  Our objective is to study the extreme and local electrodynamic properties of
Niobium (Nb), and to relate these properties to specific defects that limit the
ultimate RF performance of superconducting radio frequency (SRF) cavities made
from Nb. Specifically, we wish to develop a microscopic measure of the response
of Nb to RF magnetic fields up to the critical field (Hc) at microwave
frequencies (few GHz), and at temperatures down to 4.2 K. In order to image the
local electromagnetic response in the GHz frequency regime, a magnetic writer
from a commercial hard drive is integrated into the near field microwave
microscope and operates with the Nb sample in the superconducting state. The
microwave response of Nb thin films from a mesoscopic area are found through
linear and nonlinear microwave measurements.
