US2947902A

US2947902A - Magnetic grid

Info

Publication number: US2947902A
Application number: US835158A
Authority: US
Inventors: Richard F Post
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-08-20
Filing date: 1959-08-20
Publication date: 1960-08-02
Anticipated expiration: 1977-08-02

Description

Aug. 2, 1960 R. F. POST 2,947,902

MAGNETIC GRID Filed Aug. 20, 1959 2 Sheets-Sheet 1 33 INVENToR.

.I 347 BY R/CHARD F. Posr ATTORNEY.

Aug. 2, 1960 y R, F, POST 2,947,902

MAGNETIC GRID Filed Aug. 20, 1959 2 Sheets-Sheet 2 A T TORNE Y the* lack of same.

United States Patent 2,947,902 MAGNETIC GRID Richard F. Post, Walnut Creek, Calif., assig'uor to the 'United States of America as represented by the United States Atomic Energy Commission Filed Aug. zo, 1959, ser. No. 835,158

's claims. (Cl. 313-167) The present invention relates to an improved electronic grid adapted for use in the control of electrical discharges in vacuum or gaseous atmospheres and, more particularly, to an electronic grid employing magnetic forces for controlling the passage of charged particles.

This application is a continuation-in-part of my co- Patented Aug. 2, 1960 and the applicability of the present invention is in no wise limited to more conventional devices such as herebefore enumerated, the present invention being particularly useful in a device of the type disclosed and claimed in'my copending patent application Serial No. 816,351.

It is an object of the present invention to provide electric discharge control means producing a magnetic field of a. configuration to control by the magnitude thereof the passage of charged particles therethrough.

It is another object of the present invention to provide an electronic grid producing a magnetic field of pending application Serial No. 682,265, led September 5, 1957, now abandoned. p

Conventional grids or control electrodes employed in such as vacuum or gas tubes and more generically in any discharge device operate to produce a desired electrostatic iield thereabout for applying forces of desired magnitude and direction to charged particles in the eld thereof. Such grid fields are produced by the application of a charge or potential to the grid structure whereby the grid is surrounded by a predeterminable electrostatic eld. This conventional type of electronic grid has found wide acceptance and is employed universally in the control of electric discharges through space; however, certain fundamental limitations in this type of grid control have precluded the use thereof under certain circumstances.

The aforementioned limitation of conventional electrostatic grid control is based upon the fundamental characteristic of polarity found in all electrostatic fields. -It is this liield polarity which provides the effectiveness thereof and yet also results in the limitation upon the applicability. Thus a negatively charged grid having a corresponding electrostatic field thereabout operates to apply a repelling force to electrons, in such as a discharge tube for example, land the magnitude of the charge determines the magnitude of the force so as to control the number of electrons passing therethrough. However, in the instance such as above where a gaseous atvmosphe're surrounds the grid, ionization of the gas by l electrons produces positively char-ged ions that are thus oppositely affected by the grid field, so as to be attracted toward the grid. A certain number of such ions actual- -ly strike the grid to produce a grid drain while many others attracted thereto form a sheath of positive charges about the grid to effectively cancel the grid eld so that it no longer controls discharge. 'I'his phenomenon is Well known and it is accepted in gaseous discharge devices, such as thyratrons, ignitrons, and the like, that grids are only operable to prevent discharge but exert no control thereover after discharge initiation and consequent ion production. Further, conventional grids in gas tubes or the like are ineffectual to cut olf the tube or cease tube conduction and it has been heretofore necessary to lower the plate potential to cut olf discharge in such devices.

It is widely appreciated in the electronic arts that great advantage wouldA lie in the provision of complete grid control of gaseous discharge devices and', in fact, the applicability of such devices has been limited Iby The present invention provides such a grid. Former problems of controlling and stopping gaseous discharges are obviated by the present invention,

variable intensity for the control of charged particle passage therethrough.

It is 'a further objectof the present invention to provide an electronic control member employing magnetic rather than conventional electrostatic fields for controlling electricaldischarges.

