Collisional Cooling of Negative Ion Beams

Investigations have been conducted to determine the feasibility of using collisional cooling for reducing the energy spreads and, consequently, the emittances of negative-ion beams. We have designed a gas-filled RF-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 high energies after the cooling process. The device has been used to cool O- and F- ion beams with initial energy spreads, ΔE > 10 eV to final energy spreads, ΔE ∼ 2 eV FWHM. Overall transmission efficiencies of ∼14% for F- beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions