US2878420A - Magnetron-type beam switching tube - Google Patents

Description

March 17, 1959 {HGRQENDUK 2,878,420

MAGNEI'I'RON-TYPE BEAM SWITCHING TUBE Filed March 28. 1955 R= I00 kn.

30 70 Tom INVENTOR HENDRIK GROENDIJK BY w QL 0 ,1-

AGENT MAGNETRON-TYPE BEAM SWITCHING TUBE Hendrik Groendijk, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application March 28, 1955, Serial No. 497,287

Claims priority, application Netherlands April 22, 1954 4 Claims. (Cl. 315-846) The invention relates to a beam switching tube of the type comprising an electron tube, the electron space of which is traversed by a magnetic field, so that the electrons travel in torchoidal paths in the electron beam.

It is known that in such devices, which have been referred to as magnetron-type beam switching tubes and in which a plurality of electrodes or spades are arranged concentrically around a' cathode and the electron space is traversed by a magnetic field extending in the direction of length of the electronspace, the spades can convey current only if they possess a low positive voltage or zero potential relative to the cathode,

Opposite the gaps between the spades provision is made of anodes and in certain cases auxiliary electrodes are provided in these gaps. e

The field in the tube may be varied by means of negative pulses at one or more spades or other electrodes or by means of positive voltage pulses at the cathode and thus the electron beam can be directed in succession to different spades and anodes, since the beam travels along a particular equipotential line. By means of a further negative potential at the electrode at which this line terminates, this line is deviated and the beam strikes the adjacent electrode, the voltage of which thus drops, so that the beam is held in the new position. The sense of rotation of the beam is determined by the direction of the magnetic field. In each particular stable position voltage pulses of definite duration applied to one or United States, Patent opposite the gaps between the spades, a plurality of secondary auxiliary electrodes being provided in these gaps, the spades being connected through resistors to a positive voltage source in a manner such that, if these spades are struck by the flow of electrons, the voltage drops to approximately cathode potential and that thus the flow of electrons can be held in a particular position, in which it falls partly on a spade and partly on an anode, the beam being displaceable in a direction of re} tation determined by the magnetic field by .means of more of the electrodes, by electrically connecting directly each secondary auxiliary electrode provided between two spades to the next following spade, viewed in the direction of rotation of the beam, the secondary electrode being capable of collecting part of the flow of electrons by small plates, each of which may constitute a member of the next following spade. 5

The invention will be described more fully with reference to a drawing, in which Fig. 1 shows a particular embodiment of a tube for i use in a device according to the invention and,

Fig. 2 shows a current-voltage curve of a spade.-

Referring to Fig. 1, reference ,numeraljl designates the cathode which is surrounded symmetrically and concentrically by auxiliary electrodes or spades 2 to 11. The

spades are connected by means of high-resistors of for the beam touches a spade and its larger part strikes the anode lying opposite the gap between this spade and the next following spade, viewed in the direction of rotation of the beam. In all these known devices it is a permanent difficulty that the duration of the switching voltage pulse is subject to sharply defined limits in accordance with the time constant of the spade and the resistor through which it is connected to a positive terminal. Ifhthe duration of the pulse is too long, the

beam switches over more than one spade or position, since if the voltage drop at the anode or the spade is maintained, the beam continues to circulatepulsewise along the various spades.

Opposite each gap between two spades provision may be made of a plurality of anodes and in each gap may be arranged secondary and even tertiary auxiliary electrodes in order to direct the beam to particular anodes. These auxiliary electrodes are used as control-electrodes and may be connected alternately to high and low voltages irrespective of the primary spades However, the required critical duration of the pulse cannot be mitigated in this manner. 1

The invention has for its object to provide a material increase in the pulse duration allowed.

According to the invention this is achieved in an evacuated electron discharge 'device comprising an electron tube, the electron space of which is traversed by a magnetic field and in which a cathode is arranged parallel to this magnetic field, this cathode being surrounded concentrically by a plurality of primary auxiliary elecexample 0.1 megohm'to an annular conductor 12, which can be connected outside the tube to a voltage source of for example +100 v. or to a point 35 by means of a switch 36. Point 35 is for example at cathode potential. By pushing the switch 36 the annular conductor is connected to the cathode, so that a pulse of .l00 v. .is supplied to the spades and the beam can leap to the next following spade.

