CN112216468B - Straight-side fan main magnet of compact type medium-energy negative hydrogen strong-flow isochronous cyclotron - Google Patents
Straight-side fan main magnet of compact type medium-energy negative hydrogen strong-flow isochronous cyclotron Download PDFInfo
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- CN112216468B CN112216468B CN202011185765.9A CN202011185765A CN112216468B CN 112216468 B CN112216468 B CN 112216468B CN 202011185765 A CN202011185765 A CN 202011185765A CN 112216468 B CN112216468 B CN 112216468B
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- H01—ELECTRIC ELEMENTS
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Abstract
The invention discloses a straight-side fan main magnet of a compact type medium-energy negative hydrogen strong-current isochronous cyclotron, wherein the intersection point of two straight sides of each straight-side fan-shaped magnetic pole is not radially superposed with the central point of a cover plate, and the intersection point is positioned on the circumference of the central area of the cover plate; the circle center of the arc at the tail part of each straight-side fan-shaped magnetic pole is strictly superposed with the center of the cover plate, and the radius of the fan-shaped magnetic pole side of each straight-side fan-shaped magnetic pole is smaller than the curvature radius of the arc at the tail part of the fan-shaped magnetic pole; the reduction of the angular width of the large radius of the inlaid strip is enough larger than the arc length of the magnetic pole of the main magnet at the large radius, so that the total angular width of the magnetic pole and the inlaid strip at the large radius is reduced compared with the prior structure, namely the angular width of the magnetic pole and the inlaid strip at the large radius is reduced
Therefore, the degree of modulation increases, and the focusing force increases; the above-mentioned
The proportion of the magnet sector magnetic pole and the gib on the central plane in the circumferential direction; the magnetic field variable gradient focusing is conveniently introduced by adjusting the proportional relation between the radius of the fan-shaped magnetic pole and the curvature radius of the arc at the tail of the fan-shaped magnetic pole and combining the modes of adjusting the outline of the magnetic pole gib and the like.
Description
Technical Field
The invention belongs to the technical field of high-current proton cyclotrons, and particularly relates to a main magnet of a compact type medium-energy negative-hydrogen high-current isochronous cyclotron.
Background
The cyclotron is a device which makes charged particles perform cyclotron motion by using a magnetic field and an electric field together and repeatedly accelerates the charged particles through a high-frequency electric field in the motion, and is an important tool for the application and research of nuclear physics and nuclear technology. The medium-energy negative hydrogen strong flow isochronal cyclotron refers to that the accelerating ion species is negative hydrogen (H) - ) The final energy of the accelerated ions reaches more than 100MeV (including 100 MeV), and the beam current intensity of the accelerated and extracted ions reaches more than 200 muA. The medium-energy high-current proton cyclotron can generate high-current proton beams, target to generate high-flux neutrons and radioactive nuclear beams (RIB) for application research of national defense nuclear technology, nuclear physics foundation and nuclear technology, such as nuclear data measurement, radiation physics, neutron physics, nuclear structure, material science, life science and the like, and is an important platform for developing foundation and application research in the technical field of nuclear science.
The isochronous cyclotron system with strong negative hydrogen flow consists of negative hydrogen ion source, axial injection line, main magnet, high frequency cavity, stripping lead-out unit, vacuum chamber and other core components. The negative hydrogen beam enters the central plane of the accelerator from the ion source injection axis and then performs circular cyclotron motion, the energy of the negative hydrogen particles is increased when the negative hydrogen beams pass through the high-frequency acceleration gap every time, and the particle cyclotron radius is increased; after accelerating to the final energy through many turns (usually hundreds of turns), the high-current proton beam is continuously extracted by means of stripping extraction. Wherein, the main magnet provides a guiding magnetic field for accelerating the negative hydrogen particles.
