JPH03173100A - High-frequency multiple wire type accelerator - Google Patents

Abstract

PURPOSE:To change the final energy of ions without changing resonance frequency by generating an electric field deviated from a high frequency electric field satisfying the continuous acceleration conditions of charged particles in a space by a perturbation electrode in order to change the final energy of the charged particles. CONSTITUTION:A perturbation electrode 3 applying microfluctuation to a high- frequency electric field for acceleration is provided inside an acceleration cavity 1 for generating an electric field deviated from a high-frequency electric field satisfying a continuous accelerating condition of charged particles in a space encircled by respective electrodes 2 to be constituted for changing the final energy of the charged particles. When a high-frequency voltage value to be introduced into the cavity 1 is made a voltage value satisfying an ordinary acceleration condition, the high-frequency electric field encircled by the electrodes 2 is influenced by the perturbation electrode 3 to partially lower voltage for lowering the whole energy so that its final energy is changed. The final energy is thereby enabled to be variable without changing the resonance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a high frequency multipole linear accelerator, and more particularly to a high frequency multipole linear accelerator capable of varying acceleration energy.

<Prior Art> In a high-frequency multipole linear accelerator, plates 31a and 31b are generally attached to both ends, as shown in FIG. A plurality of electrodes (vanes) 32 are provided in the acceleration cavity 31.
... 32 are fixed, and by introducing high frequency power into this acceleration cavity 31, the electrodes 32 ... 32 are fixed.
An accelerating electric field is formed in the space 33 surrounded by the tip of the ion beam, and the ion beam can be focused and accelerated.

In addition, there are other types of quadrupole linear accelerators, such as the 40-nd type.
There are also octupole type linear accelerators, but the essential characteristics are the same as the four-vane type.

<Problems to be Solved by the Invention> The conventional high-frequency multipole linear accelerator as described above is capable of converging and accelerating an ion beam at the same time.
While it is possible to accelerate a large current ion beam to high energy, this type of accelerator is a type of high frequency resonator, so in order to change the final energy of the ions, the resonant frequency of the acceleration cavity must be adjusted. It was believed that the only way was to change (for example, Nuclear In
Strument and Methods in Ph
ysics Re5search, B57138. (1
989)+253-255. Ion Beam Acc
elation Using VariableF
RFQ”).

However, changing the resonant frequency of an accelerator, which is a complex structure, involves many difficulties, such as a reduction in the Q value of the cavity.

An object of the present invention is to provide a high-frequency multipole linear accelerator that avoids the above-mentioned difficulties, that is, can change the final energy of ions without changing the resonant frequency of the accelerator.

<Means for Solving the Problems> In order to achieve the above object, in the present invention, as shown in FIG. Perturbation electrode 3 that adds fluctuation...
... 3, and the perturbation electrodes 3, ... 3 generate an electric field that deviates from the high-frequency electric field that satisfies the condition for continuous acceleration of charged particles in the space surrounded by each electrode 2 ... 2. The device is configured to change the final energy of the charged particles.

<Operation> When the high-frequency voltage value introduced into the cavity 1 is set to a voltage value specific to this accelerator, that is, a voltage value that satisfies normal acceleration conditions, by providing the perturbation electrodes 3 in the cavity 1, the electrode The high-frequency electric field surrounded by 2...2 is affected, and the voltage partially decreases, for example, as shown in FIG. 2(C). Due to this voltage drop, the total energy acting on the particles in the acceleration cavity 1 decreases and their final energy changes.

Here, the reason why it has conventionally been said that acceleration energy cannot be changed unless the resonance frequency is changed in a high-frequency accelerator is as follows.

In other words, in a high-frequency accelerator, the resonance frequency, particle incident speed (energy), electrode arrangement position (for a drift tube linac, the arrangement pitch, for the vane type high-frequency accelerator mentioned above, the period of the vane waveform), and the applied high-frequency voltage value are factors that have a close relationship with each other. For example, even if the high-frequency voltage value is changed, as long as the other factors are constant, the acceleration energy remains constant. Rather, by decreasing the voltage, the charging It is said that particles cannot be accelerated. The reason for this is generally explained that when the high-frequency voltage is lowered, the speed of charged particles in the accelerating electric field becomes slower, and the resonance conditions are no longer satisfied in relation to the resonance frequency and the period of the electrode waveform. .

In contrast, the present inventor has developed a quadrupole radio frequency accelerator, that is, R
The high frequency voltage to be applied to the electrodes of the FQ accelerator is lower than the voltage value that satisfies the resonance condition based on the introduction speed of charged particles into the RFQ accelerator, the frequency of this high frequency voltage, and the period of the waveform formed on the electrodes. It has been experimentally confirmed that the acceleration energy of charged particles can be changed by shifting the charged particle by a predetermined amount, and a method for controlling this acceleration energy has already been proposed (Japanese Patent Application No. 176,540/1982).

In other words, in a conventional high-frequency multipolar linear accelerator, the
As shown in a), the particle entrance end X of the acceleration space.

In contrast, in the above proposal, a high-frequency electric field E0 that satisfies the conditions for continuous acceleration was uniformly applied from
The final energy is varied by applying a lower voltage high-frequency electric field E, from X to X.

The reason why the final energy of the charged particles changes due to the downward shift of this high-frequency electric field is estimated as follows in comparison with a drift tube linac and the like.

That is, it is true that in a drift tube linac, if the accelerating high-frequency voltage is lower than the design value, the beam will not be able to satisfy the resonance condition and most of the beam will be lost due to divergence or the like. Here, the drift tube linac and R
The major functional difference from the FQ accelerator lies in its beam focusing power. In the former case, the beam focusing force is obtained by an electrostatic or magnetic Q lens installed inside the drift tube, and the focusing force does not work outside the drift tube.

