US3430169A

US3430169A - Deflection yoke

Info

Publication number: US3430169A
Application number: US711830A
Authority: US
Inventors: William D Gabor
Original assignee: Sanders Associates Inc
Current assignee: Lockheed Corp
Priority date: 1965-10-23
Filing date: 1968-03-05
Publication date: 1969-02-25
Anticipated expiration: 1986-02-25
Also published as: DE1910855A1; NL6903408A; IL31691A0; NL153714B; GB1163548A; FR2034263A2; CH530712A; JPS4915645B1; NL6614729A; IL31691A; DE1564746A1; CH482292A; FR2034263B2; FR1501139A

Description

Feb. 25, 1969 w. D. GABOR ,4

DEFLECTION YOKE Filed March 5, 1968 Sheet of 6 FIG.I

DIRECTION OF MAGNETIC FIELD INVENTOR. WILLIAM D. GABOR ATTORNE Feb. 25, 1969 Sheet Filed March 5,,

Nd; x 9m UM M w o-Q A, WP o TOR.

BOR

1 WILLIAM D Feb. 25, 1969 w. o. GABOR 3,430,169.

' DEFLECTION 101m Filed March .5, 1968 Sheet 3 of e FIG.3

INVENTOR. WILLIAM D. GABOR ATTORNE BOR Feb. 25, 1969 WILLIAM D. GABOR ATTORNEY Feb. 25, 1969 9 'w. D. GABOR" 3,430,169

' DEFLEC'IION YOKE Filed March 5, 1968 Sheet. 5 or 6 IN VEN T00 WILLIAM 0. GA BOR ira/mar Feb. 25, 1969 w. o. GABOR 3,430,169

DEFLEC'I'ION YOKE Filed March 5, 1968 Sheet 6 of 6 IN VEN TOR WILLIAM D. G BOR A TTORNE Y United States Patent 3,430,169 DEFLECTION YOKE William D. Gabor, Amherst, N.H., assignor to Sanders Associates, Inc., Nashua, N.H., a corporation of Delaware Continuation-impart of application Ser. No. 503,070, Oct. 23, 1965. This application Mar. 5, 1968, Ser. No. 711,830 US. Cl. 335-213 30 Claims Int. Cl. H01f 1/00, 5/00; H013 29/76 ABSTRACT OF THE DISCLOSURE A magnetic deflection system for a cathode ray tube employs opposed pairs of single layer spiral windings whose forward ends flare to develop deflection fields which remain perpendicular to the electron beam as it is deflected in the tube. A conforming sleeve of high magnetic permeability material surrounds the windings to provide a high reluctance path for leakage fields in the system, but a low reluctance path for the deflection field developed thereby. The forward winding ends are distributed to yield a pincushion correction and the rear Winding ends are arranged to improve deflection linearity.

The application is a continuation-in-part of my copending application Ser. No. 503,070, filed Oct. 23, 1965, now abandoned.

The invention relates to an electromagnet whose construction and geometry achieve eflicient generation of a strong magnetic field and precise control over the shape of that field. It also relates to a cathode ray tube assembly incorporating the magnet as a beam deflection element. More particularly, the invention makes possible a magnetic deflection yoke of high performance and it will be described with specific reference to such a device.

A magnetic deflection yoke comprises a system of magnetic poles arranged on the neck of a cathode ray tube. The poles are used to controlledly bend the electron beam formed in the tube in one direction or another from its straight line path so that the beam strikes selected points on the tube face to provide visual indications thereon. By suitably varying the magnetic fields, the electron beam can be made to sweep up and down and back and forth across the face of the tube. Then, by simultaneously modulating the intensity of the beam, a visual presentation or picture can be formed on the face of the tube. A common use of this type of tube is in the conventional household television receiver.

Deflection yokes are usually in the form of generally saddle shaped windings arranged around the neck of the cathode ray tube. In a yoke capable of two-direction beam deflection, such as used on a television receiving tube, there are two pairs of windings. The windings of each pair are located on opposite sides of the tube neck, and the winding pairs are displaced 90 around the tube. When energized, the two pairs of windings produce orthogonal magnetic fields through the neck of the cathode ray tube. These fields are also perpendicular to the path of the undeflected electron beam generated in the tube. By appropriately varying the currents in the winding pairs, the direction and magnitude of the magnetic fields can be varied to deflect the electron beam to give the proper pattern on the tube face. Prior beam deflection yokes usually include also a jacket or sleeve of low reluctance material such as ferrite fitted snugly around the windings to help constrain the magnetic field and to increase the flux density through the neck of the tube.

Only the component of the magnetic field that is perpendicular to the electron beam contributes to beam de- 3,430,169 Patented Feb. 25, 1969 fiection. Therefore, the prior yokes whose fields are perpendicular to the undeflected beam can utilize a maximum amount of the available energy for beam deflection only so long as the beam is essentially undeflected. As the beam deviates from its straight line path, the field component that is perpendicular to the beam becomes smaller and the efiectiveness of the field decreases accordingly. At the same time the field component that is parallel to the deflected beam increases. This latter longitudinal component tends to shorten the focal length of the beam and cause defocusing of the spot on the tube face.

The defocusing effect is particularly prevalent at the two ends of the yoke. At those points, non-uniform fringe fields bow out from the ends of the yoke to provide substantial longitudinal field components unless steps are taken to prevent this.

The fringe field at the screen end of the yoke tends to produce fl LIX lines which intercept the electron beam at widely different angles depending upon the degree and direction of beam deflection. Accordingly, the amount of the available energy contributing to beam deflection varies substantially depending upon the degree of beam deflection. Even more importantly, as the electron beam bends to larger angles, the beam is defocused by different amounts. These effects are compounded by the fact that the beam has a finite cross section. Therefore, the degree of deflection and defocus of different parts of the beam is not the same. The net result is that the spot on the tube face is not only defocused as it moves out from the center of the screen but also the spot symmetry is altered from the desired round shape.

The fringe field at the gun end of the yoke also causes premature beam deflection, which in turn requires that the yoke be made shorter to prevent the beam from hitting the unflared neck of the tube. Moreover, the outwardly bowed fringe field may be intercepted by the metallic parts of the electron gun in the tube. Eddy currents thus induced in those parts by the high frequency magnetic field components cause distortion of the pattern on the tube face. This eddy current distortion is frequency dependent. It is especially troublesome in information display systems Where it is desired to trace patterns on the tube face at very high speeds.

Attempts have been made to overcome the aforementioned problems by the obvious expedient of moving the end or crossover segments of the windings which give rise to the fringe fields as far away as possible from the electron beam. Thus, the opposite ends of the windings have been flared cut, away from the neck of the cathode ray tube. Further, at the gun end of the yoke, a fringe ring of low reluctance material has been spaced from the end of the yoke to short circuit the remainder of the fringe field there.

While these steps have alleviated the problem somewhat, there have still remained appreciable fringe fields, particularly at the screen end of the yoke. More importantly, the steps taken to solve the fringe field problem have materially increased the overall inductance of the yoke without a concomitant increase in the usable magnetic flux. The fringe ring alone increases the inductance by almost 30% and the flaring out of the winding segments increases the overall inductance even further. Bearing in mind that the frequency response of the yoke is limited by its self-resonant frequency and that this in turn is inversely proportional to the product of its overall inductance and capacitance, resort to the aforementioned practices places a serious limitation on the frequency response of the yokes.

