Apparatus for Producing Light by Exciting An

Europäisches Patentamt *EP000819317B1* (19) European Patent Office

Office européen des brevets (11) EP 0 819 317 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.7: H01J 65/04, F21S 2/00, of the grant of the patent: H05B 41/24 14.11.2001 Bulletin 2001/46 (86) International application number: (21) Application number: 96908743.6 PCT/US96/03262

(22) Date of filing: 11.03.1996 (87) International publication number: WO 96/28840 (19.09.1996 Gazette 1996/42)

(54) APPARATUS FOR PRODUCING LIGHT BY EXCITING AN ELECTRODELESS LAMP WITH MICROWAVE ENERGY AND APPARATUS FOR PRODUCING HIGH INTENSITY VISIBLE LIGHT APPARAT ZUR ERZEUGUNG SICHTBAREN LICHTS MITTELS ERREGUNG EINER ELEKTRODENLOSEN LAMPE DURCH MIKROWELLENENERGIE UND APPARAT ZUR ERZEUGUNG SICHTBAREN LICHTS HOHER INTENSITÄT APPAREIL POUR PRODUIRE DE LA LUMIERE PAR EXCITATION D’UNE LAMPE SANS ELECTRODE AU MOYEN D’ ENERGIE HYPERFREQUENCE ET APPAREIL POUR PRODUIRE DE LA LUMIERE VISIBLE A HAUTE INTENSITE

(84) Designated Contracting States: • TURNER, Brian AT BE CH DE DK ES FI FR GB GR IE IT LI LU MC Damascus, Maryland 20782 (US) NL PT SE (74) Representative: (30) Priority: 09.03.1995 US 402065 Schwepfinger, Karl-Heinz, Dipl.-Ing. Prinz & Partner GbR (43) Date of publication of application: Manzingerweg 7 21.01.1998 Bulletin 1998/04 81241 München (DE)

(73) Proprietor: FUSION LIGHTING, INC. (56) References cited: Rockville, MD 20855 (US) EP-A- 0 450 131 DE-A- 4 307 946 JP-A- 56 126 250 US-A- 4 749 915 (72) Inventors: US-A- 4 887 192 US-A- 4 975 625 • SIMPSON, James, E. Gaithersburg, MD 20877 (US) • OM P. GANDHI: "Microwave Engineering and • KAMAREHI, Mohammad applications" 1981 , PERGAMON PRESS, COP. Gaithersburg, MD 20878 (US) 1981 , NEW YORK XP002061355 * page 249; • URY, Michael figure 8.5.F * Bethesda, MD 20817 (US)

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 819 317 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 0 819 317 B1 2

