US3774026A - Ion-optical system for mass separation - Google Patents

Ion-optical system for mass separation Download PDF

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Publication number
US3774026A
US3774026A US00251820A US3774026DA US3774026A US 3774026 A US3774026 A US 3774026A US 00251820 A US00251820 A US 00251820A US 3774026D A US3774026D A US 3774026DA US 3774026 A US3774026 A US 3774026A
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I Chavet
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US Atomic Energy Commission (AEC)
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/26—Mass spectrometers or separator tubes
    • H01J49/28—Static spectrometers
    • H01J49/30—Static spectrometers using magnetic analysers, e.g. Dempster spectrometer

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  • ABSTRACT An ion optical system for use with a magnetic prism with a gap of width g and having an ion beam which is arranged to emerge from an elongated object slit and whose maximum angular dispersion AB is smaller than g/l' where l is the distance between the object slit and the effective entry boundary of the magnetic field associated with the magnetic prism, the system comprising means for causing the ion beam to converge in the vertical plane, so as to focus axially substantially into a line located substantially at the effective entry boundary of the magnetic field associated with the magnetic prism.
  • This invention concerns an improved ion optical system for use with magnetic prisms such as, for example, the magnetic sectors used in mass separators.
  • the relatively high intensity of the ion beam which it is desired to obtain rules out the use of electrostatic ion lenses in mass separators and, moreover, requires that the accelerated ions emerge from the ion source through relatively long (up to cm) exit slits (or object slits), and that the ion beam will have a considerably wide aperture.
  • FIG. 1 shows a schematic plan view in the median (x,y)-plane of the ion optical system of a magnetic sector type mass separator, showing the main geometrical parameters;
  • FIG. 2a is a schematic representation of the left-hand part of the view shown in FIG. 1, showing the radial aperture angle a of one trajectory of the ion beam originating at a point located at a distance u from the median plane;
  • FIG. 2b is a schematic side view, in the vertical (x,z)- plane of the view shown in FIG. 2a, showing the axial aperture angle B of one trajectory of the ion beam originating at a point located ata distance s from the vertical plane;
  • FIG. 3a is a schematic plan view of an ion optical system according to the invention, showing three ion trajectories, the intermediate one being the principal trajectory;
  • FIG. 3b is a schematic side view of the view shown in FIG. 3a, showing a beam of ions (defined by three tra jectories), which converge to a focus in the axial (2) direction, according to the invention, which focus coincides with the magnetic field boundary;
  • FIG. 4a is a schematic horizontal cross sectional view of the ion source according to one embodiment of the invention.
  • FIG. 4b is a vertical cross section of the ion source shown in FIG. 4a showing the curved electrodes and magnetic field employed for generating the axially converging ion beam;
  • FIG. 5a is a schematic side view of an ion optical system of an ion beam collimator of the magnetic sector type.
  • FIG. 5b is a schematic top view of the ion beam collimator corresponding to FIG. 5a.
  • the direction of propagation of the ion beam is defined as the x-axis (the longitudinal direction)
  • the direction of the magnetic lines of force, which is perpendicular to x is defined as the z-axis (axial direction)
  • the y or radial direction being the third orthogonal axis and the origin of the coordinate system is located in the centre of the virtual object.
  • the x-y and x-z planes are referred to as the median and vertical planes, respectively. (See FIGS. 1 and 2).
  • u as, B which are all shown in FIGS. 2a and 2b of the accompanying drawings.
  • a and B are the radial and axial aperture angles, respectively.
  • u and s are the horizontal and vertical distances, respectively of the point of origin of the trajectory from the vertical and median planes, respectively.
  • the radial aberration Ay can be expressed as a sum of terms in various powers of u, As and B and combinations of powers of these variables. These terms can be either homogeneous, such as 0z (a second order term),
  • FIG. 1 of the accompanying drawings are:
  • entry boundary and exit boundary of a magnetic field are the effective field boundaries of the magnetic prism, which have been determined taking into account the magnetic fringe fields and as contrasted with the physical boundaries of the magnetic prisms.
  • the effective boundaries can be calculated, e.'g., according to R. I-Ierzog, Z. Naturf, 10a, 887 (1955)
  • the geometrical parameters determining lengths are hereinafter expressed in pure numbers as ratios of the radius of deflection R, which is shown in FIG. 1, while angles are expressed in radians.
  • the invention is not concerned with the variable u and since the width of the exit slit is very small compared to its length it is assumed that u in the considerations and calculations hereinafter.
  • the projection of the exit slit in the median x-y plane can be considered as a point source.
  • those aberration terms containing powers of u are neglected, hereinafter.
  • an ion optical system for use with a magnetic prism with a gap of width g and having an ion beam which is arranged to emerge from an elongated object slit and whose maximum angular dispersion AB as hereinafter defined is smaller than g/l as hereinbefore defined, means for causing the ion beam to converge in the vertical plane, so as to focus axially substantially into a line located substantially at the entry boundary as hereinbefore defined of the magnetic field associated with the magnetic prism.
  • every point of the object slit emits a narrow bundle of rays each deviating by some valve AB from the mean direction B originating at this point.
  • the present invention relates only to ion optical systems wherein this angular dispersion is relatively small, namely wherein:
  • variable AB which will appear in certain terms of the expression for the aberration, by virtue of it being very small in the systems concerned, may be regarded as a deviation of second order.
  • the homogeneous second and third order aberration terms in a can be cancelled through the proper choice of the profile of the entry boundary as expressed by r and t, which parameters were not involved in the expressions for the other optical conditions and had no effect on the particular solutions obtained for the other parameter s.