As a direct result of the redirecting and shunting of the fringe field, the efliciency of these prior yokes has suffered even more because a very substantial part of the magnetic energy in the magnetic field is not utilized for beam deflection. Field utilization efficiency of only 50% is quite common. This, coupled with the fact that the ferrite jacket gives rise to substantial hysteresis losses, results in an unduly large electric current requirement for maintenance of the proper deflecting fields.

Many of the prior systems are further disadvantaged because they require a separate device for correcting pincushion type distortion. This increases even moretheir cost and complexity. Still others are not accurate enough to be employed in applications requiring extremely precise deflection.

Accordingly, this invention aims to provide a magnetic deflection system having materially reduced energy re quirements.

A still further object of this invention is to provide a magnetic deflection system having a relatively high resonant frequency.

Another object of this invention is to provide an eflicient magnetic deflection system particularly suited as a yoke for a cathode ray tube capable of producing beam deflection of improved linearity.

Still another object of this invention is to provide an efficient magnetic deflection system particularly suited as a yoke for a cathode ray tube which minimizes defocusing out to larger deflection angles even with a flat tube face;

A further object of the invention is to provide a magnetic deflection system which dynamically corrects pincushion distortion without at the same time defocusing or otherwise distorting the electron beam.

Another object of the invention is to provide a magnetic deflection yoke characterized by low distortion, aberration and defocusing at the ends of the yoke even when the deflection windings are formed using printed circuit techniques.

Another object of the invention is to provide a magnetic deflection system which is relatively inexpensive to make.

A further object of the invention is to provide a cathode ray tube unit incorporating a deflection system having the above characteristics.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a magnetic deflection yoke embodying the principles of my invention;

FIG. 2 is an axial section of the magnetic deflection yoke shown in FIG. 1, showing its spatial relationship to a cathode ray tube on which it is mounted;

FIG. 3 is an axial section of one of the Winding forms shown in FIGS. 1 and 2;

FIG. 4 is a perspective view illustrating schematically the deflection windings and their connections;

FIG. 5 illustrates the horizontal field distribution near the front of the yoke;

FIG. 6 illustrates the horizontal field distribution near the middle of the yoke;

FIG. 7A illustrates a rectangular grid traced on a cathode ray tube undergoing pincushion distortion;

FIG. 7B is a schematic representation of a cathode ray tube employing a deflection yoke made in accordance with this invention;

FIG. 8 is a perspective view of a modified deflection section which effects very precise deflection and also corrects pincushion distortion; and

FIGS. 9A to 9D illustrate the operation of a deflection yoke employing deflection sections of the FIG. 8

yp l Generally, my improved low energy magnetic deflection yoke has materially reduced energy requirements because it uses a maximum amount of its magnetic field for beam deflection.

A low reluctance path in the form of a ferrite sleeve is provided around the outside of the windings to shape the magnetic fields and to increase the flux density through the cathode ray tube. Unconventionally, however, the sleeve is separated from the windings by an intervening space having a very high reluctance. This serves to materially reduce hysteresis losses in the yoke without appreciably reducing the efficiency thereof. It also effects a substantial reduction in the non-beam deflecting leakage field developed by the windings.

The sleeve itself is shaped to cooperate with the windings in shaping the magnetic fields especially at the ends of the yoke. Thus, at the forward or screen end of the yoke, it projects out beyond the forward ends of the deflection windings. Instead of attempting to eliminate the effects of the fringe field on the beam at the forward end of the yoke, as was the prior practice, I have flared the winding and sleeve to redistribute and shape this field, giving it a curvature that renders it generally perpendicular to the beam over the entire range of beam deflection. The formation and utilization of the fringe field at the forward end of the yoke greatly improves the chiciency of the yoke in that a maximum amount of the magnetic energy is utilized to deflect the electron beam.

In addition, the aforesaid shaping of the fringe field at the forward end of the yoke reduces defocusing to a minimum. At all beam deflection angles, the magnetic flux lines of the fringe field intercept the beam at substantially right angles. Thus the component of the flux which is parallel to the beam and causes defocusing is minimized.

At the rear or gun end of the yoke, the sleeve projects axially beyond the rear ends of the deflection windings, making the net flux there also perpendicular to the electron beam, which is always undeflected at that point. The total length of the field is shortened. Accordingly, there is less tendency for the beam to deflect prematurely. Finally, my improved deflection yoke has materially less built-in inductance and capacitance than prior comparable yokes. Consequently, it is faster and can operate at higher frequencies than those yokes.

Referring more specifically to FIG. 1 of the drawings, the yoke comprises a vertical beam deflection section indicated generally at 10 and a horizontal beam deflection section indicated generally at 12. Sections 10 and 12 are nested coaxially inside a jacket indicated generally at 14 comprising a high permeability material such as a ferrite. A terminal ring 18 is secured to jacket 14 to make electrical connections to the deflection sections 10 and 12. The assembled yoke is adapted to be slid over the end of a cathode ray tube and positioned on the neck of the tube (FIG. 2).

The vertical deflection section 10 comprises a bellshaped form 19 made of an insulating material such as transparent styrene, for example. As best seen in FIG. 3, form 19 has a generally cylindrical rear tube 20 integral with a forward flare 22 whose shape will be dealt with more particularly later. The outside surface of the flare 22 is recessed to form a circumferential band 24. The rear end of tube 20* is similarly recessed, forming a circumferential band 28.

Circumferential ribs

26 and 30 at the ends of the form 19 and a circumferential band 27 along the central portion thereof bound the recessed

bands

24 and 28.

Returning to FIG. 1, a pair of substantially identical, diametrically

opposed windings

34 and 36 are arranged around the outside of form 10 at opposite sides in a Helmholtz type coil arrangement. Each winding forms forms a rectangular spiral arranged lengthwise on and flat against the form 10. Thus, the winding 34, for example, has lengthwise segments 34a which are seated in successive pairs of slots 37 distributed around the tube 20 in a fashion to be described presently. Its front and rear end crossover segments 34b and 34c, respectively,

extend arcuately around the form in single layer fashion in the recessed

bands

24 and 28, respectively.

In the illustrated embodiment, each winding has eleven turns (FIG. 4).

Mathematically, the slots 37, and hence the winding segments 34a, are distributed with respect to the center of the Winding 34 in accordance with a sine function. In other words, proceeding out on each side from the longitudinal center line of the winding (corresponding to an angle of 0), the distance to each successive winding segment 34a corresponds approximately to a point on the sine curve. Proceeding from the center line, the successive segments 34a are spaced closer and closer together. The distribution of the longitudinal winding segments is described mathematically as follows:

. (2n-1) (n1)(d+k) where:

N is the number of turns in the winding d is the width of the conductor (the diameter of round wire) L is the length of the winding measured between the two endmost crossover segments and following the curvature of the winding k is the spacing between the conductors of adjacent crossover segments 6,, is the angular position of the nth longitudinal segment of the winding from the reference plane which is a plane passing through the center of the innermost winding loops and the longitudinal axis of the form 19 n is the longitudinal winding segment whose angular position is being calculated The second winding 36, which is arranged symmetrically in relation to the winding 34, has longitudinal segments 36a and crossover segments 36b and 36c, arranged in the same manner as their counterparts in the winding 34.

