US2218725A - Electron focusing system - Google Patents

Description

Ot- 22, 1.940-y w. scHRoEDER ELEcTRoN Focusmc SYSTEM ld May 5,

IIIIIIIIJ 9 A y INVENTOR WILLY SCHROE'DER ATTORNEY pf/Ase aff/,Free

yPatented Oct. 22, 1.9.40

` U'NiTED STAT-Es' ELEc'rRoN FocUsING SYSTEM' :s

Willy Schroeder, Berlin, Germany, assigner to4 Telefunken Gesellschaft fr Drahtlose I1`elegraphie m. b. 'H.,!Berlin, Germany, a corporation of Germany 'Application May-5.1939, seria1,No.`z71s,ss1

In'Germany April 22, 1938 'a clyaims'. (c1. 25o-2.7)

The-present invention relates to electron lens arrangement for electron-ray tubes.' Ordinarily electron lenses are predicated upon the use of electromagnetic or electrostatic fields, steady or v5L1invariahle with time. In other Words, unless an Aarrangement comprising a` permanent magnet is concerned, they presuppose the provision of a D. -C. source of supply. The use of such a source of current supply seemed indispensable with a lll-'view to securing a position of the ray intersection point' (cross-over) or electron image ex,-y

hibitingtime invariability. As a matter of fact, electronvlen's arrangements known in the prior art',` when yworkedwith A. C., would be unserv- However, v it isl frequently desirable to operate with A..C. purev l-,iceable for electron focusing.

i and simple, ormore particularly with alternating current furnished from the conventional sup-r plyline` because i this makes for simplicity of 201 constructiony in general. v

-vThe invention discloses electron llens arrange.-v ments'ior electron raysv which are adapted tof be operated with A. C.vwithout the use ofD-C.

V andv without the position ofthe focal;` point of'A '2'5 the electron ray beingv altered in any undesirable f The invention vshall now vbe, discussed and exu ments of fundamentallyv equal`r action, say, two.

annularcoils of similar size and comprising equal 'y numbers of turns, andvif they are fed with two' sine currents yof like amplitude In presenting a phasedisplacement of 90v degrees,y that is, in

45..-quadratnre relation,` then their refractive power- .sind

However, since Smau-casar is `equa1 to 1, it

follows that the refractive power of the magi netic'lens under consideration is proportional to y 5555102; 'in otherv words, independent of the time. Y

turns.

This holds'.tr'ueparticuiariy of the case that. l

the lenselds of the'two lens assemblies willf not-mutually influence each other to any lessential degree. ,l n f In:the case of coils comprising different t1'.1rn- 5-` numbers, ampere-turns `in lieu of currents imust;A be introduced in the above formula. The-fore# i going considerations yhold good inV an analogous manner alsofor coils of dissimilar forms, and` dissimilar diameters. But in such a case thecur-rf ll rents, of the coils must be `so chosen that the. focal distances determined. by thev effective values: of the currents will be equal. l

i 'On the basis of these considerations, lens semblies are obtained'according to the-invention ,15C of the kind represented by-the eXempliedemf-t; bodiments of the appendeddrawing inA which Fig. 1l shows a catho'clelray tube whiche ern-"1. bodies-my invention .of two` magnetic coils fed With alternating currents nphase quadraturevlgo,

While l Y Fig. '2 vshows a Lmodiiicationfof theembodi-ff ment 'of my invention in-Fig. 1` in Whichthreef coils are used; Fig. 3 shows two alternating currents' in phase 52. quadrature yin graphical form for explaining my; invention; Fig. 4 shows a further modification of theI embodiment shown in Fig. 1;

Fig. 5 shows schematically an arrangementlfor'r ggf l obtaining alternating currentsin phase quadi: vture fonusein .the embodiments shown in Figsgi 1, Zand, 4, and f Fig. ,fshows .-'a modiiicationjof the embodiai" yment of my` invention, lin which electrostatic'ST5v focusing systemsare used. i

In the simplest instance one may' usen-coils.; ofthe same d'ameter, and the same numberof-izv Fig. l shows comprises the coils M1. andMz, coaxially ,positioned withre'spect to the cathode, ray tube,p2| having an lelectron gun 25 for producing a beamlf of electronsand having positioneda target mem-iv ber 23 on the interior face thereof.l The target.;

member 23 may convenientlvbe va uoresc'ent:

f screen, for example, in a television receiving tube,

or may;bea mosaic :electrode structure forfa-fz cathode 'ray television transmitting tube. It will--1 i V be appreciated that deflecting systems, lwhether v150'; i electrostatic or electromagnetic, may also-beproi-g.`

vvided for scanning the target member 23.1V iSince Y these are "well known'in the art', they are-notoL shown."

