R&D work for a GEM-based high resolution TPC for the ILC

We report on R&D work for a time projection chamber (TPC) at the International Linear Collider (ILC). A high resolution TPC with gas amplification based on micropattern gas detectors is one of the options for the main tracking system at the ILC detector. The physics to be studied and the environment at the ILC pose new challenges to the performance of all detector components. For instance the momentum resolution of the tracker should be improved by an order of magnitude with respect to LEP detectors. Significant progress towards this goal has been achieved recently and we report here on results of our groups which are studying a TPC concept with triple gas electron multiplier (GEM) structures for gas amplification. The required spatial resolution of 100 μm has been achieved in measurements with a prototype TPC in high magnetic fields. The problem of ion backdrift has been studied and found to be significantly reduced in such GEM structures. In addition, a low mass TPC field cage has been designed and constructed demonstrating a way to minimise the total radiation length of the ILC tracker. A detailed simulation for a TPC has been developed. Simulations concerning the background at the ILC are ongoing.