US3670162A

US3670162A - Charged particle analyzer

Info

Publication number: US3670162A
Application number: US74694A
Authority: US
Inventors: Robert E Elmore
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1970-09-23
Filing date: 1970-09-23
Publication date: 1972-06-13
Anticipated expiration: 1989-06-13

Abstract

A charged particle analyzer for analyzing charged particles with respect to their specific mass is disclosed. The charged particle analyzer employs the principle of crossed electric and magnetic fields to obtain perfect double focusing and high resolution. The electric field is radial in direction and proportional in magnitude to the radius of the analyzer at any point in the flight cylinder and is normal to the magnetic field. A suitable source of ions is provided to permit introduction of ions into the analyzer and a suitable ion receiver is provided to receive ions from the analyzer.

Description

United States Patent Elmore 1 June 13, 1972 [54] CHARGED PARTICLE ANALYZER [72] Inventor: Robert E. Elmore, Tulsa, Okla.

[73] Assignee: Avco Corporation, Tulsa, Okla.

[22] Filed: Sept. 23, 1970 211 App]. No.: 74,694

Related [1.8. Application Data [63] Continuation-impart of Ser. No. 61,068, Aug. 5, 1970,

abandoned.

[52] US. Cl ..250/4L9 ME, 250/4 1 .9 DS [5 1 Int. Cl ..H0l j 39/34 [58] Field of Search ..250/4 1 .9 DS, 41.9 ME

[56] References Cited UNITED STATES PATENTS 2,724,056 11/1955 Slepian ..250/4L9 2,667,582 1/1954 2,945,124 7/1960 2,221,467 ll/l940 3,010,017 ll/l96l Backus ..250/419 Hall et a1. Bleakney Brubaker et a].

Primary Examiner-William F. Lindquist Attorney-Charles M. Hogan and Eugene C. Goodale [5 7] ABSTRACT A charged particle analyzer for analyzing charged particles with respect to their specific mass is disclosed. The charged particle analyzer employs the principle of crossed electric and magnetic fields to obtain perfect double focusing and high resolution. The electric field is radial in direction and proportional in magnitude to the radius of the analyzer at any point in the flight cylinder and is normal to the magnetic field. A suitable source of ions is provided to permit introduction of ions into the analyzer and a suitable ion receiver is provided to receive ions from the analyzer.

18 Claims, 10 Drawing Figures PKTENTEDJUK 1 3 [s72 SHEET 10F 5 INVENTOR. ROBERT E. ELMORE TTORNEYS.

PATENTEDJummn 3,670,162 snszrsur s INVENTOR. R OBERT E. ELMORE PATENTEDJUM 13 I972 SHEET 5 OF 5 INVENTOR. ROBERT E. ELMORE wa yg ATTORNEYS.

CHARGED PARTICLE ANALYZER BACKGROUND OF THE INVENTION This application is a continuation-in-part of my co-pending application Ser. No. 61,068, filed Aug. 5, 1970, now abandoned.

This invention relates to mass spectrometry and more particularly to an analyzer into which an ion beam is projected and by means of which the beam is resolved into its various mass components.

Mass spectrographs and mass spectrometers are instruments which analyze substances according to the mass of the constituent elements and molecules present in the sample under investigation. There are a number of different types of mass sensitive instruments which can be classified under the common name mass spectroscope. To name a few, there are the ionic mass spectroscopes, the microwave absorption mass spectroscopes, the nuclear induction mass spectroscopes, the molecular mass spectroscopes, and the optical mass spectroscopes.

Most mass spectroscopes are comprised of four basic components. They are:

l. A sample system by means of which the sample to be investigated is introduced into the instrument.

2. An ion source for producing a beam of charged ions characteristic of the sample under investigation.

3. An analyzer into which the beam is projected and by means of which it is resolved into its various mass components.

4. A detector system by means of which the resolved ion beams are rendered observable.

One form of instrument of this type has been referred to as the crossed field mass spectrometer. If a charged particle is introduced into a magnetic field it will move in a circular path to return to its point of origin. This is true regardless of the mass of the particle with particles of increasing mass traveling in circles of increasing radius, but in each instance returning to the point of origin. if a uniform electric field is imposed across the space defined by the magnetic field and normal to the magnetic field, the ions pursue a path which may be considered as rigorously circular in a coordinate system moving with uniform velocity. The movement of the coordinate system is a function of the ratio of the electric and magnetic field strengths. lf ions of a particular mass are introduced into such a field system they will complete one turn of their circular motion in a time which depends directly on the mass of the particle, and if the electric field strength is uniform so that the coordinate systems corresponding to each particle move at the same velocity the particles will converge to a series of rigorous point foci after any integral number of turns in the magnetic field, regardless of the velocity or direction of travel at the moment of introduction into the field. Since the time required for ions to complete one turn of their circular motion depends directly on the mass, and since under the condition of uniform field strength specified the rate of motion of the coordinate system is invariant to the mass of the particle involved, the focal point of the heavy particles will be displaced farther from the point of origin than the focal point of the lighter particles. This is the basic concept of the crossed field mass spectrometer.

