US3683287A

US3683287A - Heavy ion accelerator

Info

Publication number: US3683287A
Application number: US55552A
Authority: US
Inventors: Horst Miessner
Original assignee: Gesellschaft fuer Kernforschung mbH
Current assignee: Gesellschaft fuer Kernforschung mbH
Priority date: 1969-07-16
Filing date: 1970-07-16
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08
Also published as: DE1936102B2; DE1936102A1

Abstract

The invention relates to a heavy ion accelerator with an electrostatic tandem arrangement with a straight acceleration tube in whose central section kept at a high potential a gas charge exchange device is installed for the attachment of electrons, with one magnetic mirror each at each end of the tandem arrangement each of which consists of several sectors arranged symmetrical to the longitudinal axis of the tandem arrangement and which deflect the ions after each passage through a straight section of the trajectory in one direction so as to make them pass through the same straight section section of the trajectory in the reverse direction so that the trajectory of the ions follows an infinite line closed in itself, and having foils for stripping the electrons from the ions which are arranged in the trajectory of the ions in such a way that the ions traverse a foil twice between two straight passages each through the tandem assembly in such a way that the gain in energy of the accelerating section of the tandem assembly is higher than the energy loss in the decelerating section of the same assembly after passage through the gas charge exchange device.

Description

United States Patent Miessner [54] HEAVY ION ACCELERATOR [72] Inventor: Horst Miessner, Karlsruhe, Germany [73] Assignee: Gesellschat't fur Kernforschung mbH, Karlsruhe, Germany 22 Filed: July 16,1970

[2i] Appl.No.: 55,552

[30] Foreign Application Priority Data July 16, 1969 Germany ..P 19 36 102.5

[52] US. Cl ..328/233, 313/63 [51] Int. Cl. ..l'l05h 9/00 [58] Field of Search ..328/23 3-238; 313/63 [56] References Cited UNITED STATES PATENTS 3,343,020 9/1967 Gordon ..328/234 Primary ExaminerJohn Kominski Attorney-Spencer and Kaye ABSTRACT The invention relates to a heavy ion accelerator with an electrostatic tandem arrangement with a straight acceleration tube in whose central section kept at a high potential a gas charge exchange device is installed for the attachment of electrons, with one magnetic mirror each at each end of the tandem arrangement each of which consists of several sectors arranged symmetrical to the longitudinal axis of the tandem arrangement and which deflect the ions after each passage through a straight section of the trajectory in one direction so as to make them pass through the same straight section section of the trajectory in the reverse direction so that the trajectory of the ions follows an infinite line closed in itself, and having foils for stripping the electrons from the ions which are arranged in the trajectory of the ions in such a way that the ions traverse a foil twice between two straight passages each through the tandem assembly in such a way that the gain in energy of the accelerating section of the tandem assembly is higher than the energy loss in the decelerating section of the same assembly after passage through the gas charge exchange device.

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MN Q Q Q A n n m HEAVY ION ACCELERATOR Facilities of this type are required for the production of high energy particles which are used, e.g., for nuclear physics investigations where an ion beam of high intensity and energy with a small amount of scattering is to be produced with a minimum of expenditure in terms of equipment.

It is known that these requirements can be fulfilled by increasing the charge state (degree of ionization) of the ions before their entrance into the electrostatic acceleration field by stripping electrons with a solid state stripper designed, e.g., as a foil, reducing the charge state of the ions in a gas channel (gas charge exchange device) by electron attachment and decelerating the ions again in a following electric field (Zeitschrift fur Physik, vol. 176, 1963, pages 115 to 119).

In this case, the average energy of the particles increases also if the electrostatic fields used for accelerating and decelerating the ions are of equal size and of opposite directions, because the degree of ionization of the particles is higher in the accelerating section than in the decelerating section.

It is known also (DAS l 295 108 and Nuclear Instruments and Methods 45 (1966) 347-348) that ionized particles can be made to oscillate in an assembly of this kind many times during which process their average particle energy is increased by steps. The straight trajectory of the ions is limited in this case by identical magnetic mirrors at both ends in which the particles are deflected so as to leave the magnetic mirror again on the flightpath by which they had entered, i.e., they are quasi-reflected and oscillate on a straight trajectory between two magnetic mirrors. However, a positive energy balance can be achieved only of the degree of ionization of the particles is increased always before they enter the accelerating section. For this purpose, one solid state stripper each must be attached to either end of the trajectory and a gas charge exchange device kept at a negative potential must be installed in the center of the trajectory to the right and left of which facilities for generating electrostatic fields are arranged which produce forces on the ionized particles passing through the trajectory directed towards the gas charge exchange device. This results in the disadvantage of both halves of the only acceleration tube having to assume the fuctions both of accelerating and decelerating sections and of each particle having traverse to two solid state strippers in each half cycle which gives rise not only to the desired effect of chare exchange but also to an energy loss of the particles to be accelerated and a correspondingly high intensity loss as a result of scattering.

