JP4715966B2 - Short arc type discharge lamp - Google Patents

Description

  The present invention relates to a short arc type discharge lamp (hereinafter referred to as “discharge lamp”), and more particularly to an anode structure of a short arc type discharge lamp.

  A conventional discharge lamp includes an arc tube made of quartz glass having a bulged central portion, and an anode and a cathode disposed facing the inside of the bulged portion of the arc tube. The anode has a flat tip surface at the tip facing the cathode. The cathode is formed in a conical shape in which the tip facing the anode gradually decreases in outer diameter toward the tip. When this discharge lamp is energized, electrons emitted from the cathode collide with the gas in the lamp to generate charged particles. The charged particles are repeatedly collided and the substance enclosed in the arc tube, such as mercury, becomes a plasma state, and an arc is formed between the two electrodes.

Then, electrons in the plasma flow to the anode side and collide with the tip surface of the anode. Since the tip surface of the anode subjected to electron impact is flat, the electric field strength in the central part of the anode is stronger than in the peripheral part, and current flows into the central part of the anode due to the strong electric field. It is known to evaporate and wear out.
When the anode is depleted in this way, the evaporated anode constituent material adheres to the inner wall of the arc tube, causing a problem of blackening the inner wall surface of the arc tube. As the blackening of the inner wall surface of the arc tube progresses, the radiant flux from the discharge lamp decreases and the required irradiance on the irradiated surface becomes insufficient, so that the discharge lamp needs to be replaced with a new lamp.

  Therefore, measures to obtain a high irradiance maintenance rate by suppressing the temperature rise of the anode when the discharge lamp is lit and delaying the anode consumption and the progress of blackening of the inner wall surface of the arc tube. However, it has been studied conventionally.

  Patent Document 1 discloses an anode in which a porous layer is formed by sintering a mixture of tungsten carbide (WC), tantalum carbide (TaC), and tungsten (W) on the side surface excluding the tip of the anode. ing. Since this porous layer has good adhesion to the base material, it is possible to appropriately suppress the temperature rise of the anode, reduce the consumption of the anode and the blackening of the inner wall surface of the arc tube, and extend the life of the discharge lamp. It can be extended.

  Further, in Patent Documents 2, 3 and 4, as shown in FIG. 7, a recess 81 is provided at the tip of the anode 80 facing the cathode 90. The recess 81 is formed so that the strength of the electric field generated at the point of receiving the electrons emitted from the cathode 90 is made closer. According to these documents, the current density distribution on the surface of the anode 80 is dispersed, the consumption of the anode 80 is reduced, and the progress of the blackening of the inner wall surface of the arc tube is delayed, thereby achieving a high irradiance maintenance rate. The life of the discharge lamp can be extended.

  Each of the techniques disclosed in each of the patent documents 1 to 4 has been focused on extending the life of the discharge lamp, that is, increasing the irradiance maintenance rate.

Japanese Patent No. 3598475 (Japanese Patent Laid-Open No. 09-115479) Japanese Patent No. 3136511 (Japanese Patent Laid-Open No. 10-283388) Patent No. 4054198 (Japanese Patent Laid-Open No. 2003-234083) Japanese Patent No. 4132879 (Japanese Patent Laid-Open No. 2003-257365)

However, in general, a discharge lamp used in an exposure apparatus needs to have a high irradiance maintenance factor, but in addition to that, it is also required to have high radiance, that is, high radiant flux.
Accordingly, the present inventors have studied to provide a discharge lamp having a high radiance, that is, a high radiant flux, in addition to the high irradiance maintenance rate that the conventional lamp has, and prior to this application, Japanese Patent Application No. 2009- A patent application was filed as No. 154651.
This patent application is generally as follows. By providing the anode inner wall surface, a flat anode inner bottom surface, and a concave portion made of an annular corner portion on the anode tip surface, the distance between each point of the concave portion and the electrode between the cathode changes, and the position of the anode central axis and the annular shape Electric field strength peaks occur at two corners. The peak of the electric field strength at the central axis of the anode works to maintain the radiance of the discharge lamp, and the peak of the electric field strength at the annular corner. Attracts electrons and increases the current density in this part, so that local concentration of current in a part of the area on the tip surface of the anode is alleviated and works to suppress consumption of the anode.

