JP3953940B2 - High frequency acceleration cavity and particle beam accelerator using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion beam radio frequency acceleration cavity for accelerating charged particles by applying energy, and more particularly to a radio frequency acceleration cavity suitable for use in a medical or physical experiment accelerator and a particle beam accelerator using the same. It is.
[0002]
[Prior art]
A plurality of magnetic members are loaded in a space composed of a coaxial cylindrical inner conductor and an outer conductor, and high-frequency power from the outside is applied between the inner conductor and the outer conductor to generate a high-frequency magnetic field. In the high-frequency accelerating cavity that accelerates, the magnetic member generates heat from the loss component of the internal magnetic permeability.
[0003]
Conventionally, for the purpose of cooling the magnetic member that generates heat, air blowing means such as a fan or a ventilation hole is provided on two opposing side walls of the outer conductor, and air as a refrigerant is circulated in the space inside the outer conductor, thereby the magnetic member. Has been proposed (for example, see Non-Patent Document 1).
[0004]
[Non-Patent Document 1]
Loma Linda University Medical Center, “Proton Therapy Facility Engineering Design Report”, Fermi National Accelerator Laboratory, February 1987 ( February 1987)
[0005]
[Problems to be solved by the invention]
In the conventional high-frequency acceleration cavity having such a configuration, the magnetic member cannot be efficiently cooled. In particular, the central portion where the heat generation amount of the magnetic member is large cannot be efficiently cooled, which is a problem.
[0006]
The present invention has been made to solve the above-described problems, and provides a high-frequency acceleration cavity that can efficiently cool a magnetic member and has little influence on the cavity capacity component of the acceleration cavity. For the purpose.
[0007]
[Means for Solving the Problems]
A high-frequency acceleration cavity according to the present invention has a first inner conductor and a second inner conductor, which are formed in a cylindrical shape extending along an axis, are arranged in series at predetermined intervals, and in which an ion beam travels. The cylindrical acceleration gap body made of an insulator and sealingly connecting the first inner conductor and the second inner conductor, and the first inner conductor, the second inner conductor, and the acceleration gap body are coaxially connected. The outer surface of the outer conductor that forms a sealed space on the outer periphery of these and the outer surface of the inner conductor of at least one of the first inner conductor and the second inner conductor, and has a disk shape surrounding the inner conductor. A plurality of magnetic members arranged side by side so as to be orthogonal to the axis, a first air blower that is provided on a first side wall parallel to the axis of the outer conductor and flows gas into the sealed space, and a first of the outer conductor Provided on the second side wall opposite to the side wall of the first gas to flow out of the sealed space and the first side The second air blowing means that generates cooling air substantially orthogonal to the axis in the sealed space in cooperation with the air means, and the cooling provided between the two adjacent magnetic members made of a low dielectric constant dielectric. Cooling air guide means for guiding the wind toward the center of the magnetic member.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
An acceleration cavity used for ion acceleration will be described. Since the mass of ions, even the lightest proton, is about 2000 times as large as the electron mass, the relativistic effect is small. Therefore, the ion velocity is generally small, and the ion velocity changes greatly during acceleration. Therefore, in order to accelerate this to a desired energy, a magnetic body is loaded in the acceleration cavity, and the resonance frequency of the acceleration cavity is greatly reduced by the magnetic permeability of the magnetic body. And a magnetically loaded acceleration cavity that accelerates ions by matching the resonance frequency of the acceleration cavity.
[0009]
This magnetic material loaded acceleration cavity uses a magnetic material with little magnetic loss, and by applying a bias magnetic field by a bias current to the magnetic material, the permeability of the magnetic material is controlled and the resonance frequency of the acceleration cavity is adjusted. A tuning type high-frequency accelerating cavity that changes to tune to the circulating frequency of the ion and a magnetic material with a large magnetic loss are used. There are two types of non-tunable high-frequency accelerating cavities that do not require a biasing device and are easy to control by widening the resonance frequency beyond the range of the frequency of rotation. Although the present embodiment has a structure of a non-tunable high-frequency acceleration cavity, the present invention can also be applied to a tuning high-frequency acceleration cavity.