  • these aberrations can still further be minimalized empirically by changing the profile of the entry boundary of the magnet (by shimming), without thereby upsetting the other characteristics of the optics, which have previously been determined through computation.
  • the convergence and focussing of the ion beam can be effected in various ways.
  • the ion source can be designed with appropriately curved source and extraction electrodes, their common centre of curvature coinciding with the desired focus of the beam.
  • the axis of the collimating magnetic field in the source should be curved.
  • the centre of curvature of the extraction electrode should not be located at the entry boundary of the magnetic prism, but will be intermediate to this boundary and ion source.
  • the axial focussing of the ion beam, according to the invention and as represented in FIG. 3b can be expressed as a definite correlation between B and s, namely:
  • Z is the distance between the exit slit and the effective boundary of the magnetic field (see FIG. 1).
  • FIG. 3b further shows the ion beam which is axially focussed, according to the invention, and a random point at the object slit emitting a narrow bundle of rays deviating from B by the value AB, which is very small and may be regarded as a deviation of second order.
  • the aberration Ay up to and including the third order involves only the four terms in: s' a; sAB; a; a.
  • G is the radial magnification given by:
  • the remaining aberration term in a expressing the third order aperture aberration, relates to the requirement for a third order radial focussing.
  • this term can be eliminated, without disturbing the other qualities of the optical system, by giving the entry boundary a third order profile, which can be done by computation.
  • the third order aberrations due to the discrepancies of the system as compared to the theoretical values can be corrected empirically by shimrning, i.e., adding small pieces of iron sheets to the entry faces of the magnet.
  • shimrning i.e., adding small pieces of iron sheets to the entry faces of the magnet.
  • the principle of axial focussing of the ion beam is applied to the ion optical system of a magnetic prism ion collimator (see FIGS. a, 5b).
  • the function of such an instrument is to provide a beam of ions, which is parallel both in the axial (z) and the radial (y) direction.
  • Conventional ion beam collimators have usually employed magnetic and/or electrostatic lenses, and therefore were restricted to the use of small circular emission holes at the ion source.
  • the present invention permits the use, in such a system, of a long emission slit, increasing considerably the intensity of the parallel beam thus obtained.
  • FIGS. 4a and 4b show schematic cross sectional views in the horizontal and vertical planes, respectively, of an ion source according to one embodiment of the invention.
  • the ion source consists, essentially, of a box 11 made of an electrically conducting material, one wall 12 of which is cylindrically curved and provided, at its center, with an exit slit or object slit 13 consisting of a narrow rectangular opening, its longitudinal axis being parallel to the axis of curvature of this wall 12 and to the z axis of the system.
  • a side wall of the box is provided with a small aperture 14, for the entry of the ionizing electron beam (or the arc), originating at the cathode 15 which is located outside the box 11 and near the aperture 14.
  • An extraction electrode 17 is located a small distance from the curved front wall 12 of box 1 1 which is provided with the slit 13.
  • This electrode is provided with a slit 18 which corresponds in shape to the object slit l3 and it is cylindrically curved to correspond with the curvature of the front wall 12 of box 11.
  • the three centers of curvature in the (x,z)-plane of the axis 16 of the magnetic field of the ion source, of the front wall 12 provided with the exit slit 13 and of the extraction electrode 17 coincide at the point F (FIG. 4b) located at the effective entry boundary of the magnetic sector, which is also the desired focus of the ion beam in the axial (z) direction.
  • a high potential difference is maintained between the extraction electrode 17 and the ion source 11, the extraction electrode 17 being negative in respect with the ion source 11.
  • the order of magnitude of this acceleration potential, as used in mass separators is about 10 to 10 volts.
  • the ions of the isotopes to be separated are generated by electron impact along the narrow region of the arc, whose center coincides with the axis 16 of the magnetic field of the ion source.
  • the ions emerge out of the box 11 through the object slit 13, whereupon they are immediately subjected to the accelerating voltage, are propagated towards the extraction electrode 17 and by their acquired momentum pass through the slit 18 of this electrode in the direction of the focal point F on the entry boundary of the magnetic sector field.
  • An ion optical system used with a homogeneous magnetic prism having pole pieces spaced apart a distance g establishing a magnetic field in the Z direction of an orthogonal coordinate system having axes X, Y and Z comprising:
  • b. means defining an emission slit whose length s in the Z direction is large in comparison to its width in the Y direction for establishing the emitting area of the source;
  • d. means for causing the ion beam to converge in the axial X-Z plane and to be axially focused a distance I from the slit into a line perpendicular to the principal trajectory of the beam and lying in the median radial X-Y plane, where l' is the distance between the slit and the effective entry boundary of the field of the magnetic prism;
  • the ion source cooperating with the extraction system to cause the maximum angular dispersion Afl in the axial X-Z plane to be much smaller than g/l' where AB is the deviation in the X-Z plane of the trajectories of ions emitted from any point on the area of the source from a line connecting such point to the focus;
  • the angle of incidence e of the beam at the entry boundary of the magnetic field is zero for causing the principal trajectory of the beam to be normal to the entry boundary;
  • I B is a characteristic of the fringe-field geometry at the exit boundary of the magnetic prism 4.
  • l, l", d), e" and r" being such that the coefficient of the aberration term in sA/3 satisfies the following equation:
  • parameter I has the value of infinity in a both the X-Y and the X-Z planes whereby a collimated ion beam exits from the prism.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Electron Tubes For Measurement (AREA)
US00251820A 1969-10-17 1972-05-09 Ion-optical system for mass separation Expired - Lifetime US3774026A (en)

