JP7112559B1 - Standing wave excitation type electromagnetic discharge lamp - Google Patents

Abstract

A discharge lamp capable of performing electrodeless discharge without using a resonator is provided. A discharge lamp (1) that discharges and emits light by means of electromagnetic wave power supplied by an electromagnetic wave oscillator, is a transparent insulator formed in a cylindrical shape with an open base end and a closed tip end. An inner tube 12, an inner conductor 13 which is a conductor inserted into the inner tube 12 and extending in the tube axial direction of the inner tube 12, and a sealed space in which a discharge gas is sealed outside the inner tube 12 are defined. a double discharge tube 10 having an outer tube 11 which is a transparent insulator formed to form a transparent insulator, and an outer conductor 15 which is a conductor formed so as to cover the outer periphery of the outer tube 11; An impedance matching section 16 is provided for matching the impedance of the electromagnetic wave oscillator and the impedance of the double discharge tube 10 so that the standing wave is dominant in the discharge tube 10 . [Selection drawing] Fig. 3

Description

Embodiments of the present invention relate to discharge lamps.

2. Description of the Related Art Conventionally, as a long-life discharge lamp, there has been known a discharge lamp that is lit by electrodeless discharge using microwaves using a resonator. As this type of discharge lamp, a method of lighting a quartz discharge lamp filled with a discharge gas provided at a position where the electric field of an electromagnetic wave is locally concentrated (for example, see Patent Documents 3 and 4), and a method of lighting a discharge gas filled Research and development are now focused on a method of lighting a portion of the resonator where the microwave electric field is strongest (for example, see Patent Documents 1 and 2). Some of these types of discharge lamps have been put to practical use as microwave discharge metal halide lamps and sulfur lamps (for example, Patent Documents 3, 4 and 5). In a discharge lamp using such a resonator, the discharge lamp must be made smaller than the resonator, so the degree of freedom in designing the discharge lamp is significantly restricted.

As a related technique, an outer tube and an inner tube made of quartz tubes are coaxially arranged with a space for enclosing a buffer gas and a trace amount of mercury, and one end is arranged at the open end of the inner tube. A rod-shaped or pipe-shaped antenna supported by a coaxial connector or the like and inserted into the inner tube and connected to a microwave oscillation source, and a predetermined radiation arranged so as to cover the outer peripheral side of the outer tube A double-tube microwave discharge lamp characterized by comprising a metal mesh body having light transmittance is known (see, for example, Patent Document 8).

Japanese Patent No. 4757654 JP 2007-234433 A Japanese Patent Publication No. 2004-505429 Japanese translation of PCT publication No. 2009-521071 Japanese Patent No. 4294998 JP 2019-53897 A JP 2020-140919 A JP 2016-225037 A

A problem to be solved by the embodiments of the present invention is to provide a discharge lamp capable of performing electrodeless discharge without using a resonator.

In order to solve the above-described problems, the discharge lamp according to the present embodiment is a discharge lamp that discharges and emits light using electromagnetic wave power supplied from an electromagnetic wave oscillator, and is a cylinder with an open base end and a closed tip end. an inner tube that is a dielectric formed into a shape, an inner conductor that is a conductor inserted into the inner tube and extending in the axial direction of the inner tube, and a discharge gas sealed outside the diameter of the inner tube. a double discharge tube having an outer tube that is a dielectric formed so as to define a sealed space that is surrounded by a double discharge tube, and an outer conductor that is a conductor formed so as to cover the outer periphery of the outer tube; An impedance matching section is provided for matching the impedance of the electromagnetic wave oscillator and the impedance of the double discharge tube so that standing waves are dominant in the discharge tube.

According to embodiments of the present invention, electrodeless discharge can be performed without using a resonator.

