Design method of spiral deflection plate for inclined cross-section accelerator with lateral focusing force

Abstract

The present invention discloses a method for designing a spiral deflection plate of an inclined cross-section accelerator with a lateral focusing force, comprising: keeping the height of the center line between the upper and lower spiral deflection plates unchanged, and keeping the positions of the center points on the entrance and exit end surfaces of the upper and lower spiral deflection plates unchanged; while changing the cross-sectional shapes of the upper and lower spiral deflection plates into inclined cross-sectional shapes, changing the shapes of the front and rear sides of the center points on the entrance and exit end surfaces of the spiral deflection plates, so that the entrance and exit end surfaces form an angle with the beam direction. β , and the angles of the inlet and the outlet are equal in size and opposite in direction. The present invention adopts a spiral deflection plate with an inclined cross section to improve the lateral focusing force of the spiral deflection plate in addition to the deflection force; and adopts a combined change of the spiral deflection plate to provide the lateral focusing force and the edge field focusing force of the spiral deflection plate in addition to the deflection force.

Description

Technical Field

[0001] The invention belongs to the technical field of cyclotron accelerators, and in particular relates to a design method for a spiral deflection plate of an inclined cross-section accelerator with a lateral focusing force. Background Art

[0002] High-intensity proton beams play an important role in basic scientific research, national defense construction, nuclear energy development, cancer treatment, etc. One of the important limiting factors of the beam intensity of a cyclotron is the magnitude of the lateral focusing force in the central area.

[0003] The central area includes a spiral deflection plate for receiving the beam injected by the ion source and deflecting the beam from the vertical direction to the horizontal direction, an electrode structure arranged in a tiny area at the head of the high-frequency cavity in the central area for accelerating and increasing the energy of the beam, and a magnet structure arranged in a tiny area at the head of the magnet structure in the central area for deflecting the beam to provide a particle trajectory.

[0004] The existing methods for improving the lateral focusing force of the central area only stay at modifying the electrode structure and the magnetic pole structure of the central area, but ignore the modification of the spiral deflection plate structure of the central area. The spiral deflection plate is the most critical component that affects the beam intensity in the central area. The spiral deflection plate is the source of particles entering the accelerator, and the particles are injected into the accelerator from the spiral deflection plate. If the focusing ability of the spiral deflection plate is very weak, the beam drawn from the source will lose a part due to the weak focusing ability. Even if the electrode structure and the magnetic pole structure of the central area have been modified to enhance the focusing ability and reduce the beam loss, because the beam drawn from the source has lost a part during the transmission process, the overall effect of enhancing the beam intensity in the central area is not obvious.

[0005] The traditional cyclotron spiral deflection plate has a weak lateral focusing capability. Figure 1-1 , 1-2 As shown in the figure, it is a spiral track composed of two layers of spiral deflection plates. During the spiral track beam transmission process, because the electric field force always remains perpendicular to the motion track of the central ion in the spiral channel, the lateral focusing ability of the spiral deflection plate is weak, causing the beam to diverge during the transmission process and the transmission efficiency is low. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention proposes a design method for a tilted cross-section accelerator spiral deflection plate with lateral focusing force, aiming to solve the problem that the lateral focusing ability of the traditional cyclotron accelerator spiral deflection plate is weak, resulting in the failure to significantly improve the beam current intensity in the central area.

[0007] The present invention adopts the following technical solutions to solve the technical problems:

[0008] A method for designing a spiral deflection plate of a cyclotron accelerator with an inclined cross-section and a lateral focusing force comprises the following steps:

[0009] Step 1: Use the existing spiral deflection plate design method to complete the traditional spiral deflection plate design;

[0010] Step 2: keep the height of the center line of the beam trajectory between the upper and lower spiral deflection plates unchanged, and change the shape of the cross section of the spiral deflection plates to an inclined cross section in the upper, lower, left and right directions of the center line of the beam trajectory; or change the spiral deflection plates in combination: keep the height of the center line between the upper and lower spiral deflection plates unchanged, and keep the positions of the center points of the entrance and exit end surfaces of the upper and lower spiral deflection plates unchanged, and change the shapes of the front and rear sides of the center points on the entrance and exit end surfaces of the spiral deflection plates while changing the cross-sectional shapes of the upper and lower spiral deflection plates to an inclined cross section, so that the entrance and exit end surfaces form an angle β with the beam direction, and the entrance and exit angles are equal in size and opposite in direction.

[0011] The spiral deflection plate with an inclined cross section is used to provide a lateral focusing force in addition to the deflection force of the spiral deflection plate; the combined change spiral deflection plate is used to provide a lateral focusing force and a fringe field focusing force in addition to the deflection force of the spiral deflection plate;

[0012] Step 3: Use the multi-particle tracking method to simulate the particle distribution at the exit of the spiral deflection plate;

[0013] Step 4: Repeat steps 2 and 3 until the particle distribution has a smaller envelope.

