US3215893A

US3215893A - Cold cathode gaseous rectifier tube

Info

Publication number: US3215893A
Application number: US67321A
Authority: US
Inventors: Boucher Gilbert; Soulet Michel
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1959-11-24
Filing date: 1960-11-04
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02
Also published as: OA00420A; GB922875A; FR1249924A

Description

Nov. 2," 1965 g, scum- ETAL 3,215,893

COLD CATHODE GASEOUS RECTIFIER TUBE Filed Nov. 4, 1960 s Sheets-Sheet 1 wmmmmmmm Fig.1

[:1 [:1 [Q] [5] DEC [5] 11 3] [S] [N] [5] [N] S [1] 15] [51] 1] KS] 1 [3] [E C] [@l' ES] /l$] r LJ 1 Fig. 2

h 9 POLE PIECE ,POLE PIECE 10 Fig.3

INVENTORS G. BUUC'HER M-SOULET Nov. 2, 1965 a. BOUCHER ETAL 3,215,893 GOLD cA'I'HoDE GASEOUS RECTIFIER TUBE Filed Nov. 4, 1960 5 Sheets-She's: 2

INVENTORS G. BDUCHER M. SOULET 2, 1955 G. BOUCHER ETAL 3,215,893

COLD CATHODE GASEOUS RECTIFIER TUBE 3 Sheets-Sheet 3 Filed NOV. 4, 1960 (pd) crit.

VA A

Fig. 6

INVENTO RS 6. BOUCHER msouusr BY 7 $4024 svs United States Patent 1 0 3 Claims. (a. 31s 2s7 The present invention relates to electric current valves, utilizable as alternating current rectifiers at relatively elevated voltages, between some hundreds and some thousands of volts, for example.

Within this range of voltages, there are known in the prior art thermionic vacuum rectifiers and cold-cathode mercury arc rectifiers. These prior art tubes, however, are relatively complicated, for they have to be provided either with a cathode heating device in the case of the thermionic rectifiers or with a special ignition device and electrode in the case of mercury vapor rectifiers.

It is an object of the present invention to provide an electric current valve for the range of voltages indicated hereinabove which is very simple in structure and does not necessitate any of the auxiliary devices mentioned hereinabove.

It is another object of the present invention to provide a cold-cathode type rectifier utilizable at relatively elevated voltages in which the critical voltages producing conduction of forward and inverse current are spaced relatively far apart.

Still another object of the present invention resides in the provision of a cold-cathode type rectifier for relatively high voltages which may be readily manufactured, and is relatively inexpensive not only insofar as manufacture of the parts are concerned but also insofar as assembly and operation thereof is concerned.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of il lustration only, several embodiments in accordance with the present invention and wherein FIGURE 1 is a schematic longitudinal cross sectional View through a plane valve structure in accordance with the present invention, the showing thereof being limited to the arrangement in principle,

FIGURE 2 is a plan view of the plane valve structure according to the present invention as shown in FIG- URE 1,

FIGURE 3 is a somewhat schematic longitudinal cross sectional view through a cylindrical valve structure according to the present invention, also limited in its showing to the arrangement thereof in principle,

FIGURE 4 is a longitudinal cross sectional view through a preferred embodiment of a valve in accordance with the present invention,

FIGURE 5 is a transverse cross sectional view of the valve of FIGURE 4, taken along line 5-5 for FIGURE 4, and

FIGURE 6 is a typical curve representing a known law representing the discharge in gases, and referred to hereinafter for purposes of explanation of the operation of the present invention.

The valve according to the present invention is a cold emission type diode, that is a tube comprising two electrodes between which an electric field is established, the space between these electrodes being filled with a rarefied gas. It is known that when a difference of potential is applied between these electrodes, the electric field pulls out or extracts primary electrons from the electrode having a 3,215,893 Patented Nov. 2, 1965 negative polarity, thereupon these electrons ionize the gas, and thereafter the positive ions are directed towards the negative electrode and pull out or extract thereat new electrons which will reinforce the primary current. If the difference of potential is above a certain critical value, the number of positive ions formed within the gas is sufficient so that the discharge remains started, even if the primary emission thereafter diappears.

, According to the present invention, a tube of which the structure has been defined already hereinabove, is characterized by the fact that with a view to functioning as a valve, it is provided with means to lengthen substantially the path within the gas of the electrons issued from one electrode for a certain sense or direction of voltage, with respect to the path of the electrons issued from the other electrode for an opposite sense or direction of voltage.

