EP0578953B1 - High power emitting device - Google Patents

Description

Technical field

The invention relates to a high-power radiator, in particular for ultraviolet light, with a discharge space filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by an outer and an inner dielectric, the outer surfaces of the outer dielectric being provided with first electrodes, with second electrodes Electrodes on the surface of the second dielectric facing away from the discharge space, and with an alternating current source connected to the first and second electrodes for supplying the discharge.

The invention relates to a state of the art, such as that which results from EP-A 0 254 111, US-A-5 013 959 or EP-A-0 385 205.

Technological background and state of the art

The industrial use of photochemical processes depends heavily on the availability of suitable UV sources. The classic UV lamps deliver low to medium UV intensities at some discrete wavelengths, such as the low-pressure mercury lamps at 185 nm and especially at 254 nm. Really high UV powers can only be obtained from high-pressure lamps (Xe, Hg), which then distribute their radiation over a larger wavelength range. The new excimer lasers have provided some new wavelengths for basic photochemical experiments. for cost reasons for an industrial process probably only suitable in exceptional cases.

In the EP patent application mentioned at the beginning or in the conference paper "New UV and VUV excimer emitters" by U. Kogelschatz and B. Eliasson, distributed at the 10th lecture conference of the Society of German Chemists, Photochemistry Group, in Würzburg (FRG) 18. -20. November 1987, a new excimer radiator is described. This new type of emitter is based on the fact that excimer radiation can also be generated in silent electrical discharges, a type of discharge that is used on a large scale in ozone generation. In the current filaments of this discharge, which exist only for a short time (<1 microsecond), noble gas atoms are excited by electron impact, which react further to excited molecular complexes (excimers). These excimers only live for a few 100 nanoseconds and release their binding energy in the form of UV radiation when they decay.

Excimer UV lamps based on the principle of silent electrical discharges require a significantly higher voltage than the voltage required for normal operation when they are first ignited or after longer breaks. This is due to the fact that surface charges form on the dielectrics during operation, which in each case ensure easier ignition in the subsequent voltage half-wave. These surface charges are missing the first time you ignite and after long breaks.

In general it can be said that two criteria must be met for the ignition of a gas discharge. On the one hand initial electrons must be present and, on the other hand, the electric field strength must exceed a critical value (ignition criterion) so that there can be a sufficient multiplication of the initial electrons and thus the formation of electron avalanches under the influence of the applied electric field.

Methods known from lamp technology are the use of a radioactive preparation (e.g. thorium) or gas (Krypton 85) to provide the starting electrons and an overvoltage pulse to increase the starting field strength. The latter measure in particular requires additional effort in the design of the electrical power supplies and the insulation level of cables, plugs, brackets, etc.

Presentation of the invention

Proceeding from the prior art, the object of the invention is to create a high-performance radiator, in particular for UV or VUV radiation, which ignites reliably without complex measures.

To achieve this object, it is provided according to the invention in a high-power radiator of the type mentioned at the outset that, for local field distortion, the discharge space is locally narrowed by attaching additional material made of dielectric material on the wall of the dielectric tubes facing the discharge space, or that one or more interfering bodies made of dielectric material are in the discharge space are provided, which touch one or the other or both dielectrics.

The invention is based on the knowledge of forcing an initial ignition at one point by local field distortion or field elevation. The resulting UV radiation and the charge carriers of this local discharge then force the reliable ignition of the entire discharge volume. This field distortion can be realized in a simple manner by means of a quartz ball or a ball made of aluminum or titanium oxide in the discharge gap.

The invention makes it possible for the first time to create excimer UV lamps that ignite safely. The measures to be taken are simple and economical. They can also be carried out retrospectively in existing units when using an interference body, which is considered the most preferred means for field distortion.

Embodiments of the invention and the advantages which can be achieved thereby are explained in more detail below with reference to the drawing.

Brief description of the drawings

Fig.1

einen UV-Zylinderstrahlers mit konzentrischer Anordnung von innerem und äusserem Dielektrikumsrohr im Längsschnitt;

Fig.2

einen Schnitt durch den UV-Strahler nach Fig.1 längs deren Linie AA;

In the drawing, embodiments of the invention are shown schematically; in it shows

Fig. 1

a UV cylinder lamp with a concentric arrangement of the inner and outer dielectric tube in longitudinal section;

Fig. 2

a section through the UV lamp according to Figure 1 along the line AA;

Ways of Carrying Out the Invention

According to FIGS. 1 and 2, there is an outer quartz tube 1 with a wall thickness of approximately 0.5 to 1.5 mm and an outer diameter An inner quartz tube 2 of approximately 20 to 30 mm is arranged coaxially. A helical inner electrode 3 bears against the inner surface of the inner quartz tube 2.

An outer electrode 4 in the form of a wire mesh or an applied electrode structure extends over the entire outer circumference of the outer quartz tube 1.

A wire 3 is inserted into the inner quartz tube 2. This forms the inner electrode of the radiator, the wire mesh 4 the outer electrode of the radiator. The quartz tubes 1 and 2 are closed or melted at both ends by a cover 5 and 6, respectively. The space between the two tubes 1 and 2, the discharge space 7, is filled with a gas / gas mixture which emits radiation under discharge conditions. The interior 8 of the inner quartz tube 2 is filled with a liquid with a high dielectric constant, preferably demineralized water (ε = 81). This liquid also serves to cool the radiator. The coolant is supplied or removed via the connections 9 and 10. The cooling liquid also serves for the electrical coupling of the inner electrode 3 to the inner quartz tube 2, so that it is not necessary for the helical electrode 3 to rest against the inner wall everywhere.