[0014] Moreover, for the spiral deflection plate with an inclined cross-section, the distance between the pole plates at one end decreases, while the distance between the pole plates at the other end increases, and the distances between the upper and lower pole plates are opposite in the first and second halves of the spiral channel. In the first half of the spiral channel, if the distance between the upper and lower pole plates decreases, then the distance between the upper and lower pole plates in the second half increases. In the second half of the spiral channel, if the distance between the upper and lower pole plates in the first half increases, then the distance between the upper and lower pole plates in the second half decreases.

[0015] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with a combined inclined and trapezoidal cross-section. The spiral deflection plate with a trapezoidal cross-section keeps the middle position unchanged, reduces the width of the upper electrode plate, increases the width of the lower electrode plate, and has a trapezoidal cross-section; and the spacing between the upper and lower electrodes in the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower electrodes decreases, then the spacing between the upper and lower electrodes in the rear half increases. In the rear half of the spiral channel, if the spacing between the upper and lower electrodes in the front half increases, then the spacing between the upper and lower electrodes in the rear half decreases.

[0016] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with an inclined and V-shaped combined cross-section. The spiral deflection plate with a V-shaped cross-section keeps the distance between the pole plates in the middle position unchanged, and the two ends are upwardly tilted. The entire cross-section presents a V-shaped structure, and the distance between the pole plates at one end is reduced, while the distance between the pole plates at the other end is increased. In the front half and the back half of the spiral channel, the distance between the upper and lower pole plates is opposite. In the front half of the spiral channel, if the distance between the upper and lower pole plates is reduced, then the distance between the upper and lower pole plates in the back half is increased. In the back half of the spiral channel, if the distance between the upper and lower pole plates in the front half is increased, then the distance between the upper and lower pole plates in the back half is reduced.

[0017] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with an inclined, trapezoidal, and V-shaped combined cross-section, and the spacing between the upper and lower pole plates in the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates in the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates in the front half increases, then the spacing between the upper and lower pole plates in the rear half decreases.

[0018] Furthermore, the combination-changing spiral deflector includes a combination of a spiral deflector with an inclined cross-section and a spiral deflector with changed inlet and outlet end face shapes.

[0019] The electric field component of the edge field is not caused by the inclination of the upper and lower plates. Although the upper and lower plates are converged at one end and expanded at the other end, they are still parallel from the end face. The electric field component of the edge field is generated by the electric field arc of the edge field. The reason why the edge field generates an inward electric field force is that the end face of the entrance or exit is "cut off" a corner from one side to the other side. The two opposite oblique lines of the upper and lower inclined surfaces that have been "cut off" a corner can be imagined as edge lines composed of countless "steps". The reason why they are compared to "steps" is that each pair of "steps" and adjacent steps have different front and rear positions in the beam direction. Therefore, each pair of upper and lower steps generates an arc from the lower plate to the upper plate. These arcs constitute the electric field component of the edge field.

[0020] Moreover, the combination changes the spiral deflection plate, including a combination of a spiral deflection plate with an inclined and trapezoidal combined cross-section and a spiral deflection plate with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0021] Moreover, the combined changed spiral deflection plate includes a combination of a spiral deflection plate with an inclined and V-shaped combined cross-section and a spiral deflection plate with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0022] Moreover, the combination of the changed spiral deflection plates includes a combination of spiral deflection plates with inclined, trapezoidal, and V-shaped combined cross-sections and spiral deflection plates with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0023] Advantages and effects of the present invention

[0024] 1. The present invention overcomes the traditional prejudice that improving the focusing force of the central area of ​​the accelerator only requires improving the electrode structure and magnetic pole structure in the narrow space of the central area, while ignoring the improvement of the structure of the spiral deflection plate in the central area. It solves the problem of beam loss caused by weak focusing force and difficulty in significantly increasing the beam intensity in the central area from the source.

[0025] 2. The present invention organically combines the shape of the cross section of the spiral deflection plate and the shape of the inlet and outlet end faces of the spiral deflection plate, and supports each other to achieve a new effect after the combination. While providing the lateral focusing force in the spiral channel beam transmission process, it also provides the focusing force of the beam inlet and outlet edge fields, superimposing the focusing forces of the spiral deflection plate beam inlet, transmission process, and beam outlet, thereby blocking various loopholes that lead to particle loss in the beam transmission process and improving the quality of beam transmission.

[0026] 3. The present invention adopts the shape of the cross-section of an inclined spiral deflection plate in which the spacing between the pole plates at one end is reduced and the spacing between the pole plates at the other end is increased, and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel is opposite, thereby providing the ability of lateral focusing of the spiral channel as a whole and improving the beam transmission efficiency.

[0027] 4. The present invention adopts a V-shaped cross-sectional shape of the spiral deflection plate. The spiral deflection plate with a V-shaped cross-section keeps the middle position unchanged, and the two ends are upwardly tilted. The entire cross-section is a V-shaped structure, with the middle position as the origin. For the position x<0, the electric field force has an x-direction component; for the position x>0, the electric field force has a -x-direction component, thereby providing the spiral deflection plate with a focusing force in the x-direction, thereby improving the transmission efficiency.

