JPH0770359B2 - External resonance quadrupole particle accelerator - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to RFQ (Radio Frequency)
The present invention relates to an ion accelerator, and more particularly to an external resonance type quadrupole particle accelerator capable of changing the frequency over a wide range.

[0002]

2. Description of the Related Art Conventionally, as a quadrupole particle accelerator in which a high-frequency resonance circuit is provided outside an accelerating tube to make the resonance frequency of the circuit variable, there is one disclosed in Japanese Patent Laid-Open No. 60-115199. . This has a feature that the acceleration energy of ions can be freely selected. The configuration will be described with reference to FIG.

The quadrupole particle accelerator has a quadrupole electrode and a high frequency resonance circuit. Quadrupole electrode is electrode 1
a, 1b, 1c, 1d, each electrode 1a, 1b,
1c and 1d are rod-shaped members having a corrugated surface along the axial direction. The quadrupole electrodes are electrodes 1a, 1b, 1
The c and 1d are arranged so that their wavy surfaces face each other. The high frequency resonant circuit
It is configured by including a coil 2 having an inductance L ₁ and a capacitor 3 having a capacitance C ₁ . Electric power from the variable frequency type high frequency power source 5 is supplied to the coil 2 of the resonance circuit through the coupling coil 4 directly coupled to the matching box 6.

As shown in FIG. 2, the conventional high-frequency resonance circuit is arranged in the order of a coil 2, a capacitor 3, a lead wire 7, and a quadrupole electrode. Since the equivalent circuit at this time can be written as shown in FIG. 4 (parallel resonance), the resonance frequency f of the circuit is considered to be expressed by the following equation.

[0005]

[Equation 1]

However, C ₂ is the stray capacitance of the quadrupole electrode. The resonance frequency is adjusted by changing the inductance L _{1 of the} coil 2 or the capacitance C _{1 of the} capacitor 3.

When a variable capacitance capacitor is used to change the resonance frequency of the circuit, the capacitance C ₁
Will be changed. However, since the stray capacitance C ₂ exists in addition to C ₁ , the frequency variable range becomes a practically small range even if the capacitance C ₁ is greatly changed. For example, C ₂ is about twice the minimum value of C ₁ (C ₂ =
2C ₁ ), even if the capacitance C ₁ is changed 10 times, the resonance frequency f can be operated only about 2 times. Therefore, normally, the variable range of the resonance frequency is widened by discretely changing the inductance L ₁ .

[0008]

DISCLOSURE OF THE INVENTION The inventors have actually
An experiment was conducted by using a coil of one turn as the inductance L _{1 and} changing its length by three times. Since the value of L ₁ changes in proportion to the length of the coil, the resonance frequency f should change from the expression 1 to 1.7 times with respect to the change of 3 times the length. However, the result changed only 1.1 times at most. This is because the lead wire 7 has an inductance value that cannot be ignored at high frequencies, so that the resonance frequency f of the circuit does not actually have an ideal shape as shown in the equation (1). Because. Therefore, in the conventional circuit arrangement, even if L ₁ is discretely changed, the effect is hardly exhibited, and as a result, the variable range of the resonance frequency is narrowed.

The above problems will be described using specific mathematical expressions and numerical values. Since the equivalent circuit is as shown in FIG. 3 (parallel resonance), when the resonance frequency f of the circuit is calculated in consideration of the inductance (L ₂ ) of the lead wire, it can be approximately calculated by the following equation. Will be represented.

[0010]

[Equation 2]

[0011] Typically, the size of the L ₂ is, L ₁ the same level, or, because it is more, it can be seen that does not so much contribute to the variation of even changing the L ₁ f. For example, as a practical range, the capacitance C _{1 of the} capacitor 3 is 100 pF to 1
Can be changed up to 000pF, C ₂ is 500p
Consider the case where F and L ₂ are 0.3 μH. If the coils ₁ to be discretely changed have the L ₁ of 0.03 μH and 0.1 μH, the resonance frequencies are 7.2 MH, respectively.
from z to 11.3MHz and from 6.5MHz to 10.3
The frequency range from 6.5 MHz to 11.3 MHz is a variable range that can be covered as a whole. That is, the resonance frequency f can be changed only about 1.7 times, although the capacitance C ₁ is changed ten times and the inductance L ₁ is changed three times or more.

