Intense low energy positron beams

Intense positron beams are under development or being considered at several laboratories. Already today a few accelerator based high intensity, low brightness e+ beams exist producing of the order of 108-109 e+/s. Several laboratories are aiming at high intensity, high brightness e+ beams with intensities greater than 109 e+/s and current densities of the order of 1013-1014 e+ s-1 cm-2. Intense e+ beams can be realized in two ways (or in a combination thereof) either through a development of more efficient β+ moderators or by increasing the available activity of β+ particles. In this review we shall mainly concentrate on the latter approach. In atomic physics the main trust for these developments is to be able to measure differential and high energy cross-sections in e+ collisions with atoms and molecules. Within solid state physics high intensity, high brightness e+ beams are in demand in areas such as the re-emission e+ microscope, two-dimensional angular correlation of annihilation radiation, low energy e+ diffraction and other fields. Intense e+ beams are also important for the development of positronium beams, as well as exotic experiments such as Bose condensation and Ps liquid studies. (orig.)