JPH0824075B2 - High voltage high current ion beam accelerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is used in ion implantation, nuclear physics, nuclear engineering, medicine, etc., and provides a high voltage of, for example, over 1 million V and a large current of 1 mA or more. To a high-voltage high-current ion beam accelerator suitable for obtaining the above ion beam.

(Prior Art) Conventionally, as an ion beam accelerating device, a ring-shaped divided electrode which is held by an insulator c at intervals around a passage of an ion beam b emitted from an ion source a as shown in FIG. An accelerating tube g is constructed by arranging a plurality of plates d, and a potential gradient is applied from the inlet port e side of these divided electrode plates d to the outlet port f side, and the ion beam is accelerated by the potential difference. It is known to do the following.

(Problems to be Solved by the Invention) In the above-described conventional type accelerator, the divided electrode plate d has a length of 1 m.
When a high voltage of about 1 to 1,500,000 V or more is applied to obtain an ion beam with a large current of 1 mA or more, there is a disadvantage that discharge occurs and dielectric breakdown occurs. Basically, the cause of this dielectric breakdown is that flashover discharge occurs in the acceleration tube g along the inner surface of the insulator c, and secondly, ion bombardment sputtering between the divided electrode plates. Positive and negative ions are exchanged by the action, and a local small discharge is generated in the acceleration tube g. When such a primary small discharge occurs, the gas occluded on the surfaces of the insulator c and the divided electrode plate d is released, and the ionization of the gas increases the scale of the discharge, so that the entire discharge tube g is discharged. Spreads, causing a breakdown phenomenon in which the total voltage of the accelerating tube drops to zero. For this reason, conventionally, the local small discharge is generated in small steps to accelerate the gas release from the insulator c and the divided electrode plate d, and the accelerating tube g is gradually conditioned to become accustomed to a high voltage use state. It is adjusted to withstand continuous use at high voltage.

However, this method has a problem in that it takes an abnormally long time to reach a stable operating state, and the maximum voltage that can be reached is limited, and conditioning is required when the voltage exceeds 1 million V. There is the drawback of causing a breakdown despite doing so. Furthermore, the conventional high voltage accelerating tube tends to be long and large, which is inconvenient to install.

An object of the present invention is to provide a high-voltage high-current ion beam accelerator which can suppress the occurrence of discharge in the accelerating tube, reach the maximum voltage quickly, and can be downsized.

(Means for Solving the Problems) In the present invention, in order to achieve the above-mentioned object, a plurality of annular divided electrode plates, which are held by an insulator at intervals around the ion beam passage, are arranged. In an accelerating tube equipped with an accelerating column of multi-stage electrodes for accelerating an ion beam by applying a potential gradient from an inlet to an outlet with one of both ends of the electrode being ground potential and the other being a high voltage, the annular split electrode Increase the number of plates per unit length, and gradually increase the hole diameter of some of the divided electrode plates at each stage at the high voltage end to fill the inner diameter of the acceleration column at the ground potential end. Expand the diameter of the holes of other things to the full inner diameter of the acceleration column to form a substantially conical passage in the acceleration column,
Further, an electrode plate of earth potential is provided facing the earth potential end of the accelerating tube, and a cylindrical porous electrode of negative potential is provided around the passage between the earth potential end and the electrode plate. A vacuum exhaust port was provided on one side.

(Operation) The inside of the accelerating tube is evacuated to a vacuum, and 1.5 million V is applied to the electrode at the end on the inlet side where the ion beam from the ion source is introduced.
Voltage of 0 V or a voltage close to 0 V is applied to the electrode at the end on the outlet side from which the ion beam is emitted, and each of the intermediate split electrode plates interposed between the electrodes at both ends is at the inlet side. Therefore, for example, a voltage that gradually decreases in steps of tens of thousands of V is applied.

Then, when a voltage of, for example, -300 V is applied to the porous divided electrodes and an ion beam is introduced from the ion source into the accelerating tube, the ions are accelerated by the high electric field in the accelerating column and a high energy ion beam is extracted from the outlet. In this case, since the number of divided electrode plates per unit length of the acceleration column is large, the potential difference between adjacent divided electrode plates becomes small, so that flashover discharge is prevented. In addition, the diameter of the holes of some of the electrodes on each stage of the acceleration column is minimized at the high voltage end and gradually expanded to fill the inside diameter of the acceleration column at the ground potential end. Occurs between the adjacent divided electrode plates or between the individual electrode plates and the electrode plate at the ground potential outside the acceleration tube, but the potential difference between adjacent electrode plates is small as described above. Since it is in a state in which ion exchange discharge is unlikely to occur, a potential for blocking the flow of electrons or negative ions from the electrode surface to the acceleration column is provided by the negative potential porous electrode between the electrode plate at the ground potential and the electrode plate at the ground potential. Since the barrier is formed, ion exchange discharge between each divided electrode and the electrode plate at the ground potential is prevented.

At the same time, it is possible to prevent the generation of X-rays due to the electrons colliding with the divided electrode plate of the high voltage portion, and the safety is improved. Further, since the exhaust port is provided on the side of the porous electrode and the diameter of the hole of the divided electrode plate in the acceleration column is expanded to the maximum at the ground potential end, the gas discharged into the acceleration tube is exhausted at high speed. As a result, electric discharge is less likely to occur in the tube.