The main magnet is the basic guarantee that the compact strong current negative hydrogen accelerator system accelerates the strong current (more than 200 muA) negative hydrogen ion beam to the energy region more than 100 MeV. However, the straight-side fan main magnet technology of the existing compact type medium-energy strong-flow isochronous cyclotron has the following challenges:
1) The compact main magnet structure (namely, the upper and lower magnetic poles and the upper and lower magnetic yokes are uniformly arranged on the integral upper and lower cover plates in pairs) is adopted, so that the distances between the center region electrode arranged close to the center plane between the upper and lower magnetic poles of the main magnet, the high-frequency Dee plate and the edges of the magnetic poles are too close, the high-frequency ignition frequency in the running process of the accelerator is further caused, and the running stability of the accelerator under the acceleration of a high-frequency beam is influenced;
2) In the process of stable increase of particle energy in the cyclotron, the high-frequency phase of each circle passing through an acceleration gap is ensured to be basically constant, so that the magnetic field for restraining the cyclotron motion of the particles is required to be gradually increased along with the radius of a magnetic pole, and the increase of the energy of the particles can be matched with the increase of the radius of the magnetic field, which is the isochronism condition of distribution of a main magnetic ferromagnetic field of the cyclotron. This means that the magnetic field increase with increasing radius for pole arc length matches the increasing magnetic field along the pole radius required for particle acceleration. In the magnetic engineering, the actual isochronous magnetic field needs to be finely adjusted by a magnetic field shimming method, and a commonly used shimming method is to perform magnetic field shimming by correcting the side edge profile of a gib which is attached to the side edge of a magnetic pole and is formed by processing a magnetic conductive material (pure iron or low-carbon steel) with a high saturation magnetic field. One end of the inlaid strip in the height direction is generally flush with the surface of the magnetic pole, the whole height of the inlaid strip is far less than the height of the magnetic pole, and the other end of the inlaid strip in the height direction is far away from the cover plate, so that the magnetic field generated by the magnetic pole with the same angular width in the central plane is larger than the magnetic field generated by the inlaid strip in the central plane. In the prior art, the center of the fan-shaped magnetic pole is positioned at the center of the cover plate, and the angle of the fan-shaped magnetic pole cannot be too large in order to balance the isochronous magnetic field distribution in the whole magnetic pole range. Resulting in insufficient magnetic field provided by the pole body at large radii, requiring the gib to provide a greater amount of magnetic field shimming at large radii, meaning a greater gib corner width at large radii is required. The problems of increased tangential force and deformation of the panel, insufficient high-frequency acceleration gap at a large radius and the like are caused, and finally, the beam loss is increased and the flow strength is limited.
3) The conventional technology of the straight-side fan main magnet of the compact isochronous cyclotron has the problem of insufficient focusing force, and cannot ensure the axial focusing force required for accelerating negative hydrogen to the energy of more than or equal to 100 MeV; the spiral fan-shaped main magnet or the separated fan-shaped main magnet is needed to be adopted, but the spiral fan-shaped main magnet can cause the design risk and difficulty of a high-frequency acceleration system and a beam diagnosis system to be obviously increased, and the separated fan-shaped main magnet can cause the overall scale and the manufacturing cost of the accelerator to be greatly increased.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a main magnet of a straight fan of a compact type medium-energy strong-flow isochronous cyclotron, and aims to ensure that a compact type strong-flow negative hydrogen accelerator system accelerates a strong-flow (more than 200 muA) negative hydrogen ion beam to an energy region of 100MeV or more with low manufacturing cost and design risk.
A straight-side fan main magnet of a compact type medium-energy negative hydrogen strong-flow isochronous cyclotron is characterized in that:
the intersection point of two straight edges of each straight-edge fan-shaped magnetic pole is not radially superposed with the central point of the cover plate, and the intersection point is positioned on the circumference of the central area of the cover plate; the center of the circular arc at the tail part of each straight-side fan-shaped magnetic pole is strictly superposed with the center of the cover plate, and the radius of the fan-shaped magnetic pole side of each straight-side fan-shaped magnetic pole is smaller than the curvature radius of the circular arc at the tail part of the fan-shaped magnetic pole;
the main magnet structure that the intersection point of two straight lines of the fan-shaped magnetic pole of the straight-edge fan-shaped main magnet is not coincident with the central point of the cover plate, but the circle center of the arc at the tail of the fan-shaped magnetic pole is strictly coincident with the center of the cover plate, and the radius of the fan-shaped magnetic pole is smaller than the curvature radius of the arc at the tail of the fan-shaped magnetic pole is adopted, so that the arc length of the main magnet pole at a large radius is increased, and the magnetic field which is gradually increased along the radius of the magnetic pole and is required by isochronism acceleration of matched particles is facilitated;
the magnetic pole has two magnetic pole embedded strip outlines on two straight edges of the straight-edge fan-shaped magnetic pole, the magnetic pole embedded strip outlines are distributed outside the two straight edges of the magnetic pole in a bilateral symmetry mode in two irregular curves, two sides close to the intersection point of the two straight edges of the magnetic pole are connected through a small section of circular arc, the circular arc is not radially overlapped with the center point of the cover plate, the length of the large-radius embedded strip arc of the straight-edge fan-shaped magnetic pole is relatively shorter than that of the large-radius embedded strip arc of the straight-edge fan-shaped magnetic pole passing through the center point of the cover plate, the shortened arc length is replaced by the increased arc length of the straight-edge fan-shaped magnetic pole, and the increased arc length of the straight-edge fan-shaped magnetic pole is stronger in effect of increasing the magnetic field compared with the same arc length of the embedded strip.