Description [0007] Other circumstances which impact on the efficiency of illumination of the electrodeless lamp include [0001] The present invention relates to the field of interaction of the fringe field produced between the mi- electrodeless lamps. Specifically, an apparatus for uni- crowave energy source and the cavity with the elec- formly radiating an electrodeless lamp with improved il- 5 trodeless lamp. The lamp can distort the coupling fields lumination efficiency is described. between cavity and microwave energy source, introduc- [0002] Electrodeless lamps have been employed in ing an impedance mismatch and consequent power the past to generate high intensity radiant light in excess loss, lowering the system's efficiency. of 100,000 lumens. These devices are used in industrial lighting in both indoor and outdoor applications. Among 10 Summary of the Invention the advantages of electrodeless lamps is an enhanced life of between 10,000 and 20,000 hours. Further, great- [0008] It is an object of this invention to efficiently il- er power efficiency is obtained than with other conven- luminate an electrodeless lamp with microwave energy. tional light sources. [0009] It is a more specific object of this invention to [0003] Electrodeless lamps may be designed to emit 15 provide for a microwave illumination field which heats mostly infrared light, ultraviolet light or visible light. In an electrodeless lamp uniformly over its entire surface. applications wherein visible light is needed, electrode- [0010] It is yet another object of this invention to in- less lamps are sulfur or selenium filled to produce mostly crease the amount of visible light generated by a micro- visible light. Other lamps of other materials, such as wave illuminated electrodeless lamp. mercury, can be used to generate ultraviolet and infra- 20 [0011] These and other objects of the invention are red light in industrial applications where these wave- provided for by an apparatus for producing light com- lengths of light are needed. prising the features of claim 1 or by an apparatus for [0004] An electrodeless lamp which couples strong producing high intensity visible light comprising the fea- microwave fields to a very small bulb is known from US- tures of claim 5. A-4 975 625. That document discloses an apparatus for 25 [0012] The system of the invention improves the elec- providing light comprising a source of microwave ener- tromagnetic field distribution about an electrodeless gy, a cylindrical cavity coupled to the source of micro- lamp so that portions of the lamp which run cooler are wave energy, having a plurality of light emitting aper- exposed to an ascending or increasing electric field in- tures, the cylindrical cavity supporting microwave ener- tensity. The electrodeless lamp is supported for rotation gy coupled from the source in a mode which is inde- 30 in a cylindrical cavity about the cavity axis. The cylindri- pendent of the height of the microwave cavity and which cal cavity has an apertured surface which emits light includes electric field lines which are parallel to the generated by the electrodeless lamp when excited by height dimension of the cavity and wherein the height of microwave energy. the cavity is small enough to provide a strong microwave [0013] Control over the electromagnetic field distribu- field in the region near the center of the cavity. The elec- 35 tion is accomplished in a preferred embodiment of the trodeless lamp bulb is supported for rotation on a motor invention by configuring the cylindrical cavity to support driven shaft in the cylindrical cavity. That document fur- the TE112 resonant mode. In this mode, an ascending ther discloses a housing supporting at one end thereof portion of the electric field can be positioned adjacent a magnetron and at opposite end thereof a cooling fan the portion of an electrodeless lamp which would nor- which supplies forced air to the magnetron. 40 mally remain cooler, increasing the electric field intensi- [0005] Sulfur and selenium filled lamps have a light ty, thus raising the temperature of the normally cooler output which can be affected by local temperatures with- portion of the lamp. in the lamp. These gas-filled lamps show dark bands, [0014] In other embodiments of the invention, a local particularly along the top thereof, when the lamp surface discontinuity is introduced in the cylindrical cavity wall, is not uniformly heated. Cooler portions of the lamp can 45 increasing the electric field intensity on the portion of the produce discoloration which absorbs light disproportion- electrodeless lamp which normally runs cooler than the ately from the remaining portion of the lamp surface. remaining portion of the lamp. [0006] Temperature differentials within the bulb are very often the result of an uneven field distribution of the Description of the Figures microwave energy which is supported by a resonant 50 cavity containing the lamp. The uneven field distribution [0015] Figure 1 is a plan view of an apparatus for gen- produces an uneven discharge which in turn produces erating light from an electrodeless bulb. "sludge", a dark gas containing higher order sulfur mol- [0016] Figure 2 is an end view of the apparatus of Fig- ecules which degrade the lamp's performance. There- ure 1. fore, in order to avoid the consequences of local tem- 55 [0017] Figure 3 is a top view of the apparatus of Figure perature differentials within the lamp, the microwave il- 1. lumination of the bulb should produce uniform temper- [0018] Figure 4A illustrates the electric field distribu- ature across the surface of the lamp. tion within a cylindrical cavity when excited with a TE111

