TPC prototype readout with GEMs and TimePix

This contribution reports on measurements with a GEM based TPC using the TimePix CMOS ASIC as a charge collecting readout anode. Tests on a small prototype with a 6mm drift space were performed in a 5 GeV electron beam at DESY. A Si-strip-telescope serves as spatial reference for the measured tracks. Two GEMs of different hole- and pitch-geometries are tested. The point resolution for short drift distances is better than 20 μm. A time resolution as good as 8 ns at 100MHz clock frequency is achieved. Furthermore, experimental studies with an enlarged pixel size are addressed.