US3723730A

US3723730A - Multiple ion source array

Info

Publication number: US3723730A
Application number: US00203352A
Authority: US
Inventors: F Gordon; C Damm
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1971-11-30
Filing date: 1971-11-30
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

A plurality of Calutron ion sources spaced in a linear array at a 45* angle to a 90* the plane i.e., the plane parallel to the field lines of a uniform magnetic field into which the source beams are directed, and normal to the injection axis of the ion receiving device such as an accelerator column, at the entry thereto. The sources are contained in a common vacuum and respectively operated at a proper potential with respect to the strength of the magnetic field for each beam to enter a single beam accelerator presented at the plane, at a suitable relatively small acceptance angle, e.g., of the order of + OR - 3*. Not only may the array be employed to introduce a very high current beam to the accelerator column, but a composite beam of various elements and/or their isotope ions in admixture may be supplied by the array as desired.

Description

United States Patent 91 Gordon et al.

1 Mar. 27, 1973 [54] MULTIPLE ION SOURCE ARRAY [73] Assignee: The United States of America as represented by the United States Atomic Energy Commission 22 Filed: Nov. 30, 1911 211 Appl. No.: 203,352

[52] U.S. Cl. .250/4l.9 C, 250/41.9 CR, 250/4l.9 SE

--4B= CONSTANT Primary Examiner-James W. Lawrence Assistant Examiner-B. C. Anderson Anomey-Roland A. Anderson [57] ABSTRACT A plurality of Calutron ion sources spaced in a linear array at a 45 angle to a 90 the plane i.e., the plane parallel to the field lines of a uniform magnetic field into which the source beams are directed, and normal to the injection axis of the ion receiving device such as an accelerator column, at the entry thereto. The sources are contained in a common vacuum and respectively operated at a proper potential with respect to the strength of the magnetic field for each beam to enter a single beam accelerator presented at the plane, at a suitable relatively small acceptance angle, e.g., of the order of :3". Not only may the array be employed to introduce a very high current beam to the accelerator column, but a composite beam of various elements and/or their isotope ions in admixture may be supplied by the array as desired.

5 Claims, 3 Drawing Figures PATENTEDHARZY I975 3,723,730

SHEET 1 or 3 II]! I -4- B= CONSTANT B= CONSTANT MULTIPLE ION SOURCE ARRAY BACKGROUND OF THE INVENTION The invention disclosed herein was made in the course of or under Contract W-7405-ENG-48 with the United States Atomic Energy Commission.

Various contemplated controlled thermonuclear fusion machines require ion sources which can deliver proton beams or the like having a current of the order of to 50 amperes to a particle accelerator column with a very narrow angular spread, e.g., of the order of 1-3", the acceptance angle of the accelerator. Various high intensity Calcutron ion sources presently exist which can generate beams of the order of l ampere, however such Calutrons typically have a source angular spread at least on the order of :l0, which is outside of the maximum acceptance angle which can be tolerated in the contemplated fusion machines.

SUMMARY OF THE INVENTION The present invention relates to a multiple Calutron ion source arrangement for introducing a very high current ion beam to a single accelerator column with an extremely small angular spread of the ion beam, and is more particularly directed to a linear array of Calutron ion sources at a 45 angle to what is termed the 90 plane, i.e., the plane normal to the injection axis of the ion receiving device such as an accelerator, at the entry thereto and parallel to the field lines of a common uniform magnetic ion bending field, the sources being respectively operated at appropriate potentials with respect to the magnetic field strength to cause the multiple ion beams of the sources to enter a common accelerator column situated at the 90 plane with a very small divergence or angular spread of the composite beam.

It is an object of the present invention to provide a multiple ion source array for producing a very high current beam at a predetermined location with a minimum amount of angular spread of the composite beam.

It is a further object of the invention to provide a multiple ion source array of the class described wherein the individual sources are arranged to produce a composite beam comprised of ions of various elements and/or their isotopes ions at various energies or in admixture.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 is a schematic diagram of the invention multiple Calutron ion source configuration in relation to the ion receiving accelerator column.