[0028] 5. The present invention adopts a spiral deflection plate with a trapezoidal cross-section, keeps the middle position unchanged, reduces the width of the upper electrode plate, increases the width of the lower electrode plate, and has a trapezoidal cross-section. In the edge area of ​​the deflection plate, there is a component of the electric field force pointing to the inside of the deflection plate, thereby providing a focusing force in the x direction for the edge area of ​​the spiral deflection plate, thereby improving the transmission efficiency.

[0029] 6. The present invention adopts a combination structure of a ladder type and an inclined type, so that the ladder type and the inclined type focusing forces are superimposed: for the ladder type, in the edge area of ​​the deflection plate, the electric field force has a component pointing to the inside of the deflection plate; for the inclined type, the lower left-upper right focuses, the upper left-lower right defocuses, or the lower left-upper right defocuses, the upper left-lower right focuses. After the two focusing forces are superimposed, the lateral focusing force of the spiral deflection plate is further enhanced, and the transmission efficiency is improved.

[0030] 7. The present invention adopts a combination structure of a trapezoidal + V-shaped structure, and the focusing force is the superposition of the V-shaped and trapezoidal focusing forces. For the V-shaped structure, with the middle position as the origin, for the position x<0, the electric field force has a component in the x direction; for the position x>0, the electric field force has a component in the -x direction; for the trapezoidal structure, in the edge area of ​​the deflection plate, the electric field force has a component pointing to the inside of the deflection plate. After the two focusing forces are superimposed, the lateral focusing force of the spiral deflection plate is further enhanced, and the transmission efficiency is improved.

[0031] 8. The present invention adopts a V-type + inclined cross-section structure. For the V-type, the middle position is taken as the origin. For the position of x<0, the electric field force has an x-direction component, and for the position of x>0, the electric field force has a -x-direction component; for the inclined type, the lower left-upper right focuses, the upper left-lower right defocuses, or the lower left-upper right defocuses, the upper left-lower right focuses. After the two focusing forces are superimposed, the lateral focusing force of the spiral deflection plate is further enhanced, and the transmission efficiency is improved.

[0032] 9. The present invention adopts a combined cross-sectional structure of inclined, trapezoidal, and V-shaped. The focusing force is a superposition of V-shaped + trapezoidal + inclined. For the V-shaped, the middle position is taken as the origin. For the position of x<0, the electric field force has a component in the x direction, and for the position of x>0, the electric field force has a component in the -x direction; for the trapezoidal, in the edge area of ​​the deflection plate, the electric field force has a component pointing to the inside of the deflection plate; for the inclined type, the lower left-upper right focuses, the upper left-lower right defocuses, or the lower left-upper right defocuses, the upper left-lower right focuses. After the three focusing forces are superimposed, the lateral focusing force of the spiral deflection plate is further enhanced, and the transmission efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1-1 This is a first-person perspective diagram of a conventional spiral deflector;

[0034] Figure 1-2 This is a schematic diagram of a traditional spiral deflection plate from a second perspective;

[0035] Figure 2 It is a schematic diagram of the cross section of a conventional spiral deflector;

[0036] Figure 3a It is a schematic diagram of the inclined cross section of the spiral deflection plate of the present invention;

[0037] Figure 3b Schematic diagram of the difference in electric field force (y direction) of the inclined cross section of the spiral deflection plate of the present invention;

[0038] Figure 3c Schematic diagram of the electric field force (x direction) of the inclined cross section of the spiral deflection plate of the present invention;

[0039] Figure 3d It is a schematic diagram of the quadrupole electric field and the resultant forces in two directions of the inclined cross section of the spiral deflection plate of the present invention;

[0040] Figure 4 A schematic diagram of a V-shaped cross section of a spiral deflector plate of the present invention;

[0041] Figure 5-1 Schematic diagram of a trapezoidal cross section of a spiral deflector plate of the present invention;

[0042] Figure 5-2 The spiral deflector plate of the present invention has a combined trapezoidal and inclined cross section;

[0043] Figure 6 It is a schematic diagram of the combined cross-section of the spiral deflector plate of the present invention in V-shape, trapezoidal and inclined shapes;

[0044] Figure 7-1 It is a three-dimensional schematic diagram of the entrance and exit of the spiral deflection plate with fringe field focusing force of the present invention;

[0045] Figure 7-2A top view of the inlet and outlet of the spiral deflection plate with fringe field focusing force of the present invention;

[0046] Figure 7-3 It is a schematic diagram of focusing in the lower left-upper right direction and defocusing in the upper left-lower right direction of the quadrupole electric field with fringe field focusing force of the present invention;

[0047] Figure 7-4 It is a schematic diagram of focusing in the upper left-lower right direction and defocusing in the lower left-upper right direction of the quadrupole electric field with fringe field focusing force of the present invention;

[0048] Figure 8 Flowchart of the design method for a tilted cross-section accelerator spiral deflector with lateral focusing force. DETAILED DESCRIPTION

[0049] Design principle of the present invention

[0050] 1. The principle of the lateral focusing force of the deflection plate. When the cross-sectional shapes of the upper and lower spiral deflection plates are deformed, the lateral focusing force is generated. The following takes the inclined cross-sectional spiral deflection plate structure as an example to illustrate the principle.

