MXPA01005590A - Apparatus and method for reducing operating voltage in gas discharge devices - Google Patents

Abstract

The present invention is a system and method for reducing the voltage necessary to produce a glow discharge in a gas (14). This is done by fabricating the cathode (20) in a gas discharge out of a conductive material that is permeable to the subject gas rather than out of a solid material, as in the prior art. Fabricating the cathode (20) with a permeable material rather than a solid material increases the surface area of the cathode (20) and provides the gas (14) with greater access to the cathode's surface. Increasing the surface area of the cathode (20) increases the total discharge current which can be extracted from the cathode (20) without increasing the extraction voltage. This allows the gas discharge device to be operated at a lower voltage than is possible using a cathode (20) fabricated of a solid material.

Description

APPARATUS AND METHOD FOR REDUCING OPERATING VOLTAGE IN GAS DISCHARGE DEVICES FIELD OF THE INVENTION The present invention relates generally to the field of gas discharge devices, which include, but are not limited to, neon signals and gas lasers.

BACKGROUND OF THE INVENTION Gas halo discharge, also known as cold cathode discharge, is widely used in a variety of devices for applications such as advertising, lighting and decoration. This technology is also useful for a variety of other applications, including processing of materials. Some common examples of gas discharge device are neon signals and gas lasers. Gases capable of sustaining halo discharges, including but not limited to neon, are well known in the art. A gas discharge is generated when sufficient electrical current flows between the cathode and the anode in a chamber, known as a discharge tube or Ref: 130296 plasma reactor, which is filled with a suitable reactive gas, such as neon. If the cathode is capable of producing the discharge without the application of heat, the cathode is known as a cold cathode. In order to supply current flow necessary to generate a halo discharge, a voltage is applied between the cathode and the anode from an external power source. A major drawback for this technology is that very high operating voltages are required. Depending on the geometrical dimensions of the housing and the nature of the filler gas, operating voltages up to and exceeding 15 kV may be required to generate a halo discharge in the gas. Due to the high voltages required to generate halo discharge, one of the key design parameters for gas discharge devices is aimed at producing the highest possible halo discharge current while minimizing the required operating voltage. . The operating voltage is proportional to the working function of the electrons of the material comprising the cathode, and inversely proportional to the surface area of the cathode. Thus, for a given cathode material, the operating voltage can be reduced by implementing the surface area of the cathode. The cathode surface area can be increased simply by increasing the physical dimensions of the cathode, but because the cathode must be comprised within the discharge tube, this may require increasing the physical size of the discharge tube to accommodate the larger cathode . This is an undesirable result in many applications. Therefore, to date there is an unresolved need in the industry for a gas discharge device that can be operated at a lower voltage than currently available devices without increasing the physical size of the device.

BRIEF DESCRIPTION OF THE INVENTION The present invention overcomes the inconsistencies and deficiencies of the prior art as noted above, and as is generally known in the industry, by forming the cathode of a gas discharge device from a conductive material that is gas permeable. objective. In a preferred embodiment, the cold cathode is a hollow cathode with an outer wall formed with a permeable, mesh or perforated material (generally referred to herein as permeable) instead of solid wall formation typical of the art. previous. The cathode, in a preferred embodiment, can be cylindrically shaped with a side wall of a permeable conductive material, such as stainless steel mesh, and having an end that is open or closed, and an open end. The cathode is mounted inside the discharge tube and connected to an external power supply using conventional means. The permeable wall configuration increases the surface area of the cathode without increasing its physical size. The use of a permeable wall cathode therefore allows, the generation of an ion gas flow from reactive gas at lower pressure and lower temperature than a solid wall configuration of the same size. With the exception of the requirements that the cathode have an open end and the ability to be connected to a power supply, there are no fundamental limitations on the configuration of the cathode. Additional embodiments may include, but are not limited to, a configuration comprising a plurality of nested or nested side walls in one another, and a multiple wall configuration constructed of a single piece of mesh material formed in a spiral shape. It is not intended that these examples limit the generality of the invention, and there is no fundamental limitation on the various configurations that may be used in accordance with the present invention. Other objects, features and advantages of the present invention will become apparent to a person skilled in the art upon examination of the drawings and the following detailed description. All goals and additions, advantages and features are intended to be included in this description within this description.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be better understood with reference to the following drawings. The drawings do not necessarily belong to this scale, rather emphasizing clearly illustrate the principles of the present invention. In addition, in the figure, similar reference numbers designate corresponding parts throughout the various views. Figure 1 is a schematic diagram showing a generalized seventh for a gas discharge device with the cathode configured according to the present invention.

