DE29719557U1 - Cold electrode for gas discharges - Google Patents

Description

Dipl. Phys. Marcus Thielen ··* ·· ·· - 1 -

Winkelhauser Str. 81, 47228 Duisburg * **' *** ** *

Designation

Cold electrode for gas discharges

Description

State of the art

Cold electrodes for gas discharges with partial use of the hollow cathode effect have been known and used for a long time in technology, e.g. for electron tubes or lighting purposes. {e.g. U.S. Pat. I 125 476)

Cold hollow cathode electrodes are usually provided with a coating on the inside consisting of mixtures of alkaline earth oxides - hereinafter referred to as activation. (Wehnelt's principle, 1907) Since these oxides are not stable under ambient conditions, the activation is applied to the carrier material of the electrode in the form of carbonates and converted into oxides in a conditioning process during the manufacture of the discharge lamp. More recent developments are based on the direct use of materials with an inherently low photo work function to coat the carrier material, bypassing a chemical conversion during the manufacturing process (utility model DE 297 03 990.3).

Problem

The activation applied to the inside of the electrode carrier material can only be applied in a very thin layer, as the process of photoemission of electrons only takes place in the uppermost atomic layers of the surface. During operation, the surface is exposed to constant ion bombardment, which atomizes the activation layer within a short time through pulse transfer (process of cathode sputtering) or poisons it with chemically reactive foreign substances, thus rendering it unusable.

Dipl. Phys. Marcus Thielen J &Idigr; "J' * J J " "J I - 2 -

Winkelhauser Str. 81, 47228 Duisburg · * ·· *

This process significantly limits the service life of the gas discharge device.

The aim is to create an electrode that maintains the low work function of the surface for a long time even under the operating conditions of a gas discharge, thus significantly extending the service life of the gas discharge device.

Troubleshooting

The problem described is solved by the features listed in claim 1, in particular by creating a constantly renewed surface with a low photo work function. At the same time, the constant renewal of the surface during operation ensures that the electrode properties are largely independent of the boundary conditions of the manufacturing process of the gas discharge device.

Advantages

The advantage of this invention is that the service life of the electrode and thus of the gas discharge device is extended many times over conventional designs, achieved by the constant renewal of the active surface with a low photo work function. At the same time, the electrode according to the invention is largely insensitive to fluctuating conditions during processing or conditioning due to the use of chemically inert materials with a low photo work function (e.g. yttrium) and the constant renewal of the active layer during operation. The arrangement of an element made of atomizable or evaporable material with a low photo work function in such a way that this element can be hit by the ions of the gas discharge during operation means that a small amount of material with a low photo work function is constantly atomized from the element like from a reservoir and deposited on the electrode surface.

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Winkelhauser Str. 81, 47228 Duisbu#3 · ··· ··· ·· ·

The lifetime of the electrode is therefore only limited by the atomization rate or evaporation rate and the amount of material in the reservoir element, and this can be several times the amount of a thin activation layer of a conventional electrode.

Further embodiment of the invention

The embodiment of the invention according to claim 2 advantageously allows the targeted evaporation/atomization of activation material by external measures. This enables a more precisely defined conditioning of the electrode during the manufacturing process of the gas discharge lamp.

The embodiment of the invention according to claim 3 advantageously allows the use of a separate, e.g. electrical, heating device, in order to keep the heating power required to release activation material independent of the amount of material present in the reservoir.

The embodiment of the invention according to claim 4 advantageously allows an increased operational reliability of the renewal process by largely avoiding an electron or ion current from the outside of the carrier body.

The embodiment of the invention according to claim 5 advantageously allows the saving of coating or plating operations by producing the carrier body itself from material with a low work function.

The embodiment of the invention according to claim 6 advantageously allows the further reduction of the photo work function compared to the use of pure substances by creating donor or acceptor levels with very low excitation energy. This is associated with the reduction of the cathode fall and the electrical losses and thus in turn the heating of the electrode during operation.

Dipl. Phys. Marcus Thielen J J **J* * * * * **· * — 4 -

Winkelhauser Str. 81, 47228 Duisburg»? · ··· ··· ·· ·

The embodiment of the invention according to claim 7 advantageously allows the complete suppression of an electron or ion current from the outside of the carrier material, which could inhibit the regenerative mechanism and lead to the rapid destruction of the electrode.

The embodiment of the invention according to claim 8 advantageously allows the premature sputtering of the carrier material by ion attack from the edge facing the gas discharge to be prevented.

An embodiment of the invention according to claim 9 advantageously allows - at the same time as the prevention of premature atomization of the carrier material described in claim 6 - the formation of an annular channel when using the electrode in tubular casings made of insulating material, e.g. glass. This prevents the discharge from spreading to the outside of the carrier body and the power supply wires in a harmful and therefore undesirable manner.

The embodiment of the invention according to claim 10 advantageously allows a reduction in the edge sputtering of the carrier material while saving an additional protective body as according to claim 9.

The embodiment of the invention according to claim 11 advantageously allows the centering of the electrode when installed in receiving bodies, e.g. tubular glass bodies, and prevents mechanical and thermal contact between the electrode and the glass body during conditioning and operation.

The embodiment of the invention according to claim 12 advantageously allows the use of widely used production tools for rolling or deep-drawing the carrier body material in a manner known per se.

The embodiment of the invention according to claim 13 advantageously allows the noble gas atmosphere in gas discharge lamps to be kept clean by selectively absorbing any reactive gases or vapors that may be released during operation.

Dipl. Phys. Marcus Thielen JJ··;· · JJ * **l I - 5 -

Winkelhauser Str. 81, 47228 Duisbutf? · ··· ··· ·· ·

The embodiment of the invention according to claim 14 advantageously allows the use of materials with a very low work function, which would not be stable in a usable state under ambient conditions, but can be handled without problems in chemically or physically bound form.