It is yet another object of the present invention to provide an electronic control electrode for similarly controlling the passage of charged particles of either polarity.

It is still another object of the present invention to provide a control electrode for gaseous discharge devices which retains control during discharge.

Numerous other advantages and possible `objects of the invention will become evident from the following description of a single preferred embodiment of the invention chosen for illustration and depicted in the accompanying drawing, wherein:

Figure 1 is a plan view of an electronic grid embody- -ing the present invention;

Figure 2 is a schematic illustration of a portion'of the invention in section including a representative magnetic iield configuration depicted by dashed lines and charged particle paths indicated by dotted lines;

Figure 3 is a plan view of an alternative embodiment of the grid of the present invention; and

Figure 4 is a perspective view of an ignitron having the embodiment of the grid of Figure 3 mounted in operative position therein.

Considering now a simple embodiment of the invention and referring to Fig. 1 of the drawing, there is provided as a grid structure 11 a planar double spiral of electrically conducting Wire 12 or the like and comprising an outer spiral 13 extending from an external terminal 14 inward substantially to the center of a circle formed by the outer spiral turn. A second spiral 16 of wire is formed in the same plane as the first and extending from the iirst spiral end at the center outwardly in equal spacing between turnsof the iirst spiral to a second terminal 17 located outside the spirals. There will thus be seen to lbe formed a double spiral grid struc'- ture 11 wherein each turn of the second spiral is equally spaced from a pair of turns of the rst spiral. The wire 12 moreover is preferably of low resistance in order that a Wide range of current magnitudes from zero to a relatively high value may Abe readily passed therethrough.

Energization ofthe grid is accomplished by a power vsupply 18 having a pairof output terminals separately connected by leads 19 and 21 to the

spiral terminals

14 and 17. This power supply will be seen to be connected `across the ends of the double spiral so that the two serially connected

spirals

13 and 16 form a closed path between the power supply terminals for current flowA therethrough. Provision is made for` controlling the amount of current owing through the grid, as for example by means integral with the power supply and controlled by a knob 22 thereon or a rheostat 23 connected in circuit with the grid and power supply.

Considering now the operation of the present invention, Iattention is first -invited to the fact that the grid itself comprises a pair of conducto-rs disposed in spaced parallel relation and having current flowing therethrough in opposition. The significance of this situation is best understood by reference to Fig. 2 wherein alternate conductors will .be seen to carry current inthe same directions. Thus -in Fig. 2, wire 13 carries current rin one direction, say out of the plane of the drawing, and alternate wire i6 carries current in the opposite direction, sayV into the plane of the drawing. Current passing through a wire establishes `a magnetic field encircling the'V Wire with the field direction being dependent upon thev direction of current flow so that each wire is surrounded by a magnetic field, as illustrated by the dashed lines H in Fig. 2 and extending in the direction oi the arrows thereon. It will be seen from Fig. 2 that as adjacent wire portions carry current in opposite directions, the magnetic fields between each wire `are additive.

As regards the action of the magnetic `fields established by the grid, consider a stream of charged particles 31 approaching the grid. As any moving charged particle enters a magnetic lield, it is `acted upon by a resultant force perpendicular to the direction of particle motion and perpendicular to the magnetic field so that here it is seen that a charged particle entering the grid field is deflected. The degree of particle deflection is dependent in part upon the magnitude of the magnetic field and with a sufliciently strong field the particle loses substantially all motion toward the grid and is in effect turned away from the grid. As the magnitude of the magnetic field about a current carrying conductor decreases with distance from the conductor and is determined by the amplitude of the current in the conductor, it thus follows that the field strength between grid conductors isV a function of the current through these conductors. With a very low grid current, only `a weak magnetic iield exists between the grid conductors so that charged particles approaching the grid in any direction but substantially directly toward the conductors experience only a slight deection so that they pass through the grid. Increasing the grid current 4reinforces the magnetic eld about the conductors thereof so that a lesser space' between coriductors is available for particle passage without such deilection as would prevent passage of the particles through 'the grid. A still further increase in grid current additionally strengthens the grid field until the field is suiiciently strong even directly between the grid conductors so that substantially fall approaching charged particles are materially 1deflected and do not pass through the grid, and the grid may be said to be at cut-off. Inasmuch as the grid wire 12 is of low resistance, the power supply 18 maybe of la practicable size and yet have an upper limit of sutiicient proportions to produce an upper grid current magnitude at least as great as that corresponding to cut-off. The grid current may hence be varied over a wide range of lmagnitudes by adjustment of knob 22 or rheostat 23 to correspondingly vary particle iiow through the grid 11 from a maximum at zero grid current to zero at cut-off grid current.

