CLAS Drift Chambers

Charged Track Event in CLAS showing signals in all 6 superlayers of 2 drift chamber sectors

Charged particles in CLAS are tracked by drift chambers which are arranged in three regions: Region 1 is located closest to the target, within the (nearly) field free region inside the Torus bore, and is used to determine the initial direction of charged particle tracks. Region 2 is located between the Torus coils, in the region of strong toroidal magnetic field, and is used to obtain a second measurement of the particle track at a point where the curvature is maximal, to achieve good energy resolution. Region 3 is located outside the coils, again in a region with low magnetic field, and measures the final direction of charged particles headed towards the outer Time-of-Flight counters, Cerenkov counters and the Electromagnetic Calorimeters.

All three regions consist of six separate sectors, one for each of the six sectors of the CLAS. Each region within a given sector contains one axial superlayer with up to 1200 sense wires in six layers (4 layers in the case of Region 1) and one stereo superlayer with sense wires in six layers at an angle of 6 degrees with respect to the axial wires. The wires are arranged into a hexagonal pattern, with up to 192 sense wire in each layer. Each superlayer is surrounded with a row of guard wires to minimize edge effects. Click here for a picture showing the CLAS cryostat with all drift chambers installed.

Additional Links for information relevant to the CLAS drift chambers:

• Extensive information on the drift chambers (hardware status, monitoring, data analysis and Region 1 pictures) can be found on Dan Carman's Web page.
• A list of useful links for shift takers (shift taker's manuals).
• Minutes of Drift Chamber/Tracking meetings and other relevant email messages can be found in the CEBAF email archives for CLAS_DRIFT_CHAMBERS. Minutes of some 1997 meetings can be found on Rich Thompson's Web page.

• The U. of Pittsburg group has a Web site with pretty pictures from the Region 1 construction. The Region 2 group at ODU also has set up an extensive Web site on the Region 2 chambers.

• Results from a recent analysis of Time Based Tracking (TBT) by Liming Qin can be found in the following directory.
•  Junho Yun has written up the procedure used for Drift chamber calibration for EG1 (among others), based on the SSLT program.
• George Jacobs has placed the DC and Cerenkov Gas Systems manuals and drawings on the web.

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