In embodiments, a linac electron beam excited X-ray source weighing less than 50 pounds, and having a volume less than 1 cubic foot, injects electrons from an RF-excited, diamond tip cathode into a dielectric accelerator tube of diameter less than 10 mm, where the electrons are RF-accelerated to 1-4 MeV. A focusing channel having a plurality of annular permanent magnets can surround the dielectric tube, and a vacuum can be maintained in the tube by a getter pump. The accelerating RF can be 10 GHz or higher. The X-ray source can be powered by a rechargeable battery for more than an hour. Embodiments can be transported within a case having a display attached to an interior surface of its lid. An X-ray head can be removed from the case and extended up to 10 feet while remaining interconnected with the case by a flexible conduit.