Wire Chamber Gas System

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HallD Wire Chamber Gas System The HallD has two wire chamber detector systems the Central Drift Chambers (CDC) and the Forward Drift Chambers (FDC). Both detectors operate with a mixture of Argon and CO2. The Gas system is designed to operate independently for the two detectors and individual gas mixtures can be selected. A basic over view of the gas system is shown in the two pictures below:
Halld gas systemA.gif and Halld gas systemB v2.gif

The basic concept is that high pressure gas is provided from gas cylinders at high pressure. Two independent supply sources can be selected through solenoid vales for easy swapping and cylinder exchange. A high pressure regulator reduces the gas pressure from up to 3600 psig down to the range of 25 psig. This is available independently for the Argon gas and the CO2 gas. Two mass flow controller for both gas types are used to control the gas flow into two independent gas buffer volumes one for the FDC and one for the CDC. The Argon and CO2 gas will be mixed in these two volumes. These buffer volumes are equipped with a pressure sensor and a pressure relieve valve. At this point two gas lines will feed the gas mixture down into the hall. This concludes the first picture.
The second pictures shows the distribution of the gas into the different detector systems. The gas flow is controlled by mass flow controllers and the pressure is reduced again from about 1 bar above atmospheric pressure down to about 60 pascal or 0.08 psig above atmospheric pressure. A bypass system if available to decouple the detector from the gas supply. A bubbler at the input to the wire chamber protects against over pressure. At the exhaust of the chambers an additional bubbler protects the chamber against back pressure and oxygen intake. Solenoid valves are used to selectively choose one gas exhaust line to monitor the gas for the oxygen content.
Tracking Chamber Gas system : A presentation at Monitor/Controls meeting.