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The DT system operation since the 2010 LHC start up is remarkably smooth. All parts of the system have behaved very satisfactorily in the last two months of operation with LHC pp collisions. Disconnected HV channels remain at the level of 0.1%, and the loss in detector acceptance because of failures in the readout and Trigger electronics is about 0.4%.
The DT DCS-LHC handshake mechanism, which was strengthened after the short 2009 LHC run, operates without major problems.
A problem arose with the opto-receivers of the trigger links connecting the detector to USC; the receivers would unlock from transmission for specific frequencies of the LHC lock, in particular during the LHC ramp. For relocking the TX and RX a “re-synch” command had to be issued. The source of the problem has been isolated and cured in the Opto-RX boards and now the system is stable. The Theta trigger chain also has been commissioned and put in operation.
Several interventions on the system have been made, profiting from the LHC technical stops, though none of them would have caused serious degradation of the system performance.
The reliability of the Anderson Power connectors used in the CAEN power supplies of the DT low voltage system remains a point of concern. After a major campaign to replace the 670 connectors during the past shutdown, there have already been 4 instances of overheating during the last 5 months. Even though this rate is lower than what we had last year (46 instances), the effectiveness of the solution applied in the last shutdown is not completely satisfactory. Studies aimed at an optimal solution are still ongoing.
The control and monitoring software continues to evolve with the aim of providing a fast and concise summary of the status of the system. Improvements are happening on a daily basis, not only to be able detect efficiently any problems, but also focusing in providing longer term summaries. Consequently, a lot of effort is being put on the Trigger Supervisor, in the DQM and in the Web Based Monitoring tools.
Stability of the DT system continues to be a source of pride and as a result the operation will require very soon only an on-call shifter.
In a two day workshop (April 19 to 21) the evolution of detector calibration and performance with increasing integrated luminosity was discussed and the performance of the calibration procedures reviewed on the basis of the small statistics so far accumulated. The group is ready and eagerly waiting for more data.
by C. Fernandez Bedoya and M. Dallavalle