Coherence properties of a continuous atom laser

We investigate the coherence properties of an atomic beam evaporatively coo led in a magnetic guide, assuming thermal equilibrium in the quantum degene rate regime. The gas experiences two-dimensional, transverse Bose-Einstein condensation rather than a full three-dimensional condensation because of t he very elongated geometry of the magnetic guide. First order and second or der correlation functions of the atomic field are used to characterize the coherence properties of the gas along the axis of the guide. The coherence length of the gas is found to be much larger than the thermal de Broglie wa velength in the strongly quantum degenerate regime. Large intensity fluctua tions present in the ideal Bose gas model are found to be strongly reduced by repulsive atomic interactions; this conclusion is obtained with a one-di mensional classical field approximation valid when the temperature of the g as is much higher than its chemical potential, k(B)T >> \mu\.