Below, the content of the said patent application is demonstrated in detail based on FIG.
FIG. 1 is a cross-sectional view schematically showing the configuration of a discharge lamp.
The discharge lamp 10 includes a light-emitting tube including a light-emitting portion 11 formed in a substantially spherical shape and straight tubular sealing portions 12A and 12B continuous to both ends of the light-emitting portion 11, respectively. The arc tube is integrally formed of, for example, quartz glass. Power supply caps 13A and 13B each having a cylindrical shape are mounted on the sealing portions 12A and 12B, respectively.
In the discharge space S formed inside the arc tube, the cathode 2 and the anode 3 are arranged opposite to each other on the anode central axis L, and a luminescent material is enclosed.
The luminescent material is filled with mercury and at least one of xenon gas, argon gas, and krypton gas. As the luminescent substance, only one of these rare gases and mercury may be enclosed.

The cathode 2 is held by the sealing portion 12A and has a cylindrical body portion 2A facing the discharge space S, and a distal end portion formed in a conical shape whose outer diameter gradually decreases toward the distal end following the body portion 2A. 2B is integrally formed of tungsten or the like.
In the anode 3, a cylindrical body portion 3A and truncated cone portions 3B and 3C formed on the front end side and the rear end side of the body portion 3A are integrally formed of, for example, tungsten. A rod-shaped lead portion (not shown) having a diameter smaller than that of the body portion 3A is integrally provided on the rear end side truncated cone portion 3C, and the lead portion is held by the sealing portion 12B.
The anode 3 has a total length of 30 to 100 mm, a diameter of the body portion 3A of 20 to 40 mm, a tip diameter of the truncated cone portion 3B of 5 to 20 mm, and a rear end diameter of the truncated cone portion 3B of 20 to 40 mm. The interelectrode distance between the cathode 2 and the anode 3 is 3 to 40 mm.

FIG. 2A is an enlarged cross-sectional view including a cross section including the anode central axis L. FIG. FIG. 2B is a front view of the anode tip surface viewed from the direction of arrow B shown in FIG.
The anode 3 has a truncated cone part 3B whose outer diameter gradually decreases toward the tip. An anode tip surface 3D is formed at the tip of the truncated cone part 3B, and is on the anode central axis L of the anode tip surface 3D. A recess 30 is formed.

The shape of the recess 30 will be described. The recess 30 is formed following the anode inner wall surface 30A, which is a wall that is recessed from the anode tip surface 3D and formed in the circumferential direction, and the anode inner wall surface 30A. Circularly spaced from the anode central axis L at the boundary between the anode inner bottom surface 30B, which is a flat wall formed in a radial direction perpendicular to L, and the anode tip surface 3D and anode inner wall surface 30A. An annular corner portion 30 </ b> C formed in the circumferential direction is provided, and the concave portion 30 having these three configurations is formed to be recessed from the anode tip surface 3 </ b> D toward the inner side of the anode 3.
Since the recess 30 has such a shape, the overall shape thereof is a rectangular cross section including the anode central axis L, that is, a cylindrical shape. Further, the recess 30 is not limited to the cylindrical shape, and may be a rotating truncated cone shape.

When a high voltage is applied between the cathode and the anode in the discharge lamp using the anode having such a shape, an arc is formed between the electrodes.
The anode 3 shown in FIG. 2 has a flat anode inner bottom surface 30B that is recessed inward of the anode from the anode tip surface 3D, and the electric field strength increases as the anode inner bottom surface 30B approaches the anode central axis L. . Further, since the annular corner portion 30C is provided at a position spaced radially outward from the anode central axis L, the electric field strength is also high at that position.
As described above, the anode 3 is in a state where the electric field strength is high at the positions of both the anode central axis L and the annular corner 30C, so that electrons emitted from the cathode 2 are respectively in the anode central axis L and the annular corner 30C. Accordingly, the amount of electrons attracted to the anode central axis L is reduced.

