JP2935085B2 - Cyclotron beam energy estimation method. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a beam energy of a cyclotron.

[0002]

2. Description of the Related Art In a cyclotron, it is indispensable to adjust a beam extraction system device such as a deflector and a magnetic channel in order to maximize a beam extraction current value. This adjustment is performed by using a voltage, a current, and the like applied to the deflector, the magnetic channel, and the like as control parameters. For this, the beam energy inside the cyclotron must be known. This is because the optimum setting value of the control parameter changes depending on the beam energy, and it is important to know the accurate value of the beam energy inside the cyclotron in order to facilitate the adjustment operation.

The beam energy, which is calculated at the design stage, is a calculated value using fixed values, and actually varies depending on the manufacturing accuracy and assembly error of the components of the cyclotron. In addition, in the adjustment work, not only the position of the extraction system equipment is finely adjusted and the voltage and current values are changed, but also the position of the ion source at the center of the cyclotron is changed. The exact value of energy cannot be determined.

For this reason, conventionally, a method of estimating beam energy by arranging an electromagnet for analysis in front of a beam transport system of a cyclotron and measuring a radius of curvature of a beam trajectory that changes in accordance with a change in beam energy is known. Is adopted. This takes advantage of the fact that as the beam energy increases, the radius of curvature of the beam trajectory increases accordingly.

[0005]

However, in the above method, only the beam energy extracted outside from the cyclotron can be known. On the other hand, for optimal setting of control parameters, it is necessary to know the beam energy inside the cyclotron, and the optimal value of the control parameters is determined using the beam energy value obtained downstream of the equipment adjusted by the above method. Setting is difficult.

Therefore, an object of the present invention is to provide a beam energy estimating method capable of knowing the beam energy inside a cyclotron.

[0007]

According to the present invention, a beam current sensor measures a beam current distribution pattern in a radial direction of a cyclotron at at least three predetermined angular positions in a polar coordinate system having a cyclotron center as an origin. From the distribution pattern, the outermost beam trajectory radius at the three locations is determined, and a beam trajectory model determined in advance from the angle at the three locations and the measured value of the beam trajectory radius is used to calculate the beam trajectory radius among the three locations. The beam energy at the time of estimating the beam orbital radii of the remaining two places using the one point as a base point and matching the measured value and the estimated value of the beam orbital radius while changing the beam energy value as a parameter is used. Characterized in that the values are used as beam energy estimates. Guy estimation method is obtained.

[0008]

The present invention focuses on the fact that there is a close relationship between the beam energy and the radius of the outermost beam orbit inside the cyclotron. The beam energy is estimated from the pattern measurement data, and the beam energy estimated value is obtained based on the estimated value.

[0009]

FIG. 1 is a diagram showing a schematic configuration of a cyclotron to which the present invention is applied. As main components, two dee electrodes 10 and a deflector 1 as a beam extraction system are shown.
1, a magnetic channel 12, and a beam transport system 14 disposed in front of a beam outlet 13. In this embodiment,
As beam current sensors for measuring the outermost beam orbit radius, first to third probes 16, 17 and 18 are provided between two dee electrodes 10 and deflectors 11, respectively.
, Located between the deflector 11 and the magnetic channel 12. In addition, although the electromagnet for analysis is shown by the reference number 20 in order to make the description of the conventional technique easy to understand,
This is not necessary in the present invention.

A beam 30 near the outermost periphery generated from an ion source (not shown) at the center of the cyclotron and accelerated along a path shown by a broken line in FIG. The beam extraction trajectory is determined by receiving a force according to the magnetic field strength. At the time of beam adjustment, the voltage value of the deflector 11 and the magnetic channel 1
The operator finely adjusts the current value of No. 2 to guide the beam extraction trajectory to the beam exit 13.

In order to determine the optimum value of the voltage set value of the deflector 11 and the current set value of the magnetic channel 12, it is necessary to know the energy value of the beam passing therethrough. This is because the effect of the electrostatic or magnetic field on the displacement of the beam trajectory is a function of the beam energy.

The motion of a charged particle in a three-dimensional space is represented by dP / dt = q · v · B + q · E. Here, P is the momentum of the charged particle, v is the velocity, q is the number of charges, B is the magnetic field strength, and E is the electric field strength.

Therefore, if the magnetic field strength B and the electric field strength E in the three-dimensional space are obtained, certain initial conditions (P ₀ ,
The trajectory of the charged particle at v ₀ ) can be obtained by sequentially solving the above equation. In order to solve the above equation using an electronic computer, a numerical integration method such as the Runge-Kutta-Gill method is used, and as shown in FIG. 2, from the initial condition t = t ₀ , t ₁ , t ₂ , t The trajectory at ₃ can be determined. As for the magnetic field data, measurement data at the time of assembling the cyclotron is stored in a memory as mesh data as shown in FIG. 3, and magnetic field data of a section where charged particles exist at the time of simulation is used. On the other hand, as the electric field data, the electric field data near the dee electrode 10 is analytically obtained and the value is used.

