Performance of the ATLAS Transition Radiation Tracker Readout with High Energy Collisions at the LHC

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three subsystems of the ATLAS Inner Detector containing close to 350,000 thin-wall drift tubes (straws) operated with a Xenon-based gas mixture. The TRT data acquisition uses two separate front-end ASICS: the ASDBLR (analog) and DTMROC (digital). The eight-channel ASDBLR (Amplifier, Shaper, Discriminator and BaseLine Restorer) provides a three level out using two thresholds: a low one for tracking and a high one for electron identification. Two ASDBLR chips input into a single, sixteen-channel DTMROC (Digital Time Measurement and ReadOut Chip), which encodes the time over low (high) threshold in 3.125 ns (25 ns) time steps in a programmable depth pipeline awaiting a level 1 trigger. When a level 1 trigger is received, three LHC bunch crossings worth of data (75 ns) are read out. The DTMROC also provides a "Fast-OR" signal of its inputs, which has been utilized to build a level 1 trigger for cosmic rays traversing the ATLAS Inner Detector. The "Fast-OR" trigger was extremely useful during the commissioning of ATLAS and more recently to time-in the ATLAS subdetectors after winter shutdowns. This talk will describe the TRT readout electronics and data acquisition, with emphasis on the experience gained during the first two full year of operation. The performance will be illustrated with the excellent results obtained with the TRT for cosmic rays as well as for the first high energy proton-proton collisions provided by the LHC.