US3135892A - Cold cathode gas discharge tubes - Google Patents

Description

United States Patent 3,135,892 C611) CATHODE GAS DISCHARGE TUBES George hater Stenning, Stanmore, lxiddlesex, England, assignor to Hivac Limited, South Ruislip, Middlesex, England, a company of Great Britain Filed Dec. 4, 1961, Ser. No. 155,579 Claims priority, application Great Britain Dec. 8, 1969 8 Claims. (Cl. 313-438) This invention relates to cold cathode gas discharge tubes and is more particularly concerned with tubes of the so-called trigger type in which breakdown of the main discharge path between the cathode and anode of the tube is initiated by a triggering discharge brought about by application of a suitable control potential to a further or trigger electrode.

In accordance with the broadest aspect of the invention, the cathode electrode is of small size relative to the cooperating anode and is located within and is eifectively surrounded by such anode while the trigger electrode is arranged at a suitable small spacing distance from said cathode in between it and said anode.

in a preferred form of construction according to the invention, the anode has the shape of a cylinder which may be open-ended but which is preferably at least partially closed at one or both ends while the cathode has the form of a rod or fiat plate disposed within and co-arial with said anode. The trigger electrode may conveniently comprise a further cylinder co-axial with but of smaller diameter and of lesser axial length than said anode and surrounding at least a part of the cathode. The actual trigger gap is constituted in a preferred form by a wirelike extension from the trigger electrode cylinder passing into close-spaced relationship with the cathode at a position adjacent an open end of the trigger cylinder.

In an alternative construction the anode may be of semispheiical form with the cathode disposed substantially at the centre point of the anode surface.

In order that the nature of the invention may be more readily understood, a number of particular constructional embodiments thereof wih now be described by way of illustrative example only and with reference to the accompanying drawings in which:

FIG. 1 is a largely schematic axial sectional view of one form of cold cathode discharge tube according to the invention;

FIG. 2 is an enlarged end View of the electrode structure of the tube shown in FIG. 1;

FIGS. 3 and 4 are axial sectiona views of other alternative forms of electrode structure according to the invention.

Referring first to FIGS. 1 and 2 of the drawings, the tube construction shown therein comprises a cathode 1G in the form of a rectangular cross-section metal strip having a somewhat pointed upper end 11. This cathode strip is attached to an electrode support Wire 12 which is embedded within a moulded glass stem 13 integral with a button or platform 14 serving as a mouting for all of the tube electrodes. The wire 12 passes, in the usual way, to an external connection lead 25 extending outwardly from the tube envelope shown at 26.

The anode 15 is in the form of an almost, but preferably not quite, complete cylinder 16 of sheet metal which is seated at its lower end upon or in close-spaced relationship to the upper surface of the platform 14 and is closed at its opposite upper end by a closure wall 17 which is preferably of domed shape as shown. The anode is secured in position by interconnection with support/connection wires 18 which are moulded in the platform 14 and at least one of which passes to an external connection lead 25.

3,135,892 Patented June 2, 1964 The trigger electrode 19 is in the form of a further imperforate sheet metal cylinder co-axial with the anode 15 and cathode 16, said trigger electrode cylinder surrounding the cathode and extending from the upper surface of the platform 14 to a region approximately level with the upper end 11 of the cathode 10. To such cylinder 19 is attached an inwardly directed wire portion 20 which is positioned, as by bending, to pass close to the pointed end 11 of the cathode thereby to provide a trigger gap of small dimension between itself and the said cathode. The trigger gap is thus readily visible from a major area of the anode, a known requirement for reliable and consistent triggering of the main discharge within the tube. The trigger electrode is attached to a support/ connection wire 21 which is also moulded in the platform 14 and extends to another external connection lead 25.

The tube is provided with a further keep alive electrode in the form of an auxiliary cathode 22 disposed in close-spaced relationship to the inner surface of the anode cylinder 16. This keep alive electrode is attached to a support/connection wire 23 also moulded into the platform 14 and thereafter joined to a further external connection lead 25.