  The peak of the electric field strength at the position of the anode central axis L on the anode bottom surface 30B works to maintain the luminance of the discharge lamp, and the peak of the electric field strength at the position of the annular corner attracts electrons and the current in this portion is By increasing, local concentration of current on the anode tip surface is relaxed, and it works to suppress consumption of the anode.

  FIG. 8 shows a discharge lamp (hereinafter referred to as “Lamp 1”) including the anode shown in FIG. 2 having the anode inner wall surface described in paragraphs 0010 to 0015, a flat anode inner bottom surface, and a concave portion made of an annular corner. FIG. 7 shows the simulation results of the electric field strength distribution in the arc for each of the discharge lamp (hereinafter referred to as “Lamp 2”) having the anode shown in FIG. . The vertical axis in FIG. 8 indicates the electric field strength, the horizontal axis indicates the distance from the anode central axis L, the solid line indicates the electric field strength of the anode of the lamp 1, and the broken line indicates the electric field strength of the anode of the lamp 2.

  In the anode of the lamp 1, as shown by the solid line in FIG. 8, a sharp peak of the electric field strength appears at the position of the anode central axis L and the position corresponding to the annular corner 30C of the recess 30. It can be inferred that electrons in the arc concentrate on the annular corner 30C. On the other hand, since such a peak is not seen in the anode of the lamp 2, the ratio of the current drawn to the edge portion 82 of the recess 81 is small.

Thus, the lamp 1 has the flat anode inner bottom surface 30B, so that the current density of the anode central axis L is appropriately high enough to prevent the anode from being consumed, and the radiance is high. By having the annular corner portion 30C formed so as to be spaced outward in the radial direction of L, current is dispersed in the annular corner portion 30C, and local concentration of current on the anode central axis L is alleviated, so that the anode Consumption can be suppressed, and a high irradiance maintenance rate can be obtained.
Therefore, the lamp 1 can have a higher irradiance maintenance ratio while maintaining the radiance as compared with the lamp 2.
The above is the contents of Japanese Patent Application No. 2009-154651.

Even the discharge lamp of the lamp 1 described above and disclosed in Japanese Patent Application No. 2009-154651 does not sufficiently satisfy the requirements for the light source used in the exposure apparatus.
That is, even with a discharge lamp with a high radiance, a discharge lamp with a low irradiance maintenance factor will blacken the inner wall surface of the arc tube in a short time, and the required radiant flux from the lamp will not be obtained in a short period of time, resulting in a long lamp life. It is short and requires frequent replacement of the discharge lamp. In addition to the complexity of the replacement work, the exposure apparatus stop time (downtime) associated with the replacement and the time until the exposure apparatus returns to the steady temperature after the lamp is turned on become the time that cannot be used for exposure. There is a problem that the exposure apparatus becomes inferior.
Moreover, even with a discharge lamp with a high irradiance maintenance factor, if the radiance of ultraviolet light is low, the amount of exposure necessary for exposure is insufficient, resulting in an exposure apparatus with a long exposure time and poor productivity. There is a problem.

  Thus, in the exposure process, it is required to shorten the exposure time, that is, increase the throughput. In order to contribute to shortening the exposure time and improving the productivity of the exposure process, the discharge lamp has a large “integrated radiation amount” which is the total radiation amount of ultraviolet light emitted during the certain lighting time. That is also sought.

  Therefore, in view of the above problems, the present invention is a short arc type discharge lamp used in an exposure apparatus, which can maintain a high irradiance maintenance rate while maintaining radiance. An object of the present invention is to provide a discharge lamp that improves the productivity of the exposure apparatus by using a lamp having a large amount.

