Method for adjusting resonant frequency of acceleration cavity with spiral inner rod in large range

Abstract

The invention discloses a method for adjusting the resonant frequency of an acceleration cavity with spiral inner rods in a large range, and the method is based on a tuning structure which is used for short-circuiting two adjacent circles of spiral inner rods and is equivalent to short-circuiting one circle of spiral inner rods; the harmonic method comprises the following steps: selecting the same position on each circle of circumference of a spiral inner rod to place a tuning structure, and obtaining an axial frequency change rule of the short-circuited inner rod; and an inner rod ring layer currently connected with the tuning structure is determined, and on the inner rod ring layer, the tuning structure moves in the inner rod spiral direction to carry out resonant frequency offset shimming. According to the invention, by selecting the inner rod ring layer currently connected with the tuning structure, the approximate range of the resonance offset shimming of the acceleration cavity is determined; the fine tuning range of offset shimming is obtained by moving the tuning structure along the spiral direction of the inner rod, so that the difficult problem that the resonant frequency of the cavity deviates due to errors of the acceleration cavity based on the spiral inner rod in the machining and mounting process is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of radio frequency accelerator cavities of ion implanters, and in particular relates to a method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range. Background Art

[0002] For lower frequency RF accelerator cavities, a spirally structured inner rod is often used to meet the lower resonant frequency while significantly reducing the cavity volume.

[0003] The difficulty in designing an accelerating cavity based on a spiral inner rod is that there are inevitable errors between the theoretical design model of the accelerating cavity and the final processed object, and errors are also prone to occur during the assembly process of the various components of the cavity. The above-mentioned processing and installation errors of the accelerating cavity will cause the resonance frequency of the cavity to shift.

[0004] In order to solve the problem of cavity resonant frequency offset, the prior art adopts a method of installing a tuning rod at the center above the spiral inner rod, and adjusting the cavity resonant frequency offset by moving the tuning rod up and down. However, due to the weak magnetic field at the location of the tuning rod, the frequency adjustment range of this method is very small. If the rod is to have a greater impact on the cavity magnetic field, it is necessary to extend the rod into the spiral inner rod. At this time, the power loss of the cavity is greatly increased, the water cooling design of the tuning rod is very difficult, and the need for a higher power source increases the system cost. Therefore, the adjustment range of the cavity resonant frequency offset based on the tuning rod is usually only 0 to 0.5MHz. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes a method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range, aiming to solve the problem that the adjustment range of the resonance frequency offset of the cavity based on the tuning round rod is very small, only 0 to 0.5 MHz.

[0006] The present invention proposes the following technical solutions to solve the technical problems:

[0007] A method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range is based on a tuning structure, which connects two adjacent spiral inner rods, which is equivalent to short-circuiting one spiral inner rod, thereby reducing the length of the inner rod; the method is characterized in that the resonance frequency offset padding method comprises the following steps:

[0008] Step 1: Select the same position on each circle of the spiral inner rod to place the tuning structure, and obtain the axial frequency change law of the short-circuited inner rod;

[0009] Step 2: Determine the inner rod to which the tuning structure is currently connected. On the connected inner rod, the tuning structure moves along the spiral direction of the inner rod to compensate for the resonant frequency offset.

[0010] Furthermore, the specific process of step 1 is as follows:

[0011] 1) Making a tuning structure connecting two adjacent spiral inner rods;

[0012] 2) At the same position on the circumference of each circle of the spiral inner rod, a tuning structure is used to sequentially connect two adjacent circles of the spiral inner rod along the axial direction;

[0013] 3) The resonant frequency of the tuning structure when it is located at different positions is simulated and calculated, and the variation law of the resonant frequency along the axial direction of the spiral inner rod when the tuning structure is located at different positions is obtained.

[0014] Furthermore, the specific process of step 2 is as follows:

[0015] 1) Determine the resonant frequency offset to be padded currently;

[0016] 2) determining the axial position of the tuning structure according to the resonant frequency offset to be compensated; the axial position is the position of the inner rod to which the tuning structure is currently connected;

[0017] 3) The tuning structure moves along the spiral direction of the inner rod at the currently connected inner rod position to compensate for the resonant frequency offset.

