Indirect measurement of field emission electron current from the main superconducting cavities of compact ERL at KEK

The field emission electron currents from the main superconducting cavities (Cavities #3 and #4) of compact ERL at KEK, Japan, were estimated indirectly from photon dose rates measured around the cavities and on the roof of the compact ERL room. The field emission electron currents estimated from the photon dose rates measured around the cavities are in good agreement with those on the roof of the compact ERL room. The field emission electron currents increased steeply with the applied voltage. The field emission electron currents corresponding to the applied voltages were different between Cavity #3 and Cavity #4. We found that the field emission electron current exceeded 1 μA at 13.5 MV for Cavity #3 and at 15.5 MV for Cavity #4. This result was used in considering unexpected loss of field emission electrons.