The cathode 15 may be of pure metal such as molybdenum but other metals, such as nickel or tantalum, normally used for cathode construction of cold cathode gas discharge tubes may be employed. Alternatively the cathode may be one coated with emissive material. The cathode is arranged to have sufiicient outer surface area to carry the value of current desired to flow through the tube; in order to avoid the need for an inconveniently large cathode area having to be located at the centre of the surrounding anode, a relatively high gas filling pressure may be employed in some applications where large current values are desired. Such gas filling may be, for example, of neon or a mixture composed principally of neon with about 1% of argon, krypton or helium. Alternatively, for some applications, a filling consisting wholly or mainly of one of the inert gases, or even hydrogen, may be used. The filling may be at a pressure of 200-300 mm. Hg instead of the more usual pressure of 3050 mm. Hg for many applications although the more usual pressures of the last mentioned range may be used for some applications.

The arrangement of the cathode it to lie at the centre of a surrounding and substantially enclosing anode 15 has the advantage of providing a high potential gradient at the cathode which is conducive to eficiency of electron emission and sensitivity to triggering by a small current discharge between the trigger electrode and the cathode. The correspondingly low potential gradient at the anode renders the actual shaping of the anode structure non-critical. Furthermore, both the cathode and the trigger electrodes are enclosed and effectively shielded by the anode which is the electrode least sensitive to external influences.

The provision of a keep alive electrode operating in the low potential gradient conditions immediately adjacent the auode enables it to perform the function of providing ionisation without causing risk of undesired breakdown between the cathode and anode. The pres ence of the trigger electrode, which is connected to a potential intermediate that of the anode and cathode, largely surrounding the cathode, constitutes means for providing a more uniform potential gradient between the cathode and anode and in consequence of this a higher operating potential may be employed between anode and cathode for a given physical spacing distance between the electrodes and a given gas filling pressure. The use of a higher gas pressure also has the advantage tially so.

' -29 of providing a higher gap breakdown voltage and a shorter recovery or de-ionisation time.

Various modifications may be made without departing from the scope of the invention. Thus the anode need not physically enclose the cathode and trigger electrodes provided it is so shaped that it effectively surrounds the latter electrodes by its electrostatic field. This may be achieved by extending the axial length of the anode beyond the respective ends of the trigger and cathode electrodes whereby the latter are located right inside the anode as shown in FIG. 3. Another possible arrangement is shown in FIG. 4 where the metallic top closure wall 17 of the anode shown in FIGS. 1 and 2 is replaced by an insulating, e.g. mica, disc 27 which also serves in the customary manner to assist in the location of the electrode structure within the surrounding tube envelope 26. In this further embodiment,

the mounting platform 1 is replaced by the more conventional flat pinch construction as shown at 28 within which the various connecting and support wires are embedded. As a result of this, the lower end ofthe anode cylinder 16 is not completely closed but remains substan- The trigger electrode cylinder 19 preferably remains closed by being seated upon the upper surface of the pinch region 23.

I claim: 7

l. A cold cathode gase discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary cathode located within a sealed envelope containing a low pressure gaseous filling ofan inert rare gas, said cathode being of small size relative to said anode, said trigger electrode being closely spaced relative to and substantially surrounding said cathode, said anode substantially surrounding said cathode and trigger electrode and being spaced at a large. distance from the trigger electrode compared with the spacing distance between said trigger electrode and said cathode whereby a discharge between said trigger electrode and cathode can be initiated at a low voltage compared with the voltage required to cause breakdown between said anode and cathode or beween said anode and trigger electrode and said auxiliary cathode being of small size compared with said cathode electrode and being mounted in close proximity to the inner surface of said anode between said anode and said trigger electrode whereby a very low current priming discharge can be continuously maintained between said anode and said auxiliary cathode to provide fast operation of the tube with short voltage pulses applied to said trigger electrode.