[0010]
FIG. 1 is a cross-sectional view showing a high-frequency acceleration cavity according to Embodiment 1 of the present invention. 2 is a cross-sectional view taken along the line II-II of the high-frequency acceleration cavity shown in FIG. 1 is a cross-sectional view taken along the line II in FIG. In the figure, the high-frequency acceleration cavity 100 has a first inner conductor 1a and a second inner conductor 1b each having a long cylindrical shape. The first inner conductor 1a and the second inner conductor 1b extend along the axis A and are arranged in series at a predetermined interval. And between the 1st inner conductor 1a and the 2nd inner conductor 1b which left the predetermined space | interval, the cylindrical acceleration gap body 2 produced with the insulator so that both cylinders may be sealed and connected is provided. Is provided. The other ends of the first inner conductor 1a and the second inner conductor 1b are connected to a vacuum duct of a particle beam accelerator as a circular accelerator. The first inner conductor 1a, the second inner conductor 1b, and the acceleration gap body 2 allow the ion beam to travel inside while being kept in a vacuum.
[0011]
A rectangular box-shaped outer conductor 3 is provided so as to coaxially cover the first inner conductor 1a, the second inner conductor 1b, and the acceleration gap body 2 connected in series. The first inner conductor 1 a passes through the end wall 3 a on one side of the outer conductor 3. The outer peripheral surface of the first inner conductor 1a in the penetrating portion and the end wall 3a are sealed. Similarly, the second inner conductor 1b passes through the end wall 3b on the other side of the outer conductor 3, and the outer peripheral surface of the second inner conductor 1b and the end wall 3b in the penetrating portion are sealed. In this way, the outer conductor 3 forms a sealed space on the outer periphery of the first inner conductor 1a, the second inner conductor 1b, and the acceleration gap body 2.
[0012]
Four magnetic members 4 are arranged on the outer periphery of the first inner conductor 1 a inside the sealed space formed by the outer conductor 3. The magnetic member 4 has a substantially disk shape, and the first inner conductor 1a is passed through the central hole. The four magnetic members 4 are arranged at equal intervals so that the main surface is orthogonal to the first inner conductor 1a. Similarly, four magnetic members 4 are arranged on the outer periphery of the second inner conductor.
[0013]
High frequency power output from a high frequency power generator (not shown) is applied between the inner conductors 1 a and 1 b and the outer conductor 3 having a coaxial structure. This power feeding method is called direct coupling or direct power feeding. By this direct power supply, a high-frequency current is generated between the inner conductors 1 a and 1 b and the outer conductor 3. This high frequency current generates a high frequency magnetic field in the magnetic member 4, thereby generating an acceleration voltage for accelerating ions in the acceleration gap body 2.
[0014]
A first fan 5 a that functions as a first blowing means for flowing air as a refrigerant into the internal space of the outer conductor 3 is provided on the first side wall 3 c parallel to the axis A of the outer conductor 3. In addition, a second fan 5b that functions as a second air blowing unit that discharges air inside the outer conductor 3 to the outside is provided on the second side wall 3d that faces the first side wall 3c. The first fan 5a and the second fan 5b cooperate with each other to generate cooling air that flows in the sealed space inside the outer conductor 3 so as to be substantially orthogonal to the axis A.
[0015]
Cooling air guide plates 6 are respectively provided between two adjacent magnetic members 4. The cooling air guide plate 6 is made of a low dielectric constant dielectric such as epoxy resin or plastic. The cooling air guide plate 6 is provided on the two inner wall surfaces 3e and 3f facing each other in parallel with the axis A where the first fan 5a and the second fan 5b are not provided. The cooling air guide plate 6 is a triangular flat plate whose bottom portions are fixed to the inner wall surfaces 3e and 3f, respectively, and whose apex angle portion is erected in the direction of the axis A. More specifically, the cooling air guide plate 6 is a very short triangular prism having an isosceles triangular cross section with an obtuse apex angle, and the bottom surface including the base of the isosceles triangle is fixed to the inner wall surfaces 3e and 3f. The ridge line including the vertical angle is erected so as to be parallel to the axis A. Each cooling air guide plate 6 has a slope 6 a that extends in the direction of the axis A from the inner wall surfaces 3 e and 3 f of the outer conductor 3 and is inclined so as to guide the cooling air to the center side of the magnetic member 4. . That is, the cooling air guide plate 6 is provided between two adjacent magnetic members 4 to constitute cooling air guide means for guiding the cooling air toward the center of the magnetic member 4.
