Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/16—Vessels; Containers; Shields associated therewith

Definitions

• the present invention relates to an X-ray tube with a cylindrical metal part surrounding the anode and the cathode, of which at least one of the electrodes anode and cathode is electrically insulated by means of a disk-shaped ceramic insulator which is attached to an axial end of the metal is partially arranged.
• Known x-ray tubes of this type have shields in the interior of the cylindrical metal part, which are shaped and arranged in such a way that the electrical field resulting on the inner surfaces of the ceramic insulators points in its direction away from the insulator surface against the interior of the x-ray tube. This largely prevents the inside surfaces of the ceramic insulators, which are hit by unavoidable field emission electrons, from becoming electrically charged as a result of secondary electron emission and thereby reducing the dielectric strength of the X-ray tube.
• the disk-shaped ceramic insulator is designed in a stepped or ramp-shaped manner in radial directions on its axial end surface facing away from the interior of the X-ray tube in order to form an annular axial recess which is filled with an insulating material whose dielectric constant is less than that of the ceramic material and that in the case of a ceramic insulator that insulates the anode from the metal part, the recess is arranged radially on the inside and in the case of a ceramic insulator that insulates the cathode of the metal part, the recess is arranged radially on the outside.
• This configuration of the X-ray tube ensures, in a surprisingly simple manner, that the direction of the electric field on the inner insulator surface points away from the insulator surface into the interior of the tube.
• the electrical field strength is reduced at the locations where the field emission primarily occurs, namely at the so-called triple points.
• the triple point is located on the cathode side in the soldering-technical connection between the ceramic insulator and the high-voltage supply in the center of the insulator.
• the triple point lies in the soldering connection between the outer circumference of the ceramic insulator and the cylindrical metal part.
• the insulating material filling the recess of the ceramic insulator can be a part of a rubber-elastic disc which is pressed in the axial direction onto the step-shaped or ramp-shaped end face of the ceramic insulator.
• FIG. 1 shows an axial longitudinal section through an X-ray tube designed according to the invention with associated connecting parts
• 4 and 5 are analog sectional views of two further exemplary embodiments of the anode-side ceramic insulator.
• the X-ray tube shown has a cylindrical metal part 11 which is provided with a window 12 inserted in a vacuum-tight manner for the exit of the X-ray radiation.
• a window 12 inserted in a vacuum-tight manner for the exit of the X-ray radiation.
• annular disk-shaped ceramic insulator 13 At the upper axial end of the metal part 11 in FIG. 1 there is an annular disk-shaped ceramic insulator 13, the outer periphery of which is connected to the metal part 11 in a vacuum-tight manner.
• the axial end face 16 of the ceramic insulator 13 facing away from the interior of the metal part 11 is offset radially outwards by a step 17 running in the circumferential direction, so that an annular axial recess 18 is formed on the ceramic insulator 13 adjacent to its outer circumference.
• This depression 18 is filled by a part 19 of a rubber-elastic washer 20 which is pressed onto the ceramic insulator 13 in a manner known per se by means of a connecting part 21.
• the rubber-elastic washer 20 has a smaller dielectric constant than the ceramic insulator 13.
• there is a layer of insulation grease (not shown in FIG.
• the interior of the metal part 11 facing axial end surface 26 of the ab ⁇ 'ceramic insulator 23 is deposited by a Windier extending in the circumferential direction stage 27 ein ⁇ radially, so that the ceramic insulator 23 adjacent its inner periphery an annular axial recess
• This recess 28 is formed. This recess 28 is by a lot
• the rubber-elastic washer 30 is pressed onto the ceramic insulator 23 in a manner not known per se by means of a connecting part 31.
• the rubber-elastic washer 30 has a smaller dielectric constant than the ceramic insulator 23.
• the metal part 11 is connected to earth potential, while a voltage which is negative with respect to the earth potential is applied to the cathode 1 through the connection part 21 and a voltage which is positive with respect to the earth potential is applied through the connection part 31 to the anode 25.
• Potential lines then appear in the interior of the tube, as indicated, for example, by the dashed lines 32 and 33 in FIG. 1.