Opposite the apertures between the spades are arranged the anodes 13 to 22, which are connected through resistors 33'to a voltage source of +200 v. The output voltage is obtained from point 34. The resistors by which the spades are connected have a high value, in this case of 100,000 ohms and may be arranged inside the-tube. The spades may be connected through these resistors to a common annular conductor. In the gaps between the spades provision is made of the auxiliary electrodes 23 to 32 according to the invention, which are electrically connected directly to the next following spades but which in this case are shaped in the form of tags of'the' next following spades. It is assumed that the magnetic field M traverses the discharge space in a direction at right angles to the plane of the drawing in a manner such that the beam rotates in clockwise direction, if the annular conductor of the spades is always at cathode potential by means of the switch 36.

The auxiliary electrodes 23 to 32 have such a length and width that in the position of the beam shown, also the next following spade 3 begins to carry a low current,

' at a maximum 5%, in this case 3% of the beam current,

so that the voltage drops, but not to such an extent that the beam already leaps over. A negative pulse may be applied to the common annular conductor 12 for the spades, the magnitude of this pulse being such that the 3 beam will leap to the spade 3 only when it already is at a lower potential. Since the next following spade 4 has a comparatively high voltage, the beam cannot pass on immediately. If the duration of the pulse is longer than that corresponding to the time-constant of the spade 3, the

trodes or spades and one or more anodes, arranged beam cannot leap to the spade 4 before the voltage of 3 the spade 4 has dropped sufiiciently owing to the collection of electrons by the tag 25. This -will be explained more fully with reference to a numerical example.

In the known embodiment of a tube in which the spades have no tags, but which otherwise corresponds to the tube shown and in which a magnetic field of 350 gauss prevails, the spades may be connected through resistors of 100,000 ohms to a voltage source of 100 v. It is assumed that the beamis held in the position shown, so that it travels along the spade 2 to the anode 13. The beam current is 10 ma., of which 1 ma. strikes the spade 2 and 9 ma. the anode 13. The beam can be moved into the next following position (spade 3 and anode 14) by supplying a negative pulse to the anode 13 or to the spade or a positive pulse to the cathode 1. The beam can then move to the spade 3 and strikes the anode 14, since the spade 3 begins to convey current and the voltage drops until it has reached approximately zero value. Then, however, the pulse must cease, in order that the further spades can again assume 100 v., since otherwise the beam continues to move to the spade 4. Thus the pulse duration has to meet severe requirements.

If the capacity of the spades is C ppf. and the current 10 ma., the voltage of a spade drops from 100 v. to v. in the time:

10.l0- .t=100 C t=l0,000 C After this time the "beam can cross over to the next following spade 4, so that the duration of the pulse must be at a maximum 10,000 C.

As is evident from Fig. 2, which shows the currentvoltage characteristic curve of a spade without auxiliary electrodes or tags together with a load line for 100K ohm, i. e. the resistor through which the spade is connected to the annular conductor, a pulse which reduces the spade potential from 100 v. to 35 v. (point P) will provide that the beam strikes the spade to a greater extent, so that the beam current across the spade becomes so high that the voltage of the unstable point P (35 v.) drops approximately to the stable point Q (0 v.). Thus the beam will move to this spade, if the voltage difierence relative to the cathode is lower than 35 v., so that the pulse must have a voltage of at least 100-35=65 v. and a time duration of 10,000 C at a maximum. The minimum duration of the pulse must allow a voltage drop of the spade from 100 v. to 35 v.=65 v., i. e. 10.l0 t=65 C; t=6500 C. Consequently the pulse duration must lie between 6500 C and 10,000 C. Since the capacity C of each spade is low, these limits are very narrow.

If the auxiliary electrodes according to the invention are provided, the next following spade will begin to convey current when the beam is still held by the preceding spade. This current must be low, in general less than 5% of the beam current, in accordance with the construction of the tube, in this case for example 3%, i. e. 0.3 ma. The voltage of the spade 3 then drops to 70 v., while the spade 2 remains at 0 v. and the other spades at 100 v. Then a pulse having a voltage of 70-35=35 v. sufiices to produce a switching of the beam.