[0051] 1) Focusing principle of the inclined cross-section spiral deflector structure : Keep the distance between the plates in the middle unchanged (set as d), reduce the distance between the plates at one end, and increase the distance between the plates at the other end. Establish a coordinate system with the center trajectory as the origin. Figure 3a The structure shown is that the x direction increases (the change in the plate spacing is a) and the -x direction decreases. The plate spacing on the left side of the figure is da, and the plate spacing on the right side is d+a. This structure can provide focusing force for the beam, and the principle is as follows:

[0052] For the y direction, Figure 3a As shown, the electric field force Fy is related to x. The larger the x, the smaller the Fy. For the middle position Fy(0), the electric field force just deflects the beam. Fy'=Fy-Fy(0), which means that the beam is subjected to an additional force besides the deflection. Figure 3b There is a quadrupole component of the electric force, and its magnitude is related to a:

[0053]

[0054] For the x direction, Figure 3c As shown, the electric force Fx is related to y. The larger y is, the smaller Fx is. There is a quadrupole component of the electric force, and its magnitude is related to a:

[0055]

[0056] The electric field force in the spiral deflection plate is perpendicular to the beam direction, that is, there is only an electric field in the xy direction. In a constant magnetic field:

[0057]

[0058] E is the electric field. We can get:

[0059]

[0060] Since F = qE, then:

[0061]

[0062] The resultant force of the electric field in two directions is Figure 3d The quadrupole electric field generated by this structure focuses the beam in the lower left-upper right direction and defocuses in the upper left-lower right direction. If the distance between the left plate and the right plate is increased and decreased, that is, a'=-a, the focusing and defocusing directions are opposite.

[0063] There is a mature theory on the focusing characteristics of the quadrupole electromagnetic field on the charged ion beam. The combination of two quadrupole fields with equal field strength and opposite direction has a focusing effect on the beam. Let s be the distance from a point on the central trajectory to the entrance of the spiral deflection plate. Let s be s, and s = 0 at the entrance of the spiral deflection plate and s = s0 at the exit. Let a change with s to produce a quadrupole field with alternating directions. According to the above principle, this alternating quadrupole field has a focusing effect on the beam. For example, a(0) = a0 at the entrance of the spiral deflection plate, and a decreases with s. At the center of the spiral deflection plate, a(s0 / 2) = 0, and then the direction of the quadrupole field is reversed, and a(s0) = -a0 at the exit of the spiral deflection plate. In this example, a changes within half a cycle, but it can also change within one or more cycles.

[0064] 2) The structure of the inclined cross-section spiral deflector is further explained as follows

[0065] First, use the difference in electric field force to form an electric field force in the y direction upward and an electric field force in the y direction downward, such as Figure 3b As shown, the difference in electric field force is to establish a coordinate system using the center point (which is also the center point of the beam trajectory) as the origin of the coordinate system, and taking the electric field force received by the center point as the reference, the electric field force on the left side of the center point is greater than the electric field force on the center point, so the electric field force in the y direction is upward, and the electric field force on the right side of the center point is less than the electric field force on the center point, so the y direction is downward; secondly, using the difference in electric field force, an electric field force in the x direction to the right and an electric field force in the x direction to the left are formed, and taking the electric field force received by the center point as the reference, since the electric field force is from the lower plate to the upper plate, the closer to the lower plate, the stronger the electric field force. Compared with the center point, the lower part below the center point is closer to the lower plate, so the electric field force below the center point is greater than the electric field force at the center point, and the electric field force in the x direction is to the right; since the electric field force above the center point is less than the electric field force at the center point, the electric field force in the x direction is to the left. Thirdly, since one end of the plate is contracted and the other end is expanded, the electric field force in the y direction becomes weaker and weaker at the expanded end as x increases, so as shown in Figure 3bAs shown, the downward arrow of the electric field force in the y direction on the right side of the center point increases from short to long, and the longer the downward arrow is, the weaker the electric field force is; similarly, along the direction from the lower plate to the upper plate, the electric field force becomes weaker as you move up the plate. Therefore, below the center point, the length of the arrow pointing to the right in the x direction of the electric field force becomes shorter and shorter. Above the center point, since the electric field force in the x direction is pointing to the left, the arrow is in the opposite direction, so the longer the arrow is, the weaker the electric field force is. Figure 3a , 3b , 3c is finally synthesized into Figure 6-4 The distribution of the difference in electric field force: lower left to upper right is focused, and upper left to lower right is defocused.

[0066] 3) The front and rear halves of the spiral channel of the inclined spiral deflector plate are inclined in opposite directions.