Each of the windings extends approximately halfway around the form 10. Leads to the

windings

34 and 36,

which are connected in series, extend through slots 39 in rib 30. When current is supplied to the windings, a horizontally directed magnetic field is produced within the form 19 between the two

windings

34 and 36. The aforementioned distribution of the lengthwise winding segments 34a and 36a. and the forward ends of the

windings

34 and 36, which are flared in conformance with flare 22 of form 19, shape the magnetic field produced in the yoke in a fashion that will be described more particularly later.

The horizontal deflection section 12 is the same as vertical deflection section 10 except that its diameter is somewhat larger so that section 10 can nest snugly within it. Thus section 12 comprises an insulating bell-shaped form 40 having a generally cylindrical tube 41 integral with a flare 42. As before, the flare 42 has a recessed circumferential band 44 around its exterior and the tube 41 has a similar band 48. These bands are defined by ribs 46 and 49 and a centrally disposed raised band 4-7.

A pair of upper and lower deflection windings 50 and 52, respectively, are arranged on opposite sides of form 40 forming another Helmholtz type coil. As with the section 10 windings, the windings 50 and 52 are wound in spiral fashion flat against the outside of form 40. Thus, the lengthwise segments 50a and 52a are seated in longitudinal slots 54 in the band 47 in accordance with the sine function described above. The front and rear winding crossover segments 50b, 52b and 50c, 52c extend arcuately around form 40 in the recessed bands 44 and 48, respectively, just as described above in connection with section 10. Leads from the windings 50 and 52 extend through slots 58 in the rib 49.

If desired, the deflection systems 10 and 12 can be made very easily and inexpensively by using conventional etched circuit techniques. The deflection windings are then formed from thin conductive [films bonded to the plastic forms. Using these same techniques, it is even feasible to apply both the vertical and horizontal deflection windings to a single form further simplifying the yoke. In this event, the vertical deflection windings might be formed on the inside surface of the single form and the horizontal deflection windings applied to the outside surface. Of course, the windings would still be shaped and oriented as described above.

When energized, the windings 50 and 52 produce a strong magnetic field through the center of the form 40 vertically between the windings. Here again, the winding distribution and the flared forward ends of the windings shape the magnetic field as will be described later.

Still referring to FIG. 1, the deflection sections 10' and 12 are adapted to be nested inside the jacket 14. Jacket 14 includes a loose sleeve 64 fabricated from a high permeability material such as a ferrite. Sleeve 64 provides a low reluctance return path for the magnetic fields, extending across the interior of the form 19, generated by the deflection sections 10 and 12. Also, it is appreciably longer than deflections sections 10 and 12 for reasons that will become apparent. Actually, for facilitating its fabrication, sleeve 64 is made up of a series of four ring-like sections 64a-64d. Of course, the sleeve 64 may just as well comprise a single ferrite piece.

A cylindrical axial passage 66, whose diameter is appreciably larger than the outside diameter of the deflection section 12, extends through sleeve 64. A tubular cylindrical spacer 70 is snugly fitted within passage 66. For ease of illustration, spacer 70 is shown displaced rearwardly somewhat in FIG. 1. In use, it extends through rings 64b64d and its end 7011 (FIG. 2) protrudes an appreciable distance out the rear of sleeve 64. The inside diameter of spacer 7 0 is only slightly greater than the outside diameter of tube 41 of deflection section 12 so that when sections 10 and 12 are nested in jacket 14, tube 41 is snugly accommodated within sleeve 64. The spacer 70 is fabricated of a material, such as plastic, having a very low magnetic permeability as compared with the ferrite sleeve.

The inside forward edge 71 of ring 64a is beveled to conform to the flare 42 of deflection section 12 and for other reasons that will become apparent later.

The terminal ring 18 comprises simply an insulating ring for securing by screws 82 to the end of spacer 70. The ring 80 carries terminals 84 for the

deflection windings

34, 36, 50 and 52.

FIG. 2 illustrates the assembled yoke, with the deflection section 10 snugly nested coaxially inside deflection section 12 and the section 12 within the jacket 14. The components of the yoke may be bonded in place with a suitable resin. The yoke is fitted on the neck 100 of a cathode ray tube 98. Since the sections 10 and 12 are coextensive, their corresponding forward

ribs

26 and 46 and rear ribs 30 and 49 are adjacent to one another. The flare 42 of section 12 seats against the beveled edge 71 of sleeve -64. The flare 22 of section 10 seats against the flared surface 101 of the cathode ray tube 98. The two deflection sections 10 and 12 are oriented about their common longitudinal axis so that their deflection windings are angularly displaced from one another.

As mentioned previously, the sleeve 64 is appreciably longer than the deflection sections 10 and 12. As seen from FIG. 2, the beveled forward edge 71 of sleeve ring 64a extends forwardly beyond the

ribs

26 and 46 of deflection sections 10 and 12, forming there an annular beveled overhang 90. The rear end of the sleeve ring 64d also extends out beyond the rear ribs 30 and 49 of sections 10 and 12, respectively, forming there also an annular overhang 92.

Finally, insulating ring 80 is secured to the rear end 70a of spacer 70 by means of the screws 82.

FIG. 4 illustrates the relationship and connections between the four winnings of the yoke. The numerals on the terminals at the ends of the windings correspond to those on the terminals of ring 80.

When the cathode ray tube 98 is energized, it generates an electron beam which in the absence of outside forces follows a straight line path and strikes the tube face 102 at the point A on the longitudinal axis of the deflection system. When the

vertical deflection windings

34 and 36 are energized, they generate a magnetic field whose flux lines, indicated at 106 in FIG. 2, are generally horizontal (i.e. parallel to the drawing). The field tends to deflect the electron beam 104 vertically (i.e. into or out of the plane of the drawing). The energized horizontal deflection windings 50 and 52 generate a magnetic field whose flux lines (not shown) are generally vertical (i.e. perpendicular to the plane of the drawing). This vertical field accomplishes horizontal beam deflection.

Thus, viewing the tube from the front, current of a certain magnitude in one direction deflects the beam 104 to the left, where it strikes the tube face 102 at point B. Current of a lesser magnitude in the opposite direction deflects the beam 104 a smaller distance to the right of point A, where it strikes the tube face at point C. In actual practice, the two deflection sections 10 and 12 can be operated together to deflect the beam 104 to any point on the tube face 102. The deflection winding segments, distributed as aforesaid and surrounded by the ferrite sleeve 64, produce strong magnetic fields across the tube neck 100 in the interior of the yoke.

The fringe field at the forward end of the yoke, instead of being largely diverted from the exterior of the tube and thus converted to a useless leakage field, as was the prior practice, is actually shaped so that it can be utilized to a maximum extent to help deflect the beam 104 and to minimize defocusing. The gradually flared, different length, forward winding crossover segments 34b, 36b, 50b and 52b, each seated in single layer fashion inside the correspondingly beveled ferrite ring 64a, shape the vertical and horizontal magnetic deflection fields at the forward end of the yoke so that their flux lines are substantially transverse to the beam 104 no matter how the beam is deflected. For very precise shaping of the fields to obtain the best possible results, the aforesaid flair angle might have to depend somewhat on the speed of the electron generated in the tube 98. However, for the most standard tubes, a standard flare angle of about 45 can be used with excellent results. The beveled overhang 90 at the very front of the yoke cooperates with the winding arrangement by short circuiting the very forward magnetic field components, with the net effect of flattening the bowing fields somewhat and thereby helping to properly shape them.

