Development and test of iron-free quadrupole lenses with high magnetic flux densities

Abstract

Iron-free magnetic quadrupole lenses have been developed for the focusing of energetic bunched heavy-ion beams. These devices are operated in a pulsed mode and provide very strong magnetic fields. A magnetic flux density of more than 14 T has been reached in a 100 mm long quadrupole with a 20 mm wide aperture, which corresponds to a magnetic flux density of ∼1400 T/m. The pulse duration of the applied electric current is approximately 300 μs with a flat top of several μs. The calculated and measured field properties of the quadrupoles are presented. In a first test experiment with a fast-extracted 650 MeV/u 197Au 79+ beam (bunch length ∼500 ns) at GSI the focusing properties could be demonstrated. As a possible application the ion-optical design of a condenser lens system will be presented. With this system the phase-space enlargement in a nuclear reaction target can be significantly reduced, thus leading to an increased collection efficiency of a fragment separator or, more general, of any ion-optical device. In particular this is advantageous for injection of secondary beams into a storage ring.