There are three basic types of mass focusing:

l. Direction focusing, i.e., focusing of ions homogeneous as to mass and velocity but of different initial direction; Velocity focusing, i.e., focusing of ions homogeneous as to mass and direction but of different initial velocity; and

3. Double focusing, i.e., focusing of ions homogeneous in mass but of varying velocities and directions. Many mass analyzers have been developed utilizing the three basic types of focusing. These focusing conditions, however, are all approximate, either to the first order or to the second order of small quantities.

in the Physical Review, Volume 53, Page 521, April 1, I938, Bleakney and Hippie showed that a combination of crossed electric and magnetic fields possesses perfect double focusing in the plane normal to the magnetic field. This phenomenon was disclosed in U.S. Pat. No. 2,221,467, issued Nov. 12, 1940, to Bleakney. It is seen from these articles that the ion beam follows trochoidal paths, the nature of which depends upon the initial conditions. The initial conditions determine whether the orbital path of the ions is a curtate or a prolate trochoid. In the perfect double-focusing mass spectrometer, the ions of mass M and charge e emerging from a point are all focused at a distance from the original along the X axis, regardless of the initial direction or velocity of the ions. There is thus a case of perfect double focusing. McDowell, in his text Mass Spectrometry, 1963, at page 249 (Lib. of Congress No. 62-22201) states that the trochoidal instrument (Bleakney and Hipple) is the only perfect double-focusing type of mass spectrometer.

Previous analyzers of this type required large magnets in order to produce the required magnetic field. This resulted from the necessity of inserting electrostatic field shims between and normal to the field pole faces. Thus a gap of several times that necessary for a single focusing machine is usually required. This disadvantage is partially counteracted by the fact that the machine is double focusing. One analyzer of this type having a 3 inch gap and a 20 inch diameter pole resulted in a core weighing 13,000 pounds and the exciting coil weighing 4,000 pounds. The unit was excited by a motor generator. Thus, it can be seen that analyzers of this type have not to date been widely employed largely because of their sizes, weight and non-mobility.

The resolving power of the double-focusing mass spectrometer is determined by the parameters of the electrostatic analyzer alone. The parameters determining the resolving power relate to the constants of the electrostatic analyzer and on the ion beam entrance slit width. The resolving power increases linearly with the increasing value of a, which is the radius of normal ion trajectory in an electrostatic field. Hence, the resolving power may be increased by reducing the entrance slit width. In some previous instruments attaining very high resolving power, (10 or more) entrance slit widths of only a few microns have been used. The proper alignment of these slits presents a problem, however. The trend has therefore been to use a large radius curvature of the electrostatic analyzer so that comparatively wide slits may be used without sacrificing resolution. However, by increasing the radius of curvature, one sacrifices the size of the analyzer in that an increase in magnet size and weight results.

A further method of increasing resolving power would be to place analyzers in tandem such that the ion beam will travel a plurality of loops or cycles. This method is not desirable because the problems previously mentioned, i.e., size, weight, etc., will only be compounded without having a sufficiently increased benefit in resolving power.

Accordingly, it is an object of this invention to provide a charged particle analyzer having the benefits of perfect double focusing and none of the disadvantages of previous double focusing analyzers.

Another object of this invention is to provide a charged particle analyzer having high resolving power and without sacrificing weight in analyzer parameter.

Yet another object of this invention is to provide a charged particle analyzer in which many ion orbits or loops may be obtained in the same trajectory area, thus permitting increased resolving power.

A further object of this invention is to provide a charged particle analyzer in which the input energy of the particles can be considerably higher for the same instrument parameter and thereby decreasing beam spread in the axis of the magnetic field.

A still further object of this invention is to provide a charged particle analyzer which permits double focusing independently of the initial ion condition, i.e., mass charge, velocity and angle of instrument.

And yet another object of this invention is to provide a charged particle analyzer employing the principle of crossed electric and magnetic fields in a new manner to obtain perfect double focusing and higher resolution than other analyzers of comparable size.

An additional object of this invention is to provide a charged particle analyzer utilizing a conventional magnetic field and an electric field radial in direction and which varies with the radius of the analyzer.

SUMMARY OF THE INVENTION This invention provides a charged particle analyzer for providing perfect double focusing of charged particles. The charged particle analyzer employs a conventional magnetic field and an electric field which is radial in direction. The electric field varies in intensity directly with the radius. Ions are injected into the analyzer such that the ions are acted on by the crossed electric and magnetic fields. The ions uniformly progress in identical orbits about the analyzer. Means are provided such that only ions of a predetermined mass are permitted to progress about the analyzer for transmission to an ion receiver.

