Patent Application
20180277331
The invention relates to a receptacle for receiving a plug connector of a high-voltage cable for a microfocus X-ray tube with a cathode, which has a filament and a grid cap made of metal, as well as to a plug connection for a high-voltage cable for a microfocus X-ray tube, which has a plug connector and such a receptacle.
The transmission of high voltage from the outside of an open microfocus X-ray tube to the inside—the cathode chamber—of this X-ray tube under high vacuum can lead to voltage flashovers, The operation of such X-ray tubes is badly disrupted by such voltage flashovers. By microfocus X-ray tubes is meant X-ray tubes which have a focal spot (focus) in the μm range. In contrast, “normal” X-ray tubes have an effective size in the mm range.
For certain applications, it is advantageous if the X-ray tube is operated with a high voltage. For this, for the transmission of the high voltage and of the electrical current, a receptacle made of an epoxy resin as insulator has been used, for example in the case of the applicant's FXE-225 model. Through the encapsulation of the electrical connection with epoxy resin, voltage flashovers due to high field strengths are to be prevented. One problem here is, however, that epoxy plastics emit gas and thus impair the vacuum. The use of ceramic materials for the receptacle could alleviate this problem—as has already been done hitherto in the case of closed X-ray tubes—however, the problem arises here that high field strengths develop in the contact area between the plug connector and the receptacle and voltage flashovers caused thereby occur, which are precisely to be prevented. Unlike with the use of epoxy resins, it is not possible with ceramics to encapsulate the electrical contacts in order to guarantee sufficient dielectric strength.
An object of the invention is to provide a receptacle and a plug connection for a high-voltage cable for a microfocus X-ray tube, in which no voltage flashovers occur even at high voltages.
The object is achieved by a plug connector with the features of claim 1. In order to prevent voltage flashovers at high voltages in the plug connection, the receptacle according to the invention is equipped with a combination of three features. Firstly, the use of spring contacts for the transmission of the filament current from the high-voltage cable via the high-voltage plug connector to the filament; narrow gaps and thus high field strengths are thereby prevented. Secondly, the use of an extended grid cap of the cathode; shielding of the field in the area of the plug connection is thereby achieved, which reduces the field strength there. Thirdly, the use of internal metallization of the insulator in the area of the current and voltage transmission when the high-voltage plug connector of the high-voltage cable is inserted (thus, in the second cavity of the ceramic insulator); the field strength is also reduced by this. As a result of the above-named three cumulative measures according to the invention an enormous reduction in the field strengths developing in the area of the plug connection is achieved, with the result that high voltages can be applied to the microfocus X-ray tube with a small constructed size without voltage flashovers being produced. As a result of the described features according to the invention, ceramic material can thus be used in spite of the problems described above, which have until now deterred a person skilled in the art from using ceramic for microfocus X-ray tubes having a small constructed size, since these measures lead to the described drastic reduction in the field strength at the relevant points.
An advantageous development of the invention provides that the second cavity is formed cylindrical over the bulk of its axial length.
A further advantageous development of the invention provides that the third cavity is formed frustoconical over the bulk of its axial length. High-voltage cables with high-voltage plug connectors known from the state of the art, which have a corresponding shape, can thereby still be used and a surface contact forms all over without air pockets.
The object is also achieved by a plug connection with the features of claim 4. The advantages stated there result hereby analogously for the reasons already named above in relation to claim 1.
An advantageous development of the invention provides that the second area of the high-voltage plug connector has a rubber cone and/or the second area of the high-voltage plug connector is frustoconical. By means of the rubber coating in the form of the rubber cone over an HV flange the high-voltage plug connector can be pushed into the receptacle under pressure to fit precisely, with the result that there is a surface contact between receptacle and high-voltage plug connector over the whole surface and no gaps form between high-voltage plug connector and receptacle (or the ceramic insulator thereof); gaps would increase the risk of voltage flashovers, The use of frustoconical high-voltage plug connectors has the advantage that common high-voltage plug connectors can be used since these have such a shape.
The object is also achieved by the use of a receptacle according to the invention and/or of a plug connection according to the invention with the features of claim 6. The applied high voltage is at least 160 kV, preferably at least 250 kV and particularly preferably at least 320 kV. The microfocus X-ray tube can thus accommodate very high voltages with a small constructed size of the plug connection—which also makes possible a small constructed size for the whole microfocus X-ray tube—which leads to a widening of the range of application of such X-ray tubes.
All of the features of the advantageous developments indicated in the dependent claims form part of the invention both individually per se in each case and also in any desired combinations.
