A SOUTHERN AFRICAN POSITRON BEAM

The first stage of a state of the art positron beam, being constructed at the University of Cape Town, is currently being brought into opera tion. This is the first positron beam on the African continent, as wel l as being the first positron beam dedicated to solid and surface stud ies in the southern hemisphere. The project also contains a high propo rtion of local development, including the encapsulated Na-22 positron source developed by our collaboration. Novel features in the design in clude a purely magnetic in-line deflector, working in the solenoidal g uiding field, to eliminate unmoderated positrons and block the direct line of sight to the source. A combined magnetic projector and single pole probe forming lens is being implemented in the second phase of co nstruction to achieve a spot size of similar to 10 mu m without remode ration.