阅读说明：本技术 一种紧凑型回旋加速器中超导线圈的轴向对中方法 (Axial centering method of superconducting coil in compact cyclotron ) 是由 李明 张天爵 王川 于 2019-11-16 设计创作，主要内容包括：本发明公开了一种紧凑型回旋加速器中超导线圈的轴向对中方法，包括以下步骤：测量加速器中心平面超导线圈轴向磁场分布<I>Bc</I>；调整超导线圈轴向偏移位置<I>ΔZ</I>实现轴向对中。本发明克服了传统的偏见：即现有技术解决紧凑型回旋加速器中超导线圈的轴向非对中问题时，一般通过径向磁场测量的方式调整超导磁体的轴向位置，该偏见导致不但工程实施难度大，而且测量精度较难保证；本发明提出仅测量加速器中心平面超导线圈提供的轴向磁场分布，并配合束流调试阶段调整超导线圈轴向偏移位置，通过数次迭代即可实现超导线圈轴向对中，实施简单，对中精度高。(The invention discloses an axial centering method of a superconducting coil in a compact cyclotron, which comprises the following steps: measuring axial magnetic field distribution of accelerator central plane superconducting coil Bc (ii) a Adjusting axial offset position of superconducting coil ΔZ And axial centering is realized. The invention overcomes the traditional prejudice: that is, when the prior art solves the axial misalignment problem of the superconducting coil in the compact cyclotron, the axial position of the superconducting magnet is generally adjusted by means of radial magnetic field measurement, which results in not only great difficulty in engineering implementation but also difficulty in ensuring the measurement accuracy; the invention only measures the axial magnetic field distribution provided by the superconducting coil on the central plane of the accelerator, adjusts the axial offset position of the superconducting coil in cooperation with the beam debugging stage, can realize axial centering of the superconducting coil through a plurality of iterations, and is simple to implementAnd the centering precision is high.)

1. An axial centering method of a superconducting coil in a compact cyclotron is characterized in that: the method comprises the following steps:

measuring axial magnetic field distribution Bc of a superconducting coil on a central plane of an accelerator;

and step two, adjusting the axial offset position delta Z of the superconducting coil to realize axial centering.

2. The method of claim 1, wherein the axial centering of the superconducting coil in the compact cyclotron is performed by: the specific process of the step one is as follows:

⑴ during the measurement phase of accelerator magnetic field, in the superconducting coilUnder the condition of target flow intensity I, measuring to obtain axial average magnetic field distribution B of central plane of accelerator_z；

⑵ increasing the superconducting coil current by 10A, i.e. the current reaches I +10A, and measuring to obtain new axial magnetic field distribution of the center plane of the accelerator

⑶ obtaining the axial magnetic field distribution provided by the superconducting coil under the target current intensity I from the above two magnetic field distributions

⑷ according to the central plane magnetic field distribution B under the target flow intensity I_zCalculating V of different radius positions according to beam dynamics software_z,V_zThe axial focusing size of the accelerator is represented by the number of axial oscillations of one circle of particle motion.

3. The method of claim 1, wherein the axial centering of the superconducting coil in the compact cyclotron is performed by: the specific process of the second step is as follows:

⑴ at the stage of beam debugging, extending into the radial target to the small radius position of the accelerator, operating the accelerator, and providing only tiny beam current through the central area beam clamping;

⑵ the radial target is pulled radially outward to measure a series of radial positions r_iAxial position z of beam current at (i ═ 1, n)_i(i is 1, n), wherein n is the number of the measured radius positions;

⑶ passing through the axial magnetic field B in step 1_zObtaining a series of radial positions r_i(i-1, n) axial average magnetic fieldBy the axial magnetic field distribution B in step 4_cObtaining a series of radial positions r_iMagnetic field gradient at (i ═ 1, n)

⑷ the coil position is shifted axially by the upper and lower tension rods of the superconducting coil

⑸ the steps ⑴ - ⑷ are repeated until the beam current deviates from the central plane by a distance satisfying the requirement or Δ Z ≦ 0.05 mm.