The reduction of the small-radius magnetic field caused by the radial misalignment of the intersection point of two straight sides of each straight-side fan-shaped magnetic pole and the central point of the cover plate is realized, and the core column structure at the center of the magnet is adjusted and compensated by adjusting the distance between the step structure of the core column and the central plane and the radius of the step structure.
The reduction of the angle width of the large radius of the inlaid strip is enough larger than the arc length of the magnetic pole of the main magnet increased by the large radius, so that the total angle width of the magnetic pole at the large radius and the inlaid strip is reduced compared with the prior structure, namely alpha is reduced, therefore, the degree of modulation is increased, and the focusing force is increased; and alpha is the proportion of the sector magnetic pole of the magnet and the gib on the central plane in the circumferential direction.
Advantageous effects of the invention
1. The central point 4-1 of the fan-shaped magnetic pole of the straight-edge fan-shaped main magnet is not superposed with the central point 1-1 of the cover plate, but the center 4-3 of the circular arc 4-2 at the tail part of the fan-shaped magnetic pole is strictly superposed with the central point 1-1 of the cover plate, and the length of the line segment connecting the center 4-1 of the fan-shaped magnetic pole and the tail end point of the magnetic pole (namely the radius 4-4 of the fan-shaped magnetic pole) is smaller than the curvature radius 4-5 of the circular arc at the tail part of the fan-shaped magnetic pole, so that the arc length of the magnetic pole with a small radius near the center of the main magnet is reduced, the space of a corresponding magnetic pole valley area 5 for arranging a central area electrode 9 and a high-frequency Dee plate 10 at the small radius is enlarged, the problem that the distance 11 between the Dee plate 10 at the small radius and the edge of the magnetic pole 4 is too close is solved, the high-frequency sparking problem in the running process of the accelerator is further improved, and the running stability of the accelerator under the acceleration of a strong flow beam is improved;
2. the intersection point 4-1 of two straight line lines of the fan-shaped magnetic pole of the straight-edge fan-shaped main magnet is not superposed with the central point 1-1 of the cover plate, but the circle center 4-3 of the circular arc 4-2 at the tail of the fan-shaped magnetic pole is strictly superposed with the central point 1-1 of the cover plate, and the radius 4-4 of the fan-shaped magnetic pole is smaller than the curvature radius 4-5 of the circular arc at the tail of the fan-shaped magnetic pole, so that the arc length of the main magnetic pole at a large radius is increased by 12, and the magnetic field which is gradually increased along the radius of the magnetic pole and is required by isochronic acceleration of matched particles is convenient. The magnetic field that the place magnetic pole body of major radius provided has improved, and then reduced the required magnetic field of panel at major radius and shimmed the volume, meant reducing the panel angular width of major radius department. And then the tangential force and the deformation of the panel are reduced, and the problem of insufficient high-frequency acceleration clearance at the large radius is solved.
3. By adjusting the proportional relation between the radius of the fan-shaped magnetic pole and the curvature radius of the arc at the tail of the fan-shaped magnetic pole and combining the modes of adjusting the outline 8 of the magnetic pole gib and the like, the magnetic field variable gradient focusing is convenient to introduce, and the axial focusing force required for accelerating negative hydrogen to the energy of more than or equal to 100MeV can be ensured.
