Nonequilibrium kinetics of neutral atoms confined in a harmonic potential

The nonequilibrium behavior of neutral atoms confined in a harmonic potential is simulated by a Monte Carlo method. Atoms obey Maxwell-Boltzmann statistics. Initially, the probability distribution function (pdf) for each of the three energy components, Ex, Ey and Ez, is taken to be a truncated exponential with cutoff Ec. Collisions between atoms are simulated assuming s wave scattering in the center-of-mass frame. Because the energy distributions in the three different dimensions were indistinguishable, all three energy components are assumed to have the same pdf. The time-varying pdf for the energy components is modeled as a mixture of two pdfʹs. Each of the two pdfʹs in the mixture is a truncated exponential; one applies to energies below the cutoff, the other pdf applies to energies above the cutoff. Each truncated exponential is characterized by a time-dependent decay parameter. A statistical model for the time-dependent decay parameters, and a mixture parameter, is developed.