US3136908A

US3136908A - Plurally charged ion beam generation method

Info

Publication number: US3136908A
Application number: US45983A
Authority: US
Inventors: Weinman James Adolf
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-07-28
Filing date: 1960-07-28
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

June 9, 1964 J. A. WEINMAN 3,136,908

PLURALLY CHARGED ION BEAM GENERATION METHOD Filed July 28, 1960 KEY O NEUTRAL ATOMS MULTIFLY CHARGED INVENTOR Posmvs IONS SINGLY CHARGED JAMES A. WEINMAN PosmvE IONS ATTORNEY United States Patent Ofifice 3,136,908 Patented June 9, 1964 3,136,908 PLURALLY CHARGED ION BEAM GENERATION METHOD James Adolf Weinman, Downers Grove, Ill. (2506 Kendall Ave, Madison, Wis.) Filed July 28, 1960, Ser. No. 45,983 5 Claims. (Cl. 313-63) This invention relates to nuclear accelerators, and more particularly relates to a machine and a method for providing a high intensity beam of plurally charged ions of atomic number of from 2 to approximately 20 available for acceleration at a high voltage terminal of an accelerator.

The DC. acceleration of plurally charged positive ions.

has conventionally required that an ion source, ion focusing equipment and other supplementary ion beam generation equipment be installed within a high voltage terminal contained within a sealed and pressurized electrostatic or Cockroft Walton accelerator enclosure. The presence of such equipment within an enclosed high voltage terminal complicates the construction of an accelerator and renders maintenance of the ion source difiicult. It also limits the type of ions to be accelerated to those which are readily produced by a compact source.

A source of positive ions such as is usually installed in the high voltage terminal of an electrostatic accelerator provides positive ions from an electric discharge in a tenuous atomic gas, the ions of which one wishes to accelerate. The gas usedto obtain plurally charged particles may most conveniently be helium, but one is not restricted to the use of this gas. Design of such sources are manifold and are well known to those concerned with the art (D. Kamke Encylopedia of Physics, vol. 33, 1956, p. 36, et seq). This invention is not restricted to use of any particular design of poistive ion source or DC. accelerator, but proposes to place a source at a location remote from an electrostatic accelerator high voltage terminal.

This invention provides a method and a machine for generating a positive ion beam of plurally charged particles at an accelerator terminal from a beam of fast (nonthermal) neutral atoms produced at a source outside the accelerator enclosure. Generating the neutral particle beam outside the terminal enclosure greatly facilitates the adjustment and operation of the source mechanism and makes possible the production of ion beams which could not readily be produced subject to the space and power restrictions within an accelerator terminal.

It is an object of this invention to provide a high intensity beam of plurally charged ions of elemental gases having atomic numbers of from 2 to approximately 20.

Other objects will become apparent from the drawings and from the following detailed description in which it is intended to illustrate the applicability of the invention without thereby limiting its scope to less than that of all equivalents which will be apparent to one skilled in the art. In the drawings like reference numerals refer to like parts and:

The single figure is a schematic elevation of an electrostatic accelerator of this invention.

In the figure is shown electrostatic accelerator 12. Accelerator 12 comprises pressurized enclosure 11 containing positively charged high voltage terminal charging belt 15, equi-potential rings 13, and evacuated tube 22 disposed axially therewithin. Terminal 16 may be charged to a positive potential of several million volts with respect to terminal 17 by electrostatic charge transfer from belt 15, and may be electrically insulated from enclosure 11, of which terminal 17 is a portion, by insulators between equi-potential rings 13 in a manner conventional to electrostatic accelerators. Another method of achieving the high voltage on the terminal is by an electronic voltage multiplying circuit first applied to this use by Cockroft and Walton. The construction of a high voltage terminal and the means for charging and insulating the terminal form no part of this invention.

Ion source 21 is shown schematically and may include a source of suitable gas and a gas purifying device. Purification may be accomplished in conventional fashion by passing the gas through a liquid air trap to remove contaminants before it is introduced into accelerator 12.

Purified molecular gas of atomic number 2 or greater may be singly or multiply ionized in an electrical discharge of appropriate design. Means for producing positive ions are well known to those versed in the art and any suitable such means may be utilized.