Other details, uses and advantages of this invention will become apparent as the following description of an exemplary embodiment thereof shown in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show a present exemplary embodiment of this invention in which:

FIG. 1 is an exploded perspective view, partially cut away, of one exemplary embodiment of the charged particle analyzer ofthis invention;

FIG. 2 is an elevation view, partially in cross-section, of the embodiment shown in FIG. 1;

FIG. 3 is a view taken along line 3-3 of FIG. 2;

FIG. 4 is a diagrammatic illustration of one embodiment of the electrical system of this invention;

FIG. 5 is a polar graph showing paths of ion beams having different initial parameters illustrating the double focus capabilities resulting from the use of this invention;

FIG. 6 is a top view illustrating another exemplary embodiment of this invention and particularly illustrating a different electric field forming plate;

FIG. 7 is a cross-sectional view taken on the line 7-7 of FIG. 6;

FIG. 8 is a bottom view of the plate of FIG. 6; and

FIG. 9 is a greatly enlarged fragmentary cross-sectional view of the electric field forming plate taken along line 9-9 of FIG. 8; and

FIG. 10 is a fragmentary cross-sectional view along line 10-10 ofFlG. 9.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Reference is now made to FIGS. 1-3 of the drawings, which illustrate one exemplary embodiment of the charged particle analyzer of this invention, which is designated generally by the reference numeral 10. The charged particle analyzer 10 comprises parallel planes of electric

field forming means

12 and 14. The planar means 12 and 14 are mounted in spaced relation, one to the other, to define a flow space therebetween through which particles to be analyzed traverse as will be explained more fully herebelow. The planar means 12 and 14 provide a radial electrostatic field which varies in intensity directly with the radius. The radial electrostatic field is provided, in this illustrative embodiment, by a plurality of concentric ring electrodes l6a-16n which are secured to a dielectric plate 18 for the planar means 12 and complementary concentric electrode rings 20a-20n which are secured to a dielectric plate 22. Electrode rings 20a-20n are represented in FIG. 1 by the phantom line 20. Each of the respective electrode rings 16 and 20 are embedded in the

plates

18 and 22 so that a portion of each ring extends below the dielectric surface. This prevents the attachment of stray ions to the surface of the dielectric material.

An ion source 26 is secured to an entrance slit member 24. The ion source 26 is connected via lead 25 to a suitable power supply 23 (FIG. 4). The slit member 24 and ion source 26 are mounted so as to be electrically and magnetically shielded from the analyzer 10 and so positioned at the radius R, corresponding to

electrode rings

16d and 20d in the illustrative embodiment, that an ion entrance slit or aperture 28 is positioned at R The entrance slit member 24 is mounted so that the entrance slit 28 is in a plane parallel to the magnetic field created in the analyzer 10. The magnetic field may be generated by any suitable means such as

magnet pole members

30 and 32. Hence, ions produced in the source 26 enter the analyzer flow space through the slit 28 transverse to the magnetic field. The ions are illustrated in ribbon-like form as 34.

The ions 34 traverse in the flow space from the entrance slit 28 through a resolving slit 54 to an exit slit or aperture 36 in a defined path to be described herebelow. The exit slit 36 is also positioned by exit slit member 38 at R The ions 34 pass through the exit slit to a suitable ion collector 40 such as an ion-electron multiplier. The signal generated by the collector 40 may be fed through lead 41 to an amplifier and detector 43 (FIG. 4). The signal may be further transmitted to a strip line recorder (not shown) to provide a chart of the analysis.

The electrostatic field created in the flow space between the concentric rings 16 and 20 is radial in direction and varies in intensity directly with the radius of each ring from the center. This may be seen in the diagrammatic illustration of FIG. 4 wherein for purposes of illustration some of the electrode rings have been eliminated. FIG. 4 represents the planar means 14, i.e., the electrode rings 20, and it should be understood that the following description applies as well to planar means 12. Each concentric ring electrode is resistively connected to the next by a resistor 42. A source of power 44 provides the electrical energy to the respective electrode rings via resistors 42. Suitable controls 46 are connected by lead 48 to the power supply 44 to enable an operator to change the electrostatic field created so as to permit ion scan analysis. The magnetic field created between magnets 30 (shown by phantom line) and 32 is designated as B in FIG. 4 and is seen to be perpendicular to the plane of the electrode rings. Scan control 46 may be connected by a lead 47 to the magnetic

field forming poles

30 and 32 such that the magnetic field may be varied.

