Forward Drift Chamber Commissioning
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The main procedures and configurations needed for the commissioning of the Forward Drift Chamber (FDC) system of the GlueX experiment are described below. The document assumes a certain knowledge of the detector as described in the Technical Construction Report.
Commissioning activities before the beam run
All the chambers have been tested and checked channel-by-channel multiple times during the production. Each of the four packages, after its completion, has been tested in horizontal position triggering on cosmic events with scintillator paddles. For one of the packages (the third) this test was performed with all the channels connected to the electronics.
The FDC is the only detector in the GlueX experiment that is not serviceable in its final position: once installed in the bore of the magnet, there's no access to the detector, front-end electronics, cable connections, grounding, gas and cooling system connections etc.. Pulling the FDC out of the magnet is a major operation requiring also removing of the target, the Start Counter, and the Central Drift Chamber (CDC). Therefore, all the channels have been tested multiple times during the installation and after the detector has been installed.
The main challenge is that the chambers are in vertical position and only basic performance features can be tested with cosmic rays. Triggering the DAQ system is also a problem. The FDC back-end electronics, fADC125, and F1TDCV3 modules do not allow for self triggering. So far only a trigger-less DAQ system (i.e. with a random trigger) has been used to collect data from the detector reading all the samples from the fADC125 modules. To minimize the huge amount of data, sparsification has been done in the ROCs of the crates. All this required weeks of data taking in order to have some statistics that allows to evaluate the performance of all the channels.
The following activities are expected to be done before the start of the photon beam run.
- Check the operation of the gas system, cooling system, HV and LV systems and make sure all the interlocks
trips, and alarms are working as required.
- Keep the FDC under HV and study the long term stability of the detector. Correlate the results with
changes in the atmospheric pressure and ambient temperature, and try to optimize the detector performance.
- Study the noise observed on some of the FDC channels as installed. The study needs data from the DAQ
but does not require cosmic events. Correlate this noise with the one observed on the CDC and try to find and suppress the source of the noise.
- Take cosmic data from all the channels. Optimize the thresholds. Troubleshoot faulty electronics and cable connections.
We assume that we will use a trigger from the Barrel Calorimeter made as a coincidence of the top and bottom halves of the detector. We expect also that during this commissioning phase, the firmware for the fADC125 will be developed so that the data sparsification is done on the module itself.