[0018] Furthermore, in the step 1 process 2), a tuning structure is used to sequentially connect two adjacent turns of the spiral inner rod along the axial direction, and the two adjacent turns of the spiral inner rod are: starting from 0 turns to 1 turns, and ending at n-1 turns to n turns; or starting from n turns to n-1 turns, and ending at 1 turn to 0 turns; the axial direction includes a lower spiral direction and an upper spiral direction; the lower spiral direction is a direction close to the beam and perpendicular to the beam direction, and the upper spiral direction is a direction away from the beam and perpendicular to the beam direction.

[0019] Furthermore, the step 1 process 3) obtains the variation law of the resonant frequency along the axial direction of the spiral inner rod when the tuning structure is located at different positions, and the variation law includes a linear variation law and a nonlinear variation law along the axial direction of the spiral inner rod.

[0020] Furthermore, when the tuning structure changes its position along the lower spiral direction of the spiral inner rod, the linear change law is a change law from small to large; when the tuning structure changes its position along the upper spiral direction of the spiral inner rod, the linear change law is a change law from large to small.

[0021] Furthermore, the step 2 process 3) is specifically the following process:

[0022] If the current resonant frequency offset to be padded is smaller than the resonant frequency at this position, the tuning structure continues to move toward the upper spiral inner rod at the current position of the spiral inner rod; if the current resonant frequency offset to be padded is larger than the resonant frequency at this position, the tuning structure continues to move toward the lower spiral inner rod at the current position of the spiral inner rod.

[0023] Furthermore, the tuning structure of the step 1 process 1) is a rectangular tuning structure with two left and right lobes spliced ​​together, and the rectangular tuning structure connects two adjacent spiral inner rods through two upper and lower circular holes at the center after being spliced ​​together; the spacing between the upper and lower two circular holes is the spacing between two adjacent spiral inner rods; the inner diameter of the two circular holes is the outer diameter of the spiral inner rod; the circular hole and the spiral inner rod are tightly fitted.

[0024] Furthermore, the tuning structure can also connect three or more adjacent n-helical inner rods. When the tuning structure connects three adjacent spiral inner rods, it is equivalent to short-circuiting 2 spiral inner rods; when the tuning structure connects n adjacent spiral inner rods, it is equivalent to short-circuiting n-1 spiral inner rods.

[0025] Advantages and effects of the present invention

[0026] 1. The tuning method of the short-circuited inner rod of the present invention directly short-circuits the spiral inner rod with the strongest magnetic field strength, thereby changing the direction of the magnetic field and allowing the frequency to be adjusted within a wide range of 0-2.4 MHz.

[0027] 2. The present invention places a tuning structure at the same position on the circumference of each spiral inner rod, thereby obtaining the variation pattern of the resonant frequency of the acceleration cavity with the position of the tuning structure; by selecting the inner rod coil layer to which the tuning structure is currently connected, the approximate range of the offset padding of the resonant frequency of the acceleration cavity is determined; by moving the tuning structure along the spiral direction of the inner rod on the connected inner rod coil layer, the fine tuning range of the offset padding is obtained, thereby achieving the goal of large-scale adjustment of the resonant frequency of the acceleration cavity with a spiral inner rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the application effect of the acceleration cavity;

[0029] Figure 2 Stereoscopic diagram of the acceleration chamber;

[0030] Figure 3 This is a schematic diagram of the effect of installing the tuning structure of the present invention on the spiral inner rod;

[0031] Figure 4 It is a schematic diagram of the tuning structure of the present invention;

[0032] Figure 5Calculate the resonant frequencies of the tuned structure at different locations for simulation;

[0033] Figure 6 This is a flow chart of adjusting the resonance frequency of the accelerating cavity over a large range according to the present invention. DETAILED DESCRIPTION