Thus, as readily seen from FIG. 2, whether the electron beam 104 is deflected to strike the tube face 102 at points A, B or C, the curved horizontal flux lines 106a intercept the beam 104 substantially at right angles regardless of the horizontal deflection. Thus vertical deflection is relatively independent of the horizontal position of the beam. Furthermore, since only the component of the horizontal field that is perpendicular to the beam produces vertical beam deflection, it is quite apparent that a maximum amount of the magnetic field generated by the windings, even at the very front of the yoke, can contribute to vertical beam deflection. The efliciency of the yoke is thus materially increased. Magnetic energy that was formerly wasted is now utilized to a maximum extent, resulting in reduced energy requirements for the yoke.

The same condition holds true in the case of the vertical deflection field. It is shaped as aforesaid so that it intercepts the electron beam 104 transversely no matter how the beam is deflected vertically. Therefore, the outwardly bowing vertical field can be used to a maximum degree to help deflect the beam 104 horizontally.

Actually, the shaped flare at the forward end of the yoke affects the field back in the cylindrical portion of 8 the yoke. The field there tends to bow forwardly, though to a lesser degree with increasing distance from the flare. Thus, by the time the electron beam is deflected appreciably, it encounters the curved field whose flux lines are substantially perpendicular to the beam.

For certain applications, it may be desirable to extend the flare back so that it constitutes the major or entire portion of the yoke. For example, for short yokes having a very wide angle deflection capability, the yoke is preferably continuously flared or trumpet shaped. This construction insures that the magnetic flux lines all along the yoke intercept the beam at substantially right angles for maximum performance. Also it enables the beam deflected at large angles to transit the yoke Without hitting the sides of the tube.

As mentioned previously, the longitudinal segments of the deflection windings are preferably distributed in accordance with a specified sine function. The reason for this is that there is a finite spacing between the conductors of the adjacent forward crossover segments of each winding. This spacing is due in part to the insulation on the wire and in part to the unavoidable small gap between the winding segments themselves. The aforesaid spacing, which in effect means that each loop of the deflection winding has a different overall length, causes the magnetic field produced by that winding at the flared part of the yoke to bow in toward the 0,, reference plant.

FIG. 5 shows the field distribution at the front of the vertical deflection section 10 due to the longitudinal spreading of the crossover segments 34b and 36b. The magnetic flux lines on opposite sides of the horizontal plane containing the longitudinal axis of the winding section (0,, reference plane) bow in toward this plane. Moreover, the extent of the bowing increases with increasing distance from the plane. This produces a non-uniform field condition the result of which is that the horizontal magnetic flux is dense near the axis of the tube and diminishes as one moves away therefrom. Accordingly, the amount of beam deflection per unit of winding current diminishes with the distance of the beam from the tube axis. This degrades the linearity of the deflection winding current characteristic.

The modification to the sine distribution compensates for this. It produces a magnetic field in the cylindrical portion of the deflection section whose flux lines bow out slightly from the 0,, reference plane, the bowing being more pronounced as the distance from said plane increases.

For example, FIG. 6 shows the field distribution near the middle of the vertical deflection section 10. The flux lines are substantially horizontal at the middle of the sections where 0 =0. As 0,, increases, however, the flux lines become bowed out to a greater degree. With the density of the flux increasing with distance from the tube axis, the deflection per unit of winding current also increases with the distance from the axis. This increase is arranged to compensate for the decrease in the forward fringe field, thereby providing a relatively linear overall deflection characteristic.

The same situation prevails in the horizontal deflection section 12. The field in the cylindrical part of the section is bowed out sideways to compensate for the inward b0wing of the flux in the region of the flare due to the crossover segments 50b and 52b. The effects of these bowed fields on deflection linearity are compensated by the configuration in the cylindrical part of the yoke.

Referring again to FIG. 2, the aforesaid shaping of the fringe fields at the forward end of the yoke has been found to reduce the defocusing of the electron beam 104 particularly when the beam undergoes fairly large angle deflection. This is due also to the fact that the beam 104 intercepts the magnetic flux lines transversely. Thus the component of the magnetic field which is parallel to the beam and which tends to shorten the focal length is minimized. Also, even though the beam has a finite crosssection, both edges of the beam arrive at a given flux line in the field at the same time. This is in contradistinction to the situation that prevails when the beam approaches at an angle other than 90 where the degree of deflections differs slightly at the opposite edges of the beam.

At the rear end of the yoke, the fringe fields tending to bow out the rear of the yoke toward the gun end 96 of the cathode ray tube follow the low reluctance path afforded by the circumferential portion 92 of the ferrite sleeve 64 which overhangs the rear ends of the vertical and horizontal deflection windings. Thus, the fringing flux lines are short circuited by the ferrite overhang 92 so that the net field there tends to be straightened out. The field is not intercepted by the conductive components of the electron gun and there is less likelihood of the electron beam 104 being deflected prematurely.

Still referring to FIG. 2, the separation between the sleeve 64 and the cylindrical portions of deflection sections and 12 afforded by the low permeability spacer 70 sets up a high reluctance barrier to the leakage magnetic flux from individual winding turns that formerly tended to directly encircle the turns by way of the ferrite sleeve rather than bridge the cathode ray tube 98. This, in turn, increases the efliciency of the yoke, increases the field uniformity in the cathode ray tube and also materially reduces hysteresis losses in the yoke. It will be noted that the spacer also increases the reluctance of the paths for deflection fields. However, the proportional increase for the deflection fields is much less than the proportional increase in the path reluctance for the leakage fields.

The reduction in leakage fields afforded by the invention also provides a lower winding inductance and corresponding higher resonant frequency. Additionally, the spacing between the ferrite sleeve '64 and the vertical deflection section 12 tends to equalize the deflection efliciencies in the two deflection sections.

A typical set of dimensionsfor a yoke embodying the invention is as follows:

Vertical deflection section 10:

Overall length inehes 1 /2 Outside diameter of tube do 1 Flare diameter ..do 1% Flare angle degrees 45 Wall thickness inch Horizontal deflection section 12 Length inches 1 /2 Outside diameter do 1% Flare angle degrees 45 Flare diameter inches 1% Wall thickness do Ferrite sleeve 64:

Length inches 1% Outside diameter do 2 Inside diameter do 1 Bevel angle degrees 45 Spacer .70:

Length inches 1% Wall thickness do Referring now to FIGS. 7A and 7B, a preferred embodiment of my deflection system also corrects pincushiontype distortion without any material sacrifice in the desirable yoke characteristics described above. Pincushion distortion as depicted in FIG. 7A arises because of the difference in the radii of curvature of the cathode ray tube screen and the electron beam scan.

More particularly, FIG. 7B shows a cathode ray tube 120 which generates an electron beam 122 impinging on a screen 120a. The beam is focused by a conventional magnetic lens so that its cross-section decreases as it approaches the screen. A deflection yoke 124 on the neck of the cathode ray tube controlledly deflects beam 122 so that it strikes the screen at the desired points thereon. Beam 122 is deflected about a theoretical center of deflection near the middle of yoke 124. It can be deflected vertically as shown in FIG. 7B, to sweep out a vertical are indicated at 126' whose radius of curvature is the distance between are 126 and the center of deflection inside yoke 124. It can also be deflected horizontally so as to sweep out the same sort of arc in a horizontal plane.