2 3 EP 0 819 317 B1 4 mode, as is known in the prior art. over the cavity 10. [0019] Figure 4B illustrates the improved field distri- [0031] The lamp 11 includes a top portion 11a above bution from a TE112 mode. the lamp center 11b, which is subject to a local temper- [0020] Figure 5A is a section view of a cylindrical cav- ature differential with respect to the remaining portion of 5 ity having a restriction along its length for increasing the the lamp 11. When a TE111 mode is supported within the electric field near the top of an electrodeless lamp. cavity 10, the electric field in the region of lamp portion [0021] Figure 5B is a top view of Figure 5A. 11a is decreasing in intensity, and microwave illumina- [0022] Figure 6A illustrates an iris supported in the cy- tion of the lamp, particularly in the region 11a, is non- lindrical cavity for increasing the electric field near the uniform, resulting in uneven heating of the lamp 11. top of the electrodeless lamp. 10 [0032] The sulfur or selenium molecules within the [0023] Figure 6B is a top view of Figure 6A. lamp 11 are unevenly heated and may produce a dark, [0024] Figure 7A illustrates a torroidal ring within the light impermeable region in a portion 11a of lamp 11 cylindrical cavity for increasing the electric field near the above the center of the lamp 11b. This reduces the top of the electrodeless lamp. amount of light which is generated through portion 11a, [0025] Figure 7B is a section view of Figure 7A. 15 decreasing total light output and making light output non-uniform over the surface of lamp 11. Description of the Preferred Embodiment [0033] Figure 4A illustrates the field distribution within the cylindrical cavity 10 which was used in the prior art [0026] Referring to Figures 1, 2 and 3, there is shown which identifies the source of unequal heating of the respectively, plan, end and top views of an apparatus 20 lamp 11 supported on shaft 12. The solid line represents for generating light from an electrodeless lamp 11. The the sinusoidal electric field distribution of a TE111 prop- electrodeless lamp 11, in the preferred embodiment of agation mode supported within cylindrical cavity 10 with the invention, contains either sulfur or selenium, which, end 10a in the absence of a lamp. The portion of the when excited with microwave energy, generates prima- TE111 electric field distribution adjacent region 11a, is rily visible light The apparatus of Figure 1 includes a 25 descending in electric field (E) strength with the maxi- housing 20 which is open along the top, and which en- mum intensity below the lamp center 11b. Less energy closes a filament transformer 26 for providing filament is thus absorbed by the electrodeless lamp in region current to a magnetron 22, a motor 14 for rotating the 11a, resulting in a lower temperature than in the region electrodeless lamp 11, and a cooling fan 25 for providing opposite the ascending portion of the electric field dis- cooling air to the magnetron 22. 30 tribution. [0027] The magnetron 22 is a commercially available [0034] In the presence of the lamp, the broken line magnetron operating at approximately 2.45 GHz. The illustrates how the electric field strength rapidly reduces magnetron 22 has an antenna 22a coupled to a in the region 11a, resulting in a lower temperature, pro- waveguide section 23 which enters the housing 20 and ducing a light-absorbing gas in sulfur- and selenium- closes the top of housing 20. Waveguide section 23 cou- 35 filled lamps. Light production in region 11a suffers due ples the microwave energy from magnetron 22 to a lon- to the light absorbing gas. gitudinal slot 24 on the top wall of the waveguide. Mi- [0035] In accordance with a preferred embodiment of crowave energy coupled through slot 24 propagates the invention, the cavity 10 is a cylindrical cavity having along the longitudinal axis of cylindrical cavity 10 to- end 10a supporting a TE112 propagation mode. The cy- wards end 10a. 40 lindrical cavity 10 may be configured in length and di- [0028] The electrodeless lamp 11 is supported on a mensions in accordance with a conventional mode chart shaft 12 which is coupled via coupling 13 to the motor for right circular cylindrical cavities as described in the 14. As is known in the electrodeless lamp art, rotation text "Introduction to Microwave Theory and Measure- of the lamp 11 at several hundred RPM creates a uni- ments" to support a TE112 propagation mode. The TE112 form plasma in lamp 11, and provides circumferential 45 mode, as shown in Figure 4B, provides for an electric temperature uniformity to the lamp 11, thus prolonging field distribution along the axis of the cylindrical cavity its life. 10 with end 10a which has two sinusoidal peaks asso- [0029] The electrodeless lamp 11 is shown inside cy- ciated with it. The second sinusoidal peak is located lindrical cavity 10 which may include an apertured sur- such that an ascending increasing intensity of the elec- face to emit light from the lamp 11 while confining the 50 tric field (E) is adjacent the region 11a of the electrode- electromagnetic radiation within the cylindrical cavity. less lamp 11, increasing the electric field strength in the The cylindrical cavity 10 has sidewalk and an end wall region 11a above the center 11b. The increased electric 10a which may be made from a metallic mesh or screen field intensity in this region increases the temperature which emits light. of region 11a, reducing the amount of light absorbing [0030] The apertured portion of the cavity 10 is 55 gas which forms at the top of the electrodeless lamp 11a. clamped via a clamp 19 to cylindrcal flange 15 bolted to [0036] The length of the cylindrical cavity 10 is select- the surface of the waveguide 23, forming the top of ed so that the lamp 11 may be supported on shaft 12 far housing 20. A transparent protection dome 16 is placed enough away from the slot 24 to avoid coupling of the

