Ion accelerator employing crossed-field selector

Claim 2

In an ion accelerator in which the energy imparted to the ions being accelerated to form an ion beam is adjustable, a linear ion selector comprising: means for generating, over a predetermined straight line distance along the beam, a substantially constant and fixed magnetic field, which field is substantially perpendicular to said beam; means for generating, over said distance, an electric field which is substantially perpendicular to both said magnetic field and to said beam, the strength of said elEctric field on the center line of said beam being varied substantially in proportion to the square-root of the chosen ion energy, said field having a gradient in the direction of the electric field which is, on the average over said distance, varied substantially in direct proportion to the chosen ion energy.

Claim 3

Apparatus for providing ions of a preselected species at a selected energy level which is adjustable, said apparatus comprising: an ion source for providing ions of said preselected species; accelerating means; means for energizing said accelerating means including a first voltage source providing an accelerating voltage which varies substantially in direct proportion to said selected energy, thereby to provide a beam including a substantial proportion of ions of said preselected species; a linear ion selector having means for generating a magnetic field which is perpendicular to said beam and having also electrode means for generating an electric field which is perpendicular to both said beam and said magnetic field; and means for energizing said electrode means including a second voltage source which is interconnected with said electrode means to provide, on the centerline of said beam, an electric field which is varied substantially in proportion to the square root of said selected energy and including also a third voltage source interconnected with said electrode means to provide a field gradient which is varied substantially in direct proportion to said selected energy.

Claim 4

Apparatus for providing ions of a preselected species at a selected energy level which is adjustable, said apparatus comprising: an ion source for providing ions of said preselected species; accelerating means; means for energizing said accelerating means including a first voltage source providing an accelerating voltage which varies substantially in direct proportion to said selected energy, thereby to provide a beam including a substantial proportion of ions of said preselected species; a linear ion selector having means for generating a magnetic field which is perpendicular to said beam and having also electrode means for generating an electric field which is perpendicular to both said beam and said magnetic field; and means for energizing said electrode means including a second voltage source which is interconnected with said electrode means to provide, on the centerline of said beam, an electric field which is varied substantially in proportion to the square root of said selected energy and including also a third voltage source interconnected with said electrode means to provide a field gradient which is varied substantially in direct proportion to said selected energy.

Claim 5

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an adjustable energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; means for applying equal and opposite potentials to said plates, said potentials being varied substantially in proportion to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between said plates, the number of electrodes in the two series being the same whereby the corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; means for providing to each pair of electrodes a voltage which is a mixture of a voltage which is proportional to the voltage between the plates and the relative spacing of the pair together with a voltage which is varied in proportion to V and the relative spacing of the pair, thereby to provide an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.

Claim 6

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an adjustable energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; means for applying equal and opposite potentials to said plates, said potentials being varied substantially in proportion to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between said plates, the number of electrodes in the two series being the same whereby the corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; means for providing to each pair of electrodes a voltage which is a mixture of a voltage which is proportional to the voltage between the plates and the relative spacing of the pair together with a voltage which is varied in proportion to V and the relative spacing of the pair, thereby to provide an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.

Claim 7

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between sAid plates, the number of electrodes in the two series being the same whereby corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; a resistive voltage divider connected between said plates, each pair of field-grading electrodes being connected to an intermediate point in said divider corresponding to the position of the pair with said series between said plates; means for applying equal and opposite potentials to said plates, said potentials being substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis; means for algebraically adding to each of said plate voltages a focussing component voltage which is substantially proportional to V, said focussing component voltages being equal and of the same polarity; a second voltage divider, similar to said first divider, connected between the two resulting algebraic sum voltages; and means for coupling corresponding points on the two voltage dividers thereby to provide, by means of the resulting potentials thereby applied to said field-grading electrodes, an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.

Claim 8

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between sAid plates, the number of electrodes in the two series being the same whereby corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; a resistive voltage divider connected between said plates, each pair of field-grading electrodes being connected to an intermediate point in said divider corresponding to the position of the pair with said series between said plates; means for applying equal and opposite potentials to said plates, said potentials being substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis; means for algebraically adding to each of said plate voltages a focussing component voltage which is substantially proportional to V, said focussing component voltages being equal and of the same polarity; a second voltage divider, similar to said first divider, connected between the two resulting algebraic sum voltages; and means for coupling corresponding points on the two voltage dividers thereby to provide, by means of the resulting potentials thereby applied to said field-grading electrodes, an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.

Claim 9

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M, said source including supplies providing probe, extraction and focussing potentials; accelerating means associated with said source including a main accelerating potential supply; means for energizing said accelerating means and said source supplies proportionately to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of electrostatic field-defining plates on opposite sides of said beam, between said pole faces; means for applying equal and opposite potentials to said plates, said potentials being under analog control substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis and which balances the influence of the magnetic field on ions of the selected species of mass M at energy V.

Claim 10

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M, said source including supplies providing probe, extraction and focussing potentials; accelerating means associated with said source including a main accelerating potential supply; means for energizing said accelerating means and said source supplies proportionately to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of electrostatic field-defining plates on opposite sides of said beam, between said pole faces; means for applying equal and opposite potentials to said plates, said potentials being under analog control substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is substantially perpendicular to both said magnetic field and the beam axis and which balances the influence of the magnetic field on ions of the selected species of mass M at energy V.

Claim 11

An accelerator as set forth in claim 5 including analog control means for varying said extraction and focussing potentials in proportion to V.

Claim 12

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between said plates, the number of electrodes in the two series being the same whereby corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; means for applying equal and opposite potentials to said plates, said potentials being substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is suBstantially perpendicular to both said magnetic field and the beam axis; means for dividing the voltage between said plates substantially in proportion to the spacings of said electrode pairs between said plates; means for algebraically adding to each of said plate voltages a focussing component voltage which is substantially proportional to V, said focussing component voltages being equal and of the same polarity; means for dividing the difference between the two resulting algebraic sum voltages; and means for applying to each pair of field grading electrodes a voltage which is a mixture of the corresponding voltage provided by said first voltage dividing means and the corresponding voltage provided by said second voltage dividing means, thereby to provide an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.

Claim 13

An ion accelerator comprising: an ion source for providing ions of a selectable species having a mass M; accelerating means associated with said source; means for energizing said accelerating means to form a beam of ions, including a substantial proportion of said selected species, having an energy V; magnet means, including a pair of pole faces lying on opposite sides of said beam, for providing a transverse magnetic field of predetermined intensity through which said beam passes; a pair of plates on opposite sides of said beam, between said pole faces; adjacent each pole face, a series of elongate field-grading electrodes which extend substantially parallel to the beam axis and are spaced apart between said plates, the number of electrodes in the two series being the same whereby corresponding electrodes in the two series form pairs, the paired electrodes being connected together so as to be at substantially equal potentials; means for applying equal and opposite potentials to said plates, said potentials being substantially proportional to Square Root (V/M), thereby to provide, on the beam axis, an electric field of corresponding strength, which electric field is suBstantially perpendicular to both said magnetic field and the beam axis; means for dividing the voltage between said plates substantially in proportion to the spacings of said electrode pairs between said plates; means for algebraically adding to each of said plate voltages a focussing component voltage which is substantially proportional to V, said focussing component voltages being equal and of the same polarity; means for dividing the difference between the two resulting algebraic sum voltages; and means for applying to each pair of field grading electrodes a voltage which is a mixture of the corresponding voltage provided by said first voltage dividing means and the corresponding voltage provided by said second voltage dividing means, thereby to provide an electric field gradient across said beam, which gradient is proportional to V and is parallel to the electric field.