If the tube screen a coincided with are 126 (and also with the swept arc in the horizontal plane), a grid pattern swept out by beam 122 would appear perfectly rectangular since the sine of the angle of deflection of the beam is proportional to the current in the yoke 124. However, due to the difference in the radii of curvature of the beam scan and screen 120a, the grip pattern actually traced on screen 120a, looks like FIG. 7A. The grip lines bow in and they are progressively further apart as the distance from the screen center increases. This pincushion distortion increases with greater deflection angles and becomes noticeable for cathode ray tubes having a deflection angle more than 40. Therefore, it presents a serious problem in present day television and display systems employing tubes whose deflection angles may be as large as 90 or conventionally, pincushion distortion is corrected in one of three ways, each of which has its own inherent disadvantage. More particularly, it can be corrected by shaping the wave forms of the current applied to the de- 'flection windings. This technique is quite difficult and expensive to implement because it requires cross-summing of the vertical and horizontal deflection signals. Moreover, it is diflicult to keep in adjustment. The second method is to shape the deflection fields in the yoke by redistributing the deflection windings in the main part of the yoke. This method is very rarely used because it requires the generation of a nonuniform field in the main part of the yoke, which produces severe beam distortion and defocusing.

The third and most commonly used technique for compensating for pincushion distortion involves the use of a static magnetic correction lens spaced in front of the yoke. This type of corrective device may be used in the yoke described above in connection with FIGS. 1-6. However, it, too, has several drawbacks. First, it is quite difficult to adjust and it is even more difficult to obtain uniformity in such adjustment from one unit to the next when they are produced in numbers. Moreover, it is extremely difficult, if not impossible, to find an adjustment of the static lens which will correct the pincushion distortion and yet maintain an even spacing between the lines of a grid-type pattern. That is, the static lens can straighten out the vertical and horizontal lines in the grid pattern shown in FIG. 7A. However, because it is a static correction, it does not restore the uniform spacing of the grid lines. Finally, it also may introduce other distortions. Therefore, it cannot be used in applications requiring the highest precision.

FIG. 8 illustrates a vertical deflection section of a deflection system having capacity for correcting pincushion distortion while still obtaining linear beam deflection and low beam distortion, aberration and defocusing. For clarity, we have only shown a few winding turns and have exaggerated the spacing between them.

The associated horizontal deflection section is like vertical section 130 and will not be described in detail. It bears the same relationship to section 130 that deflection section 12 bears to section 10 in FIG. 1. That is, the two deflection sections are nested together and oriented at right angles to one another as fully described above. Also, the two deflection sections in this embodiment of the invention are themselves nested inside a ferrite packet similar to jacket 14 in FIG. 1. Therefore, in all respects except as described specifically below, the deflection system using the FIG. 8 deflection section 130 operates in the same manner as the system shown in FIGS. 1-6.

Section 130 comprises an insulating, bell-shaped form 132 having a generally cylindrical rear tube 134 and an integral forward flare 136 whose shape will be described in more detail later. In other respects, form 132 is the same as form 19 in FIG. 1.

A pair of substantially identical, diametrically

opposed windings

138 and 140 are arranged about the outside of form 132 in a Helmholtz-type coil arrangement. In use, section 130 is oriented so that

windings

138 and 140 generate a generally horizontal magnetic field inside form 132. This horizontal field produces vertical beam deflection as described above in connection with FIGS. l-6.

Each winding 138 and 140 forms a generally rectangular spiral arranged lengthwise on form 132. In the deflection section illustrated specifically in FIG. 8, each winding 138 and 140 has four turns. The longitudinal winding segments 138a and 140a of these windings are distributed about the circumference of form 132 in the same manner as for longitudinal segments 34a and 36a of deflection section 10 in FIG. 1. Also, the front winding crossover segments 138b and 140]; of the two windings extending circumferentially in a single layer about flare 136, while the rear crossover segments 138a and 1400 extend generally circumferentially about the rear end of tube 134.

The longitudinal winding segments 138a and 140a are distributed about the circumference of tube 134 in accordance with a sine function to produce a uniform magnetic deflection field inside tube 134.

Still, referring to FIG. 8, the forward winding crossover segments 138b are distributed on flare 136 so that, proceeding forwardly, they are spaced progressively farther apart along the surface of the flare. More particularly, in the illustrated embodiment, the spacing between successive pairs of crossover segments increases linearly. In a typical example, the spacing between the two innermost segments 138b is 0.05 inch, the spacing between the next two segments is 0.1- inch, and the spacing between the third and fourth segments is .150 inch. Flare 136 is made long enough to accommodate the desired number of crossover segments.

The winding crossover segments 14% have the same distribution as segments 13812.

A deflection system has also been constructed wherein the crossover segments 138D and 14012 are distributed in accordance with a power function, e.g. a square function. In this embodiment, the successive segments are spaced farther apart than is the case with the linear distribution. Consequently, this distribution requires a longer flare 136 to accommodate the same number of wires.

Referring now to FIGS. 8 and 9A-9D, the two

windings

138 and 140 in vertical deflection section 10, when energized, produce a generally horizontalmagnetic field which deflects the electron beam 122 (FIG. 7B) vertically as mentioned previously; and the deflection field is substantially uniform in tube 134. However, as the beam progresses toward the front section 130, and moves off the yoke axis, it encounters the crossover segment 138b and 14% which produce a nonlinearfield distribution inside flare 136 which dynamically corrects pincushionmg.

FIGS. 9A-9D illustrate the field distribution inside form 132 at the correspondingly lettered location along the longitudinal axis of section 130 in FIG. 8. The solid lines represent the field produced by vertical deflection section 130. The dotted lines represent the field developed by a similar horizontal deflection section (not shown). Actually, the fields and the flare also bow forwardly as shown in FIG. 2. However, for ease of illustration, we have shown them in FIGS. 9A to 9D with no forward bow.

FIG. 9A shows that at point A in the cylindrical portion of deflection section 130, i.e. within tube 134, electron beam 122 coincides essentially with the longitudinal axis of section 130 and its diameter is relatively large at this point. Also, the vertical and horizontal deflection fields here are very ,linear and uniform as illustrated by the substantially rectangular flux pattern. This is essential because the beam 122 diameter is a relatively large fraction of the diameter of the deflection field, or more specifically, both the beam diameter and the intensity of the deflection field are relatively large. Thus, even a small percentage distortion in the field here will result in a relatively large difference in the field strength and/or direction from one side of the beam 122 to the other. Electrons from one part of the beam would therefore be deflected quite differently from those in another part thereof, resulting in defocusing and image distortion.

The deflection fields produced by the vertical and horizontal deflection sections now move beam 122 off the longitudinal axis of the yoke in the direction of the final deflection position. Also, the cross section of the electron beam 122 gradually becomes progressively smaller due to the fact that the beam is focused by a focusing coil as noted above.

FIG. 9B is representative of the deflection fields at point B just beyond the first pair of crossover segments 138b and 14012. This pair of current-carrying wires extending around the circumference of flare 136 causes the deflection fields to have the requisite nonuniformity to correct pincushioning with the illustrated beam deviation from the yoke axis. However, the field nonuniformity still produces very little distortion of beam 122 because the deflection field is growing larger in cross section and therefore less intense, while at the same time the beam 122 cross section is growing smaller. Consequently, even with a relatively large percentage nonuniformity in the field, the absolute amount of field variation across the electron beam 122 is small and there is minimal defocusing of the beam.

