity main body 10 and storing a refrigerant which is supplied from the outside through a supply port 20a into a space formed between the refrigerant tank and the outer circumferential surface of the cavity main body 10, wherein the outer circumferential surface of the cavity main body 10 is coated with a metal coating layer 10a having a higher conductivity than the superconducting material.

TECHNICAL FIELD

The present invention relates to a superconducting accelerating cavity and an electropolishing method for a superconducting accelerating cavity.

BACKGROUND ART

A superconducting accelerating cavity is a device for accelerating charged particles such as electrons, positrons, and protons by means of an accelerating electric field generated inside the cavity by an input of high-frequency power. When the inner surface of the main body of the superconducting accelerating cavity is not smooth, or when impurities are present on the inner surface of the main body, heat generation or electrical discharge is induced, which degrades the performance of accelerating the charged particles.

It is a known practice to perform electropolishing in order to smooth the inner surface of the main body of the superconducting accelerating cavity and remove impurities from the inner surface (e.g., see PTL 1). Eiectropolishing of the superconducting accelerating cavity is performed with an electrode installed on each of the inside of the cavity main body and the outer surface of the cavity main body, while the cavity main body is filled with an electrolyte.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

After electropolishing is performed, a refrigerant tank which stores a refrigerant such as liquid helium for cooling the superconducting accelerating cavity is installed around the main body of the superconducting accelerating cavity. In order to prevent leakage of the refrigerant, etc, this refrigerant tank is installed by firmly joining multiple members by welding, etc., which are arranged so as to cover the circumference of the superconducting accelerating cavity, (e.g., see PTL 2).

The inner surface of the superconducting accelerating cavity after being electropolished is smooth and free of impurities. However, there is a possibility of foreign substances such as dirt entering into the main body of the superconducting accelerating cavity during mounting of an inlet pipe, through which charged particles from the outside are guided, and an outlet pipe, which guides the charged particles to the outside, to the main body of the superconducting accelerating cavity. Once foreign substances such as dirt enter into the main body of the superconducting accelerating cavity, heat generation or electrical discharge is induced, which degrades the performance of the superconducting accelerating cavity. This performance degradation problem can be solved by performing electropolishing again to smooth the inner surface of the main body of the superconducting accelerating cavity.

There is a problem, however/that due to the difficulty of installing electrodes at arbitrary positions on the outer surface of the cavity main body after the refrigerant tank is installed around the main body of the superconducting accelerating cavity, the degree of polishing of electropolishing becomes non-uniform depending on the presence or absence of contact with (contact state of) the electrode. Thus, it is not easy, after installation of the refrigerant tank around the main body of the superconducting accelerating cavity, to electropolish the main body of the superconducting accelerating cavity again to a uniform, degree without removing the refrigerant tank.

Having been made in view of these circumstances, the present invention has an object to provide a superconducting accelerating cavity which can be easily electro-polished again even after installation of a refrigerant tank, and an electropolishing method for a superconducting accelerating cavity.

Solution to Problem

To achieve the above object, the present invention has adopted the following solutions:

The superconducting accelerating cavity according to the present invention includes: a cavity main body formed of a superconducting material into a cylindrical shape; and a refrigerant tank installed around the cavity main body and storing a refrigerant which is supplied from the outside through a supply port into a space created between the refrigerant tank and the outer circumferential surface of the cavity main body, wherein the outer circumferential surface of the cavity main body is coated with a metal material having a higher conductivity than the superconducting material.

In the superconducting accelerating cavity according to the present invention, the refrigerant tank is installed around the cavity main body which is formed of a superconducting material into a cylindrical shape. This refrigerant tank is provided with the supply port through which a refrigerant is supplied from the outside, and anode parts connected to a positive pole of a power source can be inserted into the refrigerant tank through the supply port. Since the outer circumferential surface of the cavity main body is coated with a metal material having a higher conductivity than the superconducting material, bringing the anode parts inserted inside the refrigerant tank into contact with the outer circumferential surface of the cavity main body allows the cavity main body to be uniformly anodized for electropolishing.

Then, a cathode part connected to a negative pole of the power source is inserted inside the cavity main body and the electrolyte is supplied into the cavity main body, so that the inner surface of the cavity main body can be electropolished.

Thus, according to the superconducting accelerating cavity of the present invention, it is possible to provide a superconducting accelerating cavity which can be easily electropolished again even after installation of the refrigerant tank.

In a superconducting accelerating cavity of a first aspect of the present invention, the cavity main body has a shape formed by large diameter portions and small diameter portions, which are at a shorter distance to the central axis of the cavity main body than the large diameter portions, being alternately formed along the axial direction, and the position of the supply port in the axial direction corresponds to the position of the large diameter portion in the axial direction.

