US3174084A

US3174084A - Electron beam delection system

Info

Publication number: US3174084A
Application number: US248072A
Authority: US
Inventors: Willem F Westendorp; Tamor Stephen
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1962-12-28
Filing date: 1962-12-28
Publication date: 1965-03-16
Anticipated expiration: 1982-03-16

Description

March 16, 1965 w. F. WESTENDORP ETAL 3,174,034

ELECTRON BEAM DEFLECTION SYSTEM Filed Dec. 28, 1962 //7 van/0m:

W/Y/em F Wes/endow,-

Sfep/ven Tamar,

5 by PDW United States Patent Ofifiee 3,174,084 Patented Mar. 16, 1965 3,174,084 ELECTRON BEAM DEFLECTION SYSTEM Willem F. Westendorp and Stephen Tamor, Schenectady,

N.Y., assignors to General Electric Company, a corporation of New York Filed Dec. 23, 1962, Ser. No. 248,072 11 Claims. (Cl. 317-20i3) The present invention relates to improved means for deflecting the electron beam in electron beam apparatus such as a cathode ray tube.

Cathode ray apparatus is utilized for irradiating mate rials with a beam of high energy electrons. Usually the material to be irradiated is placed on a moving belt that passes under the window of the cathode ray apparatus from which the electron beam emerges. A deflection system in the cathode ray apparatus usually deflects the electron beam laterally in a direction normal to the direction of movement of the belt so that the electron beam irradiates the total surface area of the material in a line by line manner.

Cathode ray apparatus usually is provided with a vac uum tight envelope including a neck portion for enclosing the electron gun and accelerating electrode, and an extension thereof of triangular longitudinal cross-section which provides a drift region in which the electron beam is an-gularly deflected. The lineal width of material the beam can reach is limited by the size of the extension, and by the angular deflection the beam can achieve while still effectively reaching the material. A conventional method of extending the deflection is to increase the length of the drift region extension. However, cathode ray apparatus is already undesirably long. For example, for a width of deflection of 38 inches, cathode ray apparatus with a conventional deflection system would have a vacuum extension chamber approximately feet long.

Accordingly, an object of the present invent-ion is to provide cathode ray apparatus having a wide deflection but a short vacuum extension chamber.

A further object is to provide a deflection system for an electron beam apparatus that produces a wide deflection of an electron beam in a short drift region.

It is a disadvantage of utilizing conventional approaches to extending the width of deflection of an electron beam that the angle at which the beam strikes the irradiated material varies along the width of the material as the beam is angularly deflected. Consequently, the irradiation is not uniform along the width of material.

Hence, another object of the present invention is to provide cathode ray apparatus for irradiating material substantially uniformly across the width of the material.

A further object of the present invention is to provide a wide deflection of the beam in electron beam apparatus in which the angle of incidence for the electron beam is substantially constant for all angles of deflection.

These and other objects are achieved in one embodiment of our invention by utilization in an electron beam deflection system of two magnetic fields, one of which produces the lateral deflection scan of the electron beam and the other directing the electron beam approximately normally to the target or the material irradiated, regardless of the angle of initial deflection of the electron beam.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof all may best be understood by reference to the following description, taken in connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional side view, partially broken away, of a vacuum chamber of cathode ray apparatus including an embodiment of a deflection system of our invention; and

PEG. 2 is a cross-sectional side view of FIG. 1.

Referring now to FIGS. 1 and 2, there is illustrated the portion 19 of the neck of the envelope of a cathode ray tube along which a beam of electrons 12 is formed and accelerated by any suitable means (not shown) such as an electron gun and accelerating electrodes. Since suitable means for generating and accelerating electron beams are well known, and the particular means employed are not pertinent to the present invention, the means for gen. erating and accelerating electron beam 12 have been omitted from the drawings for simplification.

Electron beam 12 passes into a vacuum extension chamber 14, and through it along any one of an infinite number of paths A, B, C, D, etc., the particular path depending upon magnetic deflection fields therein which are to be subsequently described. Most of the electrons in beam 12 pass through a thin window 16 of light material such as beryllium which is impermeable to air so that the vacuum in chamber 14 is maintained. After passing through window 16 beam 12 strikes material 13. Material 18 may be moved in a direction normal to the present apparatus, e.g., out of the drawing, on a moving belt 20 so that as beam 12 is deflected back and forth across the width of chamber 14, it strikes the whole area of the surface of material 18 in a line-by-line manner.