As for the performance of the energy-variable quadrupole particle accelerator, in terms of application, the emitted beam energy is
From several hundred keV to several MeV, that is, in a wide range of about 10 times. On the other hand, the emitted beam energy changes with the square of the operating frequency, so in order to change the energy in a wide range of about 10 times, at least 3.
A variable frequency range of about twice is required.

[0013] Therefore hundreds keV wide range of up to several MeV from energy - to realize the ion accelerator can be accelerated to any ions in region, adverse effects due to the inductance L ₂ of the leads as shown in (L ₁ It is required to eliminate the change amount of (1) does not directly contribute to the change amount of f).

An object of the present invention can be varied in a range not wider the resonance frequency, a broad range of energy - to provide any external resonance quadrupole particle accelerator which can accelerate ions in the region.

[0015]

In order to achieve the above object, according to one aspect of the present invention, in a quadrupole particle accelerator having a high frequency resonance circuit provided outside an accelerating tube, the high frequency resonance circuit is a capacitor. An external resonance type quadrupole particle accelerator is provided, which comprises an inductance member, and the inductance member is arranged in series between the capacitor and the accelerating tube.

A conductor forming a coil can be used as the inductance member. For example, at least part of the portion of the lead conductor which electrically connects the capacitor and the quadrupole electrodes, as an inductance element, the conductor constituting the coil are arranged. Further, one preferred embodiment of the present invention, at least a portion of the lead conductors, inductance member, i.e., can be actively used as a conductor constituting the coil.

In the present invention, the high frequency resonance circuit has a configuration in which the capacitor, the coil (inductance member) and the quadrupole electrode are arranged in this order and are connected in series. Electric power is supplied to the conductors forming the coil by a coupling coil directly wired from the matching box. That is, since the coil conductors form a pair and are symmetrically arranged, the coupling coil is arranged in the space surrounded by them. For mounting the coupling coil, the method of inserting the coil conductor by opening the central portion of the coil conductor has the highest symmetry, and therefore, it can be said that the method has the highest Q value and is optimum for the resonance circuit.

As a method for changing the resonance frequency, a method using a vacuum variable capacitor, which has a proven track record in the past, is the most suitable method from the viewpoint that it needs to be driven smoothly in a vacuum. Of course, it is not limited to this.

Therefore, in the present invention in which the capacitance of the vacuum variable capacitor and a part of the lead conductor function as an inductance as a circuit for obtaining LC resonance, the inductance due to the wiring is so small that it can be practically ignored. Therefore, it can be said to be an external resonance type quadrupole particle accelerator having the most ideal circuit structure.

[0020]

In the present invention, the inductance member (coil) which constitutes the high frequency resonance circuit together with the capacitor is arranged in series between the capacitor and the electrode of the acceleration tube. With such a configuration, the capacitor and the electrode of the acceleration tube are connected using the inductance member (coil).
With such a configuration, the lead conductor can have both an inductance function and a power feeding function.

The lead conductor can be formed as a coil having a desired inductance in terms of high frequency due to its shape. Therefore, by using a coil made of this lead conductor with a vacuum variable capacitor,
An LC resonance circuit can be constructed.

The inductance L of a coil having radius a, number of turns N, and length l is expressed by the following equation.

[0023]

(3) L = Kπa ² μ ₀ N ² / l (3) where K is a constant (Nagaoka constant) determined by the ratio of a and l, μ
₀ is the magnetic permeability in vacuum.

As is clear from Equation 3, in order to change the L value of the coil, one of the coil radius a, the number of turns N, and the length l may be changed.

