RU2634310C1 - Gas scraping target - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: inside the high-voltage electrode (terminal) there is a gas scraping target in the form of a tube with a gas inlet in the middle. Before entering the target and after exiting it, there are magnets that create a transverse magnetic field that prevents the penetration of positive ions of the scraping gas into the accelerating gaps. As magnets that create a transverse magnetic field, alpha magnets are used, with the target placed perpendicular to the axis of the accelerating path of the charged particle beam.

EFFECT: obtaining a proton beam with different energies without changing the position or orientation of the gas scraping target, improving the gas conditions in the accelerating channel by directing the flow of the outflowing neutral gas from the target perpendicular to the axis of the accelerating channels, reducing the diameters of the high voltage and intermediate electrodes, reducing the accelerator dimensions and increasing the high voltage strength of accelerating gaps due to reduction of the stored energy.

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Description

The invention relates to nuclear physics and accelerator technology and can be applied in tandem charged particle accelerators, as well as in 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 capture therapy of cancer, and in security systems for the detection of explosive and narcotic substances.

The concept of a recharged particle accelerator (tandem) was proposed in the middle of the 20th century. It allowed to reduce the required voltage of the high-voltage generator and thereby reduce the size of the accelerator, using peeling (recharging) - a change in the sign of the particle charge during acceleration. In the process of stripping, a negative ion, when interacting with a special target, turns into a positive one, which makes it possible to use the same accelerating voltage twice, i.e. double the final energy of singly charged particles and several times multiply charged ones.

The stripping target is a tube filled with gas, a stream of steam or a film of solid.

Tandem accelerators in accelerator mass spectrometry (AMS) and ion implantation complexes with a characteristic beam current of less than 1 mA (milliamperes) are most widely used. Typically, tandem accelerators use a gas peeling (recharge) target made in the form of a tube with a gas inlet in the middle. Such a rechargeable gas target is described in USSR author's certificate No. 387541 of 06/21/1973. In patents No. US 5247263 from 09.21.1993, US 5293134 from 08.03.1994, JP 10223399 from 08.21.1998, KR 100166220 from 09.22.1998, US 6903336 from 07.06.2005, US 20060011866 from 01.19.2006, US 20130112869 from 09.05.05 .2013 describes such gas stripping targets as components of tandem charged particle accelerators.

Neutron capture cancer therapy requires an ion beam current of more than 5 mA.

It was previously proposed to use a tandem accelerator with vacuum insulation of electrodes for these purposes [B. Bayanov et al. Accelerator based neutron source for the neutron-capture and fast neutron therapy at hospital. Nuclear Instr. and Methods in Physics Research A 413 / 2-3 (1998) 397-426]. Also, the principle of vacuum insulation is implemented in a design protected by patent US 5293134 from 03/08/1994.

There are no accelerator tubes in such an accelerator. The potential distribution is determined by embedded electrodes forming a multilayer structure, mounted on a single sectioned bushing. The insulator is out of line of sight from the beam propagation region. This design is compact and more reliable with respect to high-voltage breakdowns.

At a beam current of more than 5 mA, the solid film used as a peeling target quickly collapses. The best option for stripping a high-current beam of charged particles is a gas target. Since with increasing beam current it is necessary to increase the diameter of the stripping tube filled with gas through which the beam passes, the flow of gas flowing out of the tube increases significantly.

Gas entering the accelerator path reduces the high-voltage strength and reliability of the accelerator. In addition, it can lead to premature stripping of negative ions, and some of the ions at the output of the accelerator will have an energy lower than necessary.

To reduce the gas flow into accelerator paths, pumping is used with a turbomolecular or sorption pump, which is located next to the stripping tube. Similar designs of gas stripping targets are described in US patents No. 6069459 from 05/30/2000 and the Russian Federation No. 2360315 from 05/28/2007. However, these constructions do not allow solving the problem associated with ionization of the stripping target gas by a high-energy ion beam. Part of the positively charged stripping gas ions generated inside the stripping tube as a result of ionization of the stripping gas by an ion beam penetrates the accelerating path on both sides of the stripping target and is accelerated by the electric field, up to the full potential of the high-voltage electrode. The formation of a beam of accelerated stripping gas ions leads to the following problems. Firstly, part of the power of the high-voltage power supply is spent on accelerating this beam. Secondly, the uneven hit of the accelerated beam of stripping gas ions on the intermediate electrodes of the accelerator path leads to a redistribution of their potentials and to a change in the conditions of acceleration and focusing of the injected beam of charged particles. Thirdly, the hit of an accelerated strip of stripping gas on the electrodes can lead to their melting and deformation.

The aforementioned problems are solved by the design of the gas target, described in RF patent No. 2558384 of 07/03/2015, by placing magnets that create a magnetic field transverse to the direction of ion propagation in the space between the stripping tube and the diaphragms of the high-voltage electrode, and the stripping tube is tilted by a small angle. A transverse magnetic field of the order of 1 kG deflects the flow of positively charged stripping gas ions in order to exclude their passage through the diaphragm of the high-voltage electrode. Also, the transverse magnetic field deflects the ion beam by a small angle, which requires the peeling target to be tilted by this angle relative to the axis of the accelerating path.

The design of the gas stripping target described in the patent of the Russian Federation No. 2558384 from 07/03/2015, selected as a prototype.

The disadvantage of the design of the prototype is that the placement of magnets in the space between the peeling target and the diaphragms of the high-voltage electrode leads to an increase in the diameter of the high-voltage electrode and intermediate electrodes and, as a result, to an increase in the stored energy in accelerator gaps. An increase in the stored energy in accelerator gaps negatively affects their high-voltage strength and increases the probability of accelerator breakdowns in full voltage.

