A Time Projection Chamber (TPC) is a candidate for the central tracker of the future International Linear Collider (ILC) detectors. TPCs have already demonstrated very good performance in past collider experiments. In order to obtain one order of magnitude improvement in momentum resolution and the highest possible track recognition efficiency, the Linear Collider TPC (LCTPC) Collaboration is pursuing R&D activities to find the best state-of-the-art technology for the TPC.   For ILC the TPC would have a diameter of 3.6 m and a length of 4.3 m. It should provide 200 space points with pad readout along a particle track, with a spatial resolution of 100 μm in the Rφ plane. To achieve these performances, a TPC equipped with Micro Pattern Gaseous Detectors (MPGD) instead of Multiwire Proportional Chambers (MWPC) is needed. Therefore the LCTPC Collaboration has built a large TPC prototype (LPTPC), with a diameter of 750 mm and a length of 600 mm, which can be equipped with Micromegas or GEMs as amplification structures.

Since the end of 2008, the LPTPC has been exposed during several weeks to an electron beam of up to 6 GeV at DESY, in presence of a magnetic field of up to 1.0 Tesla. The LPTPC is not only a testing bed for several readout techniques based on MPGDs it is also a unique opportunity to understand the issues which arise when constructing such a large TPC. In this talk we will first present the experience summarized above and then focus on the preliminary results obtained recently with the LPTPC equipped with 6 Micromegas modules, at the DESY test beam T24, in a geometry allowing the recording of tracks traversing the full radial distance of the TPC. The 6 Micromegas modules have a lower anode resistivity compared to previous versions, 3 MΩ/☐, and have been equipped with the new integrated electronic Front-End boards using the AFTER chip. This geometry allows new studies that will be discussed: performance in cracks, module misalignment and distortions.

Contact : Keisuke Fujii (keisuke.fujii_at_kek.jp)
KEKDTP seminar web page : http://rd.kek.jp/seminar_01.html