CN106211540A - 230MeV superconducting cyclotron prevents the frame for movement of draw-out area harmful resonance - Google Patents

Abstract

The present invention relates to a kind of 230MeV superconducting cyclotron and prevent the frame for movement of draw-out area harmful resonance, the magnetic pole of this structure is double-decker, lower floor is magnetic pole root, upper strata is to have a snack plate with magnetic pole root with the permeability magnetic material of material, described permeability magnetic material is had a snack plate and is fixed on the surface of lower floor's magnetic pole root, and upper strata permeability magnetic material is had a snack the protrusion side profile of plate and had bigger opisthotonos angle compared with the protrusion side profile of lower floor's magnetic pole root.The present invention, under conditions of not increasing magnetic pole radius, reduces axial resonance frequency ν before leading point_z, it is to avoid before leading point, pass through ν_zThe resonance of=1, prevents the axial quality variation of educt beaming flow caused by this resonance, reduces the beam loss of draw-out area, and then reduces the irradiation dose suffered by accelerator attendant.

Description

Mechanical structure of 230MeV superconducting cyclotron for preventing harmful resonance of extraction region

Technical Field

The invention belongs to the design technology of a cyclotron, and particularly relates to a mechanical structure of a 230MeV superconducting cyclotron for preventing harmful resonance in an extraction area.

Background

According to the isochronism principle of cyclotrons, there are

$B_0\left(r\right)=B_{center}\mathrm{\γ}\left(r\right)=B_{center}\sqrt{\frac{c^2}{c^2-{\left({\mathrm{\ω}}_{0}r\right)}^2}}---\left(1\right)$

In the formula, B_centerIs the central magnetic field, c is the speed of light, ω₀The particle cyclotron frequency and r are the cyclotron radius. Given magnetic field and cyclotron frequency B_center、ω₀The theoretical isochronous field can be given by equation (1). The cyclotron isochronous magnetic field increases with radius according to equation (1).

The free-running frequency of the isochronous cyclotron is approximated by the expression:

$v_z^2=n+\frac{N^2}{N^2-1}\·F\·(1+2{\tan }^2\mathrm{\ξ})---\left(2\right)$

$v_r^2=1-n+\frac{3\·N^2}{(N^2-1)\·(N^2-4)}\·F\·(1+2{\tan }^2\mathrm{\ξ})---\left(3\right)$

wherein the degree of modulation F is determined by the following formula:

$F=1-\frac{<B^2>}{<B{>}^2}=\frac{\mathrm{\&alpha;}\&CenterDot;(1-\mathrm{\&alpha;})\&CenterDot;{(B_{hill}-B_{valley})}^2}{{(\mathrm{\&alpha;}\&CenterDot;B_{hill}+(1-\mathrm{\&alpha;})\&CenterDot;B_{valley})}^2}---\left(4\right)$

wherein,<B>＝α·B_hill+(1-α)·B_valley(5)

α is the proportion of the magnetic pole, B_hill、B_valleyThe magnetic fields of the peak and valley regions, respectively, of the central plane, in general B_hill>B_valley。<B>Is the average magnetic field at radius r. In order to avoidThe beam loss caused by resonance is that the blade number N of the magnetic pole is more than or equal to 4 for the intermediate-energy cyclotron for extracting 230MeV proton, so the formula (3) is approximate to the formula (6):

$v_r^2=1-n---\left(6\right)$

in the formula

When the mean magnetic field of the cyclotron is not increased any more, as shown in formula (7)Namely, it isThe magnetic rigidity nearby is maximum, and v is obtained by being brought into the formula (6)_rThe magnetic rigidity is maximum near 1, namely v_rThe magnetic stiffness near the 1 resonance represents the cyclotron maximumThe magnitude of the acceleration energy, typically the isochronous cyclotron, is selected at v_rAfter a radius of 1, the magnetic field is guided out in order to make full use of the guidance field. At this time, since the average magnetic field of the cyclotron starts to decrease after the radius increases to the peak value, the magnetic field at the extraction point is already in the region where the average magnetic field decreases with the radius. As can be seen from equation (7), n is near the extraction point>0, and n rapidly increases as the average magnetic field decreasing speed becomes higher. As can be seen from the formula (2), v is possibly crossed before the point of extraction_zResonance of 1. Crossing v before exit point_zThe 1 resonance causes the axial beam quality to deteriorate.