1 is a schematic diagram showing the configuration of a discharge lamp according to an embodiment; FIG. 1 is a front view showing the configuration of a discharge lamp according to an embodiment; FIG. FIG. 3 is a cross-sectional view taken along line AA of FIG. 2; 2 is an enlarged cross-sectional view of a main part showing the configuration of a discharge lamp; FIG. FIG. 2 is a schematic diagram showing a light-emitting portion in a discharge lamp; FIG. 4 is a diagram showing a continuous discharge state due to a standing wave in the case of impedance matching so that a standing wave is stably generated; FIG. 10 is a diagram showing a local discharge state in which the discharge is not the standing wave emission but the standing wave emission when the impedance is matched so that the reflected power is minimized; FIG. 3 is a diagram showing a discharge bright portion in a discharge lamp having an inner tube; FIG. 4 is a diagram showing a discharge bright portion in a discharge lamp without an inner tube; 1 is a table showing parameters of an outer tube and an inner tube made of quartz; FIG. 4 is a diagram showing simulation results showing electric field intensity distribution in a first discharge lamp having an outer tube and an inner tube made of quartz; FIG. 5 is a diagram showing simulation results showing the electric field strength distribution in a second discharge lamp having an outer tube and an inner tube made of quartz; 1 is a table showing parameters of outer and inner tubes made of alumina; FIG. 4 is a diagram showing simulation results showing electric field strength distribution in a first discharge lamp having an outer tube and an inner tube made of alumina; FIG. 5 is a diagram showing simulation results showing the electric field intensity distribution in a second discharge lamp having an outer tube and an inner tube made of alumina; FIG. 4 is a schematic diagram showing a modification of the discharge lamp;

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Structure of discharge lamp)
The configuration of the discharge lamp according to this embodiment will be described. 1 and 2 are a schematic diagram and a front view, respectively, showing the configuration of a discharge lamp according to this embodiment. 3 is a cross-sectional view taken along the line AA of FIG. 2. FIG. FIG. 4 is an enlarged cross-sectional view of a main part showing the structure of the discharge lamp.

As shown in FIG. 1, a discharge lamp 1 according to the present embodiment is a double-tube discharge lamp connected via a coaxial cable 3 to an electromagnetic wave oscillator 2 that outputs electromagnetic wave power. The discharge lamp 1 includes a double discharge tube 10, an impedance matching section 16, and a coaxial connector 17 connected to the coaxial cable 3, as shown in FIGS. The double discharge tube 10 has an outer tube 11 , an inner tube 12 , an inner conductor 13 , a fixed conductor 14 and an outer conductor 15 . Note that the discharge lamp 1 may be connected to the electromagnetic wave oscillator 2 by a coaxial tube instead of the coaxial cable 3 .

Both the outer tube 11 and the inner tube 12 are members in which a dielectric material having a small dielectric loss, such as quartz or alumina, is formed in a substantially tubular shape. Yes, the inner tube 12 may be either a light-transmitting member or a non-light-transmitting member. Both the outer tube 11 and the inner tube 12 are formed in a substantially cylindrical shape as a whole in this embodiment. The outer tube 11 has a larger diameter than the inner tube 12, and the outer tube 11 and the inner tube 12 are positioned coaxially, that is, the tube axis of the outer tube 11 and the tube axis of the inner tube 12 are approximately equal to each other. The inner tube 12 is accommodated in the inner space of the outer tube 11 so as to match. The outer tube 11 is formed to have a closed top surface and a bottom surface, thereby defining a sealed space having a constant radial width between the outer tube 11 and the inner tube 12 . This sealed space is filled with a discharge gas for generating plasma. In this embodiment, excimer gas is enclosed in the sealed space as will be described in detail later. As shown in FIGS. 3 and 4, the inner tube 12 is formed in a substantially cylindrical box shape with an open top and a closed bottom, and the top opening is closed by an internal conductor 13 and a fixed conductor 14, which will be described later. In the axial direction of the outer tube 11 and the inner tube 12, the bottom side where the inner tube 12 is closed will be referred to as the front end side, and the opposite top side will be referred to as the base end side.

