CN111295034B - Spoke cavity structure for large hadron accelerator - Google Patents
Spoke cavity structure for large hadron accelerator Download PDFInfo
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- CN111295034B CN111295034B CN202010122263.5A CN202010122263A CN111295034B CN 111295034 B CN111295034 B CN 111295034B CN 202010122263 A CN202010122263 A CN 202010122263A CN 111295034 B CN111295034 B CN 111295034B
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- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
- H05H7/04—Magnet systems, e.g. undulators, wigglers; Energisation thereof
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Abstract
The invention discloses a spoke cavity structure for a large-scale hadron accelerator. This spoke chamber structure that large-scale hadron accelerator was used improves on the basis of traditional spoke chamber structure, sets up the arc convex surface through the first fillet periphery in traditional spoke chamber structure, can effectively improve the homogeneity of near first fillet electromagnetic field distribution, effectively realizes reducing the purpose of the effective secondary electron emission coefficient in spoke chamber to acceptable scope simultaneously, avoids the influence that the plug itself led to the fact electromagnetic field distribution.
Description
Technical Field
The invention relates to the technical field of accelerators, in particular to a spoke cavity structure for a large hadron accelerator.
Background
The spoke cavity, a superconducting high frequency cavity, is commonly used for the acceleration of medium energy particles (0.4< beta <0.7), where beta is the ratio of the particle velocity to the speed of light. Compared with an ellipsoid cavity, the spoke cavity has the advantages of high mechanical strength, wide range of accelerated particle speed and the like, so that a plurality of international large-scale hadron accelerators adopt the spoke cavity as a medium-energy accelerating structure of particles. However, in practical applications, the operating state of the spoke cavity is affected by the effective secondary electron emission coefficient, and if the structural design is not reasonable, the working cavity pressure will be in an interval with a large effective secondary electron emission coefficient (< SEY >), which may lead to the cavity not working normally in severe cases. Therefore, the reasonable cavity structure design for reducing the effective secondary electron emission coefficient is the key for improving the operation stability of the cavity.
In the currently commonly used spoke cavity, the secondary electron emission of the dual acceleration gap spoke cavity generally exists in two positions (i.e. at the first fillet 1 and the second fillet 2 shown in fig. 1 or fig. 2), wherein the effective secondary electron emission coefficient at the second fillet can be suppressed to an acceptable range by increasing the fillet radius (i.e. < SEY > less than 1.4); however, for the effective secondary electron emission coefficient at the first round corner, the effective secondary electron emission coefficient cannot be reduced by changing the radius of the round corner generally, because the mandrel 3 damages the circumferential cavity structure, the electromagnetic field distribution at the first round corner is not uniform, and further the uncertainty of the secondary electron emission trajectory is caused.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a spoke cavity structure for a large-scale hadron accelerator, which can effectively improve the uniformity of electromagnetic field distribution near a first fillet and achieve the purpose of reducing the effective secondary electron emission coefficient of the spoke cavity to an acceptable range.
The technical scheme of the invention is as follows: the spoke cavity structure for large-scale hadron accelerator has core rod with two ends with arc raised surfaces protruding outwards and passing through the spoke cavity along the radial direction.
The middle part of the end face of the core rod is a circular through hole, the arc-shaped convex face is located on the periphery of the circular through hole, and the circumference of the circular through hole is internally tangent to the peripheral outline of the projection face of the arc-shaped convex face.
The arc convex surface comprises a first convex surface and a second convex surface which are symmetrically positioned on two sides of the circular through hole.
In the arc convex surfaces, the outer contours of the radial cross sections of the first convex surface and the second convex surface are arc sections, and the circular ring or the elliptical ring where each arc section is located is intersected with the radial outer circumference of the spoke cavity.
The first convex surface and the second convex surface are respectively intersecting parts formed by rotating a circle by taking the circumferential edge of the top of the mandrel as the center through a circle with the radius of 30mm, and the intersecting parts are crescent-shaped. Through experimental detection, the first convex surface and the second convex surface of the radius are suitable for a single-core rod spoke cavity structure with the working frequency of 648MHz, the first convex surface and the second convex surface can be further optimized according to the actual working frequency requirement of the spoke cavity and the secondary electron emission calculation structure, and the radius of a circle forming the structure is adjusted.
The border of circular through-hole is the fillet form, and the outer border of first convex surface and second convex surface also is fillet form.
The arc convex surface is a part of a circular spherical surface or an elliptical spherical surface.
The core rod comprises a first cylindrical section, a first conical section, a middle connecting section, a second conical section and a second cylindrical section which are sequentially connected, and the outer end face of the first cylindrical section and the outer end face of the second cylindrical section are respectively connected with the arc-shaped convex face.
The diameter of the middle connecting section is smaller than that of the first cylindrical section and the second cylindrical section, and the first cylindrical section and the second cylindrical section are symmetrically arranged.
In the spoke chamber structure for the large-scale hadron accelerator, the principle is as follows: the arc convex surface is arranged to replace a first fillet in a traditional spoke cavity structure, and as the arc curve generation mode of the arc curved surface is along the diameter direction of the spoke cavity, a circular ring or an elliptical ring is inscribed on the end surface of the core rod (namely the circular through hole), and the circular ring or the elliptical ring is intersected with the outer circumference of the spoke cavity, the arc convex surface protruding out of the cylindrical surface of the outer circumference of the spoke cavity is formed; because the magnetic field inside the excited spoke cavity is mainly concentrated at the position with large radius of the cavity, the area of the magnetic field area can be indirectly increased by the arrangement of the arc convex surface, and the structure of the circular through hole (namely the first fillet in the traditional spoke cavity structure) is unchanged, so that the electromagnetic field distribution near the circular through hole is more uniform, and the purpose of reducing the effective secondary electron emission coefficient of the spoke cavity to an acceptable range is better achieved.
Compared with the prior art, the invention has the following beneficial effects:
this spoke chamber structure that large-scale hadron accelerator was used improves on the basis of traditional spoke chamber structure, sets up the arc convex surface through the first fillet periphery in traditional spoke chamber structure, can effectively improve the homogeneity of near first fillet electromagnetic field distribution, effectively realizes reducing the purpose of the effective secondary electron emission coefficient in spoke chamber to acceptable scope simultaneously, avoids the influence that the plug itself led to the fact electromagnetic field distribution.
Drawings
Fig. 1 is a schematic diagram of an electromagnetic calculation model of a conventional spoke cavity structure.
Fig. 2 is a cross-sectional view a-a of fig. 1.
Fig. 3 is an electron microscope image of the secondary electron emission trajectory at the first fillet in the conventional spoke cavity structure.
Fig. 4 is a schematic diagram of the change of the effective secondary electron emission coefficient of the conventional spoke cavity structure under different acceleration gradients (wherein the abscissa represents the acceleration gradient and the ordinate represents the effective secondary electron emission coefficient).
FIG. 5 is an electron microscope image of the magnetic field distribution of a conventional electromagnetic calculation model of the spoke cavity structure.
FIG. 6 is an electron microscope image of the electric field distribution of the electromagnetic calculation model of the conventional spoke cavity structure.
Fig. 7 is a diagram illustrating a magnetic field distribution curve corresponding to the first rounded corner shown in fig. 1.
FIG. 8 is a schematic diagram of an electromagnetic calculation model of the present spoke cavity structure.
Fig. 9 is a cross-sectional view B-B of fig. 8.
Fig. 10 is a cross-sectional view C-C of fig. 8.
FIG. 11 is an electron microscope image of a secondary electron emission trajectory at a first fillet in the electromagnetic calculation model of the present spoke cavity structure.
Fig. 12 is a schematic diagram of the change of the effective secondary electron emission coefficient of the electromagnetic calculation model of the spoke cavity structure under different acceleration gradients (wherein the abscissa represents the acceleration gradient and the ordinate represents the effective secondary electron emission coefficient).
FIG. 13 is an electron microscope image of the magnetic field distribution of the electromagnetic calculation model of the present spoke cavity structure.
FIG. 14 is an electron microscope image of the electric field distribution of the electromagnetic calculation model of the present spoke cavity structure.
Fig. 15 is a diagram illustrating a magnetic field distribution curve corresponding to the first rounded corner shown in fig. 9.
