US2821648A

US2821648A - Ion deflection thyratron

Info

Publication number: US2821648A
Application number: US348981A
Authority: US
Inventors: George W Baker
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-15
Filing date: 1953-04-15
Publication date: 1958-01-28
Anticipated expiration: 1975-01-28

Description

Jan. 28, 1958 G. w. BAKER 2,821,648

10N' DEFLECTION THYRATRON Filed April 15, 1955 3 sheets-sheet 1 FIG.2

5 Sheets-Sheet 2 G. W. BAKER ION DEFLECTION THYRATRON Wunsch.

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1N V EN TOR.

Jan. 28, 1958 G. w. BAKER 2,821,648

ION DEFLECTION TI-IYRATRON 3 Sheets-Sheet 5 Filed April l5, 1953 hao 4o 50i. soh POTEA/T/ALS FOR CoNTRoL ELECT/MDE A 001 0LV o9 og ov os: oa ol o sg January 'www12/0d 37m/mod wub/Q NVNTOR 8 y? MEM@ Bf M5L/Mm Fles United States Patent O ION DEFLECTION THYRATRON George W. Baker, Stamford, Conn.

Application April 15, 1953, Serial No. 348,981

7 Claims. (Cl. 313-196) This invention relates to gas-filled tubes, particularly to thyratrons, and has for its object the provision of a new type of thyratron affording new and useful control characteristics. According to the invention, thyratrons of this new type are provided with ion deflection means and may therefore be termed ion deflection thyratrons.

The invention provides a new method of controlling the firing or activation of thyratrons. Whereas ring of an lordinary thyratron is effected only under control of a change in the magnitude of the potential established .around the 4cathode as a result Iof the potentials of the anode and of the other electrodes, my invention introduces an additional, new factor of orientation or direction of the electric field established in the space between the anode region and the cathode. According to the invention, the orientation of this electric field will control the defiection of positive ions from the cathode vicinity to determine whether the tube will fire upon an increase in the magnitude of the potential established around the cathode.

The firing of a thyratron depends upon positive ions reaching the vicinity of the cathode in sufficient quantity to reduce appreciably the negative space charge around the cathode. These positive ions are formed in the anode region by electrons that flow from the cathode to the anode colliding under ionizing conditions with the molecules of the gas contained in the tube and by the further -collision of the products of the ionization with more, unionized molecules.

In the before-firing phase of the tube, a small electron current flows from the cathode to the anode and a small portion of the ions formed in the anode region reach the vicinity of the cathode, the major portion being collected by the shields and grids. The effect of each positive ion reaching the cathode vicinity is to neutralize the space charge produced by a particular number of electrons, resulting in a reduction of the space charge and an increase in the electron current flow from the cathode. -In the before-firing phase of the ordinary thyratron, the increase in electron flow from the cathode causes additional positive ions to reach the cathode vicinity, but too few to sustain the increase in electron flow. The current flow in this phase is consequently stable and is greater than if no gas were present.

If the electrode potentials are altered to increase the initial flow of electrons from the cathode to the anode, the number of ions -formed in vthe anode region is increased at a rate exceeding the rate `of increase of the initial electron fiow. In the conventional thyratron, the increased rate of production of the ions in the anode region produces a resulting increase in positive ion current to the cathode at a rate greater than the increase in the initial electron current. When the incremental value of positive ion current to the cathode is sufficient or is greater than required to sustain the incremental electron fiow from the cathode, the neutralization of space charge by positive ions and the increase in electron current beice come accumulative, and the electron current rises to a high value and the thyratron is said to have fired. In thyratrons as previously known, this effect is initiated by appropriate alteration of the control grid potential for producing a suitable increase in the magnitude of the electric field `at the cathode.

Departing from conventional principles of thyratron firing control, my invention provides for firing to be controlled by selective orientation of the electric field in the space between the cathode and the anode region, whereby an alteration of the electrode voltages to increase the initial flow of electrons from the cathode is or is not effective to cause ring, depending on the orientation of this electric field. According to the invention, the thyratron is provided with a novel control electrode system which, in addition to controlling the magnitude lof the electric eld .at the cathode, also controls the orientation of the electric field in the space between the anode region and the cathode. With this novel control electrode system, it'y is possible to employ control electrode potentials that permit a comparatively large initial flow of electron current from the cathode and, consequently, the formation of a comparatively large number of positive ions without firing the thyratron, because the orientation of the electric field in the space between the anode region and the cathode can rbe such as to deflect the positive ions away from the direction of the cathode and to be collected on the other electrodes.