The internal conductor 13 is a conductor formed in a substantially rod-like or substantially pipe-like shape so as to extend in the tube axial direction of the outer tube 11 and the inner tube 12, and the tip thereof is positioned near the bottom surface of the inner tube 12. The proximal end is supported by the impedance matching section 16 so as to be inserted into the inner tube 12 and positioned coaxially with the outer tube 11 and the inner tube 12 . A stator 131 for fixing the inner conductor 13 to the inner tube 12 is provided at the tip of the inner conductor 13, as shown in FIGS. In this embodiment, the stator 131 is formed in an annular shape having an inner diameter through which the inner conductor 13 can be inserted and an outer diameter corresponding to the inner diameter of the inner pipe 12 so as to be insertable into the inner pipe 12 . Any one formed to contact the inner wall of the tube 12 and the inner conductor 13 may be used. Also, the stator 131 is made of a dielectric having low dielectric loss, such as alumina, quartz, or Teflon (registered trademark). A plurality of stators 131 may be provided for the inner conductor 13 .

The fixed conductor 14 is generally formed in a substantially cylindrical shape or a substantially disc shape having a diameter substantially matching that of the outer tube 11, and is a conductor formed so that the impedance matching portion 16 can be attached thereto. The fixed conductor 14 has a diametrically inner portion made of Teflon and a radially outer portion made of aluminum and formed in a substantially annular shape surrounding the diametrical inner portion. As shown in FIG. 4, the radial inner portion 141 is formed with a hole through which the inner conductor 13 can be inserted in the tube axial direction, and the radial outer portion 142 is formed so that the outer conductor 15 can be attached. The outer conductor 15 is formed so as to cover the entire outer circumference of the outer tube 11 in the axial direction when attached to the radially outer portion 142, and has a plurality of radially opening openings in a so-called mesh shape. It is a substantially cylindrical conductor formed in the . In addition, the outer conductor 15 is attached to the outer diameter 142 so as to be coaxially positioned with respect to the outer tube 11 , the inner tube 12 , and the inner conductor 13 . Further, the outer conductor 15 is formed so as to protrude toward the front end of the outer tube 11 by 1/10 or more of the wavelength output from the electromagnetic wave oscillator 2 and open at the front end. It may be formed so as to be closed. The plurality of openings in the outer conductor 15 are desirably formed to have an optical transmittance of 90% or more and an opening ratio that prevents leakage of electromagnetic waves.

As shown in FIGS. 3 and 4, the impedance matching section 16 has a non-grounded conductor 161, a grounded conductor 162, and a matching element 163. The impedance of the discharge tube 10 is matched so that the standing wave is dominant in the double discharge tube 10. FIG. The non-grounded conductor 161 and the grounded conductor 162 constitute a coaxial transmission line electrically connected to the coaxial cable 3 via the coaxial connector 17 . The base end of the internal conductor 13 is fitted to the non-grounded conductor 161 , thereby electrically connecting the non-grounded conductor 161 to the internal conductor 13 . Also, the ground-side conductor 162 is electrically connected to the external conductor 15 via the fixed conductor 14 . The matching element 163 is at least one reactance element that electrically connects the non-grounded conductor 161 and the grounded conductor 162 . In this embodiment, the coaxial transmission line in the impedance matching section 16 is configured as a microstrip line, but may be configured as a coaxial line or a stripline. When the coaxial transmission line is configured as a coaxial tube, the matching element 163 is configured as a ring-shaped dielectric. Also, the impedance matching unit 16 may further include a discharge lamp ignition device.

As will be described later, the discharge lamp 1 configured in this way does not require a resonator and can perform discharge lighting by means of a standing wave. The degree of design freedom is high without being restricted by the shape of the resonator or the resonance mode.

(Operation of discharge lamp)
The operation of the discharge lamp will be explained. FIG. 5 is a schematic diagram showing a light-emitting portion in a discharge lamp.