3 5 EP 0 819 317 B1 6 fringe field associated with slot 24 with the lamp 11 as wave energy coupled from said source (22) shown for example in Figure 1. having an electric field intensity which varies si- [0037] The increased electric field at the top of the nusoidally along an axis of said cylindrical cav- lamp provides a more uniform discharge and prevents ity (10); and the formation of sludge or higher order molecules which 5 an electrodeless lamp (11) supported for rota- degrade the lamp's light generation efficiency. The rate tion on a motor driven shaft (12) in said cylin- of energy absorption, particularly in a sulfur plasma with- drical cavity (10) along the axis of said cavity at in the lamp, is increased near the top of the lamp, in- a location which is distant from a location (24) creasing plasma heating of the gas molecules. which produces fringe fields from coupling said 10 [0038] In the TE111 mode, positioning the bulb further microwave source (22) to said cylindrical cavity down the cavity where the electric field intensity is rising (10), and located so that a portion (11a) of said would result in better heating of the top of the lamp. How- electrodeless lamp (11) above a center (11b) of ever, this would reduce the optical access to the lamp, said electrodeless lamp (11) is illuminated by a and would promote near field interaction with the fringe portion of said electric field which is increasing fields produced at the boundary between the cylindrical 15 in intensity along a length of said cavity (10), cavity 10 and the slot 24 of the waveguide 24. whereby said electrodeless lamp (11) has a [0039] Other techniques for locally increasing the surface area which is heated at a substantially electric field intensity near the top of the lamp 11 are constant temperature across the surface area shown in Figures 5A, 5B, 6A, 6B, 7A and 7B. thereof. 20 [0040] These techniques do not require the TE112 resonant mode. These alternative techniques are illustrat- 2. The apparatus of claim 1, wherein said cylindrical ed using reference numerals which are common to the cavity (10) has a length and diameter selected to embodiment of Figures 1 to 3 and 4B. support a TE112 mode of operation. [0041] Figures 5A and 5B show a narrowing of the cavity 10 in the region 11a (see Figure 5A) of the lamp 25 3. The apparatus of claim 1, wherein said cylindrical to create a restriction 30 (see Figure 5A) for increasing cavity (10) includes an iris (31) along said length for the electric field intensity in region 11a. creating said increasing electric field intensity. [0042] Figures 6A and 6B illustrate an iris 31 which is located within the cylindrical cavity 10 at a location op- 4. The apparatus of claim 1, wherein said cylindrical posite region 11a (see Figure 6A) for increasing the 30 cavity (10) includes a toroidal ring (32) along the electric field intensity in the region above the lamp cent- length of said cylindrical cavity (10) for increasing er 11b. said electric field intensity. [0043] Figures 7A and 7B illustrate the use of a sus- pended torroidal metallic ring 32 which increases the 5. An apparatus for producing high intensity visible field intensity in the region 11a of the lamp 11 (see Figure 35 light comprising: 7A). [0044] Each of the foregoing embodiments achieves a housing (20) supporting at one end thereof a the objective of maintaining the lamp 11 sufficiently dis- magnetron (22) and at an opposite end thereof tant from the slot 24 to avoid coupling with the fringe a cooling fan (25) which supplies forced air to field produced from the coupling slot 24. Further, the 40 said magnetron (22), and further including a height of the lamp 11 from the housing 20 permits full motor (14) with a driven shaft (12) extending optical access to the lamp. through said housing (20); [0045] Thus, there has been described with respect an electrodeless lamp (11) supported on said to several embodiments, a technique for efficiently illu- driven shaft (12); and minating an electrodeless bulb which avoids local tem- 45 a light emitting cylindrical cavity (10) supported perature differentials in the bulb, thus increasing light on said housing, said cylindrical cavity (10) en- output. closing said electrodeless lamp (11), and coupled through said housing (20) to said magnetron (22), whereby microwave energy generat- Claims 50 ed by said magnetron (22) is coupled to said cavity (10), said cavity (10) supporting said mi- 1. An apparatus for producing light, comprising: crowave energy having an electric field which increases in intensity along a longitudinal axis a source (22) of microwave energy ; of said cylindrical cavity (10) in a region (11a) a cylindrical cavity (10) coupled to said source 55 above a center (11b) of said lamp and adjacent of microwave energy (22), having a plurality of an end of said electrodeless lamp (11), thereby light emitting apertures, said cylindrical cavity decreasing local temperature variations in said (10) supporting microwave energy, said micro- lamp (11).

