1. A thermionic RF gun, comprising:a first RF cavity;
a second RP cavity connected to the first RF cavity along an axis;
a thermionic cathode configured to generate electrons for entry into the first RF cavity; and
a dual RF feed configured to provide input power to each of the first and second RF cavities independently, so as to generate an RF field in each of the first and second RF cavities;
wherein a length of the first RF cavity is less than 0.25 inches so as increase a launch phase ?BB at which back-bombardment occurs, thereby reducing an electron back-bombardment power of the thermionic RF gun;
wherein a center of the second RF cavity is located at a distance not more than 1.5 inches from a center of the first RF cavity, along the axis, thereby increasing an electron capture rate of the thermionic RF gun;
wherein an electric coupling between the first and second RF cavities is cancelled out by a magnetic coupling between the first and second RF cavities, so that a phase of the RF field in the first RF cavity is controllable independently of a phase of the RF field in the second RF cavity.