These means in accordance with the present invention may be constituted, especially in case of a plane structure, by the establishment within the space between the electrodes of a magnetic field having a component directed perpendicularly to the electric field, that is parallelly to the surfaces of the electrodes, the intensity of this component being progressively variable or abruptly changeable in the direction perpendicular to the surfaces thereof. For example, the magnetic field may be 10- calized within the vicinity of an electrode and may be essentially zero within the vicinity of the other.

These means in accordance with the present invention may also be constituted by the suitable geometry of the electrodes, that is by the realization of a cylindrical structure, jointly with the establishment within the space between the cylindrical electrodes of a magnetic field having an axial component, whereby the intensity of this field may be uniform.

Preferably however, the different means mentioned hereinabove are combined, that is, a cylindrical structure is used having a magnetic field provided with an axial component of which the intensity will vary progressively or abruptly in the radial direction, for example, by restricting or localizing the magnetic field to the vicinity of the inner electrode.

Referring now to the drawing wherein like reference numerals are used throughout the various views thereof to designate corresponding parts, and more particularly to FIGURES l and 2 thereof,

reference numerals

1 and 2 designate therein two electrodes having plane parallel surfaces, which are enclosed within a vessel or enclosure (not illustrated) or are incorporated within the walls of such an enclosure. The vessel or enclosure is thereby filled with a gas at low pressure, for example, of the order of 10- or 10- Torr. A difference of potential is applied between these electrodes through

connections

3 and 4, which creates within the inter-electrode space an electric field perpendicular to the surfaces of the

electrodes

1 and 2. According to the presentinvention, a zone within which is established a component of magnetic field perpendicular to this electric field, is created, for example, inthe vicinity of electrode 2 whereas the zone adjacent the electrode 1 is essentially free of any magnetic field. Such a zone is produced, for example, by disposing below the electrode 2 a network of ferrite cubes 5 having alternately opposed polarities for adjacent cubes on the faces thereof contiguous to the electrode. The lines of force of this assembly of ferrites, represented by reference numeral 6 in FIGURE 1, shows that the field thereof includes a component parallelto the surfaces of the

electrodes

1 and 2. On the other hand, it is known that in such a system the intensity of the magnetic field decreases very rapidly with the distance from the surface of the ferrite system, that is, the intensity of the magnetic field is considerable in the vicinity of the electrode 2 but diminishes rapidly in the direction of the electric field and becomes essentially zero in the vicinity of the electrode 1.

FIGURE 3 represents in longitudinal cross sectional view a modified embodiment in which the geometry of the electrodes is cylindrical. The diode is thereby constituted of an axial electrode 7 and of an external cylindrical electrode 8. The magnetic pole pieces 9 and of opposite polarity establish a uniform axial magnetic field across the space between the

electrodes

7 and 8. The walls of the cylinder 8 are fixed to the surfaces of the

poles

9 and 10 in such a manner as to form a vessel or enclosure which is filled with a gas under low pressure. The electrode 7 is supported by an insulating piece 11 which obturates or closes off the channel 12 within the pole piece 9 across which passes the connection 3 for the electrode 7. The difi'erence of potential is applied between the

electrodes

7 and 8 by means of

connections

3 and 4.

With the modifications of FIGURES 1, 2 and 3 described only as to the principle thereof, a preferred embodiment will now be described which is illustrated in longitudinal cross-section in FIGURE 4 and in transverse cross-section in FIGURE 5, taken along line 5-5 of FIG- URE 4. A diode of cylindrical structure, as shown in FIGURE 3, and a magnetic field localized in the vicinity of one of the electrodes, as shown in FIGURE 1, will be found in the embodiment of FIGURES 4 and 5. The diode is constituted by an inner hollow cylindrical electrode 13 closed at one end thereof and by an external cylindrical electrode 14, also closed at one end thereof. These

electrodes

13 and 14 may be of the same metal or may also be of different metals. Any non-magnetic metals susceptible to being utilized industrially may be envisaged for purposes of the present invention such as, for example, copper, molybdenum, non-magnetic nonoxidizable steel, platinum, etc.

The electrode 14 is brazed to an annular copper member 15 on which is secured an external connecting collar, thereupon the enclosure continues successively by an annular Kovar member 16, an annular glass member 17, a second annular Kovar member 18 and a closure member 19 made of copper which also supports the inner electrode 13.

