Abstract: An X-ray source apparatus contains an X-ray target which emits X-ray when bombarded with electrons from an electron source. A strong magnetic field, e.g. from a superconducting solenoid, having curved lines of magnetic flux interlinks the target and electron source. The magnetic field has sufficient strength over the entire electron path of travel to constrain the electrons emitted from the source with components at angles to the magnetic field to execute helical paths about the field lines to the target. An aperture means is positioned to block the straight line paths between the source and the target but permits the passage of substantially all electrons traveling along the lines of flux.