と表される。
紫外線の総放射量である「積算放射量φ」は、時刻ｔにおける「ランプから放射される放射束」Ｌ_１（ｔ）の時間積分で表されるので、以下の式（４）に示すようになる。

ここで、放射照度維持率η（ｔ）は発光管内面への上記蒸発物の堆積に密接に関連しており単純な指数関数で近似することができるので、点灯ｔ_０時間後の放射照度維持率をη（ｔ_０）％とすると、その減衰定数を以下の式（５）で表すことができる。

したがって、式（４）を用いると、点灯ｔ_０時間後の積算放射量φは、更に式（６）のように表される。

この式（６）から、積算放射量φは、「点灯初期のアークから放射される放射束」Ｌ_０と、ｔ_０時間経過後の放射照度維持率η（ｔ_０）を用いて算出することができることが分かる。
後段の段落００４２、００４３において、積算放射量φを求める際には、この「点灯初期のアークから放射される放射束」Ｌ_０と、ｔ_０時間経過後の放射照度維持率η（ｔ_０）とを使用することになる。 Here, consider the relationship between this integrated radiation amount, radiance, and radiant flux.
Assuming that the arc radiance distribution is B, the “radiant flux radiated from the arc” L is obtained by integrating the radiance distribution B by area (ds) and solid angle (dΩ) as shown in the following equation (1). Sought by doing.
Formula (1) L = ∬BdsdΩ
Since the “radiant flux radiated from the arc at the beginning of lighting” L ₀ is taken out through the arc tube, the “radiant flux radiated from the lamp after a certain period of time” L ₁ is determined by the transmittance of the arc tube T Then, it is represented by the product of the radiant flux L ₀ and the transmittance T as shown in the following formula (2).
Expression (2) L ₁ = L ₀ T
This transmittance T is largely caused by blackening or light scattering due to the evaporant from the anode or the like adhering to the arc tube with time, so the irradiance maintenance rate η ( t) (%) can be approximated. Therefore, “radiant flux radiated from the lamp” L ₁ (t) at time t is

It is expressed.
The “total radiation amount φ”, which is the total radiation amount of ultraviolet rays, is represented by the time integration of the “radiant flux radiated from the lamp” L ₁ (t) at time t. become.

Here, the irradiance maintenance rate eta (t) so can be approximated by a simple exponential function is closely related to the deposition of the evaporant to arc tube surface, irradiance maintenance after lighting t ₀ hours When the rate is η (t ₀ )%, the attenuation constant can be expressed by the following equation (5).

Therefore, when using the equation (4), the accumulated radiation amount φ after the lighting t ₀ hours is further expressed as the equation (6).

From this equation (6), the integrated radiation amount φ is calculated using “radiant flux radiated from the arc at the beginning of lighting” L ₀ and the irradiance maintenance factor η (t ₀ ) after t ₀ hours. You can see that
In the subsequent paragraphs 0042 and 0043, when calculating the integrated radiation amount φ, this “radiant flux radiated from the arc at the beginning of lighting” L ₀ and the irradiance maintenance rate η (t ₀ ) after elapse of t ₀ time are used. And will use.

The short arc type discharge lamp according to claim 1,
In a short arc type discharge lamp in which an anode and a cathode are disposed so as to face each other in the arc tube, and an arc is generated by applying a voltage between the anode and the cathode.
The anode is formed with a recess on the anode central axis of the anode tip surface,
The recess is recessed in the anode tip surface from the anode inner wall surface and formed in the circumferential direction, and the anode inner wall surface formed continuously from the anode inner wall surface and radially extending with respect to the anode central axis. And an annular corner formed in a circumferential direction at the boundary between the anode tip surface and the anode inner wall surface in a radial direction away from the anode central axis, and the recess composed of these three components is the anode tip It is recessed from the surface toward the inner side of the electrode,
When the index representing the size of the arc is D0 and the diameter of the recess is D1 (mm), the ratio value D1 / D0 satisfies 0.25 ≦ D1 / D0 ≦ 1.2 ,
And the depth of the said recessed part is 0.1 mm-0.5 mm, It is characterized by the above-mentioned .
The index D0 representing the size of the arc is defined by the following equation.
D0 = 1.4 + 2.5 (P-1.6) ^0.5
Where P is lamp power (kW)

