RU2582588C2 - Tandem accelerator with vacuum insulation - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to acceleration engineering and can be used for production of charged particle beams for ion implantation, neutron capture therapy of cancer or for detecting explosives and narcotic drugs. Traditionally voltage to accelerator is supplied from high-voltage power supply via feedthrough insulator with ohmic divider. Novelty is that high-voltage power supply of sectional type is placed inside insulator, on which are fixed high-voltage and intermediate electrodes of accelerator. Voltage on high-voltage and intermediate electrodes of accelerator is supplied from sections of high-voltage power supply.

EFFECT: technical result is improvement of compactness and reliability of accelerator.

1 cl, 2 dwg

Description

The invention relates to the technique of accelerators and can be used to create accelerators of charged particles, as well as devices based on them. Such devices can be used for research in the physics of atomic and nuclear collisions, in the semiconductor industry for ion implantation, in medicine for neutron and neutron capture therapy for cancer, and in security systems for the detection of explosive and narcotic substances.

A charged particle accelerator is a device for producing high-energy charged particles. The accelerator operation is based on the interaction of charged particles with electric and magnetic fields. Structurally, accelerators can be divided into two large groups. These are linear accelerators, where the particle beam passes accelerating gaps once, and cyclic accelerators in which the beam moves along closed curves, passing accelerating gaps many times.

In the simplest linear accelerator, charged particles are accelerated by a constant electric field and move linearly in the accelerator tube, to the ends of which a high voltage is applied. Structurally, the accelerating tube is made in the form of alternating ring insulators and electrodes. A vacuum is created inside the accelerating tube, the area outside is filled, if necessary, with insulating gas under pressure, usually with SF6 gas. The voltage on the intermediate electrodes is fed through a resistive divider. The ion source is placed under the high voltage potential.

A recharged particle accelerator (tandem) was proposed in the middle of the 20th century. It consists of two accelerating tubes and a peeling (rechargeable) target between them, which is under a high-voltage potential. An accelerated negative hydrogen ion, when interacting with a stripping target, turns into a positive one, and then accelerates in the second accelerator tube with the same potential. The use of the same accelerating voltage twice allows one to double the final energy of singly charged particles and several times multiply charged ones. An important advantage of tandem accelerators is the placement of an ion source under a grounded potential.

The tandem accelerators in accelerator mass spectrometry and ion implantation complexes with a characteristic beam current of less than 1 mA (milliamperes) are most widely used. Typically, such tandem accelerators use a gas stripping target made in the form of a tube with a gas inlet in the middle.

The interaction of an accelerated beam of charged particles with residual gas in a vacuum volume leads to the appearance of electrons, ions and ultraviolet radiation, which reduce the high-voltage strength of accelerating vacuum gaps and vacuum surfaces of the insulating rings of the accelerating tube.

To preserve the high voltage strength of accelerating vacuum gaps with increasing beam current, various solutions are proposed, including a tandem accelerator with vacuum insulation.

The first tandem accelerator with vacuum insulation was proposed in 1994 [G. Proudfoot, R. McAdams, A.J.T. Holmes. A new design of a compact high current ion accelerator. Nuclear Instruments and Methods in Physics Research B 89 (1994) 1-7]. The proposal is that the entire tandem accelerator is placed in a vacuum volume. Those. vacuum is created not only inside the accelerator tube, but also in the area outside, which in traditional devices is filled with SF6 gas. In the description by them of the executed patent US 5293134 dated 03/08/1994 it is emphasized that this proposal allows you to get rid of the use of potentially dangerous and expensive SF6 gas.

Later in 1998 [V. Bayanov et al. Accelerator based neutron source for the neutron-capture and fast neutron therapy at hospital. Nuclear Instruments and Methods in Physics Research A 413 / 2-3 (1998) 397-426] also proposed a tandem accelerator with vacuum insulation, fundamentally different from that described above. The main idea was not to get rid of the use of SF6 gas, but to take the insulator away from the beam of charged particles to maintain the high voltage strength of the vacuum gap. In such a vacuum-insulated tandem accelerator, accelerator tubes as such are absent. The potential distribution is set by embedded electrodes forming a multilayer structure, mounted on the vacuum part of a single sectioned bushing insulator filled with SF6 gas. The insulator is out of line of sight from the beam propagation region. Coaxial tubes are located inside the bushing, which transmit the potential to the high-voltage electrode from the high voltage source and to the intermediate electrodes from the ohmic divider installed on the gas part of the bushing. The high voltage source and the gas part of the bushing are placed in a single volume filled with gas under pressure.

