Sub-nanosecond electrical gating for metal Field Emitter Arrays

Field Emitter Arrays (FEA) are an attractive candidate to replace thermionic and photo-cathodes as a source of a high quality electron beam, reducing cathode power consumption and increasing reliability. For some applications (accelerators, microwave amplifiers) it is necessary to modulate or produce electron pulses with sub-nanosecond time structure. Sine wave grid modulation of an FEA cathode up to few GHz has already been demonstrated [1, 2]. Sub-microsecond pulsed electron emission was also reported by S. Leemann et al. [3]. Our interest was to explore the limitations of short electron pulses generation based on electrically gated FEAs. Since field emission is an instantaneous process the main modulation speed limitation is due to the finite FEA gate capacitance. Using short current pulses to control the gate potential we demonstrated that FEAs are capable of generating single sub-nanosecond electron pulses. The practical implementation of the method and its limitations are discussed.