[0016]
The cooling air guide plate 6 guides the cooling air toward the center of the magnetic member 4 as indicated by arrows in FIG. For comparison, FIG. 3 shows how the cooling air flows in the high-frequency accelerating cavity where the cooling air guide plate 6 is not provided. In the accelerating cavity without the cooling air guide plate 6, the cooling air flowing in from the first fan 5a hits the inner conductor 1a and is divided in the left-right direction in FIG. 3, and then flows along the inner wall surface of the outer conductor 3, It flows out from the second fan 5b. Thus, the cooling air which collided with the inner conductor 1a vigorously hits the inner conductor 1a and is divided into two directions. Therefore, strong cooling air does not flow on the back side of the inner conductor 1a, that is, near the outer periphery of the inner conductor 1a on the second fan 5b side. The same applies to the inner conductor 1b.
[0017]
Here, the heat generation of the magnetic member 4 will be described. FIG. 4 is an explanatory diagram for explaining the magnetic field distribution of the high-frequency acceleration cavity. 4A shows a coaxial cylindrical inner conductor 1 and outer conductor 3 of a general high-frequency acceleration cavity. (B) has shown the strength of the magnetic field H which generate | occur | produces in the high frequency acceleration cavity of (a). In the high-frequency acceleration cavity having such a structure, the magnetic field H is proportional to 1 / radius r as shown in the following equation (1).
[0018]
H∝1 / r Formula (1)
[0019]
That is, the magnetic field H is strongest in the vicinity of the outer peripheral portion of the innermost inner conductor 1 in the space formed by the inner conductor 1 and the outer conductor 3. And since the heat generation of the magnetic member surrounding the inner conductor 1 is composed of a loss component of the magnetic permeability in the magnetic body, the heat generation increases as the magnetic field H increases. For this reason, in the disk-shaped magnetic member 4, heat generation is greatest at a portion relatively close to the inner conductor 1, that is, a portion near the center of the magnetic member 4. The same applies to the case of a cylindrical inner conductor and a square cylindrical outer conductor as in the present embodiment.
[0020]
In the high-frequency accelerating cavity shown in FIG. 3, the strong cooling air does not flow as described above near the outer periphery of the inner conductor 1a opposite to the side where the cooling air is blown. Many parts are not cooled and the efficiency is poor. In addition, when the magnetic body temperature is close to the Curie point, the magnetic permeability starts to decrease rapidly, the impedance rapidly decreases, the circuit is broken, and the magnetic body itself is cracked.
[0021]
On the other hand, the high-frequency accelerating cavity according to the present embodiment has the cooling air guide plate 6 that guides the cooling air toward the center of the magnetic member 4, and therefore, as shown in FIG. Strong cooling air also flows in the vicinity of the outer periphery on the side opposite to the side where the cooling air is blown, and the cooling air is concentrated on the portion of the magnetic member 4 where heat is generated most, so that the cooling capacity is remarkably improved. And the concentration of the heat generation of the magnetic member 4 can be avoided and the cooling efficiency can be improved. Further, since the cooling air guide plate 6 is made of a dielectric material having a low dielectric constant, the impedance characteristic of the acceleration cavity is not deteriorated, and the cavity capacity component of the acceleration cavity is hardly affected. .
In addition, although the triangular top part of the cooling air guide plate 6 blocks the cooling air toward the outer peripheral part of the magnetic member 4, as described above, the amount of heat generated at the outer peripheral part of the magnetic member 4 is larger than that of the inner peripheral part. Since it is small, the overall cooling efficiency is greatly improved over those without the cooling air guide plate 6.
[0022]
Further, the cooling air guide plate 6 has an inclined surface 6a that extends in the direction of the axis A from the inner wall surfaces 3e and 3f of the outer conductor 3 and is inclined in a direction for guiding the cooling air to the center side of the magnetic member 4. The cooling air can be reliably guided to the center side of the magnetic member 4 with a simple configuration, and the cooling air can be efficiently guided to the back side of the inner conductor 1a.
