Emittance of a Field Emission Electron Source
NAVAL RESEARCH LAB WASHINGTON DC
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An analytical formula of the emittance of a field emitter is given. In contrast to thermal and photoemission, such a formula contains complexity due to the multidimensional nature of the source. A formulation of emittance is given for one- and three-dimensional 3D field emitters. The 3D formulation makes use of the point charge model of a unit cell emitter coupled with a trajectory analysis to follow electrons to an evaluation plane where emittance is determined. The single tip theory is extended to an array and the resulting theory predicts the emittance of a Spindt-type square array of emitters 0.2 cm on a side producing 2000 Asq cm is 23 mm mrad. Theory compares favorably with experimental measurements in the literature from ungated and gated sources. The impacts of several complications are estimated the effects of a gate for modulating the emitter the influence of space charge within the unit cell on the beam and constraints imposed by modulation frequency, emitter dimensions, and risefall time requirements for turning a beam on and off, as determined by the arrays RLC characterization.
- Lasers and Masers
- Electricity and Magnetism
- Nuclear Physics and Elementary Particle Physics