Emittance Measurements of a Nanopatterned Cathode on the DC beam line

In the generation of photoemitted electron bunches for the use in accelerators, metals are limited by their low QE. Previous work [P. Musumeci et al., Phys. Rev. Lett. 110(2013)] has shown that charge yield from infrared light is increased by a factor of 120 by etching nanopatterns into the cathode. However, utility of the electron bunch is also based on its thermal emittance, or angular spread, which is conserved during transit along the beam line. In that same work, a measure of (1.4 ± 0.1) mrad was found in the emittance for a copper nanopatterned cathode held in an electric field strength of 75 MV m−1. It is proposed that the presence of the nanopattern will alter the electric field and likely the emittance. Measurements were taken for the same cathode in an electric field strength of (1.6 ± 0.2) mrad. Hence no apparent effect of the electric field strength on the emittance was found.