US2876351A - Ionic time-delay apparatus - Google Patents

Description

March 3, 1959 A. J. CANN IONIC TIME-DELAY APPARATUS 3 Sheets-Sheet 1 Filed Aug. 29, 1955 FILAMENT VOLTAGE TIME DE LAY Fig. '2

Alfred J. Conn IN V EN TOR.

Attorney March 3, 1959 A. J. CANN IONIC TIME-DELAY APPARATUS Filed Aug. 29, 1955 5 Sheets-Sheet 2 III Fig. 3

ELECTRONS R w 8 6 4 2 O ozoomwOmo ELECTRONS FEET (b) Alfred J. Conn A wozoommom z INVENTOR.

a w m Attorney I March 3, 1959 A. J. CANN.

IONIC'TIMEDELAY APPARATUS Filed Aug. 29, 1955 3 Sheets-Sheet 3 VOLTAGE CONTROL Fig.

Alfred J. Conn INVENTOR. BY 9.,f4 R- 911 Attorney United States Patent O IONIC TIME-DELAY APPARATUS Alfred J. Cann, Nashua, N. 'H., assignor, 'by mesne assignments, to Sanders Associates, Inc.,.Nashua,.N. H., a corporation of Delaware ApplicationAugust 29, 1955, SerialNo. $31,115

3 Claims. (Cl..25.027)

This invention relates to time-delay apparatus. More particularly, this invention relates to time-delay'apparauts of the type in which an ionic beam is utilized.

In U. S. Patent 2,456,466 issued to .D. C. Sunstein, December 14, 1948, there is disclosed a variable timedelay electro-nic apparatus which utilizes an electron beam. Time-delay devices such as this are severely limited either in the total delay time available, the frequency bandpass characteristic, or the ability to vary delay time at a high speed. For example, the length of a time-delay tube utilizing an electron beam becomes impracticably great as the required time-delay :is increased. The time-delay which can ,be realized from an electron beam device is a function of its beam velocity. The velocity of the electron can be derived from the equation for kinetic energy:

( W= /2mv.

where Wis the kinetic energy, m the .mass of the particle and v its velocity. The energy gained by particles acwhere q equals the charge of the particle and E the accelerating voltage. Substituting in Equation 1 above, the

, velocity v is then expressed:

For electrons, v equals 593,000 V75 meters per second.

In an electron beam there inevitably exists a distribution of electron velocity due to the emission process. For thermionic emission the distribution of thermal energy has a range of approximately 0.3 electron volt. Consequently, the leading and trailing edges of a group of electrons representing a signal pulse randomly shift with thermal energy changes and gradually diffuse. This disturbance affects the rise time of a pulse. It has been determined that the rise time is a function of the thermal energy range divided by the accelerating voltage. Since both the time-delay and rise-time are functions of the voltage E, the delay/rise-time ratio R has been found to be:

(4) R= /E/ .3 for electron beam devices For a typical ratio of -to-1, E is 30 volts and the corresponding electron velocity is 3.25 X 10 meters per second. Thus, for a delay time of 10- micro-seconds, the beam must travel 32.5 meters, an impractical length.

It is, therefore, an object of the present invention to provide an improved time-delay apparatus for producing a wide range of time delays.

It is a further object of the invention to provide an improved time-delay apparatus for introducing a variable. time-delay to encode signals.

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A stillifurther object 'of the invention is to provide an improved time-delay apparatus utilizing an ion beam :for introducing a variable time-delay.

It is ta further object of the invention to provide an improved time-delay apparatus for producing time delay effects with relatively high delay/rise-time ratios.

Other and further objects of the invention will be apparent-from the following description of a preferred embodiment and method of practicing the invention, taken in connection with the accompanying drawings.

In accordance with the invention there is provided an ionic, time-delay apparatus. The apparatus includes n .ion discharge device having a source of ions and -a drift tubemeans responsive to the ions for directing the flow thereof. Control means are provided in the path of the .ions .for varying the density of the ionic flow in accordance with an input signal. Input generator means are coupled to the control means for providing an ordered sequence of input pulses spaced apart by predetermined time intervals. A time-delay control signal generator means is coupled to the drift tube means for varying the time intervals between input signal pulses with respect to the predetermined time intervals.

.In the accompanying drawings:

Fig. l is a schematic, partially fragmentary, threedimensional view -of a time-delay tube embodying the present invention;

Fig. .2 is a voltage gradient curve illustrating an aspect of .tne operation of the embodiment of Fig. 1;

.Fig. 3 is .a series of diagrams further illustrating the operation of the embodiment of Fig. l;

Fig. 4 is a graph comparing the available time delays for devices utilizing ion and electron beams; and

Fig. 5 is a series of graphs further illustrating the operation of the embodiment in Fig. 1.