[0067] Since the spiral deflection plate with an inclined cross-section focuses in two directions and defocuses in two directions, a spiral deflection plate with an opposite inclination angle must be set in the spiral channel in the second half to obtain focusing and defocusing in the opposite directions to the upper half. In this way, the inclined cross-sections in two directions can compensate for the defects of focusing in only two directions and defocusing in the other two directions.

[0068] 2. Principle of fringe field focusing force. When the entrance or exit end face of the spiral deflection plate forms an angle β with the beam direction, the fringe field electric force is generated. The angle β is the angle between the entrance or exit end face and the plane perpendicular to the beam direction at the center point, which is formed by extending one end of the entrance or exit end face along the beam direction and shortening the other end of the end face along the beam direction.

[0069] 1) The difference between "edge field focusing" and "changing the deflection plate cross section focusing": Figure 3a The method of "changing the deflection plate cross section to focus" in Figure 5-3 all adopts the method of allowing the electric field force between the upper and lower plates to generate electric field components in the y direction and the x direction, such as Figure 3a , the electric field force in the x direction is one to the left and one to the right, because the upper and lower plates are tilted, resulting in electric field force components. The electric field component of the edge field is not due to the tilt of the upper and lower plates. Although the upper and lower plates are closed at one end and expanded at the other end, they are still parallel from the end surface. The electric field component of the edge field is generated by the electric field arc of the edge field. The inward part of the electric field arc of the edge field generates the electric field component in the x and y directions (the outward part of the electric field arc of the edge field exceeds the beam range and has no effect on the beam, so Figure 7-1Not drawn). The reason why the fringe field generates an arc-shaped inward electric field force is that the end face of the entrance or exit is "cut off" from one side to the other side, forming an oblique angle with one end facing forward (beam direction) and the other end contracting backward. The two opposite oblique lines of the upper and lower oblique surfaces that have been "cut off" can be imagined as edge lines composed of countless "steps". The reason why they are likened to "steps" is that the front and rear positions of each pair of "steps" and the adjacent steps in the beam direction are different. Therefore, each pair of upper and lower steps generates an arc from the lower plate to the upper plate. These arcs constitute the electric field components of the fringe field, such as Figure 7-1 shown.

[0070] 2) Using the "position electric field force" and the "electric field force difference" between the "center position of the spiral deflection plate". The "position electric field force" is as follows: Figure 7-1 As shown: through the front end W of the upper plate and the lower plate entrance or exit, make a surface perpendicular to the beam direction, such as Figure 7-1 The force of the edge field on the particles on the xy plane varies with their positions on the xy plane, so it is called "position electric field force". The front end is the front end W along the beam direction on the entrance or exit end surface; the "deflection plate center position" is the center position of the beam trajectory, such as Figure 7-1 The intersection O of the xy plane is the center position of the deflection plate. The direction of the "difference in electric field force" is different from the direction of the electric field force. When the electric field force has a component, the component is upward and rightward. The direction of the "difference in electric field force" can be that the electric field force in the y direction is upward, the electric field force in the y direction is downward, the electric field force in the x direction is rightward, and the electric field force in the x direction is leftward. When the electric field force is compared with the electric field force at the center point, the electric field force in the x direction is smaller than the electric field force at the center point, then the electric field force in the x direction is leftward. Similarly, the electric field force is weaker in the upper plate direction. When the electric field force in the y direction is smaller than the electric field force at the center point, then the electric field force is downward.

[0071] 3) The electric field force is the largest at the point closest to the front end W of the electrode port. Figure 7-2 for Figure 7-1 Side view of the electrode, where l is the width of the electrode and d is the height between the upper and lower electrodes. Figure 7-2 and Figure 7-3 It can be seen that Figure 7-3 The electric field force is the largest at the position closest to the front end W of the port. The closest position includes the x direction and the y direction.

[0072] 4) Analysis of the difference in electric field force in the y direction: First, compared with the -l / 2 area and the l / 2 area: In the -l / 2 area, due to the comparison of the electric field force at the point O and the point W at the center of the deflection plate, the electric field force of the edge field at the point O is farther away from the entrance end face or the exit end face than that at the point W. Therefore, the electric field force received by the point O (from the lower plate to the upper plate) is weaker than that received by the point W, and the difference in electric field force is a positive electric field force in the y direction upward; Second, although the electric field force in the -l / 2 area is upward, the difference in electric field force gradually weakens from left to right, because when viewed from above, Figure 7-2 Look, the end face of the x inlet or outlet is inclined from front to back, so the position electric field force on the xy plane weakens with the increase of x, so in the -l / 2 area, as x increases, the upward shoulder of the electric field force difference becomes shorter and shorter; thirdly, in the l / 2 area on the right end of the deflection plate center position O, as x increases, the position electric field force in the l / 2 area is weaker than the electric field force at point O. The electric field force at point O is negative compared with the position electric field force in the l / 2 area. The electric field force in the l / 2 area is downward in the y direction. Since the larger the negative number, the smaller it is, the length of the downward arrow in the y direction of the electric field force becomes longer and longer.