In the short arc type discharge lamp of the present invention, the anode has a recess formed on the anode central axis of the anode tip surface, and the recess is formed on the anode inner wall surface, the flat anode inner bottom surface, and radially outward from the anode center axis. By providing the annular corners spaced apart from each other, it is possible to maintain a radiance and obtain a lamp with a high irradiance maintenance rate.
Further, the ratio value D1 / D0 of the index D0 indicating the size of the arc formed between the anode and the cathode and the diameter D1 (mm) of the recess provided in the anode is 0.25 ≦ D1 / D0 ≦ 1. By satisfying the relationship (2), it is possible to obtain a lamp with a large accumulated radiation amount.

  Furthermore, when the depth of the concave portion of the anode is 0.1 mm to 0.5 mm, both the radiance and the irradiance maintenance rate can be reliably increased.

It is sectional drawing which shows an example of a structure of a discharge lamp. It is explanatory drawing of the anode applied to a discharge lamp. It is sectional drawing which shows the state of the arc formed between a cathode and an anode at the time of lighting of a discharge lamp. The profile of the radiance distribution of the ultraviolet light with a wavelength of 365 nm radiated | emitted from the arc shown in FIG. 3 is shown. It is a graph which shows the relationship between "the parameter | index showing the magnitude | size of an arc" D0 and the lamp electric power P. FIG. It is a graph which shows the relationship between relative integrated radiation | emission amount, and the value D1 / D0 of the ratio of "the parameter | index showing the magnitude | size of an arc" D0 and the diameter D1 of a recessed part. It is sectional drawing which shows the electrode structure of the conventional short arc type discharge lamp. It is a figure showing electric field strength distribution.

Hereinafter, the discharge lamp of the present invention will be described with reference to the drawings.
The configuration of the discharge lamp is the same as described in paragraphs 0010 to 0015 and the contents of FIGS. 1 and 2, and will be omitted by citing the description of this portion.

  When a high voltage is applied between the cathode 2 and the anode 3 of the discharge lamp 10, dielectric breakdown occurs between the two electrodes, and an arc AR is formed between the cathode 2 and the anode 3. A conceptual diagram of the arc AR is shown in FIG. The arc AR expands or contracts around the anode central axis L depending on the lamp power P (kW). That is, when the lamp power increases, the arc AR expands and increases, and when the lamp power decreases, the arc AR contracts and decreases. If the size of the recess 30 is constant, the arc AR may extend beyond the annular corner 30C of the recess 30 to the anode tip surface 3D, or may remain inside the annular corner 30C of the recess 30. .

From the relationship between the size of the concave portion 30 and the arc AR, the ratio value D1 / D0 of the size D1 of the concave portion 30 and the size D0 of the arc AR is obtained. When the ratio value, that is, the extent to which the arc AR covers the concave portion 30 is changed, the effect of the annular corner portion 30C attracting a part of the current by the electric field is affected. This affects the flow of electrons generated in the light source, and the amount of radiation fluctuates.
Therefore, the value D1 / D0 of the ratio of the size of the recess 30 and the size of the arc AR is closely related to the “integrated radiation amount” described in paragraph 0022, and the optimum range of the integrated radiation amount is D1 / D0. It can be found as a function. Here, the size D1 of the recess is a value used as an index representing the degree of coverage of the arc, and it is necessary to compare this D1 with the size of the arc. The diameter of the part is used.

Next, how to specify the size of the arc will be examined.
The arc refers to a region where the inclusion has been turned into plasma, and its size is difficult to measure and identify.
Therefore, for example, the arc is naturally closely related to the current density distribution, and the current density distribution can be regarded as one form of the arc distribution. Therefore, it is conceivable to measure the current density distribution to determine the size of the arc. . However, it is considered difficult to measure this current density distribution precisely and directly, and since this current density distribution changes continuously, the arc distribution can also be clearly defined by this current density distribution. It is difficult to specify the size of the arc. Thus, it is extremely difficult or impossible to specify the “arc size” by measuring the “current density distribution”.