Technical Field

The invention belongs to the technical field of compact superconducting cyclotrons, and particularly relates to an axial centering method of a superconducting coil in a compact cyclotron.

Background

In a cyclotron, the magnetic field consists of two parts: one part is provided by the coil itself and one part is generated by the magnet after it is magnetized. In the case of a room temperature magnet (non-superconducting magnet), the room temperature accelerator only needs to have magnets that are vertically symmetrical because the magnetic field is relatively weak, the magnetic field contributed by the coil in the room temperature magnet is very small, and the coils are not vertically symmetrical even if there is a little.

The superconducting magnet is different from a normal-temperature magnet, the proportion of a magnetic field provided by a superconducting coil in the superconducting cyclotron is large, so the superconducting coil in the superconducting cyclotron is required to be symmetrical, the superconducting coil is also required to be symmetrical as shown in figure 1, namely, the central planes of an upper pair of coils and a lower pair of coils are required to be coincident with the central plane of the accelerator or are arranged on the same horizontal line on each plane, the magnetic field is in an upper-lower symmetrical state as shown in the left figure of figure 1 under an ideal condition, and the central plane only has a downward magnetic field component B field_zThe beam packet having a downward magnetic field component B in the axial direction of the accelerator_zUnder the action of the force, the central plane rotates along the force bearing direction. As the right diagram of fig. 1 is the case of the coil being asymmetric up and down, because the coil is not processed like the magnet (because the magnet is processed and it is easy to ensure the up and down symmetry), but the coil is wound and the wound coil is difficult to be symmetric up and down, the magnetic field generated by the asymmetric coil will generate a horizontal leftward radial magnetic field component B on the central plane_rDue to the generation of a radial magnetic field component B_rThe particles are subjected to axial force to deviate from the central plane of the accelerator; when the acting force is large enough, particles can hit the upper and lower magnetic poles or the high-frequency cavity, so that the magnet is damaged or high-frequency ignition is carried out, and the operation stability of the accelerator is affected.

In order to axially center the coil, the prior art has often used a method of measuring the magnetic field of a superconducting magnet to determine the axial centering of the superconducting coil, for example, a hall probe to measure B of the central plane magnetic field_rAdjusting the axial position of the superconducting magnet until the central plane B_rTo a minimum. This method often requires the manufacture of a relatively complicated magnetic field measuring device, and the B of the magnetic field_rComponent relative to the main magnetic field B_zThe component is a small quantity, and the axial high-precision positioning of the superconducting coil is difficult to realize by a magnetic field measurement mode.

Disclosure of Invention

The invention provides an axial centering method of a superconducting coil in a compact cyclotron aiming at overcoming the defects of the prior art, and aims to solve the problem of large beam loss caused by deviation of beams from a central plane of the cyclotron in the compact cyclotron.

The invention provides the following technical scheme for solving the technical problems

A method of axial centering of a superconducting coil in a compact cyclotron, comprising the steps of:

measuring axial magnetic field distribution Bc of a superconducting coil on a central plane of an accelerator;

and step two, adjusting the axial offset position delta Z of the superconducting coil to realize axial centering.

The specific process of the step one is as follows:

⑴ at the stage of measuring the magnetic field of the accelerator, under the target current intensity I of the superconducting coil, the axial average magnetic field distribution B of the center plane of the accelerator is measured_z；

⑵ increasing the superconducting coil current by 10A, i.e. the current reaches I +10A, and measuring to obtain new axial magnetic field distribution of the center plane of the accelerator

⑶ obtaining the axial magnetic field distribution provided by the superconducting coil under the target current intensity I from the above two magnetic field distributions

⑷ according to the central plane magnetic field distribution B under the target flow intensity I_zCalculating V of different radius positions according to beam dynamics software_z,V_zThe axial focusing size of the accelerator is represented by the number of axial oscillations of one circle of particle motion.

