Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/02—Details
  • H01J61/30—Vessels; Containers
  • H01J61/32—Special longitudinal shape, e.g. for advertising purposes
  • H01J61/327—"Compact"-lamps, i.e. lamps having a folded discharge path
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/02—Details
  • H01J61/54—Igniting arrangements, e.g. promoting ionisation for starting
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/70—Lamps with low-pressure unconstricted discharge having a cold pressure < 400 Torr
  • H01J61/76—Lamps with low-pressure unconstricted discharge having a cold pressure < 400 Torr having a filling of permanent gas or gases only
  • H01J61/78—Lamps with low-pressure unconstricted discharge having a cold pressure < 400 Torr having a filling of permanent gas or gases only with cold cathode; with cathode heated only by discharge, e.g. high-tension lamp for advertising
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/48—Generating plasma using an arc
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/48—Generating plasma using an arc
  • H05H1/50—Generating plasma using an arc and using applied magnetic fields, e.g. for focusing or rotating the arc
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
  • H05H1/461—Microwave discharges
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
  • H05H1/4645—Radiofrequency discharges
  • H05H1/4652—Radiofrequency discharges using inductive coupling means, e.g. coils

Definitions

• the present invention relates to a glow discharge lamp and a lighting method that can be implemented in such a lamp.
• glow discharge lamps the two main embodiments of which are commonly called “neon” tubes and compact fluorescent bulbs.
• fluorescent lamps with electrodes are based on the emission of ultraviolet (UV) radiation generated in a linear tube (neon tube) or folded back on itself (fluorescent bulb) by a periodic discharge low frequency (by example 50 or 60 Hz), the UV being transformed into visible light by phosphors covering the inside of the tube.
• UV ultraviolet
• the gas mixtures generally used are mixtures of noble gases (mainly argon) inoculated with mercury, the active element whose main UV emission lines are at 254 nm (the largest line), 297 nm, 313 nm and 365 nm (UVA) (non-exhaustive list), wavelengths where the fluorescence yields, that is to say of conversion of the UV photons in visible light on the phosphors lining the inside of the lamps, are the highest.
• noble gases mainly argon
• UVA UVA
• the plasma is obtained by applying a voltage between the two electrodes.
• the most energetically efficient plasma production zone is constituted by the so-called positive column region R2 along which the axial electric field adjusts so that the average power transferred by the Electron electric field e for maintaining the plasma allows for exactly compensate the radial losses of the plasma on the walls along the positive column, so as to keep the discharge lit.
• cathode region R1 In the region of the cathode (called cathode region R1), however, there is a very large voltage drop (more than two or three hundred volts) which accelerates the ions i of the discharge to the cathode, thus creating secondary electrons e 2 which, in turn, are injected into the high energy gas, thus allowing the ionization of the gas mixture.
• anodic sheath the region R4 located in the vicinity of the anode, where the electrons at the edge of the positive column R2 are accelerated towards the anode.
• the electrodes are inverted at each alternation.
• the cathode region where the electrode is polarized very negatively relative to the anode, corresponds to a region where there is a great loss of energy, not usable for effective lighting.
• the positive ions are accelerated with an energy of several hundred electron volts (eV) on the cathode, thus allowing the emission of secondary electrons, accelerated in opposite directions, which allow the ignition and the maintenance of the glow discharge and its positive column.
• eV electron volts
• the cathode region allows the ignition and then the maintenance of a glow discharge, it constitutes a region of high energy loss dissipated in the ion bombardment of the cathode.
• glow discharge lamps have several drawbacks, among which a capricious ignition (especially at low temperature) of current lamps based on mixtures of rare gases ; the difficulty, if not the impossibility, of lighting discharges containing plasma gases other than rare gas mixtures; the degradation of the electrodes related to their ion bombardment (cathodic drop); reduced life expectancy, especially during frequently repeated extinguishing and lighting; the impossibility of controlling the lighting by a dimmer; the presence of mercury in the gas mixture, which poses a problem of toxicity and recycling.
• An object of the invention is to provide a glow discharge lamp to prevent the loss of energy due to intense bombardment of the cathode (or more generally the electrodes in the case of the application of a periodic voltage).