In this way, the anode parts which are inserted from the supply port can foe easily brought into contact with the large diameter portion of the cavity main body which is disposed at the position close to the supply port of the refrigerant tank.

In a superconducting accelerating cavity of a second aspect of the present invention, the cavity main body has a shape formed by large diameter portions and small diameter portions, which are at a shorter distance to the central axis of the cavity main body than the large diameter portions, being alternately formed along the axial direction, and the coating thickness of the metal material in the large diameter portions is larger than the coating thickness of the metal material in the small diameter portions.

In this way, current can flow more easily in the large diameter portions which are farther away from the central axis of the cavity main body, in which the cathode is disposed during electropolishing, than in the small diameter portions which are closer to the central axis. Thus, the defect of the degree of polishing of electropolishing becoming non-uniform on the inner surface of the cavity main body can be suppressed.

In the superconducting accelerating cavity of the second aspect of the present invention, the ratio between the distance to the central axis of the large diameter portions and the distance to the central axis of the small, diameter portions/and the ratio between the coating thickness in the large diameter portions and the coating thickness in the small diameter portions may substantially correspond to each other.

In this way, the coating thickness in the large diameter portions and the coating thickness in the small diameter portions of the cavity main body can be adjusted to a proper coating thickness according to the distance from the central axis of the cavity main body in which the cathode is disposed during electropolishing.

An electropolishing method for a superconducting accelerating cavity of the present invention is an electropolishing method for a superconducting accelerating cavity which includes: a cavity main body formed of a superconducting material into a cylindrical shape; and a refrigerant tank installed around the cavity main body and storing a refrigerant which is supplied from the outside through a supply port into a space created between the refrigerant tank and the outer circumferential surface of the cavity main body, the outer circumferential surface of the cavity main body being coated with a metal material having a higher conductivity than the superconducting material, wherein the electropolishing method includes: inserting an anode part which is connected to a positive pole of a power source through the supply port and bringing the anode part into contact with the outer circumferential surface of the cavity main body; inserting a cathode part which is connected to a negative pole of the power source into the cavity main body; supplying an electrolyte into the cavity main body; and starting energization by the power source and electropolishing the inner surface of the cavity main body.

According to the electropolishing method of the present invention, since the outer circumferential surface of the cavity main body is coated with a metal material having a higher conductivity than the superconducting material, bringing the anode part into contact with the outer circumferential surface of the cavity main body by the anode installation step allows the cavity main body to be uniformly anodized for electropolishing.

Then, the cathode part connected to the negative pole of the power source is inserted inside the cavity main body by the cathode installation step and the electrolyte is supplied into the cavity main body by the supply step, so that the inner surface of the cavity main body can be electropolished.

Thus, according to the electropolishing method for a superconducting accelerating cavity of the present invention, it is possible to provide an electropolishing method for a superconducting accelerating cavity by which electropolishing can be easily performed again even after installation of the refrigerant tank.

In an electropolishing method for a superconducting accelerating cavity of a first aspect of the present invention, the cavity main body has a shape formed by large diameter portions and small diameter portions, which are at a shorter distance to the central axis of the cavity main body than the large diameter portions, being alternately formed along the axial direction, and the position of the supply port in the axial direction corresponds to the position of the large diameter portion in the axial direction.

In this way, the anode part which is inserted from the supply port can be easily brought into contact with the large diameter portion of the cavity main body which is disposed at the position close to the supply port of the refrigerant tank.

In an electropolishing method for a superconducting accelerating cavity of a second aspect of the present invention, the cavity main body has a shape formed by large diameter portions and small diameter portions, which are at a shorter distance to the central axis of the cavity main body than the large diameter portions, being alternately formed along the axial direction, and the coating thickness of the metal material in the large diameter portions is larger than the coating thickness of the metal material in the small diameter portions.

In this way, current can flow more easily in the large diameter portions which are farther away from the central axis of the cavity main body, in which the cathode is disposed during electropolishing, than in the small diameter portions which are closer to the central axis. Thus, the defect of the degree of polishing of electropolishing becoming non-uniform on the inner surface of the cavity main body can be suppressed.

In an electropolishing method for a superconducting accelerating cavity of a third aspect of the present invention, the ratio between the distance to the central axis of the large diameter portions and the distance to the central axis of the small diameter portions, and the ratio between the coating thickness in the large diameter portions and the coating thickness in the small diameter portions may substantially correspond to each other.

In this way, the coating thickness in the large diameter portions and the coating thickness in the small diameter portions of the cavity main body can be adjusted to a proper coating thickness according to the distance from the central axis of the cavity main body in which the cathode is disposed during electropolishing.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a superconducting accelerating cavity which can be easily electropolished again even after installation of a refrigerant tank, and an electropolishing method for a superconducting accelerating cavity.