More specifically, according t-o the invention, a thyratron is provided with a plurality of control grids to which potentials may be separately applied to control the magnitude of the electric field at the cathode and, also to control the orientation of the electric field in the space between the anode region and the cathode to determine whether the tube shall fire.

Other objects of the invention will be brought out in the following parts of the specification and will be evident from the drawings which show by way of illustration an exemplary embodiment of the invention.

Fig. 1 is .a perspective view of the new thyratron, with parts broken away and sectioned for clarity of showing.

Fig. 2 is a plan section of the tube, with the envelop omit-ted, and indicates the tube in a biased, zero signal phase.

Fig. 3 is a similar View, indicating the electrical conditions in the immediately-before-firing phase.

Fig. 4 is also .a similar View but with the electric field between the anode region and the cathode oriented, as indicated by the equipotential lines, to preclude firing.

Fig. 5 shows control characteristic curves for the new thyratron.

Fig. 6 is a typical circuit arrangement showing biasing sources by block diagram.

The illustrative embodiment of the invention includes within an envelop t, a filament cathode K, an anode P, two separate and conductively unconnected control grids A and B respectively located at opposite sides of the path of positive ion ow from the anode region to the cathode vicinity, and a shield S around the anode, cathode, and control grids. The shield S is integrally provided with a baffle 1I), formed with a window 10a, between the anode region and the electrodes K, A and B. Window 10a is in the path of positive ion flow from the anode region and between electrodes A and B to the cathode vicinity, limiting the flow to this path and also limiting the number of positive ions emerging from the anode region.

The firing of this thyratron is controlled by the magnitude of the electric field at the cathode and by the orientation of the electric field, indicated by the equipotential lines in Figs. 2, 3 and 4, between the anode region and the cathode. As shown in Fig. 2, with both grids A and B at like potentials of -3 volts, they orient the electric field in the space between the anode and the cathode symmetrically about the axis of'ifl'owofwpsitive ions toward the cathode. The positive ions are thus prientedhinthe direction ofthe cathoderbut with, the gridsfA and B at .-3 volts the electriceldat the' cathode is ofinsutiicient magnitude to cause iiring. In Fig. 3, .the grids A and B are also at equal potentials, producing -similar orientation of the electric field in theA space between the anode region and the cathode, but the grid potentials have now been increased to l volt, thereby increasing the magnitude of the electric field at the cathode suiciently to cause tiring to be initiated.

,Fig 4 shows the eleet on the electric tield between the anode region and the cathode of unequal potentials on the control grids A and B. This electric field is .now oriented unsymmetrically so as to deect the positive ions away from the direction of the cathode. As an example, grid B is at a potential of -|8 volts while grid A remains biased at -3 volts. The increased potential on grid B increases the magnitude of the electric field at the cathode, so that there is an appreciable electron current from the cathode and a consequent forma tion of a large number of positive ions in the an'ode region. However, with the orientation indicated in Fig. 4, the positive ions emerging from the anode region window a are so strongly urged toward the grid A that very few reach the vicinity of the cathode and the tube does lnot tire. Thus, it is seen that a large positive potential may exist on one or the other of the control electrodes A and B and yet the tube will not be permitted to re if the electric eld between the anode region and the cathode is so oriented by the difference in potential between the control electrodes as to deflect the positive ions away from the cathode vicinity.

The illustrative tube is assumed to contain argon for which the ionizing potential is approximately 16 volts. The voltages indicated for the anode and shield are typical. in Fig. 5, three control characteristic curves are plotted for the illustrative tube. Curve #l is with reference to various potentials measured at the control electrodes A and B or as though they were signal potentials applied through zero resistances. Curve #2 is with reference to signal potentials applied through 100,000 ohm resistances to the grids A and B. Curve #3 gives the control characteristics with reference to signal potentials applied through respective l megohm resistances to the control grids. The dot-and-dash line ax indicates the axis of travel of the positive ions when not deflected from their AWay to the cathode. The change in position and shape of these curves with change in impedance of y the signal voltage supply results from the currents that ow in the signal electrodes A and B. When a control electrode A or B is negative by a volt or more, a positive ion current ows to this electrode, rendering it less nega tive than the voltage measured at the voltage supply side of the impedance. When a signal electrode is positive, an electron current ows to the electrode and makes it less positive than the voltage measured at the voltage supply side of the impedance. Curve #3 shows that it electrode A, for instance, is supplied with a bias of -3 volts or more, a signal as large as l0() volts or more applied through (or from a source impedance of) l megohm will not re the tube. The flow of current in the control electrede is an important factor in attaining some ot the useful characteristics of the tube in response to control signals, as is indicated by consideration of its use as a coincidence thyratron. Assume the control grids A and B are supplied each with a normal bias of -3 volts and that signals are applied through l megohm resistances to the control grids. Curve #3 shows that a positive signal of l0() volts or more applied to one or the other of the grids A and B does not tire the tube, but a signal of less than 2 volts applied coincidentally to the control grids will tire the tube.

