US2478446A - Gaseous discharge tube - Google Patents

Description

Aug. 9, 1949. H. o. e. ALFVEN GASEOUS DISCHARGE TUBE 2 Sheets-Sheet 1 Filed Feb. 14, 1945 1w 6 412 20 1110. 6 J2 Lfv 610 VA 3 m M" trFEE s- 9 9- H. o. G. ALFVEN 2,478,446

GASEOUS DISCHARGE TUBE 2 Sheets-Sheet 2 Filed Feb. 14, 1945 Inn 10/ O. G.flZ/v e12) Jig-H Patented Aug. 9, 1949 GASEOUS DISCHARGE TUBE Hannes Olof Giista Alfvn, Stockholm, Sweden, assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a company of Sweden Application February 14, 1945, Serial No. 577,888 In Sweden February 26, 1944 2 Claims. I

It is well known that the appearance and character of a gaseous discharge in a gaseous discharge tube may be. influenced by a magnetic field. The obtainable results however have hitherto been penetrated only to a very little extent. It has been stated that a magnetic field reduces the so-called cathode drop and that the influence on. the positive column most often is an increased voltage drop in the column. This increased voltage drop is probably caused by the fact that the positive column is pressed towards the wall of the discharge tube.

This invention which constitutes one of the results of my investigations as to these phenomena discloses a method which consists in the generation of electrical impulses utilizing gaseous discharge tubes of the kind employing arc or glow discharge and is i. a. characterized by a fluctuating transverse magnetic field acting on the discharge path. These investigations have shown that it is possible to obtain technical effects with magnetic control of a gaseous discharge of the same kind as with grid controlled electron tubes. It is for instance possible to use magnetically controlled gaseous discharge tubes as rectifiers, amplifiers, modulators or oscillators for low frequency purposes. It is also possible to obtain eiIects which have no adequate correspondence in the electron tube art as for instance a reproduction of a mechanical motion (of the control magnet) by means of a meter pointer motion. A further application of the invention is to provide a reproduction of a low voltage current fluctuation (e. g. the current from a thermoelement) as an increased current variation with a higher electromotive force, usable for remote indication.

The control of the discharge is carried out by the fluctuating magnetic field influencing the cathode drop or the positive column or both. The cathode may be of the cold, self-sustaining or heated type. If a cold cathode is provided, the tube has the advantage of being ready for use at any moment.

The invention may be described with reference to the drawings in which Fig. I is a glow discharge tube in a typical apparatus according to the invention; Fig. II a current characteristic showing the operation of an apparatus illustrated in Fig. I; Fig. III illustrates a modified form of the apparatus shown in Fig. I; Figs. IVa, IV?) and IVc show usable end views of the arrangements illustrated in Figs. I and II; Fig. V shows an oscillator according to the invention; Fig. VI a selfstabilizing tube; Fig. VII a self-stabilizing ampli- 2 fier; Fig. VIII a cascade of two amplifier tubes according to Fig. VII; Fig. IX an amplifier with twin-anode; Fig. X finally an amplifier with twinanode and a magnetic selector.

In Fig. I, i represents an envelope containing air, carbon dioxide, hydrogen or an inert gas of a pressure of say 3' mm. Hg. (When a mercury cathode is used the gas will of course consist in mercury-vapor). The envelope (tube) contains a cathode 2, an auxiliary electrode 3 (may often be omitted) and an anode 4. These electrodes may be made of aluminum, molybdenum or other suitable metal and purely metallic or coated. The lower part of the tube where the positive column occurs is surrounded by the poles of a magnet N S. The cathode 2v of the tube is connected to a current source, represented by a battery 6, by means of a resistance 5. The stabilizing auxiliary electrode 3 is via a resistance 1 connected to a suitable point of the battery ii. A voltmeter V is connected to the end terminals of the tube.

Fig. II shows a characteristic curve of an apparatus illustrated in Fig. I. The ordinates show the voltage over the meter V of Fig. I against the magnet current values for (or the field strength of) the magnet N S given by the 'abscissas. In observations made on an experimental laboratory system according to Fig. I the current source had a voltage of 1000 volts and the resistance 5 a value of 30,000w. The voltmeter reading was in creased from 400 to 600 volts for an increase in the magnetization current from zero to 0.1 amp. The coil resistance of the magnet was 40 ohms, thus the voltage drop being 4 volts. The variation of the voltage V is due to the fact that the positive column is forced against the wall of the envelope under the influence of the magnetic field, thus decreasing the discharge area of the column to the effect that the difiusion losses to the wall are increased. The voltage drop of the positive column thus increases against an increase of the density of the magnetic field transversing the electron path.

As shown by the diagram of Fig. II the characteristic curve has an infiexion point (Vo,io) which represents a suitable operating point. If the tube is used as an amplifier it is advisable to have a certain initial magnetization corresponding to the bias for common electron tubes.

Instead of varying the field strength of the magnet it is possible to move the magnet itself.

In Fig. III the same numerals are used as for corresponding parts in Fig. I. The apparatus shown difiers from the arrangement of Fig I by an auxiliary electrode 8 and a potentiometer 9 between which the voltmeter V is connected. It is obvious that this potentiometer may be adjusted to a point where the voltmeter reads zero for a certain magnetic field strength transversing the positive column of the tube. It is also obvious that the sensitivity for fluctuations in magnetomotive force is very high.

In Fig. IV a numeral I represents a cross section of the tubes of Fig. I and II at the location of the magnet. The latter is polarized by aid of the permanent magnet n-s which gives an initial magnetic field corresponding to the desired operating point V0,i of Fig. II. The total magnetic field may be varied in relation to the constant, permanent magnet field by aid of the coil 49.