[0073] 5) Analysis of the difference in electric field force in the x direction: First, compared with the -d / 2 region and the d / 2 region, in the -d / 2 region, the closer to the lower plate W point, the stronger the electric field force. As the y axis increases, the larger the y is, the farther away from the W point is. The farther away, the weaker the fringe field electric field force on the particle is relative to the W point. Therefore, the electric field force close to the lower plate on the xy plane minus the electric field force at the center position O of the deflection plate is positive, and the electric field force is to the right in the x direction. However, as y increases, the difference in electric field force becomes smaller, so in the -d / 2 region The horizontal rightward arrow in the domain is also getting shorter and shorter; secondly, in the d / 2 region, since the electric field force of the lower plate on the particle weakens with the increase of y, the electric field force at the center of the deflection plate is greater than the electric field force in the d / 2 region. Therefore, the electric field force at point O at the center of the deflection plate minus the electric field force in the d / 2 region is a negative number. At this time, a horizontal leftward arrow is used to represent a negative number. Since in the d / 2 region, the closer to the upper plate, the greater the negative number of the electric field force difference, the horizontal leftward arrow becomes longer as it goes up.

[0074] 6) Lower left - upper right focus, upper left - lower right defocus. Figure 7-2 The inlet or outlet inclination mode finally leads to Figure 7-2 The entrance or exit is tilted to focus from lower left to upper right, and defocus from upper left to lower right.

[0075] 7) The angle β between the exit and the entrance must be in opposite directions to ensure that the total fringe field from the entrance to the exit is focused. Figure 7-2When the angle is set to -β, the lower left-upper right defocusing and the upper left-lower right focusing are introduced. In this way, the defocusing of the entrance is replaced by the focusing of the exit, and the defocusing of the exit is also replaced by the focusing of the entrance, so that the total edge field of the entrance and exit is focused.

[0076] 8) If Figure 7-1 Change to the situation where the lower left-upper right direction is defocused and the upper left-lower right direction is focused. Figure 7-1 The inclination angle should be in the opposite direction, the edge of the end face close to the x direction extends forward, and the edge close to the -x direction shortens backward. At this time, the corresponding edge field arc should be Figure 7-1 The arc on the right side of the electric field component x is to the left at the lower plate and to the right at the upper plate; at this time, point W is relatively farther from the vertical plane xy, and point Y is relatively closer to the vertical plane xy. Since the -x direction is the enhancement direction and the x direction is the weakening direction, the longer the arrow in the -x direction, the stronger the electric field, and the shorter the arrow, the weaker the electric field; the longer the arrow in the x direction, the weaker the electric field, and the shorter the arrow, the stronger the electric field.

[0077] Based on the above invention principle, the present invention proposes a design method for a spiral deflection plate of an inclined cross-section cyclotron accelerator with a lateral focusing force, comprising the following steps:

[0078] Step 1: Use the existing spiral deflection plate design method to complete the traditional spiral deflection plate design;

[0079] Step 2: keep the height of the center line of the beam trajectory between the upper and lower spiral deflection plates unchanged, and change the shape of the cross section of the spiral deflection plates to an inclined cross section in the upper, lower, left and right directions of the center line of the beam trajectory; or change the spiral deflection plates in combination: keep the height of the center line between the upper and lower spiral deflection plates unchanged, and keep the positions of the center points of the entrance and exit end surfaces of the upper and lower spiral deflection plates unchanged, and change the shapes of the front and rear sides of the center points on the entrance and exit end surfaces of the spiral deflection plates while changing the cross-sectional shapes of the upper and lower spiral deflection plates to an inclined cross section, so that the entrance and exit end surfaces form an angle β with the beam direction, and the entrance and exit angles are equal in size and opposite in direction.

[0080] The spiral deflection plate with an inclined cross section is used to provide a lateral focusing force in addition to the deflection force of the spiral deflection plate; the combined change spiral deflection plate is used to provide a lateral focusing force and a fringe field focusing force in addition to the deflection force of the spiral deflection plate;

[0081] Supplementary Note 1:

[0082] 1) If Figure 3bAs shown, the height of the center line of the beam trajectory between the upper and lower spiral deflection plates is kept unchanged. The center line is the dot at the center of the figure. Because the beam is facing the paper, it looks like a dot. The height unchanged in the present invention means that the height of the dot in the figure remains unchanged.

[0083] 2) If Figure 7-1 , 7-3 As shown in 7-4, the position of the center point on the inlet and outlet end surfaces of the upper and lower spiral deflection plates is kept unchanged, and the position of the center point is point O in the figure.

[0084] 3) Figure 3b The center line and Figure 7-1 , 7-3 The center point of 7-4 refers to the center point of the beam centerline, which is a concept. The latter is the center point viewed from the entrance and exit end surfaces of the spiral deflection plate.

[0085] Step 3: Use the multi-particle tracking method to simulate the particle distribution at the exit of the spiral deflection plate;

[0086] Step 4: Repeat steps 2 and 3 until the particle distribution has a smaller envelope.