[0023]
Further, since the cooling air guide plate 6 is a triangular flat plate whose base portions are fixed to the inner wall surfaces 3e and 3f and whose apex portion is directed in the direction of the axis A, the cooling air is supplied to the center of the magnetic member 4. Cooling air guiding means for guiding in the direction can be easily realized.
[0024]
In the present embodiment, the cooling air guide means is a triangular flat plate, but is not limited to this, and may have an inclined surface 6 a that is inclined so as to guide the cooling air to the center side of the magnetic member 4. For example, a predetermined effect can be obtained even in various shapes.
[0025]
The outer conductor 3 of the present embodiment has a rectangular box shape that covers the inner conductors 1a and 1b coaxially. However, the outer conductor 3 is not limited to a rectangular cross section, and the cross section may be a circle. .
[0026]
Furthermore, the air blowing means of the present embodiment is configured by the first fan 5a and the second fan 5b that make a pair, but the fan that flows in the cooling air and the fan that flows out are not necessarily provided in a one-to-one relationship. It is not necessary to be provided, and any one of the inflow side and the outflow side may be a simple ventilation hole.
[0027]
Moreover, although the magnetic member 4 of this Embodiment is provided in both the 1st inner conductor 1a and the 2nd inner conductor 1b, it may be provided only in any one.
[0028]
Embodiment 2. FIG.
FIG. 5 is a cross-sectional view showing a high-frequency acceleration cavity according to Embodiment 2 of the present invention. In the high-frequency accelerating cavity 110 according to the present embodiment, the cooling air guide plate 16 functioning as cooling air guiding means is made of a dielectric material having a low dielectric constant, and the bottom surfaces of the inner wall surfaces 3e and 3f of the outer conductor 3 are respectively provided. Are fixed, and the apex angle portion is erected in the direction of the axis A, but a plurality of small-diameter holes 16b are drilled in the main surface. As in the first embodiment, the triangular flat plate is formed with an inclined surface 16 a that is inclined so as to guide the cooling air toward the center of the magnetic member 4. Other configurations are the same as those of the first embodiment.
[0029]
In the high-frequency acceleration cavity having such a configuration, the same effects as those of the first embodiment can be obtained, and the plurality of small-diameter holes 16a are drilled in the main surface, so that the acceleration cavity can be reduced in weight. it can. Further, since the volume of the cooling air guide plate 16 is reduced, the impedance characteristics of the acceleration cavity are not further deteriorated, and the influence of the cavity capacity component of the acceleration cavity is further reduced.
[0030]
Embodiment 3 FIG.
FIG. 6 is a transverse sectional view showing a high-frequency acceleration cavity according to Embodiment 3 of the present invention. In the high-frequency accelerating cavity 120 of the present embodiment, the cooling air guide plate 26 that functions as the cooling air guiding means is made of a low dielectric constant dielectric material, is bent in a dogleg shape, and both ends are formed of the outer conductor 3. It is a thin strip-shaped plate that is fixed to the inner wall surfaces 3e and 3f and that directs the refracting portion in the direction of the axis A. The outer peripheral surface on one side of the belt-like plate that is bent in a dogleg shape forms an inclined surface 26 a that is inclined so as to guide the cooling air toward the center side of the magnetic member 4. Other configurations are the same as those of the first embodiment.
[0031]
In the high-frequency accelerating cavity configured as described above, the same effects as those of the first embodiment can be obtained, and the cooling air guide plate 26 is a thin strip-shaped plate that is bent into a square shape. The weight of the cavity can be further reduced. Further, since the volume of the cooling air guide plate 26 is further reduced, the impedance characteristic of the acceleration cavity is not further deteriorated, and the influence of the cavity capacity component of the acceleration cavity is further reduced.
[0032]
Embodiment 4 FIG.
FIG. 7 is a transverse sectional view showing a high-frequency acceleration cavity according to Embodiment 4 of the present invention. In the high-frequency accelerating cavity 130 of the present embodiment, the cooling air guide plate 36 that functions as cooling air guide means is made of a dielectric material having a low dielectric constant, and the first side wall 3c and the second side wall 3c of the outer conductor 3 are formed. It is two strip-shaped plates with a small thickness provided so as to be bridged between the side wall 3d. The two cooling air guide plates 36 are installed so as to be substantially parallel to the inner wall surfaces 3e and 3f (third and fourth side walls).
