Ion sources for fission fragment accelerators

Abstract

At the Grenoble and Munich high-flux reactors fission fragment accelerators are under design which will deliver beams of very neutron-rich fission products with a final energy between 3 and 6 MeV/u. In order to obtain an efficient acceleration in a compact accelerator, charge conversion of the 1+ ion beams from the in-pile ion source to a q/A⩾0.16 has to take place. In the chain from production to acceleration, ion sources are the key elements to reach high beam intensities of over 1010 s−1. For the in-pile part the target-ion source assembly has not only to be very efficient, but should also be highly selective for the desired elements (which go from nickel to europium) on one hand and robust against the hostile environment (high neutron and gamma flux) on the other hand. Foreseen types are a surface ionization source, which could also be run as laser ion source for resonant photo ionization, and, for rare gases, a plasma ion source coupled via a transfer line to the target. For the charge state breeding several different schemes are considered: the combination of a Penning trap for bunching, cooling, and mass separation and an electron beam ion source (EBIS) as charge breeder, similar to REX-ISOLDE, an EBIS with direct injection of a dc beam of 1+ ions (“accu-EBIS”) or an electron cyclotron resonance ion source (ECRIS) with either continuous or bunched extraction. The EBIS may provide higher charge states, whereas the ECRIS is able to work with much higher beam intensities and allows cw-operation. The advantage of each scheme is explained and some design requirements of the different sources are presented.