The use of the radio frequency superconducting ion linacs has grown steadily over the past 15 years, primarily for applications in nuclear and atomic physics where flexibility n ion species and energy are required. This technology continues to be actively developed at several laboratories worldwide. A recent development at the Argonne tandem linac accelerator system (atlas) for the new positive ion injector is the low velocity interdigital structure. This simple structure can be extended, through several innovations now being considered, to lower cost per volt of acceleration with even lower velocity heavy ions. The primary objective of this study will be to generate the design of an optimized extended interdigital superconducting structure for use in nuclear physics research and industrial applications. Phase I will establish the operating regime for the extended interdigital structure and variations of it that include radio frequency quadrupole-like focusing to increase the beam dynamics performance. The planned development study will use the experimental results of a simple superconducting interdigital structure to develop an extended interdigital structure for use in nuclear physics applications for very low velocity heavy ions.