DESCRIPTION OF EMBODIMENTS

First Embodiment

In the following, a superconducting accelerator100of a first embodiment of the present invention will be described by usingFIG. 1.FIG. 1is a longitudinal cross-sectional view showing the configuration of the superconducting accelerator of the first embodiment of the present invention.

InFIG. 1, the superconducting accelerator100includes a superconducting accelerating cavity30, and a vacuum vessel90housing the superconducting accelerating cavity30. The superconducting accelerating cavity30includes a cavity main body10formed of a superconducting material such as niobium (Nb) into a cylindrical shape, and a refrigerant tank20installed around the cavity main body10. The refrigerant tank20stores a refrigerant which is supplied from the outside through a supply port20ainto a space created between the refrigerant tank and the outer circumferential surface of the cavity main body10. As the refrigerant, for example, liquid helium is used.

The outer circumferential surface of the cavity main body10is coated with a metal material having a higher conductivity than the superconducting material. This coated part forms a metal coating layer10a. As the metal material having a high conductivity, for example, copper, gold, silver, or aluminum is used. The reason for coating the outer circumferential surface of the cavity main body10with a metal material having a high conductivity is, as described later, to make the cavity main body10function as an anode during electropolishing. In this embodiment, the coating thickness of the metal coating layer10ashall be substantially constant regardless of the position in the direction of the central axis of the cavity main body10. A constant coating thickness of the metal coating layer10aallows a substantially constant potential to be applied to the entire cavity main body10.

The cavity main body10have equatorial portions (large diameter portions)10d,10e,10f, and10gat a distance R1 from a central axis A. In addition, the cavity main body10have iris portions (small diameter portions)10h,10i, and10jat a distance R2 from the central axis A. As shown inFIG. 1, the distance R2 to the central axis A of the iris portions10h,10i, and10jis shorter than the distance R1 to the central axis A of the equatorial portions10d,10e,10f, and10g. As shown inFIG. 1, the cavity main body10has a shape formed, by the equatorial portions10d,10e,10f, and10g, and the iris portions10h,10i, and10jbeing alternately formed along the direction of the central axis A.

Since the refrigerant is stored in the refrigerant tank20, the refrigerant tank20and the cavity main body10are firmly joined by welding, etc. at areas contacting with each other. Due to such a structure, it is difficult to remove the refrigerant tank20from the cavity main body10after the refrigerant tank20is joined to the cavity main body10.

The supply port20ais connected with a supply pipe40which supplies the refrigerant. The supply pipe40is a pipe for supplying the refrigerant, which is supplied from an external refrigerant tank (not shown), to the supply port20a. Liquid helium supplied from the supply pipe40and stored in the refrigerant tank20is used for cooling the cavity main body10to an ultralow temperature and keep the cavity main body in a superconducting state.

Part of the liquid helium stored in the refrigerant tank20absorbs the heat generated in the cavity main body10and is gasified into a helium gas. The helium gas is discharged from a discharge port20bto the outside of the superconducting accelerating cavity30, and is discharged to the outside of the superconducting accelerator100through a discharge pipe50. The helium gas discharged to the outside is reliquefied by being compressed by a compressor (not shown.) and returned to the refrigerant tank.

The position of the supply port20aof the refrigerant tank20in the direction of the central axis A corresponds to the position of the equatorial portion10d. In addition, the position of the discharge port20bof the refrigerant tank20corresponds to the position of the equatorial portion10g. The reason for this arrangement is, as described later, to make it easier to bring anode parts230and240to be inserted from the supply port20aand the discharge port20binto contact with the metal coating layer10aformed on the outer circumferential surface of the cavity main body10when the cavity main body10is made to function as an anode for electropolishing.

The cavity main body10is provided with an inlet part10cand an outlet part10b, which are openings, at both ends in the direction of the central axis. The inlet part10cis connected with an inlet pipe70through which charged particles from the outside are guided, and the inlet part10cguides the charged particles guided through the inlet pipe70to the cavity main body10. The outlet part10bis connected with an outlet pipe80which guides the charged particles to the outside, and the outlet part10bguides the charged particles accelerated in the cavity main body10to the outlet pipe80.

A waveguide60, which is provided so as to foe connected with the outlet part10bof the cavity main body10, is a pipe for introducing high-frequency power generated by a high frequency source (not shown) such as a klystron into the cavity main body10. When high-frequency power is input from the outside through the waveguide60, a positive electrode and a negative electrode are generated on the inner surface of the cavity main body10, and an accelerating electric field for accelerating the charged particles is produced.

