| | In order to further understand the relation between the
high-field Q-drop and the native oxide layer on the
surface of SRF niobium cavities, we tried to alter the
oxidation of niobium by applying a small voltage between
a large-grain niobium cavity and a niobium rod inserted in
the center, during buffered chemical polishing (BCP). The
cavity RF test results at 1.7 K and 2.0 K did not show any
major difference in the Q-drop behavior, compared to a
standard BCP treatment. In one case, dark gray regions
were visible inside the cavity and were responsible for
additional losses, as seen with temperature maps. In order
to better understand the electrochemical process occurring
during the "polarized" BCP treatment, measurements of
the polarization curve have been made on a cylindrical
niobium sample, with a cylindrical niobium rod in the
center. | |