Performance of a large area drift chamber operating with a He-iC(4)H(10) mixture

We have measured the performances of a large (115 x 57) cm(2) planar drift chamber filled with a He-iC(4)H(10) (70-30) mixture in a beam. The spatial resolution is better than 100 mu m along the whole drift cell. Local and integrated efficiencies are 99.3 +/- 0.2% and 98.1 +/- 0.2% respectively. The coordinate along the wire is measured by the charge division method and the resolution at the center is 0.61% of the wire length.