A rotatable anode for an X-ray tube comprises a first unit (901) for being hit by a first electron beam, and at least a second unit (902) being hit by at least a second electron beam, the second unit being electrically isolated from the first. In addition, an X-ray system comprises the anode, a main cathode for generating an electron beam, and first electrical potential, and an auxiliary cathode for influencing a second electrical potential. The main cathode deflects the electron beam to heat the auxiliary cathode. Furthermore, a device determines electrical potential by detecting a point of impact of the electron beam onto the anode and/or by detecting an X-ray spectrum of radiation starting from the anode. The electron beam hits the first unit and is deflected, wherein the deflected beam hits the second unit the point of impact. The first unit and/or second unit emit radiation.