  The system of a quarkonium confined by an impenetrable spherical cavity
filled with a hot quantum chromodynamics (QCD) medium is studied by solving the
Schr\"{o}dinger equation. This is the first time this issue has been raised for
discussion. The Schr\"{o}dinger equation with an appropriate boundary condition
of a quarkonium in an impenetrable cavity filled with a hot medium is derived.
The numerical results are obtained with the help of Gaussian Expansion Method.
Binding energies and radii of the ground and low-excited states are obtained as
a function of the medium temperature and the cavity radius. We find the
behaviour of quarkonium in this cavity is different from that in infinite
space. Our results show that the quarkonium dissociation temperature decreases
as the cavity radius decreases and the finite volume effects on the ground
state are more obvious than on the excited states. We also find that the less
mass of the constituents and the bigger radius of the quarkonium lead the
finite volume effects to become more obvious.
