  The computational and theoretical analysis carried out in this article
demonstrates the existence of a nontrivial mechanism for the compression of a
submicron-sized gas bubble formed by a gas of classical ions and a gas of
degenerate electrons. This mechanism fundamentally differs from conventional
compression mechanisms. It is shown that taking into account the quantum effect
of a large spatial scale in the distribution of electrons qualitatively changes
the character of cumulative processes. Because of a large-scale electric field
caused by quantum shell effects, the compression process is characterized by
the formation of multiple shock waves. The values of gas temperature and
pressure achieved during compression occur higher by two orders of magnitude as
compared with the classical adiabatic regime. The analysis is carried out
within the framework of the following model: the dynamics of the electron
subsystem is described by equations of a quantum electron fluid, while the
hydrodynamic approximation is adopted for the ionic subsystem. The large scale
effect is taken into account by means of effective external field acting on
electrons. The theoretical analysis carried out within this approach clarifies
the nature of the cumulative process in the system under consideration; some
quantitative characteristics obtained with numerical simulation are presented.
The possibility of experimental observation of this cumulative mechanism is
analyzed. It is suggested that the manifestation of the effect can be observed
during laser compression of a system of submicron targets by measuring the
neutron yield.
