An RF Beam Sweeper for Purifying In-Flight Produced Rare Isotope Beams

The Argonne Tandem Linac Accelerator System (ATLAS) is the only national user facility for low-energy stable heavy ion beams. Beams of radioactive nuclei produced by the in-flight method provide access to more than 100 short-lived isotopes. After traversing the production target, the primary beam is energy degraded and acquires a long low-intensity energy tail from the multiple- scattering processes in the target material. For the low intensity rare isotope beams, these tails can easily dominate the total delivered beams. In response to this problem, RadiaBeam Technologies proposes to develop an RF sweeper, operating at the ATLAS fundamental frequency of 12 MHz, and using a cosine-wave biased design, which will be able to provide voltages more than factor of two higher than the existing sweeper. We will improve the electrical and thermal design to allow operation at 150 kV. Also, we plan to develop an efficient solid-state source to drive the sweeper, allowing up to 70% wall-plug power efficiency. In Phase I, we will compare different approaches, including lumped element circuits, DC bias, second harmonic and RF cavity. We will generate the electromagnetic design of the sweeper and complete the conceptual engineering design with 3D thermal analysis to ensure that it will be capable of operating at the design field levels. A prototype of the solid-state RF source will be built and tested. The results of this work will be of immediate benefit to the ATLAS facility. In addition, a similar buncher could be used at other radioactive ion beam facilities. RF sweepers are also of interest for mass-spectrometry as they can provide very precise isotope separation, which is critical for security, defense, and environmental applications. Finally, the efficient solid-state RF source will have applications in industrial and defense markets.