Patent ID: 8217577

Claim:
An electron gun comprising: an input cavity operatively coupled to a radio-frequency drive circuit; an anode located outside of the input cavity; a cathode located within the input cavity and biased to maintain a voltage potential difference between the cathode and the anode and further adapted to emit an electron beam that propagates substantially toward the anode; a first control grid situated in close proximity to the cathode and defining a grid-to-cathode (G-K) gap between the cathode and the first control grid; and a second control grid situated in close proximity to the first control grid and defining a grid-to-grid gap between the first control grid and the second control grid; wherein: a radio-frequency (RF) signal from the radio-frequency drive circuit is coupled into the input cavity such that: the electron beam interacts with the RF signal as it propagates across the G-K gap and acquires velocity modulation; the electron beam is shielded from the RF signal as it propagates through the first control grid such that the velocity modulation produces spatial bunching of the electron beam; and the electron beam interacts with the RF signal as it propagates across the grid-to-grid gap such that the spatial bunching is intensified.