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6. The apparatus of claim 5, wherein said cavity (10) TE112-Betriebsmode unterstützt wird. supports microwave energy having an TE112 mode. 3. Vorrichtung nach Anspruch 1, wobei der zylindri- 7. The apparatus of claim 5, wherein said cavity (10) sche Hohlraum (10) eine Irisblende (31) entlang der includes means (30, 31, 32) located above the cent- 5 Länge enthält, um die zunehmende elektrische er (11b) of said electrodeless lamp (11) for increas- Feldstärke zu erzeugen. ing the electric field intensity in the region (11a) above said lamp center (11b). 4. Vorrichtung nach Anspruch 1, wobei der zylindrische Hohlraum (10) einen kreisförmigen Ring (32) 8. The apparatus of claim 7, wherein said means lo- 10 entlang der Länge des zylindrischen Hohlraums cated above said center (11b) of said lamp (11) (10) enthält, um die elektrische Feldstärke zu erhö- comprises a restriction (30) for narrowing a width of hen said cavity (10). 5. Vorrichtung zur Erzeugung sichtbaren Lichts hoher 9. The apparatus of claim 7, wherein said means lo- 15 Intensität, umfassend: cated above said lamp center (11b) includes an iris (31) in said cavity (10). ein Gehäuse (20), das an seinem eigenen En- de ein Magnetron (22) und an seinem entge- 10. The apparatus of claim 7, wherein said means lo- gengesetzten Ende einen Lüfter (25) trägt, der cated above said lamp center (11b) includes a toroi- 20 dem Magnetron (22) Gebläseluft zuführt, und dal ring (32) connected to said cavity (10). das zudem einen Motor (14) mit einer Antriebs- welle (12) enthält, die sich durch das Gehäuse (20) erstreckt; Patentansprüche eine elektrodenlose Lampe (11), die auf der An- 25 triebswelle (12) gehalten wird; und 1. Vorrichtung zur Erzeugung von Licht, umfassend: einen lichtaussendenden, zylindrischen Hohl- raum (10), der auf dem Gehäuse gehalten wird, eine Mikrowellen-Energiequelle (22); wobei der zylindrische Hohlraum (10) die elek- einen an die Mikrowellen-Energiequelle (22) trodenlose Lampe (11) umschließt und über gekoppelten zylindrischen Hohlraum (10), der 30 das Gehäuse (20) mit dem Magnetron (22) ge- mehrere lichtaussendende Öffnungen auf- koppelt ist, wobei eine durch das Magnetron weist, wobei die zylindrische Hohlraum (10) Mi- (22) erzeugte Mikrowellenenergie in den Hohl- krowellenenergie unterstützt, wobei die von der raum (10) eingekoppelt wird, der Hohlraum Quelle (22) ausgekoppelte Mikrowellenenergie (10), der die Mikrowellenenergie unterstützt, eine elektrische Feldstärke aufweist, die sinus- 35 ein elektrisches Feld aufweist, dessen Stärke förmig entlang einer Achse des zylindrischen entlang einer Längsachse des zylindrischen Hohlraums (10) variiert; und Hohlraums (10) in einem Bereich (11a) ober- eine elektrodenlose Lampe (11), die drehbar halb der Mitte (11b) der Lampe und angrenzend auf einer motorgetriebenen Motorwelle (12) in an ein Ende der elektrodenlosen Lampe (11) dem zylindrischen Hohlraum (10) entlang der 40 zunimmt, wodurch örtliche Temperaturunter- Achse des Hohlraums an einer Stelle gehalten schiede in der Lampe (11) verringert werden. wird, die von einer Stelle (24) entfernt liegt, die aufgrund der Kopplung der Mikrowellenquelle 6. Vorrichtung nach Anspruch 5, wobei der Hohlraum (22) mit dem zylindrischen Hohlraum (10) (10) eine Mikrowellenenergie in einem TE112-Mode Streufelder erzeugt, und die so angeorndet ist, 45 unterstützt. daß ein Abschnitt (11a) der elektrodenlosen Lampe (11) oberhalb einer Mitte (11b) der elek- 7. Vorrichtung nach Anspruch 5, wobei der Hohlraum trodenlosen Lampe (11) von einem Teil des (10) Mittel (30, 31, 32) enthält, die oberhalb der Mit- elektrischen Feldes bestrahlt wird, dessen te (11b) der elektrodenlosen Lampe (11) angeord- Stärke entlang einer Länge des Hohlraums (10) 50 net sind, um die elektrische Feldstärke in dem Be- zunimmt, wodurch die elektrodenlose Lampe reich (11a) oberhalb der Lampenmitte (11b) zu er- (11) einen Oberflächenbereich aufweist, der höhen. auf eine über die Oberfläche im wesentlichen konstante Temperatur erwärmt ist. 8. Vorrichtung nach Anspruch 7, wobei das oberhalb 55 der Mitte (11b) der Lampe (11) angeordnete Mittel 2. Vorrichtung nach Anspruch 1, wobei der zylindri- eine Begrenzung (30) zur Einengung einer Weite sche Hohlraum (10) eine Länge und einen Durch- des Hohlraums (10) aufweist. messer aufweist, die so gewählt sind, daß ein