The two electrodes 3, 4 are connected to the two poles of an alternating current source 11. The alternating current source supplies an adjustable alternating voltage in the order of magnitude of several 100 volts to 20,000 volts at frequencies in the range of technical alternating current up to a few 1000 kHz - depending on the electrode geometry, pressure in the discharge space and composition of the filling gas.

The filling gas is, for example, mercury, noble gas, noble gas-metal vapor mixture, noble gas-halogen mixture, optionally under Use of an additional further noble gas, preferably Ar, He, Ne, as a buffer gas.

Depending on the desired spectral composition of the radiation, a substance / substance mixture according to the following table can be used: Filling gas radiation helium 60-100 nm neon 80 - 90 nm argon 107 - 165 nm Argon + fluorine 180-200 nm Argon + chlorine 165-190 nm Argon + krypton + chlorine 165-190, 200-240 nm xenon 160-190 nm nitrogen 337 - 415 nm krypton 124, 140-160 nm Krypton + fluorine 240 - 255 nm Krypton + chlorine 200-240 nm mercury 185, 254,320-370,390-420nm selenium 196, 204, 206 nm deuterium 150-250 nm Xenon + fluorine 340 - 360 nm, 400 - 550 nm Xenon + chlorine 300-320 nm

• Ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit einem Gas bzw. Dampf aus F₂, J₂, Br₂, Cl₂ oder eine Verbindung die in der Entladung ein oder mehrere Atome F, J, Br oder Cl abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit O₂ oder einer Verbindung, die in der Entladung ein oder mehrere 0-Atome abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) mit Hg.

In addition, a whole series of other filling gases are possible:

• An inert gas (Ar, He, Kr, Ne, Xe) or Hg with a gas or vapor made of F ₂ , J ₂ , Br ₂ , Cl ₂ or a compound that contains one or more atoms F, J, Br or in the discharge Cl cleaves;
• a noble gas (Ar, He, Kr, Ne, Xe) or Hg with O ₂ or a compound that releases one or more 0 atoms in the discharge;
• an inert gas (Ar, He, Kr, Ne, Xe) with Hg.

When an alternating voltage is applied between the electrodes 3 and 4, a large number of discharge channels (partial discharges) form in the discharge space 7. These interact with the atoms / molecules of the filling gas, which ultimately leads to UV or VUV radiation.

In the silent discharge that forms, the electron energy distribution can be optimally adjusted by the thickness of the dielectrics and their properties as well as pressure and / or temperature in the discharge space.

So far, excimer UV lamps are known.

In order to solve the ignition problem described at the outset, a number of possibilities are provided according to the invention, all of which are based on the idea of locally forcing a field distortion or field increase at a point in the discharge space 7. The resulting UV radiation and the charge carriers of this local discharge then force the reliable ignition of the entire discharge volume.

A first variant is shown in Fig. 1, right upper half (Fig. 2 in dashed lines). The outer dielectric tube 1 is provided with an indentation or dent 12. This extends approximately up to half the gap width to the inner dielectric tube 2.

A second variant shows Fig. 1, lower right half (Fig. 2 also dashed). There, the inner dielectric tube 2 is provided with a dent or bump 12a, which reaches the outer dielectric tube 1 approximately up to half the gap width.

While these two variants of field distortion would have to be provided from the outset, the embodiment shown in FIG. 1, left half, and FIG. 2 can also be used retrospectively in the case of emitters.

These two variants are known from EP-A-0 547 366 and represent prior art in accordance with Art. 54 (3) EPC.

In the discharge space 7 there is a ball 13 made of dielectric material, e.g. Quartz, preferably made of aluminum or titanium oxide, with an outer sphere diameter equal to or slightly smaller than the gap width of the discharge space 7. This sphere can, but need not, be attached to one or both dielectric walls. The exact spherical geometry is not important. Two or more of these balls can also be provided, in particular in the case of elongated radiators. The combination of ball (s) and dents or humps is also possible.

Another measure that can also be taken subsequently with radiators is to melt quartz drops 12b or 12c on the inner surface of the outer dielectric tube 1 or on the outer surface of the inner dielectric tube 2 in order to achieve the desired field distortion.

Label list

1

outer quartz tube

2nd

inner quartz tube

3rd

helical inner electrode

4th

Outside electrode

5.6

cover

7

Discharge space

8th

Interior of 2

9

Coolant drain

10th

Coolant drain

11

AC power source

12th

Dent or hump on 1st

12a

Dent or hump on 2

12b

Quartz trofen on 1st

12c

Quartz trofen on 2nd

13

Ball made of aluminum or titanium oxide

Claims (2)

1. High-power emitter, in particular for ultraviolet light, with a discharge chamber (7) filled with filler gas emitting radiation under discharge conditions, the walls of which are formed by an outer (1) and an inner dielectric (2), in which the outer faces of the outer dielectric are provided with first electrodes (4), with second electrodes (3;3') on the surface of the second dielectric (2) facing away from the discharge chamber (7), and with an alternating current source (11) connected to the first (4) and second electrodes (3;3') to supply the discharge, characterised in that for the local field distortion the discharge chamber is locally narrowed through the application of additional material (12b, 12c) of dielectric material on the wall of the dielectric tube (1,2) facing the discharge chamber, or that in the discharge chamber (7) one or more interference bodies of dielectric material are provided, which touch one or other or both of the dielectrics (1, 2).
2. High-efficiency radiator according to Claim 1, characterised in that the interference body or bodies consist of quartz, aluminium- or titanium oxide.

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