[0033]
The two cooling air guide plates 36 cause the cooling air flowing into the outer conductor 3 by the first fan 5a to flow in the central portion with the first cooling air f1 flowing in the peripheral portion of the inner space of the outer conductor 3. Divided into the second cooling air f2. At this time, for example, the two cooling air guide plates 36 are configured such that the second cooling air f2 flowing through the central portion is larger than the first cooling air f1 flowing through the peripheral portion of the inner space of the outer conductor 3. That is, the cooling air is divided so that the flow velocity of the second cooling air f2 is faster than the flow velocity of the first cooling air f1.
That is, the two cooling air guide plates 36 allow the cooling air to pass through the inner space of the outer conductor 3 surrounded by the outer walls of the two cooling air guide plates 36 and the inner wall surfaces 3e and 3f (third and fourth side walls). Are divided into a first cooling air f1 flowing in the peripheral part of the first cooling air and a second cooling air f2 flowing in the center of the inner space of the outer conductor 3 surrounded by the inner walls of the two cooling air guide plates 36, The flow rate of the cooling air f2 is made larger than the flow rate of the first cooling air f1.
Further, the two cooling air guide plates 36 have inclined surfaces 36 a that are inclined in a direction in which the second cooling air f 2 is guided to the center side of the magnetic member 4.
In the present embodiment, the two cooling air guide plates are such that the second cooling air f2 flowing through the central portion is larger than the first cooling air f1 flowing through the peripheral portion of the inner space of the outer conductor 3. However, it is not always necessary that the second cooling air f2 be larger than the first cooling air f1. In short, the cooling air is guided by the two cooling air guide plates 36 and It is sufficient that strong cooling air flows on the back side of the conductor 1a, that is, near the outer periphery of the inner conductor 1a on the second fan 5b side. Since the two cooling air guide plates 36 have slopes 36a that are inclined in a direction in which the second cooling air f2 is guided to the center side of the magnetic member 4, the first cooling air f1 and the second cooling air are provided. Even if the flow rate of f1 is the same, the cooling air can be efficiently guided to the back side of the inner conductor 1a.
[0034]
In the high-frequency accelerating cavity having such a configuration, for example, by increasing the amount of the second cooling air f2 flowing through the central portion of the inner space of the outer conductor 3, the center side of the magnetic member 4 can be more efficiently moved. Cooling air can be efficiently guided to the back side of the inner conductor 1a. Further, since the cooling air guide plate 36 is a thin strip-shaped plate, the volume of the cooling air guide means can be reduced, the impedance characteristic of the acceleration cavity is not deteriorated, and the cavity capacity component of the acceleration cavity is further increased. Less impact.
[0035]
Using the high-frequency acceleration cavity of the first to fourth embodiments described above, the other ends of the first inner conductor 1a and the second inner conductor 1b are connected to a vacuum duct of a circular accelerator (not shown). By configuring the particle beam accelerator, it is possible to provide a particle beam accelerator with high cooling efficiency, small size, light weight, and high performance.
[0036]
【The invention's effect】
A high-frequency acceleration cavity according to the present invention has a first inner conductor and a second inner conductor, which are formed in a cylindrical shape extending along an axis, are arranged in series at predetermined intervals, and in which an ion beam travels. The cylindrical acceleration gap body made of an insulator and sealingly connecting the first inner conductor and the second inner conductor, and the first inner conductor, the second inner conductor, and the acceleration gap body are coaxially connected. The outer surface of the outer conductor that forms a sealed space on the outer periphery of these and the outer surface of the inner conductor of at least one of the first inner conductor and the second inner conductor, and has a disk shape surrounding the inner conductor. A plurality of magnetic members arranged side by side so as to be orthogonal to the axis, a first air blower that is provided on a first side wall parallel to the axis of the outer conductor and flows gas into the sealed space, and a first of the outer conductor Provided on the second side wall opposite to the side wall of the first gas to flow out of the sealed space and the first side The second air blowing means that generates cooling air substantially orthogonal to the axis in the sealed space in cooperation with the air means, and the cooling provided between the two adjacent magnetic members made of a low dielectric constant dielectric. Since cooling air guide means for guiding the wind toward the center of the magnetic member is provided, concentration of heat generated by the magnetic member can be avoided and cooling efficiency can be improved. In addition, since the cooling air guide plate is made of a dielectric having a low dielectric constant, the impedance characteristics of the acceleration cavity are not deteriorated, and the cavity capacity component of the acceleration cavity is hardly affected.
