Test of a small prototype of the COMET cylindrical drift chamber

The performance of a small prototype of a cylindrical drift chamber (CDC) used in the COMET Phase-I experiment was studied by using an electron beam. The prototype chamber was constructed with alternating all-stereo wire configuration and operated with the He-iC$_{4}$H$_{10}$ (90/10) gas mixture without a magnetic field. The drift space-time relation, drift velocity, d$E$/d$x$ resolution, hit efficiency, and spatial resolution as a function of distance from the wire were investigated. The average spatial resolution of 150 $\mu$m with the hit efficiency of 99% was obtained at applied voltages higher than 1800 V. We have demonstrated that the design and gas mixture of the prototype match the operation of the COMET CDC.