Professor Christopher Foot

Abstract:

We have simulated the evaporative cooling of trapped atoms using a very efficient method originally introduced for the study of molecular gas dynamics. This straightforward and intuitive method allows the dynamics of the evaporative cooling process to be studied and requires fewer simplifications and assumptions than other methods. In particular, the method is not restricted to distributions close to equilibrium and therefore it can model accurately rapid forced evaporative cooling, which is an important technique for cooling trapped atoms. We present the results of simulations for forced evaporative cooling in one, two and three dimensions.

Abstract:

Evaporative cooling is a simple and very effective way of cooling atoms in a magnetic trap. A modelling method for this technique was developed by considering the physics of gas flow. Using this method, cross-dimensional mixing in homogeneous and inhomogeneous gases and continuous cuts in two and three dimensions are studied. The two-dimensional cut model is similar to the evaporative process in a TOP trap because atoms in this trap are removed in the basis of their radial positions. Initially, a two dimension cut retains atoms in the trap but atom loss becomes greater than with a three dimension cut because the velocity component along z is relatively hot and gives up more energetic atoms.

Abstract:

A simulation of the forced evaporative cooling process is made using a classical Monte Carlo method. This powerful method is complementary to other recent studies of evaporative cooling and does not need the assumption that a gas has recovered thermal equilibrium after each cut of potential well or the assumption of sufficient ergodicity. Direct simulation by Bird's method can be done in any arbitrary potential and can be used to study the deviation between three components of translational temperature during forced evaporation.