The specific process of the second step is as follows:

⑴ at the stage of beam debugging, extending into the radial target to the small radius position of the accelerator, operating the accelerator, and providing only tiny beam current through the central area beam clamping;

⑵ the radial target is pulled radially outward to measure a series of radial positions r_iAxial position z of beam current at (i ═ 1, n)_i(i is 1, n), wherein n is the number of the measured radius positions;

⑶ passing through the axial magnetic field B in step 1_zObtaining a series of radial positions r_iAxial average magnetic field B at (i ═ 1, n)_i(i ═ 1, n); by the axial magnetic field distribution B in step 4_cObtaining a series of radial positions r_iMagnetic field gradient at (i ═ 1, n)

(i ═ 1, n); by V in step 4_zCurve interpolation results in a series of radius positions r_iV at (i ═ 1, n)_zi(i ═ 1, n); obtained according to the above data

⑷ the coil position is shifted axially by the upper and lower tension rods of the superconducting coil

⑸ repeating the second ⑴ - ⑷ steps until the distance of beam current from the central plane meets the requirement or the delta Z is less than or equal to 0.05 mm.

Advantageous effects of the invention

The invention overcomes the traditional prejudice: that is, when the prior art solves the axial misalignment problem of the superconducting coil in the compact cyclotron, the axial position of the superconducting magnet is generally adjusted by means of radial magnetic field measurement, which results in not only great difficulty in engineering implementation but also difficulty in ensuring the measurement accuracy; the invention only measures the axial magnetic field distribution provided by the superconducting coil on the central plane of the accelerator, adjusts the axial offset position of the superconducting coil in cooperation with the beam debugging stage, can realize axial centering of the superconducting coil through a plurality of iterations, and has simple implementation and high centering precision.

Drawings

FIG. 1 is a schematic diagram of axial centering and axial shifting of a superconducting coil center plane of a compact accelerator;

FIG. 2 illustrates the axial centering adjustment step of the superconducting coils in the compact cyclotron of the present invention;

FIG. 3 shows the axial average field variation for different cases;

FIG. 4 is a graph showing the change of the axial position of the beam along the radius before and after the axial centering adjustment of the superconducting coil according to the present invention;

in the figure: 1: measuring an axial average magnetic field under the operating flow intensity I; 2: axial average magnetic field measured under the current intensity I + 10A; 3: under the operating current intensity I, the axial average magnetic field contributed by the superconducting coil; 4: adjusting the axial positions of the beam current measured by radial targets at different radius positions before the superconducting coil; 5: adjusting the axial offset of the superconducting coil, and measuring the axial positions of the beam current by radial targets at different radius positions; 6: and theoretically calculating the beam axial deviation caused by the coil axial deviation.

Detailed Description

Design principle of the invention

1. Principle of beam deviation from central plane caused by axial non-centering of superconducting coil

The force of the charged particles in the magnetic field in the center plane of the accelerator can be expressed as follows according to the right-hand rule:

wherein q is the particle charge;

the beam vector of the particle in the central plane including the radial velocity component

And angular velocityA component; in the same way, the method for preparing the composite material,

are particlesMagnetic field, including radial component, felt at central plane

And a magnetic field component

And

angular unit vectors and radial unit vectors. When the central planes of the superconducting magnet and the magnet are axially aligned, the accelerator structure is symmetrical up and down, and only axial magnetic field components exist in the central planes

The particles are forced in an angular direction, thus making a gyratory motion in the central plane; when the superconducting magnet is not axially centered, a radial magnetic field component exists in a central plane

At this point, the particle is forced to have an axial component, and thus is displaced from the central plane.

2、Solving principle of axial non-centering quantity delta Z of superconducting coil

According to the basic principles of cyclotron physics, the axial motion of particles in a cyclotron can be expressed as:

z and r are the axial and radial positions of the particles, B_rAnd

the radial magnetic field and the axial average magnetic field of the current position. V_zThe number of the axial oscillations of the particles in one circle reflects the magnitude of the axial focusing force of the magnetic field at the current radius position. In compact cyclotrons, acceleration is a relatively slow process, and the term on the right of the equation can be viewed as a variable that gradually changes from zero, the equationThe solution can be expressed as:

when no radial magnetic field component B is present_rWhen z is 0, the particle moves in the central plane.

