  Particle dynamic in an axi-symmetric mirror machine with an extremely high
plasma pressure equal to pressure of vacuum magnetic field (so-called regime of
diamagnetic confinement) is investigated. Extrusion of magnetic field from
central region due to plasma diamagnetism leads to non-conservation of the
magnetic moment and can result in chaotic movement and fast losses of
particles. The following mechanisms can provide particle confinement for
unlimited time: absolute confinement of particles with high azimuthal velocity
and conservation of adiabatic invariant for particle moving in smooth magnetic
field. The criteria of particle confinement and estimations of lifetime of
unconfined particles are obtained and verified in direct numerical simulation.
Particle confinement time in the diamagnetic trap in regime of gas-dynamic
outflow is discussed.
