  Expulsion of ambient flux has been shown to be crucial to obtain high quality
factors in bulk niobium SRF cavities. However, there remain many questions as
to what properties of the niobium material determine its flux expulsion
behavior. In this paper, we present first results from a new study of two
cavities that were specially fabricated to study flux expulsion. Both cavities
were made from large grain ingot niobium slices, one of which had its slices
rolled prior to fabrication, and none these slices were annealed prior to
measurement. Expulsion measurements indicate that a dense network of grain
boundaries is not necessary for a cavity to have near-complete flux trapping
behavior up to large thermal gradients. The results also contribute to a body
of evidence that cold work is a strong determinant of flux expulsion behavior
in SRF-grade niobium.

Accelerator Physics