Description of the drawings:
FIG. 1a is a perspective view of the compact type intermediate energy negative hydrogen high current isochronous cyclotron below the central plane;
FIG. 1b is a top view of the compact type of the isochronous cyclotron with strong negative hydrogen flux from below the central plane;
FIG. 1c is a schematic diagram of a core leg structure for compensating for a reduction in the magnetic field in the central region according to the present invention;
FIG. 1d is a schematic view of the mating relationship of the core column and the magnetic pole of the present invention;
FIG. 2a is a comparison of the front and rear of the main magnet according to the present invention;
FIG. 2b is an enlarged view of the central region of the magnetic field of FIG. 2a after the modification;
3a, 3b and 3c are schematic diagrams of the relationship between alpha and the degree of modulation F;
in the figure: 1. a yoke (fig. 1 a); 1-1: cover plate center point (fig. 2 b); 1-2: the central zone magnetic field (fig. 2 b); 2: a cover plate (fig. 1 a); 3: evacuation holes (fig. 1 a); 4: magnetic poles (fig. 1 a); 4-1: the intersection point of two straight sides of the straight-side fan magnetic pole; 4-2: the arc of the tail of the sector pole (fig. 2 a); 4-3: the center of the arc at the tail of the sector magnetic pole (fig. 2 a); 4-4: sector pole radius (fig. 2 a); 4-5: radius of curvature of the arc at the end of the sector pole (shown by the dashed-dotted line in fig. 2 a); 5: magnet valley regions (fig. 1 a); 6: coil mounting slots (fig. 1 a); 7: a stem (fig. 1 a); 7-1 radius of the first step of the stem (fig. 1 c); 7-2: a first step of the stem (fig. 1 c); 7-3: stem second step (fig. 1 c); 8: pole-insert profiles (fig. 1a, 1c, 2b, 3); 9: a central region electrode; 10: high frequency Dee plate (fig. 1 b); 11: distance of Dee plate from edge of pole at small radius (fig. 1 b); 12: the major radius arc length of the main magnet magnetic pole is increased (fig. 1b, fig. 2 a); 13: improving the total angular width of the magnetic pole and the panel at the large radius; 14: improving the total angular width of the magnetic pole and the panel at the large radius position before improvement; 15: the total radian of the magnetic pole and the gib at the large radius is reduced after improvement (figure 2 a); h1 is the thickness of the magnetic pole insert, H2 is the thickness of the magnetic pole except for the insert, and H3 is the thickness of the magnetic pole cover plate 2.
The implementation mode is as follows:
the invention is further described below with reference to the accompanying drawings:
design principle for improving axial focusing force
The isochronous principle of the cyclotron is expressed as follows:
in the formula, B 0 (R) is the average magnetic field of zero isochronism error at radius R; b is center Is a central point magnetic field of the main magnet assembly on a central plane; γ (R) is a relativistic factor at radius R, i.e. the ratio of the total energy of the particle at radius R to the resting energy of the particle; c =3 × 10 8 m/s is the speed of light; omega 0 Is the frequency of the cyclotron motion of the particles; r is the radius of the particle. Given the magnetic field at the center point and the frequency of the particle's convolution from equation (1), if it is to be ensured that the phase of the particle is substantially constant each time it passes through the high frequency gap, then the average magnetic field at any radius is determined, according to the principle of isochronism.
The approximate expression of representing the magnitude of the axial focusing force of the cyclotron is as follows: (Here, the axial free-running frequency v is used z Representing accelerator axial focus force):
wherein v z The larger the axial focusing force is characterized. In the formula, N is the number of fan blades, ξ is the spiral angle of the magnetic pole, and for a straight fan magnetic pole, ξ ≈ 0, so that the condition (2 a) of the straight fan magnetic pole becomes:
finding out the relation between F and alpha:
alpha is the total angular width ratio of the magnetic pole at the large radius and the panel, the relationship between F and alpha is found out, and v is also found out z Relationship to α: i.e. decrease alpha, increase of modulation F, focus force v z And (4) increasing.
