WO2000065627A1

WO2000065627A1 - High pressure arc discharge lamp

Info

Publication number: WO2000065627A1
Application number: PCT/US2000/011317
Authority: WO
Inventors: William Lawrence Manning
Original assignee: Eg & G, Inc.
Priority date: 1999-04-27
Filing date: 2000-04-26
Publication date: 2000-11-02
Also published as: AU4495200A

Abstract

A high pressure arc discharge lamp (10) includes a sealed envelope (12); a pair of spaced electrodes (20 and 22) in the envelope; an ionizable medium (16) in the envelope for generating a plasma arc (18) between the electrodes; and a magnetic field source (40) for generating a magnetic field for suppressing plasma jet instability (24) emanating from the plasma arc.

Description

HIGH PRESSURE ARC DISCHARGE LAMP

FIELD OF INVENTION This invention relates to an improved high pressure arc discharge lamp.

BACKGROUND OF INVENTION

High pressure discharge lamps exhibit certain instabilities such as transverse plasma jets due to the self-induced magnetic field of the arc discharge. High pressure arc discharge lamps include those using halides, noble gases, e.g., argon, neon, xenon, mercury and heavy metals, e.g., indium, gallium, sodium. These jets can be particularly troublesome: in high pressure mercury arc discharge lamps the instabilities result in a jet of high velocity and very hot mercury-xenon plasma although not as dense and hot as the main discharge itself, but still nevertheless hot enough to damage the quartz envelope that surrounds the arc-discharge. This hot jet impinges on the inside surface of the quartz envelope, and through a gradual process breaks down its surface and gradually leads to catastrophic failure.

BRIEF SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved high pressure discharge lamp.

It is a further object of this invention to provide such an improved high pressure discharge lamp which controls plasma jet instability.

It is a further object of this invention to provide such an improved high pressure discharge lamp which increases the useful light output of the plasma arc. It is a further object of this invention to provide such an improved high pressure discharge lamp which selectively deploys the plasma jet to more nearly

thermally balance the ionization mechanism.

The invention results from the realization that an improved high pressure discharge lamp which controls plasma jet instability to prevent catastrophic failure of the envelope can be effected by employing a magnetic field to suppress the plasma jet and even redirect it to increase light output and more nearly thermally balance the ionizable medium.

The invention features a high pressure arc discharge lamp including a sealed envelope and a pair of spaced electrodes in the envelope. There is an ionizable medium in the envelope for generating a plasma arc between the electrodes and a magnetic field source for generating a magnetic field for suppressing plasma jet instability emanating from the plasma arc.

In a preferred embodiment the ionizable medium may be mercury or may be any one of a number of materials selected from the group including halides, argon, xenon, krypton, indium and gallium. The envelope may be quartz. The magnetic field source may generate a magnetic field generally transverse to the

plasma jet instability. The instability may extend laterally from the arc. The electrodes may include an anode and a cathode and the instability may typically occur closer to the anode than to the cathode. The magnetic field source may be

disposed proximate the anode and it may provide a magnetic field of approximately 1,000-2,000 gauss at the plasma jet instability. The invention also features a high pressure short arc mercury discharge lamp including a sealed envelope, a pair of spaced electrodes in the envelope, and a charge of mercury in the envelope for generating a plasma arc between the electrodes. There is a magnetic field source for generating a magnetic field for suppressing plasma jet instability emanating from the plasma arc.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

Fig. 1 is an improved diagrammatic side sectional elevational view with parts broken away of a high pressure discharge lamp exhibiting plasma jet instability;

Fig. 2 is a view similar to Fig. 1 employing a magnetic field to control the plasma jet instability according to this invention;

Fig. 2A is a view similar to Figs. 1 and 2 illustrating a magnetic field source rotatable relative to the lamp envelope;

Fig. 3 is an illustration of the decrease in magnetic field required with the increase in length of the plasma jet instability;

Fig. 4 is a view similar to Fig. 2 showing the magnetic field source;

Fig. 5 is a side view of the lamp and source of Fig. 4;

Figs. 6, 7 and 8 are views of permanent magnetic field sources usable in Figs. 2 and 4;

Fig. 9 is a view similar to Figs. 1 and 2 using an electromagnetic field source disposed about the lamp;

Fig. 10 is a view similar to Figs. 1 and 2 with a reflector added and an electromagnetic field source disposed about the reflector; and

Fig. 11 is a more complete detailed view of a discharge lamp according to this invention.

There is shown in Fig. 1 a high-pressure arc discharge lamp 10 including an envelope 12 creating a sealed chamber 14 in which an ionizable medium 16 is disposed. Envelope 12 may typically be quartz and the ionizable medium may be any suitable material such as halides including sodium halide, vanadium halide, mercury halide, cesium halide, neodymium halide, dysprosium halide; the medium may also include heavy metals such as mercury, indium and gallium, for example, and noble gases including argon, xenon and krypton, for example.

In one preferred embodiment the plasma medium 16 is mercury. There is also included a measure of xenon in the charge as the medium to strike the initial low voltage arc. When lamp 10 is operating, a plasma arc 18 is struck between anode 20 and cathode 22 with the mercury vapor acting as the ionized medium. Due to these self-induced magnetic fields in plasma arc 18, certain instability occurs such as shown for example, by plasma jet instability 24 which extends laterally a distance or length D away from centerline 19 of arc 18. Jet 24 is typically closer to anode 20 than to cathode 22. Plasma jet 24 includes mercury

vapor and may also include some xenon which has been used for the starting

medium. In operation, the temperature is in the range of 700-800°F and there is intense pressure in chamber 14 on the order of 16-20 atmospheres. Plasma jet 24, striking the inside of envelope 12, causes it to etch, eventually weakening the quartz envelope in that area indicated at 24, and eventually causing catastrophic failure. Jet 24 also consumes a portion of the energy that should be contained in arc 18 and so detracts from the overall efficiency and useful light output of lamp 10. In addition, a cooler area of chamber 14 may collect droplets 26 of the plasma medium, or mercury in this case.

