Ion beam extracted from a 14GHz ECRIS of CAPRICE type

An ion beam extracted from an ECRIS suffers from the inhomogeneous distribution of cold electrons within the minimum B configuration, necessary to confine the plasma. Especially for higher ion currents, the space charge force is not negligible any more, and because of the nonlinear force, emittance growth will occur. Measurements of the profile and the emittance of the beam directly behind the source show the complicated correlation between extraction voltage and plasma density. The emittance has been measured with a pepper pot device to account for the inhomogeneous azimuthal distribution of the beam. These results indicate that further information about the profile is required. To visualize the beam profile a tantalum foil with a thickness of 20 mu m has been used for an electrical beam power between 10 and 50W. Looking on the back side of the foil with a CCD camera it is possible to record the profile in real time. As a more sensitive diagnostic tool viewing targets made from BaF has been used. Three dimensional computer simulations have been used to identify the reason for the structures, observed in measurements.