Performance evaluation of Low-Pressure Multi-Wire Drift chamber for RI beam

We are developing Low-Pressure Multi-Wire Drift Chambers (LP-MWDCs) as tracking detectors of light heavy ions with $Z$ = 1--8 at 100--300$A$ MeV in RIKEN RI Beam Factory (RIBF). The thickness of the LP-MWDCs is designed to be about $10^{-4}$ of the radiation length to reduce multiple scattering. The LP-MWDCs have 3 anode layers ($X$, $U$, and $Y$). The anode $U$ is tilted at 30$^\circ$ with respect to the anode $X$. Pure isobutane gas is used at a pressure of 10~kPa. In order to discriminate signals of the ions from the ones of $\delta$-rays, data equvalent to pluse heights are also recorded as well as the standard timing data. The performances of the LP-MWDCs were evaluated for RI beams such as $^{6}\rm{He}$, $^{12}\rm{B}$, and $^{12}\rm{N}$ at 200--250$A$ MeV. We report the efficiencies and position resolutions as a function of ions and high voltages.