Regarding further the grid action of the present invention, it is noted that the grid action on approaching charged particles is the same regardless of particle polarfity. Thus the grid impartially controls the passage of charged particles regardless of the charge polarity therefof. Even though the direction of deflection of positively :and negatively charged particles is opposite upon enter- :ing the grid eld, yet the same result is obtained insofar las the grid action is concerned, for particles of either polarity are deflected not to pass through the grid.

It is to be noted that the particular coniiguration shown in Fig. l is only illustrative of the present invention and a multitude of different grid wire coniigurations are possible. in this respect, reference is made to Fig. 3 wherein a grid '31 .is illustrated as comprising a single folded grid wire 32 having a zigzag configuration. This grid 31 has alternate portions or sections of the wire thereof extending in substantially opposite 4directions so that a current liowing through the grid actually flows in opposite directions in space through adjacent grid sections. Grid energization is accomplished from a power supply 33 connected through a switch '34 across the grid. With the particular circuit shown herein, the grid would be effective only to gate a discharge in such 'as an ignitron or other tube. With the switch 34 closed `a suicient current flows through the grid to establish a relatively strong magnetic field thereabout preventing the passage of charged particles therethrough. With the lswitch 34 open no grid energization is provided so that the Vgrid exerts no influence upon charged particles passing therethrough. With this circuitry a pulsed grid operation is contemplated wherein a discharge is periodically gated by the gri-d and the switch may, of cou-rse, comprise such as an electronic valve controlled, for example, by some desired electrical phenomena associated with discharge passing through the grid. Although alternative circuitry is shown in Fig. 3, the grid structures of Figs. l and 3 are equally operable with either illustrated circuit, `as well as with other energizing and control circuits.

Considering now the manner in which the magnetic grid may be operatively employed in a gas iilled tube, eg., an ignitron, to effectually precisely cut oli the tube or otherwise exert control over the discharge therein, and referring to Fig. 4, there is provided therein an ignitron 36 having a sealed low pressure envelope 37 of insulating material with an inwardly stepped anode supporting portion 38 at its top and a re-entrant cathode pool forming portion 39 at its bottom end face. An anode 41 is suspended transversely in the upper regions of the envelope by means of an electrically conducting support rod42 extending longitudinally through portion 38 and externally Secured thereat to an electrically conducting cap 43 engaging same. In the annulus formed at the bottom of the envelope between re-entrant portion 39 and the outer wall of the envelope there is contained mercury, forming a cathode pool 44. VAn igniter 46 is immersed in the pool and suspended by a lead-in conductor 47 secured thereto and leading exteriorly of the envelope through the recessed face of re-entrant portion 39. A lead-in conductor 48 is immersed in the pool 44 and similarly led exteriorly of the envelope through portion 39. All of the foregoing structural arrangement is conventional in ignitrons and the` ignitron 36 may be connected in a circuit in a conventional inanner to switch large amounts of current by connection of the anode cap 43 to a more positive potential than the cathode lead-in conductor 48. A trigger pulse may then be applied to igniter lead-in conductor 47 to initiate conduction through the tube. Once conduction is established in the conventional ignitron, however, there is no provision for precisely gating off the tube, it Vbeing possible to only terminate conduction in an unprecise manner by lowering the anode potential. In addition, the amount of current flowing through the ignitron cannot be controlled other than by pre-selection of the constants of the circuit in which employed. I'hese difficulties of a conventional ignitron arel overcome by a magnetic grid 49 in accordance with theV present invention, e.g., similar to the zigzag grid 31 previously described, disposed transversely of the ignitron envelope 37 axially intermediate cathode pool 44and anode 41 in the path of the discharge established therebetween upon pulsing of the igniter 46. More-specifically, the magnetic grid 49 may be secured in the above-noted position within the envelope by fusing to the'interior walls thereof or any other suitable attachment method familiar to those skilled in the tube art. The`ends of conductor 51 forming grid 49 are led exteriorlyv of the envelope `as shown at 52, 53 respectively, tor facilitate series connection of the grid in an energization circuit such as either of those depicted in Figs l'or 3 and hereinbefore described. With the circuit ofFig. 3 connected to grid 49, for example, subsequent to initiation 0f `,conduction through the ignitron, the tube may be gated off magnetically with substantial precision by the flow of a current pulse through the grid. Alternatively, with the circuit of Fig. 1 employed with grid 49, the current flow through the ignitron may be varied as desired in response to variation of the flow of magnetic field generating current through the magnetic grid.

