Development of radiofrequency carpets for ion transport at the NSCL

The low-energy research program at the NSCL is dependent on gas thermalization techniques to convert the energetic nuclear reaction products (100 MeV/u) from projectile fragmentation reactions into high quality low-energy beams (eV). The NSCL is currently developing a gas-filled reverse cyclotron to provide a high stopping efficiency for the incoming fast beams at pressures that will allow rf ion-guiding techniques to be effective. In this work, the development and characterization of rf carpets for the efficient ion-guiding and extraction of projectile fragments from a cyclotron gas stopper was achieved. The transport of Rb ions within the pressure range expected for cyclotron gas stopper operation of 40 - 110 torr and over transport distances (up to 40 cm) were investigated. Ion extraction from the rf carpet was also successfully demonstrated. This work shows that large rf carpets can be constructed that will work in the cyclotron gas stopper.