• Another object of the invention is to provide a glow discharge lamp which makes it possible to remedy, as far as possible, the other disadvantages and defects mentioned above.
• a glow discharge lamp comprising:
• a device for applying an electric field suitable for maintaining a plasma in the region of the so-called positive column envelope comprising two electrodes constituting an anode and a cathode located in the envelope, at each end of said envelope,
• a source of microwave or radiofrequency cathode plasma arranged in the envelope relative to the electrode constituting the cathode so as to generate a high frequency discharge (that is to say, depending on the nature of the source, micro or radio frequency) located on the surface of said electrode to generate said plasma.
• This source of cathodic plasma makes it possible to generate plasma without having to resort to a high cathodic drop to produce secondary electrons.
• the lamp may be powered by a periodic voltage at 50 or 60 Hz, so that each electrode alternately constitutes the cathode and the anode according to the polarity of the applied voltage; the lamp may then comprise two alternating plasma sources located in the envelope with respect to each of the two electrodes so as to generate a high frequency discharge (radiofrequency or microwave depending on the nature of the source) located on the surface of each of said electrodes.
• each source of cathodic plasma is an inductive radiofrequency source and the lamp further comprises a device for applying a static axial magnetic field at said plasma source;
• each cathode plasma source is a microwave source and the lamp further comprises a device for applying a static magnetic field whose intensity is equal to the electron cyclotron resonance intensity (i.e. say the intensity for which the frequency of the microwave electric field is equal to the frequency of gyration of the electrons in the magnetic field) at said plasma source;
• the lamp further comprises a device for applying a static axial magnetic field of decreasing intensity from the cathode to the positive column, said device for applying the axial magnetic field possibly comprising, for example, a solenoid wound around the source of cathodic plasma or permanent magnets delivering an axial magnetic field (at least on the axis of the tube);
• the lamp further comprises a device for applying a static axial magnetic field along the positive column, said device for applying the static axial magnetic field may be a solenoid wound around the envelope.
• the envelope is in the form of a straight tube.
• the envelope is in the form of a spirally wound tube or any other geometric shape such as a circle or an oval.
• Another object of the invention relates to a method of illumination by a glow discharge lamp, said lamp comprising an elongated envelope, transparent to illumination radiation and containing a plasmagenic gas, and two electrodes constituting an anode and a cathode located in the envelope, at each end of the envelope, said method being characterized in that it comprises:
• microwave or radiofrequency cathodic plasma by means of a high frequency discharge (microwave or radiofrequency) located at the surface of the electrode constituting the cathode,
• the voltage applied between the electrodes is advantageously a DC voltage or an AC voltage at 50 Hz or 60 Hz.
• the applied voltage is an alternating voltage at 50 or 60 Hz; the cathodic plasma can then be alternately generated in the region of the one and the other electrode, namely the electrode constituting the cathode according to the polarity of the applied voltage.
• the plasma is a radiofrequency plasma, that is to say generated at a frequency between 1 MHz and 100 MHz.
• the plasma is a microwave plasma, that is to say generated at a frequency between 100 MHz and 5.8 GHz.
• the pressure in the envelope does not exceed a few torr (i.e., less than 10 torr) and is preferably less than or equal to 1 torr (133 Pa).
• FIG. 1 is a diagram of the distribution of the electric field in a neon tube lamp with conventional glow discharge
• FIGS. 2A and 2B illustrate two embodiments of the envelope, forming part of a neon tube and a compact fluorescent bulb, respectively;
• FIG. 3 is a diagram of the distribution of the electric field in a glow discharge neon tube type lamp according to the invention.
• FIG. 4 is a block diagram of a glow discharge lamp according to a first embodiment of the invention, in which the cathodic plasma is excited by radiofrequency
• FIG. 5 is a block diagram of a glow discharge lamp according to a second embodiment of the invention, in which the cathode plasma is excited by microwaves
• FIG. 6 schematically illustrates an embodiment in which, in the region where the radiofrequency cathodic plasma is generated, a static axial magnetic field is provided for providing a helical coupling mode
• FIG. 7 schematically illustrates an applicator. a microwave cathode plasma which furthermore makes it possible to apply a static magnetic field providing a mode of coupling to the electronic cyclotron resonance
• FIG. 8 schematically illustrates an embodiment in which, in the region where the cathode plasma is generated, a decreasing static magnetic field gradient from the cathode to the positive column is applied,
• Figure 9 schematically illustrates an embodiment in which a conductive solenoid is wound all along the positive column to apply a static axial magnetic field thereon.