On the other hand, in the latter case, the high-frequency voltage induced in the vane converges and accelerates the particles at the same time, so that the particle beam is spatially continuous and always receives a strong convergence force.

Therefore, in the RFQ accelerator, even a beam that cannot satisfy the resonance condition is accelerated to the end without divergence due to its strong focusing force. However, since the resonance condition is not satisfied, the final acceleration energy is considered to shift to a lower energy side than the designed value.

Now, the present invention is an attempt to further develop the technology based on the above proposal.In the above proposal, the high frequency voltage in the acceleration space was shifted downward in the direction of
As illustrated in C), a perturbation electrode 3... is installed in the acceleration cavity.
・By providing 3, the voltage in a part of the acceleration space is lowered, and the final energy control characteristics are made more finely than the above proposal.

<Example> Fig. 1 is a block diagram of an example of the present invention, showing an example in which the present invention is applied to a four-vane type high-frequency accelerator. In the diagram, (b)
is a cross-sectional view taken along line bb. Note that the cutting line in Figure (a) is indicated by a-a in Figure (b).

In this embodiment, a high frequency power source and its control system,
Since the components such as a vacuum pump and the like are the same as those of the conventional system, they are not shown in FIG.

The configuration of the acceleration cavity 1 and the four vanes 2 . Assume that the light is incident on something with a predetermined energy from the side.

In this configuration, by introducing high-frequency power into the cavity 1, a converging and accelerating high-frequency electric field is excited in the space surrounded by the vanes 2...2, and the ion beam that has entered the cavity 1 is inside this acceleration space. It is accelerated while undergoing convergence.

In this embodiment, four perturbation electrodes 3 are slidably supported on the plate 1b on the ion exit side at axially symmetrical positions with the central axis of the cavity 1 as the axis of symmetry. and a portion thereof is inserted into the cavity 1. The amount of insertion of each perturbation electrode 3 into the cavity 1 can be adjusted by a perturbation electrode drive device 4 fixed to the outside of the plate 1b.

Each perturbation electrode 3...3 is at the same potential as the cavity 1, for example, the ground potential, and each perturbation electrode 3...3 is interlocked with each other, and the amount of insertion into each cavity 1 is always equal. It's supposed to be.

In the above embodiment, a voltage E0 that satisfies continuous acceleration conditions is applied to each vane 2, . . . 2, for example, as in the conventional case. In this state, for example, X is shown in FIG. 1(a). Insert the perturbation electrodes 3...3 up to the position shown.

As a result, the ground potential of the part where the perturbation electrodes 3...3 are inserted is closer to the ground potential for the vanes 2...2 than other parts, and the voltage decreases only in this part. As shown in Figure 2 (C), the vane voltage is Eo from the arrangement position X of plate 1a to X, but it is lower from xc to the arrangement position X of plate 1b. The potential becomes E2. Here, perturbation electrode 3...
...Since all three potentials are the same and the amount of insertion is the same, the high frequency electric field is partially shifted to the lower potential side, but its axial symmetry is not impaired.

When ions are introduced in this state, the energy received by the ions in the acceleration cavity 1 is reduced compared to the case where a -like voltage E0 is applied from Xl to Xb, and the final energy is lowered.

In this embodiment, the amount of change in the high-frequency electric field (the amount of deviation from the voltage E0 that satisfies the continuous acceleration condition) can be controlled by changing the amount of insertion of the perturbation electrodes 3...3 into the cavity 1. can.

In the present invention, the arrangement position of the perturbation electrode is not limited to the above-mentioned embodiment; for example, the perturbation electrode may be provided on the plate 1a on the ion incidence side, or the perturbation electrode may be provided on both plates.

Further, in the above embodiments, the perturbation electrode is set to the ground potential like the cavity, but a DC potential or an AC potential can also be applied to the perturbation electrode.

Furthermore, the present invention is not limited to vane type accelerators, but can also be applied to Ronde type high frequency multipole linear accelerators, and is of course applicable to octupole high frequency acceleration in addition to quadrupole.

<Effects of the Invention> As explained above, according to the present invention, it is possible to vary the final energy of a high-frequency multipole linear accelerator without changing the resonant frequency, which was difficult with the conventional technology, and the It is expected that this will bring about revolutionary progress in the field of ion acceleration technology, which accelerates ion beams to high energy. This is useful, for example, in an ion implantation step in a semiconductor manufacturing process that uses a high-energy ion beam, and has great applicability in that technical field.

Moreover, by providing perturbation electrodes in the acceleration cavity of a high-frequency multipole linear accelerator, the final energy can be changed by partially changing the high-frequency electric field in the acceleration space.
Compared to the previously proposed techniques described above, the controllability of the high-frequency electric field and, by extension, the control characteristics of the final energy can be made more precise.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of its operation, and FIG. 3 is a configuration explanatory diagram of a conventional four-vane type high-frequency accelerator. 1...Acceleration cavity 2...2...Vane 3...3...Perturbation electrode 411. , perturbation electrode drive device

Claims (1)

[Claims] By introducing high-frequency power into a cavity in which a plurality of electrodes are arranged, the cavity is caused to resonate and a high-frequency electric field is generated in which charged particles converge and accelerate in the space surrounded by the tips of the plurality of electrodes. In the device, a perturbation electrode is provided in the cavity to apply minute fluctuations to the high-frequency electric field,
A high-frequency multipolar linear accelerator characterized in that the perturbation electrode is configured to generate an electric field in the space that deviates from a high-frequency electric field that satisfies continuous acceleration conditions for charged particles, thereby changing the final energy of the charged particles. .