2. A cold cathode gas discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary cathode located within a sealed envelope containing a low pressure gaseous filling, said cathode being of small size relative to said anode, said trigger electrode being closely spaced relative to and substantially surrounding said cathode, said anode substantially surrounding said cathode and trigger electrode and being spaced at a large distance from the trigger electrode compared with the spacing distance between said trigger electrode and said cathode whereby a discharge between said trigger electrode and cathode can be initiated at a low voltage compared with the voltage required to cause breakdown between said anode and cathode or between said anode and trigger electrode, said auxiliary cathode being of small size compared with said cathode and being mounted in close proximity to the inner surface of said anode between said anode and said trigger electrode whereby a very low current priming discharge can be continuously maintained between said anode and auxiliary cathode, and said gaseous filling comprising an ionisable medium including at least one of the rare gases to provide fast operation of the tube with short voltage pulses applied to said trigger electrode.

3. A cold cathode gas discharge tube comprising a ti. cathode, an anode, a trigger electrode and an auxiliary cathode located within a sealed envelope containing a low pressure gaseous filling, said cathode being of small surface area relative to said anode, said trigger electrode being closely spaced relative to and substantially surrounding said cathode, said anode substantially surrounding said cathode and trigger electrode and being spaced at a large distance from the trigger electrode compared with the spacing distance between said trigger electrode and said cathode whereby a discharge between said trigger electrode and cathode can be initiated at a low-volage compared with the voltage required to cause breakdown between said anode and cathode or between said anode and trigger electrode, said auxiliary cathode being of small area compared with said cathode and being mounted in close proximity to the inner surface of said anode between said anode and said trigger electrode whereby a very low current priming discharge can be continuously maintained between said anode and auxlow pressure gaseous filling, said cathode being ofsmall surface area relative to said anode, said trigger electrode being closely spaced relative to and surrounding said cathode, said anode substantially surrounding saidcathode and trigger electrodes and being spaced at 'a large distance from the trigger electrode compared with the spacing distance between said trigger electrode and said cathode whereby a discharge between said trigger electrode and cathode can be initiated at a low voltage com! pared with the voltage required to cause breakdown between said anode and cathode or between said anode and trigger electrode, said auxiliary cathode being of small surface area compared with said cathode and being mounted parallel with and in close proximity to the inner surface of said anode whereby a very low current priming discharge can be continuously maintained between said anode and auxiliary cathode, and said gaseous filling comprising not less than 99% neon at a pressure of the order of 20030O mm. Hg to provide fast operation of the tube with short voltage pulses applied between said trigger electrode and said cathode.

5. A cold cathode gas discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary athode located within a sealed envelope containing a low 7 pressure ionisable gaseous filling, said cathode being in the form of a short rod-like member having a surface area many times smaller than said anode, said trigger electrode being an imperforate cylinder closely spaced relative to and surrounding said cathode, said anode surrounding and enclosing said cathode and trigger electrodes and being spaced at a large distance from the trigger electrode compared with the spacing distance between said trigger electrode and said cathode whereby a discharge between said trigger electrode and cathode can be initiated at a low voltage compared with the voltage required to cause reakdown between said anode and cathode or between said anode and trigger electrode and said auxiliary cathode being of smaller surface area than said cathodeelectrode and being mounted in close proximity to the inner surface of said anode between said anode and said trigger electrode whereby a very low current priming discharge can be continuously maintained between said anode and said auxiliary cathode to provide fast operation of the tube with short voltage pulses applied between said trigger electrode and said cathode.

6. A cold cathode gas discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary cathode electrode in a sealed envelope, in which said anode is in the form of a cylinder closed at each end and surrounding all of the other electrodes, said cathode is in the form of a linear element of a length short compared with that of the axial length of said anode and disposed co-axial with said anode at approximately the centre of the anode length, said trigger electrode is also of cylindrical shape and disposed co-axial with said cathode and anode, said trigger electrode being of imperforate character and of a diameter such that the radial spacing dis tance between said cathode and said trigger electrode is small compared with the radial spacing distance between said trigger electrode and said anode and said auxiliary cathode comprising a plate of a size small compared with that of such cathode and which is located in parallel relationship to the inner surface of said anode with a spacing distance which is small compared with the spacing distance between said cathode and trigger electrode, and in which said envelope contains an ionisable gaseous filling comprising at least 99% neon at a pressure of the order of 200300 mm. Hg.

