Collisional cooling of negative-ion beams

Studies have been conducted to determine the feasibility of using collisional cooling for reducing emittances and energy spreads in negative-ion beams to levels commensurate with effective isobaric purification with conventional high-resolution electromagnetic isobar separators as required for use at the Holifield Radioactive Ion Beam Facility (HRIBF). We have designed a gas-filled radio frequency quadrupole ion cooler equipped with provisions for retarding energetic negative-ion beams to energies below thresholds for electron detachment at injection and for re-acceleration to initial energies after the cooling process. The device has been used to cool several ion beams with initial energy spreads, DeltaE > 10 eV to final energy spreads, DeltaE similar to 2 eV FWHM, including O- and F-. Overall transmission efficiencies of similar to14% for F- beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions. (C) 2002 Elsevier Science B.V. All rights reserved.