Asymmetric Multi-Wire Proportional Chamber with reduced requirements to mechanical precision

An asymmetric-type MWPC prototype with an inclined wire plane has been studied. It has been demonstrated that at proper choice of the negative potential on the field wires the dependence of the gain on the cathode flatness can be completely eliminated for the closer cathode. Such feature allows us to construct MWPCs with thin cathode planes and wires positioned relatively close to one of the cathodes since the requirement to the precision of cathode flatness is largely reduced. The relevance of these two advantages, especially to achieve low material budget, are presented for the prototype of the High pT Trigger Detector (HPTD) for the ALICE VHMPID detector system. A number of such designs are in operation for over a year, and have been tested with cosmic rays as well as in pion beam at the CERN PS.