Expansion cooling and heating for a thermal magnetic trapped gas

We analyze the expansion process of a thermal trapped gas taking place during the detection of Bose-Einstein condensation through an expansion of the condensate. By extending our Monte Carlo method to study this phenomenon, we demonstrate that the velocity distributions of the thermal trapped atoms are anisotropic due to anisotropic explosion of atoms. The radial and axial components of translational temperature are different from the trap temperature and have opposite evolution tendencies with the gas expansion.