By forming a coaxial line between the inner conductor 13 and the outer conductor 15, the electromagnetic wave power input from the electromagnetic wave oscillator 2 to the discharge lamp 1 is propagated in the TEM mode. This allows the discharge lamp 1 to utilize broadband electromagnetic waves from RF (Radio Frequency) waves to microwaves. Electromagnetic wave power incident from the base end of the discharge lamp 1 reaches the tip of the discharge lamp 1 as a traveling wave and is totally reflected, and a standing wave is generated by the reflected wave and the traveling wave due to total reflection.

As shown in FIG. 5, when a standing wave is ideally generated in the double discharge tube 10, a plurality of light emitting portions LM corresponding to antinodes of the standing wave are arranged in the tube axis direction of the double discharge tube 10. FIG. In the vicinity of this antinode, the electromagnetic field is oriented in the radial direction of the double discharge tube 10, and the lines of electric force pass through the outer tube 11 and the inner tube 12 and then terminate on the surfaces of the inner conductors 13 and 15, respectively. Since such an electrode structure and electric field direction are the same as those of the dielectric barrier discharge, it is possible to generate a low-temperature plasma P having a high electron temperature but a low ion temperature in the vicinity of the antinode of the standing wave in the discharge lamp 1 as well. can. Dielectric barrier discharge has been put to practical use in excimer lamps that are lit by HF (High Frequency) power, but has not yet been realized in the microwave region.

As a condition of the dielectric barrier discharge, it is necessary that the movement distance L of electrons in the discharge space accelerated by the electromagnetic field is longer than the gap G in the discharge space. As shown by the following equation, L is proportional to the electromagnetic wave electric field _E0 and inversely proportional to the electromagnetic wave frequency f and the sealed gas pressure p.

ここで、ｅは電子の素電荷、ｍ_ｅは電子の質量、ωは電磁波角周波数、ν_eは電子の衝突周波数である。

Here, _e is the elementary charge of the electron, me is the mass of the electron, ω is the angular frequency of the electromagnetic wave, and ν _e is the collision frequency of the electron.

Practical excimer radiation power can be obtained by generating low-temperature plasma with the pressure of the excimer gas in the closed space of the double discharge tube 10 set to about 50 kPa to 100 kPa near the atmospheric pressure. At this time, excimer gas species enclosed in the closed space include KrBr (207 nm), KrCl (222 nm), XeI (253 nm), XeBr (283 nm), XeCl (308 nm), Xe (172 nm), Kr (146 nm), and the like. is mentioned. According to the discharge lamp 1 using excimer gas as the discharge gas, it is possible to emit radiant light in the VUV (Vacuum Ultra Violet) to UV wavelength range that can be used for ultraviolet sterilization, ultraviolet curing, ultraviolet radiation cleaning, etc. during excimer discharge. can.

It is also possible to use the discharge lamp 1 as a low-pressure mercury discharge lamp that emits UV-C light that has a strong bactericidal effect. In this case, the discharge lamp 1 is compact, long-life, and highly efficient compared to existing AC/DC discharge low-pressure mercury discharge lamps, and can be applied to a wide range of fields such as air sterilization and water sterilization equipment. When the discharge lamp 1 is used as the above-mentioned low-pressure mercury discharge lamp, the buffer bus pressure in the discharge lamp 1 is set to 1.0 to 10.0 Torr (7.5 to 75 mPa), and the minimum temperature of the lamp wall is set to 40 to 50. C. and a mercury vapor pressure of 2 to 10 mTorr (15.times.10.sup.- ⁶ to 150.times.10.sup.- ⁶ Pa) is desirable to maintain a high UV-C conversion efficiency.