[0034] Design principle of the present invention

[0035] 1. The innovation of the present invention: The direction of the magnetic field is changed by the method of "short-circuiting the inner rod", so that the frequency padding range is increased from 0 to 0.5MHz in the prior art to 0 to 2.4MHz. The method of "short-circuiting the inner rod" is to connect adjacent spiral inner rods with a tuning structure. The magnetic field in the acceleration cavity is distributed in the space of the large cylinder where the spiral inner rod is located, and the closer to the surface of the spiral inner rod, the stronger the magnetic field. After short-circuiting two circles of the inner rod in this embodiment, there is basically no magnetic field on the surface of the short-circuited circle of the inner rod, and the magnetic field will change direction and no longer go around the surface of the short-circuited circle of the inner rod, but only around a small section of the vertical surface of the adjustment structure. The difference between this embodiment and the prior art is that the prior art is to arrange a tuning round rod that can move up and down above the spiral inner rod, and adjust the frequency by moving the round rod. Due to the limited water cooling design of the tuning round rod and the power loss of the cavity should not be too large, the round rod is usually only arranged at a position with weaker magnetic field strength, and the ability to influence the frequency is also weak. Therefore, the frequency adjustment range of the short-circuited inner rod in the present invention is relatively large. The frequency adjustment range of the spiral inner rod from the 0th turn to the 6th turn is 0-2.4MHz, while the tuning rod adjustment range of the comparative document is only 0-0.5MHz.

[0036] 2. Design principle of the present invention:

[0037] 1) Obtaining the frequency variation law of the tuning structure along the axial short-circuited inner rod; when obtaining the frequency variation law, the circumferential position of the tuning structure is fixed, that is, the circumferential position of the tuning structure in each circle of the inner rod is the same. The axial direction can be the direction of the lower spiral or the direction of the upper spiral.

[0038] 2) According to the frequency variation law and the requirement for compensating the resonance frequency offset of the acceleration cavity, the position of the short-circuited inner rod of the tuning structure is selected;

[0039] 3) Frequency padding is performed by utilizing the characteristic that each turn of the spiral inner rod has countless adjustment points. Since each turn of the spiral inner rod is spirally ascending or spirally descending, there are countless tuning points on the same turn, and the height of each point is different. When using this characteristic to perform frequency padding, the axial position of the tuning structure is fixed, that is, during the tuning process, the short-circuited spiral inner rod is fixed. After the short-circuited spiral inner rod is fixed, the tuning structure can move upward or downward along the spiral direction on the short-circuited inner rod.

[0040] 3. Relationship between short-circuiting the inner rod and changing the frequency: The coaxial resonant cavity can be equivalent to an RLC resonant circuit, so its resonant frequency f can be expressed by the following formula:

[0041]

[0042] The equivalent inductance L is concentrated on the spiral inner rod of the cavity, and the equivalent capacitance C is concentrated on the accelerating electrode of the cavity. We connect two adjacent circles of inner rods, which is equivalent to short-circuiting one circle of the spiral inner rod, reducing the length of the inner rod, reducing the value of the equivalent inductance L, and increasing the resonant frequency. If there is a need to adjust the resonant frequency in a larger range, three or more circles of the spiral inner rods can be connected at the same time to short-circuit them.

[0043] Based on the above principle, the present invention designs a method for adjusting the resonance frequency of the accelerating cavity with a spiral inner rod over a large range. Figure 1 , Figure 6 As shown, the method is based on a tuning structure such as Figure 3-4 As shown, connecting two adjacent spiral inner rods is equivalent to short-circuiting one spiral inner rod, thereby reducing the length of the inner rod; the characteristic is that the resonant frequency offset padding method includes the following steps:

[0044] Step 1: Select the same position on each circle of the spiral inner rod to place the tuning structure, and obtain the axial frequency change law of the short-circuited inner rod; the specific process is as follows:

[0045] 1) Making a tuning structure connecting two adjacent spiral inner rods;

[0046] The tuning structure is a rectangular tuning structure with two left and right lobes spliced ​​together. The rectangular tuning structure connects two adjacent spiral inner rods through two upper and lower circular holes at the center after splicing; the spacing between the upper and lower two circular holes is the spacing between two adjacent spiral inner rods; the inner diameter of the two circular holes is the outer diameter of the spiral inner rod; the circular hole and the spiral inner rod are tightly matched.

[0047] 2) At the same position on the circumference of each circle of the spiral inner rod, a tuning structure is used to sequentially connect two adjacent circles of the spiral inner rod along the axial direction;

[0048] The tuning structure is used to sequentially connect two adjacent spiral inner rods along the axial direction, and the two adjacent spiral inner rods are: starting from 0 turns to 1 turns, and continuing until n-1 turns to n turns; or starting from n turns to n-1 turns, and continuing until 1 turn to 0 turns; Figure 2 As shown, the axial direction includes a lower spiral direction and an upper spiral direction; the lower spiral direction is a direction close to the beam and perpendicular to the beam direction, and the upper spiral direction is a direction away from the beam and perpendicular to the beam direction.

