US2776374A - Electron discharge devices - Google Patents

Description

Jan. 1, 1957 H. P. fSKENDERIAN 2,776,374 ELECTRON DISCHARGE DEVICES Fix ed Sept. 15, 1951 SIGNAL SOURCE INVENTOR HA/G P. ISKENDERIAN ATTORNEY United States Patent ELECTRON DISCHARGE DEVICES Ha s P- 'l k ue E n st, 1 1-, a s nq to Int rn t imal Te e ne nd raph C ro fiq e ra qn f Ma nd Appli a i n S pt m 1 1 1. Se ia N 24 .801

4 Gl m 1- 2 0-1 This invention relates to electron discharge devices having a long time delay and particularly to such devices in which the electron beam follows a trochoidal path.

Electron tubes in which the electron beam follows a trochoidal path are known in the art. Electrons are caused to travel along such a .path by being subjected to cross electric and magnetic fields of the proper relative strengths. Such tubes have been disclosed heretofore wherein the crossed electric field is established by a plurality of electrodes and the electron beam isswitched from one electrode to another. It is the purpose of this invention to provide trochoidal beam tube circuits in which substantially the entire electron beam is fed to a collector electrode distinct from the electrodes producing the crossed electric field and in which the collector electrode is provided with an output circuit. The tube may be provided with circuits for generating oscillations, or for reproducing a signal with a controllable time delay.

It is therefore an object of this invention to provide an oscillation generator utilizing a trochoidal type of time delay tube.

Another object of this invention is to provide means to variably modulate by one or more signals the phase, f equen y, fl w i ens t 2f h lectr n been r t intervals of a sequence ofoscillations or pulses.

..S 11 ano he je s t pro a it s iqa 'bssm ub and rcu s h efo lhsus e hi h sisu it asi ratio.

Still another object of this invention is to provide a trochoidal time delay tube in which the electron beam is well focused and has ,a high current density.

Another object of this invention is to produce a trochoidal beam :tube having a high signal to-noise ratio by providing it with an electron gun which ,is magnetically shielded in orderto prevent-therecapture ofemittedelectrons.

A further object of this invention is to increase the amplification factor of trochoidal beam tubesand render them sensitive to small controlvoltages.

Further objects and advantages of the invention will be apparent from the following description of the drawing, in which:

'Fig. l is a cross-sectional ,view of an electron time delay device together with a circuit therefor illustrating somefeatures of my invention;

Fig. 2 shows the electron tube. of Eig. 1 provided with circuits for forming an; oscillation generator; and

Fig.3 shows an electron tubehayinga spiral configuration.

:It has been found that trochoidal pa h tubes tend to have a low ,signal-toenoise ratio. While a poor signaltosnoise ratio maybe tolerablein st ch tubeswhen they are-used f switch sp pqs s i s hishlyugd si sbl he e e tub is used a aaemrlifisr lmqslslstsr a ansds a ,dsv s s s i :1 .st;5 9 9-ths t sis ssssh tube -M. errissa s ly e s s al s; 7-. as i th atlw essd t s ssgsn is See negative delay control electrode or rail. The tulle shown in Fig. l substantially eliminates these defects ,and provides a trochoidal beam tube .Which is useful for vtranslating signals without appreciable distortion.

It has also been found that trochoidal beam tubes tend to have a very low amplification factor, which may be less than unity. The defect prevents the trochoidal beam tube from being .usable in many applications in which ordinary electron tubes have been used. I have found that the amplification factor of the trochoidal beam tube can be significantly increased by providing the tube with an electron gun for producing a thin, well-focussed, .high density electron beam. When, additionally, the electron gun is magnetically shielded and the cathode is biased to prevent electrons from falling back to the cathode or onto the negative delay control electrode, then the tube noise is reduced to such an' extent that small signals can be amplified without substantial distortion. The .trochoidal time delay tube when thus improved becomes useful as an amplifier, modulator, oscillator and other electron discharge tube applications.

The time delay tube shown in Fig. 1 includes an evacuated envelope 1. Within the envelope there are positioned a pair of juxtaposed delay electrodes 2 and 3' and a collector electrode 4. The delay control electrodes 2 and 3 may be elongated parallel'rails or plates and are biased positively and negatively, respectively. The collector electrode 4 is biased positively. The collector electrode 4 is positioned at one end of the channel formed by electrodes 2 and 3. Near the other end of the channel formed by electrodes 2 and 3, an electron gun is pro vided. The electron gun includes a cathode 5 and a pa'ir of focusing electrodes 6 and7, which may be connected together and biased negatively with respect to the cathode, as is well understood in the art. The electron gun is also provided with a control grid 8 and an anode 9. The cathode 5 mayhave a.concave electron emittingsur face to facilitate focusing of the beam, and the control grid 8 is preferablyconforrned to the curvature of .the cathode as indicated in Fig. 1. The entire electron gun is enclosed in a magnetic shield 1!) which is adapted to exclude the magnetic held from the electron gun, and particularly from the region occupied by the space charge. The delay 'tube is provided with amagnet 11 for producing a magnetic vfield of suitablestrength throughout the space defined by the electrodes 2 and 3. The magnet 11 may be a permanent magnet or ,electromagnet. i