Electrode ring 20d. corresponding to R is maintained at a zero potential or ground. The electrode ring 20a is maintained at a higher positive potential than rings 20b and 200. The potential of the respective concentric rings 20e-20n becomes increasingly negative towards the analyzer center is relative to R while the energy gradient between each ring decreases in intensity towards the center. Hence, as ions having a positive charge are injected into the analyzer 10 at R from the ion source 26, the velocity of the ions will increase from R, towards the center but the acceleration or rate of change of the ion velocity will decrease. Hence, the uniform magnetic field created by

magnets

30 and 32 will have a greater effect on the positively charged ions as the radius from center decreases because of the decreased rate of change of the ion velocity as compared to a unifonn rate of change.

The path of the ions generated in the analyzer I0 is represented by the ribbon 34 and is similar in nature to a trochoid but the mathematical formula for the derivation of path 34 is different from the true trochoid. As the ions 34 exit from the slit 28, the velocity or speed of the ions increases toward the center until the rate of change of velocity decreases sufficiently so that the efiect of the magnetic field can cause the ion to turn or curve away from the center and outwardly towards the periphery of the analyzer. The rate of change of the ion velocity decreases as the ions continue towards the

rings

16a and 20a until the increasing positive where mr mrd =1",-

m mass of the ion r radial displacement F radial velocity F radial acceleration a t =angular velocity angular acceleration a force in the 0 direction F r force in the radial direction For a radial electric field crossed by a normal magnetic field, force in the 0 direction is obtainable from the Lorentz equation, which is:

F Q (E v X B) and F 9 becomes {QBF. Then equation 1 becomes -21L i EL F force Q particle charge E electric field strength v velocity of particle B magnetic field strength Force in the radial direction from the Lorentz equation is F, :QE iota/0 where and equation (2) becomes Note that although the sign of the terms containing QB is arbitrary, they mu st be opposite for the two equations (thus :QB? and iQBrO).

Utilizing the above equation, it was found that double focusing was not obtainable. Therefore, modifications to the electric and magnetic field were investigated to bring about double focusing. It was discovered that double focusing was found to occur when the electric field varied directly with the radius vector. Therefore, equation (4) remains the same but equation (6) becomes: 0 a

The applicable differential equations of motion for use in the charged particle analyzer of this invention are then (l 0) r02] 2 I z ten It can also be seen that 6 is a periodic function whose angular period is given by u r 0) E l 4 The angular period )t is independent of the initial conditions of r F 6,, and 0;. Therefore, a particle of mass m crossing the position of r and 0,, with velocities F and 0,, will again cross r at an angular displacement of 6;: n A, with velocity in and 0,. This is the condition necessary for double focusing. Particles of mass greater than m have greater A while those of mass less than in have smaller A Note the term m/e or m/Q often appears in mass spectrometry and, in fact, mass spectrometers actually separate particles by their m/Q ratio. Throughout this application 1 am assuming the ions to be singly charged for convenience and clarity. However, the equations properly account for multiply charged ions. Where Q actually means nq, q is the elemental quantity 1.60210 X 10" coulombs and n is any integer.

The parameters of a charged particle analyzer may mathematically be obtained by numerical integration of equations (8) and (9) or directly from equations l0) and l l As an example, realistic parameters were assigned to the constant terms of equations (8) and (9) as follows:

m= 1.66043 X 10' Kg= AMU Q= 1.60210 X 10 coulombs B= 3.00000 X 10 webers/meter E, 4.20879 X 10" volts/meter 33.67 volts/centimeter at R 0.08000 meters 8 centimeters The resulting calculations define an instrument 20 centimeters in diameter with double focusing at r= R 8.00000 centimeters and 0 n X 1.30900 radians. The resolution obtained is 473.4 per cycle ofn as follows:

)t,,,= 101 1.315012 radians A, 100 1.309000 radians 0.006012 radians beam separation in radians Then 0.006012 X 0.08 000048096 meters 0.48096 mm which is the beam separation along r,, and 0.48096 mm x 39.3700 X 10" inches/mm 18.93540 X 10* inches. With slit widths of 2 X 10 inches, the beam width is 4 X 10' inches and resolution is defined as x Beamwidth Mass Units Resolution Then (18.93540 X 10 /4 X 10') X 100 473.385 For ionelectron multiplier detection this particular configuration will allow an n as high as 22; thus, a resolution of 22 X 473.4 or approximately 10400 could be achieved with 2-mil slits. One-mil slits would result in the resolution exceeding 20,000 mathematically.

The path between entrance slit 28 and double focusing point 50 is considered as one loop or orbit of the ion beam 34 and is mathematically defined by the simultaneous solutions of equations (8) and (9). The ion beam 34 will continue to progress in identical loops or orbits about the flow space of analyzer 10 wherein double focusing occurs at R for each loop or orbit. The ion beam 34 will continue individual orbits around the analyzer 10 and if unimpeded will continue making identical loops or orbits about the analyzer 10 to uniformly progress thereabout until the ions enter an ion receiver means, such as an ion-electron multiplier 40. The signal generated by electron multiplier 40 is representative of the number of particles in the ion beam which have the mass for which the analyzer is adjusted.

