JPS6012655A - X-ray generator - Google Patents

Abstract

PURPOSE:To eliminate any concentric circular cone and alleviate the mechanical tolerance of an X-ray generator by introducing a water flow along the surface of an X-ray anode having a concave curvature going along the water flow and using a large amount of water to given cooling water a centripetal acceleration for removing bubbles evaporated near the high temperature surface of the anode. CONSTITUTION:A target is provided with a conical anode 11 having a concave curvature going along a water flow. Owing to such a wall of the rotary anode 11, the acceleration of a flow vertical to the wall is very easily separated by the phase according to the difference between the densities of the fluid and steam thereby increasing the inertia of the fluid and bumping it against the wall. As a result, light bubbles immediately after their generation are made large enough to be moved apart from the surface. Water mixes with a jet from an inlet 13, and flows expanding along the surface of the conical anode 11 at a relatively constant speed. Since the circular cone is placed in a reservoir 15 of water moving at a far slower speed, the jet gradually mixes with the water. Owing to the above constitution, any mechanical grooves do not exist around the anode 11 and the lateral mechanical tolerance is widely alleviated. An end guide 17 which is the only member existing in the water inlet 13, works to introduce the flow almost parallel to the conical surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an X-ray generator, and more particularly to a water-cooled X-ray anode used in X-ray phosphorography.

[Prior art]

Fixed X-ray source with conical anode is 1nstr, Met
b126.99 (1975) J, C, Ga1
J. nes and R4° Hansen, and was further improved (a cross-sectional view thereof is shown in FIG. 4).

Vac, Sci, i″cch, 16.1942
(1979) by Maldenado et al. in X-ray phosphorography. The important feature of both devices is that the line of intersection between the outer surface of the anode and the vertical section corresponding to the cross section of FIG. 1 is essentially straight over the entire length of the surface.

These devices are used to create hollow cones.
It is superior to the conventional shape in terms of uniform illuminance and tJt power consumption. Since the target cone is biventricularly applied uniformly from all sides, there is no heel effect (h
In addition to the absence of eel e1' (ecL), the cone has a large surface area, so heat can be effectively dissipated. A significantly higher capacity is therefore generated within the stationary anode. A force of 4 kW can be obtained within an effective diameter of 3 mm against a palladium target, and even higher forces can be obtained by increasing the spot size. However, in the shape of a cone, t
[, C effect as a non-effective blackbody absorber for
There is an advantage that is not often noticed: Incoming electrons tend to be projected onto the apex of the cone, increasing the brightness without increasing the spot size and reducing the problem of energy being deposited in undesired areas. Another advantage of the inverted conical shape is that it is structurally very strong and can support very large pressure differences well. Therefore, the walls of the cone can be extremely thinned, which is a highly desirable property for cooling purposes.

Thinner walls reduce the thermal stress in the walls and lower the temperature on the vacuum side of the walls. Q′j, is C equal to 4 for palladium? It is advantageous for This is because this material can undergo regrowth at high temperatures, resulting in increased grain size and structural failure after ischemia. For thin anodes, the surface temperature can be made low enough that these effects do not occur; therefore, the heat flux can be increased to the extent that burnout occurs. It is determined by the boundary conditions.

Since the heat flux used in lithography X-ray tubes is generally very strong, the anode cooler σ operates in a state of nucleate boiling heat transfer. In this condition, the temperature of the heat exchange wall is above the boiling point of the cooling fluid under local static pressure.

As a result, vapor bubbles constantly arise and leave the surface,
Subsequently, the boundary layer breaks down. The reason why a very large heat flux can be obtained from this cooling state h is that the microscopic flow violently hits the wall surface and mixes. The amount of latent heat of evaporation carried away by bubbles that contributes to heat transfer is extremely small (estimated to be only about 5% to 10%) (H, K,
Forster and H, Znl]er.

4,F',chJ:,Jour,l,531 (195
5 years)).

However, this cooling method has the following drawbacks. As the heat flow through the wall increases, the temperature of the wall increases and the number and size of vapor bubbles generated increases. As the heat flow increases further, the bubbles create a blanket of water vapor and the metal body, separating the liquid phase from the surface. The walls are then only cooled by radiation and vapor phase convection. Once that happens, the temperature rises rapidly and melting occurs. However, in order to avoid such burnout, it is important to avoid being covered by such a film.

To this end, increasing the linear velocity of the flow increases the shear force on the bubbles. This causes the bubbles to quickly become trapped in the body of fluid. Alternatively, the static pressure of the fluid may be increased by F.

This increases the saturation temperature by -F and reduces wall superheating, thereby reducing the size and number of bubbles. However, neither of these solutions is particularly desirable. The reason is that the linear velocity of the flow at the allowable flow rate required for the first method requires very tight mechanical tolerances to provide the desired cooling, and the saturation temperature is sufficiently high. In order to obtain a static fluid pressure, it is necessary to increase the inlet pressure enough to overcome the steady water head.

[Summary of the invention]

According to an embodiment of the present invention, a water stream is introduced along the surface of the X-ray anode having a concave curvature along the flow, and a large amount of water is used to eliminate evaporated air bubbles near the hot surface of the anode. An x-ray target is presented having a pressurized water inlet adapted to impart cardiac acceleration to the cooling water. The X-ray anode is placed in a water reservoir rather than in a concentric cone that forms a flow path as in conventional technology, and the curvature along the flow allows cooling water to flow smoothly onto the surface of the high temperature anode and gradually fill the water reservoir. mix with water. Since concentric cones are eliminated, mechanical tolerances are much relaxed.