The electrons emitted by the cathode ,5 are controlled in any desired manner by thepotentials impressed on the control grid 8. The modulated electron stream is then focused by the electron gun into a narrow, highdensity electron beam which is projected through an open ing 12 in the .magnetic shield. The electron beam thus enters the space between .theelectrodes 2 and 3}where it is subjected to the electric field between electrodes 2 and 3 and to the magnetic field perpendicular to. th e,electrio-field. .As is .explained iri ;U. s. Patent No. 2,513,269, and .the copending application .of Labin, .Serial- .No. 233,900,..filed une. 27,, .1951, now :Batent No. 2,723,3.7l 6', dated N o vemb e'r'fi, .1955, the electron .beamrlill 'then travel along .a .t rochoid al path to the l 'collec'tor .elect'rode 4, lithe relative strength .of the .lelectric and magnetic fields areproperly adjusted. i

The circuit illustrated in Fig. 1 mayoperate a s.a time delay device, a modnlatpnoran amplifier. A sourcelof signalvoltage -13 is connect ed between .the control grid .8 and cathode5. Thes g als suppliedbythe source 13 may be continuous osc' ns or pulscs haying ahv s ssas iis z i ris s i suitably ii tf s h fl psl' i z p sj i i i les e Malt s saw-"# D slsstrsd is connected to the negative end of the potentiometer 14. Electrode 2 is biased to a positive potential by any suitable means such as a voltage source 16. Modulating potentials from a source 17 are applied between the cathode 5 and electrode 2 in series with voltage source 16. The collector electrode 4 is connected to the cathode through a load impedance 18 and voltage source 19. The output signals are derived from the load impedance 18 at the terminals 20, the upper of which is connected through blocking condenser 21 to load impedance 18. The focusing electrodes 6 and 7, for simplicity, are shown connected to the magnetic shield 10 and hence are at the same negative potential as the electrode 3. It will be understood, however, that the potential of the focusing electrodes may be at any other suitable value.

In previous trochoidal beam tubes the cathode is in the magnetic field required for operation of the tube. The magnetic field increases the space charge effects, limiting the effective cathode emission and causing amplitude distortion of signals impressed on the tube. The magnetic field also causes electron velocity selection, and the magnitude of electron velocity obtainable in the pres ence of strong fields differs from that required for the best operating conditions of the tube. The electrons falling back on the cathode under the influence of the magnetic field increases the noise and distortion produced by the tube. These defects, which seriously impair the operation and limit the usefulness of previous trochoidal beam tubes, are overcome in the instant invention by providing an electron gun having a magnetic shield 10 which substantially excludes the magnetic field. Since the gun is magnetically shielded it is possible to operate it with low electron velocities. The magnetically shielded electron gun therefore enables operation with a minimum of space charge effects on the cathode emission, and reduced dispersion of the electron velocities, and therefore permits a well focused, low velocity electron beam to be projected through the orifice 12 into the channel between electrodes 2 and 3.

It has been found, also, that the tube noise can be reduced to a mini-mum by biasing the cathode 5 to an optimum value with respect to control electrode 3. When cathode 5 is biased to such an optimum value, the electron current flowing to control electrode 3 is minimized and virtually all the electron discharge current flows to the collector electrode 4- over a Wide range of signal voltages from source 13 and delay control voltages from source 17. This also results in substantially increased signal amplification. The optimum value of the bias may be determined by placing a microammeter in the connection between delay control electrode 3 and potentiometer 14 and adjusting the cathode bias until the microammeter indicates a minimum current, which in most instances can be made practically equal to zero.

The operation of the circuit shown in Fig. 1 is as follows: The signal voltages from the source 13 impressed on the grid 8 vary the amplitude of the electron beam. If the signal voltagesare in the form of pulses, the grid 8 may be biased to cutoff, so that the electron beam will flow only while the signal pulses are impressed on the grid. If a steady voltage is applied to electrode 2, the signal pulses or oscillations from source 13 will appear at the terminals 20 after a time delay determined by the length of the trochoidal path between the electron gun and the collector electrode 4. On the other hand, if the potential of the electrode 2 is varied in accordance with a signal supplied by the source 17, the signal voltages will be modulated. If the signal voltages are continuous oscillations, they will be modulated in phase or frequency. If the signals are pulses, the time interval between the pulses will be varied in accordance with the modulating signals from the source 17. In other words, the circuit will then function as a pulse time modulator. The pulse time modulated output will be developed across the load impedance 18 and will appear at the terminals 20.