Figure 2A is a schematic diagram showing the front view of a cathode configured according to a first embodiment of the present invention. Figure 2B is a schematic diagram showing the rear view of the cathode of Figure 2A. Figure 3 is a schematic diagram showing a generalized system for a gas discharge device with the cathode and the anode configured in accordance with the present invention. Figures 4A and 4B are schematic diagrams showing, respectively, front and back views of a cathode configured in accordance with a second embodiment of the present invention. Figures 5A and 5B are schematic diagrams showing, respectively, the front and rear views of a cathode configured according to a third embodiment of the present invention. Figures 6A and 6B are schematic diagrams showing, respectively, the front and rear views of a cathode configured according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring now to the drawings in which similar reference numerals designate corresponding portions throughout the various views, FIG. 1 illustrates a generalized system for a gas discharge device, configured in accordance with the present invention. Two electrodes, a cathode 20 and an anode 16, are enclosed with a gas 14 in a discharge pipe 15. The gas 14 is chosen from the group of halo discharge gases which are well known in the art. The cathode 20 is formed of a conductive material that is gas permeable. The anode 16 is a conventional electrode. The cathode and the anode are mounted within the discharge tube in the desired orientation and connected to an external, high voltage power supply 11 via electrical connections 12 and 13, respectively, using conventional means. The connections through the end walls of the discharge tube are kept vacuum-tight. When sufficient voltage is applied between the cathode and the anode, a current is induced through the gas and a halo discharge is produced in the gas. It is well known in the art that for a particular pressure and discharge gas, the discharge operating voltage in halo is proportional to the working function of the electrons of the cathode material and inversely proportional to the surface area of the cathode. A preferred embodiment of the system of Figure 1 consists of a glass tube with an internal diameter of about 5 cm (2 inches), about 30 inches in length having a separate gas inlet and pumping gates at opposite ends of the tube. The inlet gate is used to control the flow of gases into the system and is connected to a gas flow pipe consisting of flow control valves, pressure regulators, gas storage cylinders accommodated and connected using conventional means known to persons of ordinary skill in the art. A pumping line is used to evacuate the gas in the system and is connected to a regulating or intake valve, the cold trap of liquid nitrogen and a metal pump by conventional means. The removable glass end caps are fastened to each end of the large tube. A vacuum tight seal is achieved between the end layers and the glass tube by means of a compressible elastomeric O-ring. A stainless steel rod with a diameter of 6.4 mm (1/4 inch) passes through the wall of an end layer by means of a vacuum-tight seal. The stainless steel rod extends into the glass tube approximately 6 inches. The permeable cathode is spot welded to the end of the "rod that is inside the tube.The end of the rod extending out of the tube is electrically connected to a power supply.The cathode body is approximately 2.5 cm (1"). inch) in diameter and 8.2 cm (3 inches) in length and formed from a stainless steel mesh with apertures of approximately 1 mm in the screen or mesh and having approximately a 50% fill factor. stainless steel rod about 1/4 inch in diameter passes through a vacuum seal in the other end layer, a 2.5 cm (1 inch) diameter stainless steel flange is welded to the end The rod and rod assembly forms the anode in the system, the end of the rod that extends outside the tube is electrically connected to the power supply. to create a hydrogen halo discharge, chlorine, helium, nitrogen, argon, and mixtures of these gases at pressures in the range of 10 m Torr to several Torr. The current through the halo discharge has varied from a few to several hundred milliamps at voltages exceeding 3 kV.

Figure 2A and 2B illustrate front and rear views, respectively, of a first embodiment of the cathode 20 illustrated in the system of Figure 1. The cathode 20 is a hollow cathode of a permeable wall having a tubular wall 21 made of a permeable material , in mesh or perforated, conductor such as stainless steel mesh. The material is chosen so that the gas 14 can pass through the openings in the material. The cathode has two ends: a first open end 23, and a second end 22, which is connected to the power supply using conventional means. The second end may be opened or closed with an end piece (not shown). If an end piece is used, the end piece can be made of a solid or permeable material. Other materials such as aluminum may be preferred for the cathode material and the cathode may be coated with gold or other conductive material. Different materials may also be preferred for different reactive gases. Due to the proportional relationship between the operating voltage and the working function of the electrons of the cathode material, materials with low work functions are preferred. Another important aspect is that the material should not react with or interfere with the reactive gas.