Exemplary execution

Fig. 1 shows an exemplary embodiment of the invention. The electrode is shown in longitudinal section. The layer thicknesses are not shown to scale for clarity.

The electrode according to the invention consists of the carrier body (1) made, for example, from iron and designed, for example, in the form of a cup, with an opening facing the gas discharge. In the space enclosed by the carrier body (1), the element (2) is mounted as a reservoir in such a way that the ions of the gas discharge, which enter the enclosed space of the carrier body through the opening, can hit the element (2).

The material dusted from the reservoir element (2) by ion impact is deposited on the inside of the carrier body (1) as an active layer (3). This layer consists of material with a low photoelectric work function, e.g. yttrium. The outside of the carrier body is coated here, for example, with a material with a high photoelectric work function (4), e.g. nickel or platinum, or an insulating material, e.g. aluminum oxide or silicon dioxide. The power supply wires (5) are attached to the closed end of the carrier body, here in the form of a spherical cap, in a manner known per se, e.g. by spot welding.

Figure 2 shows, by way of example, a longitudinal section through an electrode according to the invention, installed in a tubular receiving body (8) - here made of glass - in a known design as part of a gas discharge vessel, e.g. for use in high-voltage fluorescent tubes. The opening of the carrier body is fixed in the receiving body perpendicular to the axial direction by a centering body (6), e.g. made of mica, and here

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Winkelhauser Str. 81, 47228 Duisburg» · ··· ··· ·· ·

for example, provided with a protective body with a collar (7), e.g. made of aluminum oxide ceramic. The reservoir element (2) is here for example hollow to accommodate a heating device (9). The heating device (9) consists, for example, of an insulated tungsten wire, which has been introduced into the hollow reservoir element (2).

The power supply wires (5), as well as a pump tube (12), which serves to evacuate the gas discharge vessel in a known manner, and also the power supply (11) of the heating device (9) are led through the receiving body (8) in a vacuum-tight manner in the connection-side end (10), e.g. here as a glass squeeze foot.

Claims (1)

Dipl. Phys. Marcus Thielen · J ··" · JJ · ··· J &mdash; 7 &mdash; Winkelhauser Str. 81, 47228 Duisburg» · ··· ·»· ·· · Protection claims 1. Cold electrode for gas discharges of a known design, in which a completely or partially enclosed space is formed by electrically conductive material - hereinafter referred to as carrier material (e.g. metal) - with at least one opening in the direction of the gas discharge, characterized by the fact that in this space, an atomizable or vaporizable element is arranged in such a way that it can be struck by the ions of the gas discharge with or without external electrical or magnetic auxiliary fields and that the material vaporized or sputtered by this element can precipitate on the inner boundary surfaces of the space delimited by the carrier material and this precipitated material has a lower photo work function than the material of the outer boundary surfaces of the space. 2. Electrode according to claim 1, characterized in that the element can be atomized or vaporized by external electromagnetic fields or by the passage of current. . Electrode according to claim 1 or 2, characterized in that the element can be atomized or vaporized with the aid of a heating device. 4. Electrode according to claim 1 to 3, characterized in that the carrier material is provided on the outside with a coating which has a particularly high photo work function. 5. Electrode according to claim 1 to 4, characterized in that the carrier material forming the electrode itself consists of material with a low photoelectric work function. &bull; J Dipl. Phys. Marcus Thielen J J ···« »J J · &diams;·· Winkelhauser Str. 81, 47228 Duisburg· · 6. Electrode according to claims 1 to 5, characterized in that the element or the material deposited therefrom contains targeted impurities (so-called dopants) to reduce the photo work function compared to the pure substance. 7. Electrode according to claims 1 to 6, characterized in that the outside of the carrier material is provided with an electrically insulating coating or an electrically insulating sheath to suppress an electron or ion current emanating from this outside. 8. Electrode according to claim 1 to 7, characterized in that the edges of the opening facing the gas discharge are coated with an electrically insulating, temperature and vacuum resistant material (e.g. ceramic). 9. Electrode according to claims 1 to 7, characterized in that an electrically insulating sleeve as a protective body, which is provided with a specially shaped collar, is inserted into the opening and fastened in such a way that the collar covers the edges of the opening of the carrier material in the direction of the gas discharge. 10. Electrode according to claim 1 to 9, characterized in that the edge of the opening facing the gas discharge is bent or flanged or shaped in another suitable manner to reduce the electric field gradient at the opening. 11. Electrodes according to claims 1 to 10, characterized in that when installing the electrode in tubular receiving bodies with a cross-section that is not necessarily round, a centering element made of poorly heat-conducting, electrically insulating material (e.g. ceramic or mica) is used. &bull; t ■ * · tfc ti··· Dipl. Phys. Marcus Thielen · · ·■»»· · · · · 4·· ■» - 9 - Winkelhauser Str. 81, 47228 Duisburg· · ··· <·· .· * 12. Electrode according to claims 1 to 11, characterized in that the carrier body is in the form of a hollow cylinder, cup or hollow cone and the atomizable or vaporizable element is shaped as a plate, rod, foil, grid, pellet, tube or sphere. 13. Electrode according to claims 1 to 12, characterized in that a substance that selectively binds reactive gases (so-called getter) is applied to the atomizable or vaporizable element, its holder or the heating device, the power supply lines, the carrier body, the receiving body, the protective body or the centering body. 14. Electrode according to claims 1 to 13, characterized in that the atomizable or vaporizable material of the element is not introduced in its usable form, but rather is created from a chemical reaction or a physical process during conditioning or operation of the electrode.