It will be evident that this circuit provides a relatively simple means for producing pulse time modulation.

Fig. 2 shows a trochoidal beam tube oscillator circuit. The electrodes 2 and 3 are adjustably biased with respect to each other and the cathode by means of the voltage sources 22 and 23. Anode 9 of the electron gun is suitably biased by the voltage source 24. Focusing electrodes 6 and 7 are shown connected in the same manner as in Fig. 1, although, as is well-known in the art, they may be provided with any suitable biasing potential. Collector electrode 4 is connected to cathode 5 through parallel resonant circuit 25 and 26 and voltage source 19. Control grid 8 is coupled by a coil 27 to the inductance 26. The grid leak resistor 28 and condenser 29 in the grid circuit supply a suitable bias to the grid. The circuit of Fig. 2 operates as an oscillator at a frequency determined by the parallel resonant circuit 25 and 26, since the electron tube has a sufficiently high amplification factor. The frequency of oscillation depends on the transit time of the delay characteristics of the electron tube. The tube may be adjusted so as to generate continuous oscillations or discrete trains of oscillations by varying the transit time. The tube may also be used for mixing or multiplying two or more signals by modulating the amount of delay,

When very long delay periods are desired in tubes occupying a limited space the tube may have a convoluted configuration so that the base line or axis of the trochoidal path follows any given curve instead of a straight line. In Fig. 3 there is shown by way of example, a tube in which the axis of the trochoidal path is a spiral. The electron gun 31 is placed at one end of the spiral and the collector electrode 34 is placed at the other end of the spiral formed by parallel plates 32 and 33. The axis of the trochoidal path of the electrons will lie along the equipotential plane defined by parallel plates 32 and 33. Plates 32 and 33 may be given any other configuration which will provide an elongated path in a limited space.

While the principles of my invention are exemplified in the above description and the drawing, many variations of these principles within the scope of my invention will be evident to those skilled in this art. It is to be understood, therefore, that the present disclosure is presented by way of illustration only and not as a limitation on the objects of the invention and the appended claims.

I claim:

1. An electron discharge device comprising a pair of spaced substantially parallel elongated electrodes defining a long narrow channel therebetween, electron emissive means disposed at one end of said channel to produce an electron beam focused transversely of said channel in the direction of one of said electrodes, a collector electrode disposed at the other end of said channel, means to apply a voltage differential to said elongated electrodes to establish an electric field therebetween, magnetic means disposed to establish a magnetic field crosswise of said channel at right angles to said electric field, said electric and magnetic fields causing said electron beam to flow in a trochoidal path between said elongated electrodes in the direction of said collector electrode, a casing for said electron emissive means to shield the electron emissive means from said magnetic field and means for biasing said electron emissive means to a predetermined potential with respect to the potentials of said elongated electrodes to minimize dispersion of the electrons of said beam as the beam flows transversely into said channel.

2. An electron discharge device comprising a pair of spaced substantially parallel elongated electrodes defining a long narrow channel therebetween, electron emissive means disposed at one end of said channel to produce an electron beam focused transversely of said channel, a collector electrode disposed at the other end of said channel, means to apply a voltage differential to said elongated electrodes to establish an electric field therebetween, magnetic means disposed to establish a magnetic field crosswise of said channel at right angles to said electric field, said electric and magnetic fields causing said electron beam to flow in a trochoidal path between said elongated electrodes in the direction of said collector electrode, means to shield the electron emissive means from said magnetic field, said electron emissive means having a control electrode, a load impedance connected between said collector electrode and said electron emissive means, and means for regeneratively coupling said control electrode to said load impedance.

3. An electron discharge device comprising a pair of spaced substantially parallel elongated electrodes defining a long narrow channel there'oetween, one of said electrodes having an opening therethrough adjacent one end thereof, electron emissive means disposed adjacent said opening to produce an electron beam focused through said opening transversely of said channel, a collector electrode disposed at the other end of said channel, means to apply a voltage differential to said elongated electrodes to establish an electric field therebetween, magnetic means References Cited in the file of this patent UNITED STATES PATENTS 2,233,779 Fritz Mar. 4, 1941 2,414,121 Pierce Jan. 14, 1947 2,530,373 Bowen Nov. 21, 2,563,807 Alven et al Aug. 14, 1951 2,603,764 Rostas July 15, 1952

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