This process continues so that while the correcting field nonuniformity becomes progressively greater as beam 122 moves toward the screen, the field intensity and beam diameter decrease concomitantly. For example, FIG. 9C shows the deflection fields at point C just beyond the third pair of crossover segments 13812 and 14%. The three pairs of circumferential winding segments cause a relatively large nonuniformity in the fields illustrated by the inwardly bowing magnetic flux lines. This large nonuniformity is required to obtain the requisite pincushion correction because the beam is now relatively far away from the yoke axis. However, again the field intensity and beam diameter are much less than at points A and B. Consequently, the nonuniform field still causes relatively little spot distortion and defocusing.

Progressing along the longitudinal axis of section 130, the deflection fields become even more nonuniform and larger as we proceed to point D at the forward end of the yoke in order to apply the requisite correction to the beam which is now a maximum distance away jfrom the yoke axis. By the same time, however, the field intensity and cross section of beam 122 are still smaller so that there is little difference in field intensity and direction across the beam. Therefore, even at this point, the nonuniform fields do not distort or defocus beam 122 to any appreciable extent.

In this fashion, the progressively changing field nonuniformities created by the flared, distributed crossover segments 13812 and 14% achieve a dynamic pincushioning correction while still causing minimum beam distortion. This is because as the field nonuniformity increases, the product of field intensity and cross section decreases at an even faster rate so that the nonlinear fields have minimum tendency to distort and defocus the beam.

It is important to emphasize at this point that the present yoke produces a pincushion correction which is dynamic rather than static. That is, the nonuniform correcting fields to which beam 122 is subjected change progressively as the beam passes out through flare 136.

The advantage of this dynamic correction over the standard static magnetic lens correction is that the former not only corrects pincushioning, but does so without causing any change in the line spacing of the ideal rectangular grid pattern such as occurs in a conventional system employing a fixed magnetic correction lens.

As best seen in FIG. 1, when the windings are flared as are those in deflection section 12, for example, the longitudinal winding segments 50a, 52a, grow further apart as they progress up flare 42 due to the curvature of the flare. I have found that a pincushioning correction can be obtained by properly distributing the wires in the windings as they progress up the flare.

For example, when the longitudinal segments in each winding are positioned at a uniform distance from one another as they progress up flare 44, instead of at constant angle from the center of section 12, a nonuniform field is developed at the flare end which sufiices to correct pincushioning. This corrective wire distribution can be used instead of the technique described in connection with FIG. 8. Alternatively, it may be used along with the FIG. 8 construction to obtain an additional pincushion correction.

In addition to eliminating the usual static pinc-ushion correction lens, the present yoke construction also somewhat improves deflection efliciency. This is because the crossover segments 138b and 14% are spaced progressively further apart. This reduces the overall capacitance of the yoke, even though there may be more winding turns in the present construction than in a comparable conventional yoke. Further, the present construction eliminates the difiicult production and servicing adjustment problems found in conventional magnetic lens correction devices.

As mentioned previously, it is especially important that a uniform field be maintained at the gun or rear end of the yoke because here the electron beam cross section is largest and therefore most susceptible to minor field nonuniformities. The performance of the FIG. 1 yoke is quite good in terms of low aberration and beam distortion. However, due to the insulation between the individual rear crossover segments 34c, 36c, 50c and 520, the deflection fields are slightly nonuniform at the rear end of the yoke. This makes such a yoke less desirable for use in high resolution displays which require extremely precise deflection, as well as low beam distortion, aberration and defocusing.

This problem is aggravated when the deflection sections are fabricated using printed circuit techniques. This is because the plating operation requires that the spacing between the plated crossover segments be even larger than when enameled wire is used for the windings as in FIG. 1.

The deflection system illustrated in FIG. 8 also corrects this field nonuniformity at the end of the section by properly shaping the winding crossover segments on tube 134. More particularly, as stated above, in order to obtain a uniform field everywhere in tube 134, the longitudinal winding segments 138a and 140a are distributed circumferentially on tube 134 in accordance with a sine function.

In actual practice, this distribution is governed by a set of equations whose derivation assumes that the number of field generating winding turns remains constant all along tube 134. However, progressing toward the rear of tube 134, to point I, we go beyond the innermost crossover winding segment; hence there are two less winding turns (i.e. one on each side of tube 134). Consequently, the radial distribution of winding segments 138a, 140a as determined by the original set of equations does not produce a perfectly uniform field in this region.

In progressing from point 1 to point m, another crossover segment is passed and again there are two less winding turns. Consequently, in the region between the two outermost crossover segments, the field nonuniformity becomes even more pronounced.

We have shown only a few winding turns in section 130. However, it will be appreciated that with a deflection section having many turns, the field nonuniformity at the rear end thereof might be further aggravated and give rise to considerable beam distortion and aberration.

A yoke employing deflection sections made in accord ance with FIG. 8 corrects these field nonuniformities at the rear end of the yoke by shaping the crossover segments (e.g. at l and m).

More particularly, I alter the angular distribution on tube 134 of the longitudinal winding segments 138a, 140a in the regions bet-ween the successive crossover segments 138e, 1400, to compensate for the decreased number of winding turns in those regions. For example, for the regions containing points I and m; the basic distribution equations are changed to correct for the reduced number of turns there. That is, N in Equation 1 decreases by two in each case. These corrected equations then define a new winding segment distribution :for these regions which will produce a uniform field there.

As seen from FIG. 8, the distribution corrections manifest themselves as rounded corners on the turns of winding 138 and similar rounded corners 152 on winding 140 at the rear end of section 130. Ideally, each corner is made up of one or more short wire segments 150a, 152a representing the angular redistribution required in successive regions to correct for smaller number of winding turns. These segments are quite noticeable in FIG. 8 because only a few winding turns are shown and their spacing is exaggerated. It is seen that ideally each segment begins and ends off the end of a crossover segment. In actual practice, however, where a number of relatively closely spaced turns are used, the

corners

150, 152 would appear more gradually rounded.

This same correction can be made at the flare end of a yoke such as shown in FIG. 1 to further improve its performance. In this case, an electron beam at any position in the yoke, including both crossover regions thereof, encounters a very uniform field. This correction will ordinarily not be made in the flare end of deflection sections of the FIG. 8 type because the redistribution of the seg ments as just described is not fully compatible with the winding distribution required in the flare to correct for pincushioning.

A yoke made in accordance with FIG. 8 is further advantaged in that the separation between the crossover segments lowers the capacitance between the winding turns. This raises the resonant frequency of the yoke and in creases its speed of response. Without the aforesaid angular distribution of the windings at the crossovers, it has not been practical until now to separate the winding segments and still obtain a high performance yoke.

Relative to the center of the conductors, one can derive a conductor distribution independent of the factors d, k and L of Equation 1. Such a distribution may be represented as follows:

X 1 6 tan Y where and Expressions (2), (3) and (4) also contain ambiguities that may sometimes result from the use of Equation 1. However, it should be noted that, like Equation 1, they provide a sinusoidal distribution. In fact, although Expression (2) is in terms of the tangent, a simple trigonometric substitution yields the equivalent sin function.