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IL33204A IL33204A (en) 1969-10-17 1969-10-17 An improved ion-optical system

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JP (1) JPS5124910B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FR (1) FR2068339A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5198083A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1975-02-26 1976-08-28
US4578589A (en) * 1983-08-15 1986-03-25 Applied Materials, Inc. Apparatus and methods for ion implantation
US5309064A (en) * 1993-03-22 1994-05-03 Armini Anthony J Ion source generator auxiliary device
US5808416A (en) * 1996-11-01 1998-09-15 Implant Sciences Corp. Ion source generator auxiliary device
US5852345A (en) * 1996-11-01 1998-12-22 Implant Sciences Corp. Ion source generator auxiliary device for phosphorus and arsenic beams

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5629586U (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1979-08-10 1981-03-20
JPS5761696U (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1980-09-26 1982-04-12
JPS5890556U (ja) * 1981-07-15 1983-06-18 クラリオン株式会社 テ−プ再生速度調製装置
JPS5885962A (ja) * 1981-11-18 1983-05-23 Gohei Takahashi カラオケ用テ−プ速度調整装置

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2975277A (en) * 1955-05-10 1961-03-14 Vakutronik Veb Ion source
US3122631A (en) * 1960-02-05 1964-02-25 Atlas Werke Ag Apparatus for focusing a line type ion beam on a mass spectrometer analyzer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2975277A (en) * 1955-05-10 1961-03-14 Vakutronik Veb Ion source
US3122631A (en) * 1960-02-05 1964-02-25 Atlas Werke Ag Apparatus for focusing a line type ion beam on a mass spectrometer analyzer

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5198083A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1975-02-26 1976-08-28
US4578589A (en) * 1983-08-15 1986-03-25 Applied Materials, Inc. Apparatus and methods for ion implantation
US5309064A (en) * 1993-03-22 1994-05-03 Armini Anthony J Ion source generator auxiliary device
US5808416A (en) * 1996-11-01 1998-09-15 Implant Sciences Corp. Ion source generator auxiliary device
US5852345A (en) * 1996-11-01 1998-12-22 Implant Sciences Corp. Ion source generator auxiliary device for phosphorus and arsenic beams

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IL33204A (en) 1972-12-29
FR2068339A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1971-08-20
IL33204A0 (en) 1970-02-19
JPS5124910B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1976-07-27

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