• the lamp comprises an elongated envelope containing a plasma gas.
• the envelope is transparent to the illumination radiation, which may be ultraviolet or visible radiation.
• the inner wall of the envelope may be at least partly covered with phosphors capable of converting the ultraviolet radiation provided by the glow discharge into visible radiation.
• elongated is meant that the casing has a larger dimension in a direction, said axial direction, than in the two orthogonal directions, which define a radial direction.
• Two electrodes are disposed in the envelope, at each end of said envelope, said ends being opposite to each other in the axial direction.
• the electrodes are connected to a continuous or alternating voltage source U at 50 or 60 Hz.
• the envelope may have a substantially constant section in the axial direction.
• said envelope may have the general shape of a tube.
• the envelope may be linear, that is to say it is substantially rectilinear in the axial direction.
• the envelope may form a turn (to form a circular or oval lamp) or a number of turns, as in the case of so-called "compact fluorescent" bulbs.
• FIG. 2B An example of such a bulb is shown in Figure 2B.
• envelope may be arranged in any other form without departing from the scope of the invention.
• the plasma gas may be any gas or gas mixture used for illumination.
• the plasma gas may be a mixture of noble gases (mainly argon) seeded with mercury, the active element whose main UV emission lines are at 254 nm (the largest line), 297 nm, 313 nm and 365 nm (UVA) (non-exhaustive list).
• the choice of gases and active elements is carried out so that the fluorescence yields, that is to say the conversion of UV photons. in visible light on the phosphors lining the inside of the envelope, are the highest.
• a suitable voltage is applied between the two electrodes to generate a discharge in the plasma gas and thereby generate the plasma.
• the invention proposes to replace the cathodic drop zone present in the conventional lamps by a cathode plasma source adapted to generate the plasma in a localized manner at the surface of the cathode and to apply between the two electrodes a voltage suitable for apply an axial electric field sufficient to maintain the plasma thus generated in the positive column.
• the source of cathodic plasma is, like the electrodes, arranged in the envelope.
• the cathode plasma source may be a source of the microwave type or of the inductive radiofrequency (RF) type.
• RF radiofrequency
• each electrode alternately constitutes the cathode or the anode according to the polarity of the applied voltage.
• the invention proposes, in a preferred embodiment of the invention, to use two sources of cathodic plasma placed at each of the two electrodes so as to alternately generate a high frequency discharge on the surface of the electrode which constitutes the cathode.
• the invention makes it possible to reduce the power required for discharging and maintaining it with respect to known glow discharges.
• the cathode plasma source can be a source of low power, namely of the order of a watt, that is to say a fraction of a watt to a few watts (depending on the section of the lamp , for example for 1 cm 2 ).
• the invention provides a gain of a factor of the order of 2 to 4 on the power required to maintain the discharge compared to current glow discharges.
• FIG. 3 illustrates the distribution of the electric field E along a DC glow discharge obtained using a cathode plasma source as described above.
• the cathode drop R1 and the negative glow R3 observed in FIG. 1 are replaced by a source of cathodic plasma R1 having a greatly reduced cathodic drop with respect to the cathode drop R1 of FIG. are the electrons of the cathodic plasma that are injected into the positive column (the generation of the plasma in the positive column therefore no longer requires secondary electrons produced from the cathode drop).
• the electric field within the cathodic plasma is very small, and, on the other hand, the electric field in the cathode drop of the cathode plasma R1 is decreased by a significant factor (greater than one factor 2 to 4) with respect to the electric field encountered, in this same region, in the case illustrated in FIG.
• the anode jacket R4 is unchanged.
• the invention makes it possible in the first place to considerably reduce the energy losses due to the ion bombardment of the cathodes in the current glow discharges.