(Operation of impedance matching section)
The operation of the impedance matching section will be described. 6 and 7 respectively show the discharge state of the discharge lamp when impedance matching is performed so that standing waves with consecutive antinodes are generated, and when impedance matching is performed only with the aim of minimizing the reflected power. FIG. 4 is a diagram showing;

In the discharge lamp 1, although there are no major restrictions on the length and diameter of the double discharge tube 10, the impedance of the double discharge tube 10 in a non-discharging state should be close to the characteristic impedance (for example, 50Ω) of the coaxial cable 3. In addition, it is desirable to determine the respective diameters of the outer tube 11, the inner tube 12, and the inner conductor 13, and the radial distance of the sealed space.

The impedance matching section 16 matches the impedance of the electromagnetic wave oscillator 2 and the impedance of the double discharge tube 10 so that the standing wave is dominant. Here, the impedance matching unit 16 preferably uses at least one or more reactance elements while checking the discharge state, and performs impedance matching so that a stable standing wave discharge can be obtained. As a result, the standing wave is maintained from the distal end to the proximal end of the double discharge tube 10, and as shown in FIG. Discharge uniformity and luminous efficiency (lamp radiant light power per electromagnetic wave input) are improved. It should be noted that some reflected power is observed when impedance matching is performed so that the standing wave is dominant. That is, residual reflected power is observed. This reflected power is observed to be larger than when impedance matching is aimed at the minimum reflected power.

On the other hand, when the impedance matching section 16 performs impedance matching so as to minimize the reflected power from the discharge lamp 1, the standing wave cannot be excited with the same amplitude in the axial direction of the double discharge tube 10. , the probability that a strong discharge is formed only partially in the direction of the tube axis increases, and as shown in FIG.

(Effect of inner tube)
The effect of the inner tube will be explained. 8 and 9 are diagrams showing a bright discharge portion in a discharge lamp with an inner tube and a bright discharge portion in a discharge lamp without an inner tube, respectively.

Experiments confirmed the difference in the discharge mode depending on the presence or absence of the inner tube 12 . In this experiment, the outer conductor 15 of the discharge lamp 1 was formed so as to be open at the tip. In this experiment, the inner tube 12 is made of quartz, and the electromagnetic wave oscillator 2 outputs microwave power of 2.45 GHz. A discharge tube without the inner tube 12 is not an electrodeless discharge tube because the inner conductor 13 is exposed to plasma and emits impurities, which may shorten the lamp life.

As shown in FIG. 8, when the discharge lamp 1 is provided with the inner tube 12, the standing wave is generated so that the antinode is positioned at the tip of the double discharge tube 10, thereby forming the discharge bright portion. be. It can be seen from FIG. 8 that the discharge bright portion is generated over the length of 150 mm in the tube axis direction of the double discharge tube 10 and the standing wave wavelength is 36.7 mm. The standing wave wavelength of a 2.45 GHz microwave with a free space wavelength of 120 mm is 60 mm. This difference is due to the shortening of the microwave propagation wavelength to 61 mm, which is the value divided by the square root of the dielectric constant, since the inner tube 12 is made of quartz having a dielectric constant of 3.8. Also, the standing wave wavelength is shorter than the standing wave wavelength before the discharge is formed, and it can be seen that the dielectric constant of the discharge plasma shortens the standing wave wavelength.

On the other hand, when the discharge lamp 1 is not provided with the inner tube 12, as shown in FIG. is eliminated and the discharge is restricted to only a portion of the lamp.

(simulation)
The results of simulating the influence of the outer tube and the inner tube on the standing wave wavelength will be described with reference to FIGS. 10 to 15. FIG.

The wavelength of the standing wave depends on the respective thicknesses and dielectric constants of the outer tube 11 and the inner tube 12 . Also, by shortening the wavelength of the standing wave, the number of discharge bright portions in the double discharge tube 10 increases, and the luminous efficiency and discharge uniformity of the discharge lamp 1 can be improved.