In order to reduce the front axial resonance frequency v of the extraction point_zAccording to the formula (2), the field drop index n in the small region before the leading-out point needs to be reduced, the modulation degree F in the small region before the leading-out point needs to be reduced, or the spiral angle ξ in the small region before the leading-out point needs to be reduced, but the reduction of the field drop index n means that the radius of a magnetic pole is increased, the design of a leading-out system is difficult, the leading-out voltage is too high, the modulation degree F in the small region is changed very slowly and cannot meet the requirement of local reduction, and the reduction of the spiral angle ξ in the small region before the leading-out point structurally has difficulty.

Disclosure of Invention

The invention aims to solve the problems in the prior art, and provides a mechanical structure of a 230MeV superconducting cyclotron for preventing harmful resonance in an extraction area, which reduces the axial resonance frequency v before an extraction point under the condition of not increasing the radius of a magnetic pole (not influencing the design of an extraction system)_zAvoid crossing v before leading-out point_zResonance of 1.

The technical scheme of the invention is as follows: the utility model provides a 230MeV superconductive cyclotron prevents mechanical structure of induction zone harmful resonance, the magnetic pole is bilayer structure, and the lower floor is the magnetic pole root, and the upper strata is the magnetic conduction material shimming board with the magnetic pole root with the material, magnetic conduction material shimming board fix the surface at lower floor's magnetic pole root, the protruding side profile of upper strata magnetic conduction material shimming board compares with the protruding side profile at lower floor's magnetic pole root and has bigger reverse dog-ear.

Further, the 230MeV superconducting cyclotron as described above prevents the mechanical structure of the extraction region from unwanted resonance, wherein the thickness of the shim plate of magnetically conductive material is smaller than the height of the root of the magnetic pole.

Further, the 230MeV superconducting cyclotron as described above has a mechanical structure for preventing unwanted resonance in the extraction region, wherein the magnetic conductive material shim plate is fixed to the surface of the root of the lower magnetic pole by means of bolts.

Further, the 230MeV superconducting cyclotron as described above prevents the mechanical structure of the extraction region from the unwanted resonance, wherein the shape and size of the magnetically conductive material shim plate provided on the root of each magnetic pole are the same for a cyclotron having a plurality of magnetic poles.

Further, the 230MeV superconducting cyclotron as described above has a mechanical structure for preventing unwanted resonance in the extraction region, wherein the magnetic field in the extraction region is locally fine-tuned by processing the outer surface profile of the padding plate of magnetically conducting material, thereby improving the resonance of the beam in the extraction region.

The invention has the following beneficial effects: by adopting the scheme of the invention, when the magnetic field of the cyclotron is measured and padded, the magnetic field of the lead-out area can be locally and finely adjusted by machining the side profile of the magnetic conducting material padding plate, and the resonance of the beam current in the lead-out area is improved. The invention reduces the axial resonance frequency v before the leading-out point under the condition of not increasing the radius of the magnetic pole (not influencing the design of the leading-out system)_zAvoid crossing v before leading-out point_zThe resonance of 1 prevents the deterioration of the axial quality of the extracted beam caused by the resonance, reduces the beam loss of the extraction area and further reduces the irradiation dose received by the accelerator maintenance personnel.

Drawings

FIG. 1 is a schematic diagram of a 230MeV superconducting cyclotron;

FIG. 2 is a side view of a pole structure of a 230MeV superconducting cyclotron to prevent unwanted resonance in the extraction region;

FIG. 3 is a top view of a magnetic pole structure of a 230MeV superconducting cyclotron to prevent unwanted resonance in the extraction region;

FIG. 4 is a diagram showing the results of magnetic field and particle tracking calculation after shimming the magnetic pole by using the structure of the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

The structure of the 230MeV superconducting cyclotron is shown in fig. 1, where 1 is a magnetic pole and is spiral, which is well known in the art. The magnetic pole structure of the 230MeV superconducting cyclotron for preventing the harmful resonance in the lead-out area is designed into a double-layer structure, as shown in figure 2, the lower layer is a magnetic pole root part 2 (namely a main body of the magnetic pole), the upper layer is a magnetic conducting material padding plate 3 which is made of the same material as the magnetic pole root part 2, the magnetic conducting material padding plate 3 is fixed on the surface of the magnetic pole root part 2 of the lower layer through bolts, and the thickness H1 of the magnetic conducting material padding plate 2 is far smaller than the height H2 of the magnetic pole root part 3.

