Wobbler facility for biomedical experiments at Bevalac

A new method has been developed to deliver large uniform fields of accelerated heavy ions without resorting to the use of scattering material in the beam. The charged particle beam is made to sweep, painting a circle at the target, by a pair of dipole magnets placed in tandem with their field axes pointing orthogonally and powered sinusoidally but 90 degrees out of phase from each other. By superimposing several circles of appropriate diameters and intensities, large (up to 30 cm in diameter for 670 MeV/nucleon ions), uniform (+-2% in intensity) fields are delivered. A secondary emission monitor, three multielement ionization chambers, and two dual-plane multiwire chambers monitor the delivered dose and dose uniformity at the target. New ridge filters are developed to spread Bragg peaks of wobbled beams. Measurements of the beam quality, i.e., dose-averaged and track-average LET, have been made with a thin silicon dE/dx counter and thick germanium solid state detector telescope (BERKLET) at various positions in the wobbled beams. The wobbler system is used for biomedical experiments from the beginning of 1985