According to this invention a magnetic field 30, Fig. 2, as indicated by magnetic lines 32, is directed toward lamp 10. The jet 24 can be suppressed more or less, depending upon the strength of the magnetic field applied. For example, it can be suppressed to the position shown at 24a or to even smaller positions of 24b and 24c, or it can be completely restored to plasma arc 18 whereupon it returns all the consumed energy to plasma arc 18 thereby improving the efficiency and overall light output of lamp 10. Beyond merely being suppressed, jet 24 can be controlled so that it emerges on the other side of plasma arc 18 such as shown at 24d, or it can be driven even further as shown at 24e, whereby its heat can be used to vaporize the droplets 26 of mercury or other plasma medium to improve the efficiency of lamp 10. For example, as shown in Fig. 2A„ a small AC or DC motor 21 with shaft 23 attached to one end 25 of envelope 12 to relate it three revolutions per minute with respect to magnet 40 so that the jet sweeps around inside the envelope. Commutation rings 27, 29 are provided at the other end 31 of envelope 12 for electrical connection. Alternatively, the magnet 40 could be rotated relative to envelope 12.

The magnetic field required is a function of the distance D of the plasma jet from the center line 19. This is illustrated in Fig. 3 where the distance D is indicated along the abscissa and the critical flux density in gauss is indicated along the ordinate.

The magnetic field 30, Fig. 4, may be provided by a magnet such as permanent magnet 40, Fig. 4, which may be a one-inch diameter ring magnet

placed at a distance F approximately ^lA to 5/8 inch from plasma arc 18 and at an angle α of 20°-30° between its axis 42 and center line 19 as shown more clearly in

Fig. 5.

Any of a variety of magnetic field sources may be used as shown in Figs. 6, 7 and 8 where for example magnetic field source 40a is a permanent ring magnet approximately A to % inch long with an OD of 1 to VΛ inches, Fig. 6. Bar magnet 40b, Fig. 7, is a permanent magnet of approximately 3 inches in length and YΛ to Vi inch in diameter. Permanent magnet 40c, Fig. 8, is a cylindrical magnet approximately A to % inch long and about the same diameter, but clad in a nonmagnetic sleeve 44.

Although thus far the magnetic field sources have been represented as permanent magnets, this is not a necessary limitation of the invention. For example, as shown in Fig. 9 the magnetic field source may be an electromagnet 40d surrounding envelope 12. The magnetic field source need not be placed right on or at the envelope of the lamp. For example, as shown in Fig. 10, lamp 10b may be

encased in a reflector 50 and the magnetic field source 40e may be implemented as an electromagnetic coil and disposed on the outside of reflector 50.

The basic lamp structure may be made in accordance with any of the prior art designs, for example, such as the one shown in U.S. Patent No. 4,978,884, Van Vliet et al., December 18, 1990. A typical lamp 10c, Fig. 11, has its cathode connected at solder joint 60 to a pigtail connection 62 and its anode 20 connected to a lug or terminal 74 which has a threaded end 66 for electrical connection and mounting purposes. Anode 20 is connected to terminal 64 by means of anode conductor 68 and cathode 22 is connected to terminal 60 by means of cathode conductor 70. Arc 18 is typically .05 inch in length. The overall length of lamp 10c is approximately 2.8 inches and the arc is positioned just about dead center. Lamp 20 has an OD at the bubble of approximately .5 inch and the bubble is approximately 3/10 inch long. Pigtail 62 is typically stranded nickel wire. A gold cladding or heat retainer 74 surrounds the quartz envelope 12 at cathode 22 and cathode conductor 70 to avoid cold spots and keep the mercury hot and volatile. The walls of bubble 72 are typically 2 mm in thickness.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention.

Other embodiments will occur to those skilled in the art and are within the following claims:

What is claimed is:

Claims

1. A high pressure arc discharge lamp comprising: a sealed envelope; a pair of spaced electrodes in said envelope; an ionizable medium in said envelope for generating a plasma arc between said electrodes; and a magnetic field source for generating a magnetic field for suppressing plasma jet instability emanating from said plasma arc.

2. The high pressure arc discharge lamp of claim 1 in which said ionizable medium includes mercury.

3. The high pressure arc discharge lamp of claim 1 in which said ionizable medium includes a material selected from the group including halides, argon, xenon, krypton, indium and gallium.

4. The high pressure arc discharge lamp of claim 1 in which said envelope is quartz.

5. The high pressure arc discharge lamp of claim 1 in which said

magnetic field source generates a magnetic field generally transverse to said plasma jet instability.

6. The high pressure arc discharge lamp of claim 1 in which said plasma jet instability extends laterally from said arc.

7. The high pressure arc discharge lamp of claim 6 in which said electrodes include an anode and a cathode.

8. The high pressure arc discharge lamp of claim 7 in which said plasma jet instability occurs closer to said anode than said cathode.

9. The high pressure arc discharge lamp of claim 8 in which said magnetic field source is disposed proximate said anode.

10. The high pressure arc discharge lamp of claim 1 in which said magnetic field source provides a magnetic field of approximately 1000-2000 gauss at the plasma jet instability.

11. A high pressure short arc mercury discharge lamp comprising: a sealed envelope; a pair of spaced electrodes in said envelope; a charge of mercury in said envelope for generating a plasma arc between said electrodes; and a magnetic field source for generating a magnetic field for suppressing plasma jet instability emanating from said plasma arc.