A high efficiency RF quadrupole ion beam cooler for negative ions

A gas-filled RF quadrupole ion beam cooler has been significantly improved for cooling negative ion beams. Electron detachment plays a significant role in determining the transmission of negative ions. It has been suggested that collisions with the residual buffer gas in the deceleration and injection region of the ion beam cooler, where the ions still possess relatively large energies, could result in substantial losses in negative ions due to electron detachment. The ion beam cooler is modified to improve the pumping conductance in the quadrupole entrance region for effectively removing the buffer gas and minimizing the residual gas escaping to the deceleration and injection region. This significantly reduces the collisions encountered by the ions before they are retarded to energies below the threshold for electron detachment. Overall transmission efficiencies of more than 50% have been obtained with the modified cooler for some negative ions.