In the familiar heavy ion accelerator the beam injection can be achieved by directing the beam to the magnetic mirror under a predetermined angle on the side facing away from the acceleration stage. Introduction of the beam into the straight section of the trajectory is performed by the magnetic mirror. However, this type of injection has the disadvantage of requiring a very expensive injector accelerator.

It is possible also to inject the beam past the magnetic mirror and the foil stripper so that a much smaller injector will be sufficient. However, in that case the beam must be deflected in the direction of the trajectory which requires a correspondingly complicated deflection system because of the relatively large angle of deflection.

From Nuclear Instruments and Methods," 63 (1968), 61-65, a tandem acceleration device is known where a common pressure vessel contains two separate parallel acceleration tubes and a magnetic deflection device for deflecting the ion beam emerging from one acceleration tube after its passage through a charge exchange foil into the other acceleration tube. However, this device is not suited for the acceleration of heavy ions to very high energies by repeated passage through the same acceleration potential because the ion trajectory does not constitute an infinite line closed in itself.

Therefore, the invention is based on the objective of creating a heavy ion accelerator which allows a repeated passage of the ions through the same acceleration potential while maintaining only a predetermined direction of motion in all sections of the trajectory and, at the same time, the design and arrangement of the systems necessary for acceleration and deceleration, respectively, of the ions in such a way that an ion beam of higher energy and intensity with less scattering and, hence, less intensity losses, is generated at less expenditure. Another purpose of the invention is the simplification of the injection of the ion beam and the reduction of the expenditure for the injection system and the deflection systems.

In the invention, this problem is solved by the tandem assembly having two separate parallel acceleration tubes (21 and 22, respectively) each of which is equipped with individual accelerating section (41) and decelerating sections (421, 422) and, moreover, by dividing each of the magnetic mirrors symmetrical to the longitudinal axis of the tandem arrangement into halves (611 and 63, 612, and 72, 712 and 73, 711, respectively) in such a way that the ion beam on each way out through the tandem arrangement passes through one (21) of the acceleration tubes and on the way back in the other (22) acceleration tube and, finally, by arranging the foils (11, 12) so that the ion beam traverses once only one of the foils between two successive passages through one (21) and the other (22) acceleration tube.

As a result of the division of the sections of the trajectory it is possible to install only one foil in each of these to increase the degree of ionization in such a way that the ions penetrate through the foil before entering into the magnetic mirror, because the deflection of particles with a higher degree of ionization is less complicated.

Moreover the division of the trajectory into one section for the outward flight and another for the return flight allows the arrangement of additional gas charge exchange devices in one or both sections of the accelerator according to the invention so that the ions after successive charge exchange in several gas charge exchange devices attain a lower charge state within the decelerating section than with one gas charge exchange device only.

This gives rise to less energy losses during the deceleration process, and a much higher energy gain per half cycle is achieved. Thus, in the acceleration of uranium in a familiar accelerator under conditions of injection according to the invention the energy gain over the first five half cycles is 30 MeV with an acceleration potential of 4 MeV, while it is MeV in the accelerator proposed herein.

Hence, the number of acceleration cycles necessary to reach a predetermined particle energy is much smaller and so are the intensity losses caused as a result of scattering and the energy losses produced in traversing the foil.

The average energy gain per half a cycle achieved for the familiar accelerator is and for the accelerator according to the invention with one additional gas charge exchange device maintained at V/2 potential it is per half cycle if e= 1.602 X coulomb=electron charge V= potential 5 (E) mean charge state of the ions at the energy E before acceleration s==solid state stripper (foil) g gas charge exchange device.

Thus, despite the additional gas charge exchange devices, surprisingly enough a considerably higher gain in energy is achieved because the much lower equilibrium thicknesses of gas charge exchange devices relative to the solid state stripper cause but neglibigly small losses in energy and intensity but allow high energy gains as a consequence of charge exchange effects so that the overall result is an improved positive energy balance. For this reason, it is possible also to implement the gas charge exchange devices in the decelerating sections by filling the entire decelerating section with a charge exchange gas of the proper pressure (continuous gas charge exchange device).

One example embodying the invention is shown on the diagram and explained in detail below.

FIG. 1 shows a heavy ion accelerator with magnetic mirrors and a straight trajectory section for outward and return flights of the ions.

FIG. 2 shows a heavy ion accelerator with divided magnetic mirrors and two parallel straight sections of the trajectory for separate outward and return flights of the ions.

In the heavy ion accelerator shown in FIG. 1 an ion beam is moved on trajectory l in such a way that the ions pass through its straight section alternately in both directions. This part of the trajectory is situated mainly in an acceleration tube 2 in the central section of which a gas charge exchange device 3 is installed which is maintained at a negative potential, on both sides of which section there are

electrostatic acceleration devices

41 and 42 whose eletrostatic fields generate acceleration forces on the ions which are directed at the gas charge exchange section. The acceleration tube is surrounded by a gas filled pressure vessel 5. The straight section of the trajectory is limited on both sides by identical magnetic mirrors consisting of three

segments

61, 62, 63, and 71, 72, 73.