The basis of the high frequency circuit design in the MHz band is to minimize the parasitic inductance and the stray capacitance due to the length of the wiring and obtain the resonance frequency as designed. Therefore, when the coil is arranged in series between the capacitor and the electrode of the acceleration tube as in the present invention,
A quadrupole particle accelerator with a wide frequency variable range can be realized.
In particular, if the wiring itself is used as an inductance to cause external resonance, the most ideal variable frequency quadrupole particle accelerator can be provided.

According to the present invention, since the external resonance circuit performance of the energy variable quadrupole particle accelerator can be utilized to the maximum, the energy can be extended over a wide range of 100 times or more.
It is possible to provide a high-energy, high-current ion implantation device in which the energy can be changed. Further, since the resonance circuit can be efficiently constructed, the entire device can be made more compact.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1 (A) and its sectional view, FIG. 1 (B).

The quadrupole particle accelerator of the present embodiment is an accelerating tube 9 having an electrode forming a quadrupole therein, and an accelerating tube 9 outside the accelerating tube 9 for supplying a high frequency resonance voltage to the electrode. And a resonance circuit.

The quadrupole electrodes are electrodes 1a, 1b, 1c, 1 made of a rod-shaped member having a corrugated surface along the axial direction.
d, whose electrodes 1a, 1b, 1c, 1d are arranged with their wavy surfaces facing each other. These electrodes 1a, 1b, 1c, 1d are insulated from the acceleration tube 9 via an insulator 8.

The external resonance circuit is 100 pF to 1000 pF.
a capacitor 3 having a capacitance C ₁ whose capacitance can be changed up to pF,
The coil conductors 10a and 10b function as wiring conductors and inductance members. As a means for supplying high frequency power to the resonance circuit, a variable frequency high frequency power source 5 for oscillating, amplifying and outputting high frequency power is used.
And a matching coil 6 for feeding the output high frequency power to the external resonance circuit, and a matching box 6 for impedance matching the high frequency power supply 5 and the coupling coil 4.

The coil conductors 10a and 10b are both formed of a bent metal plate, and each has an inductance L ₁
/ 2. Both have substantially the same shape and are arranged symmetrically across the space to form a pair. One end of the coil conductor 10a is connected to the capacitor 3, the other end is connected to the electrode 1b, and is further connected to the electrode 1d via the lead conductor 7a. Also, the coil conductor 10b
Has one end connected to the capacitor 3 and the other end connected to the electrode 1c.
To the electrode 1a via the lead conductor 7b.
Connected to. Thereby, the coil conductors 10a and 10b
They are arranged in series between the capacitor 3 and the acceleration tube 9, at the same time the inductance functions as an inductance element is L _1/2, also functions as a lead conductor for supplying power to each electrode.

The lead conductor 7a has electrodes 1b and 1d.
, The lead conductor 7b also makes a connection between the electrodes 1c and 1a. Alternatively, the lead conductors 7a and 7b may be connected to the electrodes 1b and 1d without being connected to the coil conductors 10a and 10b, and power may be supplied to the electrodes 1a and 1d via the electrodes.

Since the length of the quadrupole electrode is usually about 1 to 2 meters, the length of the coil conductor can be freely changed up to the length of the quadrupole electrode. As for the actual lengths of the coil conductors 10a and 10b, a minimum length of 10 cm and a maximum length of 2 m can be gradually prepared in consideration of cooling. From Equation 3, the coil conductors 10a and 10b are
The combined inductance L ₁ can be changed about 20 times.

The equivalent circuit of the resonance circuit in this embodiment shown in FIG. 1 is a series resonance circuit as shown in FIG. The resonance frequency f of this equivalent circuit is expressed by the following equation.