In the above figures, the components indicated by the respective reference numerals are as follows: the radial spoke cavity comprises a first round angle 1, a second round angle 2, a core rod 3, a first cylindrical section 3-1, a first conical section 3-2, a middle connecting section 3-3, a second conical section 3-4, a second cylindrical section 3-5, an arc-shaped convex surface 4-1, a first convex surface 4-2, a second convex surface 4-2, an arc-shaped section 5 and a radial outer circumference 6 of the spoke cavity.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Examples
In the spoke cavity structure for the large-scale hadron accelerator, as shown in fig. 8 to 10, two ends of a core rod 3 are respectively provided with arc-shaped convex surfaces 4, each arc-shaped convex surface protrudes out of an outer circumferential cylindrical surface of the spoke cavity, and the core rod passes through the spoke cavity along the radial direction of the spoke cavity.
As shown in fig. 8, the middle of the end surface of the mandrel is a circular through hole, the arc-shaped convex surface is located at the periphery of the circular through hole, and the circumference of the circular through hole is inscribed with the peripheral contour of the projection surface of the arc-shaped convex surface.
The arc convex surface is a part of a spherical surface or an elliptic spherical surface. The arc convex surfaces comprise a first convex surface 4-1 and a second convex surface 4-2 which are symmetrically positioned at two sides of the circular through hole. The radial cross section of the first convex surface and the radial cross section of the second convex surface are both arc-shaped sections (as shown in fig. 10), and the ring or the elliptical ring where each arc-shaped section 5 is located intersects with the radial outer circumference 6 of the spoke cavity. First convex surface and second convex surface are respectively through the radius for the intersection that 30 mm's circle used plug top circumference border to rotate the round formation as the center, and the intersection presents crescent, and the border of circular through-hole is the fillet form, and the outer border of first convex surface and second convex surface also is the fillet form. Through experimental detection, the first convex surface and the second convex surface of the radius are suitable for a single-core rod spoke cavity structure with the working frequency of 648MHz, the first convex surface and the second convex surface can be further optimized according to the actual working frequency requirement of the spoke cavity and the secondary electron emission calculation structure, and the radius of a circle forming the structure is adjusted.
As shown in fig. 10, the mandrel includes a first cylindrical section 3-1, a first tapered section 3-2, a middle connecting section 3-3, a second tapered section 3-4, and a second cylindrical section 3-5, which are connected in sequence, and the outer end surface of the first cylindrical section and the outer end surface of the second cylindrical section are respectively connected with the arc-shaped convex surface. The diameter of the middle connecting section is smaller than that of the first cylindrical section and the second cylindrical section, and the first cylindrical section and the second cylindrical section are symmetrically arranged.
In the spoke chamber structure for the large-scale hadron accelerator, the principle is as follows: the arc convex surface is arranged to replace a first fillet in a traditional spoke cavity structure, and as the arc curve generation mode of the arc curved surface is along the diameter direction of the spoke cavity, a circular ring or an elliptical ring is inscribed on the end surface of the core rod (namely the circular through hole), and the circular ring or the elliptical ring is intersected with the outer circumference of the spoke cavity, the arc convex surface protruding out of the cylindrical surface of the outer circumference of the spoke cavity is formed; because the magnetic field inside the excited spoke cavity is mainly concentrated at the position with large radius of the cavity, the area of the magnetic field area can be indirectly increased by the arrangement of the arc convex surface, and the structure of the circular through hole (namely the first fillet in the traditional spoke cavity structure) is unchanged, so that the electromagnetic field distribution near the circular through hole is more uniform, and the purpose of reducing the effective secondary electron emission coefficient of the spoke cavity to an acceptable range is better achieved.
Comparative example
The following calculation methods are adopted to calculate the secondary electron emissivity of the traditional spoke cavity structure and the spoke cavity structure respectively (the solver and the calculation method adopted in the following calculation process are both the existing calculation method). The specific process of the calculation method is as follows:
(1) calculating the lowest-order eigenmode electromagnetic field distribution by adopting an eigenmode solver of a CST microwave working chamber;
(2) establishing a shell mold, and arranging an emission electron source which is generally arranged at a first round angle and a second round angle of the spoke cavity structure;
(3) introducing the electromagnetic field distribution calculated in the step (1) as an initial parameter for calculating the secondary electron emissivity;
(4) calculating the probability of the initial electrons emitted by the electron source colliding with the cavity wall and generating secondary electrons under the action of an electromagnetic field by using a Particle Tracking Solver working by CST microwaves;
if the calculation result shows that the generation rate of the secondary electrons is more than 1 (namely the number of the secondary electrons generated by 1 electron collision cavity wall is more than 1), the secondary electron multiplication phenomenon is considered to occur, and the effective secondary electron emission coefficient < SEY > is more than 1.