In the following, an advantageous embodiment example of a receptacle according to the invention is explained in the context of its connection to a cathode of an open microfocus X-ray tube.
In
In the following, the embodiment example of
The receptacle according to the invention has, as base body, a ceramic insulator 1, which consists of a ceramic material. In the represented embodiment example, this ceramic material is Al2O3. The ceramic insulator 1 essentially has three sections.
A first cavity 2 is formed in its, in
A second cavity 3 follows the end of the contact plate 26 facing away from the grid unit 15. It is also formed cylindrical with the same diameter as the first cavity 2. At its lower end, facing away from the grid unit 15, it has a short part (in relation to the axial direction seen in comparison with the cylindrical part), which tapers towards the bottom. The surface of the second cavity 3 is provided with a metal layer 9 (here made of an alloy of molybdenum, manganese and nickel). The metal layer 9 was deposited on the inner surface of the ceramic insulator 1 by means of methods known to a person skilled in the art. Two spring contacts 7, which are in contact through the contact plate 26 with the two electrical conductors 6 which transport the filament current, project into the second cavity 3 from the contact plate 26. A third electrical conductor 6 in the first cavity 2 which conducts the high voltage is in contact through the contact plate 26 with an electrically conducting centre pin 8, which likewise extends into the second cavity 3 along the central longitudinal axis of the ceramic insulator 1. In the assembled state of the high-voltage plug connector 18 of the high-voltage cable 23, the second cavity 3 serves to make the electrical contact between high-voltage cable 23 and filament 17 or grid 27.
Towards the bottom, a third cavity 4 follows the conical part of the second cavity 3, which third cavity 4—except for a cylindrical part that is very short in relation to the axial direction—widens conically towards the bottom and forms a frustoconical part. This frustoconical part serves to receive a rubber cone 22 of the high-voltage plug connector 18 (see
Hitherto, only the internal shape of the ceramic insulator 1 has been described with reference to its three cavities 2, 3, 4, The description of the outer surface of the ceramic insulator 1 now follows.
In the area of the first and second cavities 2, 3, the outer surface of the ceramic insulator 1 is formed cylindrical. The cylindrical shape extends into the upper area of the third cavity 4. There, the ceramic insulator 1 widens via a circumferential projection 28 and transitions into an area widening conically towards the bottom. Another cylindrical area is then finally connected thereto.
At the upper end of the ceramic insulator 1, a metallic grid cap 10 is firmly connected to the ceramic insulator 1. The grid cap 10 is formed axially symmetrical about the central longitudinal axis of the ceramic insulator 1 and centrally has a through hole, through which the electrical contacts 5 pass without a conductive connection. At the upper end, the grid cap 10 is formed cup-shaped with the result that a receiving recess, the grid receptacle 14 (see
In the area of the first and second cavities 2, 3 of the ceramic insulator 1—the lower area of the grid cap 10—the grid cap 10 is substantially in the shape of a cylinder barrel and is connected in one piece to the previously-described upper area of the grid cap 10 via a shoulder 29. At the lower end, the outer surface of the grid cap 10 widens slightly, Between the inner surface of the lower area of the grid cap 10 and the outer surface of the ceramic insulator 1, a substantially constant cylindrical air gap 12 is formed. In the area of the shoulder 29, just described, of the grid cap 10, a triple point 13 is formed (this is actually a ring, which extends concentrically about the central longitudinal axis of the ceramic insulator 1), at which three different media meet: metal of the grid cap 10, ceramic of the ceramic insulator 1 and air/vacuum of the air gap 12. Between the lower end of the grid cap 10 and the projection 28 of the ceramic insulator 1, there is a space in the axial direction which leads to a circumferential groove 11,
In
Through the design according to the invention of the receptacle, the field strengths developing in operation—when the high-voltage plug connector 18 is assembled—can be very greatly reduced with the result that, in spite of the use of ceramic instead of epoxy resin for the ceramic insulator 1, the risk of voltage flashovers is negligible, even when high voltages of 320 kV are applied. Even at the most problematic spring contacts 7, field strengths of less than 6 kV/mm are achieved at a voltage of 225 kV. This is achieved by the combination according to the invention of spring contacts 19 on the receptacle in conjunction with ring contacts 7 on the high-voltage plug connector 18, a very long grid cap 10 and the internal metallization of the second cavity 3 of the ceramic insulator 1 by means of the metal layer 9.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017105546.0 | Mar 2017 | DE | national |
This application is related to and claims priority under 35 U.S.C. § 119(a) to German patent application No. 102017105546.0, filed Mar. 15, 2017, the contents of which are incorporated by reference herein in its entirety.