However, the current density distribution of the arc is closely related to the radiance distribution, and by measuring the “radiance distribution”, it is possible to know the “current density distribution” of the arc and thus the “size of the arc”. become.
Therefore, the radiance distribution is measured.
When the luminescent material is mercury, when a high voltage is applied between the cathode 2 and the anode 3, electrons emitted from the cathode 2 collide with mercury atoms enclosed in the discharge space S, and the mercury atoms are excited. When entering a state and transitioning from an excited state to a lower energy state, various emitted lights are emitted. This radiated light is passed through a bandpass filter that passes only a specific wavelength, for example, a wavelength of 365 nm, and a luminance distribution of the radiation is obtained. The luminance distribution of ultraviolet light having a wavelength of 365 nm is a radial luminance distribution at an arbitrary point on the electrode central axis L, and is shown in FIG. This distribution profile can be approximated by the following formula (7), where J (r) is the radiance, and r is the distance from the electrode central axis in the radial direction.
Equation _{(7) J (r) =} J 0 exp [- _{(r / r} ^{0) 2]}
Here, J ₀ is the radiance at the center of the arc, and r ₀ is the distance (mm) from the center where the radiance J ₀ at the center attenuates to 1 / e (≈0.37). . Equation (7) of the radiance distribution indicates that most of the current flowing through the arc is concentrated within the distance r ₀ from the center of the electrode.
When 2r ₀ obtained by doubling r ₀ is considered as a “virtual diameter”, this 2r ₀ can be used as “an index indicating the size of an arc” D 0. However, it should be noted that the actual arc size extends beyond the value of the virtual diameter “index indicating arc size” D0.

  As described above, the “index indicating the size of the arc” can be obtained from the radiance distribution, but this method measures the radiance distribution every time it is necessary to obtain the “index indicating the size of the arc”. This is complicated. However, the authors' diligent research has found that the radiance distribution has a strong correlation with the lamp input power. If the relationship between the lamp power and the radiance distribution is obtained in advance, the radiance The complexity of measuring the distribution can be eliminated, and an “index indicating the size of the arc” can be obtained from the lamp power.

In order to obtain a relationship between the lamp power and the “index indicating arc size” D0, the following experiment was performed.
By the way, the shape of the arc changes under the influence of the physical shape of the electrode tip. If an attempt is made to create the index using a discharge lamp using an electrode having a recess provided on the anode tip surface, the arc is affected differently from the recess for each lamp having a different size of the recess. In this case, the “index indicating the magnitude of the arc” D0 differs for each lamp and cannot be used as a reference index. The “index indicating the magnitude of the arc” D0 is an index and a value to be used as a reference, and therefore must be a value that does not vary and does not change. Therefore, in order to prevent the arc from being affected by the shape of the anode tip, an “index indicating the size of the arc” D0 is created using a discharge lamp using an ordinary anode that is flat and does not have a recess. It was used as a standard index.

Therefore, as the experimental discharge lamps A1 to A5 used in the experiment for creating the “index indicating the size of the arc” D0, an ordinary anode that is flat without a concave portion on the tip surface of the anode was used. Then, five kinds of experimental discharge lamps A1 to A5 were produced by changing the amount of mercury to be enclosed and the distance between the electrodes.
The experimental discharge lamps A1 to A5 are turned on with the lamp power P shown in Table 1, the radiance distribution of the arc near the anode is measured, and fitting is performed on the radiance distribution according to the equation (7). r ₀ was determined, and the value of “index indicating arc size” D 0 was determined.
Table 1 shows the experimental results.