The superconducting accelerating cavity30is disposed inside the vacuum vessel90. The inside of the vacuum vessel90is maintained in a substantially vacuum state by a vacuum device (not shown), and the vacuum vessel90prevents external heat from transferring to the superconducting accelerating cavity30.

Next, an electropolishing device200of this embodiment will be described by usingFIG. 2.FIG. 2is a longitudinal cross-sectional view showing the superconducting accelerating cavity30and the electropolishing device200of this embodiment. The electropolishing device200is constituted of the parts excluding the superconducting accelerating cavity30shown in the configuration ofFIG. 2. InFIG. 2, a pair of rotation holding tools300which is shown inFIG. 7and described later is not shown.

The electropolishing device200includes: an electrolyte supply device210which circulates the electrolyte inside the cavity main body10; a cathode part220disposed inside the cavity main body10; the anode part230inserted in the supply port20aof the refrigerant tank20; and the anode part240inserted in the discharge port20bof the refrigerant tank20. The cathode part220is connected to the negative pole of the power source250, while the anode parts230and240are connected to the positive pole of the power source250. The current supply from the power source250to each electrode can be switched on and off by the switch260.

Caps270and271for preventing leakage of the electrolyte are attached to the respective ends of the cavity main body10. The cathode part220, which is a hollow cylindrical member, is supported by the cap270and the cap271at both ends so as to be disposed coaxially with the central axis of the cavity main body10. Actuating a pump280causes the electrolyte inside a tank290to be supplied into the cathode part220through the cap270. As the electrolyte, various electrolytes can be used; for example, hydrogen fluoride, sulfuric acid, etc. are used.

The cathode part220which is a hollow cylindrical member is provided with multiple openings220a. The electrolyte flowing inside the cathode part220flows out through the multiple openings220ainto the cavity main body10, and the electrolyte is supplied into the cavity main body10. The electrolyte which flows inside the cathode part220without flowing out through the openings220ais returned via the cap271to the tank290.

The anode part230is constituted of a cable connection part231, a rod part232, a contact part233, and a cap234, Each member constituting the anode part230is constituted of a metal having a high conductivity such as copper. Each member constituting the anode part230is substantially at the same potential as the positive pole of the power source250.

A cable coupled with the positive pole of the power source250is connected to the cable connection part231. The cable connection part231is coupled with the rod part232, and the rod part232is coupled with the contact part233. The rod part232is a rod-like member with a male thread formed on the outer circumferential surface, and is engaged with a female thread formed on the inner circumferential surface of a hole provided at the center part of the cap234. The cap234is fastened with a bolt to a flange which is provided at the supply port20aof the refrigerant tank20.

Rotating the cable connection part231coupled with the rod part232causes the rod part232to move in the axial direction of the rod part232relative to the cap234. In accordance with this movement, the contact part233coupled with the leading end of the rod part232is moved closer to or away from the metal coating layer10aprovided on the outer circumferential surface of the equatorial portion10dof the cavity main body10.

Fastening the cap234with a bolt to the flange provided at the supply port20aof the refrigerant tank20and rotating the cable connection part231can bring the contact part233gradually closer to the metal coating layer10a. The contact part233is adjusted so as to come into contact with the metal coating layer10aprovided on the outer circumferential surface of the equatorial portion10dof the cavity main body10. In this way, the positive pole of the power source250and the metal coating layer10aare electrically connected, so that the metal coating layer10afunctions as an anode for electropolishing.

The anode part240is constituted of a cable connection part241, a rod part242, a contact part243, and a cap244. Each member constituting the anode part240is constituted of a metal having a high conductivity such as copper. Each member constituting the anode part240is substantially at the same potential as the positive pole of the power source250.

A cable coupled with the positive pole of the power source250is connected to the cable connection part241. The cable connection part241is coupled with the rod part242, and the rod part242is coupled with the contact part243. The rod part242is a rod-like member with a male thread formed on the outer circumferential surface, and is engaged with a female thread formed on the inner circumferential surface of a hole provided at the center part of the cap244. The cap244is fastened with a bolt to a flange provided at the discharge port20bof the refrigerant tank20.

Rotating the cable connection part241coupled with the rod part242causes the rod part242to move in the axial direction of the rod part242relative to the cap244. In accordance with this movement, the contact part243coupled with the leading end of the rod part242is moved closer to or away from the metal coating layer10aprovided on the outer circumferential surface of the equatorial portion10gof the cavity main body10.

Fastening the cap244with a bolt to the flange provided at the discharge port20bof the refrigerant tank20and rotating the cable connection part241can bring the contact part243gradually closer to the metal coating layer10a. The contact part243is adjusted so as to come into contact with the metal coating layer10aprovided on the outer circumferential surface of the equatorial portion10gof the cavity main body10. In this way, the positive pole of the power source250and the metal coating layer10aare electrically connected, so that the metal coating layer10afunctions as an anode for electropolishing.