0,, sm (1 N+l (5) While I have described an improved magnetic deflection system capable of two-direction deflection, it will be apparent that the invention is also effective in applications where only single-direction deflection is required. In this event, a yoke comprising only one of the aforementioned deflection sections can be used. Also, in some applications, it may only be necessary to provide high frequency deflection in only one direction, say the horizontal direction. Here, a yoke comprising the deflection section 12 combined with a conventional lower speed vertical deflection section may accomplish the desired result. Morever, as a general proposition, my system may be used in conjunction with other types of particle generator to controllably bend any particle beam having a charge, e.g. a proton beam.

In summation, the deflection system described above shapes the magnetic fields generated therein sothat they are used to a maximum extent to deflect the beam. The overall yoke inductance is kept to a minimum so that the yoke is capable of fast response. Moreover, the deflection is accomplished in a highly uniform fashion, rendering a visual presentation which is marked by high linearity and sharpness even near the edges of the tube face. With improved efliciencies made possible with my system, on the order of 75 percent, the energy requirements for the system are kept to a minimum.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall in between them.

I claim:

1. A magnetic deflection system comprising (A) means for directing a beam of charged particles along a path,

(B) magnetic deflecting means positioned adjacent said path, said deflecting means (1) producing a magnetic field which deflects said beam as said beam travels from one end to the other of said deflecting means, and (2) including deflection windings positioned on opposite sides of said path, each of said windings having (a) segments extending generally in the direction of said path, and (b) forward crossover segments extending generally transverse to said path, said crossover segments being distributed in a longitudinal direction over and outwardly flared extension of a tube defined by said windings so as to produce a curved magnetic deflection field whose flux lines bow out in the direction of said path, whereby the flux lines are generally perpendicular to the electron beam as it is deflected by said deflected means toward said crossover segments of said windings.

2. A magnetic deflection system as defined in claim 1 wherein said deflecting means further includes a high permeability sleeve positioned about said windings, said sleeve extending over said crossover segments.

3. A magnetic deflection system as defined in claim 2 wherein said sleeve overhangs appreciably said crossover segments.

4. A magnetic deflection system comprising (A) a generally cylindrical tubular form having a flared forward end,

(B) a pair of diametrically opposed series connected spiral deflection windings positioned on opposite sides of said form to produce a deflection field within said form, each of said windings having (1) longitudinal winding segments distributed around said form, and

(2) forward crossover segments flared in conformance with said form so as to shape the magnetic fields at said forward ends of said windings to be perpendicular to a beam of charged particles passing through said form.

5. A magnetic deflection system as defined in claim 4 further comprising a high permeability cylindrical tubular sleeve positioned coaxially around said form, said sleeve being spaced appreciably from said windings so as to provide a high reluctance overall path for the leakage fields from the individual turns of said windings but a relatively low reluctance overall path for said deflection fields.

6. A magnetic deflection system as defined in claim 5 wherein said sleeve extends axially beyond the opposite ends of said windings forming annular low reluctance paths for leakage fields at the opposite ends of said windmgs.

7. A magnetic deflection system as defined in claim 5 wherein said sleeve is constructed of a ferrite material.

8. A magnetic deflection system comprising (A) a first cylindrical tubular form, said form having a flared forward end,

(B) a pair of diametrically opposed, series-connected, spiral, single-layer windings arranged on said form to produce a first deflection field within said form, each of said windings having (1) longitudinal winding segments distributed around said form,

(2) forward winding crossover segments extending arcuately around said flared forward end of said form so as to shape said deflection field there to be perpendicular to a deflected electron beam passing through said form.

9. A magnetic deflection system as defined in claim 8 further comprising (A) a second cylindrical tubular form, said second form having (1) a flared forward end, and

(2) a diameter such that said first form and its associated windings can nest coaxially within said second form,

(B) a second pair of diametrically opposed, series connected spiral windings arranged on said second form to produce a second deflection field within said form perpendicular to said first field, each of said second windings having (1) longitudinal winding segments distributed around said second form, and

(2) forward winding crossover segments extending arcuately around said flared forward end of said second form so as to shape said second deflection field there to be perpendicular toa deflected electron beam passing through said form. 1

10. A magnetic deflection system as defined in claim 9 and further comprising a conforming sleeve-like jacket positioned coaxially over said forms, said jacket being (A) fabricated of a material having a high magnetic permeability, and

(B) spaced appeciably from said windings to create a cylindrical high reluctance path for leakage fields from said windings between said windings and said sleeve.

11. A magnetic deflection system comprising (A) means defining a beam path,

(B) a pair of serially connected, diametrically opposed spiral windings juxtaposed on opposite sides of said path in a Helmholtz type coil arrangement, each of said windings having '1) longitudinal winding segments running parallel to said path, the totality of said longitudinal segments of the pair of windings defining a cylinder around said path, and

(2) forward and rear winding crossover segments extending transversely to said path, said forward crossover segments being flared out conically away from said path so as to shape the magnetic field between the crossover segments of said windings to be perpendicular to an electron beam deflected by said windings,

(C) a high permeability sleeve shaped to conform to said windings, said sleeve (1) being positioned around said windings,

(2) extending appreciably beyond said forward and rear crossover segments, and

(3) being spaced appreciably from said longitudinal winding segments, by an intervening cylindrically shaped material having a low magnetic permeability.

12. A magnetic deflection system as defined in claim 11 wherein said material is in the form of a cylindrical plastic tube fitted snugly between said windings and said sleeve.

13. A magnetic deflection system comprising (A) first and second tubular deflection sections coa-xially nested together, each section comprising (1) aninsulating form, said formhaving (a) a generally cylindrical rear portion, the outside surfaceof said rear portion having a first circumferential recessed band near one end thereof,

(b) a flared forward portion integral with the other end of said rear portion, the outside surface of said forward portion having a second circumferential recessed band intermediate its ends,

(c) first and second diametrically opposed arrays of longitudinal slots extending between said first and second bands, said slots of each array being distributed around said form,

(2) a pair of diametrically opposed magnetic de flecting field producing spiral windings wrapped around said form, said windings having (a) longitudinal winding segments seated in the slots of the corresponding slot arrays,

(b) rear winding crossover segments extending arcuately around said form as a single layer in said first band, and

() forward crossover segments extending arcuately around said form as a single layer in said second band, said forward crossover segments being flared out in conformance with said form so as to geometrically shape said field at the flared portion of said form so that its flux lines are substantially perpendicular to an electron beam deflected by said field,

(3) the forms of each of said deflection sections being oriented about their common longitudinal axis so that their respective deflection windings are angularly displaced 90 from one another,

(B) a cylindrical tubular spacer positioned coaxially around said cylindrical rear portion of the adjacent deflection section, said spacer (1) being of a material having a low magnetic permeability, and

(2) extending appreciably out beyond said rear winding crossover segments,

(C) a cylindrical tubular sleeve positioned coaxially around said deflection sections, said sleeve (1) being fabricated of material having a high magnetic permeability,

(2) being arranged and adapted to snugly engage said spacer,

(3) having its forward edge beveled so as to snugly receive the flared portion of the adjacent deflection section,

(4) extending appreciably beyond said forward winding crossover segments so as to form an annular beveled extension which short circuits any leakage fields appearing at the forward end of said windings, v

(5) extending appreciably beyond said rear crossover segments so as to form an annular extension which short circuits any leakage fields appearing at the rear end of said deflection windings, and

(D) terminals secured to the rear end of said spacer, said terminals being electrically connected to said windings.

