JP2021072271A - Long life ion source - Google Patents

Abstract

To provide a laser ablation ion source for a beam accelerator, and more specifically provides a long life ion source that can be used for a long time and is maintenance-free for a long time, which is suitable for medical use (for example, completely ionized carbon beam therapy).SOLUTION: A long life ion source according to the present invention includes a chamber that houses a target to be irradiated with laser and communicates with an extraction mechanism that transports ablation plasma generated by the laser irradiation to a predetermined position, a horizontal movement mechanism that moves the target in a horizontal direction, and a vertical feed mechanism that moves the target in the vertical direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laser ablation ion source of a beam accelerator, and more particularly to a long-life ion source that can be used for a long time and is maintenance-free for a long time, which is suitable for medical use (for example, completely ionized carbon beam therapy).

An electron cyclotron resonance ion source (Patent Document 1) using a microwave near 10 GHz has been used as an ion source for carbon beam therapy. If propane gas is used as the neutral gas, the electron energy is not sufficient in this frequency band and an ion source of about tetravalent is generated, but completely ionized carbon beam ions cannot be obtained.

Even with the conventional electron cyclotron resonance ion source, a method of producing completely ionized carbon ions using a large-scale and expensive device using a superconducting mirror magnetic field has been proposed, but there is no report of its realization.

After accelerating a tetravalent carbon wire to about 6-8 MeV with an injector such as RFQ and DTL, the remaining two electrons in the carbon thin film are stripped off and incident on a high-frequency synchrotron, which is a driver accelerator for carbon beam therapy. It was taken. This technique cannot be used with carbon beam therapy drivers that do not use an injector.

Although the generation of completely ionized carbon rays has been demonstrated with a laser ablation ion source using a 10 cm x 10 cm graphite plate or carbon thin film as a target (Non-Patent Document 1), it has a long life that can withstand use as actual carbon beam therapy. There was no.

The carbon target of heavy ion beam therapy is required to have a long life of at least one month and maintenance-free operation. On the other hand, a technique of an induced acceleration synchrotron capable of directly injecting completely ionized carbon beam ions from an ion source and accelerating has been established (Patent Document 1).

JP-A-2017-84818 (microwave ion source and its activation method) Japanese Unexamined Patent Publication No. 2006-310013 (All-type ion accelerator and its control method)

N.Munemoto, S.Takano, T.Adachi, K.Takayama et al., “Direct injection of fully stripped carbon ions into a fast-cycling induction synchrotron and their capture by the barrier bucket”, Phys. Rev. Accel. And Beams 20, 080101 (2017).

Therefore, the present invention relates to a laser ablation ion source of a beam accelerator, and more specifically, to provide a long-life ion source that can be used for a long time and is maintenance-free for a long time, which is suitable for medical use (for example, completely ionized carbon beam therapy). With the goal.

(1)
A chamber that houses the target to be irradiated with the laser and communicates with the extraction mechanism that transports the ablation plasma generated by the laser irradiation to a predetermined position.
A horizontal movement mechanism that moves the target in a horizontal phrase,
A vertical feed mechanism that moves the target in the vertical direction,
A long-life ion source characterized by consisting of.
(2)
On the laser irradiation side of the target,
Debris removal provided with a debris shield tape that is provided with a slit for laser passage, controls the shape of the ablation plasma group that propagates downstream, suppresses the diffusion of debris, and a winding device that winds the debris shield tape. The long-life ion source according to (1), wherein the mechanism is arranged.
(3)
The long-lived ion source according to (1), wherein the target is a carbon thin film.
(4)
The long-life ion source according to (1), wherein a free-rotating retainer for stabilizing the ionic strength is arranged on the anti-laser irradiation side of the target.
(5)
The horizontal movement mechanism
The rail located in the chamber and
A slider that slides the rail and
The drive shaft that moves the slider and
It consists of a first motor that operates the drive shaft.
The long-lived ion source according to (1), wherein the target can move in the horizontal direction as the slider moves.
(6)
The vertical feed mechanism
The inner frame attached to the horizontal movement mechanism and
A first drum around which the unused thin film rotatably fixed to the inner frame is wound,
A second drum that winds up the used thin film,
The long-life ion source according to (1), which comprises.
(7)
The long-life ion source according to (6), wherein the longitudinal feed mechanism is unitized and can be exchanged integrally.
And said.

