Some thoughts on the focusing regime for an Alvarez linac

When designing an Alvarez linac the perennial problem arises as to what is the optimum phase advance and focusing structure. This report discusses this question and makes recommendations based on simple criteria. The general conclusions are valid over a wide range of parameters, but the detailed simulations given in the report can be used to calculate the optima more carefully for a particular beam current and energy range. This study is complementary to the AUSTRON Feasibility Study for a fast-cycling, synchrotron-driven neutron spallation source.