7. A cold cathode gas discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary cathode electrode all mounted on a common platform of insulating material in a sealed envelope, in which said anode is in the form of an imperforate sheet metal cylinder seated by one end on said platform and closed at its other end so as to surround all of the other electrodes, said cathode is in the form of a linear element of a length short compared with that of the axial length of said anode and disposed co-axially within said anode at approximately the centre thereof, said trigger electrode is also of cylindrical shape and disposed co-axially With said cathode and anode with one end seated on said platform and its opposite end level with one end of said cathode element, said trigger electrode being of imperforate character and of a diameter such that the radial spacing distance between said cathode and said trigger electrode is small compared With the radial spacing distance between said trigger electrode and said anode and said auxiliary cathode comprising a plate having an area small compared with that of such cathode and located in parallel relationship to the inner surface of said anode with a spacing distance which is small compared with the spacing distance between said cathode and trigger electrode, said sealed envelope containing a gaseous filling comprising at least 99% neon at a pressure of the order of 200-300 mm. Hg.

8. A cold cathode gas discharge tube comprising a cathode, an anode, a trigger electrode and an auxiliary cathode electrode all mounted on a platform of insulating material in a sealed envelope, in which said anode is in the form of an imperforate metal cylinder seated at one end on said platform and closed at its other end by an imperforate metal wall so as to surround all of the other electrodes, said cathode is in the form of a metal strip pointed at one end and of a length short compared with that of the axial length of said anode and disposed coaxially within said anode at approximately the centre thereof, said trigger electrode is also of cylindrical shape and disposed co-axially with said cathode and anode with one end level with the pointed end of said cathode, said trigger electrode being of imperforate character and of a diameter such that the spacing between the cathode and sad trigger electrode is small compared with the spacing between said trigger electrode and said anode, said trigger electrode having a wire extension projecting inwardly to lie close to the pointed end of said cathode, and said auxiliary cathode comprising a plate having a surface area small compared with that of such cathode and located in parallel close spaced relationship to the inner surface of said anode, said sealed envelope having gaseous filling of an ionisable rare gas.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A COLD CATHODE GASE DISCHARGE TUBE COMPRISING A CATHODE, AN ANODE, A TRIGGER ELECTRODE AND AN AUXILLIARY CATHODE LOCATED WITHIN A SEALED ENVELOPE CONTAINING A LOW PRESSURE GASEOUS FILLING OF AN INERT RARE GAS, SAID CATHODE BEING OF SMALL SIZE RELATIVE TO SAID ANODE, SAID TRIGGER ELECTRODE BEING CLOSELY SPACED RELATIVE TO AND SUBSTANTIALLY SURROUNDING SAID CATHODE, SAID ANODE SUBSTANTIALLY SURROUNDING SAID CATHODE AND TRIGGER ELECTRODE AND BEING SPACED AT A LARGE DISTANCE FROM THE TRIGGER ELECTRODE COMPARED WITH THE SPACING DISTANCE BETWEEN SAID TRIGGER ELECTRODE AND SAID CATHODE WHEREBY A DISCHARGE BETWEEN SAID TRIGGER ELECTRODE AND CATHODE CAN BE INITIATED AT A LOW VOLTAGE COMPARED WITH THE VOLTAGE REQUIRED TO CAUSE BREAKDOWN BETWEEN SAID ANODE AND CATHODE OR BETWEEN SAID ANODE AND TRIGGER ELECTRODE AND SAID AUXILIARY CATHODE BEING OF SMALL SIZE COMPARED WITH SAID CATHODE ELECTRODE AND BEING MOUNTED IN CLOSE PROXIMITY TO THE INNER SURFACE OF SAID ANODE BETWEEN SAID ANODE AND SAID TRIGGER ELECTRODE WHEREBY A VERY LOW CURRENT PRIMING DISCHARGE CAN BE CONTINUOUSLY MAINTAINED BETWEEN SAID ANODE AND SAID AUXILIARY CATHODE TO PROVIDE FAST OPERATION OF THE TUBE WITH SHORT VOLTAGE PULSES APPLIED TO SAID TRIGGER ELECTRODE.

Images