A pump-out stem 20 is provided at the annular member 17 for initially evacuating the enclosure between the

electrodes

13 and 14, and for thereafter filling the space therebetween with a gas, for instance, with hydrogen, at a relatively low pressure, for instance, at 5-1()" Torr.

The distance D between the

electrodes

13 and 14 is chosen as a function of the nature and of the pressure of the gas utilized. For example, for the particulars given hereinabove, there is selected the distance D:22 mm; this choice will be justified mathematically more fully hereinafter. The external diameter of the electrode 13 is thereby chosen, for example, to be at 43 mm. and the internal diameter of the electrode 14 at 87 mm.

A second metallic member 21 which supports coaxially a tubulure 22 of brass passing in a tight manner across the member 21, is threadably secured on the member 19 with the interposition of a tight joint. This tubulure 22 serves as support for the device producing the magnetic field, constituted by a stack of ferrite washers 23 alternated with pole pieces 24 of soft iron. The adjacent washers 23 are disposed with identical polarities thereof face to face, i.e., north against north and south against south. The magnetization of the ferrites in this example is such that the axial field measured at 5 mm. from the external surface of the electrode 13 is approximately 400 Gauss. The height of the stack may be of the order of 80 mm. with the dimensions indicated hereinabove. The stack is tightened by means of a nut 25 between two pierced or apertured

washers

26 and 27, whereby the washer 26 abuts against the member 28 secured to the tubulure 22. The magnetic device is introduced together with the tubulure 22 into the inside of the electrode 13, thereupon the member 21 is screwed onto the member 19 in such a manner as to form on the inside thereof a cavity 29 which is water-tight. An output connecting member 30 for the cooling liquid penetrates into the cavity 29 across the member 19.

A circulation of cooling liquid is established through the tubulure 22 up to the closed extremity of the electrode 13, thereupon through the interstices between the peripheries of the ferrite washers 23 and the internal Wall of the electrode 13, the cavity 29 and the connecting member 30.

FIGURE 4 represents also a practical example of utilization for the described tube in a rectifier circuit. This circuit includes a conventional source of alternating current 31 connected to the connection 4 leading to the annular member 15 of the electrode 14, while the output through the connection 3 electrically connected with the electrode 13 is connected with a suitable filter 32 followed by a direct current load or utilization device 33.

Operation The operation of the tube described in terms of a current valve will now be explained in detail, reference being had in particular to the embodiment of FIGURES 4 and 5.

To that effect, it must be remembered at first that the discharges within the gas are regulated by the Paschen law, which is valid for plane as well as cylindrical structures and which establishes a relation between the critical starting voltage V and the product p-d, in which p is the pressure of the gas and d the distance between the electrodes.

FIGURE 6 represents a typical curve for a given gas, corresponding to this relation. It may be readily seen in FIGURE 6 that the curve is composed of a branch which rapidly decreases for values of p-d smaller than a certain threshold (p-d) then, at this threshold, the starting voltage passes through a minimum, and the curve finally continues through a branch slowly rising or essentially horizontal.

If it is assumed that there is no magnetic field within the cylindrical structure of FIGURE 5, then the electrons, regardless of whether they are issued from the

electrode

13 or 14, traverse a radial trajectory of which the length d is equal to the inter-electrode distance D. The product rd is therefore the same in both cases, the starting voltage corresponds to the same point along the Paschen curve regardless of the direction of the applied voltage, and there is practically no valve effect.

However, in the case of the present invention, there exists a magnetic field established by the ferrite washers 23 or any other suitable equivalent source. The lines of force of this magnetic field are indicated by reference numeral 34 in FIGURE 4, and it may be readily seen therein that the lines of force include an axial component. The intensity of this component diminishes rapidly away from the electrode 13, as in the case of FIGURE 1, and is essentially zero in the vicinity of the electrode 14. Consequently, it may be considered for all practical purposes that the magentic field is localized on the inside of an annular zone 35, covered by crosses shown in FIG- URE 5.