An example of the beam energy estimation method according to the present invention will be described in order. Here, each of the first to third probes 16 to 18 has an angle θ with respect to the positive X axis as a base line in a polar coordinate system whose origin is the center of the cyclotron.
It is assumed that they are installed near the outermost periphery of ₁ , θ ₂ and θ ₃ .

First, the first to third probes 16 to 1
8 are respectively scanned in the radial direction of the cyclotron (pulled out of the cyclotron from the state of being inserted into the cyclotron), and the radial distribution of the beam current is measured. Radial distribution patterns of the beam current by the first to third probes 16 to 18 are as shown in FIGS. 4, 5, and 6, respectively. 4 to 6, the radii r ₁ , r ₂ , and r ₃ from the center of the cyclotron when the beam current suddenly decreases from a substantially constant level to reach a half of the constant level are respectively shown. The radius of the outermost beam. When the beam current decreases in two stages as shown in FIG. 6, the radius r ₃ at the half level is adopted for the higher stage.

Here, the reason for obtaining the radius of the outermost beam as described above is as follows. That is, if a probe using a high-resolution current sensor is used, the radial distribution pattern of the beam current becomes as shown by the solid line in FIG.
The pattern should show a peak for each beam trajectory. However, the probe used in practice has insufficient resolution, so that the pattern of the beam current cannot be distinguished from the peak for each beam trajectory as shown by the broken line. Therefore, this is a region where the beam current suddenly decreases when the probe deviates from the outermost beam, and is about 1/2 of the steady level.
Is treated as the radius of the outermost beam.

[0017] Next, as shown in FIG. 8, in a polar coordinate system with the origin at the San black Tron center, assuming a certain beam energy value E _x, is the beam movement direction alpha, the installation position of the first probe 16 angle theta _1, based on the orbital radius of the measured values r ₁ of the outermost beams to estimate a trajectory radius r _e2, r _e3 at an angle theta _2, theta ₃ by numerical integration method described above.

[0018] Then, the beam energy value E _x, when to change the direction of movement α exploratory _{r e2 = r 2, r e3} = r 3 become condition is obtained, to determine the beam energy value E _x at that time Beam energy estimate.

In the above description, the case where the number of probes is a minimum of three has been described. However, it goes without saying that the accuracy of estimating the orbital radius is improved by increasing the number of probes. As shown in FIG. 9, a septum electrode 11-1 is provided in the deflector 11, and the radial position of the septum electrode 11-1 is measured experimentally by the measurement of the orbital radius of the outermost beam by the second probe 17. Since it is close to r ₂ , the second probe 17 can be omitted by using the septum electrode 11-1 as a substitute for the second probe 17.

FIG. 10 is a diagram showing the results of the experiment according to the above-described embodiment, from which the effectiveness of the present invention can be understood.

[0021]

As described above, according to the present invention, since the beam energy value inside the cyclotron can be known, it is easy to adjust the control parameters such as the voltage value and the current value in the extraction system at the time of beam adjustment. become.
As a result, the burden on the operator can be reduced and the adjustment work time can be reduced, which can greatly contribute to improving the operability of the cyclotron.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a cyclotron to which the present invention is applied.

FIG. 2 is a diagram for explaining a beam trajectory estimation method used in the present invention.

FIG. 3 is a diagram for explaining an example of a method of creating measurement data used in the present invention.

FIG. 4 is a diagram showing a measurement result by a first probe shown in FIG. 1;

FIG. 5 is a diagram showing a measurement result obtained by a second probe shown in FIG. 1;

FIG. 6 is a diagram showing a measurement result by a third probe shown in FIG. 1;

FIG. 7 is a view for explaining the measurement principle of each probe shown in FIG. 1;

FIG. 8 is a diagram for explaining a beam trajectory estimation method according to the present invention.

FIG. 9 is a view for explaining another example of the second probe shown in FIG. 1;

FIG. 10 is a diagram showing measurement results and beam energy estimation results of the first to third probes shown in FIG. 1;

[Explanation of symbols]

 Reference Signs List 10 Dee electrode 11 Deflector 11-1 Septum electrode 12 Magnetic channel 13 Beam outlet 14 Beam transport system 16 First probe 17 Second probe 18 Third probe 20 Electromagnet for analysis 30 Beam orbit

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H05H 7/00-15/00 G01T 1/00-7/12 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A beam current sensor measures a beam current distribution pattern in a radial direction of a cyclotron at at least three predetermined angular positions in a polar coordinate system having a cyclotron center as an origin. The beam orbit radius of the outer periphery is obtained, and
The beam trajectory radius of the remaining two locations is estimated from one of the three locations as a base point by using a predetermined mathematical model of the beam trajectory from the angle and the measured value of the beam trajectory radius at the location. The measured value of the beam orbit radius and the estimated value are made to coincide with each other while changing the parameter as a parameter, and the energy value at the time of coincidence is used as the energy estimated value.