The status of the ALICE TRD project

During the year 2008 the Transition Radiation Detector project of the ALICE experiment at LHC has accomplished important milestones and has progressed towards readiness for data taking. We will review the status of the project and the various ongoing activities. The chamber production was completed in 2008, so that now all 540 individual readout chambers (ROC) of TRD are ready. The chambers are equipped with front-end electronics (manufactured in industry based on our own design and tested in Heidelberg) and the readout functionality tested in Frankfurt and at GSI (on a newly setup test stand). The chambers are then shipped to Münster, where they are assembled in supermodules (each containing 30 chambers). Extensive measurements with cosmic-rays are undertaken at this stage. As the individual readout chambers are no longer accessible once the super-module is assembled, rigorous testing is necessary at this stage. For this purpose, all necessary infrastructure for the operation of super-modules has to be available in Münster and as similar as possible to the conditions found in the final installation in the ALICE pit. This includes lowand high-voltage power supplies, gas and cooling as well as computers for slow control and data aquisition. In addition, a trigger system for cosmic rays has been developed to acquire data for a first calibration pass. The assembly of a supermodule starts with the assembly of the supermodule hull including distribution of low voltage and cooling water. Afterwards, the readout chambers are installed layer by layer. Each layer undergoes tests of electronics, gas tightness, high-voltage distribution and cooling. The integration of a supermodule is concluded by several days of cosmics data taking to produce a calibration data set. The tightness of the gas volume is tested by flushing the ROCs of one layer with a mixture of argon and carbon dioxide while the pressure is regulated by a fan. The oxygen content at the outlet of the layer is a measure for the leaks in the layer. Separate tests at overand underpressure of 1 mbar allow for the distinction of diffusive and high resistity viscous leaks. The average leak conductance per chamber is less than 1 Nl/bar·h1, consistent with single ROC tests performed at GSI and well below the limit of 3 Nl/bar·h set by the cost of xenon. A large acceptance trigger for cosmic rays is used to acquire data for supermodule testing and calibration. The trigger consists of two arrays of scintillators above (40 scintillators, 220 × 173 cm) and below (50 scintillators, ∗The list of members and institutions is available at http://www-alice.gsi.de/trd 11 Nl/bar·h corresponds to a leakage of 1 ml of gas under normal conditions per hour at a differential pressure of 1 mbar Figure 1: Cosmic ray setup in Münster .