Since the long-life ion source of the present invention has the above configuration, it can be used as a laser ablation ion source that supplies fully ionized carbon ions required for next-generation carbon beam therapy that does not require an injector and a fast-repeating synchrotron. Can be adopted. More specifically, it realizes long-term use and long-term maintenance-free operation that can withstand continuous operation for 2,000 hours at 10 Hz operation. In the long-life ion source of the present invention, the carbon thin film and the plastic debris shield tape are consumables, and under the above conditions, they may be replaced about every two months.

The carbon thin film of the present invention can also be produced by the existing manufacturing apparatus of another manufacturer that manufactures a long carbon thin film for consumer use. It can be stocked in carbon beam therapy facilities, and it is not expensive in terms of cost.

On the other hand, even in the existing carbon beam therapy, if the completely ionized carbon ions are used from the most upstream stream, it is possible to avoid the deterioration of the carbon ion beam emittance generated when passing through the electron exfoliation foil.

FIG. 1 is a schematic frontal sectional view of a long-life ion source of the present invention. FIG. 2 is a schematic vertical sectional side view of the long-life ion source of the present invention. FIG. 3 is an explanatory diagram of the function of the debris shield tape. FIG. 4 shows the trajectory of the laser spot of the carbon thin film in the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following examples.

As shown in FIGS. 1 to 3, the long-lived ion source 1 of the present invention includes a chamber 2, a horizontal moving mechanism 3 for moving the target in the horizontal direction, a vertical feeding mechanism 4 for moving the target in the vertical direction, and the like. It includes a free-rotating retainer 6 and a debris removing mechanism 7.

Here, the target was a carbon thin film 5 for carbon beam therapy. Depending on the purpose and application, various existing targets of elemental species that can be used for acceleration can be used.

The chamber 2 houses the target to be irradiated with the laser 9 in the vacuum required for acceleration, the carbon thin film 5 is housed therein, and the ablation plasma 11 generated by the irradiation of the laser 9 is transported to a predetermined position such as an accelerator. It communicates with the pull-out mechanism 10.

The horizontal movement mechanism 3 includes a rail 3c that is positioned (may be fixed) in the chamber 2, a slider 3d that slides the rail 3c, a drive shaft 3b that moves the slider 3d, and a first motor that operates the drive shaft 3b. It consists of 3a. As a result, as the slider 3d moves, the target, here the entire vertical feed mechanism 4, can move in the horizontal direction (both directions). As a result, the carbon thin film 5 also slides and the position can be controlled.

As the first motor 3a, a stepping motor can be exemplified. The first motor 3a slides the longitudinal feed mechanism 4 in the horizontal direction in synchronization with the operation repetition of the accelerator, shifts the position of the carbon thin film 5 irradiated with the laser 9, and controls the position of the laser spot 9a. .. Examples of the drive shaft 3b include a piston shaft, a screw shaft, and a ball screw.

The vertical feed mechanism 4 includes an inner frame 4a detachably attached to the horizontal movement mechanism 3, a first drum 4b on which an unused carbon thin film 5 rotatably fixed to the inner frame 4a is wound, and a laser 9. Is examined and consists of a second drum 4c that winds up the used carbon thin film 5. The second drum 4c is rotated by a second motor 4d fixed to the inner frame 4a.

The second motor 4d may use a stepping motor or the like and synchronize with the first motor 3a to keep the movement timing constant. Further, the rotational drive is transmitted to the take-up drum (second drum 4c) to rotate it, and the other sending drum (first drum 4b) maintains an appropriate tension so that the carbon thin film 5 does not loosen and break. It is preferable to provide a rotation control (rotation resistance) mechanism.

A free-rotating retainer is placed on the target of the thin film, here on the irradiation side of the anti-laser 9 of the carbon thin film 5. The free-rotating retainer 6 uses the same substance as the target or a material that is hard to ionize, such as tungsten. The stability of the ablation plasma is ensured by the free rotation presser 6. In the case of a carbon thin film, the free-rotating retainer 6 may be a carbon rod. Here, it is attached to the inner frame 4a in a rotatable state. As a result, the vertical feed mechanism 4 is unitized and can be replaced integrally.

With the convergent irradiation of the laser 9, a conical irradiation mark with a depth of 50 μm and a diameter of 400 μm remains on the surface of the carbon thin film 5, and a part of the substance (carbon atom) in this part becomes ablation plasma, but other Most of the material amount becomes a debris jet and jumps forward. According to the law of conservation of momentum, the carbon thin film 5 receives a reaction as a periodic impact force of 10 Hz and causes natural vibration. The free rotation retainer 6 of the carbon rod is arranged on the back of the carbon thin film 5 on the anti-laser irradiation side for the purpose of suppressing fluctuations in the ion beam intensity due to vibration at the position of the laser spot 9a of the carbon thin film 5. When friction occurs, it is preferable to rotate the free-rotating retainer 6 to prevent the target from being broken.