The spade 3 drops from 70 to 0 v. in the time .of 10.10 .t=70 C; t=7000 C, but the pulse voltage of 35 v. cannot produce a further move of the beam to the spade 4 until the voltage of this spade 4 has dropped from 100 v. to 70 v., for which at the collected current of 0.3 ma. is required .a time T, to be calculated from 0.3.10" T=30 C; T=100,000 C Only after this time can the beam move on. The-minimum pulse duration must be such that the spade 3 drops from 70 to 35 v. before the pulse ceases. Thus Thus the invention enlarges the limits of the duration of the pulse from 6500 C and 10,000 C to 3500 C and 100,000 C at a pulse voltage which may be approximate ly half of that of known devices. The pulse duration will thus be chosen between 3500 C and 100,000 C.

Of course, the switching "time will be increased from 10,000 C to 100,000-C, but in'a counting device this is a disadvantage only for the tube which must record the units. However, inthis case the pulse voltage may be chosen to be so high that switching overtakes place even if the next following spade is at v. To this tube, however, then apply again the aforesaid narrow limits for the pulse duration. The tube of the invention is thus universal. Since the capacity of the spades may be low, a switching time of 100,000 C may in general, be sufficiently low.

It is obvious that the principle of the invention may be employed with other known trochotron switching tubes or counting tubes. The auxiliary electrodes need not form part of the spades; they may be separate plates, of which the dimensions of the arrangement may be such that, if the .beam is held by the precedingspade, at a maximum such a quantity of the beam current is collected that the spade obtains a sufliciently large voltage drop. As an alternative, the spades may be shaped in a difierent form, for example in .the form .of curved or straight, preferably radially arranged plates. Instead of using a plurality of separate anodes, use may be made of a single anode arranged cylindrically around the spades. As a further alternative use may be made of a screen having apertures opposite the anodes and arranged between anodes and spades.

What is claimed is:

1. In a vacuum tube of the type comprising a central cathode surrounded concentrically by a plurality of spaced, spade-type electrodes and an anode electrode, and wherein a magnetic field is provided in the direction that the cathode extends and thus electrons in an electron beam from the cathode describe a trochoidal path to the anode, and the electron beam is capable of occupying a plurality of stable positions equal in number to the number of spade electrodes and .in each stable position impringes partly on the anode and partly on one spade electrode, and the beam can be rotated in a given direction by applying voltage pulses to the electrodes, the improvement comprising providing at each of the stable positions of the beam means connected directly to a spade electrode adjacent said one spade electrode at the stable position already receiving a portion of the beam but on the side thereof lying in said given direction of rotation, for receiving and collecting a small portion of the electron beam in its stable position whereby the duration of the applied voltage pulses for causing rotation of the beam becomes less critical.

.2. The vacuum tube as set forth in claim 1 wherein the collecting means collects less than about 5% of the beam current when the beam occupies a stable position.

3. The vacuum tube as set forth in claim 1 wherein the collecting means comprises a small, plate-like member secured to and integral with said spade electrode adjacent said one spade electrode.

4. In a beam-switching tube of the vacuum-type comprising a central, elongated cathode surrounded coaxially by a plurality of spade-type electrodes and a plurality of anode electrodes and wherein a magnetic field is provided in the direction of the axis of the coaxial electrode system and electrons in an electron beam from the cathode describetrochoidal paths to the anodes, and each anode and adjacent spade electrode on one side thereof defines a stable position for said electron beam whereat the beam impinges partly on said anode and partly on said spade electrode, and the beam can be rotated in a given direction and thereby switched to different anode electrodes by applying voltage pulses to the electrodes, the .improvementcomprising providing means between said anode and the spade electrode on the other References Cited in the tile of this patent side thereof and connected directly to the latter spade UNITED STATES PATENTS electrode for collecting and conveying some of the beam current when in its stable position to said spade electrode 2'404920 Overbeck July 1946 on the other side thereof and lying in said given direc- 5 2432508 Desch 1947 tion of rotation, whereby the duration of the applied gi a g- Ag 111 f t d hin b b I voltage p ses or con rollc switc g of the cam e 2,795,732 Kuchinsky July 11, 1957 I 2,791,357 Kuchinsky June 25, 1951

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