Central Drift Chamber Commissioning
Introduction
This document describes the commissioning process for the GlueX central drift chamber (CDC).
Commissioning and Alignment with Cosmic Events
The CDC consists of 3522 8mm radius aluminum plated kapton straw tubes. Each tube contains a 20 micron diameter gold-plated tungston wire strung in the middle of the straw. The wires are operated at positive potential, about 2kV, above the grounded straw tubes. The chamber is filled with a 50--50 mixture argon and carbon dioxide, and the gas mixture combined with the nominal atmospheric pressure of the gas determines the voltage operating point of each wire. Each wire has been brought to high voltage, and cosmic signals observed several times during the commissioning process. First at Carnegie Mellon University, before the chamber was transported to Jefferson Lab. Again, at Jefferson Lab when the chamber was in a test lab, and finally, after the chamber was installed and hooked up in its final position in Hall D. As of the date of this report, all channels are operating, and considered to be at their nominal voltage.
A trigger has been set up to collect events which are seen by both the barrel calorimeter (BCAL) and the CDC. This trigger runs at a rate of few Hz, with about 0.5Hz, yielding CDC data. In the time between the middle of July and the middle of October, it should be possible to run these trigger on nights an weekends. A reasonable estimate is probably 50 hours per week of data collection, which yields about 90,000 events per week. This should yield sufficient data to run initial passes of the calibration and alignment procedures, but a dedicated cosmic run should be planned after the November commissioning run. It is currently estimated that about 300,000 reasonable CDC events are needed for alignment. This is probably just compatible with the night and weekend running prior to the November run. The following activities are expected to be done using cosmic events.
- Study and minimize noise observed on the CDC as installed. This study does not require cosmic events, but work on making sure that the grounding and isolation of the CDC is fully optimized and set up according to specifications.
- Measure efficiency of hits on individual wires being used on tracks. This study can be carried out with about 50,000 events with good tracks in the CDC.
- Final relative alignment between the CDC and the BCAL. An initial study can be carried out with on the order of 50,000 events with good tracks in the CDC
- Optimization of the time and amplitude algorithms that will run on the FPGAs in the Flash 125 modules. This study requires around 10,000 events with good tracks in the CDC.
- Final alignment of relative wire positions in the CDC. This requires ~300,000 good cosmic events.