The coincidence thyratrou has a large teld of use.

Some of the coincidence circuits to which this thyratron can bewpplied"ar'cosmic ray telescopecirciuts, and circuits of electronic computers, pulse analysis circuits, radio activity measurements by coincidence counters in the presence of noise, interlocking safety circuits and signal circuits.

The use of the tube is not limited to coincident circuits. Curve #l (Fig. 5), for instance, shows that the tube can be used as a thyratron that tires on a negative signal when a positive bias is applied to one of the grids A and B. As an example, assume grid A at 0 volts and grid B at 5. volts. The intersection of the coordinates of these grid values is outside the curve #1, indicating that the tube will not tire. If a negative signal is now applied to grid B to depress its potential to 3 volts, the tube wil tire. It is also evident that the tube will fire if a positive signal increases the potential of grid A from 0 volts to about 3 volts. These examples indicate that the tendency of the tube to tire increases as the orientation of the electric field in the space between the anode region and the cathode approaches symmetry with respect to the axis of travel which the positive ions would take toward the cathode if undetlected.

Any tendency for the tube to tire when one control .grid is biased below critical potential (-3 volts in the illustrative embodiment) and the other grid is increased in .potential can be eliminated by suitably limiting the fnuinberof positive ions emerging from the anode region.

It is not intended moreover to tire the tube by increasing the potential on one grid to the ionization potential of the gas in the tube, since the other grid would then have no control over the tiring.

' The new principle of control of thyratron tiring, the control of the orientation of the electric field to dellect 'positive ions away from the vicinity of the cathode, can

be applied to tube structures beside the one shown in Figs. 1 to 4. The control electrodes are not limited to two, and one or more of the control grids may be a composite electrode, such as a rod surrounded by a mesh operating at a different potential than the rod, or shields may be interposed between the signal electrode and the remainder of the tube, or the grids may be so formed and the tube so constructed as to eliminate the need for any shield. Other variations from the embodiment specifically disclosed may be made by those skilled in the art without departing from the invention. It is therefore the intention to be limited only as indicated by the following claim.

` :I claim:

1. kIn controlling a thyratron type tube which has an venvelop containingean ionizable medium, an anode, an electron emitting cathode, and at least two conductively unconnected cathode emission control electrodes respectively having portions interposed between the anode and cathode and spaced to opposite sides of the path of positive ion flow from the anode region to the cathode vicinity and at least `one of. which control electrodes may be at or above a critical potential inducing a degree of electron emission from the cathode and consequent formation of positive ions of said medium adequate on ow in said path to the cathode vicinity to initiate tube tiring; the method of further controlling tube tiring which consists in electrostatically deflecting the positive ion tlow from said path and away from the cathode vicinity by producing an electrostatic force across said portions of the electrodes and transversely of said path through the imposition of a suitable potential difference between said electrodes, whereby tube firing is restrained until the deection force is reduced by decreasing the potential difference between the electrodes sufficiently to enable adequate flow of the positive ions along said pathto the'cathode vicinity to initiate tube iiring. v

2. In controlling a thyratron type tube which has an envelop containing-.an ionizable medium, an anode, an electron emitting cathode, and a pair of interposed conductively unconnected cathode emission control grids spaced apart laterally of the path of positive ion ow from the anode region to the cathode vicinity to afford a passage between them for said ion ow and either or both of which grids may be individually at potential levels adequate to permit sufficient electron emission from the cathode and consequent formation of positive ions of said medium effective on flow in said path to the cathode vicinity to initiate tube tiring; the method of further controlling tube firing, while a rst of said grids is at such adequate potential level, which consists in electr-ostatically deflecting the positive ion flow from said path by imposing on the other grid a potential level sufficiently different from that of said first grid to develop an electrostatic force across said grids transversely dellecting the ion flow from said path and away from the cathode vicinity to an extent precludiug tube firing until the potential level of said other grid is altered to reduce the potential difference between the grids and thereby diminish the electrostatic deflecting force sufficiently to permit positive ion iiow to the cathode vicinity to a degree effective to initiate tube firing.

