WG504
HZB, Berlin, Germany
Bergische Universität Wuppertal, Wuppertal, Germany
Bi-alkali antimonide K2CsSb is a baseline photocathode material for the production of a high brightness electron beam with high average current for future 4th generation multi-user light sources. The low beam emittance required for these projects demands very high field gradient on the photocathode surface, increasing the probability of enhanced field emission (EFE) in the superconducting gun cavity. Molybdenum can be used as a substrate to reduce the lattice mismatch with the cathode crystal. Therefore we have measured the EFE from a flat Mo sample by means of field emission scanning microscopy (FESM) up to 180 MV/m surface field (Es). First EFE (1 nA) was noticed at Es = 60 MV/m, but a strong emitter activation resulted in a finally lower EFE onset at Es = 46 MV/m. Local I(E) measurements have revealed Fowler-Nordheim behavior with enhancement factors of 10-70, however with a wide range of emitting areas (0.1 nm2 - 4300 μm2) which hint for adsorbate or oxide effects. Finally the located emission areas were investigated by SEM/EDX to identify the origin of the EFE.
