Development of a Multistep Parallel-Plate Chamber as Time Projection Chamber End-Cap or Vertex Detector

We have tested a prototype two-step parallel-plate avalanche chamber capable of large stable gains (in excess of 105) and having very good intrinsic localization and timing properties. The only active electrode consists of a printed-circuit board with densely packed readout strips alternated with small pad rows. Recording pulse-height distributions on several adjacent strips and pads, we have determined the gain characteristics of the device and its localization accuracy in the detection of soft X-rays. The results are promising, and with this device we intend to study the timing and localization properties in the detection of minimum-ionizing particles, in a geometry similar to the one of the TPC.