A betatron, especially in X-ray testing apparatus is provided, that includes a rotationally symmetrical inner yoke having two interspaced parts, an outer yoke connecting the two inner yoke parts, at least one main field coil, a toroidal betatron tube arranged between the opposing front sides of the inner yoke parts, and at least one contraction and expansion coil. An individual CE coil is respectively arranged between the front side of the inner yoke part and the betatron tube, and the radius of the CE coil is essentially the same as the nominal orbital radius of the electrons in the betatron tube.