14. A magnetic deflection system as defined in claim 13 wherein said longitudinal winding segments of each array are distributed in accordance with a modified sine function.

15. A magnetic deflection system as defined in claim 14 wherein said modified sine function is as follows:

where:

N is the number of turns in the winding,

d is the width of the conductor,

L is the length of the winding measured between the two endmost crossover segments and following the curvature of the winding,

k is the spacing between the conductors of adjacent crossover segments,

0,, is the angular position of the nth longitudinal segment of the winding from the reference plane which is a plane passing through the center of the innermost winding loops 'and the longitudinal axis of the form (19), and

n is the longitudinal winding segment whose angular position is being measured.

16. A magnetic deflection system comprising (A) a pair of diametrically opposed flared deflection windings, said deflection windings being (1) in the form of rectangular spirals having longitudinal segments,

(2) concave toward one another to define a cylinder, and

(3) in a coil arrangement providing a magnetic field extending between said windings,

(B) each of said windings having its adjacent winding segments spaced apart, said spacing decreasing with increasing distance from the center of the winding so that said magnetic field between said windings bows outwardly away from the plane passing through the centers of said windings and through the longitudinal axis of said cylinder, whereby the strength of said field within said cylinder increases with increasing distance from said plane.

17. A magnetic deflection system as defined in claim 16 wherein said longitudinal winding segments of each of said windings are distributed around said cylinder in accordance with a modified sine function.

18. A magnetic deflection system as defined in claim 17 in which each of said deflection windings has its forward crossover winding segments arranged in a flared fashion so that the magnetic field between said windings bows inwardly toward the plane passing through the centers of said windings and also through the longitudinal axis of said cylinder whereby the strength of said field between said crossover segments decreases with increasing distance from said plane.

19. A magnetic deflection system as defined in claim 18 wherein said modified sine function is as follows:

N is the number of turns in the winding,

d is the width of the conductor,

k is the spacing between the conductors of adjacent crossover segments,

0,, is the angular position of the nth longitudinal segment of the winding from the reference plane which is a plane passing through the center of the innermost winding loops and the longitudinal axis of the form (19), and

n is the longitudinal winding segment whose angular position is being measured.

20. A magnetic deflection system comprising (A) a pair of diametrically opposed deflection windings, said windings being (1) in the form of spirals having forward crossover segments,

(2) concave toward one another to define a cylinder, and

(3),in a coil arrangement providing a magnetic deflection field extending between said windings,

(B) a high permeability tubular sleeve positioned coaxially around said windings, said sleeve overlying said crossover segments and being spaced appreciably from said windings so as to provide a high reluctance overall path for the leakage fields from the individual turns of said windings, but a relatively low reluctance path for said deflection field.

21. A magnetic deflection system comprising (A) a curved screen,

(B) means for directing a beam of charged particles along a path toward said screen,

(C) magnetic deflecting means positioned adjacent said path, said deflecting means (1) producing a magnetic field which deflects said beam as said beam travels from one end to the other of said deflecting means, and

(2) including deflection windings positioned at opposite sides of said path, each of said windings having (a) segments extending generally in the direction of said path, and (b) forward crossover segments extending generally transverse to said path, said crossover segments being distributed in a longitudinal direction over an outwardly flared extension of a tube defined by said windings so as to produce a nonlinear magnetic field whose flux lines bow in toward the longitudinal axis of said tube so that (1) the nonlinear field corrects pincushion-type distortion of the pattern traced on said screen due to the difference in the radius of curvature of said screen and the radius of deflection of said beam, and (2) there is a minimum difference in the field across the beam cross section.

22. A magnetic deflection system as defined in claim 21 wherein said forward crossover segments of each said winding are spaced progressively further apart on said flare.

23. A magnetic deflection system as defined in claim 22 wherein said spacing between said crossover segments increases linearly in a direction outwardly along said flare.

24. A magnetic deflection system as defined in claim 22 wherein said spacing between said crossover segments increases in a direction outwardly along said flare in accordance with a power law.

25. A magnetic deflection systemas defined in claim 21 wherein said forward crossover segments are also distributed so that said magnetic flux lines also bow out in the direction of said path, whereby said flux lines are generally perpendicular to the electron beam as it is deflected by said deflecting means toward said crossover segments of said windings.

26-. A magnetic deflection system comprising (A) means for directing a beam of charged particles along a path,

(B) magnetic deflecting means positioned adjacent said path, said deflecting means (1) producing a magnetic field which deflects said beam as said beam travels from one end to the other of said deflecting means, and (2) including generally rectangular spiral deflection windings positioned at opposite sides of said path, each of said windings having (a) longitudinal segments extending generally in the direction of said path, and (b) rear crossover segments extending generally transverse to said path, said rear crossover segments being distributed generally parallel to said path, and (c) the turns of each said winding having corners at the rear of said winding which are shaped so as to maintain a uniform field in the region between said rear crossover segments.

27. A magnetic deflection system as defined in claim 26 wherein each said winding has forward crossover segments which are distributed so that the magnetic flux lines also bow out in a direction of said path, whereby said flux lines are generally perpendicular to the electron beam as it is deflected toward said forward crossover segments.

28. A magnetic deflection as defined in claim 27 wherein the corners of each said winding at the forward end thereof are shaped so as to maintain a uniform field in the region between said forward crossover segments.

29. A magnetic deflection system as defined in claim 26 wherein said longitudinal winding segments are distributed as follows:

0,, S111 (1 N+1 where:

0,, is the angular position of the nth longitudinal segment of the winding from the reference plane which is a plane passing through the center of the innermost winding loops and the longitudinal axis of the tubular form,

N is the number of turns in the winding, and

n is the longitudinal winding segment whose angular position is being measured, with 0,, being recomputed at each rear crossover segment to account for the reduced value of N, said value being N 2n.-

30. A magnetic deflection system comprising (A) means for directing a beam of charged particles along a path,

(B) magnetic deflection means positioned adjacent said path, said deflecting means (1) producing a magnetic deflection field which deflects said beam as said beam travels from one end to the other of said deflecting means, and

(2) including deflection windings positioned at opposite sides of said path, each of said windings having (a) segments extending generally along said path, and (b) forward crossover segments extending generally transverse to said path, said crossover segments being distributed in a longitudinal direction over a outwardly flared extension of a tube defined by said windings so as to produce a nonlinear magnetic field whose flux lines bow in toward the longitudinal axis of said tube so that (1) the nonlinear field corrects pin-cushion distortion, and (2) there is a minimum difference in the field across the beam cross section,

(c) said crossover segments also being distributed so that said magnetic flux lines also how out in the direction of said path, whereby said flux lines are generally perpendicular to the electron beam as it is deflected toward said forward crossover segments of said windings,

(d) each of said windings also having rear crossover segments distributed in a direction generally parallel to said path, and

(e) the turns of each said winding having cornets at the rear of said winding which are shaped so as to maintain a uniform field in the region between said rear crossover segments.

References Cited UNITED STATES PATENTS 1/1958 Kratz et a1 313-76 XR 4/1958 Marley 335-213 XR 10/1961 Corpew 335-213 1/1963 Snyder 335213 6/1965 Nero 335213 XR GEORGE HARRIS, Primary Examiner.

US. Cl. X.R.