Singly and multiply charged positive ions may be extracted from ion source 21 of FIGURE 1 by electrode 26. Electrode 26 may be negatively charged to between and 2000 kilovolts and preferably to between 500 to 1000 kilovolts with respect to ion source 21, if positive helium ions are to be used. Voltage of this magnitude can readily be obtained either by an electrostatic generator, or by a voltage multiplying electronic circuit. The positive ions (multiply and singly charged) from source 21 are then passed through evacuated tube 22. Either the positive ion source 21 may be at ground potential and target 27 be negatively biased with respect thereto, or target 27 may be at ground potential and the ion source 21 be positively biased with respect to target 27 (not illustrated for simplicity), or the two components may be biased to opposite polarities with equal effect to provide a suitable potential between the two (also not illustrated for simplicity). It may be desirable to provide between ion source 21 and electrode 26 a suitable means for focusing the ion beam such as an electrostatic lens (not shown).

Within electrode 26 is charge exchange target 27. Target 27 is preferably a canal in which a quantity of gaseous matter (e.g. hydrogen, nitrogen, argon, or oxygen) is disposed in the path of travel of the particle beam, such matter having a concentration substantially greater than matter in adjacent areas through which the beam passes. It may also consist of a thin metal or carbon foil disposed across the path of the beam. Both gaseous and foil charge exchange targets are known in the art and form no part of this invention. The ions, upon passing through target 27 pick up electrons and emerge therefrom as neutral particles, i.e. a beam of fast (non-thermal) atoms. The charged particles (both multiply and singly charged) that then remain in the beam may then, if desired, be deflected by charged collector ring or magnet 31 and be removed from the beam. The uncharged atoms which comprise the operable portion of the beam can then drift with the energy previously given herein, i.e. (in the case of helium isotopes, for example) from 100 to 2000 kilo electron volts, and preferably from 500 to 1000 kilo electron volts, into the electric field of terminal 16 which is maintained at a high positive potential, e.g. several million volts, without being repelled. Thereupon the atoms can pass through target 28.

Target 28 may be a quantity of matter similar to target 27, e.g. a metal or carbon foil or a gas filled duct. Gas is the preferred target material and can most conveniently be oxygen or nitrogen, although other gas might also be used. Some of the atoms in the beam upon passing through target 28 in terminal 16 are ionized by collisions with the matter of target 28 and consequently lose their electrons. Some may lose one electron to form singly charged ions and some lose two or more electrons to form multiply charged ions. The ions that are formed may then be accelerated to ground potential at terminal 17 in a single main stage of acceleration in conventional.

such emergent ions which are multiply charged; since their The ions emerge with an energy proportional to chargewill be twice as great or more than twice as great as the charge of singly charged ions, their energy on Usually the emergence will be at least twice as great. beam of multiply charged ions which emerges from: terminal'17 will also contain singly charged ions and neutral.

atoms. It is desirable, for the purposes of the invention,

a that a significantfractionof the atoms which pass through terminal 16 are stripped of two -or more electrons so that theemergent beam at 17 contains a significant fraction of multiply charged ions. Useful and valuable results are obtained if at least .002% of the particles which emerge at 17 are multiply charged ionsso that a significant fraction or portion is to beconsiclercd to be .002% in the case of this invention.

charged ions may then be provided by passing the beam through a magnetic field, which may be created in any suitable manner, such as by magnet 35, whereupon the beam of multiply charged ions is bent so that it emerges as indicated by arrow 36; the paths of singly charged ions are bent less with the result that they strike the wall of the tube; the paths of neutral atoms are of .course. not

changed by the magnetic field ancl they ofcourse likewise "30 a intensity beam of multiply charged. positive ions having an;

strike the wall of the tube -at 35. The term thermal velocity as it is used velocities not greater than 2x 10 cm./sec.

herein denotes fFast (nonthermal) atoms or ions are those having a velocity of a v I 7 atoms having an atomic number of "from 210 20 drifting .toward a terminal having a high positive potential of 10 -cm./sec. or greater; a I

The following chart shows, as anexample, the relationship between some energies and velocities for two isotopes of helium for use in'the accelerator'ofthis inven- While certain modifications and embodiments of the invention have been described, it is of course to be then removing more than one electron from a significant.

