  Cavitation is a common phenomenon in nature and has numerous applications. In
contrast to a cavitation bubble in a free domain, a cavitation bubble in a thin
tube is restricted by the tube wall, which is expected to significantly affect
bubble evolution but its mechanism is still unclear. In this study, the
dynamics of a cavitation bubble in a thin circular tube is studied by numerical
simulation, focusing on the confinement effects of the tube. The results show
that besides affecting the size and lifetime of the bubble, the confinement
effects of the tube lead to the generation of counter jets and a ring jet
during the contraction process of the bubble, and the curvature of the two
counter jets determines the ring jet's peak velocity. When the bubble deviates
from the midpoint of the tube in the axial direction, the two sides of the
bubble along the axial direction show asymmetric behaviors, which results in
the bubble migrating toward the midpoint. The tube diameter, tube length,
liquid viscosity, and initial bubble position, can significantly influence the
degree of confinement effects, which can be characterized by the variations of
several key indicators, such as bubble size, lifetime, degree of deformation,
counter jet velocity, ring jet velocity, and axial migration of the bubble.