[0035]

[Equation 4]

For example, as described above, as a practical range, C ₁ of the capacitor 3 is 100 pF to 1000 pF.
It can be changed up to F, C ₂ is 500 pF, and it is 0.03 μ as L ₁ of the coil conductor which is changed discretely.
When the value is changed three times from H to 0.1 μH, the variable range that can be entirely covered is the frequency range from 27.6 MHz to 100.7 MHz. In the case of the present embodiment, unlike the conventional case, an extra L,
Since there is no C value, the amount of change contributes directly to the amount of change in f, and it has become possible to change the frequency by 3.6 times, which was impossible in the past. As a result, the energy can be changed 13 times.

Furthermore, in this embodiment, as described above, the combined inductance L of the coil conductors 10a and 10b is L.
_{If 1 is changed} to a maximum of 20 times and the capacity of the capacitor 3 is changed to the maximum, the variable range of f is expanded to 10 times or more. If so, the energy can be changed 100 times or more.

As described above, according to this embodiment, since the external resonance circuit performance of the energy variable quadrupole particle accelerator can be maximized, the energy can be changed over a wide range of 100 times or more. A high energy-high current ion implantation device can be provided. Further, since the resonance circuit can be efficiently constructed, the entire device can be made more compact.

Further, in this embodiment, as shown in FIG.
The accelerating tube and the external resonance circuit are arranged so that the power supply from the resonance circuit to the electrodes 1a, 1b, 1c, and 1d is symmetrical. That is, the accelerating tube 9 is installed so that the respective electrodes 1a, 1b, 1c, 1d of the quadrupole electrodes are arranged in an X shape with respect to the external resonance circuit. And the electrode 1
b and 1c are directly fed with power from the coil conductors 10a and 10b, and the electrodes 1a and 1d are respectively fed with lead conductors 7a and 7a.
Power is supplied via 7b. The coil conductors 10a and 7a and the coil conductors 10b and 7b are symmetrically arranged by using the metal pieces having substantially the same shape for the lead conductors 7a and 7b and arranging them symmetrically. It This makes it possible to equalize the positive and negative high frequency voltages applied to the quadrupole electrodes.

Further, in this embodiment, electric power is directly supplied to the electrodes 1b and 1c, and the electrodes 1a and 1d are supplied from the lead conductors 7a and 7b, respectively , but the coupling coil 4 is connected to the electrodes 1b-1a. It may be configured to be arranged between the spaces 1a-1d and 1d-1c. This also has the same effect as that of the above-described embodiment, and moreover, the positive and negative high frequency voltages applied to the quadrupole electrode can be made more uniform.

A second embodiment of the present invention will be described with reference to FIG. This embodiment has the same basic configuration as the embodiment shown in FIG. Here, the different points will be described.

In this embodiment, instead of the capacitor 3 shown in FIG. 1, two capacitors 3 having the same capacity are arranged in series, and the middle point thereof is grounded. By doing so, the individual capacitors 3 can completely equalize the positive and negative high frequency voltages applied to the respective quadrupole electrodes. This is also effective when applied to the conventional parallel resonant circuit shown in FIG. 2, for example.

[0043] In There third embodiment Nitsu of the present invention will be described with reference to FIG. This embodiment has the same basic configuration as the embodiment shown in FIG. Here, the different points will be described.

In this embodiment, as shown in FIG. 7, the inductance L has a structure in which the length of the coil in the circumferential direction can be continuously changed (equivalent to changing a in Formula 3).
₁ is continuously variable. That is, the conductors 12a and 12b arranged in parallel as a coil and the conductor 1
And a conductor 12c that movably connects between 2a and 12b. One end of the conductor 12a is connected to the electrode 1b. The conductor 12b has one end connected to the capacitor 3. In addition, the conductors 13a, 13 having the same configuration
b, 13c.

With such a structure, not only can the frequency variable range be further widened, but also the positive and negative high frequency voltages applied to the quadrupole electrodes can be made completely equal, as in the case of the embodiment of FIG. be able to.

Further, even if the axial length of the coil is continuously variable, the same effect can be obtained (equivalent to changing l in the equation 3).

A fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, the basic configuration is
This is the same as the embodiment shown in FIG. Here, the different points will be described.

In this embodiment, as shown in FIG. 8, the entire resonance circuit can be adjusted to an arbitrary DC potential. That is, for example, the DC power supply 14 is connected to the coil conductor 10b via the choke coil 11. As a result, the energy of the ion beam incident on the accelerating tube 9 can be arbitrarily set, so that the ion source, which is the ion beam generation source, is always kept in an optimum state, and the maximum value is always maintained even for various ion species. It is possible to obtain a beam current of At this time, as shown in the figure, by inserting a choke coil 11 or the like between the DC power supply and the resonance circuit, the DC power supply 14
Can be insulated at high frequencies.

Further, instead of floating the whole resonance circuit from the ground potential, it is possible to insulate only the accelerating tube 9 and adjust it to an arbitrary DC potential, which has the same effect. Accelerator tube 9
As a method of insulation, there may be considered a method of inserting a capacitor between the acceleration tube 9 and the coil conductor.

Each of the embodiments described above can incorporate the features of the other embodiments.

[0051]

According to the present invention, there is an effect that the resonance frequency can be changed in a wide range and any ion can be accelerated in a wide energy range.

[Brief description of drawings]

FIG. 1 shows a configuration of a first embodiment of an accelerator of the present invention,
(A) is a top view showing the top surface of the accelerator of this embodiment, (B)
FIG. 4 is a cross-sectional view schematically showing a cross section of the accelerator of this embodiment.

FIG. 2 is a sectional view showing a conventional external resonance type quadrupole particle accelerator.

FIG. 3 is a circuit diagram showing an equivalent circuit of a conventional external resonance type quadrupole particle accelerator.

FIG. 4 is a circuit diagram showing an equivalent circuit of a conventional external resonance type quadrupole particle accelerator.

FIG. 5 is a sectional view schematically showing the configuration of the second embodiment of the present invention.

FIG. 6 is a circuit diagram showing an equivalent circuit of the external resonance type quadrupole particle accelerator of the present invention.

FIG. 7 is a sectional view schematically showing the configuration of the third embodiment of the present invention.

FIG. 8 is a sectional view schematically showing the configuration of a fourth embodiment of the present invention.

[Explanation of symbols]

1a, 1b, 1c, 1d ... Electrode, 2 ... Coil, 3 ... Capacitor, 4 ... Coupling coil, 5 ... Frequency variable type high frequency power supply, 6 ... Matching box, 7 ... Lead conductor,
8 ... Insulator, 9 ... Accelerator tube, 10a, 10b ... Coil conductor, 11 ... Choke coil.

Claims (7)

[Claims] 1. A quadrupole particle accelerator comprising: an accelerating tube having an electrode forming a quadrupole therein; and a high frequency resonance circuit outside the accelerating tube for supplying a resonance voltage to the electrode. A quadrupole particle accelerator, wherein the high-frequency resonance circuit includes a capacitor and an inductance member, and the inductance member is arranged in series between the capacitor and the acceleration tube. 2. The quadrupole particle accelerator according to claim 1, wherein a variable capacitance type capacitor is used as the capacitor. 3. A quadrupole particle accelerator according to claim 1, wherein a conductor forming a coil is used as the inductance member. 4. The quadrupole particle accelerator according to claim 3, wherein the conductors forming the coil are a pair of two sheets and each is made of a metal plate having substantially the same shape. 5. The quadrupole particle accelerator according to claim 4, wherein the conductors forming the coil are symmetrically arranged. 6. The quadrupole particle accelerator according to claim 1 or 2, wherein a variable inductance type coil is used as the inductance member. 7. A DC power supply is connected to the inductance member according to claim 1, 2, 3, 4, 5 or 6, so that the potential of the quadrupole electrode in the acceleration tube can be adjusted to an arbitrary DC potential. This is a quadrupole particle accelerator.