THE CHAOS SPECTROMETER FOR PION PHYSICS AT TRIUMF

The Canadian high acceptance orbit spectrometer (CHAOS) is a unique ma gnetic spectrometer system recently commissioned for studies of pion i nduced reactions at TRIUMF. It is based on a cylindrical dipole magnet producing vertical magnetic fields up to 1.6 T. The scattering target is located in the center of the magnet. Charged particle tracks produ ced by pion interactions there are identified using four concentric cy lindrical wire chambers surrounding the target. Particle identificatio n and track multiplicity are determined by cylindrical layers of scint illation counters and lead-glass Cherenkov counters, which also provid e a first level trigger. A sophisticated second level trigger system p ermits pion fluxes in excess of 5 MHz to be employed, The detector sub tends 360 degrees in the horizontal plane, and +/-7 degrees out of thi s plane for a solid angle coverage approximately 10% of 4 pi sr. The m omentum resolution delivered by the detector system is 1% (sigma).