fraction of each of: said .atoms at'said first terminal to form multiply chargedvpositiveions, then only once accelcrating said ions toward and through said second terminal f 4 a tensity beam of multiply charged positive ions having an atomic number of from 2 to 20, comprising the steps of providing a quantity of thermal neutral atoms-having an atomic number of from 2 to 20, io nizing said atoms tot r-positive ions, accelerating said ions across a first voltage differential to provide a beam of fast (non'-thermal)'ions,

then adding electrons to said ions tdprovide" a beam of fast (non-thermal) neutral atoms drifting toward a first terminal having a higher positive potential of several million volts with respect .to a secondterminal than the potential difference across said first'voltage differential,

with respect to which'said first terminal hasllsaid high positive potential to provide a high energy and high intensity :beam of multiply charged 'fromsaid second. terminal. r p 20 7 A beam which contains substantially only multiply 7 positive ions: emerging ybeam to add said electrons thereto and passing said beam of drifting fast (non-thermal) neutral atoms through a quantity of matter present at said first terminal in greater concentration than in' adjacent portions of. said path of said beam 'to remove more than one electron from a significantfraction of-each o f said atoms. I

3; The method of providing-a'high energy and high atomic number" of from 2 to 20, .comp'rising the steps of firstproviding a beamofjfast non-thermal) neutral several million volts with respect to a'sec'ond terminal,

tion. The superscripts denote the atomic weight of the positive ion.

CmJsec. 100 kev 1000 kev 1 2000 kev.

' Ee 2.s 10 231x10 11x10. 7 He 2.2 10 6.9X108 9.7 10

then removing electrons from said neutral atoms at said first terminal to form multiply charged positive'ions, then accelerating said ions toward and through said secondter-f minal with respect to which'said first terminal has said i 7 "positive potential to provide a high energy, and high intensity beam of multiply charged positive ions'emerging' from said second terminal, said potential of several million'volt's adding more energy to saidions than'added to f provide said fast neutral atoms.

4. The method-of claim 3 further, characterized by v passing said beam of drifting fast (non-thermal) neutral V 5. The method of claim 3 characterized by at least a i significantly large proportion of said positive ions emerging from said second terminalbeing doubly charged helium ions.

understood that there are a great number of variations which will suggest themselves to anyone familiar with the subject-matter thereof and his to be distinctly understood that this invention should not be limited except by "such limitations as are clearly imposed in the appended claims V V 1 I claim:

References Cited in the file ofthis" patent 7 Vi UNITED "STATES PATENTS oTHER REFERENCE-S7. j

' Bennett, July 2, 1940; Kuhnet al. 0m. 22 1940

Claims

1. THE METHOD OF PROVIDING A HIGH ENERGY HIGH INTENSITY BEAM OF MULTIPLY CHARGED POSITIVE IONS HAVING AN ATOMIC NUMBER OF FROM 2 TO 20, COMPRISING THE STEPS OF PROVIDING A QUANTITY OF THERMAL NEUTRAL ATOMS HAVING AN ATOMIC NUMBER OF FROM 2 TO 20, IONIZING SAID ATOMS TO POSITIVE IONS, ACCELERATING SAID IONS ACROSS A FIRST VOLTAGE DIFFERENTIAL TO PROVIDE A BEAM OF FAST (NON-THERMAL) IONS, THEN ADDING ELECTRONS TO SAID IONS TO PROVIDE A BEAM OF FAST (NON-THERMAL) NETURAL ATOMS DRIFTING TOWARD A FIRST TERMINAL HAVING A HIGHER POSITIVE POTENTIAL OF SEVERAL MILLION VOLTS WITH RESPECT TO A SECOND TERMINAL THAN THE POTENTIAL DIFFERECE ACROSS SAID FIRST VOLTAGE DIFFERENTIAL, THEN REMOVING MORE THAN ONE ELECTRON FROM A SIGNIFICANT FRACTION OF EACH OF SAID ATOMS AT SAID FIRST THERMINAL TO FORM MULTIPLY CHARGED POSITIVE IONS, THEN ONLY ONCE ACCELERATING SAID IONS TOWARD AND THROUGH SAID SECOND TERMINAL