Numerical analysis of the space charge effect in a MWPC

A numerical calculation code was developed by employing a two-dimensional continuum model for the detailed design of MWPC (Multi-Wire Proportional Chamber) detectors. The temporal evolutions of electron and ion density distributions were evaluated for the time period required by ions to travel between the anode and the cathode. The temporal evolution of the electric field was also calculated to take into account the space charge effect caused by ions. The output signals of an anode, which were multiplied by electron avalanche, were estimated from an electron flux into anodes. By comparing the gain curve evaluated from the output signals with that obtained by theoretical calculations, we confirmed that the numerical code is capable of quantitative estimations of the gas gain. From these results, we discuss the dependence of the output signal on the space charge effect, and the relations between the ion distribution and the space charge effect.