As shown inFIG. 7, the electropolishing device200includes the pair of rotation holding tools300which rotatably holds the superconducting accelerating cavity30around the central axis A, and a rotation device (not shown) which rotates the superconducting accelerating cavity30, which is held by the rotation holding tools300, around the central axis A.FIG. 7is a cross-sectional view along the arrow A-A of the superconducting accelerating cavity30and the electropolishing device200shown inFIG. 2.

The rotation holding tool300includes an annular rail part310disposed in a plane perpendicular to the central axis A, and support parts320and330supporting the rail part310against a ground surface G. The support parts320and330fix the rail part310relative to the ground surface G. AlthoughFIG. 7shows the rotation holding tool300which is present at the position of the anode part230, the other rotation holding tool300is present at the position of the anode part240.

Thus, the superconducting accelerating cavity30is held relative to the ground surface G by the pair of rotation holding tools300disposed at the position of the anode part230and the position of the anode part240. The superconducting accelerating cavity30held by the pair of rotation holding tools300is rotated around the central axis A by the rotation device (not shown).

The rotation device includes a motor (not shown) which rotates a gear coupled with another gear (not shown) provided on the outer circumferential surface of the superconducting accelerating cavity30. Rotating the motor causes the superconducting accelerating cavity30to rotate around the central axis A.

The cable connection part231of the anode part230is a rotating member which rotates while being engaged with the rail part310. In addition, the cable connection part231is electrically connected with the positive pole of the power source250, which is connected to the outer circumferential surface of the rail part310, through the conductive rail part310.

Thus, rotating the superconducting accelerating cavity30allows the electrolyte to spread over the entire inner surface of the cavity main body10, so that the inner surface is uniformly electropolished.

Next, an electropolishing method of this embodiment will be described by usingFIG. 3.FIG. 3is a flowchart showing the electropolishing method for the superconducting accelerating cavity30of this embodiment. The electropolishing method of this embodiment is performed in such a case where, after the superconducting accelerating cavity30is integrated into the superconducting accelerator100shown inFIG. 1and the superconducting accelerator100is operated, inclusion of foreign substances inside the superconducting accelerating cavity30is suspected as a result of a measurement.

The superconducting accelerating cavity30is supposed to be removed to the outside of the vacuum vessel90from the superconducting accelerator100shown inFIG. 1before the electropolishing method of this embodiment is performed.

Step S301is an anode installation step of installing the anode part230in the supply port20aof the refrigerant tank20and installing the anode part240in the discharge port20bof the refrigerant tank20. The anode part230is installed in the supply port20a, and the cable connection part231is rotated to adjust the position of the contact part233, and the contact part233is brought into contact with the metal coating layer10aof the cavity main body10. In the same way, the anode part240is installed in the discharge port20b, and the cable connection part241is rotated to adjust the position of the contact part243, and the contact part243is brought into contact with the metal coating layer10aof the cavity main body10.

Thus, the anode installation step S301is a step of inserting the anode part230, which is connected to the positive pole of the power source250, from the supply port20aand bringing the anode part230into contact with the metal coating layer10aon the outer circumferential surface of the cavity main body10. In addition, the anode installation step3301is a step of inserting the anode part240, which is connected to the positive pole of the power source250, from the discharge port20band bringing the anode part240into contact with the metal coating layer10aon the outer circumferential surface of the cavity main body10. Performing the anode installation step S301causes the positive pole of the power source250and the metal coating layer10ato be electrically connected, so that the metal coating layer10afunctions as an anode for electropolishing.

Step S302is a cathode installation step of installing the cathode part220coaxially with the central axis of the cavity main body10. The cathode part220is inserted into the cavity main body10, and the cap270is installed at the outlet part10bof the cavity main body10, while the cap271is installed at the inlet part10cof the cavity main body10, and thereby the cathode part220is installed coaxially with the central axis of the cavity main body10. After the cathode part220is installed, the caps270and271are connected with the pipe of the electrolyte supply device210so that the electrolyte can be supplied by the electrolyte supply device210. In addition, the negative pole of the power source250and the cathode part220are electrically connected so that the cathode functions as a cathode for electropolishing.

Step S303is an electrolyte supply step of supplying the electrolyte into the cavity main body10. The pump280of the electrolyte supply device210is driven and the electrolyte inside the tank290is supplied to the cathode part220, and thereby the electrolyte is supplied through the openings220ainto the cavity main body10. When the amount of electrolyte supplied into the cavity main body10has reached a predetermined amount, driving of the pump280is stopped to stop the electrolyte supply to the cavity main body10.

