JPS63131457A - High pressure discharge lamp - Google Patents

Abstract

PURPOSE:To prevent generation of cracks in a bulb and to remove bad effects on stability and a starting characteristic of the arc by forming a top point part inclusive of a coil part of an electrode axis so that its diameter is smaller than that of a base part of the electrode axis. CONSTITUTION:In a starting operation, arc spots are generated in the following regions: a base part 4a of an electrode axis in a cathode 3, a boundary part of a top point part 4b smaller in diameter than the base part 4a or a coil part near this boundary part. Consecutively the arc spots move smoothly to an adjacent coil part 5 and besides to the base part 4b of the electrode axis. Because the top point part 4b of the electrode axis, where the arc spots are finally formed, is smaller in diameter than the base part 4a, the arc spot generated at the top point part 4b during a normal lighting operation is small in its moving range, so that the arc becomes stable. Further because of a quick rise in temperature of the top point part 4b much smaller in diameter, effective emission can be obtained and a starting characteristic can be improved.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a high-pressure discharge lamp that is operated using direct current.

(Prior art) A high-pressure discharge lamp used for lighting with direct current, such as a short-arc mercury lamp, has a large tungsten anode at both ends of a thick-walled quartz glass bulb with high pressure resistance, and a smaller tungsten anode. A cathode formed by winding a coil made of tungsten wire around an electrode shaft having a uniform shaft diameter is placed facing each other at a distance of, for example, 2 to 61111 mm, and contains a rare gas for starting and steam during lighting. pressure is 1
It is made by enclosing enough mercury to create a pressure of 0 to 50 atmospheres.

Such a lamp is used as a light source for semiconductor exposure equipment because the distance between the electrodes is short and high brightness can be obtained. Incidentally, recently there has been a demand for shortening the index of semiconductor exposure work to improve work efficiency, and for this reason the above-mentioned lamps have also been improved in the direction of shortening the distance between the electrodes and increasing the lamp power. ing.

Generally, the larger the lamp power, the longer the distance between the electrodes.

If you try to shorten the distance between the electrodes, you will increase the protrusion length of the electrodes into the pulp, which will lower the temperature at the base of the electrodes and make it easier for the encapsulated mercury to solidify in this area, making it difficult to achieve the desired mercury vapor pressure. It becomes difficult to get caught.

As a countermeasure against this problem, the lamp is generally arranged in a vertical lighting position so that the cathode side is located at the top and the anode side, which is hot, is located at the bottom, and in addition, the length of the cathode is made longer, that is, the length of the anode is made shorter. One possible method is to increase the temperature of the coldest part of the anode, that is, the root part of the anode located on the lower side.

However, if such measures are taken.

When the cathode has a conventional structure, that is, a coil (5) is wound around an electrode shaft (4) having a uniform shaft diameter as shown in Fig. 3 (Conventional Example 1), the structure of the cathode (3) is Cracks may develop in the quartz glass bulb near the base, causing leaks and malfunctioning lamps. Regarding these phenomena,
Furthermore, when comparing the lamp with an AC lamp, we found that even when the lamp is stable in steady state, an arc spot is formed at the base of the cathode when the lamp is lit with a power source that does not have polarity reversal.

It was found that this spot sometimes did not migrate to the cathode tip, and it was found that most of the lamps that continued to be lit in this state for several hours developed a rack as described above. In contrast, in the case of AC lighting, although discharge started from the base of the electrode immediately after starting, the arc spot moved to the tip of the electrode in all lamps in a short period of time, and no cracks occurred. This phenomenon is presumed to be due to the following reasons. That is, even in the case of an alternating current power source with no polarity reversal, the discharge starts with a long discharge distance because the pressure is low at 1 atm or less immediately after startup. However, as time passes, the temperature inside the arc tube rises and the pressure within each arc tube rises, reaching a high pressure of 1 atm or more during rated lighting, for example, 10 atm or more in the case of a short arc mercury lamp. therefore.