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9. Vorrichtung nach Anspruch 7, wobei das oberhalb que. der Lampenmitte (11b) angeordnete Mittel eine Iris- blende (31) in dem Hohlraum (10) enthält. 5. Dispositif pour produire de la lumière visible à haute intensité, comprenant: 10. Vorrichtung nach Anspruch 7, wobei das oberhalb 5 der Lampenmitte (11b) angeordnete Mittel einen un boîtier (20) qui porte à une de ses extrémités kreisförmigen Ring (32) enthält, der mit dem Hohl- un magnétron (22) et à une extrémité opposée raum (10) verbunden ist un ventilateur (25) amenant au magnétron (22) de l'air pulsé, et qui contient en outre un moteur 10 (14) avec un arbre d'entraînement (12) qui Revendications s'étend à travers le boîtier (20),

1. Dispositif de production de lumière, comprenant : une lampe (11) sans électrode qui est maintenue sur l'arbre d'entraînement (12), et une source (22) d'énergie hyperfréquence , 15 une cavité (10) cylindrique émettrice de lumiè- une cavité (10) cylindrique couplée à la source re, qui est maintenue sur le boîtier, la cavité (10) (22) d'énergie hyperfréquence, qui présente cylindrique entourant la lampe (11) sans élec- une pluralité d'ouvertures émettrices de lumiè- trode et étant couplée au magnétron (22) par re, la cavité (10) cylindrique soutenant l'énergie 20 l'intermédiaire du boîtier (20), de l'énergie hy- hyperfréquence, l'énergie hyperfréquence cou- perfréquence produite par le magnétron (22) plée depuis la source (22) ayant une intensité étant couplée à la cavité (10) cylindrique, la ca- de champ électrique qui varie sous forme sinu- vité (10) qui soutient l'énergie hyperfréquence soïdale le long d'un axe de la cavité (10) présentant un champ électrique dont l'intensité cylindrique ; et 25 augmente le long d'un axe longitudinal de la ca- vité (10) cylindrique dans une zone (11a) située une lampe (11) sans électrode qui est mainte- au-dessus du milieu (11b) de la lampe et adja- nue en rotation sur un arbre (12) entraîné par cente à une extrémité de la lampe (11) sans moteur dans la cavité (10) cylindrique le long électrode, grâce à quoi des différences de tem- de l'axe de la cavité, à un emplacement qui est 30 pérature locales dans la lampe (11) sont rédui- éloigné d'un emplacement (24) qui produit des tes. champs de dispersion en raison du couplage de la source hyperfréquence (22) avec la cavité 6. Dispositif selon la revendication 5, dans lequel la (10) cylindrique, et qui est agencée de manière cavité (10) soutient une énergie hyperfréquence 35 qu'une portion (11a) de la lampe (11) sans élec- ayant un mode TE112. trode, au-dessus d'un milieu (11b) de la lampe (11) sans électrode, soit illuminée par une par- 7. Dispositif selon la revendication 5, dans lequel la tie du champ électrique dont l'intensité aug- cavité (10) contient des moyens (30, 31, 32) qui mente le long d'une longueur de la cavité (10), sont agencés au-dessus du milieu (11b) de la lampe la lampe (11) sans électrode présentant ainsi 40 (11) sans électrode pour augmenter l'intensité de une région de surface qui est chauffée à une champ électrique dans la zone (11a) au-dessus du température sensiblement constante sur toute milieu de la lampe (11b). la région de surface 8. Dispositif selon la revendication 7, dans lequel le 2. Dispositif selon la revendication 1, dans lequel la 45 moyens agencé au-dessus du milieu (11b) de la cavité (10) cylindrique présente une longueur et un lampe (11) présente un étranglement (30) pour ré- diamètre choisis pour soutenir un mode opération- trécir une largeur de la cavité (10). nel TE112. 9. Dispositif selon la revendication 7, dans lequel le 3. Dispositif selon la revendication 1, dans lequel la 50 moyen agencé au-dessus du milieu (11b) de la lam- cavité (10) cylindrique contient un iris (31) le long pe contient un iris (31) dans la cavité (10). de la longueur pour créer l'intensité de champ élec- trique qui augmente. 10. Dispositif selon la revendication 7, dans lequel le moyen agencé au-dessus du milieu (11b) de la lam- 4. Dispositif selon la revendication 1, dans lequel la 55 pe contient une bague torique (32) qui est reliée à cavité (10) cylindrique contient une bague torique la cavité (10). (32) le long de la longueur de la cavité (10) cylindrique pour augmenter l'intensité de champ électri-

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