A resolving member or baffle 52 having a slit or aperture 54 formed therein is mounted in analyzer 10 on R The resolving slit 54 is placed at a double focus point so that only ions of the desired mass pass therethrough. The location of the resolving slit 54 depends on the number of loops or orbits desired and the size of the loops. The exit aperture 36 follows the resolving slit 54 by a predetermined distance, such as the distance at which ion beam 34 passes R in the outward direction.

The collector has been illustratively described as of the ionelectron multiplier type. Other type collectors may be used. As, an example, the Faraday Cup detector is commonly used in mass spectrometers when there is sufiicient beam intensity. The Faraday Cup detector is simpler but less sensitive than an ion-electron multiplier. Referring to FIG. 4, a Faraday Cup detector 56 is mounted in analyzer 10 and is shown as a dashed line. The Faraday Cup detector 56 would collect the ions after they pass through the resolving slit 54. In this embodiment then, the ion-electron multiplier 40 would not be used and the Faraday Cup detector 56 would be connected with appropriate circuitry to provide the desired analysis signal.

Suitable baffles, known in the art, may be placed in the flow space of analyzer 10 to prohibit the passage of unwanted ions. The baffles may be placed within the first two quadrants of the analyzer 10 to effectively eliminate the passage of all ions except the particular mass which it is desired to analyze.

Referring now to FIG. 5, there is shown a polar coordinate drawing of the paths or orbits generated by ions of the same mass but having different input parameters. For purposes of clarity, the entrance member 24 and aperture 28; resolving member 52 and aperture 54; and exit member 38 and aperture 36 have been superimposed on the polar drawing at R,,. The path designated 58 represents ions having an initial direction 20 off normal incidence and having 57eV. The path designated 60 represents ions having a normal incidence and l04eV. The path represented by 62 represents ions having a normal incidence and 52eV. lt is seen that the path ofeach ion orbit returns to double focus on R, at 64.

If it is assumed that the entrance slit 28 of an ion source is positioned on R at 0 and using the example hereinbefore set forth, it is seen that double focusing occurs at 0=n 1.30900 radians or approximately 75. Thus, it is noted that double focusing for loops or orbits l, 2, 3 and 4 occurs respectively at R at approximately 75, 150, 225 and 300. These points of double focusing are respectively shown at 64, 66, 68 and 70. The double focus at 300 would represent the completion of four orbits. The completion of the fifth orbit would make the double focusing occur at approximately 15 which is designated 72. It is seen that the orbits and double focusing position progress approximately 15 with each complete revolution about the analyzer of the orbits. The points on R represented by 74, 76, 78, 80 and 82 indicate points of double focusing for l0, 15, 20, 21 and 22 orbits, respectively. The exit aperture 36 is placed on R, at 84 which is advanced from double focusing point 82. Hence, all ions would exit through the aperture 36 into a suitable ion receiver or electron multiplier. In the illustrated example, it was noted that the resolution at one orbit, utilizing the parameters given, was 473.4. The resolution which has been obtained by utilizing the exit aperture at 84 which has pennitted 22 orbits has been raised from 473.4 to approximately 10,400 without any physical change in the parameters of the analyzer l0, i.e., size ofinstrument, entrance slit width, etc. There has been no sacrifice in weight or size in order to obtain increased resolution. To provide an even higher resolution, it is only necessary to adjust the exit aperture to permit additional orbits of the ion paths or to adjust the electrostatic field, i.e., changing the potentials on the concentric rings such that the angle 0 is decreased.

In order to scan a spectrum of masses, one would select a desirable angular displacement A between entrance and successive double focusing points and adjust E or B to bring the desired mass to double focus at this angular displacement. The particles of the mass selected may be detected immediately inside the resolving slit or they may be allowed to continue their trajectory until they are again directed outward where they may be withdrawn for detection.

A selected mass range may be scanned by changing the voltage applied to the flight cylinder inversely with the mass. For example, to observe l0 AMU, E, becomes l0 X 4.20879 X volts/meter or 336.7 volts per centimeter at r,,. Obviously, this becomes a problem if one wishes to observe mass 1, for E then becomes 3367 volts per centimeter at r,,. The alternative method is to scan magnetically or with a combination of magnetic and electric change. For example, this instrument may be scanned magnetically from AMU l to AMU 300 by varying the magnetic field from 300.000 gauss to 5 l96. l5

gauss, leaving the electric field constant at 33.67 volts per centimeter at r,,.