Next, the relationship between the “index indicating arc magnitude” D0 in Table 1 and the lamp power P (kW) is indicated by a circle in FIG. The equation of the approximate curve connecting the circles shown in FIG. 5 was obtained, and the following equation (8) was obtained.
Formula (8) D0 = 1.4 + 2.5 (P-1.6) ^0.5
From this equation (8), for a lamp whose lamp power P (kW) is known, the “index indicating the size of the arc” D0 can be obtained without measuring the radiance distribution. .

Thus, when the “index indicating the magnitude of the arc” D0 is determined from the lamp power P (kW), as described in paragraph 0030, the ratio D1 / D0 is used as a variable, and the optimum range of the integrated radiation amount is determined. Can be found.
Therefore, an experiment for obtaining the integrated radiation amount was performed by using the value D1 / D0 of the ratio between the diameter D1 of the recess and the “index indicating the size of the arc” D0 as a variable.

In conducting the experiment, experimental discharge lamps B1 to B10 were prepared and prepared. The experimental discharge lamps B1 to B10 have a common basic lamp configuration described below.
<Basic configuration of lamps B1 to B10>
-Depth of concave portion of anode 3: 0.4 mm
・ Mercury amount: 25 mg / cm ³
・ Xenon gas: 2 × 10 ⁵ Pa at room temperature
・ Distance L between electrodes: 5.5 mm
・ Lamp power P: 7.5kW (constant power)
The anode of each lamp has a concave portion composed of an anode inner wall surface, an anode inner bottom surface formed flat and an annular corner portion on the tip surface, and the size of the concave portion is as shown in Table 2. The ratio D1 / D0 of the diameter D1 (mm) of the recess 30 with respect to the “index indicating the size of the arc” D0 is made different.
As a comparative example, a comparative discharge lamp X having a ratio value D1 / D0 of zero, that is, an anode having no recess was prepared and prepared. The comparative discharge lamp X has the same basic configuration as the experimental discharge lamp B except that there is no recess on the anode tip surface.

  Since the lamp power of the experimental discharge lamps B1 to B10 and the comparative discharge lamp X is 7.5 kW, the “index indicating the size of the arc” D0 is set to P = 7.5 in the equation (8) in paragraph 0037. It can be obtained by substitution, and is obtained as D0 = 7.5.

  For the experimental discharge lamps B1 to B10 and the comparative discharge lamp X, the irradiance of ultraviolet light having a wavelength of 365 nm was measured at the initial lighting time and after 800 hours of constant power lighting. This is set as experiment a. The “irradiance maintenance rate (%)” in Table 2 represents the ratio of the irradiance after lighting for 800 hours to the irradiance at the beginning of lighting for each lamp.

In addition, the experimental discharge lamps B1 to B10 and the comparative discharge lamp X are turned on, and the radiance of ultraviolet light having a wavelength of 365 nm at the beginning of lighting is measured for each of the discharge lamps. to obtain a radiation flux L ₁ of initial lighting by integration of luminance. This is experiment b. In Table 2, the ratio of the radiant flux at the initial stage of lighting of the experimental discharge lamp B to the radiant flux at the initial stage of lighting of the comparative discharge lamp X is obtained from the result of the experiment b, and this relative value is defined as “relative radiant flux”. It is described.

  The “integrated radiation amount” is obtained from Equation (6) in paragraph 0022 using “irradiance maintenance rate (%)” and “relative radiant flux” in Table 2. It is expressed as a “relative integrated radiation amount” which is a relative value where the maximum value of the integrated radiation amount is 1.

As can be seen from equation (6), “radiant flux radiated from the arc at the beginning of lighting” is required for calculation of the integrated radiation amount. As a precaution, the relationship between this radiant flux and “radiant flux radiated from the lamp in the early stage of lighting” will be described.
In the expression (3) in the paragraph 0022, since the time t is 0 in the initial lighting state, T (t) is almost 1 at T (0), and L ₁ (0) = L ₀ . This is because the radiant flux at the beginning of lighting of each lamp obtained in Experiment b is “radiant flux radiated from the lamp at the early stage of lighting” L ₁ (0). It indicates that equivalent from the initial lighting of the arc to the radiant flux "L ₀ emitted. Therefore, it can be understood that the value of the radiant flux L _{1 at} the initial stage of lighting of each lamp obtained in the experiment b can be substituted for the “radiant flux radiated from the arc at the initial stage of lighting” L ₀ in Equation (6).