[0087] Moreover, for the spiral deflection plate with an inclined cross-section, the distance between the pole plates at one end decreases, while the distance between the pole plates at the other end increases, and the distances between the upper and lower pole plates are opposite in the first and second halves of the spiral channel. In the first half of the spiral channel, if the distance between the upper and lower pole plates decreases, then the distance between the upper and lower pole plates in the second half increases. In the second half of the spiral channel, if the distance between the upper and lower pole plates in the first half increases, then the distance between the upper and lower pole plates in the second half decreases.

[0088] Supplementary Note 2:

[0089] like Figure 3d As shown, for a type of spiral deflection plate with an inclined cross-section, the final focusing effect is that the electric field quadrupole field is focused in 2 directions and defocused in 2 directions. In order to achieve focusing in all 4 directions of the electric field, it is necessary to use two sets of spiral deflection plates with inclined cross-sections in different directions. Therefore, the present invention adopts opposite spacings between the upper and lower plates in the front and rear halves of the spiral channel. In the front half of the spiral channel, if the spacing between the upper and lower plates decreases, then the spacing between the upper and lower plates in the rear half increases. In the rear half of the spiral channel, if the spacing between the upper and lower plates in the front half increases, then the spacing between the upper and lower plates in the rear half decreases.

[0090] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with a combined inclined and trapezoidal cross-section. The spiral deflection plate with a trapezoidal cross-section keeps the middle position unchanged, reduces the width of the upper electrode plate, increases the width of the lower electrode plate, and has a trapezoidal cross-section; and the spacing between the upper and lower electrodes in the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower electrodes decreases, then the spacing between the upper and lower electrodes in the rear half increases. In the rear half of the spiral channel, if the spacing between the upper and lower electrodes in the front half increases, then the spacing between the upper and lower electrodes in the rear half decreases.

[0091] Supplementary Note 3:

[0092] like Figure 5-2 As shown, a. For the ladder type + inclined type combination structure, since the inclined type is included, the spacing between the upper and lower plates in the first half and the second half of the spiral channel is opposite. In the first half of the spiral channel, if the spacing between the upper and lower plates decreases, the spacing between the upper and lower plates in the second half increases. In the second half of the spiral channel, if the spacing between the upper and lower plates in the first half increases, the spacing between the upper and lower plates in the second half decreases. b. For the ladder type + inclined type combination structure, the focusing force is the superposition of the ladder type and inclined type focusing forces; for the ladder type, in the edge area of ​​the deflection plate, the electric field force has a component pointing to the inside of the deflection plate; for the inclined type, the lower left-upper right focuses, and the upper left-lower right defocuses.

[0093] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with an inclined and V-shaped combined cross-section. The spiral deflection plate with a V-shaped cross-section keeps the distance between the pole plates in the middle position unchanged, and the two ends are upwardly tilted. The entire cross-section presents a V-shaped structure, and the distance between the pole plates at one end is reduced, while the distance between the pole plates at the other end is increased. In the front half and the back half of the spiral channel, the distance between the upper and lower pole plates is opposite. In the front half of the spiral channel, if the distance between the upper and lower pole plates is reduced, then the distance between the upper and lower pole plates in the back half is increased. In the back half of the spiral channel, if the distance between the upper and lower pole plates in the front half is increased, then the distance between the upper and lower pole plates in the back half is reduced.

[0094] Supplementary Note 4:

[0095] For the V-type + inclined type combined cross-sectional structure, a. Due to the inclusion of the inclined type, the spacing between the upper and lower plates in the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower plates decreases, then the spacing between the upper and lower plates in the rear half increases. In the rear half of the spiral channel, if the spacing between the upper and lower plates in the front half increases, then the spacing between the upper and lower plates in the rear half decreases. b. For the V-type + inclined type combined structure, the focusing force is the superposition of the V-type + inclined type. For the V-type, with the middle position as the origin, for the position x<0, the electric field force has an x-direction component, and for the position x>0, the electric field force has a -x-direction component; for the inclined type, the lower left-upper right focuses, and the upper left-lower right defocuses.

[0096] Moreover, the spiral deflection plate with an inclined cross-section includes a spiral deflection plate with an inclined, trapezoidal, and V-shaped combined cross-section, and the spacing between the upper and lower pole plates in the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates in the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates in the front half increases, then the spacing between the upper and lower pole plates in the rear half decreases.

[0097] Supplementary Note 5:

[0098] like Figure 6 As shown, for the inclined, trapezoidal, and V-shaped combined cross-sectional structures, a. Due to the inclusion of the inclined type, the spacing between the upper and lower plates in the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower plates decreases, then the spacing between the upper and lower plates in the rear half increases. In the rear half of the spiral channel, if the spacing between the upper and lower plates in the front half increases, then the spacing between the upper and lower plates in the rear half decreases. b. For the V-type + trapezoidal + inclined type combined structure, the focusing force is the superposition of the V-type + trapezoidal + inclined type. For the V-type, the middle position is taken as the origin. For the position x<0, the electric field force has a component in the x direction, and for the position x>0, the electric field force has a component in the -x direction; for the trapezoidal type, in the edge area of ​​the deflection plate, the electric field force has a component pointing to the inside of the deflection plate; for the inclined type, the lower left-upper right focuses, and the upper left-lower right defocuses.