` .Through the coil M1: by wayAv of the terminals 155i'l an yelectroni'A lens system which; 0?

5 and 5a is caused to flow an alternating current of sine form, that is, of a kind as shown by the graph Si, Fig. 3. Through the coil M2 by way of terminals and 6a is passed also a 5 sinusoidal A. C. having the same frequency as the A. C. traversing coil Mi, While presenting a phase displacement angle thereto of.l 90 degrees, as shown` by curve S2 in Fig. 3; By theaid of the system comprising coils i and 2 it is poslO sible to produce a sharp electron-optical image` or focus quite readily with alternating current in a Way as above explained.

Fig. 2 illustrates another lens system Which is adapted to be energized with ArC. This organization comprises three constituent'coils, theV central one of these coils indicated at M4 containing the same number o-f turns, asith'e two.- outer coils Ma and Ms combined. "IIhesaid. central coil M4 by Way of terminals 'i wand la,

is fed with an A. C. which has a phase displacement of. 90 degrees in relation to the A; C. fed toitheouter. coils throughthe terminalsand 8a. Inside.4 the scopeA of the invention,.more than two, say, n coils could be used, each of the coils 25, being traversed. bythecurrentof a phase of an n-phase supply line or network. The coils coordinated to the various phases could also be divided or splitVandf, similarlyas shown for the coils M3 and Ma, Fig. 2, they couldbe disposed upon bothn sides of one or. more coils which carry a current of different phase. So far as the relative spacing ofV the.coils.is concernedthis should be kept in mind, as. already pointed out, that the lens fields. of the constituent coils vshould y not mutually react, for inthe same measure as such mutual reaction occurs, the focus or pic-v ture sharpness will suffer, that is, be distorted, to a certain degree. In order that as satisfactory anrimage as possiblev may be secured, this 4,0,i general rule will have tol be observed that the distance of the coils in axial direction does-not` become lessi than: 1/3 the inside coil diameter. The coilsmay also be individually shielded to` avoid interaction.

The. arrangements ashereinV before described will'. generally be found.` serviceable for electronF optic imaging in which. the rotation of the electron paths on' traversing.` the various coils does not disturb, that is to say, for. instance, in the imaging of electron sources or apertures ofdiaphragms in picture scanning or picture rfc-creator# tubes, in oscillographic` tubes,. orV thev like. If the rotation dealt With is such troublesome,.for instance, inthe imaging of a photo-cathode of -largearea as used inwhat is known'. as picture converters or transducers,.arrangements must be made sothat the rotation of the imageV occurring at the frequency of the A..C`. Will be compensated. This is accomplished by causing the cur.u rent of a certainphase to introduce rotational actionsvvhich` will neutralize one another.

An exemplifiedembodiment of this nature is illustrated inFig. 4, M5, andMs andLMe and Mfs designate the coils which are traversed by A. C.

of a definite phase. All of the coils arevvound ini the same sense. The coils pertaining to one and the same phase, however, are traversed by current in contrary direction, in a Way as'` indi(' cated byithe arrows. In this way, ifthe in- -tensities of the coil fields be properly chosen,

perfect compensation of' rotation is achieved.

In Fig. 5, I- have shown schematically the methodofobtaining the alternating currents in' phase quadrature. A source of alternatingcur- 75..rent.. 3l. mayY be supplied'y directly to.v 'one of; the

coils, such as M1 through the terminals Si. A phase shiftingnetwork or phase shifter such as Well known in the art may be connected in parallel with the source of alternating current 3| to shift the alternating current 90 degrees, the phase shifter being represented diagrammatically by the block 33, since-these are Well known in the art. The output of thev phase shifter is then supplied through the terminals S2 to the Vsecond of the tWo coils Mz in Fig. l. 10

Instead of lens assemblies which comprise electromagnetic lenses, it would, of course, also be feasible'touse electrostatic lenses operated in a corresponding manner with alternating potentials; theelectrostatic lenses being formed by the 15 eld set up between two or more lens electrodes as shownv in Fig.6.