FIG. 2 is a schematic diagram showing one of the inventive multiple Calutron ion source and configuration geometry illustrating the method of beam formation.

FIG. 3 is a schematic diagram showing one of the inventive Calutrons multiple ion emission slit configuration geometry for forming the beam.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

The Calutron ion source array as shown in FIG. 1 comprises four Calutron ion sources 14 enclosed in a vacuum and lying within a uniform magnetic field (B= constant 0) normal to the plane of the drawing and represented by arrowhead points 10, each source situated along a line 11 which lies at a 45 angle to a plane plane 12 lying parallel to the magnetic field lines and situated at the entry to an ion receivingdevice such as an accelerator 14 at the entry thereto, normal to the axis 14a. Beam radius R1 represents the distance from the 90 plane 12 to the Calutron ion source 1, radius R1 generally describing the path of the ions as they are emitted from the ion emission aperture slits 13.

The uniform magnetic field illustrated by arrowhead points 10 in FIG. 1 may be of the type produced by a long solenoid (not shown). In such an arrangement, the ion source beams are taken out of the solenoid between separated wire turns or at an opening between distorted turns of the coil. The field then is terminated at the 90 plane 12 coincident with accelerator 14 by means of iron magnetic shields or the like. The Calutron ion sources 1-4 are spaced as closely together as insulation and mechanical features will allow. Alternatively, the field could be generated by an iron core magnet, although a different source array design may be necessary. In either case, the entire source array would be contained in a single vacuum vessel.

Each ion source 1-4 is operated at a voltage potential to impart a velocity to each emitted ion such that the interaction of the ion with the magnetic field causes the ion to follow a proper beam radius in order that the multiple beams (of ions) enter the single beam accelerator 14 at suitable acceptance angles with respect to the injection axis 14a of the accelerator 14. The paths followed by the beams from the Calutron ion sources are represented generally by radii Rl-R4.

Reference to FIG. '2 shows the idealized extraction geometry illustrating the method of beam formation. Three particle trajectories (21, 22, 23) are shown leaving accelerator slit 24 of Calutron 1. All the trajectories are assumed to originate on a line focus. The beam is assumed to be monoenergetic and the magnetic field uniform to a distance R from the line focus (where R is the particle orbit radius of curvature), i.e., to the 90 plane 12, and null beyond. The Z-axis component (into the paper)'of particle velocity is assumed to be zero. The central ray 22 then completes exactly 90 of arc and emerges wholly in the X direction. The other rays, 21 and 23, leaving the source 1 at angles i a to the y direction, cross the magnetic boundary at 12 at an angle of B E 11 /2 to the X direction (shown by dotted lines), both rays sloping slightly downward. For angles a l rad, a considerable reduction in beam spreading is achieved. The beam width, W, equal approximately to 2Ra, depends upon the target distance (down the accelerator tube) as well as R and a. For a given radius R, the useful range of angles a is therefore set by the target size and distance. The relationship of beam width as a function of target distance is made more evident in the article entitled High Intensity Source of 20-keV Hydrogen Atoms, The Reviewof Scientific Instruments, Vol. 34, No. 9, September 1963, pp. 967-8, the authors identical with the present inventors. From the above consideration, it is noted that the central angles (a O) with the highest beam density also have the lowest divergence (B E 01 /2), and are most favorably conserved. Rays originating with positive a are directed toward the center of the beam, and the source I can be positioned to favor these rays. In addition, there exists the possibility of recovering the beam in the wider angles by magnetic shimming.