The method comprises the following specific steps:
(2a) (2B) wherein the radial gradient of the magnetic field falling index n and the magnetic field B
Specifically, the following formula is used:
the degree of modulation F is determined by the following equation:
wherein, the first and the second end of the pipe are connected with each other,
<B>＝α·B hill +(1-α)·B valley ；<B> 2 ＝B Hill 2 α+B Valley 2 (1-α) (5)
alpha is the proportion of the magnet sector magnetic pole and the gib in the circumferential direction on the central plane, B Hill 、B Valley Respectively the magnetic fields of the magnetic pole peak area and the magnetic field of the magnetic pole valley area on the central plane. In actual accelerator magnet engineering, α ∈ (0.3,0.6) is generally used. If alpha is too small, the proportion of iron is too small, the magnetic field share of the coil is too high under the condition of needing the same magnetic field, the ampere turns of the coil are too high, and the running cost is high; if α is too small, the ratio of iron is too large, and the degree of modulation is too small and the focusing force is insufficient as can be seen from the analysis later.
There is a need forNote that the variable v in the formulae (2 a) to (5) z 、n、B、F、α、B Hill 、B Valley In fact, the variable with the radius R is the value v z (R)、n(R)、B(R)、F(R)、α(R)、B Hill (R)、B Valley Abbreviation of (R).
From (1), it can be seen that in the whole acceleration region, when the particle energy increases, the radius R increases, and the isochronic magnetic field also increases with the radius, i.e. the average magnetic field B should be a monotonically increasing function of the radius R, there are
(except that the central region is locally subject to local non-isochronism introduced for local focus adjustment artifacts, the monotonically increasing relationship of the average magnetic field B to the radius R is destroyed).
On the other hand, as shown in (3), n is less than 0, but the axial focusing force is increased as shown in (2 b) by adjusting the ratio of the radius 4-4 of the sector magnetic pole to the radius 4-5 of curvature of the circular arc at the tail of the sector magnetic pole, and by adjusting the contour 8 of the magnetic pole insert, etc., to reduce the local n.
On the other hand, for the medium-energy normal-temperature cyclotron for accelerating negative hydrogen excited by normal-temperature coil (copper coil, non-superconducting material), the magnetic field B of magnetic pole area (peak area) Hill And valley region magnetic field B Valley Ratio of B Hill /B Valley Generally between 5 and 15, and typical B is found in (4) Hill /B Valley Value (B) Hill /B Valley = 9), the variation of the modulation F with the ratio α of the magnet sector poles to the gibs in the circumferential direction on the central plane is as shown in fig. 3a, 3b, and 3c below. From 3a, 3b and 3c, it is understood that the smaller the α, the larger the degree of modulation F in the range of α ∈ (0.3,0.6). Beyond this range: if alpha is too small, the iron proportion is too small, the magnetic field share of the coil is too high under the condition that the same magnetic field is needed, the ampere-turn number of the coil is too high, and the operation cost is high; if α is too large, the ratio of iron is too large, and the degree of modulation is too small and the focusing force is insufficient as can be seen from the later analysis.
Fourth step
As shown in fig. 2a and 2b, a main magnet structure is adopted in which the intersection point 4-1 of two straight side lines of the fan-shaped magnetic pole of the straight-side fan-shaped main magnet is not coincident with the central point 1-1 of the cover plate, but the center 4-3 of the circular arc 4-2 at the tail of the fan-shaped magnetic pole is strictly coincident with the central point 1-1 of the cover plate, and the radius 4-4 of the fan-shaped magnetic pole is smaller than the curvature radius 4-5 of the circular arc at the tail of the fan-shaped magnetic pole, so that the arc length of the main magnet pole is increased in a large radius, such as marked 12, and the magnetic field which is gradually increased along the radius of the magnetic pole and is required by isochronous acceleration of particles is convenient to match.
Because the major magnetic iron magnetic pole increases the arc length of the major radius, such as the mark 12, and improves the magnetic field provided by the magnetic pole body at the major radius, the magnetic field shimming amount required by the gib at the major radius and the gib angle width required by the gib at the major radius are greatly reduced, and the reduction 15 of the gib angle width of the gib at the major radius is enough larger than the arc length 12 of the major magnetic iron magnetic pole at the major radius, so that the total angle width of the magnetic pole at the major radius and the gib is reduced compared with the existing structure, such as the mark 15, namely alpha is reduced, therefore, the degree of modulation is increased, and the focusing force is increased according to the result (2 b).