The disadvantage of the prototype is that with its use it is possible to obtain a proton beam with a strictly defined energy. Since when the ion energy changes, their angle of departure changes, it will be necessary to change the angle of inclination of the gas stripping target from the magnet.

The invention is aimed at creating a device that not only provides a stripping of a beam of negative ions with a current of more than 5 mA and excludes the formation of an accelerated beam of ions of stripping gas, but also ensures the safety of high-voltage strength of accelerator gaps and the ability to change the energy of a beam of charged particles without changing the angle of inclination of the gas stripping target.

To solve the problem in a known device containing a peeling tube, a gas supply system, a gas source, magnets located in front of the target and after exiting it and creating a transverse magnetic field, it is proposed that the magnets be made in the form of alpha magnets that rotate the ion beam at an angle of 270 °, while the gas stripping target is perpendicular to the axis of the accelerating path of the negative ion beam.

A feature of an alpha magnet, which is rarely used in accelerator technology, mainly in electron accelerators [B.S. Ishkhanov, V.I. Shvedunov. Electron accelerators and the physics of electromagnetic interactions at the Research Institute of Nuclear Physics, Moscow State University. The preprint of the Research Institute of Nuclear Physics, Moscow State University, - 2008, - 5/841], consists in the fact that in an alpha magnet the injected ion beam is rotated through an angle of 270 ° so that when the ion energy changes, the angle of their emission does not change - they are parallel displaced. The author first established that the use of an alpha magnet will eliminate the disadvantage of the prototype and obtain a proton beam of different energy without changing the angle of inclination of the gas stripping target.

The invention is illustrated in FIG. 1. The diagram shows:

1 - input diaphragm of a high voltage electrode;

2 - high voltage electrode;

3 - input alpha magnet;

4 - axis of the accelerating path of the beam of negative ions;

5 - tube gas stripping target;

6 - output diaphragm of a high voltage electrode;

7 - sectioned bushing;

8 - output alpha magnet;

9 - gas supply system.

In FIG. 1 also schematically shows the direction of propagation of a beam of high-energy ions (negative hydrogen ions H ^- and protons P) and the direction of the magnetic field (B). In FIG. 1, the gas source is not shown - it is located in the high voltage terminal of the high voltage source.

The device operates as follows. A beam of charged particles created by a source of negative ions (not shown) is accelerated by the first stage of the tandem accelerator along the axis of the accelerator path 4. Through the input diaphragm of the high-voltage electrode 1, the high-energy negative ion beam enters the high-voltage electrode 2, where, thanks to the input alpha magnet 3, it is rotated through an angle 270 °, peels off in the tube of the gas stripping target 5 and turns into a beam of positive high-energy ions. The beam of high-energy positive ions emerging from the gas stripping tube is rotated again by an output magnet 8 through an angle of 270 ° and through the output diaphragm of the high-voltage electrode 6 leaves the high-voltage electrode 2, after which it is accelerated by the second stage of the tandem accelerator. Gas is supplied to the gas stripping target tube from a gas cylinder (not shown) by means of a gas supply system 9.

Propagation of a beam of high-energy charged particles through a gas of a stripping target leads to partial ionization of the gas and the formation of positive ions with low energy. The positive ions of stripping gas emerging from the tube of the gas stripping target 5 are deflected in the magnetic field of alpha magnets and neutralized by interaction with the wall of the absorber (not shown).

The use of alpha magnets allows you to provide the following technical results, unattainable in the prototype:

1. Receive a proton beam with different energies without changing the position of the gas stripping target or its inclination. This technical result is due to the fact that the beam of charged particles after passing through an alpha magnet becomes rotated through an angle of 270 ° relative to the initial direction of motion, regardless of the energy of the charged particles.

2. Improve the high-voltage strength of the accelerator gaps and make the accelerator operation more reliable. Improving the high-voltage strength of the accelerator gaps is achieved by reducing the gas flow from the stripping target to the accelerator gaps and by reducing the stored energy in the accelerator gaps. The first is achieved by the fact that there are no structural materials in the alpha magnet along the direction of gas outflow from the gas stripping target (along the axis of the gas stripping target) and the gas flows unhindered from the stripping target in the direction perpendicular to the axis of the accelerating paths. The gas and ultraviolet radiation flowing from the stripping tube is directed not perpendicularly, but perpendicularly, and in one of the directions directly to the cryogenic pump through the louvers of the accelerator's intermediate electrodes. The second is achieved by the fact that the vertical location of the gas stripping target inside the high-voltage electrode makes it possible to reduce the diameter of the high-voltage electrode from the existing 60 cm to 20-30 cm and reduce the diameters of all other intermediate electrodes. A decrease in the area of the electrodes entails a decrease in the stored energy in the gaps, which positively affects their high-voltage strength and makes the operation of the accelerator more reliable.

3. Reduce the diameter of the accelerator vacuum tank. Due to the vertical location of the gas stripping target inside the high-voltage electrode and reducing the diameter of all the electrodes, the accelerator can be made more compact, which is important for its use in oncology clinics with the aim of carrying out boron-neutron capture therapy of malignant tumors.

Claims (1)

A peeling gas target for stripping a beam of negative ions, containing a peeling tube, a gas supply system, a gas source, magnets located in front of and after leaving the target and creating a transverse magnetic field, characterized in that the magnets are made in the form of alpha magnets, rotating the ion beam through an angle of 270 °, while the gas stripping target is placed perpendicular to the axis of the accelerating path of the negative ion beam.

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