3. A thyratron type tube containing an ionizable gaseous medium, an anode, a hot cathode, and a tiring control electrode system includingr at least two separate ring control electrodes respectively provided between the anode and the cathode with portions spaced apart laterally to opposite sides of the path of positive ion flow from the anode region to the cathode vicinity, the two control electrodes coacting in response to a suitable difference in their respective potentials during the pre-firing phase to produce across their respective portions an electrostatic force detlecting the positive ion ow transversely from its path and away from the cathode vicinity to an extent precluding reversal of the tube to its fired phase until the potential on one or both of the control electrodes is altered to reduce the difference in their potentials and, thereby the electrostatic dellecting force sufficiently to permit the positive ions to reach the cathode vicinity and trigger the tube to its tired phase, and a plurality of separate sources of potential respectively coupled to the two control electrodes to impress them separately with desired potentials either at a high relative magnitude suitable to preclude tiring or at an appropriately lower relative magnitude to permit firing.

4. A thyratron type tube containing an ionizable medium, an anode, a cathode, and at least two separate firing control electrodes respectively provided between the anode and the cathode with portions spaced apart laterally to opposite sides of the path of positive ion flow from the anode region to the cathode vicinity, the two control electrodes acting according to their potentials relative to the cathode to govern electr-on emission and resulting positive ion formation as one factor in the control of tube tiring, the two control electrodes further coacting with each other in the pre-firing phase to develop across their respective portions an electrostatic force determined by the difference in potentials on the two control electrodes for variably deflecting the positive ion flow transversely from its path and away from the cathode vicinity as a second factor in the control of tube firing, and a plurality of sources of potential respectively coupled to the two control electrodes to impress them individually with desired potentials conjointly controlling tube tiring in accordance with a combination of the rst and second factors.

5. A thyratron type tube containing an ionizable gaseous medium, an anode, a hot cathode, and at least two separate firing control electrodes respectively provided between the anode and the cathode with portions laterally spaced apart to opposite sides of the path of positive ion ow from the anode region to the cathode vicinity, means for biasing a rst of said control electrodes relative to the cathode at a level inducing a degree of electron emission from the cathode for producing sufficient positive ions in the anode region capable upon reaching the cathode vicinity to trigger the tube to its fired status, and other means for applying potential to the other control electrode effectively biasing it relative to said first control electrode during the pre-tiring phase to develop an electrostatic force across said portions of the control electrodes deflecting the positive ion iow transversely from its path and away from the cathode vicinity to an extent precluding the positive ions from triggering the tube to red status pending change of the potential on the said other control electrode to reduce its bias relative to said first control electrode.

6. A thyratron type tube containing an ionizable medium, an anode, a cathode, and a pair of separate tiring control electrodes interposed between the anode and the cathode and spaced apart laterally to opposite sides of the path of positive ion flow from the anode regi-ou to the cathode vicinity, either or both of which control electrodes may be at a potential relative to the cathode adequate to induce sufficient electron emission from the cathode and consequent formation of sufficient positive ions in the anode region to trigger the tube to fired status upon reaching the cathode vicinity, the two control electrodes coacting during the pre-firing phase while a first is at such adequate potential and the other at a potential sufficiently higher or lower than that on the iirst control electrode to produce an electrostatic force across the control electrodes deflecting the positive ions transversely from the cathode vicinity to an extent precluding them from triggering the tube to red status, means for placing said rst control electrode at said adequate potential and other means for selectively impressing the other control electrode either with a potential suiciently higher or lower than that on the first control electrode to preclude tube firing or with a potential less diderent than that on the rst control electrode to an extent permitting tube firing.

7. A thyratron type tube containing an ionizable medium, an anode, a cathode, and a pair of intervening control grids spaced apart laterally to afford a passage between them for positive ion flow from the anode region to the cathode vicinity, -either or both of said control electrodes coacting with the cathode while at adequate potential relative to the cathode to induce sufficient electron emission from the cathode for producing positive ions in the anode region adequate on ow between said grids to the cathode vicinity to trigger the tube to its fired status, the two grids coacting during the pre-firing phase while a rst grid is at said adequate potential and the other grid at a sufficiently higher potential to develop an electrostatic force across the grids deecting the positive ion ow transversely from the cathode vicinity to an extent precluding firing until the potential level on said other grid is reduced to decrease the potential difference between the grids, means to place said rst grid at said adequate potential and other means to supply the other grid with potential either at a level sufficiently higher than that on the first grid to preclude tiring or alternatively at a reduced level sufficiently close to that on the rst grid to permit tube firing.

References Cited in the file of this patent UNITED STATES PATENTS 2,039,101 McArthur Apr. 28, 1936 2,185,239 Von Ardenne Jan. 2, 1940 2,236,016 Steenbeek Mar. 25, 1941 2,506,186 Wittenberg May 2, 1950 2,611,884 Webster et al Sept. 23, 1952 2,753,489 Jacobi July 3, 1956