Based on the principle, the invention designs a straight-side fan main magnet of a compact type medium-energy negative hydrogen strong-flow isochronous cyclotron. The main magnet is used for a compact type medium-energy negative hydrogen strong flow isochronous cyclotron which is shown in figures 1a, 1b and 1c and comprises a main magnet assembly used for generating a main magnetic field; the main magnet assembly is divided into three layers from the outside to the inside in the radial direction: the outer layer is a columnar main magnet yoke 1, and a cake-shaped main magnet upper cover plate and a cake-shaped main magnet lower cover plate 2 of the upper end surface and the lower end surface of the main magnet yoke 1, and a plurality of vacuumizing holes 3 are distributed on the main magnet upper cover plate and the main magnet lower cover plate 2; the inner layer is a straight-edge fan-shaped main magnet pole 4 distributed around the center point of the accelerator, the number of the main magnet poles is 8, the number of the upper and lower planes is 4 respectively, and a plurality of main magnet poles of each plane are uniformly distributed at intervals in the circumferential direction; a magnet valley region 5 is arranged between the magnetic poles, two 180-degree symmetric valley regions 5 are respectively provided with a high-frequency cavity 10 (figure 1 c), and the high-frequency cavity 10 is used for accelerating particles on each circulation track until the particles are accelerated to a high-energy extraction region and are extracted; the main magnet exciting coil is positioned in the middle layer and is arranged in a coil mounting groove 6 between the magnetic pole 4 and the magnetic yoke 2;
a straight-side fan main magnet of a compact type medium-energy negative hydrogen strong-flow isochronous cyclotron is characterized in that:
as shown in fig. 2b, the intersection point 4-1 of the two straight sides of each straight-side fan-shaped magnetic pole is not radially superposed with the central point 1-1 of the cover plate, and the intersection point 4-1 is positioned on the circumference 1-2 of the central area of the cover plate; as shown in fig. 2a, the circle center 4-3 of the circular arc at the tail of each straight-side fan-shaped magnetic pole is strictly superposed with the center 1-1 of the cover plate, and the side radius 4-4 of the fan-shaped magnetic pole of each straight-side fan-shaped magnetic pole is smaller than the curvature radius 4-5 of the circular arc at the tail of the fan-shaped magnetic pole (dotted line);
supplementary explanation:
fig. 2b is an exaggerated drawing of the central area of fig. 2a, the scale in fig. 2b being larger than in reality for the purpose of making the 4 arcs of the pole inserts near the central area clear. The actual situation is that: the radius of the arc of the pole band 4 is only a few centimeters, while the radius of the magnet is 2 meters.
As shown in fig. 2a and 2b, the intersection point 4-1 of two straight side lines of the straight-side fan-shaped main magnet is not coincident with the central point 1-1 of the cover plate, as shown in fig. 2a, but the center 4-3 of the circular arc at the tail of the fan-shaped magnetic pole is strictly coincident with the central point 1-1 of the cover plate, and the radius 4-4 of the fan-shaped magnetic pole is smaller than the curvature radius 4-5 (dotted line) of the circular arc at the tail of the fan-shaped magnetic pole, so that the arc length of the main magnet pole at a large radius is increased, as shown in fig. 1b and 2a, and 12 is marked, thereby facilitating the matching of the magnetic field which is required by isochronism acceleration of particles and is gradually increased along the radius of the magnetic pole;
as shown in fig. 1a, two straight edges of each straight-edge fan-shaped magnetic pole are further provided with magnetic pole panel outlines 8, the magnetic pole panel outlines 8 are distributed on the outer sides of the two straight edges of the magnetic pole in a bilateral symmetry mode in the form of two irregular curves, two sides close to a crossing point 4-1 of the two straight edges of the magnetic pole are connected through a small section of circular arc 8-1, the circular arc 8-1 is not radially overlapped with a central point 1-1 of a cover plate, and a large-radius panel arc length 13 of the straight-edge fan-shaped magnetic pole is relatively shortened compared with a panel arc length 14 which passes through the central point of the cover plate at the crossing point of the two straight edges of the straight-edge fan-shaped magnetic pole, the shortened arc length is replaced by an increased arc length 12 of the straight-edge fan-shaped magnetic pole, and the increased arc length 12 of the straight-edge fan-shaped magnetic pole is stronger for increasing the effect of a magnetic field compared with the same arc length of the panel.