Referring again to Figures 2A and 2B, gas can flow into and out of the hollow interior of the cathode through the open end 23, as well as through the wall 21 of the permeable outer body of the cathode 20. When building the cathode a permeable material instead of a solid material, the present invention increases the surface area of the cathode without increasing its physical size and allows greater movement of the gas within the discharge flow, which allows the generation of a larger flow of ions from the Reactive gas at lower pressure and temperature than a solid wall configuration. For some halo discharge applications, such as those utilizing a direct current (DC) power supply, it is only necessary to configure the cathode from a permeable material in order to achieve the advantages of the present invention. In such applications, the anode may be of a conventional configuration. In other applications, however, it may be desirable to configure both electrodes from a permeable material. For example, in applications that use alternating current (AC), either alone or in combination with a direct current (DC), each of the electrodes functions as a cathode during the alternate portions of the cycle. In these applications, it is desirable to configure both electrodes from a material permeable to the subject gas, to increase the surface area of the cathode during the entire cycle. Figure 3 illustrates a system in which both electrodes are configured from a permeable material. The system of Figure 3 is identical to the system of Figure 1, with the exception that the cathode 20 and the anode 16 are configured of a permeable material, as illustrated in Figures 2A and 2B. Although the cathode and the anode are described in Figure 3 having identical geometries, this is not required, and should not be construed as limiting the invention. In fact, there is no such limitation and the cathode and anode of the system described in Figure 3 need not be identically configured. There is likewise no fundamental limitation on the size and specific shape of a cathode configured in accordance with the present invention. For example, the cathode may be a single wall, permeable, hollow wall cathode, or may include a plurality of similarly shaped, nested or nested structures, all having permeable walls. Figures 4A and 4B illustrate front and rear views, respectively, of a second cathode embodiment that can be used to further increase the surface area of the cathode without increasing its physical dimensions. In this modality, the cathode 20 has a wall 31 of cylindrically shaped outer body, and two walls 33 and 34 of internal body, similarly shaped, nested or fitted. The outer and inner body walls are made of a conductive material that is conductive to the reactive gas. The nested walls are separated from one another by open areas 36 and 37. The cathode has two ends: the end facing the anode is open, while each of the nested layers are connected to each other and the power supply on the other end 32, which, except for this electrical connection between the nested layers, may be either open or closed, as shown in Figure 4B. The embodiment illustrated in Figures 4A and 4B is not intended to be restrictive, but is simply an illustration of a nested or nested configuration. With the exception of the requirements that one end of the cathode be open and that each nested layer be electrically connected to a power source (and the practical considerations of size imposed by the thickness of the permeable material and the desired size of the cathode), there are fundamental limitations on the number of nested layers that can be used or on the size of the spaces between the layers. There is likewise no requirement that any cathode end be closed or that the nested layers be made from the same conductive, permeable material. Both ends of the cathode can be opened and each of the nested layers can be made from the same or different conductive, permeable materials. Nested layers can, but do not need, are electrically connected to each other. Each of the layers can be connected to the same power source; alternatively, a plurality of nested layers may be connected to a plurality of energy sources operating at different voltages. Figures 5A and 5B illustrate front and back views, respectively, of a third cathode mode, which is another alternative embodiment of a nested configuration. In this embodiment, the cathode 20 has a wall 31 of conical outer body, and two walls 43 and 44 of similarly shaped, nested inner body, the outer and inner walls are made of a permeable, conductive material. The nested layers are separated one from the other by open areas 46, 47 and 48. Due to the conical shape of the nested body walls, the open areas become progressively smaller until all the layers meet at the base of the cone 42. At that point, all the nested layers are connected to each other and to the power supply. The other end of the cathode is the open end of the cone.