As beam 12 leaves neck 1d and enters chamber 14- it is deflected by an alternating current magnetic field from circular radially laminated pole pieces 22 energized by a magnetic circuit and windings 24 coupled to an AC. current source 26. The deflection current from source 26 may be a sine wave or a linear wave arranged to cause linear deflection of the electron beam across material 18. The magnetic field across pole pieces 22 is preferably constant for a given instantaneous value of current. The angle of deflection of the electron beam as the electron beam passes between the circular pole pieces is equal to an angle 6 where tan 2 is equal to where a=-radius of the pole pieces and R=r=adius of curvature of the electron path in the magnetic field produced between the pole pieces. Since for given electron energy, the radius R is inversely proportional to the magnetic flux density B, and B is proportional to the magnetizing current i, from the source 26, we may write tan =bi where b is a constant.

According to the invention, it is now desired to redirect this angular deflection of the electron beam so that electron beam for any angle 6 meets window 16 substantially perpendicular to the window. It is also in general quite (a desirable to have a simple relationship between linear deflection, A, along the output window as measured, e.g., from the central axis of the system, and the current i which causes the first deflection at pole pieces 22. Then a given deflection current applied to coils 24 will cause a controllable linear deflection A. In the embodiment of FIGS. 1 and 2, the linear deflection, A, is arranged to be directly proportional to the current i, whereby constant velocity electron beam scanning corresponds to linear change of current with time. In the principal embodiment of FIGS. 1 and 2, there is accordingly provided second pairs of deflection pole pieces 23-30 and 32-34. The electron beam passes between the members of one pair or the other depending upon the deflection already imparted to the beam by pole pieces 22. Pole pieces 28- 30 or 32-34 act in the same manner as pole pieces 22 and produce another angular deflection of the electron beam. However, the pole pieces 28-30 and 32-34 are shaped to cause angular deflection of the electron beam substantially the reverse of that originally imparted thereto by means of pole pieces 22. The new deflection takes place along an arcuate path, desirably at a constant turning radius or radius of curvature, as the electron beam passes between a pair of pole pieces. The arcuate extent or width of the pole pieces along the electron beam path is preferably just sufficient for redirecting the electron beam perpendicularly of the window, at a constant beam turning radius, for any initial electron beam path between =90 and 0=-90.

In order for each path to have a constant radius, it is preferred to magnetize the pole pieces 28-30 and 32-34 with a steady magnetic field provided by means of a magnetic circuit 36 and magnetizing coils 38 energized with direct current. This provides a radius of curvature, p, which is constant for the electron beam passing between a set of pole pieces. For convenience the radius of curvature p is made equal to half A where A, is the maximum lateral deflection at path G. A is the linear deflection that corresponds to a maximum deflection current, i in deflection coils 24, and in which case 0:9 the maximum feasible initial angular deflection. In the embodiment shown the

pole pieces

30 and 32 are north poles in the magnetic circuit, and

pole pieces

38 and 34 are south poles.

The pole piece pairs are situated such that, in addition to causing the change in angular deflection of the electron beam in the reverse sense to that caused by pole pieces 22, the pole piece pairs also establish the desired linear relation between the deflection current from source 26 and the lateral deflection A at the output window. These relations can be set up in the following manner: As previously stated,

0 a tan For convenience, the above ratio As previously mentioned, A takes place at maximum deflection current in coil 24- and when 6:90".

In order to determine the extent of the pole piece pairs, radial lines may first be drawn from the center of round pole pieces 22, for example, a line 40 in PEG. 1 at a given A=A tan 3 developed above. This value A is marked by a vertical line, e.g., line 42 in FIG. 1, corresponding to electron beam path F. The lines 4% and 42 are then joined with a circular electron beam arc of radius ,0, which, as above indicated, is conveniently chosen to equal half A The arcuate extent or Width dimension of the

pole pieces

30 and 34 for electron path P are established in this manner. The pole pieces extend along path P between a point 44 where the arcuate deflection must start and a point 46 where it should end in order for the beam to pass perpendicularly through the window. A similar construction may be made for other electron paths, i.e. paths A through G, to establish other points on the shape of the pole pieces.

Pole pieces

28 and 32 are reflections of

pole pieces

30 and 34, or their dimensions may be graphically determined in a similar manner.

It is seen the shape of the pole pieces is determined so the electron beam leaves the area of the pole pieces at the desired angle and at a desired distance, A, from the center of the system, for any initial deflection between and +90".