Fig. IVb shows a modified form of the pole arrangement of Fig. IVa characterized by a pair of pole pieces, ll and 42, mounted within the tube envelope in order to increase the magnetic field strength in the open part of the tube section. The pole pieces are supported by a non-magnetic metal piece 43 provided with a terminal 44. In Fig. IVc the pole pieces are provided with inclined inner surfaces, The metal piece 93 in Fig. N12 has for its purpose to receive and to carry ofi charges conveyed by ions and electrons to the surfaces of M, 42 and 43. The arrangement shown in Fig. IVc gives a characteristic which is non-symmetric with regard to the operating point, thus causing a rectification if the magnet is fed by an alternating current. The high transconductance is obtained at one of the branches of the characteristic curve due to the inhomogeneous magnet field which gives a high amplification for this part of the characteristic.

It may furthermore be suitable to arrange a, plurality of pole systems in the discharge path, each system being electrically and magnetically isolated from other systems.

Fig. V shows schematically an oscillator circuit according to the invention. The field magnet 59 is of the same shape as in Fig. IVa. The magnetizing winding is connected to a capacitance 52. The cathode current passes the tuned circuit SI, 52. If the magnetizing winding is correctly polarized and the tube current decreases from balance in a certain operating point, the magnetic field transversing the positive column increases to the effect that the current decreases still more and so forth. Thus the operating point gets instable and the tube begins to oscillate, controlled by the tuned circuit.

In Fig. VI, illustrating an apparatus in which the tube is used to obtain a constant current, numeral 99 indicates an electromagnet, energized by the tube current. If the supply voltage increases, the field strength of the magnet increases too followed by an increase in the tube resistance. The tube current will thus remain nearly independent of the supply voltage within certain limits,

In Fig. VII, representing a, self-stabilizing amplifier, I9 is an electromagnet energized by the cathode current of the discharge tube, this current then automatically being kept at a nearly constant value. II indicates a polarized electromagnet as illustrated in Fig. IVa energized by the input current which has to be amplified. An auxiliary electrode 12 is inserted between the magnets 19 and II. A circuit for utilization of the amplified output current is connected to the auxiliary electrode 12. As the cathode current of the tube is practically constant, the variation in resistance of the positive column transversed i by the field from the magnet II will cause a voltage change of the auxiliary electrode 12.

Fig. VIII illustrates an amplifier with two magnetically controlled tubes in cascade. The input current is connected to the magnetizing Winding 82, 83 of the first tube 89. The amplified current from the auxiliary electrode 84 of this tube 89 is connected to the control magnet winding of the second tube 8|. The current, thus amplified in two stages, is for instance utilized in a loud speaker connected to the auxiliary electrode of the tube 8|. The amplifier tubes may of course differ from the tubes of Fig. VIII. Each of them may for instance be arranged as in Fig. III and it is further possible to combine a magnetically controlled tube according to the invention with common grid controlled high vacuum tubes in a cascade.

Fig. IX shows an amplifier tube with two anodes, 9I, 92, arranged in two separate branches 93, 99 of the envelope, a polarized magnetic field transversing each one of the branches. The pole piece is provided with a winding 96, 9'], for the input current. The amplified current passes the anode resistances 99, 99. If the winding 96, 97 is energized by a current impulse the magnetic field of the tube branch 93 is increased and the field oi the branch 94 decreased or vice versa. In the first case the anode current from anode 92 increases while the current from anode III decreases. The output voltage is then given as the difference of the voltage drops in the anode resistances 98 and 99 while the total current of the tube remains practically constant. The device corresponds in behalf of its action to the push-pull circuit for grid controlled vacuum tubes.

Fig. X finally shows a tube, essentially similar to the tube of Fig. IX, which may be used as a non-metallic two-way switch or selector, in which it is also possible to introduce an amplificative effect. A control magnet of the same kind as shown in Fig. IVa provided with a winding I9I, I92 is arranged at the upper part of the positive column where the discharge path is common for the two branches. The lower part of the tubes with the branches I93 and I94 is surrounded by a U-formed pole piece I95, I99, of soft iron. A movable magnet NS, one end of which may be brought from one of the tube branches to the other extends from the centre of the pole piece. In the position shown in the figure the magnetic field in the tube branch I93 is stronger than the field in the tube branch I94, thus causing the current to take its way to the anode I 99 if only the field strength of the magnet is suificiently great. The discharge through the branch I94 will cease while it will start in branch I93 if the magnet is brought in a direction indicated by the arrow towards the wall of branch I94. The amplified input impulses at the winding I9I, I92 may thus be distributed either to terminal H9 or to terminal III.

Several modifications within the scope of the invention with regard to the device illustrated in Fig. X are possible,

I claim:

1. In a gaseous discharge tube having separate discharge paths in separate branches of the tube envelope, acathode, at least two anodes arranged in the separate branches of the envelope, means for controlling the discharge by at least one magnetic field, said magnetic field acting upon the positive column in the branch of the envelope of the tube in order to change the potential drop in the column, and at least one auxiliary electrode REFERENCES CITED arranged between the cathode and said means The following references are of record in the for controlling the discharge. file of this patent.

2. Gaseous discharge tube according to claim 1, characterized by means to control the distri- 5 UNITED STATES PATENTS bution of the discharge between the anodes by Number Name Date magnetic fields acting upon the positive column 329,447 Vreeland 23 1906 of the discharge in the branches of the envelope. 991,304 Hewitt May 1911 1,118,173 Arnold Nov. 24, 1914 HANNES OLOF GOSTA ALFVEN- 10 1,402,933 Hewitt Jan. 10, 1922

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