The idea of a tandem accelerator with vacuum insulation was developed in [R. Beasley, O. Heid, T. Hugles. A new life for high voltage electrostatic accelerators. Proc. of the International Particle Accelerator Conference, Kyoto, Japan (2010) 711-713]. They suggested using the natural capacitance between the electrodes. If you cut the embedded electrodes in half and connect them in the form of a ladder with diodes, then the Cockcroft-Walton cascade generator (voltage multiplier) is realized directly inside the vacuum volume of the accelerator. However, the authors of this proposal did not consider the technological aspects of the practical implementation of such a design.

As a prototype, the design of the tandem accelerator with vacuum insulation, described in [V. Bayanov et al. Accelerator based neutron source for the neutron-capture and fast neutron therapy at hospital. Nuclear Instruments and Methods in Physics Research A 413 / 2-3 (1998) 397-426].

A prototype diagram is shown in FIG. 1. A beam of negative hydrogen ions is injected into the accelerator 1 and accelerated therein to 1 MB. In a gas stripping target 4 mounted inside the high-voltage electrode 3, negative hydrogen ions are converted into protons, which are then accelerated by the same potential of 1 MB to an energy of 2 MeV. The potential for high-voltage 3 and five intermediate electrodes of the accelerator 2 is supplied from the high-voltage voltage source 8 through a bushing, which consists of two parts: a vacuum part 5 and a gas part 6. An ohmic divider 7 is installed on the gas part of the bushing insulator to supply the corresponding potential to the accelerator intermediate electrodes . As a high-voltage voltage source 8, an electron accelerator rectifier of the ELV series is used, containing the primary winding 11, rectifier sections 10 and a high-voltage electrode 9. The vacuum volume of the accelerator is pumped out by the turbomolecular and cryogenic pumps through the louvers of the intermediate electrodes. The bushing and high-voltage rectifier are filled with insulating gas SF ₆ at a pressure of 3 atm and 6 atm, respectively. The arrows in FIG. 1 shows the direction of movement of negative hydrogen ions (H ^- ) and protons (p).

This design has a large total height (7 m), since it is necessary to ensure the high voltage strength of the power source, the high voltage strength of the gas part of the bushing on the side of the power source and the high voltage strength of the vacuum part of the bushing on the side of the accelerator.

The invention is directed to the creation of a compact tandem accelerator with vacuum insulation.

To solve this problem in a known device containing a tandem accelerator with vacuum insulation, a bushing and a sectioned rectifier, the latter is placed inside the housing of the vacuum part of the bushing. The high-voltage and intermediate electrodes of the accelerator are connected directly to the corresponding sections of the rectifier and there is no need for a bushing with an ohmic divider. The case of the vacuum part of the bushing is used as an insulator for attaching high-voltage and intermediate electrodes, as well as a case of a sectioned rectifier.

Since the case of a sectioned rectifier is not a grounded metal tank, but an insulator with distributed potential, the high-voltage strength of the rectifier is significantly improved and the gaps or pressure of the insulating gas can be reduced.

In addition to reducing the dimensions of the installation and the great stability of the potential of the intermediate electrodes, this change entails a decrease in the number of parts and an increase in reliability.

The invention is illustrated in FIG. 2.

In FIG. Figure 2 shows a diagram of a tandem accelerator with vacuum insulation with an integrated high-voltage power supply. The diagram shows:

1 - tandem accelerator with vacuum insulation;

2 - intermediate electrodes;

3 - high voltage electrode;

4 - gas peeling target;

5 - insulator;

6 - sectioned rectifier.

The device operates as follows. A partitioned rectifier 6 is placed inside the insulator 5. Using a modern element base (avalanche high-voltage diodes RVF30, capacitors FHV12AN) and switching to a higher frequency (20 kHz instead of 400 Hz) allows you to make the high-voltage power supply significantly smaller than the one shown on FIG. 1. The internal volume of the insulator is filled with SF6 gas to ensure the high-voltage strength of the gaps. The high-voltage 3 and intermediate 2 electrodes of the accelerator 1 are connected directly to the corresponding sections of the sectioned rectifier 6.

Claims (1)

A vacuum-insulated tandem accelerator containing a tandem-type ion accelerator, an insulator and a high-voltage power supply, characterized in that the high-voltage power supply is partitioned and placed inside the insulator, the high-voltage and intermediate electrodes of the accelerator are connected directly to the high-voltage power supply sections, high-voltage and intermediate electrodes are mounted on the housing of the vacuum part of the insulator, which is also the housing of the sectioned high-voltage source Power nick.

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