Next, FIG. 6 shows the relationship between the ratio value D1 / D0 and the relative accumulated radiation amount in Table 2.
The vertical axis represents the relative integrated radiation amount, and the horizontal axis represents the ratio value D1 / D0.
In the region where the ratio value D1 / D0 is small, the relative accumulated radiation amount hardly changes, increases from around 0.2, reaches a maximum around 0.65, and then decreases. The ratio value D1 / D0 is the same as when the ratio value D1 / D0 is around 1.2 and the ratio value D1 / D0 is 0, and then decreases further.

  When no concave portion is provided at the electrode tip, that is, when the ratio value D1 / D0 is 0, the value of the relative accumulated radiation amount is 0.959. By setting the value in a range exceeding 0.959, it is possible to obtain a discharge lamp having a larger amount of relative accumulated radiation than a lamp having an anode without a recess. Therefore, it is understood that the ratio value D1 / D0 is 0.25 to 1.2 in the range effective as the relative integrated radiation amount.

  Further, if the ratio value D1 / D0 is 0.39 to 1.1, the integrated radiation amount shows a higher value, and a more remarkable effect is obtained.

Further, the depth H of the recess 30 is 0.1 mm to 0.5 mm . The reason is as follows.
When the depth H of the recess 30 exceeds 0.5 mm, the distance between the electrodes becomes long, and the lamp voltage increases. Since the short arc type discharge lamp 10 uses a constant power source as a lighting power source, when the lamp voltage increases as described above, the lamp current supplied between the cathode and the anode is controlled to decrease, and the radiance is increased. Will drop. Such a decrease in radiance becomes more prominent as the depth H of the recess 30 increases.
On the other hand, when the depth H of the concave portion 30 is less than 0.1 mm, the concave portion 30 is substantially eliminated, and the effect of concentration of the electric field strength by the annular corner portion is lost, and a high irradiance maintenance rate cannot be obtained.
Therefore, in order to minimize the decrease in the radiance of the discharge lamp and to maintain high irradiance, the depth H of the recess 30 is 0.1 mm to 0.5 mm .

DESCRIPTION OF SYMBOLS 10 Short arc type discharge lamp 11 Light emission part 12A, 12B Sealing part 13A, 13B Base 2 Cathode 2A Trunk part 2B Tip part 3 Anode 3B, 3C Frustum part 3A Trunk part 3D Anode tip surface 30 Recess 30A Anode inner wall surface 30B Anode Inner bottom surface 30C Annular corner AR arc

Claims (1)

In a short arc type discharge lamp in which an anode and a cathode are disposed so as to face each other in the arc tube, and an arc is generated by applying a voltage between the anode and the cathode.
The anode is formed with a recess on the anode central axis of the anode tip surface,
The recess is recessed in the anode tip surface from the anode inner wall surface and formed in the circumferential direction, and the anode inner wall surface formed continuously from the anode inner wall surface and radially extending with respect to the anode central axis. And an annular corner formed in a circumferential direction at the boundary between the anode tip surface and the anode inner wall surface in a radial direction away from the anode central axis, and the recess composed of these three components is the anode tip It is recessed from the surface toward the inner side of the electrode,
When the index representing the size of the arc is D0 and the diameter of the recess is D1 (mm), the ratio value D1 / D0 satisfies 0.25 ≦ D1 / D0 ≦ 1.2 ,
And the depth of the said recessed part is 0.1 mm-0.5 mm, The short arc type discharge lamp characterized by the above-mentioned .
The index D0 representing the size of the arc is defined by the following equation.
D0 = 1.4 + 2.5 (P-1.6) ^0.5
Where P is lamp power (kW)

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