The shape of the pole piece pairs may also be calculated mathematically. It can be shown the bottom edge of each of the above described pole pieces forms a curve having the following formula:

2A... 2 2 Here the ordinate, Z, is measured vertically down from a horizontal line through the axis of the round pole pieces 22. The equation represents a parabola with the vertical axis of symmetry at A: /2A and an apex at Z=%A The curve of the upper edge of the pole piece pairs can best be expressed around the center of round pole pieces 22 at a radial distance r, where tan 2 sin 0 Various departures from the preferred embodiment are possible within the scope of the present invention. For example, although it is preferred the electron beams exit perpendicularly from window 16, it is appreciated the pole pieces can be oriented such that various electron beam paths all exit at some other common direction, or have some given spread relative to one another. Also, pole pieces 22 need not be round but can take other shapes, with pole pieces 28 to 34 acting to compensate such irregularities. Moreover, although it is usually convenient for the electron beam paths to exit in the same direction but spaced from the axis of entering beam 12, the electron beam 12 may enter at some other convenient angle. In such case, it is desirable to regard the electron beam paths exiting from window 16 as achieving a deflection relative to a selected axis, i.e., the axis of undeflected path A, rather than relative to the initial path of electron beam 12.

It is also appreciated the electron beam deflection may be made the function of some other electrical input parameter, e.g. voltage rather than deflection current. Furthermore, a non-uniform flux density may be provided along the pole piece pairs 28-30 and 32-34 with the shape of the pole pieces allowing for such non-uniformities as may occur with time or with deflection along the pole pieces.

Wide beam deflection is accomplished in accordance with the present invention and is produced within a comparatively short beam path length allowing the overall tube to be relatively short.

While we have shown and described several embodiments of our invention, it will be apparent tothose '5 skilled in the art that many other changes and modifications may be made without departing from our invention in its broader aspects; and we therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the Uni-ted States is:

1. A system for producing Wide deflection of an electron beam from an initial path relative to a selected axis comprising first means for periodically scanning said electron beam at an angle to said selected axis and magnetic deflection means for producing an arcuate direction change in said electron beam to a direction substantially parallel to said selected axis.

2. A system for producing wide deflection of an electron beam from an initial path relative to a selected axis comprising first means for periodically scanning said electron beam at angles to said selected axis in response to an electrical parameter and magnetic deflection means for producing an arcuate direction change in said electron beam to a second path substantially parallel to said selected axis, wherein the separation between said second path and said selected aXis is proportional to the said electrical parameter.

3. A system for producing wide deflection of an electron beam from an initial path comprising first magnetic means for periodically scanning said electron beam through a first changing angle in a first deflection direction and second magnetic means for deflecting said electron beam through the same angle in the reverse deflection direction to cause said beam to follow a second path substantially parallel to said initial path.

4. A system for producing wide deflection of an electron beam from an initial path comprising first magnetic means for continuously scanning said electron beam at a varying angle to said initial path in response to a continuously varying deflection current, a function of said angle being proportional to said deflection current, and second magnetic means for producing an arcuate direction change in said electron beam to a second path substantially parallel to said initial path, wherein the separation between said paths is also proportional to said function of said angle and therefore proportional to said current.

5. A system for producing deflection of an electron beam from an initial path comprising first means for deflecting said electron beam to continuously varying angles relative to a selected axis in response to varying deflection current, and magnetic means having magnetic pole pieces generating a constant D.C. field for producing an arcuate direction change of constant radius but varying arc length in each electron beam path to a final direction substantially parallel to said selected axis, said magnetic pole pieces having a face width adjacent the electron beam path proportioned to produce said arc length at a constant turning radius.

6. A system for producing deflection of an electron beam from an initial path comprising first means for scan ning said electron beam at a continuously varying angle relative to a selected axis in response to a changing deflection parameter, and magnetic means having magnetic pole pieces generating a constant D.C. field for producing an arcuate direction change of constant radius but varying arc length in the varying electron beam path to a final direction path substantially parallel to said selected axis, said magnetic pole pieces having a face width adjacent said electron beam path proportioned to produce said arc length, and said pole pieces being positioned to provide a deflection distance between initial and final electron beam paths proportional to said parameter.