• the invention overcomes most of the disadvantages of current glow discharges.
• the invention provides a very long lifetime of glow discharge lamps, sputtering the electrodes by ion bombardment being avoided.
• the lamps according to the invention can operate under extended operating conditions, in terms of the frequency of the electromagnetic wave, power, pressure and nature of the gas, in connection with those of the cathode plasma source.
• the invention also allows operation of the lamp under extreme conditions.
• the cathode plasma source is able to ignite immediately. It allows an immediate ignition of the glow discharge.
• FIG. 4 illustrates an embodiment of the invention in which the glow discharge is initiated from an inductive RF type plasma produced by a source 3 on the surface of one of the electrodes acting as a cathode (in FIG. the example illustrated, it is the electrode E1).
• the glow discharge is maintained by the application of a voltage U between the electrodes E1 and E2.
• the applied voltage may be continuous or periodic (for example at 50 or 60 Hz).
• inductive RF plasmas are generated at frequencies that can cover the range of the order of the MHz to the hundred MHz, and in particular to ISM frequencies (industrial, scientific, medical) such as 13.56 MHz, 27.12 MHz or 40.68 MHz and with very varied antenna geometries, well known in the state of the art of inductive plasmas.
• FIG. 5 illustrates another embodiment of the invention, in which the glow discharge is initiated from a microwave plasma produced by a source 3 on the surface of one of the electrodes acting as a cathode ( in the example illustrated, it is the electrode E1).
• Said source 3 may be a cavity containing an antenna, or a coaxial structure formed of a central conductive core and an outer conductor defining a microwaves propagation volume.
• the glow discharge is maintained by the application of a voltage U between the electrodes E1 and E2.
• the applied voltage may be continuous or periodic (for example at 50 or 60 Hz).
• microwave plasmas can be generated at frequencies ranging from about 100 MHz to a few GHz, and in particular at ISM frequencies of 433 MHz, 2.45 GHz or even 5.80 GHz.
• a number of improvements according to the invention can be provided by the use of magnetic fields, either at the plasma source or sources, or at the level of the positive column.
• This helical coupling mode derives from the assumed propagation mode of the wave in the presence of a magnetic field [4].
• This helical mode makes it possible to achieve higher densities at a given RF power due, on the one hand, to the confinement due to the magnetic field, and, on the other hand, to the very efficient coupling mode of the RF power to the plasma.
• a static axial magnetic field B is applied to the surface of the inductive RF type plasma source 3 so as to obtain a coupling according to the mode W.
• the intensity of such a magnetic field is of the order of a hundred gauss.
• This magnetic field can be obtained, in a manner known per se, from permanent magnets, and / or from magnetic or solenoid coils.
• the magnetic field is provided by a permanent magnet 4 with axial magnetization placed in the vicinity of the cathode.
• This embodiment relates to microwave-type plasma sources which, in the presence of a static magnetic field, can operate in a resonant coupling mode called electron cyclotron resonance (ECR).
• ECR electron cyclotron resonance
• the intensity of the magnetic field B 0 necessary for the ECR coupling is therefore:
• m e is the mass of the electron and its charge.
• a static magnetic field of intensity equal to the resonance value B 0 is applied at the level of the plasma source so as to obtain the ECR coupling mode.
• This intensity of the static magnetic field can be obtained from magnetic or solenoid coils and / or from permanent magnets.
• conventional permanent magnets samarium-cobalt or barium ferrite and strontium can provide the magnetic field strength required for ECR coupling.
• the intensity of the required resonance magnetic field is lower.
• B 0 0.0155 tesla at 433 MHz.
• the applied magnetic field is axial.
• the plasma source is a coaxial microwave applicator comprising a central core 30 and an outer conductor 31 separated by a microwave propagation volume 32, which further comprises:
• a cylindrical permanent magnet 33 arranged at the end of the central core 30 and whose direction of magnetization is parallel to the axis of the applicator; said magnet 33 preferably has a radius substantially identical to that of the central core (concretely, said magnet may have a radius slightly less than that of the central core and be housed in a cylindrical housing provided at the end of the central soul);
• An annular magnet 34 arranged at the end of the outer conductor 31 of the coaxial assembly and whose magnetization direction is parallel to the axis of the applicator and in the same direction as that of the cylindrical magnet.