Inlig. 6-.is shown the electron gun 4| for producing a beam of electrons and the lens electrodes 153, 15, 47 and 49 enclosed Within an en- 20 velope 5l. Suitable leads are provided fo-r supplying one alternating current potential Si to the. electrodes d3 and/l5, while an alternating current potential, in quadrature to Si is supplied from the source Sato the electrodes 41 and 49. 'I'here 25.= is thus provided alternating electrostatic. fields which are nphase quadrature.

Having describedmy invention, what I claim 1s:

1. The method of focusing'abeam; of electrons. 30 which comprises producing an alternating focus-1 ing magnetic field having axial symmetry aboutthe beam of electrons, and producing a second alternating focusing magnetic eld longitudinally displaced from the first produced field and in 35 phase quadrature with the first produced eld,. said second produced field having axial symmetry with the electron beam.

2. lIfhe method of focusing a beam of ,electrons-i Which comprises producing.,l anvalter-nating focus- 40.,

ing magnetic field having axial symmetry about the beam of electrons, and producing a second alternating focusing magnetic field of a magnitude equal to the magnitude of the first produced field longitudinally displaced from the first pro- 45,

duced field and in phase quadrature With the first` produced field, said second produced field having axialsymmetry with the electron beam.

3. The method of focusing a beam of electrons which comprises producing. an alternating focus- 50A ing f eldhaving axial symmetry about the beam of electrons, and producing a second alternating' focusing field longitudinally displaced from the rst produced field and in phase quadrature With l the first produced eld, said second produced 55- eld havingv axial symmetry With the electron` beam.

4. The methodoffocusing arbeam of electrons' which comprises Y producing an` alternatingv focus ing field having axial symmetry about the beam 60 of electrons, and` producing a second'alternating" focusing eldfof a magnituder equal to themag'- nitude of the first produced eld longitudinally displaced from the irst produced field and in phase quadrature with the rst produced field, said second produced field having axial symmetry with the electron beam'.`

5. The method of focusing a beam of electrons. which comprises producing an alternating focus- 70 ing electrostatic eld havingY axial symmetry about the beam of electrons, and producing a second alternating focusing electrostatic eld longitudinally displaced from. the first-produced.

field. andin phase quadrature withthe rst pro-V f` for producing a beam of electrons, means for pro'-` ducing an alternating focusing magnetic field duced field, said second produced field having axial symmetry with the electron beam.

6. The method of focusing a beam of electrons which comprises producing an alternating focusing electrostatic iield having axial symmetry about the beam of electrons, and producing a second alternating focusing electrostatic eld of a magnitude equal to the magnitude of the rst produced field longitudinally displaced from the first produced eld and in phase quadrature with the rst produced fie1d,lsaid second produced eld having axial symmetry with the electron beam.

7. A cathode ray tube system comprising means for producing a beam of electrons, means for producing an alternating focusing magnetic field having axial symmetry about the beam o-f electrons, and means for producing a second alternating focusing magnetic field longitudinally displaced from the first produced field and in phase vquadrature with the rst produced field, said second produced field having axial symmetry With the electron beam.

8. A cathode ray tube system comprising meansr having axial symmetry about the beam o-f electrons, and means for producing a second alternating focusing magnetic iield of a magnitude equal to the magnitude of the rst produced field longitudinally displaced from the rst produced eld and in phase quadrature with the rst produced field, said second produced field having axial symmetry with the electron beam.

9. A cathode ray tube system comprising means for producing a beamy of electrons, means including an annular coil for producing an alternating focusing magnetic eld having axial symmetry about the beam of electrons and means including a second annular coil for producingy a second alternating focusing magnetic iield longitudinally displaced from the rst produced field and in phase quadrature with the rst produced eld, said second coil being longitudinally displaced from said first named coil by a distance greater than one third the annular diameter.

' WILLY SCHROEDER.

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