The convex side profile of the lower magnetic pole root is in smooth transition in the leading-out area, and the processing is easy. Because the thickness H1 of magnetic conduction material shimming board 2 is less than the height H2 of magnetic pole root 3 far away, more convenient processing, consequently, the protruding side profile of upper strata magnetic conduction material shimming board can process bigger reverse dog-ear with the protruding side profile of lower floor's magnetic pole root for avoid the harmful resonance of extraction area, as shown in fig. 3, 4 is the profile of lower floor's magnetic pole root protruding side in the picture, and 5 is the profile of upper strata magnetic conduction material shimming board protruding side in the picture. Through processing alone upper layer magnetic material shimming board, form bigger reverse dog-ear in protrusion side profile department, then pass through the bolt with upper layer magnetic material shimming board and the surface coordination installation of lower floor's magnetic pole root, just so avoided carrying out the degree of difficulty of processing to whole magnetic pole. And when the magnetic field of the cyclotron is measured and compensated, the magnetic field of the lead-out area can be locally and finely adjusted by machining the outer surface profile of the magnetic conduction material compensation plate 2, and the resonance of the beam current in the lead-out area is improved.

For a cyclotron having a plurality of magnetic poles, the shape and size of the magnetically conductive material shim plate provided on the root of each magnetic pole are the same. The magnetic field of the lead-out region can be adjusted by processing the size of the reverse bend angle of the convex side profile of the magnetic conducting material shim plate.

Examples

Take a certain intermediate energy superconducting cyclotron as an example. The accelerator has four magnetic pole blades, and the radius R of the magnetic pole is 860 mm. According to the magnetic field calculation, in order to avoid passing through v before leading out a point_zAt a resonance of 1, a reverse bend angle occurs from a pole radius r of 810 mm. The root of the lower magnetic pole starts from the radius r of the magnetic pole which is 770mm, the contour of the side where the magnetic pole protrudes smoothly transits to facilitate processing, and the upper magnetic conducting material padding plate (with the thickness H1 which is 50mm) starts to process a large reverse folding angle from the radius r of the magnetic pole which is 770mm, wherein the reverse folding angle is about 110 degrees and is used for adjusting the magnetic field of the leading-out area and avoiding harmful resonance. The calculation result of fig. 4 shows that v can be ensured before the extraction region is extracted by adopting the size of the magnetic conductive material shim plate_z<1, avoid v_z1.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims (5)

1. A mechanical structure of a 230MeV superconducting cyclotron for preventing unwanted resonance in the extraction region, comprising: the magnetic pole is bilayer structure, and the lower floor is the magnetic pole root, and the upper strata is the magnetic conduction material shimming board with the same material of magnetic pole root, the magnetic conduction material shimming board fix the surface at lower floor's magnetic pole root, the salient side profile of upper magnetic conduction material shimming board compares with the salient side profile of lower floor's magnetic pole root has bigger reverse dog-ear.

2. The mechanical structure of a 230MeV superconducting cyclotron of claim 1 for preventing unwanted resonance in the extraction region, wherein: the thickness of the magnetic conductive material shim plate is smaller than the height of the root of the magnetic pole.

3. The mechanical structure of a 230MeV superconducting cyclotron as claimed in claim 1 or 2 for preventing unwanted resonance in the extraction region, wherein: and the magnetic conductive material shimming plate is fixed on the surface of the root part of the lower-layer magnetic pole through a bolt.

4. The mechanical structure of a 230MeV superconducting cyclotron as claimed in claim 1 or 2 for preventing unwanted resonance in the extraction region, wherein: for a cyclotron having a plurality of magnetic poles, the shape and size of the magnetically conductive material shim plate provided on the root of each magnetic pole are the same.

5. The mechanical structure of a 230MeV superconducting cyclotron as claimed in claim 1 or 2 for preventing unwanted resonance in the extraction region, wherein: the magnetic field of the lead-out area is locally and finely adjusted by processing the outer surface profile of the magnetic conduction material padding plate, and the resonance of the beam current in the lead-out area is improved.