The reduction of a small-radius magnetic field caused by the radial misalignment of the intersection point 4-1 of two straight edges of each straight-edge fan-shaped magnetic pole and the central point 1-1 of the cover plate is adjusted and compensated by the core column 7 structure at the center of the magnet through adjusting the distance between the step structure of the core column and the central plane and the radius of the step structure.
Supplementary notes:
the magnetic field loss of the central area is reduced by adjusting the step structure of the core column 7, and the design principle is as follows:
firstly, the magnetic field of the central area is reduced by adopting a main magnet structure that the central point 4-1 of the fan-shaped magnetic pole of the straight-edge fan-shaped main magnet is not superposed with the central point 1-1 of the cover plate, but the circle center 4-3 of the circular arc 4-2 at the tail part of the fan-shaped magnetic pole is strictly superposed with the central point 1-1 of the cover plate, and the length of a line segment connecting the center 4-1 of the fan-shaped magnetic pole and the tail end point of the magnetic pole (namely the radius 4-4 of the fan-shaped magnetic pole) is smaller than the radius 4-5 of curvature of the circular arc at the tail part of the fan-shaped magnetic pole, so that the magnetic field of the central area is reduced due to the reduction of the arc length of the small-radius magnetic pole near the center of the main magnet. The invention reduces the magnetic field loss of the central area by two steps, namely a structure for arranging the central area of the main magnetic pole and a structure for arranging the core column 7.
Second, main magnetic pole central zone structure: the main pole central area structure is composed of two cylindrical hollow areas with different diameters penetrating through the upper surface and the lower surface of the main pole. The diameter of the upper cylindrical hollow area is narrow, the diameter of the lower cylindrical hollow area is wider, the diameter of the lower cylindrical hollow area is matched with the diameter of the core column 7, the core column 7 is arranged in the lower cylindrical hollow area, and the radius Rplus of the core column 7 is slightly larger than the radius 1-2 of the intersection point of the two straight lines of the magnetic pole in fig. 2 b.
Third, the structure of the stem 7: as shown in fig. 1c, the stem 7 comprises a first step, a second step. The first step and the second step are bounded by the upper surface of the core column, a section of space from the upper surface to the lower surface of the magnetic pole is a height space H0 of the first step, a section of space from the lower surface of the upper surface to the lower surface of the magnetic pole is a height space Hplug of the second step, the height space H0 of the first step is larger than H1, and the height space Hplug of the second step is smaller than H2; h1 is the thickness of the magnetic pole insert, H2 is the thickness of the magnetic pole excluding the magnetic pole insert, and the thickness of the magnetic pole = H1+ H2;
the distance H0 from the center plane of the first step 7-2 of the core column and the radius R of the first step of the core column plug 7-1, height H of the stem second step 7-3 plug Both have a great influence on the magnetic field in the central region by adjusting the distance H0 of the first step of the core column from the central plane and the radius R of the step structure plug 7-1, and adjusting the height H of the second step 7-3 plug Performing magnetic field compensation: for example:
the distance H0 from the first step 7-2 of the core column to the central plane is adjusted, the upper surface of the core column is changed from a plane to a concave-convex shape, four straight edge regions except four arcs of the four corners of the upper surface are adjusted to be convex, the height of the four arcs of the four corners of the upper surface is unchanged, the four straight edge regions of the upper surface respectively correspond to four valley regions of the magnetic pole, and the loss of the magnetic field is further compensated by heightening the height of the core column 7 in the valley regions of the magnetic pole.
Radius R of stem 7 plug The size of 7-1 determines the thickness of the core column body or the strength of the magnetic field of the core column body.
The second step has cut respectively partly cylinder and circumference evenly distributed's four vertical planes by the vertical direction on the stem cylinder and constitutes, and the width and the height of these four vertical planes are all by the influence to magnetic field: when the width is constant, the height H plug The larger the magnetic field is, the more the height H is adjusted plug It is possible to compensate for the reduction of the magnetic field in the central zone to a desired value. The benefits of using the core column to regulate the magnetic field are: 7-1,7-2,7-3 of the core column are far away from the central plane, and the central area electrode and the high-frequency cavity space are not occupied.
