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Final Activity Report Summary - CONT-BECS (Evaporative of a guided atomic beam: towards a continous Bose-Einstein condensate source.)

The long term goal of the experiment on which I have worked is the realisation of a continuous atom laser, which corresponds to the generation of a continuous source of Bose-Einstein condensate. For this purpose, one has to realise an intense source of slow and cold atoms confined by a two-dimensional magnetic guide. One possible scheme that we have investigated consists in periodically launching fast packets of atoms into a magnetic guide that are subsequently slowed down by an elastic collision with a magnetic potential barrier moving along the guide. Once the beam generated, its temperature can be reduced by applying an energy-selective 'knife' (named evaporative cooling) which removes atoms having a transverse energy above the average. As the remaining atoms propagate further downstream and re-thermalise through elastic collisions, the beam temperature decreases and the phase-space density of the beam increases.

We have implemented this technique of evaporative cooling on a magnetically guided beam, resulting in a gain of one order of the on-axis phase space density, which constitutes a 'premiere' in the domain. It is important to emphasise that applying evaporative cooling on an atomic beam is significantly more difficult than on a trapped packet of atoms, since there is no longitudinal confinement which is responsible for the decrease of the dimensionality of evaporation as well as for the dilution of the atomic density. In order to overcome these limitations, we have also achieved a three-dimensional moving chain of magnetic traps to simultaneously trap and transport several packets of atoms at low speed and cool them down by evaporative cooling before releasing them into the magnetic guide to form a continuous atomic beam. All these achievements paved the way for the generation of a continuous and intense source of Bose-Einstein condensate.

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