In order for the discharge to remain stable, the well-known law Pd
=const, (P is pressure, d is discharge distance) The arc spot moves from the electrode base side to the electrode tip, and moves in the direction where the discharge distance d becomes shorter. This phenomenon is caused by the fact that in the case of alternating current, each electrode acts as both a cathode and an anode in each half cycle, so when it is an anode, the arc concentrates on the entire electrode and the tip of the electrode is also heated. However, as the temperature increases, the arc easily moves to the electrode tip.

When there is no polarity reversal, such as in direct current, the arc forms a spot on the cathode side and concentrates on only a small portion of the electrode. Therefore, although the temperature rises only in the concentrated area, immediately after starting, the temperature at the electrode tip does not rise to a level sufficient to emit electrons even if the pressure inside the arc tube increases sufficiently since it is on the base side of the electrode. Since there is no reversal of polarity, it is inferred that the movement of the arc from the spot position once formed may not occur unless there is some kind of trigger.

This transition of the arc spot on the cathode side from the root side to the tip is a competition between the following two functions. One of these is that the pressure inside the arc tube increases, so the discharge distance is shortened, and the other is that emissions are generated from locations with good electron emission.

For example, if the temperature gradient between the tip of the electrode and the base of the cathode where the arc spot occurs is small and the temperature of the tip of the cathode is sufficiently high, the arc will easily move to the tip of the cathode as the pressure inside the tube increases. There is a part with particularly good emission at the base of the cathode.

If the discharge happens to start from that point and the temperature gradient with the cathode tip is large, that is, the diameter is uniform throughout, as in the case of the cathode (3) shown in FIG. 3 above.

In addition, in the case where the coil (5) was wound around the relatively thin electrode shaft (4), the arc spot did not move to the cathode tip and continued to maintain discharge at the base side until the end.

If these shortcomings are addressed and the entire cathode electrode shaft is configured in this way, the root of the electrode shaft is thick, making it difficult for the temperature to rise during startup, and arc spots will occur in the coil, and as the mercury vapor pressure increases, Move to the tip of the electrode shaft. However, since the tip of the electrode shaft is also relatively thick, the range of movement of the arc spot is widened, resulting in a lack of stability and poor starting performance.

(Problem that the invention attempts to solve) As mentioned above, in a DC lighting type high pressure discharge lamp.

When trying to shorten the distance between the electrodes and increase the lamp power, with the conventional cathode structure, it becomes difficult for the arc spot generated at the cathode root to migrate to the tip, causing cracks in the quartz glass bulb. In addition, if the cathode electrode shaft is made thicker and the coil diameter is made smaller as a countermeasure to this problem, the stability and startability of the arc are adversely affected.

Therefore, the present invention aims to eliminate the above drawbacks.

The purpose is to provide a high-pressure discharge lamp for direct current lighting with a short distance between electrodes and large lamp power without causing cracks in the quartz glass bulb or adversely affecting arc stability and starting performance. shall be.

[Structure of the invention]

(Means for Solving the Problems) In the high-pressure discharge lamp for direct current lighting according to the present invention, the cathode has an electrode shaft whose tip portion is smaller in diameter than the base portion.

It consists of a coil wound around the tip of this electrode shaft.

Further, the diameter of the tip portion including the coil portion is formed to be smaller than the diameter of the electrode shaft base portion.

(Function) With this configuration, during startup, the arc spot will be generated from the boundary between the electrode shaft base portion of the cathode and the tip portion with a smaller diameter, and then smoothly spread to the coil portion and then to the tip end of the electrode shaft. Because of the migration, cracks will not occur in the quartz glass bulb near the base of the cathode. In addition, since the tip of the electrode shaft, where the arc spot is ultimately formed, has a small diameter, the movement range of the arc spot at the tip during steady lighting is small, so a stable arc can be obtained. Furthermore, since the temperature at the tip of the small-diameter electrode shaft rises quickly, startability can also be improved.

(Example) The present invention will be described in detail below based on the example shown in the drawings. Figure 1 shows an embodiment of the present invention, 500W (50W).
FIG. 2 shows a schematic structural diagram of a mercury lamp, and FIG. 2 shows a structural diagram of a cathode, which is the main part thereof. - (1) is a quartz glass bulb with a predetermined amount of starting rare gas and mercury sealed inside.

