  The main source of RF losses leading to lower quality factor of
superconducting radio-frequency cavities is due to the residual magnetic flux
trapped during cool-down. The loss due to flux trapping is more pronounced for
cavities subjected to impurities doping. The flux trapping and its sensitivity
to rf losses are related to several intrinsic and extrinsic phenomena. To
elucidate the effect of re-crystallization by high temperature heat treatment
on the flux trapping sensitivity, we have fabricated two 1.3 GHz single cell
cavities from cold-worked Nb sheets and compared with cavities made from
standard fine-grain Nb. Flux expulsion ratio and flux trapping sensitivity were
measured after successive high temperature heat treatments. The cavity made
from cold worked Nb showed better flux expulsion after 800 C/3h heat treatments
and similar behavior when heat treated with additional 900 C/3h and 1000 C/3h.
In this contribution, we present the summary of flux expulsion, trapping
sensitivity, and RF results.