Another exemplary embodiment of this invention is illustrated in FIGS. 6-9 of the drawings which illustrate another fonn of the planar electrode means. While this embodiment only describes one planar electrode means, it is understood that two electrode means are utilized. Referring particularly to FIGS. 6 and 7, it is seen that the dielectric member 86 is circular in shape and is made from a ceramic or other similar material having like electrical qualities. The disk 86 is preferably glazed so as to prevent gas adsorption. Electrode rings 88a-88k are placed on one side of the ceramic disk 86 and are a conductive film such as palladium or a compatible substitute. The disk 86 and rings 88 are then heated to bond the rings to the disk.

It can be seen that the resulting surface of the planar electrode means, i.e., disk 86 and rings 88, is substantially flat. The charged particles traversing between the two disks would have a tendency to adhere to the dielectric surfaces between the cr .uctive rings 88. This problem is eliminated by the applic' .ion of a resistive coating 89 (FIG. 10) being applied over the entire surface of the disk 86 and conductive rings 88. The overall coat of resistive film 89 is approximately 10 megohms per square and serves to render the ceramic surface of disk 86 conductive to ions which may strike it and thus prevents a charge buildup on the disk. The coating ends at groove 98. The resistive coating may be applied by any known process such as vacuum deposition, spraying a tin chloride solution to the surface and then heating the structure or by the application of a resistive ink, paint, or spray to the disk 86 and rings 88. The structure is then fired so that the resistive ink bonds to the entire exposed surface.

A groove 90 corresponding to the double focusing radius R, is formed between

rings

88e and 88f. Slot or

apertures

92 and 94 are formed in the disk 86 at R and are positioned along groove 90. The

apertures

92 and 94 are used to respectively position the entrance and exit slit members (not shown in this embodiment).

Referring to FIG. 8, a plurality of apertures 96 extends from the bottom of the disk 86 to the groove 90. The apertures 96 permit means, such as screws, to be inserted therethrough so as to hold a solid ring or baffle (not shown) in place at R The purpose of the baffle has previously been described.

A groove 98 is formed in the disk 86 at a radius greater than that of conductive ring 880. A plurality of apertures 100 extends from the bottom of the disk 86 and terminates in groove 98. Suitable means, such as screws or the like, extend through apertures 100 to secure a screen arrangement, not shown, within groove 98. A plurality of apertures 102 are formed around the periphery of the disk 86. Suitable means, now shown, extend through apertures 102 and serve to support the two planar electrode means in parallel positions and suitable spacers are placed on the support means to keep the two planar electrode disks separated. The spacers and support means are maintained at ground potential. Accordingly, the screen which is supported in groove 98 is maintained at a higher positive potential than the potential of conducting ring 88a to prevent any disruption of the electric field because of the effects of the spacers which are held at ground potential.

As previously described, the conducting rings 88 are connected to a suitable power supply so that the electrical field varies in intensity with the radius of each ring. To make such connection, a plurality of radial grooves or slots l04a-l04k are formed in the bottom surface of the disk 86. The radial slots permit lead lines from the power supply to be inserted therein so as to make connection with the conductive rings. Each slot 104 terminates in an aperture l06a-l06k which extends from the slot through the disk 86 to the conductive ring 88. It should be noted that each slot and aperture designated with a letter designation cooperates with the conductive ring having a like letter designation. Radial slots 108 and 110 permit the power supply connection with the bafile and screen respectively supported in

grooves

90 and 98.

Referring to H6. 9, it is seen that a conducting pin 112, such as a copper pin, is placed in each slot terminating aperture 106. The pin 112 completes the circuit between each respective conducting ring 88, baffle and screen, with the respective lead line from the power supply.

By using the construction of the embodiment described in FIGS. 6-9, the resulting electric field more closely varies with the radius at every point within the flow path. In addition, the thickness of each planar electrode means is decreased which reduces the required magnetic gap which makes the required magnetic field easier to obtain. it should be noted that the use of the concentric conductive film rings placed on the surface of the ceramic disk is the preferred form. However, other means might be utilized in order to obtain a substantially flat surface. One such example would be to embed the conductive rings of FIGS. l-3 in the dielectric material so that their upper surface is flush with the surface of the dielectric material. A resistive coating would then also be applied to the entire sur' face.

It can be seen that this invention provides a charged particle analyzer which is capable of adaptation to precision laboratory work, air pollution analysis, medical breath analysis, undersea laboratory analysis, and space vehicle instrumentation. An analyzer employing a typical 12-inch magnet capable of 10,000 gauss or more would be capable of exceeding a resolution of 20,000, while a flight model employing a 4-inch permanent magnet would be capable of exceeding a resolution of 2,000.