A large deaf anode (2) and a smaller cathode (3) are placed opposite each other at a distance of 3 m from each other in the sealed portions (la) and (lb) at both ends thereof.

The content of the cathode is 0, for example 2%, as shown enlarged in Figure 2.
An electrode shaft (4) made of tungsten containing Doria and a coil (5) made of pure tungsten, for example, wound around it.
It consists of.

The diameter do of the base portion (4a) of the electrode shaft (4) is 3.0 m
On the other hand, the diameter d1 of the tip (4b) is set to a smaller diameter of 2.0 cmK, and the diameter d2 of the wire of the coil (5) is 0.4 cm, so the electrode including the coil (5) part The diameter d3 on the tip side of the shaft (4) is (dt + 2 dz) =
2.0 mm + 2 x 0.4 m5 = 2.8 fl, which is set smaller than the diameter d6 of the electrode shaft base portion (4a) = 3.0 ball.

With such a configuration, at the time of starting, an arc spot is generated from the boundary between the electrode shaft base portion (4a) of the cathode (3) and the tip portion (4b) having a smaller diameter, or from the coil portion near the boundary. There is a smooth transition to the adjacent coil (5) section and further to the electrode shaft tip section (4b). Also.

The electrode shaft tip (4b), where the arc spot is finally formed, has a smaller diameter than the base (4a), so the movement range of the arc spot at the tip (4b) during steady lighting is limited. is small, so a stable arc can be obtained, and furthermore, the temperature of the small-diameter tip m (4b) rises quickly, making emission effective and improving startability.

The table below compares the characteristics of the lamp of the present invention with the lamps of the same type equipped with the respective cathodes of Conventional Example 1 and Conventional Example 2 described above.

As shown in the table O Good and X Bad, it can be seen that according to the present invention, each of the drawbacks of the conventional example can be overcome.

1. Based on the results of various experiments conducted by the present inventor.

do (base diameter)/di (tip diameter) is 1.3 to 1
．． 7 is particularly preferable; when it is less than 1°3, starting performance gradually deteriorates and arc instability tends to occur; on the other hand, 1.
If it exceeds 7, the diameter of the base portion becomes thicker, which affects the reduction in pressure resistance strength of the lamp.

Also, It, (lamp current A)/core (tip diameter ms)
A value of 1.6 to 4.4 is particularly preferable; if the tip of the cathode electrode shaft becomes too thin, such as less than 1.6, the life characteristics will gradually deteriorate; on the other hand, if it exceeds 4.4, arc instability may occur. Qualitativeness is more likely to occur.

Furthermore, the present invention is not limited to short arc mercury lamps.
It can also be applied to other DC-lit high-pressure discharge lamps.

〔Effect of the invention〕

As described above, according to the configuration of the present invention, even if the distance between the electrodes is shortened or the lamp power is increased.

It is possible to provide a DC lighting type high pressure discharge lamp that does not cause bulb cracks and does not adversely affect arc stability or startability.

[Brief explanation of the drawing]

Fig. 1 is a schematic structural explanatory diagram of an embodiment of the high-pressure discharge lamp of the present invention, Fig. 2 is an explanatory diagram of the structure of the cathode, which is the main part of the first embodiment, and Fig. 3 is the structure of the cathode of a conventional lamp. An explanatory diagram is shown. (1)・・・・・・Quartz glass bulb. (2)・・・・・・Anode. (3)・・・・・・Cathode. (4)・・・・・・・・・Cathode electrode axis. (4a) Base portion of the electrode shaft. (4b)...The tip of the electrode shaft. (5)・・・・・・・・・Coil. cio...... Diameter of the base portion (wL). dl...Diameter of the tip (n). dl・・・・・・Diameter of coil wire (m+). d3: Diameter of the tip including the coil.

Claims (1)

[Claims] In a high-pressure discharge lamp that has an anode and a cathode placed opposite each other at both ends of a quartz glass bulb and is used for lighting with direct current, the cathode has an electrode shaft whose tip has a smaller diameter than the base, and the tip of the electrode shaft. What is claimed is: 1. A high-pressure discharge lamp comprising a coil wound around the electrode shaft, and wherein the diameter of the tip portion including the coil is smaller than the diameter of the electrode shaft base portion.