• the potential lines 32 in the region of the ceramic insulator 13 assume a diverging profile that deviates from the axis-parallel direction, in such a way that on the flat inner end face 3 ⁇ of the ceramic insulator 13, the electrical field vectors 35, which are always at right angles to the potential lines 32, have directions pointing away from the ceramic insulator 13 towards the interior of the X-ray tube.
• the depression 28 of the other ceramic insulator 23, which is filled with insulating material 29 with a lower dielectric constant, has the result that the potential lines 33 in the area of the ceramic insulator 23 assume a converging course and therefore the electric field vectors 36 on the flat inner end surface 37 of the ceramic insulator 23 have directions facing away from the inside of the X-ray tube.
• the angle between the field vectors 35 and 36 on the one hand and the inner end surface 34 and 37 of the ceramic insulator 13 and 23 on the other hand is due to the difference in the dielectric constant of the ceramic material and the rubber-elastic insulating material due to the radial width and the axial depth of the Indentation 18 and 28 and determined by the dimensions of the ceramic insulator 13 and 23 respectively.
• the X-ray tube according to FIG. 1 has a noticeably higher joint dielectric strength.
• the advantages described were checked and confirmed using a test X-ray tube.
• the experimental X-ray tube with the structure shown in FIG. 1 had ceramic insulators 13 and 23 with an outside diameter of 107 mm and an inside diameter of 45 mm.
• the axial thickness dimension of the ceramic insulators was 10 mm and was reduced to 7 mm at the location of the recess 18 or 28, so that the steps 17 and 27 had a height of 3 mm.
• the rubber-elastic washers 20 and 30 consisted of silicone rubber with a dielectric constant of 3.2 and a Shore hardness of 28.
• each rubber-elastic washer 20 and 30 were flat and parallel, and the outside - The knife was 100 mm, the inside diameter was 45 mm and the axial thickness was 10 mm.
• the X-ray tube could easily be operated with a voltage of up to 340 kV between the anode and cathode.
• the ceramic insulator 113 shown in FIG. 2 for the cathode side of the X-ray tube has, on its axial end face 116 to be turned outwards, two steps 117 running in the circumferential direction, by means of which an axial recess 118 adjacent to the outer circumference of the ceramic insulator is formed.
• the example of a ceramic insulator 213 shown in FIG. 3 for the cathode side of the X-ray tube has a ramp-shaped step 217 on its axial end face 216 to be turned outwards, by means of which an axial depression 218 adjoining the outer circumference of the ceramic insulator is formed.
• the ceramic insulator 123 shown in FIG. 4 for the anode side of the X-ray tube has on its outward-facing axial end face 126 two steps 117 running in the circumferential direction, by means of which an axial depression 128 adjacent to the inner circumference of the ceramic isolator is formed.
• the ceramic insulator 223 for the anode side of the X-ray tube can also have a ramp-shaped step 227 on the axial end surface to be turned outwards, so that an axial recess 228 adjacent to the inner circumference of the ceramic insulator is formed .
• the depressions 118, 218, 128 and 228 of the ceramic insulators 113, 213, 123 and 223 according to FIGS. 2 to 5 are each made with rubber-elastic insulating material when the X-ray tube is assembled or installed, the dielectric constant of which is smaller than that of the ceramic material, completely filled out. '
• X-ray tubes in which the cathode or the anode is electrically conductively connected to the cylindrical metal part.
• the cathode or the anode is electrically conductively connected to the cylindrical metal part.
• only the other anode or cathode is insulated from the cylindrical metal part by a ceramic insulator.
• the invention can also be used with such X-ray tubes in that the then only existing ceramic insulator in the manner described above is provided on its axial end surface facing away from the inside of the X-ray tube with a depression which is completely filled with an insulating material whose dielectric constant is smaller than that of the ceramic material.

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• X-Ray Techniques (AREA)
• Microwave Tubes (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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ID=4208683

Family Applications (1)

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Cited By (2)

Families Citing this family (3)

Citations (6)

• 1985
  • 1985-03-28 CH CH1363/85A patent/CH665920A5/de not_active IP Right Cessation
• 1986
  • 1986-03-13 EP EP86901329A patent/EP0215034B1/de not_active Expired
  • 1986-03-13 JP JP61501464A patent/JPS62502796A/ja active Granted
  • 1986-03-13 AT AT86901329T patent/ATE40767T1/de not_active IP Right Cessation
  • 1986-03-13 WO PCT/CH1986/000035 patent/WO1986005921A1/de active IP Right Grant
  • 1986-03-13 DE DE8686901329T patent/DE3662079D1/de not_active Expired

Patent Citations (6)

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