[0049] 3) Simulate and calculate the resonant frequencies of the tuning structure at different locations. Figure 5 As shown, the variation law of the resonant frequency along the axial direction of the spiral inner rod when the tuning structure is located at different positions is obtained;

[0050] The obtained tuning structure is located at different positions, and the resonant frequency changes along the axial direction of the spiral inner rod, and the change law includes a linear change law and a nonlinear change law along the axial direction of the spiral inner rod;

[0051] Supplementary Note 1

[0052] like Figure 5 As shown in the figure, when the tuning structure is connected to 0-1 turns, 1-2 turns, 2-3 turns, 3-4 turns, and 4-5 turns respectively, the frequency basically rises linearly, and when the tuning structure is connected to 4-5 turns to 5-6 turns respectively, the corresponding frequency decreases. When selecting the axial position of the tuning structure, it is only selected within the linearly rising frequency range, and the nonlinear rising range is not the selected range.

[0053] When the tuning structure changes its position along the lower spiral direction of the spiral inner rod, the linear change law is a change law from small to large; when the tuning structure changes its position along the upper spiral direction of the spiral inner rod, the linear change law is a change law from large to small.

[0054] Step 2: Determine the inner rod to which the tuning structure is currently connected. On the connected inner rod, the tuning structure moves along the spiral direction of the inner rod to compensate for the resonant frequency offset. The specific process is as follows:

[0055] 1) Determine the resonant frequency offset to be padded currently;

[0056] 2) determining the axial position of the tuning structure according to the resonant frequency offset to be compensated; the axial position is the position of the inner rod to which the tuning structure is currently connected;

[0057] 3) The tuning structure moves along the spiral direction of the inner rod at the currently connected inner rod position to compensate for the resonant frequency offset; the specific process is as follows: if the current resonant frequency offset to be compensated is smaller than the resonant frequency at this position, the tuning structure continues to move toward the upper spiral inner rod at the current position of the spiral inner rod; if the current resonant frequency offset to be compensated is larger than the resonant frequency at this position, the tuning structure continues to move toward the lower spiral inner rod at the current position of the spiral inner rod.

[0058] The tuning structure can also connect three or more adjacent n-helical inner rods. When the tuning structure connects three adjacent spiral inner rods, it is equivalent to short-circuiting 2 spiral inner rods; when the tuning structure connects n adjacent spiral inner rods, it is equivalent to short-circuiting n-1 spiral inner rods.

[0059] Embodiment 1:

[0060] 1. Install the tuning structure on the spiral inner rod. Figure 3-4 As shown, the tuning structure is composed of two left and right lobes, which are tightened by screws. The screws can be located above the upper circular hole and below the lower circular hole, or between the upper and lower circular holes.

[0061] 2. Simulate and calculate the resonant frequency of the tuning structure at different positions. The calculation results are as follows: Figure 5 As shown, when moving from the 0-1st circle to the 1-2nd circle, from the 2-3rd circle to the 3-4th circle, and from the 3-4th circle to the 4-5th circle, the frequency basically rises linearly, and when moving from the 4-5th circle to the 5-6th circle, it rises nonlinearly.

[0062] 3. When making up for the resonant frequency offset, the moving range of the tuning structure should be selected from the range of the spiral inner rod where the frequency is basically linearly increased. For example, the frequency within 0-5 turns is basically linearly increased, so the range of 0-5 turns is the moving range of the tuning structure. Or, the frequency within 5-0 turns is basically linearly decreased, so the range within 5-0 turns is the moving range of the tuning structure.

[0063] 4. Assume that the current resonant frequency offset to be compensated is 20.68MHz. Figure 5 It can be seen that 20.68MHz is greater than 20.65 and less than 20.15 in the table, and the frequency of 20.68MHz is closer to the frequency of 20.65 in the table. The frequency of 20.65 in the table is the frequency when the tuning structure is connected to the spiral inner rod with 1-2 turns. Therefore, the tuning structure is connected to the spiral inner rod with 1-2 turns. Since the direction of the lower spiral (the direction of downward rotation is the direction of the lower spiral, that is, the direction close to the beam is the direction of the lower spiral) is the direction of increasing frequency, the tuning structure moves downward clockwise along the spiral direction. As it moves downward, the frequency gradually increases until the frequency of the tuning structure at the current position reaches the padding frequency of 20.68MHz.