The presence of this zone introduces a dissymmetry in the path of the electrons issued from one or the other electrode, and modifies totally the properties of the tube. In effect, the electrons issued from the electrode 14 when the latter is at a negative voltage, are initially directed radially toward the electrode 13 and are subjected along this path or trajectory to an acceleration in such a manner that at the entrance into the zone 35, the electrons possess sufficiently large velocity so that the trajectories thereof are not noticeably deviated notwithstanding the presence of the magnetic field. The electrons therefore describe trajectories such as 36 (FIGURE 5) voltage, for direction of current considered, is little different from that which it would be without magnetic In contradistinction hereto, the electrons issued from the electrode 13 when the latter is at the negative potential, enter into the magnetic field of the zone 35 as soon as they leave the electrode 13, i.e., essentially only with the extraction speed. Under these circumstances, the trajectories thereof are strongly curved by the axial component of the magnetic field in such a manner, that if the field is superior to the critical value, the electrons will describe several arcuate paths of cycloids. Each collision between electrons and molecules which takes place in the course of the cycloidal trajectory diminishes or annuls the speed of the electrons which under influence of the electric field restart anew by describing a series of cycloidal arcs along a diameter larger than the first series, and so on until they leave the zone of the magnetic field 35 and reach the zone in which they are directed practically radially toward the electrode 14. Consequently, the electrons leaving the electrode 13 describe trajectories such as 37 of which the length d between the point of departure from the electrode 13 and the point of impact on the electrode 14 is vastly superior to that of the distance d The inter-electrode distance D is preferably selected of the same order of magnitude as the average free path d of the electron within the gas, i.e., a mean trajectory between two collisions within the medium without magnetic field. This average free path may be calculated according to the known formula:

One obtains, therefore, for the electrons traversing the distance d, the following equation:

pd gpDr-"ipd gl (approximately for hydrogen) By referring to the Paschen curve for hydrogen, one may find that the value P Torr X mm= 1 is very much smaller than (pdh in such a manner that the corresponding point is located on the almost vertical branch of the curve to the left of the threshold, for example at point A in FIGURE 6. At this point A, the starting voltage is very elevated, and below this voltage the tube will not permit the passage of current in the direction considered, which corresponds to the negative polarity of the electrode 14.

In contrast thereto, for the opposite direction, the electrons traverse a distance d which is very much greater than d and the value of pd is such that the point on the Paschen curve is situated near the threshold (pdh or therebeyond along the almost horizontal branch, for example, at point B. The starting voltage at point B is, therefore, very much lower to that of point A in such a manner that in the direction considered, i.e., for a negative polarity of the electrode 13 the tube will permit the passage of current when the starting voltage is exceeded.

Applicant has determined experimentally that with the embodiment of FIGURES 4 and 5, a current of 1 ampere may be extracted for a voltage of 700 volts applied thereto with a negative polarity of the electrode 13 whereas in the opposite direction, there is no measurable current even for an inverse voltage of 10,000 volts.

After the detailed explanation of the operation of the tube of FIGURES 4 and 5, the operation of the modifications of FIGURES 1-2 and 3 is easy to understand from analogous consideration. In FIGURES 1 and 2, the dissymmetry of the trajectories is produced by the localized magnetic field in the same fashion as in FIG-

URES

4 and 5 in such a manner that the operation is the same, except however that the efficiency is more reduced because the absence of the cylindrical form impedes the trajectories which must be lengthened, to describe cycloids with a great number of arcs, before leaving the magnetic field zone. In the embodiment of FIGURE 3, notwithstanding the uniformity of the magnetic field, the dissymmetry is introduced into the trajectories by the single fact of the cylindrical symmetry of the electrodes, in combination with the effect of the magnetic field. In effect, in the cylindrical structure, the electric field is variable in the radial direction in such a manner that the electrons which fall into the crossed electric and magnetic fields at the exit of the electrode, move with different speeds, determined by the ratio between the intensities of the electric field and the magnetic field, depending on Whether they are issued from the internal or external electrode. As this movement takes place within zones of respectively different dimensions near the internal and external electrode, there results therefrom a difference in length of the respective trajectories, and consequently a valving effect in the same manner as in the embodiment in FIGURES 4 and 5, even though with a lesser efficiency.

It might also be mentioned that the cooling means for the ferrite, provided in FIGURE 4 are motivated by the desire to avoid variations in the magnetic field which might !be produced as a result of generation of heat during prolonged operation of the tube. It is known, in effect that the ferrites react poorly to elevated temperatures which entrain modification in the properties thereof which in turn manifest themselves by a reduction in the magnetic field.

While we have shown several embodiments in accordance with the present invention it is understood that the present invention is not limited thereto but is susceptible of many changes and modifications within the spirit and scope thereof. In particular, the system for producing the magnetic field :by means of ferrites may be replaced by any equivalent system producing within the interelectrode space a localized field or a field which varies from one electrode to the other. Even though the main application of the present invention is to rectification. of alternating current, and in particular to rectification at higher voltages than the starting voltage corresponding to the direction of passage of the current through the valve, other applications such as constituting a relay protecting against overcurrents may be envisaged with the tube according to the present invention which is applicable in all cases in which an electric current valve must be inserted into a circuit operating with voltages of the indicated range.

