Variable Wedge Degrader for Rare Isotope Beams

Facilities that generate rare isotope beams employ fragment separators for various ion species. The ion-optical system consists of energy dispersive media to purify the specific beam. The purifier is shaped in a wedge and reduces the beam energy via atomic interactions. The wedge requires high degree of precision in angle and thickness tolerances. Additionally, selecting different beams often requires swapping the wedge, which is a time-consuming process that takes away from beam time to users. In this proposal, we will develop a variable wedge purifier for use in fragment separation at rare isotope beam facilities. The wedge will be tapered from sub-mm to many mm in thickness, over a relatively long distance. The insertion of the wedge into the beam allows the beam to sample various thicknesses, thereby allowing selection of different energy isotope beams, without the need to swap out wedges for different experiments. The Phase I efforts are focused on fabrication of a high-quality wedge, the key component of the system. The fabrication methods employed include standard machining techniques, using a wire electric discharge machining method to achieve the appropriate dimensions, and an iterative lapping procedure complemented with high-precision optical metrology for inspection. In addition, a two-metal wedge fabrication that may relax the given tolerances will also be tested. Finally, a novel supersonic gas jet as an energy degrader will be studied, which can effectively replace the solid metal wedge, where the variable density of the jet is used to select different beam energy. The advantage of a gas jet is that there is no damage and does not require constant maintenance, however implementation requires design of a differential pumping system. Additional work includes engineering design on remote control manipulation and custom cooling solution for high power beam locations. The results of these efforts can provide immediate benefits for facilities that generate rare isotopes and will expedite beam selection by reducing downtime associated with replacement. In addition, the technology developed is directly applicable in the enhancement of commercial medical accelerators that require purified beams for targeted dose delivery.