[0064] 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 adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range, the method is based on a tuning structure, the tuning structure connects two adjacent turns of the spiral inner rod, which is equivalent to short-circuiting one turn of the spiral inner rod, thereby reducing the length of the inner rod; the method is characterized by: The resonant frequency offset shimming method comprises the following steps: Step 1: Select the same position on each circle of the spiral inner rod to place the tuning structure, and obtain the axial frequency change law of the short-circuited inner rod; Step 2: Determine the inner rod to which the tuning structure is currently connected. On the connected inner rod, the tuning structure moves along the spiral direction of the inner rod to compensate for the resonant frequency offset.

2. A method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 1, characterized in that: The specific process of step 1 is as follows: 1) Making a tuning structure connecting two adjacent spiral inner rods; 2) At the same position on the circumference of each circle of the spiral inner rod, a tuning structure is used to sequentially connect two adjacent circles of the spiral inner rod along the axial direction; 3) The resonant frequency of the tuning structure when it is located at different positions is simulated and calculated, and the variation law of the resonant frequency along the axial direction of the spiral inner rod when the tuning structure is located at different positions is obtained.

3. The method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 1, characterized in that: The specific process of step 2 is as follows: 1) Determine the resonant frequency offset to be padded currently; 2) determining the axial position of the tuning structure according to the resonant frequency offset to be compensated; the axial position is the position of the inner rod to which the tuning structure is currently connected; 3) The tuning structure moves along the spiral direction of the inner rod at the currently connected inner rod position to compensate for the resonant frequency offset.

4. The method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 2, characterized in that: In the step 1 process 2), a tuning structure is used to sequentially connect two adjacent turns of the spiral inner rod along the axial direction, and the two adjacent turns of the spiral inner rod are: starting from 0 turns to 1 turns, and continuing to n-1 turns to n turns; or starting from n turns to n-1 turns, and continuing to 1 turn to 0 turns; the axial direction includes a lower spiral direction and an upper spiral direction; the lower spiral direction is a direction close to the beam and perpendicular to the beam direction, and the upper spiral direction is a direction away from the beam and perpendicular to the beam direction.

5. A method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 4, characterized in that: The step 1 process 3) obtains the variation law of the resonant frequency along the axial direction of the spiral inner rod when the tuning structure is located at different positions, and the variation law includes a linear variation law and a nonlinear variation law along the axial direction of the spiral inner rod.

6. A method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 5, characterized in that: When the tuning structure changes its position along the lower spiral direction of the spiral inner rod, the linear change law is a change law from small to large; when the tuning structure changes its position along the upper spiral direction of the spiral inner rod, the linear change law is a change law from large to small.

7. A method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 3, characterized in that: The step 2 process 3) is specifically the following process: If the current resonant frequency offset to be padded is smaller than the resonant frequency at this position, the tuning structure continues to move toward the upper spiral inner rod at the current position of the spiral inner rod; if the current resonant frequency offset to be padded is larger than the resonant frequency at this position, the tuning structure continues to move toward the lower spiral inner rod at the current position of the spiral inner rod.

8. The method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 2, characterized in that: The tuning structure of step 1 process 1) is a rectangular tuning structure with two left and right lobes spliced ​​together. The rectangular tuning structure connects two adjacent spiral inner rods through two upper and lower circular holes at the center after being spliced ​​together; the spacing between the upper and lower two circular holes is the spacing between two adjacent spiral inner rods; the inner diameter of the two circular holes is the outer diameter of the spiral inner rod; the circular hole and the spiral inner rod are tightly fitted.

9. The method for adjusting the resonance frequency of an accelerating cavity with a spiral inner rod over a large range according to claim 1, characterized in that: The tuning structure can also connect three or more adjacent n-helical inner rods. When the tuning structure connects three adjacent spiral inner rods, it is equivalent to short-circuiting 2 spiral inner rods; when the tuning structure connects n adjacent spiral inner rods, it is equivalent to short-circuiting n-1 spiral inner rods.

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