[0099] Furthermore, the combination-changing spiral deflector includes a combination of a spiral deflector with an inclined cross-section and a spiral deflector with changed inlet and outlet end face shapes.

[0100] Supplementary Note 6:

[0101] like Figure 7-1 , 7-2As shown in FIG. 1 , when the entrance or exit end face of the spiral deflection plate forms an angle β with the beam direction, the fringe field electric force is generated. The angle β is the angle between the entrance or exit end face and the plane perpendicular to the beam direction at the center point, formed by extending one end of the entrance or exit end face along the beam direction and shortening the other end of the end face along the beam direction.

[0102] The electric field component of the edge field is not caused by the inclination of the upper and lower plates. Although the upper and lower plates are contracted at one end and expanded at the other end, they are still parallel from the end face. The electric field component of the edge field is generated by the electric field arc of the edge field. The reason why the edge field generates an arc-shaped electric field force is that the end face of the entrance or exit is "cut off" from one side to the other side. The two opposite oblique lines of the upper and lower inclined surfaces that have been "cut off" a corner can be imagined as edge lines composed of countless "steps". The reason why they are likened to "steps" is that each pair of "steps" and adjacent steps have different front and rear positions in the beam direction. Therefore, each pair of upper and lower steps generates an arc from the lower plate to the upper plate. These arcs constitute the electric field component of the edge field, such as Figure 7-1 shown.

[0103] Moreover, the combination changes the spiral deflection plate, including a combination of a spiral deflection plate with an inclined and trapezoidal combined cross-section and a spiral deflection plate with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel is opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0104] Moreover, the combined changed spiral deflection plate includes a combination of a spiral deflection plate with an inclined and V-shaped combined cross-section and a spiral deflection plate with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0105] Moreover, the combination of the changed spiral deflection plates includes a combination of spiral deflection plates with inclined, trapezoidal, and V-shaped combined cross-sections and spiral deflection plates with changed inlet and outlet end face shapes; and the spacing between the upper and lower pole plates at the front and rear halves of the spiral channel are opposite. In the front half of the spiral channel, if the spacing between the upper and lower pole plates decreases, then the spacing between the upper and lower pole plates at the rear half increases; in the rear half of the spiral channel, if the spacing between the upper and lower pole plates at the front half increases, then the spacing between the upper and lower pole plates at the rear half decreases.

[0106] It should be emphasized that the above specific embodiments are merely explanations of the present invention, and they are not limitations of the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without any creative contribution as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for designing a spiral deflection plate of a cyclotron accelerator with an inclined cross-section and a lateral focusing force, characterized in that: The following steps are involved: Step 1: Use the existing spiral deflection plate design method to complete the traditional spiral deflection plate design; Step 2: keep the height of the center line of the beam trajectory between the upper and lower spiral deflection plates unchanged, and change the shape of the cross section of the spiral deflection plates to an inclined cross section in the upper, lower, left and right directions of the center line of the beam trajectory; or change the spiral deflection plates in combination: keep the height of the center line between the upper and lower spiral deflection plates unchanged, and keep the positions of the center points on the entrance and exit end surfaces of the upper and lower spiral deflection plates unchanged, and change the shapes of the cross sections of the upper and lower spiral deflection plates to an inclined cross section while changing the shapes of the front and rear sides of the center points on the entrance and exit end surfaces of the spiral deflection plates, so that the entrance and exit end surfaces form an angle β with the beam direction, and the entrance and exit angles are equal in size and opposite in direction; The spiral deflection plate with an inclined cross section has a reduced plate spacing at one end and an increased plate spacing at the other end, and the spacings at both ends of the upper and lower plates are opposite in the front and rear halves of the spiral channel. In the front half of the spiral channel, if the spacings at both ends of the upper and lower plates are reduced, then the spacings at both ends of the upper and lower plates are increased in the rear half, and in the rear half of the spiral channel, if the spacings at both ends of the upper and lower plates in the front half are increased, then the spacings at both ends of the upper and lower plates in the rear half are reduced; the spiral deflection plate with an inclined cross section is used to provide a lateral focusing force in addition to the deflection force of the spiral deflection plate; the combination-changing spiral deflection plate is used to provide a lateral focusing force and an edge field focusing force in addition to the deflection force of the spiral deflection plate; Step 3: Use the multi-particle tracking method to simulate the particle distribution at the exit of the spiral deflection plate; Step 4: Repeat steps 2 and 3 until the particle distribution has a smaller envelope.

2. The method for designing a spiral deflection plate of a cyclotron accelerator with an inclined cross-section and a lateral focusing force according to claim 1, characterized in that: The combined and changed spiral deflection plate comprises a combination of a spiral deflection plate with an inclined cross section and a spiral deflection plate with changed inlet and outlet end face shapes.

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