(Embodiment) An embodiment of the present invention will be described with reference to the attached drawing. In FIG. 2, reference numeral (1) is an ion source for generating a high-current ion beam, and (2) is the ion source (1). An ion beam accelerator that introduces the extracted ion beam (3) from the introduction port (4) and accelerates it from the extraction port (5) of the electrode plate (5a) at the ground potential, and (6) is the ion beam ( 3)
A plurality of annular split electrode plates (9) held by an insulator (8) around the passage of (1) are arranged and an inlet (4) for accelerating the ion beam (3). Side high voltage end electrode (9a) to outlet (5) side ground potential end electrode (9
This is an accelerating column that is applied with gradually lower voltage to b).

The interval (7) between the electrodes (9) is set to about 4 mm, which is much smaller than the interval of 10 mm or more in the conventional acceleration column, and the number of divided electrode plates (9) per unit length is arranged to be large. Further, the diameter d of every few electrode plates (9c) among the divided electrode plates (9) is the smallest on the inlet (4) side, and gradually decreases toward the outlet (5) side. Spread,
A substantially conical passage was formed in the acceleration column (6).

(10) is the ground potential end electrode (9b) of the acceleration column (6)
Shows a negative potential cylindrical porous electrode provided far away from the ion beam around the passage between the electrode plate (5a) and the ground potential electrode plate (5a), the porous electrode (10) is composed of, for example, a mesh, -300V Is given a negative potential of. (11) is a vacuum exhaust port provided on the side of the porous electrode (10), and the exhaust port (11) is connected to a vacuum pump having a large capacity of exhaust capability.

To explain its operation, the vacuum column (6) is evacuated from the vacuum exhaust port (11) to a pressure of, for example, about 10 ^-6 to 10 ^-7 Torr, and the high voltage of the 50 electrodes (9) is Edge electrode (9
A potential of 1.5 million V is applied to a), and a potential of 1.47 million V and 1.44 million V, which decreases by 30,000 V in sequence, is applied toward the front of the electrode (9b), that is, closest to the outlet (5). The ground potential end electrode (9b) of is set to 0V. Then, -300 V is applied to the porous split electrode (10) and the ion beam (3) is introduced from the ion source (1) through the inlet (4), the ion beam (3) is accelerated in the acceleration column (6), and the ion beam (3) is guided. Derived from the exit (5).

In this case, the maximum potential difference in the accelerating column (6) is in the state of 1.5 million V, and discharge is normally likely to occur, but the number of divided electrode plates (9) per unit length is large and the number of adjacent divided electrodes is large. Since the potential difference between the electrode plates is as small as 30,000 V, the occurrence of discharge between the divided electrode plates (9) and (9) is prevented.

Further, when the ions hit the electrode plate (5a) at the ground potential, negative ions and electrons are generated, which are attracted by the high electric field leaking from the acceleration column (6) and collide with the split electrode plate (9). Then, ion exchange discharge occurs and causes breakdown, but the potential is increased by the negative potential cylindrical porous electrode (10) between the end of the acceleration column (6) and the electrode plate (5a) at the ground potential. Since the barrier is provided, the negative ions and electrons generated by the ion collision with the electrode plate (5a) at the ground potential are prevented from flowing into the acceleration column (6), and the ion exchange discharge is prevented. Further, the gas released from the surface of the split electrode plate (9) and the insulator (8) in the acceleration column (6) is expanded as the diameter d of the split electrode (9) is closer to the outlet (5) side. Since it is present, the gas can be quickly discharged to the exhaust port (11), and the discharged gas can be prevented from accumulating and discharging in the acceleration column (6).

In the illustrated example, the diameter d of the ten divided electrode plates (9a) is gradually expanded, but the diameters d of all the electrodes (9) may be gradually expanded. If necessary, negative ions may be introduced from the ground potential side to accelerate the low energy side acceleration tube of the tandem accelerator.

(Effect of the invention) As described above, according to the present invention, the number of divided electrode plates of the ion beam acceleration column per unit length is increased and the diameter of the annular divided electrode plate is changed from the high voltage end to the ground. A cylindrical negative potential porous split electrode is provided around the passage between the end of the accelerating tube and the earth potential electrode plate equipped with the outlet, and the vacuum exhaust port is provided on the side Since a flashover discharge does not occur even when a high voltage is applied between the electrodes, the porous electrode of negative potential prevents secondary ions from flowing into the accelerating column, so that ion exchange discharge occurs. Can be prevented, long-term conditioning can be eliminated, and the length of the device can be shortened to reduce the size.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional example, and FIG. 2 is a cutaway side view of an embodiment of the present invention. (3) …… Ion beam (4) …… Inlet port (5) …… Outlet port (5a) …… Electrode plate at earth potential (6) …… Acceleration column (7) …… Interval (8) …… Insulation Body (9) (9c) ...... Split electrode plate (9a) ...... High voltage end electrode (9b) ...... Ground potential end electrode (10) ...... Porous electrode (11) ...... Vacuum exhaust port

Claims (1)

[Claims] 1. A plurality of annular split electrode plates, which are held by an insulator at intervals around the ion beam passage, are arranged, one end of each of these electrodes being a ground potential and the other being a high voltage inlet port. In an accelerating tube provided with an accelerating column of multi-stage electrodes for accelerating the ion beam by applying a potential gradient from the outlet to the outlet, increasing the number of the annular divided electrode plates per unit length, Expand the hole diameter of some of the split electrode plates to the maximum inner diameter of the acceleration column while gradually increasing the hole diameter of the other part to the minimum at the high voltage end and at the earth potential end to fill the inner diameter of the acceleration column. To form a substantially conical passage in the accelerating column, and to provide an earth potential electrode plate facing the earth potential end of the accelerating tube, and to provide a negative potential around the passage between the earth potential end and the electrode plate. Provide a cylindrical porous electrode Further high-voltage large-current ion beam accelerating device characterized by providing the evacuation port on the side of the porous electrode.