7. A system for producing wide deflection of an elec tron beam from an initial path and relative to a selected axis comprising first means for deflecting said beam to a second path of varying angle in response to a changing deflection parameter, and second means for producing a direction change in said second path to a final path in a direction substantially parallel with said selected axis at a distance therefrom proportioned to said deflection parameter, each said arcuate direction change having an arc length and radius of curvature smoothly joining said second and said final paths.

8. A system for producing a wide deflection of an electron beam from an initial path comprising first means for directing said electron beam to a varying second path in response to a changing deflection parameter, and second magnetic deflection means for producing an arcuate direction change in said second path to a third path parallel to said selected axis, said arcuate direction change having an arc length and a common radius of curvature for smoothly joining said second and third paths.

9. A system for producing wide deflection of an electron beam from an initial path comprising first circular magnetic pole pieces disposed on either side of said electron beams initial path, a coil and a magnetic circuit for energizing said magnetic pole pieces in response to deflection; a varying current causing a magnetic field between said pole pieces varying with time and producing a first varying angular deflection of said electron beam as a function of said deflection current, second magnetic pole pieces disposed on either side of said electron beam as deflected for producing a steady magnetic field causing deflection of said electron beam in a reverse sense at a relatively constant radius of curvature between said second pole pieces, said second magnetic pole pieces being extended along electron beam paths to cause a change in direction thereof to a direction parallel to said selected axis at a distance therefrom in proportion to said deflection current.

10. A system for producing wide deflection of an electron beam from an initial path comprising first circular magnetic pole pieces disposed on either side of said electron beams initial path, a coil and magnetic circuit for energizing said magnetic pole pieces in response to an oscillatory deflection current causing a scanning magnetic field between said pole pieces and producing a first changing angular deflection of said electron beam as a function of said deflection current at deflection angles between zero for zero deflection current and for maximum deflection current, second magnetic pole pieces disposed on either side of said electron beam as initially eflected for producing a steady D.C. magnetic field causing a deflection of said electron beam in a reverse sense to its first deflection at a relatively constant radius of curvature, the extent of said second pole pieces relative to said electron beam at a first deflection of 90 establishing a maximum linear deflection of said electron beam to a path substantially parallel to said first path, and wherein said second pole pieces relative to said electron beam path have an extent along the beam for producing deflection of said electron beam to a final path parallel to said first path, the distance between said final path and said first path as divided by said maximum linear deflection equaling the ratio between the deflection current corresponding to said final path and the maximum deflection current.

11. A system for producing wide deflection of an electron beam from an initial path comprising first circular magnetic pole pieces disposed on either side of said electron beams initial path, a coil and magnetic circuit for energizing said magnetic pole pieces in response to alternating deflection current causing a substantially uniform magnetic field between said pole pieces at a given point in time and producing a first varying angular deflection of said electron beam as a function of said deflection current, where the tangent of half the angle of deflection equals bi, where i is the current in said deflection coil and b is a constant, said tangent also equaling aweoaa Where a is the radius of the circular pole pieces and R is the radius of curvature of the electron path in the field of the pole pieces, second magnetic pole pieces dispose on either side of said electron beam as first deflected for initial deflection angles between -90 and +90", said second magnetic pole pieces producing a steady DC. magnetic field for causing deflection of said electron beam in a reverse sense to the first deflection and at a relatively constant radius of curvature between said second pole pieces, the extent of said second pole pieces relative to said electron beam at a first deflection of 90 establishing a maximum linear deflection of said electron beam, A to a path perpendicular to said first path, wherein the said second pole pieces relative to said electron beam path have an extent for producing deflection first path wherein of said electron beam A to a final path parallel to said UNITED STATES PATENTS 2,897,365 7/59 Dewey et al 313-76 2,909,688 19/59 Archald 317-200 2,941,077 6/60 Marker 317-200 3,013,154 12/61 Trump 317-200 LARAMIE E. ASKTN, Primary Examiner.

FGHN F. BURNS, Examiner.

Claims

1. A SYSTEM FOR PRODUCING WIDE DEFLECTION OF AN ELECTRON BEAM FROM AN INITIAL PATH RELATIVE TO A SELECTED AXIS COMPRISING FIRST MEANS FOR PERIODICALLY SCANNING SAID ELECTRON BEAM AT AN ANGLE TO SAID SELECTED AXIS AND MAGNETIC DEFLECTION MEANS FOR PRODUCING AN ARCUATE DIRECTION CHANGE IN SAID SLECTRON BEAM TO A DIRECTION SUBSTANTIALLY PARALLEL TO SAID SELECTED AXIS.