In one embodiment, the invention includes an x-ray source having a cathode with (1) a pointed end or (2) an elongated blade oriented substantially transverse with respect to a longitudinal axis of the cathode. The pointed end or blade can be pointed towards an anode. In another embodiment, the invention includes an x-ray source having a window with an annular-shape, forming a hollow-ring. A convex portion of a half-ball-shape of an anode can extend into a hollow of the annular-shape of the window.