As previously stated, the grid action of the present invention is dependent upon the establishment of magnetic fields that in whole or in part deflect and ultimately repel approaching charged particles of either polarity. As seen from Fig. 3, it is not necessary that the fields be established by currents flowing exactly in parallel opposition in space for satisfactory field congurations are possible with somewhat unparallel current fiow. With a greater grid wire displacement a larger current therethrough is, of course, required to produce a desired magnetic field strength half way between same and thus an increased current ow can be made to compensate for lack of parallelism in current paths, the term substantially parallel being herein employed to encompass those configurations such as illustrated in 1Fig. 3 wherein the establishment of suitable fields are yet possible without exactly parallel grid sections.

There has been described above a novel magnetic grid having a wide range of utility and a multitude of possible structural variations within the scope of the invention land thus it is not intended to limit the present invention by the foregoing description but instead reference is made to the following claims for a precise definition of the invention.

What I claim is:

1. A magnetic grid for controlling charged particle discharge comprising at least one low resistance grid Wire having more than two sections spaced apart and extending in substantially opposite directions in the same plane with said grid Wire'adapted for electrical energization to pass current therethrough of sufficient magnitude that magnetic fields established about adjacent sections of said wire deflect charged particles from the grid.

2. A magnetic grid comprising a uniplanar double spiral of low resistance grid conductor with a first spiral turning inward to the center and a second spiral turning outward from connection to the first spiral at the center thereof and spaced equally between turns of said first spiral, and means forcing a controllable electric current through said double spiral to establish magnetic fields thereabout that are additive between adjacent grid conductors to deflect charged particles approaching the grid.

3.l A magnetic control grid for controlling the passage of charged particles comprising means defining a low resistance electrical current path with alternate spaced portions in opposite directions and in the same plane, and means forcing a controllable electric current through said path for establishing additive magnetic fields between adjacent portions thereof for defiecting approaching charged particles in proportion to the magnitude of current 'flow through the path, said means having an upper controllable current limit of at least the current corresponding to magnetic deflection of all charged particles from paths through the plane ofthe current path portions.

4. A magnetic control grid for controlling passage of charged particles comprising folded conducting means defining opposed low resistance electric current paths in spaced substantially parallel disposition in the same plane, power supply means connected to energize said conducting means, and control means for controllably pulsing the current flow through said conducting means and establishing a current pulse of suicient magnitude therein to magnetically gate ofi the passage of particles through the plane of the conducting means.

5. In an ignitron having at least a cathode pool and anode disposed at opposite ends of a sealed low pressure envelope with an igniter immersed in the cathode pool and separate input leads extending from the cathode pool, anode, and igniter exteriorly of the envelope, the combination comprising a magnetic control grid disposed transversely of the envelope intermediate the cathode pool and anode and comprising folded conducting means defining opposed low resistance electric current paths in spaced substantially parallel disposition and in the same plane with each end of the conducting means leading exteriorly through said envelope for series connection to a current source.

References Cited in the le of this patent UNITED STATES PATENTS