Consequently, the present invention is quite obviously susceptible of many changes and modifications, and we, therefore, do not wish to be limited to the particular details shown and described herein but intend to encompass all such changes and modifications thereof as are encompassed by the scope of the appended claims.

We claim:

1. An electric current valve comprising a pair of planar essentially parallel mutually facing electrodes, a relatively low pressure gas in the space between said electrodes, means for establishing in said space an electric field of a predetermined strength and direction whereby one of said electrodes operates as an anode and the other as cold emissive cathode, and magnetic field generating means for generating in said space a magnetic field having at least a component essentially parallel to the surfaces of said electrodes and varying in strength in the direction perpendicular to said surfaces so that the strength of said component is larger near one of said electrodes than near the other, said magnetic field generating means comprising a lattice of ferrite cubes located outside of said space near the surface of one of said electrodes and having faces turned towards said surface with alternate polarities for each pair of successive adjacent cubes.

2. An electric current valve, comprising within a gastight enclosure a pair of cylindrical essentially co-axial electrodes defining therebetween an interelectrode space, a low pressure gas in said enclosure, means for establishing in said interelectrode space an electric field of a predetermined strength whereby one of said electrodes operates as anode and the other as cold emissive cathode, and magnetic field generating means for generating in said interelectrode space a magnetic field having at least an essentially axially component and a varying strength in the radial direction so that the strength of said component is greater near one of said electrodes than near the other, said magnetic field generating means generating said axial magnetic field component with a strength substantially higher near the inner of said electrodes than near the outer electrode, and said magnetic field generating means including a stack of ferrite washers with alternately reversed polarities, said stack being located outside of said inner electrode space and adjacent to the surface of said inner electrode.

3. A cold cathode gaseous rectifier tube comprising within a gas tight enclosure a pair of cylindrical essentially coaxial electrodes defining therebetween an interelectrode space, a low pressure gas in said enclosure, means for establishing a voltage diiference of changing polarity between said electrodes so as to produce an electric field in said interelectrode space, and magnetic field generating means disposed within said inner cylindrical electrode for generating in a portion of said interelectrode space a magnetic field having a component parallel to the axis of said pair of electrodes, said magnetic field being non uniform within said interelectrode space with the strength of said component being greater adjacent said inner cylindrical electrode, said magnetic field generating means comprising a stack of ferrite washers with alternately reversed polarities.

References Cited by the Examiner UNITED STATES PATENTS 2,165,805 7/39 Morgan 313- 161 2,182,736 12/39 Penning.

2,217,187 10/40 Smith 313-161 2,660,687 11/53 Coleman 313l61 2,813,992 11/57 Linder 313161 GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner.

Claims

1. AN ELECTRIC CURRENT VALVE COMPRISING A PAIR OF PLANAR ESSENTIALLY PARALLEL MUTUALLY FACING ELECTRODES, A RELATIVELY LOW PRESSURE GAS IN THE SPACE BETWEEN SAID ELECTRODES, MEANS FOR ESTABLISHING IN SAID SPACE AN ELECTRIC FILED OF A PREDETERMINED STRENGTH AND DIRECTION WHEREBY ONE OF SAID ELECTRODES OPERATES AS AN ANODE AND THE OTHER AS COLD EMISSIVE CATHODE, AND MAGNETIC FIELD GENERATING MEANS FOR GENERATING IN SAID SPACE A MAGNETIC FIELD HAVING AT LEAST A COMPONENT ESSENTIALLY PARALLEL TO THE SURFACES OF SAID ELECTRODES AND VARYING IN STRENGTH IN THE DIRECTION PERPENDICULAR TO SAID SURFACES SO THAT THE STRENGTH OF SAID COMPONENT IS LARGER NEAR ONE OF SAID ELECTRODES THAN NEAR THE OTHER, SAID MAGNETIC FIELD GENERATING MEANS COMPRISING A LATTICE OF FERRITE CUBES LOCATED OUTSIDE OF SAID SPACE NEAR THE SURFACE OF ONE OF SAID ELECTRODES AND HAVING FACES TURNED TOWARDS SAID SURFACE WITH ALTERNATE POLARITIES FOR EACH PAIR OF SUCCESSIVE ADJACENT CUBES.