This invention provides distinct advantages over the previously known conventional perfect double focusing trochoid mass spectrometers. The input energy of the particles to be analyzed can be considerably higher for the analyzer of this invention than a conventional trochoid instrument having the same instrument parameter, thus decreasing ion beam spread in the axis of the magnetic field. In addition, many ion loops or orbits can be obtained over the same trajectory area, thus mul tiplying the resolution tremendously.

This invention is readily adaptable to allow air pollution analysis since one of the major problems in this field is the separation of CO and N which differs in mass by only a few hundredths atomic mass unit. This invention can be easily miniaturized for space flight or undersea instrumentation and retain higher resolution than any other known instrument. Thus, it is seen that the objects of this invention hereinbefore set forth have been accomplished.

While a present exemplary embodiment of this invention has been illustrated and described, it will be recognized that this invention may be otherwise variously embodied and practiced by those skilled in the art.

What is claimed is: 1. Apparatus for analyzing charged particles with respect to their specific mass comprising: first planar electrode means; second planar electrode means parallel to said first planar electrode means, each electrode means being formed to present alternate conductive and non-conductive sections radially outward from the center, said first and second electrode means defining an annular space therebetween;

supply means connected to said first and second planar electrode means to provide a high positive potential at the peripheral conductive section and the potential of the remaining conductive sections becomes respectively increasingly negative towards the central axis wherein the electrical field is radial and varies in intensity directly with the radius within said space;

means providing a magnetic field within said space normal to the electric field;

means for projecting a sample of charged particles into said space at a radial distance R from the axis, the radial distance R being the radial distance at which ion focusing occurs wherein said charged particles are acted on by said electric and magnetic fields whereby particles of the same mass are caused to focus irrespective of the initial input conditions; and

receiver means spaced a distance from said projecting means along the radial distance R for receiving particles of a given mass.

2. Apparatus as set forth in claim 1 in which said first and second planar electrode means each comprises a plurality of concentric electrode members wherein the potential of the peripheral member is maintained at a high positive potential, the member at the radial distance R is a reference potential and the potential of the members from the R member to the innermost member become increasingly negative.

3. Apparatus as set forth in claim 2 in which said plurality of concentric electrode members comprises conducting rings embedded in a dielectric base.

4. Apparatus as set forth in claim 1 in which said first and second planar electrode means each comprises a dielectric base and a plurality of concentric conducting rings secured to said dielectric base and further comprising means for connecting each of said rings with a source of power wherein the electrical potential becomes increasingly negative towards the analyzer center while the energy gradient between each respective ring decreases in intensity towards the center.

5. Apparatus as set forth in claim 4 in which each of said conducting rings is an annular electrode ring embedded in said dielectric base.

6. Apparatus as set forth in claim 4 in which each of said conducting rings is a conductive film bonded to the surface of said dielectric base.

7. Apparatus as set forth in claim 4 in which said dielectric base is formed with a plurality of apertures, each aperture extending from the side opposite the conducting ring side through said dielectric base to each conducting ring; and in which said connecting means comprises a conducting pin inserted in said apertures to make contact with said conducting ring and connect said ring with a lead from a power supply.

8. Apparatus as set forth in claim 7 further comprising a plurality of radially extending grooves formed in said dielectric base, each of said grooves terminating at one of said apertures wherein the respective leads from a power supply is placed in said groove so as to make contact with said conducting pin.

9. Apparatus for analyzing charged particles with respect to their specific mass comprising:

an ion source;

an ion receiver;

a beam of ions traversing a periodic path therebetween;

means providing a uniform magnetic field normal to the path of the ion beam; and

means including a pair of planar electrodes on either side of said ion beam path, each comprising a plurality of annular electrodes of increasing radius for establishing a radial electric field varying in intensity directly with the radius and acting normal to the magnetic field for focusing ions emitted from said ion source at said ion receiver, said ion source and said ion receiver being mounted between said planar electrodes at a radial distance from the central axis at which ion focusing occurs.

10. Apparatus as set forth in claim 9 in which said means for providing a radial electric field comprises a first plurality of concentric electrode rings; a second plurality of concentric electrode rings complementary with said first plurality of electrode rings and mounted parallel thereto; and further comprising supply means for applying a potential to said electrodes whereby the potential of each ring becomes increasingly negative towards the analyzer center while the energy gradient between each respective concentric ring decreases in intensity towards the center.

11. Apparatus as set forth in claim 10 further comprising control means connected to said supply means to vary the electrical potential wherein the electric field between said first and second electrode rings can be changed to permit ion scan analysis.

12. Apparatus as set forth in claim 10 further comprising means to vary the intensity of the magnetic field to permit ion scan analysis.