Step S304is an electropolishing step of electropolishing the cavity main body10in which the anode parts230and240and the cathode part220are installed and the electrolyte is supplied to the inside. In step S304, the switch260is switched, from the off state to the on state. Switching the switch260to the on state brings the anode parts230and240to the same potential as the positive pole of the power source250, and the cathode part220to the same potential as the negative pole of the power source250, turning the cathode part into a cathode.

Since the anode parts230and240are in contact with the metal coating layer10aon the outer circumferential surface of the cavity main body10, the entire metal coating layer10afunctions as an anode. Since the cathode part220is constituted of a conductive metal material over the entire length in the axial direction, the cathode part220functions as a cathode over the entire length in the axial direction. Thus, current flows through the electrolyte between the cathode part220and the inner circumferential surface of the cavity main body10over the entire length of the cathode part220in the axial direction, causing electrolysis of the electrolyte. The inner circumferential surface of the cavity main body10is polished due to this electrolysis.

While the electropolishing step S304is in progress, the superconducting accelerating cavity30is kept rotating around the axis by the rotation device. Rotating the superconducting accelerating cavity30allows the electrolyte to spread over the entire inner surface of the cavity main body10, so that the inner surface is uniformly electropolished. The amount of polishing achieved in the electropolishing step S304can be adjusted by adjusting the output voltage of the power source250or the time of electropolishing, and the amount of polishing is, for example, set to approximately 100 μm.

Step S305is an aftertreatment step which is performed after the electropolishing step S304. The aftertreatment step includes treatment of discharging the electrolyte remaining inside the cavity main body10to the outside, and cleaning treatment of cleaning the inner circumferential surface of the cavity main body10with hydrogen peroxide water or ultrapure water. In addition, the aftertreatment step S305includes treatment of removing the anode parts230and240and the cathode part220from the superconducting accelerating cavity30.

After the aftertreatment step S305, the electropolished superconducting accelerating cavity30is installed back into the vacuum vessel90to make the superconducting accelerator100usable again.

Next, a modified example of the anode parts230and240will be described by usingFIG. 4.FIG. 4is a view showing the modified example of the anode part installed in the refrigerant tank20, and is an enlarged view of the cross-section of the superconducting accelerating cavity30viewed from the front side. The anode parts230and240described above are adapted such that the positions of the contact parts233and243are adjusted by means of the male thread provided on the outer circumferential surfaces of the rod parts232and242. In contrast, an anode part400shown inFIG. 4is adapted such that the position of a contact part403is adjusted by means of the elastic force of a coil spring404.

As shown inFIG. 4, the anode part400of the modified example is constituted of a cable connection part401, a cap402, a contact part403, the coil spring404, and a metal spring405. Each member constituting the anode part400is constituted of a highly conductive metal such as copper. Each member constituting the anode part400is substantially at the same potential as the positive pole of the power source250.

A cable coupled with the positive pole of the power source250is connected to the cable connection part401. The cable connection part401is coupled with the cap402. The cap402is fastened with a bolt to the flange provided at the supply port20aor the discharge port20bof the refrigerant tank20. The cap402is provided with a cylindrical portion, and the coil spring104having substantially the same diameter as the inner diameter of this cylindrical portion is inserted into the cylindrical portion.

The cylindrical contact part403having a larger inner diameter than the outer diameter of the cylindrical portion of the cap402is disposed around the cylindrical portion. A biasing force in the direction of bringing the contact part403into contact with the metal coating layer10aof the cavity main body10is applied to the contact part403by the coil spring404which is inserted in the cylindrical portion of the cap402.

A metal spring405is provided between the outer circumferential surface of the cylindrical portion of the cap402and the inner circumferential surface of the contact part403. The metal spring405allows the outer circumferential surface of the cylindrical portion of the cap402and the inner circumferential surface of the contact part403to be electrically connected with each other and reliably energized. The biasing force applied by the coil spring404causes the contact part403to be disposed in contact with the metal coating layer10aof the cavity main body10. Thus, the positive pole of the power source250and the metal coating layer10aare electrically connected, so that the metal coating layer10afunctions as an anode for electropolishing.

Next, another modified example of the anode parts230and240will be described by usingFIG. 5.FIG. 5is a view showing the another modified example of the anode part installed in the refrigerant tank20, and is an enlarged view of the cross-section of the superconducting accelerating cavity30viewed from the side surface (in the direction of the central axis). Description of the anode part230shown inFIG. 5, which is the same as the anode part230described inFIG. 2, will be omitted.FIG. 5differs fromFIG. 2in that a contact point member235is added.

