  The effect of mid-T heat treatment on flux trapping sensitivity was measured
on several 1.3 GHz single cell cavities subjected to vacuum annealing at
temperature of 150 - 400 $^\circ$C for a duration of 3 hours. The cavity was
cooldown with residual magnetic field $\sim$0 and $\sim$20 mG in the Dewar with
cooldown condition of full flux trapping. The quality factor as a function of
accelerating gradient was measured. The results show the correlation between
the treatment temperature, quality factor, and sensitivity to flux trapping.
Sensitivity increases with increasing heat treatment temperatures within the
range of (200 - 325 $^\circ$C/3h). Moreover, variations in the effective
penetration depth of the magnetic field and the density of quasi-particles can
occur, influencing alterations in the cavity's electromagnetic response and
resonance frequency.