13. Apparatus as set forth in claim 9 in which said ion receiver is an ion-electron multiplier.

14. Apparatus as set forth in claim 9 in which said ion receiver is a Faraday Cup detector 15. Apparatus as set forth in claim 9 in which said means for providing a radial electric field is first and second planar electrode means, each electrode means comprising a dielectric base and a plurality of concentric conducting rings secured to said dielectric base and further comprising means for connecting each of said rings with a source of power wherein the electrical potential becomes increasingly negative towards the analyzer center while the energy gradient between each respective ring decreases in intensity towards the center 16. Apparatus as set forth in claim in which each of said conducting rings is a concentric electrode ring embedded in said dielectric base.

17. Apparatus as set forth in claim 15 in which each of said conducting rings is a conductive film bonded to the surface of 12 said dielectric base.

18. Apparatus as set forth in claim 9 in which said planar electrodes further comprise a plurality of concentric conducting rings secured to a dielectric base and further comprising a source of supply means connected to said conducting rings to provide a high positive potential at the peripheral ring and an increasingly negative potential to each respective conducting ring towards the central axis wherein the periodic path of the ion beam simultaneously acted on by the radial electric field and the uniform magnetic field is mathematically defined by the simultaneous solution of equations and UNITED sTATEs PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,670 J Dated June 13, 1972 Robert E. Elmore Inventor(s) It is certified that error appears in the above-identified patent and that said Letters'Patent are hereby corrected as shown below:

In the grant (only) insert the attached sheet.

Signed and sealed this TZ 'Oth dayof February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 6037 6-1 69 FORM P0-1050 (10-69) a 0.5. covzmmzm manna omcs Ins o-ass-:m.

3 670,162" June 13,1972

SCAN

CONTROLS 5g -48 POWER SUPPLY --1 SOURCE ELL-21% 40 INVENTOR. 23m ROBERT E. ELMORE POWER g-g3 ER WWW A SUPPLY 25 5 DETECTOR f TTORNEYS.

Claims

1. Apparatus for analyzing charged particles with respect to their specific mass comprising: first planar electrode means; second planar electrode means parallel to said first planar electrode means, each electrode means being formed to present alternate conductive and non-conductive sections radially outward from the center, said first and second electrode means defining an annular space therebetween; supply means connected to said first and second planar electrode means to provide a high positive potential at the peripheral conductive section and the potential of the remaining conductive sections becomes respectively increasingly negative towards the central axis wherein the electrical field is radial and varies in intensity directly with the radius within said space; means providing a magnetic field within said space normal to the electric field; means for projecting a sample of charged particles into said space at a radial distance Ro from the axis, the radial distance Ro being the radial distance at which ion focusing occurs wherein said charged particles are acted on by said electric and magnetic fields whereby particles of the same mass are caused to focus irrespective of the initial input conditions; and receiver means spaced a distance from said projecting means along the radial distance Ro for receiving particles of a given mass.

2. Apparatus as set forth in claim 1 in which said first and second planar electrode means each comprises a plurality of concentric electrode members wherein the potential of the peripheral member is maintained at a high positive potential, the member at the radial distance R0 is a reference potential and the potential of the members from the R0 member to the innermost member become increasingly negative.

9. Apparatus for analyzing charged particles with respect to their specific mass comprising: an ion source; an ion receiver; a beam of ions traversing a periodic path therebetween; means providing a uniform magnetic field normal to the path of the ion beam; and means including a pair of planar electrodes on either side of said ion beam path, each comprising a plurality of annular electrodes of increasing radius for establishing a radial electric field varying in intensity directly with the radius and acting normal to the magnetic field for focusing ions emitted from said ion source at said ion receiver, said ion source and said ion receiver being mounted between said planar electrodes at a radial distance from the central axis at which ion focusing occurs.

14. Apparatus as set forth in claim 9 in which said ion receiver is a Faraday Cup detector.

15. Apparatus as set forth in claim 9 in which said means for providing a radial electric field is first and second planar electrode means, each electrode means comprising a dielectric base and a plurality of concentric conducting rings secured to said dielectric base and further comprising means for connecting each of said rings with a source of power wherein the electrical potential becomes increasingly negative towards the analyzer center while the energy gradient between each respective ring decreases in intensity towards the center.

16. Apparatus as set forth in claim 15 in which each of said conducting rings is a concentric electrode ring embedded in said dielectric base.

17. Apparatus as set forth in claim 15 in which each of said conducting rings is a conductive film bonded to the surface of said dielectric base.

18. Apparatus as set forth in claim 9 in which said planar electrodes further comprise a plurality of concentric conducting rings secured to a dielectric base and further comprising a source of supply means connected to said conducting rings to provide a high positive potential at the peripheral ring and an increasingly negative potential to each respeCtive conducting ring towards the central axis wherein the periodic path of the ion beam simultaneously acted on by the radial electric field and the uniform magnetic field is mathematically defined by the simultaneous solution of equations mr theta -2mr theta + or - QBr and mr mr theta 2 -QEor + or - QBr theta .