The debris removal mechanism 7 is located on the irradiation side of the target laser 9, and a slit 8a for passing the laser 9 is bored. After the irradiation of the laser 9, the slit 8a automatically controls the shape of the ablation plasma group. A debris shield tape 8 that suppresses the diffusion of a large amount of debris (broken line in FIG. 3) and a winding device for winding the debris shield tape 8 are provided and are detachably installed in the chamber 2. As a consumable item, the debris removing mechanism 7 may be unitized and replaced integrally.

The winding device includes a third drum 7a that winds and sends out the fresh debris shield tape 8, a fourth drum 7b that winds the used debris shield tape 8, and a third motor 7c that rotates the fourth drum 7b. .. The third motor 7c is operated by a timer manually even if it is synchronized with the operation of the accelerator, and is updated regularly.

Debris causes deterioration of the vacuum inside the chamber 2 in the vacuum state, and also causes surface contamination of the focusing lens (not shown) of the laser 9 arranged in the chamber 2. Prevention of surface contamination of the focusing lens is important for maintaining the beam intensity. In order to avoid this, only the position of the laser spot 9a is left, and the entire other surface of the carbon thin film 5 is covered with the plastic debris shield tape 8 that adsorbs carbon debris immediately after the ablation plasma is generated.

As shown in FIG. 4, a laser in which the entire surface area of a carbon thin film (for example, thickness 20-50 μm, width 20 cm, length 75-150 m) is converged on the surface of the carbon thin film 5 by a condensing lens according to the repetition frequency of ion generation. Irradiate.

Since the position of the laser spot 9a is fixed, the carbon thin film 5 is moved in the horizontal and vertical directions. Similar to the film camera, the carbon thin film 5 wound around the first drum 4b is discontinuously wound and collected by the second drum 4c at the other end. The longitudinal feeding mechanism 4 including the carbon thin film 5 is mounted on the slider 3d of the horizontal moving mechanism 3 as a unit, and is continuously moved at 1 cm / sec in the horizontal direction, for example. During this time, the winding of the first and second drums 4b and 4c is stopped. When the horizontal movement of positive and negative 10 cm is completed, the carbon thin film 5 is wound in the vertical direction by the second drum 4c for one step (1 mm), and the horizontal movement direction of the vertical feed mechanism 4 is reversed.

1 Long-life ion source 2 Chamber 3 Horizontal movement mechanism 3a First motor 3b Drive shaft 3c Rail 3d Slider 4 Vertical feed mechanism 4a Inner frame 4b First drum 4c Second drum 4d Second motor 5 Carbon thin film 6 Free rotation retainer 7 Debris removal mechanism 7a Third drum 7b Fourth drum 7c Third motor 8 Debris shield tape 8a Slit 9 Laser 9a Laser spot
10 Drawer mechanism 11 Ablation plasma

Claims (7)

A chamber that houses the target to be irradiated with the laser and communicates with the extraction mechanism that transports the ablation plasma generated by the laser irradiation to a predetermined position.
A horizontal movement mechanism that moves the target in a horizontal phrase,
A vertical feed mechanism that moves the target in the vertical direction,
A long-life ion source characterized by consisting of. On the laser irradiation side of the target,
Debris removal provided with a debris shield tape that is provided with a slit for laser passage, controls the shape of the ablation plasma group that propagates downstream, suppresses the diffusion of debris, and a winding device that winds the debris shield tape. The long-life ion source according to claim 1, wherein the mechanism is arranged. The long-lived ion source according to claim 1, wherein the target is a carbon thin film. The long-life ion source according to claim 1, wherein a free-rotating retainer for stabilizing the ionic strength is arranged on the anti-laser irradiation side of the target. The horizontal movement mechanism
The rail located in the chamber and
A slider that slides the rail and
The drive shaft that moves the slider and
It consists of a first motor that operates the drive shaft.
The long-lived ion source according to claim 1, wherein the target can move in the horizontal direction as the slider moves. The vertical feed mechanism
The inner frame attached to the horizontal movement mechanism and
A first drum around which the unused thin film rotatably fixed to the inner frame is wound,
A second drum that winds up the used thin film,
The long-life ion source according to claim 1, wherein the ion source comprises. The long-life ion source according to claim 6, wherein the longitudinal feed mechanism is unitized and integrally replaceable.

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