Solid state foils

81 and 82 are arranged in the trajectory immediately ahead of the

segments

61 and 71. The particles may be injected either by an accelerator 9 of, e.g., 6 MV through the magnetic mirror or an accelerator 10 of, e.g., 10 kV past the magnetic mirror under a relatively large angle relative to the straight section of the trajecto 1.

i? the ions move in the direction from A to B, they are accelerated in section 41 of the acceleration tube and decelerated after electrons attachment in the gas charge exchange device 3 in segment 42; on the way back from B to A, however, they are accelerated in the segment 42 of the acceleration tube and decelerated in segment 41.

If the base segments of the magnetic mirrors are subdivided symmetrically into the

segments

611 and 612, and 711 and 712, respectively, this results in the accelerator shown in FIG. 2 with the

acceleration tubes

21 and 22 which are passed by the ions in one predetermined direction only. The gas

charge exchange devices

31 and 32, respectively, arranged in the center of the acceleration tubes can now be followed by one or more gas charge exchange devices 31 1 and 321, respectively, in the direction of the flight. The acceleration tubes now have defind accelerating sections 41 and decelerating

sections

421 and 422. The additional gas charge exchange devices installed in the decelerating sections are kept at a potential which is equal so that of adjacent electrodes of the decelerating section. Before entering into the

segments

612 and 712, respectively, of the magnetic mirrors the ions pass through the stripper foils 11 and 12, respectively. This arrangement of stripper foils results in easier deflection of the particle beam as a consequence of its higher degree of ionization.

The particles may be injected through the gap between the

segments

611 and 612 under a very small angle relative to the trajector 1 by means of an accelerator 13 of, e.g., 10 to 800 kV. The advantages offered by the invention are in particular the fact that a solid state stripper causing the highest loss in intensity and energy of the particles to be accelerated in comparison to a gas charge exchange device must be passed only once per half cycle. In this way, the energy losses are reduced to half and the intensity losses caused by scattering are reduced considerably.

Moreover, because of the lower intensity losses caused by scattering higher transmission and particle intensity are achieved.

Subdivision of the trajectory and its guidance through two acceleration tubes for separate outward and return flights of the particles creates the conditions for the establishment of separate acceleration and deceleration sections. As an additional advantage this offers the possibility of setting up additional gas charge exchange devices in the deceleration sections. This in turn, results in a higher energy gain per cycle because the additional loss in intensity produced in the gas charge exchange devices is negligibly small.

Moreover, the subdivision of the magnetic mirror allows injection of the beam through the gap between the magnets, which enables very small angles of injection and very low injection energies to be attained.

I claim:

1. Heavy ion accelerator with an electrostatic tandem arrangement with a straight acceleration tube in the central section of which, which is kept at a high potential, there is a gas charge exchange device for electron attachment, with two magnetic mirrors at both ends of the tandem arrangement each of which consists of several sectors arranged symmetrical to the longitudinal axis of the tandem arrangement and which deflect the ions after each passage through a straight section of the trajectory in one direction in such a way as to make them pass through the same straight section of the trajectory in the reverse direction so that the trajectory of the ions follows an infinite line closed in itself, and with foils for stripping electrons from the ions arranged in the trajectory of the ions so that the ions pass through a foil twice between two straight passages each through the tandem arrangement so that the energy gain in the accelerating sections of the tandem arrangement is higher than the energy loss on the decelerating sections of the same arrangement after passage through a gas charge exchange section, where the tandem arrangement has two separate parallel acceleration tubes with respective separate accelerating sections and decelerating sections and, moreover, each of the magnetic mirrors is arranged symmetrical to the longitudinal axis of the tandem assembly in halves in such a way that the ion beam upon each outward passage through the tandem arrangement passes through one of the acceleration tubes and on the return direction through the other acceleration tube and, finally, the foils are arranged so that the ion beam passes once through only one of the foils between two successive passages through one and the other acceleration tube.

2. Heavy ion accelerator as claimed in claim 1 where both acceleration tubes are arranged in a common pressure vessel.

3. Heavy ion accelerator as claimed in claim 1 whose solid state strippers (foil) are arranged so that the ions pass through them always before entering into one of the magnetic mirrors.

4. Heavy ion accelerator according to claim 1 with additional gas charge exchange devices arranged in the decelerating section of one or both acceleration tubes.

5. Heavy ion accelerator as claimed in claim 1 where the entire decelerating section is filled with a charge exchange gas of a predetermined pressure (continuous gas charge exchange device).

6. Heavy ion accelerator as claimed in claim 1 where an injector for the ions to be accelerated is so arranged as to cause the ions to be injected through the gap separating the halves of one of the magnetic mirrors.