  Using the high-resolution observations from New Vacuum Solar Telescope (NVST)
jointly with the Solar Dynamics Observatory data, we investigate two successive
confined eruptions (Erup1 and Erup2) of a small filament in a decaying active
region on 2017 November 10. During the process of Erup1, the overlying magnetic
arcade is observed to inflate with the rising filament at beginning and then
stop the ongoing of the explosion. In the hot EUV channel, a coronal sigmoidal
structure appears during the first eruption and fade away after the second one.
The untwisting rotation and disintegration of the filament in Erup2 are clearly
revealed by the NVST H_alpha intensity data, hinting at a pre-existing twisted
configuration of the filament. By tracking two rotating features in the
filament, the average rotational angular velocity of the unwinding filament is
found to be ~10.5 degree/min. A total twist of ~1.3 pi is estimated to be
stored in the filament before the eruption, which is far below the criteria for
kink instability. In the course of several hours prior to the event, some
photospheric flux activities, including the flux convergence and cancellation,
are detected around the northern end of the filament, where some small-scale
EUV brightenings are also captured. Moreover, strongly-sheared transverse
fields are found in the cancelling magnetic features from the vector
magnetograms. Our observational results support the flux cancellation model, in
which the interaction between the converging and sheared opposite-polarity
fluxes destabilizes the filament and triggers the ensuing ejection.
