Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Reexamination Certificate
1999-06-04
2001-02-06
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
C209S223100, C250S281000
Reexamination Certificate
active
06182831
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to applications of charged particles transport where a dispersion of the particles is desired by either a function of mass, energy or charge. More particularly, the invention relates to charged particle separation including, but not limited to, mass or energy spectrometers.
BACKGROUND OF THE INVENTION
In many applications in the manipulation of charged particle beams, the separation of the constituents of the beam by their mass, energy or charge is required. Magnet separators or sectors are often used to achieve this. Such magnet separators are used in mass and energy spectrometers. These magnet separators employ uniform fields perpendicular to the incident charged particle. Those skilled in the art of magnetic design go to great lengths to ensure uniformity. Charged particles in a uniform field follow curved trajectories. The trajectory that a charged particle with a mass m, an energy E, and a net charge q follows is given by the following equation:
R
2
=
C
1
B
2
(
m
E
q
)
(
1
)
Where R is the radius of the trajectory of the charged particle, or radius of curvature of the charged particle, and C is a constant of proportionality dependent upon the units of the parameters. The dependence of the square of the radius of curvature R in Equation (1) upon the mass-energy-to-charge ratio mE/q results in a dispersion of the charged particles entering into a uniform field according to the square root of their various mE/q ratios.
Depending upon the specific charged-particle separation application, many adaptations and embodiments of the uniform field magnet separator are employed. Mass spectrometers, for example, may use uniform magnet separators with permanent magnets or electromagnets to achieve a spatial separation of ions according to their mass and charge when accelerated to a fixed energy. The advantage of the uniform magnetic separator is that for a collimated charged particle beam it provides a focus along a plane parallel to the magnetic field along which the particles of all mE/q are focused. This plane lies at an angle of 45 degrees from the initial input beam trajectory. That is to say, that the trajectories of parallel charged particles of equivalent mE/q converge after the particles have followed an arc of their trajectories of 135 degrees from initial contact with the magnetic field. The disadvantage of the uniform field magnetic sector is that the separation of adjacent particles with mE/q differing by fixed amounts is a non-linear function of position. That is to say, larger mass-energy-to-charge ratios lie significantly closer than lower ratios.
For non-collimated charged particle beams, the uniform-field magnet sector is often modified to include a transverse gradient which provides focusing to compensate for the non-collimation.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention to provide a magnetic separator for charged particle beam separation that provides a focused linear or nearly linear dispersion of the charged particles proportional to their charge-to-mass or energy ratio along a plane.
Another object of the present invention is to provide a magnetic separator for charged particle separation that employs an inhomogeneous magnetic field in one plane and a homogeneous magnetic field in another for a linear dispersion of mass-energy-to-charge separation along a plane.
Another object of the present invention is to provide a magnetic separator with inhomogeneous fields providing a linear or near linear mass-energy-to-charge ratio focus dispersion beams along a plane parallel to the magnetic field with an additional transverse gradient magnetic field providing focusing for uncollimated charged particle beams.
According to a second aspect, the invention is a method for producing the required inhomogeneous field with causes collimated charged particles of varying mass-energy-to-charge ratios to be focused onto a plane with a separation of the various species directly proportional to their respective mass-energy-to-charge ratios.
According to a third aspect, the invention is a method of producing inhomogeneous fields providing a linear mass-energy-to-charge ratio focus dispersion along a plane parallel to the magnetic field with an additional transverse gradient magnetic field providing focusing for uncollimated charged particle beams.
According to one aspect, the invention comprises a magnet having two poles made of magnetically soft permeable material spaced apart to define a gap therebetween. Each pole extends parallel to the axis in the transverse direction. In the other direction the gap between the poles enlarges. In one embodiment, the enlargement is symmetrical. The gap increases along the axis at a rate such that the field decreases at a given rate as a function of the distance from entrance of the magnet. The magnetic field created within the gap between the poles subjects collimated charged particles injected into gap to follow a curved trajectory. The changing gap subjects these charged particles to a varying magnetic field as they execute curved trajectories. This varying magnetic field is determined by the profile of the poles and is chosen such that along a specific transverse plane perpendicular to the plane of symmetry between the poles the charged particles are focused according to a linear separation dispersion according to their mass-energy-to-charge ratio.
The poles receive magnetic induction by either electrical, or by permanent fully polarized hard magnetic material such as ferrite or rare-earth permanent magnets (REPM). This creates a magnetic field between the poles. A flux return yoke consisting of highly permeable soft magnetic material may be present to enhance the efficiency of the magnetic circuit. The overall shape of the magnetic separator can either be rectilinear or curved to follow the curved charged particle trajectories and minimize the mass of the sector. Likewise, in order to reduce the total sector weight specific high energy product rare-earth permanent magnet (REPM) materials such as classes known as neodymiumiron-boron (NdFeB) or samarium-cobalt (SmCo) may be used. The pole and yoke material may be made from iron cobalt alloys commonly known as vanadium permendur and described in the ASTM Specification A801.
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patent: 5457324 (1995-10-01), Armour et al.
Gottschalk Stephen C.
Jones Patrick L.
Robinson Kem
Scheidemann Adi A.
Christensen O'Connor Johnson & Kindness PLLC
Nguyen Tuan N.
University of Washington
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