[Brief description of the drawings]
FIG. 1 is a transverse sectional view showing a high-frequency acceleration cavity according to Embodiment 1 of the present invention.
2 is a cross-sectional view taken along the line II-II of the high-frequency acceleration cavity shown in FIG.
FIG. 3 is a cross-sectional view showing how cooling air flows in a conventional high-frequency acceleration cavity without a cooling air guide plate.
FIG. 4 is an explanatory diagram for explaining a magnetic field distribution in a high-frequency acceleration cavity.
FIG. 5 is a cross sectional view showing a high frequency acceleration cavity according to a second embodiment of the present invention.
FIG. 6 is a transverse sectional view showing a high frequency acceleration cavity according to a third embodiment of the present invention.
FIG. 7 is a transverse sectional view showing a high frequency acceleration cavity according to a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1a 1st inner conductor, 1b 2nd inner conductor, 2 acceleration gap body (insulation member), 3 outer conductor, 3c 1st side wall, 3d 2nd side wall, 4 magnetic member, 5a 1st fan (1st 1b), 5b second fan (second blower), 6, 16, 26, 36 cooling air guide plate (cooling air guide), 6a, 16a, 26a, 36a slope, 16b small diameter hole, 100, 110, 120, 130 High-frequency acceleration cavity, f1 first cooling air, f2 second cooling air, A axis.

Claims (7)

A first inner conductor and a second inner conductor, which are formed in a cylindrical shape extending along an axis, arranged in series at a predetermined interval, and in which an ion beam travels;
A cylindrical acceleration gap body made of an insulator and sealingly connecting the first inner conductor and the second inner conductor;
An outer conductor that coaxially covers the first inner conductor, the second inner conductor, and the acceleration gap body to form a sealed space on the outer periphery thereof;
A plurality of discs are provided on the outer periphery of at least one inner conductor of the first inner conductor and the second inner conductor, surrounding the inner conductor and having a principal surface orthogonal to the axis. An attached magnetic member;
A first air blowing means that is provided on a first side wall parallel to the axis of the outer conductor and flows gas into the sealed space;
Provided on the second side wall of the outer conductor facing the first side wall, gas flows out from the sealed space and cooperates with the first air blowing means to be substantially orthogonal to the axis in the sealed space. Second air blowing means for generating cooling air to be
A high-frequency accelerating air comprising cooling air guide means that is made of a dielectric material having a low dielectric constant and is provided between two adjacent magnetic members to guide the cooling air toward the center of the magnetic member. Torso. The said cooling air guide means has an inclined surface extended in the said axial direction from the inner wall surface of the said outer conductor, and inclined so that the said cooling air may be guide | induced to the center side of this magnetic member. High frequency acceleration cavity. 3. The high frequency according to claim 2, wherein the cooling air guide means is a triangular flat plate whose bottom is fixed to the inner wall surface of the outer conductor and whose apex angle is erected in the axial direction. Accelerated cavity. The high-frequency accelerating cavity according to claim 3, wherein the triangular flat plate has a plurality of small-diameter holes drilled in a main surface. The high-frequency acceleration according to claim 2, wherein the cooling air guide means is a belt-like plate that is bent in a dogleg shape and has both end portions fixed to the inner wall surface of the outer conductor and a refracting portion directed in the axial direction. Cavity. The cooling air guide means is provided between the first side wall and the second side wall of the outer conductor, and third and opposite to the first and second side walls. The inner space of the outer conductor, which is a pair of belt-like plates provided so as to be substantially parallel to the four side walls, and is surrounded by the outer wall of the pair of belt-like plates and the third and fourth side walls. And a second cooling air flowing through the central portion of the inner space of the outer conductor surrounded by the inner walls of the pair of strip-shaped plates, and the second cooling air is divided into the second cooling air. The high-frequency accelerating cavity according to claim 1, further comprising a slope inclined in a direction leading to a center side of the magnetic member. A particle beam accelerator using the high-frequency acceleration cavity according to claim 1.

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