FIG. 3 illustrates the angular spread y of the multiple beams at the 90 plane 12 due to the separation S between the multiple ion exit slits 13 of the Calutron source 1. The multiple slits are necessary to achieve maximum ion output from the Calutron sources. The angular spread at the 90 plane 12 due to the separation, S, between exit slits 13 is given by y E S/R, where y is in radians. For an example, if S 0.300 inch and R 3.5 inch, 7 a 49. In our inventive system, an angle of 149 would probably not be acceptable, however, as a practical .matter, S and R can be adjusted to give suitable y, for instance, S 1 cm and R 30 cm, 7 19. Thus, referring to FIGS. 2 and 3, it can be seen that the width of the accelerator beam W and the angular spread y are inversely related and must be compromised. Table below illustrates the resultant y (in degrees) and W (in cm) for varying values of R, B, and V (the accelerating voltage applied to the Calutron ion sources). S was set equal tol cm, a chosen to be 8, and the ion was a proton.

TABLE I B(Gauss) V (Volts) B 4 V B V R(cm) yW (cm) 1440 14,400 720 576 12 4.8 3.4 40,000 10,000 6,400 20 2.9 5.6

Calutrons characteristically are a source of selectable elements and/or their isotope ions, which, because of the plurality of Calutrons utilized in the subject invention, permits combination of various elements or isotope ions in admixture to comprise the composite beam. The radius R for each particular ion product will vary, as the bending radius in the uniform magnetic field is a function of ion weight and charge, and the accelerating voltage applied to the Calutron. Final beam positioning adjustments to the ion source array will include varying the Calutron accelerating voltage in accordance with the beam radius desired.

' Although the foregoing embodiment has been described in detail, there are obviously many other embodiments and variations in configuration which can be made by a person skilled in the art without departing from the spirit, scope, or principle of the invention. For example, the invention may use any number of Calutron ion sources, the limitations only being spatial confinement, and the Calutron ion sources can be either positive or negative ion sources. In the case of a line array of negative ion sources, the line will lie at an angle of from the line array illustrated in FIG. 1, but still at a 45 angle with respect to the 90 plane. Therefore, this invention is not to be limited except in accordance with the scope of the appended claims.

What we claim is:

1. An arrangement for generating an intense beam of ions with a very small angular spread in the order of i3, for delivery to an accelerator, comprising means generating in a vacuum vessel a uniform magnetic field normal to the trajectory of said beam, and a plurality of calutron sources within said vessel disposed in an aligned array extending at a 45 angle to a 90 plane parallel to the field lines of said magnetic field and normal to the ion-receiving axis of said accelerator, said sources being operable simultaneously at selected electrical potentials with respect to the st're n th of said magne sources to ic field to cause the beams from sai traverse curved trajectories at radii intersecting a conimon line in said 90 plane.

2. The combination of claim 1, further defined in that said ion sources are incrementally spaced along a line forming a linear array, and the beam radii for the respective sources decrementally shortened the closer said sources are disposed to said 90 plane.

3. The combination of claim 2 further defined in that said ion sources comprise various selectable element ion sources whereby said resultant ion beam is a composite of said ions in admixture.

4. The combination of claim 3 further defined in that said ion sources comprise various selectable isotope ion sources whereby said resultant ion beam is a composite of said ions in admixture.

5. The combination of claim 4 further defined in that said ion sources comprise various selectable element ion sources and isotope ion sources whereby types of resultant ion beam is a composite of both said ions in admixture.

l il l I 11

Claims

1. An arrangement for generating an intense beam of ions with a very small angular spread in the order of + OR - 3*, for delivery to an accelerator, comprising means generating in a vacuum vessel a uniform magnetic field normal to the trajectory of said bEam, and a plurality of calutron sources within said vessel disposed in an aligned array extending at a 45* angle to a 90* plane parallel to the field lines of said magnetic field and normal to the ion-receiving axis of said accelerator, said sources being operable simultaneously at selected electrical potentials with respect to the strength of said magnetic field to cause the beams from said sources to traverse curved trajectories at radii intersecting a common line in said 90* plane.

2. The combination of claim 1, further defined in that said ion sources are incrementally spaced along a line forming a linear array, and the beam radii for the respective sources decrementally shortened the closer said sources are disposed to said 90* plane.