The contact point member235is provided at the leading end of the contact part233, and is a member for improving the electrical contact between the contact part233and the metal coating layer10a. As the contact point member235, various materials, such as plain-knitted copper wire or a copper leaf spring, etc., which can enhance electrical contact can be used. The provision of the contact point member235makes it possible to improve the electrical contact between the contact part233and the metal coating layer10aso that the metal coating layer10acan more reliably function as an anode for electropolishing.

The contact point member235may also be provided at the leading end of the contact part403of the anode part400of the above-described modified example.

As has been described above, in the superconducting accelerating cavity30of this embodiment, the outer circumferential surface of the cavity main body10is coated, with the metal coating layer10ahaving a higher conductivity than the superconducting material. Thus, according to the electropolishing method for the superconducting accelerating cavity30of this embodiment, bringing the anode parts230and240into contact with the outer circumferential surface of the cavity main body10by the anode installation step S301allows the cavity main body10to be uniformly anodized for electropolishing.

Then, the cathode part220which is connected to the negative pole of the power source250is inserted into the cavity main body10by the cathode installation step S301, and the electrolyte is supplied into the cavity main body10by the electrolyte supply step S303, so that the inner circumferential surface of the cavity main body10can be electropolished.

Thus, according to the electropolishing method for the superconducting accelerating cavity30of this embodiment, it is possible to provide an electropolishing method for a superconducting accelerating cavity by which electropolishing can be easily performed again even after installation of the refrigerant tank20.

The superconducting accelerating cavity30of this embodiment has a shape formed by the equatorial portions (large diameter portions)10d,10e,10f, and10g, and the iris portions (small diameter portions)10h,10i, and10j, which are at a shorter distance to the central axis A than the equatorial portions10d,10e,10f, and10g, being alternately formed along the axial direction. In addition, the position of the refrigerant supply port20ain the axial direction corresponds to the position of the equatorial portion10din the axial direction. Moreover, the position of the refrigerant discharge port20bin the axial direction corresponds to the position of the equatorial portion10gin the axial direction.

In this way, the anode part230inserted from the supply port20acan be easily brought into contact with the equatorial portion10dof the cavity main body10which is disposed at the position close to the supply port20aof the refrigerant tank20. In addition, the anode part240inserted from the discharge port20bcan be easily brought into contact with the equatorial portion10gof the cavity main body10disposed at the position close to the discharge port20bof the refrigerant tank20.

Second Embodiment

In the following, a cavity main body600of a superconducting accelerator of a second embodiment will be described by usingFIG. 6.FIG. 6is a view showing the cavity main body600of a superconducting accelerating cavity of the second embodiment of the present invention. Although the refrigerant tank is provided around the cavity main body600, the refrigerant tank is not shown inFIG. 6.

The second embodiment is a modified example of the first embodiment; unless otherwise described in the following, the second, embodiment is the same as the first embodiment, and description thereof will be omitted.

The coating thickness of the metal coating layer10aof the first embodiment is substantially constant regardless of the position in the direction of the central axis of the cavity main body10. In contrast, the coating thickness of a metal coaxing layer600aof the second embodiment varies depending on the position in the direction of the central axis A of the cavity main body600.

The cavity main body600shown inFIG. 6includes equatorial portions (large diameter portions)600d,600e,600f, and600gat a distance R3 from the central axis A. In addition, the cavity main body600includes iris portions (small diameter portions)600h,600i, and600jat a distance R4 from the central axis A. As shown inFIG. 6, the distance R4 to the central axis A of the iris portions600h,600i, and600jis shorter than the distance R3 to the central axis A of the equatorial portions600d,600e,600f, and600g. As shown inFIG. 6, the cavity main body600has a shape formed, by the equatorial portions600d,600e,600f, and600g, and the iris portions600h,600i, and600jbeing alternately formed along the direction of the central axis A.

The outer circumferential surface of the cavity main body600is coated with a metal material having a higher conductivity than the super conducting material. This coated part forms the metal coating layer600a. As the metal material having a high conductivity, for example, copper, gold, silver, or aluminum is used. The reason for coating the outer circumferential surface of the cavity main body600with a metal material having a high conductivity is to make the cavity main body600function as an anode during electropolishing.

As shown inFIG. 6, the coating thickness of the metal coating layer600avaries depending on the position in the direction of the central axis A of the cavity main body600. More specifically, the metal coating layer600ahas a coating thickness T2 in the equatorial portions (large diameter portions)600d,600e,600f, and600g. On the other hand, the metal coating layer600ahas a coating thickness T1 in the iris portions (small diameter portions)600h,600i, and600j. The coating thickness T2 is larger than the coating thickness T1. The coating thickness of the metal coating layer600abetween the iris portions adjacent to the equatorial portion has a shape gradually decreasing in coating thickness from the equatorial portion toward the iris portions.