Referring now to the drawings, and with particular reference to Fig. 1 representing one embodiment of timedelay apparatus in accordance with the present invention including an ionic time-delay tube 101, the tube 101 comprises an hermetically sealed shield or envelope enclosing a gas generally indicated at 106, for example mercury vapor at a pressure of 2 l0- millimeters of metcury and surrounds a plurality of electrodes. An emitter cathode 102 including an internal filament, which is con nected to a source 103 of filament voltage, provides a source .of electrons. The tube 101 includes between the cathode 102 and a collector anode 111, a perforated anode 104 connected through a voltage dropping resistor 120 to a source of positive voltage labeled B+, for example volts. A control grid 105 comprises means for varying the density of ion flow in the tube. The grid 105 is connected through a voltage dropping resistor 450 volts. The tube 107 is utilized to direct the flow of the ions. The drift-tube 107 has grids 109 and 110 enclosing its ends to minimize the efiect of fringing fields. The collector 111 is connected through a load resistor 112 in parallel with the drift-tube 107 to B', as shown.

The collector 111 comprises means for discharging the ions and for producing an electron current flow to develop an output signal delayel with respect to the input signal. An input signal generator 114 is coupled through a capacitor 115 to the control grid circuit, as shown, one

. side of the generator 114 being grounded. The output of the .device is coupled from the collector 111 through the capacitor 116 to an output load 117 which is connected to ground as shown. The output load may typically be a resistor or a transformer. A time-delay con trol signal generator 118 has one side grounded and 1 3 the othercoupled through a capacitor. 119 .to the drifttube cathode 107 as shown The operation of the invention will now be discussed with particular reference to Figs. :1 through 5. In Fig. ;2,' a.voltage-gradient curve illustrates the static accelerating potential present in thetube 101.:. Thus, it will be seenthat electronsare accelerated from the emitter cath- =odejl02 to the perforated anode 104 by the relatively positive potential on the anode 104. When the voltage -on the anode 104 is of the order of 115 to 20 volts, the electrons gain sufficient velocity to ionize mercury vapor .atoms as in a conventional mercury vapor rectifier.

In the statiecondition a .small positive biasing voltage on .theioncontrol grid 105 electrostatically shields the ions .from .enteringthe accelerating region between the grid -105 and the drift-tube-l07.- When in input signal in the form of a negative pulse is applied to the grid, positive ionsare admitted to the accelerating region. The differential voltage between the grid 105 and the drift-tube r107 determines the velocity of the ions entering the drift- .tube 107. The tube 107 provides a Faraday cage or field- .free region. '1 "he ions consequently travel through the tube at their initial velocity as determined by the potential difference between the ion control grid 105 and the drift- .tube .107. At pressures on the order of '2 X 10- milli- 1.05 and the consequent formation of. a cloud of ions passing through the control grid l05jthe cloud of'inns approxrmatelyhalf way along the length of the tube and the cloud of ions being discharged at the collector 111.

As indicated by Equation 4 above, the delay/rise-time ratio is principally determined by two factors: the thermal distribution in electron volts and the accelerating potential. As is well known, the thermal distribution is a function of absolute temperature. Since the electrons are'initially emitted at the cathode temperature, a greater range of initial velocities may be expected than is exhibited by the ions which are essentially at the much lower ambient temperature. The transmission of electron velocities to .the ions because of electron-gas mclecule collisions is substantially negligible since the ionic mass is so much greater than that of an electron. Thus, the energy distribution of the ions has a range of only .045 electron volt. From the Equation 4 above, the delay/ rise-time ratio R for ions is expressed:

Then, only a minimum of 4.5 volts are required for a delay/rise-time ratio of 10. Since the mass of a mercury ion is approximately 360,000 times that of an electron, the ionic velocity v, for a given voltage is only approximately that of the corresponding electron velocity v,,. Thus, in accordance with the Equation 3 above, the ion velocity v, equals approximately 980VE For E equal to 4.5 volts, the ionic velocity v, turns outto be approximately 2000 metersper second. For the i0 microsecond time delay a tube length of 2000 10- or 2 centimeters is requiredas opposed to 32.5 meters for a time-delay logarithmically calibrated in microseconds and the abscissa linearly calibrateiin feet to present a plot of delay-time versus drift-space length. In the curve (b) of Fig. 4, the ordinate is linearly calibrated in microseconds as shown.

In the curves of Fig. 5 a series of pulses, numbered 1 through 15 and occurring in a time sequence as shown, are assumed to be applied to the ion control grid 105. A suitable voltage as shown in curve 5(b) is developed by the time-delay generator 118 and coupled through the capacitor 119 to the drift-tube and through the resistor 112 to the collector 111 effectively to vary the time delay in accordance with the curve 5(c). It is to be noted that when the variation in time delay has a positive slope as at 122, the time"separation'be'tween pulses is expanded as illustrated by pulses 1, 2 and 3 in the curve 5(d). The more positive the drift-tube 107 with respect to the grid105, the longer the time of travel for the ionic pulse through the drift-tube. When the delay is decreasing, in other words, the potential on the drift-tube going negative as at 123, the pulses are compressed in timeas illustrated by the pulses 3, 4, 5 and 6 as opposed to the pulses .1, .2 and 3. The pulses 7 through 12 coincide with a negative unity slope as shown at 124. This has the unobvious effect of causing the pulses to occur simultaneously at the collector 111 at an enhanced amplitude as shown.