Figures 6A and 6B illustrate the front and rear views, respectively, of a fourth cathode mode. In this embodiment, the cathode 20 is formed from a single piece of permeable material in a spiral shape. The base of the spiral 52 is connected to the power supply. The other end of the spiral is the open end of the cathode. The above illustrative examples of the cathode embodiments are not intended to limit the generality of the present invention in any way. In addition to the specific embodiments illustrated in the drawings, any geometrical configuration of permeable surfaces can be used as long as the cathode is connected to a power supply and open on the other end. Permeable surfaces in any chosen size form can also be corrugated to further increase the available surface area. A cathode according to the present invention can be processed as follows: a stainless steel mesh length is wrapped around a mandrel having the desired shape (such as cylindrical). The length of the mesh is cut to size, so that it has two adjacent edges running longitudinally of the mandrel. The two edges are welded by points or otherwise fastened together. One end of the formed wire mesh tube is formed in a cone manually, and is mounted within the discharge tube and coupled to the power supply connection by conventional means such as welding or clamping. The mandrel is removed. A nested permeable wall cathode according to the present invention can be made by forming a group of cylinders of varying diameters. The cylindrical walls are concentrically welded to one side of a stainless steel plate, starting with smaller diameter cylinder. The plate is mounted within the discharge tube and coupled to the power supply connection by conventional means such as welding or clamping. The cathode currently described allows the operating voltage of a gas charging device to be decreased by at least 2 times due to its greater electron emission surface area. The permeable wall allows the free flow of reactive gas and plasma, and improves operating parameters such as plasma pressure, temperature and stability. While the specific forms for making a cathode according to the present invention are described, it should be understood that alternative forms are anticipated. In addition, it will be obvious to those skilled in the art that many variations and modifications may be made to the preferred embodiments as described above, without departing substantially from the spirit and scope of the present invention. It is intended that all such variations and modifications be included within the scope of the present invention, as described in the following claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention.

Claims (14)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A system for establishing a halo discharge in a gas, characterized in that the system comprises: a shell containing a gas, the gas is capable of produce a halo discharge when stimulated by an electric current; a cathode in the envelope, the cathode comprises: a body having an opening, the body comprises a plurality of layers constructed of at least one conductive material that is gas permeable, each of the plurality of layers having a different diameter, the layers are nested or nested one inside the other so that the layers are substantially concentric and spaced apart from one another, and means for supporting the plurality of layers nested one in the other; an anode in wrapping; and means for inducing a flow of electrical current through gas between the cathode and the anode.
2. 2. The system according to claim 1, characterized in that the cathode body is a spiral-shaped surface constructed of a conductive material that is permeable to gas.
3. 3. The system according to claim 1, characterized in that the layers are concentric cones.
4. 4. The system according to claim 1, characterized in that the layers are concentric cylinders.
5. 5. The system according to claim 1, characterized in that concentric spirals.
6. 6. An electrode for the use of a gas discharge tube, the electrode is characterized in that it comprises: a body having a first end and a second end, the first end is open, the body comprises a plurality of layers constructed from minus a conductive material that is permeable to gas in the gas discharge tube, each of the plurality of layers has a different diameter, each of the layers is nested one inside the other, so that the layers are substantially concentric and spaced one from the other; the body further comprises means for supporting the plurality of layers nested one in the other; and means to connect the body to a power supply.
7. The electrode according to claim 6, characterized in that the electrode body is a spiral-shaped surface constructed of a conductive material that is permeable to gas.
8. 8. The system according to claim 7, characterized in that the layers are concentric cones.
9. 9. The system according to claim 7, characterized in that the layers are concentric cylinders.
10. The system according to claim 7, characterized in that concentric spirals.
11. 11. A method for producing an electrode for use in a halo discharge device, characterized in that the method comprises the steps of: selecting at least one conductive material that is gas permeable in a halo discharge device; the shaping of at least one conductive material in a plurality of elongated bodies having different diameters, each of the bodies having a substantially circular cross section, at least a partially hollow interior, a first end, and a second end, the first end It's open; the nesting or nesting of each of the plurality of elongated bodies within a successively larger elongated body, so that the bodies are substantially concentric and spaced from one another; and connecting one end of each of the plurality of elongated bodies to a connecting member about a common axis.
12. 12. The method according to claim 11, characterized in that the elongated bodies are concentric cones. The method according to claim 11, characterized in that the elongate bodies are concentric cylinders. The method according to claim 11, characterized in that the elongated bodies are concentric spirals.