〔Example〕

FIG. 1 shows a sectional view in a vertical plane passing through an X-ray target of an X-ray generator according to the invention. The target has a conical anode 11 with a concave curvature along the flow instead of the straight sides of the upright cone of the prior art. Concave curvature along the flow is an orientation such that the second derivative of the lowest point set by cutting the outer surface of the anode at any vertical plane passing through the apex of the cone is the highest point within that plane. This means that it is larger than O when placed in . If the cone is oriented to be the lowest point in its plane, the second derivative will be negative to obtain the desired curvature.

Figure 1 shows a water inlet 13 that supplies high-pressure, high-speed cooling water.
, and a water reservoir 15 surrounding the anode surface 11 for collecting and discharging cooling water that has once passed through the surface of the anode. By forming the wall of the anode 11 to have a concave curvature along the flow, the acceleration of the flow perpendicular to the wall is very well separated due to the density difference between the fluid and vapor, and the inertia of the fluid is increased. is pressed against the wall, thereby making it large enough to displace light nascent air bubbles away from the surface.

Figure 2, taken from a photograph (sprayed into the air), demonstrates the general effect.

The water mixes with the jet from inlet 13 and flows and spreads along the conical anode 110 surface at a relatively constant velocity. Since the cone is contained within a pool of water moving much more slowly, the jet gradually mixes with the water.

This confinement is a significant advantage over prior art devices in that there is no need for distinct grooves on the cooling surface. In prior art devices that locally increase the velocity of the fluid, the conical gap between the anode and the water guide becomes very narrow, resulting in noise.

Therefore, relative lateral displacement of the two generally results in asymmetric flow and may cause burnout to occur prematurely. Therefore, tolerances must be extremely tight. However, according to the present invention, there is no mechanical groove around the anode and the lateral mechanical tolerances are significantly relaxed. The only part of the cone inside the water inlet is the end guide 17, which serves mostly to direct the flow parallel to the conical surface, and the vertical displacement of the inlet groove directs the flow to the surface. Generally speaking, it is not definitive as far as guidance is concerned.

FIG. 3 is a detailed side view of the anode 11. The overall height L1 of the anode, including the end guide 17, is typically about 1.64 cm (0.645 inches).

The height L2 of the anode extending below the bottom of the water inlet 13 is approximately 1
．． 43 cm (0,562 inches) and a radius of curvature 1 (1 is approximately 2.Q cm (0,78 inches)).
It is equipped with The inside of the cone is approximately rt85CTL in height (
Since the pitch is configured to change at 81 points (0,335 inches), there are two different angles: A1 = 12.5 degrees at the top of the cone and A2 = 18.5 degrees at the bottom. 1 electron can enter a wide solid angle.

The radius R2 of the bottom of the cone is approximately 0.40CTL (0.15
6 inches), and the diameter D1 of the water inlet pipe 13 is approximately (1,
2CTL (0, □B□, inches). The end guide 17 has an outer diameter of approximately (1,12 CrIl (0,046 inch)) and an inner diameter of approximately 0.08 cm (0,031 inch), is typically made from Inconel, and has a solder insert in the target portion 19 of the pole 11. The target part 19 is not made of pure palladium, but is typically made of an alloy of 95% palladium and 5% ruthenium.This alloy has high mechanical strength and is difficult to grow and recrystallize particles. This is because Inconel thermally matches the palladium cone.
l'3 is located at a height H2 of approximately Q, Ol 3 cm (0,005 inch) and approximately 0.74 cm (0,291 inch). Other materials can also be used as anodes, such as copper or palladium-lanthanum. However, the general dimensions will vary depending on the thermal and mechanical properties of the material chosen and the desired cooling capacity. The above specific dimensions for a palladium-ruthenium alloy target are (
(although other pressures can be used as well)
1? This is typically used in cooling systems equipped with high-pressure pumps. Also, about 1 cone
Static pressure is commonly applied to the sump to maintain a static back pressure of 20 psi. In the case of this device, 50
, 100 m/corresponding to a cardiac acceleration of the order of 0OOG.
Fluid velocities close to s are easily obtained.

Of course, other accelerations can be obtained if the speeds are different. - With the above parameters, the device has a total power of 4 kW and 1 s kW/cr
Average power densities incident on the wall of the order of /1 can be easily handled. Additionally, additional experiments have made it very clear that targets with flow-aligned curvature have significantly increased cooling efficiency and can dissipate more power density for the same flow rate than conical targets with straight surfaces. ing.

Different curvatures, different wall thicknesses, and somewhat hollow dimensions are generally used to optimize for other selected parameters. Similarly, the concept of using a concave curvature along the flow to increase the cooling efficiency of the It should not be limited to just conical anodes, as the concept of extending the duration of the anode can be applied to other configurations as well. It is also clear that only the hot part of the anode requires a clear concave curvature for flow.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the X-ray generator of the present invention. FIG. 2 is an explanatory diagram of the X-ray generator of the present invention. FIG. 3 is a detailed side sectional view of the anode of the X-ray generator of the present invention. FIG. 4 is a sectional view of a conventional X a generator. ll: Anode 13: Water inlet 15: Water reservoir 17: End guide. Applicant: Yokogawa-Hyulet Kenpan Card Co., Ltd. Agent: Patent Attorney Tsuguo Hasegawa] 5-1

Claims (1)

[Claims] An inlet for injecting a cooling fluid, an anode having an X-ray target and a side surface formed with a curvature that follows the flow, and an inlet for the fluid to flow along the side surface. and means for directing said fluid.
Line generator.