When the slope of the curve is negative and greater than unity-,as'indicated at 125, an actual inversion takes .place.:. ' iThusjthei pulses 13, 14 and 15 in the curve 5(a) :have their order completely inverted-as shown in the curve 5(c) with the same time separation between them. The structure of the drift tube 107- .permits. such; an extraordinary resultto be realized. The ionic flow within the drift-tube 107 proceeds at substantially its initial ve- =-locity as determined by the diflerential potentialbetwcen ;the control grid 105 and drift-tube 107. .A group of ions.

' introduced to the drift-tube at a higher velocity-than an earlier group can overtake .the earlier group and actually pass through it. This result is not possible with any prior art device. The densities of the groups of ions are such as to permit a given cloud of ions literally to pass through another cloud of ions without losing its identity. Some distortion takes place due to collisions between ions of the two groups. The probability of such collisions, however, is sutriciently low that the resultant dispersion is negligible.

In continuous-wave applications the device can be used to transform an input wave form at the controlgrid to quite a difierent wave form in its output by a suitable velocity modulation signal as produced by the time delay control signal generator 118.

The ionic variable-time-delay apparatus of'the present invention greatly enhances the art of time control in that larger variations in time delay at higher speeds are now possible. It will be apparent that the present invention has wide application in the art of electronic control.

While there has been hereinbefore described what is at present .considered a preferred embodiment of the invention, it will be apparent that many and various changes and modifications may be made with respect to the embodiment illustrated, without departing from the spirit of the invention. It will be understood, therefore, that all such changes and modifications asfall fairly within the scope of the present invention, as defined in the appended claims, are to be considered as a part of the present invention.

What is claimed is:

1. An ionic, time-delay apparatus, comprising: an ion discharge device having a source of ions, a drift tube means responsive to said ions for directing the flow thereof, control means in the path of said ions for varying the density of said ionic flow in accordance with an in-. put'signal, and collector means responsive to the ions issuing from said drift tube for discharging said ions and for producing an electric current flow to develop an output signal delayed with respect to said input signal; input generator means coupled to said control means for pro viding an ordered sequence of input pulses spaced apart by predetermined time intervals; and time delay control signal generator means coupled to said drift tube means for varying the time intervals between output signal pulses with respect to said predetermined time intervals.

2. An ionic, time-delay apparatus, comprising: an ion discharge device having a source of ions,, a drift tube means responsive to said ions for directing the flow thereof, control means in the path of said ions for varying the density of said ionic flow in accordance with an input signal, and collector means responsive to the ions issuing from said drift tube for discharging said ions and for producing an electric current flow to develop an output signal delayed with respect to said input signal; input generator means coupled to said control means for providing an ordered sequence of input pulses spaced apart by predetermined time intervals; and time delay control signal generator means coupled to said drift tube means for varying the time intervals between output signal pulses with respect to said predetermined time intervals for providing an output ordered sequence of pulses with at least one pair of pulses reversed in time with respect to said input pulses.

3. An ionic, variable time-delay apparatus, comprising: a housing-tube oriented along a given axis; a source of ions within said tube; a cylindrical drift tube means disposed within said housing-tube and oriented along said axis for directing an ionic flow therethrough, said drift tube having conductive grids enclosing its opposite ends; control means disposed within said housing-tube between said source of ions and said drift tube for varying the densityof said ionic flow in accordance with an input signal; collector means disposed within said housingtube in the path of said ions emanating from said drift tube for effecting their discharge and producing an electron current fiow to develop an output signal delayed in time with respect to said input signal; direct current means coupled to said drift tube and said collector for applying a negative voltage to said drift tube and said collector to control the velocity of ionic flow and provide an adjustment to vary the time delay; input signal generator means coupled to said control means for producing a sequence of input pulses spaced apart by predetermined time intervals; and time delay control signal generator means coupled to said drift tube to vary said negative voltage further to control the velocity of ionic flow and vary the ordering of ions emanating from said drift tube in a predetermined manner to provide an output sequence of signal pulses spaced apart by time intervals varying from said predetermined time intervals.

References Cited in the tile of this patent UNITED STATES PATENTS 2,401,945 Linder June 11, 1946 2,442,662 Peterson June 1, 1948 2,508,228 Coeterier May 16, 1950 2,683,251 Ramo July 6, 1954 2,697,169 Emslie Dec. 14, 1954 2,706,788 Wiley Apr. 19, 1955 2,737,585 Wolff Mar. 6, 1956 2,776,374 Iskenderian Jan. 1, 1957

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