The reduction of the angle width of the large radius of the inlaid strip is enough larger than the arc length of the magnetic pole of the main magnet increased by the large radius, so that the total angle width of the magnetic pole at the large radius and the inlaid strip is reduced compared with the prior structure, namely alpha is reduced, therefore, the degree of modulation is increased, and the focusing force is increased; and alpha is the proportion of the sector magnetic pole of the magnet and the gib on the central plane in the circumferential direction.
By adopting the straight-side fan-shaped main magnet with the structure, the magnetic field is distributed on the large radius of the magnetic pole to introduce the radial gradient focusing of the magnetic field in a manner of comprehensively adjusting the radius of the fan-shaped magnetic pole, the curvature radius of the circular arc at the tail part of the fan-shaped magnetic pole, the contour of the magnetic pole gib and the like, so that the axial focusing force is improved, and the energy of accelerating negative hydrogen to be more than or equal to 100MeV is realized.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (3)
1. A straight-side fan main magnet of a compact type medium-energy negative hydrogen strong flow isochronous cyclotron is characterized in that:
the intersection point of two straight edges of each straight-edge fan-shaped magnetic pole is not radially superposed with the central point of the cover plate, and the intersection point is positioned on the circumference of the central area of the cover plate; the center of the circular arc at the tail part of each straight-side fan-shaped magnetic pole is strictly superposed with the center of the cover plate, and the radius of the fan-shaped magnetic pole side of each straight-side fan-shaped magnetic pole is smaller than the curvature radius of the circular arc at the tail part of the fan-shaped magnetic pole;
the main magnet structure that the intersection point of two straight lines of the fan-shaped magnetic pole of the straight-side fan-shaped main magnet is not superposed with the center point of the cover plate, but the circle center of the circular arc at the tail part of the fan-shaped magnetic pole is strictly superposed with the center of the cover plate, and the radius of the fan-shaped magnetic pole is smaller than the curvature radius of the circular arc at the tail part of the fan-shaped magnetic pole is adopted, so that the arc length of the main magnet pole is increased in a large radius, and the magnetic field which is gradually increased along the radius of the magnetic pole and is required by isochronism acceleration of matched particles is facilitated;
the magnetic pole has two magnetic pole embedded strip outlines on two straight edges of the straight-edge fan-shaped magnetic pole, the magnetic pole embedded strip outlines are distributed outside the two straight edges of the magnetic pole in a bilateral symmetry mode in two irregular curves, two sides close to the intersection point of the two straight edges of the magnetic pole are connected through a small section of circular arc, the circular arc is not radially overlapped with the center point of the cover plate, the length of the large-radius embedded strip arc of the straight-edge fan-shaped magnetic pole is relatively shorter than that of the large-radius embedded strip arc of the straight-edge fan-shaped magnetic pole passing through the center point of the cover plate, the shortened arc length is replaced by the increased arc length of the straight-edge fan-shaped magnetic pole, and the increased arc length of the straight-edge fan-shaped magnetic pole is stronger in effect of increasing the magnetic field compared with the same arc length of the embedded strip.
2. The main magnet of a straight fan of a compact type moderate energy negative hydrogen strong flow isochronous cyclotron according to claim 1, wherein: the reduction of the small-radius magnetic field caused by the radial misalignment of the intersection point of two straight sides of each straight-side fan-shaped magnetic pole and the central point of the cover plate is realized, and the core column structure at the center of the magnet is adjusted and compensated by adjusting the distance between the step structure of the core column and the central plane and the radius of the step structure.
3. The straight-side fan main magnet of a compact type medium-energy negative-hydrogen strong-flow isochronous cyclotron according to claim 1, wherein: the reduction of the angular width of the inlaid strip at the large radius is enough larger than the arc length of the main magnetic pole at the large radius, so that the total angular width of the magnetic pole at the large radius and the inlaid strip is reduced compared with the prior structure, namely alpha is reduced, therefore, the degree of modulation is increased, and the focusing force is increased; and alpha is the proportion of the sector magnetic pole of the magnet and the gib on the central plane in the circumferential direction.
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| CN114916118A (en) * | 2022-05-23 | 2022-08-16 | 中国原子能科学研究院 | Can accelerate alpha particles and H 2+ Cyclotron for particles and high-gain high-precision method |
| CN116170933B (en) * | 2023-01-09 | 2023-09-05 | 中国科学院近代物理研究所 | Magnetic field device for application type isochronous cyclotron |
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