FIG. 10 is a table showing parameters of outer and inner tubes made of quartz. Q1 and Q2 shown in the table are discharge lamps in which the outer tube 11 and the inner tube 12 are made of quartz having a dielectric constant of 3.8, and the outer tube 11 and the inner tube 12 have different thicknesses. A first discharge lamp and a second discharge lamp are shown, respectively. The wavelengths of the standing waves shown in the table are those before discharge formation, and are calculated by simulation for the first discharge lamp Q1 and the second discharge lamp Q2. 11 and 12 are diagrams showing simulation results showing electric field strength distributions in the first discharge lamp Q1 and the second discharge lamp Q2, respectively.

FIG. 13 is a table showing the parameters of outer and inner tubes made of alumina. A1 and A2 shown in the table are discharge lamps in which the outer tube 11 and the inner tube 12 are made of alumina having a dielectric constant of 10.0, and the outer tube 11 and the inner tube 12 have different thicknesses. A first discharge lamp and a second discharge lamp are shown, respectively. The wavelengths of the standing waves shown in the table are those before discharge formation, and are calculated by simulation for the first discharge lamp A1 and the second discharge lamp A2. 14 and 15 are diagrams showing simulation results showing electric field strength distributions in the first discharge lamp A1 and the second discharge lamp A2, respectively.

10 to 15 that the higher the dielectric constant of the material of the outer tube 11 and the inner tube 12 and the thicker the thickness of the inner tube 12, the shorter the standing wave wavelength. In addition, as described above, when discharge occurs, there is an effect of shortening the standing wave wavelength due to the dielectric constant of the plasma. The double discharge tubes used in FIGS. 8 to 15 all have a length of 150 mm and a diameter of 10 mm, but the same effect can be obtained with double discharge tubes of other sizes.

(Modification of discharge lamp)
A modification of the discharge lamp will be described. FIG. 16 is a schematic diagram showing a modification of the discharge lamp.

In the above-described embodiment, the straight tube type discharge lamp 1 is configured so that each element of the double discharge tube 10 is coaxially positioned with respect to the linear tube axis. The shape of 10 is not limited to a straight tube type, and may be a circular ring type or a spiral type. For example, as shown in FIG. 16, an annular discharge lamp 1A may be configured in which each element of the double discharge tube 10 is positioned coaxially with respect to the substantially circular tube axis in plan view.

Embodiments of the invention are provided by way of example and are not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

1 discharge lamp 10 double discharge tube 11 outer tube 12 inner tube 13 inner conductor 15 outer conductor 16 impedance matching section

Claims (6)

A discharge lamp that discharges and emits light by electromagnetic wave power supplied by an electromagnetic wave oscillator,
An inner tube, which is a cylindrical dielectric with an open proximal end and a closed distal end, and a conductor inserted into the inner tube and extending in the axial direction of the inner tube. An inner conductor, an outer tube that is a dielectric formed so as to define a closed space in which discharge gas is enclosed on the radially outer side of the inner tube, and a conductor that is formed to cover the outer periphery of the outer tube. a dual discharge tube having an outer conductor;
A discharge lamp comprising: an impedance matching section that matches the impedance of the electromagnetic wave oscillator and the impedance of the double discharge tube so that a standing wave is dominant in the double discharge tube. A stator, which is a dielectric that contacts the inner wall of the inner tube and the inner conductor and fixes the inner conductor to the inner tube, is provided at the tip of the inner conductor. Item 1. The discharge lamp according to item 1. 3. The impedance matching unit matches the impedance of the electromagnetic wave oscillator and the impedance of the double discharge tube so that reflected power from the double discharge tube remains. The discharge lamp described in . 4. The discharge lamp according to claim 1, wherein the discharge gas is an excimer gas. 5. The discharge lamp according to claim 1, wherein the outer conductor is formed with a plurality of openings opening in a radial direction. The discharge lamp according to any one of claims 1 to 5, wherein the discharge lamp is a UV-C low-pressure mercury lamp.

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