US2491234A - Cold cathode discharge tube - Google Patents

Description

Dec. 13, 1949 c. F. VEENEMANS ET AL 2,491,234

COLD CATHODE DISCHARGE TUBE' I Filed Feb. l2, 1947 z v w M" u n Y V .r

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Patented Dec. 13, 1949 COLD CATHODE DISCHARGE TUBE Cornelis Frederik Veenemans and Pieter Geert van Zanten, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application February 12, 1947, Serial No. 728,014

In Belgium November 3, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires November 3, 1964 (Cl. Z50-27.5)

1 Claim.

This invention relates to a device having an electrode system which comprises an electronemitting electrode, from which the electrons emerge by iield emission. This is to be understood to mean an electrode which consists of at least one conducting substratum and a very thin insulating layer, and with which a high eld strength occurs in this insulating lm if a potential diierence is set up between this electrode and another conducting electrode energized to function as a suction electrode. Therefore, such first-mentioned electrode supplies electrons in the cold state. An example of such an electrode has been described by Malter in Physical Review 1936, vol. 49, page 478. In that case the said electrode is not used as a primary but as a secondary cathode. An electrode of the kind described here may be built up in various ways, but it is necessary that it comprises a thin insulating layer in which a high field strength occurs.

The current emerging from an electrode thus built cannot be controlled in the usual way by placing a negative grid in front of it, because a space charge cloud, as occurs in normal cathodes, does not ensue with a cathode of the kind referred to above, owing to the fact that the electrons emerge at a comparatively high velocity (30 to 50 volts).

True, by varying the voltage in the plane of the suction electrode a small variation of the electron current can be obtained.

Researches have shown that control with a steeper slope is possible when making use of a device according to the present invention, which is characterized in that it comprises a cathode emitting by field-emission, and in addition a plurality of grids and an anode, with the second grid, viewed from the cathode to the anode, or with a grid nearer to the anode, functioning as a control grid, and on the cathode side of the control grid there being a grid to which is applied a voltage which is positive with respect to the cathode.

In a device according to the invention it appears that the control grid, in a definite voltage range of this grid, has a negative anode-current control-grid voltage characteristic i. e. that an increase in grid Voltage involves a decrease in anode current and conversely.

This may be due to the fact that electrons return in front of the grid and dislodge positive spots at the insulating layer of the electronemitting electrode. as a result of which the emission of the cathode increases as the grid voltage decreases. Energetically this can be explained in such a manner that by the special construction of the cathode the electrons, upon emerging from the insulating layer, frequently have a velocity exceeding 0 volt; this velocity may, for instance, be commensurate to 3D to 50 volts. Consequently, since these electrons return to the layer at the same velocity, they will be capable of dislodging there positive spots.

In a particular form of construction of the present invention the second grid, viewed from the cathode to the anode, functions as a control grid, and a positive voltage is applied to the first grid. This voltage may, for instance, have a value between and 250 volts. It is possible, however, that the control grid constitutes one of the next grids, in which case a preceding grid has a positive voltage. It is pointed out in this respect that the grids may be Wound at will and that it is advisable not to wind these grids in such a manner that the turns are located one behind the other.

In order that the invention may be clearly understood and readily carried into eiect it will now be described more fully with reference to the accompanying drawing, given by way of example, in which a system to be used in a device according to the invention is represented diagrammatically.

Figure 1 is a side elevational view of an electron discharge tube with a portion of the envelope broken away to show the relative location of the electrodes within the tube; and

Figure 2 is a schematic sectional view of the electrode arrangement and showing particularly the construction of the cathode.

In this drawing the reference numeral I denotes a nickel wire which functions as a conducting substratum for the cathode. This wire carries an insulating layer 2, for example, of magnesium oxide, which has a thickness of some few microns and is covered with a material 3. for instance caesium oxide, having a high electron-emitting capacity. The cathode thus designed and emitting by eld emission is surrounded by two grids 4, 5 and an anode 6. To the grid 4 is applied a direct voltage of 200; the grid 5 acts as a control grid and to the anode is applied a voltage of 250.

What we claim is:

An electron discharge tube comprising a cathode having a thin insulating layer for establishing a localized high field strength under the iniiuence of an impressed field, the cathode being adapted to be operated as a cold electrode and to cause secondary emission at the 'cathode and thereby establish a negative impedance effect in the tube.

CORNELIS FREDERIK VEENEMANS. PIETER GEERT VAN 4 REFERENCES CITED The following references are of record in the file of this patent:

Number Name Date 1,750,058 Schmierer Mar. 11, 1930 1,779,550. Loewe Oct. 28, 1930 1,511,051 Holst 1 June 23, 1931 1,9845877 Jobst et al Dec. 18, 1934 2,235,498 H'er'l Mar. 18, 1941

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