When the cyclotron coil current is loaded to the running current I, the axial magnetic field of the central plane consists of two parts: a part provided by magnetization of a magnet, denoted as B_m(ii) a A part provided by the superconducting coil itself, denoted B_c. Can be expressed as

B_z＝B_m+B_c(3)

Super-superThe magnet in the cyclotron reaches a polar saturation state, and after the coil current is increased by 10A, the magnet magnetizes part of the magnetic field There is substantially no change any longer that is,while the superconducting coils themselves provide a magnetic field proportional to the current, the total magnetic field is then expressed as

From the formulae (3) and (4)

Further, assuming that the axial misalignment of the superconducting coils is Δ Z, the radial magnetic field generated at the central plane can be obtained by maxwell's equations:

the term in parentheses in the above formula is the gradient of the axial magnetic field in the radial direction. The axial deviation of the beam (i.e. the amount of deviation from the central plane) brought by the axial non-centering of the superconducting coil is obtained by combining the formulas (2) and (6):

wherein the content of the first and second substances,

in the actual operation process of the accelerator, the axial position of the beam current can be measured by adopting the radial target to obtain a series of radial positions r_iAxial position z of beam current at (i ═ 1, n)_iAnd (i is 1 and n), wherein n is the number of the measured radial positions. In fact, because other factors causing the axial deviation of the beam exist in the accelerator, the measured axial position of the beam cannot be consistent with the formula (7), but the axial position of the coil can be adjusted to minimize the deviation of the beam from the central plane, namely solving

In the above formula G_iΔ Z represents a radius position r obtained by theoretical calculation_iThe beam current is axially shifted. By least squares

Due to calculation and measurement errors, in practice, the axial deviation of the beam current can be minimized by multiple iterations; when the delta Z is less than or equal to 0.05mm, the axial deviation of the beam caused by other factors rather than axial non-centering of the superconducting coil is always dominant.

Based on the principle of the invention, the invention designs an axial centering method of a superconducting coil in a compact cyclotron, as shown in fig. 2:

a method of axial centering of a superconducting coil in a compact cyclotron, comprising the steps of:

measuring axial magnetic field distribution Bc of a superconducting coil on a central plane of an accelerator;

the specific process is as follows:

⑴ at the stage of measuring accelerator magnetic field, under the condition of superconducting coil target current intensity IObtaining the axial average magnetic field distribution B of the central plane of the accelerator_z；

⑵ increasing the superconducting coil current by 10A, i.e. the current reaches I +10A, and measuring to obtain new axial magnetic field distribution of the center plane of the accelerator

⑶ obtaining the axial magnetic field distribution provided by the superconducting coil under the target current intensity I from the above two magnetic field distributions

⑷ according to the central plane magnetic field distribution B under the target flow intensity I_zCalculating V of different radius positions according to beam dynamics software_z,V_zThe axial focusing size of the accelerator is represented by the number of axial oscillations of one circle of particle motion.

And step two, adjusting the axial offset position delta Z of the superconducting coil to realize axial centering.

The specific process is as follows:

⑴ at the stage of beam debugging, extending into the radial target to the small radius position of the accelerator, operating the accelerator, and providing only tiny beam current through the central area beam clamping;

⑵ the radial target is pulled radially outward to measure a series of radial positions r_iAxial position z of beam current at (i ═ 1, n)_i(i is 1, n), wherein n is the number of the measured radius positions;

⑶ passing through the axial magnetic field B in step 1_zObtaining a series of radial positions r_i(i-1, n) axial average magnetic field

By the axial magnetic field distribution B in step 4_cObtaining a series of radial positions r_iMagnetic field gradient at (i ═ 1, n)

(i ═ 1, n); by V in step 4_zCurve interpolation results in a series of radius positions r_iV at (i ═ 1, n)_zi(i ═ 1, n); obtained according to the above data

⑷ the coil position is shifted axially by the upper and lower tension rods of the superconducting coil

⑸ repeating the second ⑴ - ⑷ steps until the distance of beam current from the central plane meets the requirement or the delta Z is less than or equal to 0.05 mm.