• the set of magnets arranged at the end of the applicator has the same sense of magnetization.
• said annular magnet 34 has an inner radius equal to that of the outer conductor 31, which corresponds to the outer radius of the annular volume 32 of propagation of microwaves, noted R (concretely, said magnet 34 may have a slightly greater inner radius to that of the outer conductor and an outer radius slightly less than that of the outer conductor and be housed in an annular housing provided at the end of the outer conductor).
• the magnets 33, 34 can be made integral with the coaxial assembly by any appropriate means.
• the magnetization of the cylindrical magnet 33 and the annular magnet 34 is chosen so as to form a magnetic field capable of providing, in a zone distant from the exit plane of the applicator, an electron cyclotron resonance coupling with the Microwave electric field generated by the applicator.
• the cylindrical magnet 33 and the annular magnet 34 make it possible to generate magnetic field lines which pass through the electron cyclotron resonance coupling zone in a direction substantially parallel to the axis of the applicator. This effect can be obtained by a judicious choice of the outer radius and the magnetization of the annular magnet 34.
• the electron cyclotron resonance zone is delimited, in the radial direction, by the zone in which the microwave electric field is the strongest, the use of an annular magnet whose outside radius is much greater than the radius of this zone makes it possible to obtain an ECR zone substantially parallel to the exit plane of the applicator.
• This zone of strong electric field is considered to extend over a radius of the order of twice the radius R of the applicator.
• the annular magnet has an outer radius greater than the radius of the strong electric field area, the ECR area is substantially parallel to the exit plane of the applicator over its entire radius 2R range.
• the field lines starting from the pole located at the exit plane of the applicator to reach the opposite pole remain substantially parallel to the axis of the applicator during their crossing of the ECR area of radius 2R, including the periphery of this zone.
• the annular magnet has the effect of "straightening" the field lines at the periphery of the ECR area.
• a static axial magnetic field is applied in the region R1 of the plasma source or sources according to an amplitude which, in the source zone, decreases continuously from the cathode to the column positive.
• Such a static magnetic field may be generated, for example, by a solenoid 5 whose turns are spaced apart from an increasing pitch from the cathode to the positive column.
• the current flowing in said solenoid can be, for example, provided by the supply current of the transistors of the plasma source or sources. It is therefore a continuous current.
• accelerated electrons in the plasma source convert in the magnetic field gradient the rotation speed acquired at the source in translational speed towards the positive column due to the conservation of the magnetic moment of the electron along its trajectory (first adiabatic invariant).
• the ions are driven by the electrons so that the plasma produced in the plasma source (s) at the cathode is "injected" to the positive column.
• This embodiment applies to both microwave and RF plasma sources.
• the solenoid 5 is advantageously placed outside the plasma and surrounding the source 3 of cathode plasma, it also performs the function of electromagnetic shielding vis-à-vis the microwave or RF waves.
• a source 3 of RF plasma has been placed in the region of each electrode and a solenoid 5 around each of these sources but it goes without saying that this embodiment can be implemented with a single source of cathodic plasma and a single solenoid surrounding it.
• a static axial magnetic field is applied along the positive column so as to reduce the radial losses along the positive column, and thus improve the overall energy efficiency of the glow discharge.
• this static magnetic field can be obtained by a direct current flowing in a solenoid-type conductive winding 6 surrounding the glow discharge over its entire length.
• the solenoid 6 is wound outside the tube 1, inside a tube 7 transparent to the emitted radiation which contains the tube 1.
• the solenoid 6 is electrically isolated, it can be placed inside the tube 1, in the vicinity of its inner wall.
• the direct current flowing in the winding can for example be provided by the supply current of the transistors of the plasma sources at the ends of the glow discharge.
• the conductive winding can also, in addition, if necessary, shield the electromagnetic waves emitted by certain plasma sources.
• a source 3 of RF plasma has been placed in the region of a single electrode (E1) but it goes without saying that this embodiment can be implemented with two sources of cathode plasma.

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