An outlet part600band an inlet part600cof the cavity main body600are cylindrical openings. As shown inFIG. 6, the diameter of the inner circumferential surface of the outlet part600band the inlet part600ccorresponds to the diameter of the inner circumferential surface of the iris portions600h,600i, and600j, and the each of the diameters is D1. On the other hand, the diameter of the inner circumferential surface of the equatorial portions600a,600e,600f, and600gis D2.

The ratio between the distance R3 to the central axis A of the inner circumferential surface of the equatorial portions and the distance R4 to the central axis A of the inner circumferential surface of the iris portions, and the ratio between the coating thickness T2 of the metal coating layer600ain the equatorial portions and the coating thickness T1 of the metal coating layer600ain the iris portions correspond to each other as expressed by the following equation (1), or substantially correspond to each other.
R4/R3−T1/T2  (1)

The reason for thus making the coating thickness of the metal coating layer600athicker in the equatorial portions and making the coating thickness of the metal coating layer600athinner in the iris portions is to substantially equalize the amount of polishing of the inner circumferential surface of the cavity main body600by electropolishing between the iris portions and the equatorial portions. As shown inFIG. 2, the cathode is installed inside the cavity main body during electropolishing. Therefore, if the coating thickness of the metal coating layer600ais constant along the central axis A, the amount of polishing of electropolishing becomes larger in the iris portions which are closer to the cathode, while the amount of polishing of electropolishing becomes smaller in the equatorial portions which are farther away from the cathode. In this embodiment, in order to reduce the difference in the amount of polishing between the iris portions and the equatorial portions, the coating thickness of the metal coating layer600ais made thicker in the equatorial portions, and the coating thickness of the metal coating layer600ais made thinner in the iris portions.

Making the coating thickness of the metal coating layer600alarger in the equatorial portions allows the current to flow more easily to the equatorial portions. On the other hand, making the coating thickness of the metal coating layer600asmaller in the iris portions makes the current flow relatively less easily to the iris portions. For example, by setting the coating thickness of the metal coating layer600ain the equatorial portions and the coating thickness of the metal coating layer600ain the iris portions as expressed by the equation (1), the difference in the amount of polishing between the iris portions and the equatorial portions can be reduced. While the coating thickness of the metal coating layer600ain the equatorial portions and the coating thickness of the metal coating layer600ain the iris portions can be set, for example, as expressed by the equation (1), the coating thicknesses can be appropriately set according to the various conditions so that the amount of polishing is equalized between the iris portions and the equatorial portions.

As has been described above, in the superconducting accelerating cavity of this embodiment, the cavity main body600has a shape formed by the equatorial portions (large diameter portions) and the iris portions (small diameter portions), which are at a shorter distance to the central axis A than the equatorial portions, being alternately formed along the direction of the central axis A. In addition, the coating thickness T2 of the metal coating layer600ain the equatorial portions is larger than the coating thickness T1 of the metal coating layer600ain the iris portions.

In this way, current can flow more easily in the equatorial portions which are farther away from the central axis of the cavity main body600, in which the cathode is disposed during electropolishing, than in the iris portions which are closer to the central axis. Thus, the defect of the degree of polishing of electropolishing becoming non-uniform in the inner surface of the cavity main body600can be suppressed.

In the superconducting accelerating cavity of this embodiment, the ratio between the distance R3 to the central axis A of the equatorial portions and the distance R4 to the central axis A of the iris portion, and the ratio between the coating thickness T2 of the metal coating layer600ain the equatorial portions and the coating thickness T1 of the metal coating layer600ain the iris portions correspond to each other or substantially correspond to each other.

In this way, the coating thickness T2 in the equatorial portions and the coating thickness T1 in the iris portions of the cavity main body600can be adjusted to a coating thickness according to the distance from the central axis of the cavity main body600in which the cathode is disposed during electropolishing.

Other Embodiments

In the first embodiment, the anode part230is inserted into the supply port20aand the anode part240is inserted into the discharge port20b; however, the present invention may have a different aspect. For example, the anode part may be inserted into only one of the supply port20aand the discharge port20b. Since the metal coating layer10ais evenly formed on the outer circumferential surface of the cavity main body10, even when the anode part is inserted into only one of the supply port20aand the discharge port20b, the entire outer circumferential surface of the cavity main body10can be at the same potential as the positive pole of the power source250.

The cavity main body10of the first embodiment shown inFIG. 1is formed by four equatorial portions (large diameter portions) and three iris portions (small diameter portions) being alternately formed along the central axis A; however, the present invention may have a different aspect. For example, N equatorial portions and N−1 iris portions may be alternately formed (where N is an integer larger than, one).