DIVERGENCE PROFILE OF A WEDGE-TYPE ION-BEAM

In ion beams emitted from a slit, commonly employed in high current electromagnetic isotope separators, the control of the beam divergence is important to achieve the best machine performance. The variation of the divergence with the various extraction parameters was measured with a precision higher than for previously reported data. The results obtained can be well approximated by a simple relation derived from the sum of the initial divergence due to the meniscus curvature and the lens effect of the electrode slit, neglecting space charge and assuming a uniform acceleration field. Other secondary features of the angular intensity distribution curve (width of the sides and concavity of the top) were also investigated and empirical relations proposed for predicting their values for any set of operating conditions. All results were obtained with a simple extraction geometry, i.e. plane electrodes and bevelled emission slit. This geometry was found to be more convenient for general use than a true Pierce geometry calculated for a divergent beam. © 1978.