Development of a multi-grid type microstrip gas chamber

Conventional MSGCs have suffered from many difficulties such as low gas gains and sparking, etc. We have proposed a new multi-grid type MSGC (M-MSGC) in order to overcome the difficulties. New grid strips are inserted between the anode and the cathode in this new type of MSGC. Gaps between these strips are very small such as ~10 μm where one can effectively remove surface charges. Owing to the existence of grid strips of lower potentials than the anode, the field strength around the neighboring grid to the anode strip becomes very small compared with conventional small gap MSGCs. The contribution of the surface streamer to the damage is greatly suppressed because the grid electrodes decrease the electric field parallel to the surface. However, the existence of grid electrodes also screens the entire electric field upper than the substrate and we cannot observe induced signals from backside of the substrate. To overcome the difficulty, we develop a signal readout method using another patterning approach. Floating pads are placed near the cathode strip on the surface of the M-MSGC and the induced charges are read out through the pads. If the area of pads is sufficiently large and the positive charges are moving toward the pads, backside electrodes can obtain the induced charge. Collected charges on the pads are leaked through the surface resistance. An experiment has been performed and the backside signal through 2.3-mm thick glass readout of the position along the cathode strips is successfully observed