1. Field of the Invention
The present invention is directed to an x-ray tube of the type having an evacuated housing rotatable around a rotational axis with a drive arrangement in which, firmly connected to the housing, a cathode that emits electrons and an anode onto which the electron beam accelerated with an electrical field, strikes are arranged, and having a non-rotating (stationary) electromagnetic system for the deflection and focusing of the electron beam that includes a number of current-permeated coil elements.
2. Description of the Prior Art
An x-ray tube of the above type is described in U.S. Pat. No. 4,993,055. In this rotating bulb tube, the elements required for generating the x-radiation, i.e. the cathode and the anode, are firmly connected to the housing and rotate together with it during the operation of the x-ray tube. In order to be able to guide the beam on a predetermined path during the rotation so that the path proceeds quasi stationarily and always strikes the rotating anode in the same focal spot, a stationary electromagnetic system is provided that is fashioned for the deflection as well as for the focusing of the electron beam. According to this patent, this electromagnetic system has four coils, known as quadrupole coils, that are arranged around the housing of the tube and that enable operation in a combined deflection/focusing mode on the basis of corresponding control. In this way, it is possible to control the electron beam and the generated focal spot on the anode from the exterior within broad ranges.
The arrangement and fastening of the individual coil elements represents a significant problem, since the coil elements are to be provided in the region of the housing in as simple a way as possible, but a high alignment precision must be achieved at the same time. U.S. Pat. No. 4,993,055, wherein rectangular coils having large dimensions are employed, does not disclose a satisfactory solution.