Initial Emittance Measurements for Polarized Electron Gun with NEA‐GaAs Type Photocathode

Extremely low emittance electron beams are necesarry for new generation accelerators. The value of the required emittances is as low as 0.1 π.mm.mrad. NEA‐type photocathodes have an intrinsic advantage for generating such a low emittance beam. In this paper, emittance measuremets of photelectrons extracted from two different NEA phtocahtodes are described. The measurements were carried out using Nagoya University 200kV polarized electron source. The normalized RMS emittances of bulk‐GaAs and GaAs‐GaAsP superlattice strained photocathodes are as low as 0.12–0.17 ± 0.02 π.mm.mrad and 0.09 ± 0.01 π.mm.mrad with very low charge density, respectively.