Online tests of the Advanced Cryogenic Gas Stopper at NSCL

Linear gas stoppers filled with helium have become a common tool to convert high energy rare isotope beams into low-energy beams. The National Superconducting Cyclotron Laboratory (NSCL) has designed and fabricated a new cryogenic gas stopper to maximize efficiency and beam rate capability in order to increase scientific reach at the facility. The Advanced Cryogenic Gas Stopper (ACGS) will increase extraction efficiency, reduce transport time, reduce molecular contamination of the isotope of interest, and minimize space charge effects. A novel 4-phase Radio Frequency wire-carpet generates a traveling electrical wave for fast ion transport, cryogenic cooling of the helium gas chamber reduces unwanted molecular formation, and the new planar geometry with the wire-carpet in the mid-plane of stopper alleviates space charge effects. Prototype testing of ACGS components have shown wire-carpet transport efficiencies greater than 95% and transport speeds up to 100 m/s. This presentation will show the first online tests with radioactive beams and report the efficiencies of the ACGS.