The calculation result of the secondary electron emissivity of the traditional spoke cavity structure is as follows:
the electron emission locus at the first round corner is shown as a dark part in fig. 3, the change of the effective secondary electron emission coefficient under different acceleration gradients is shown in fig. 4, the magnetic field distribution is shown in fig. 5 or fig. 7, and the electric field distribution is shown in fig. 6. As can be seen from fig. 3 and 4, secondary electron multiplication occurs at the first fillet (i.e., at the joint between the mandrel and the cylindrical surface of the outer periphery of the spoke cavity), the maximum effective secondary electron emission coefficient reaches 1.69, and the region with severe secondary electron multiplication occurs at the middle of the first fillet near the spoke cavity structure. In the process of calculating the emissivity of the secondary electrons, the electromagnetic field at the position where the multiplication of the secondary electrons occurs is unevenly distributed, which results in the increase of the effective secondary electron generation coefficient, and the uniform distribution of the electromagnetic field cannot be realized by increasing or decreasing the radius of the first fillet shown in fig. 1.
The calculation result of the secondary electron emissivity of the radial cavity structure of the wheel is as follows:
the electron emission locus at the first round corner (i.e., the periphery of the circular through hole) is shown as a dark part in fig. 11, the change of the secondary electron emission coefficient under different acceleration gradients is shown in fig. 12, the magnetic field distribution is shown in fig. 13 or fig. 15, and the electric field distribution is shown in fig. 14. The result of calculating the secondary electron emissivity proves that in the spoke cavity structure, the magnetic field distribution at the joint of the core rod and the spoke cavity (namely, at the first round angle) is more uniform, the distribution curve is smoother, the fluctuation of the magnetic field value is smaller than that of the traditional spoke cavity structure, the effective secondary electron generation coefficient is reduced, and as can be seen from fig. 12, the maximum electron emission coefficient is 1.371, and the design requirement that the maximum electron emission coefficient is less than 1.4 is well met.
As mentioned above, the present invention can be better realized, and the above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention; all equivalent changes and modifications made according to the present disclosure are intended to be covered by the scope of the claims of the present invention.
Claims (6)
1. A spoke cavity structure for a large-scale hadron accelerator is characterized in that two ends of a core rod are respectively provided with arc-shaped convex surfaces, each arc-shaped convex surface protrudes out of the peripheral cylindrical surface of a spoke cavity, and the core rod penetrates through the spoke cavity along the radial direction of the spoke cavity;
the middle part of the end surface of the core rod is a circular through hole, the arc-shaped convex surface is positioned on the periphery of the circular through hole, and the circumference of the circular through hole is internally tangent to the peripheral outline of the projection surface of the arc-shaped convex surface;
the arc-shaped convex surfaces comprise a first convex surface and a second convex surface which are symmetrically positioned at two sides of the circular through hole;
the first convex surface and the second convex surface are respectively intersecting parts formed by rotating a circle by taking the circumferential edge of the top of the mandrel as the center through a circle with the radius of 30mm, and the intersecting parts are crescent-shaped.
2. The spoke cavity structure for the large hadron accelerator as claimed in claim 1, wherein the radial cross section of the first convex surface and the radial cross section of the second convex surface in the arc-shaped convex surfaces are arc-shaped sections, and the ring or the elliptical ring where each arc-shaped section is located intersects with the radial outer circumference of the spoke cavity.
3. The spoke cavity structure for the large hadron accelerator as claimed in claim 1, wherein the edge of the circular through hole is in a shape of a fillet, and the outer edges of the first convex surface and the second convex surface are also in a shape of a fillet.
4. The spoke cavity structure for a large hadron accelerator as claimed in claim 1, wherein the arc-shaped convex surface is a part of a spherical surface or an elliptical spherical surface.
5. The spoke cavity structure for the large-scale hadron accelerator as claimed in claim 1, wherein the core rod comprises a first cylindrical section, a first conical section, a middle connecting section, a second conical section and a second cylindrical section which are connected in sequence, and the outer end face of the first cylindrical section and the outer end face of the second cylindrical section are respectively connected with the arc-shaped convex surface.
6. The spoke cavity structure for the large hadron accelerator as claimed in claim 5, wherein the diameter of the middle connecting section is smaller than that of the first cylindrical section and the second cylindrical section, and the first cylindrical section and the second cylindrical section are symmetrically arranged.
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