Prototype studies and design considerations for the CLAS Region 2 drift chambers

The CEBAF Large Acceptance Spectrometer (CLAS) has recently been commissioned in Hall B of the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The six “Region 2” drift chambers, built by Old Dominion University with technical support from Jefferson Lab, are located between the coils of the CLAS super-conducting toroidal magnet. The endplates were constructed from non-conducting fiberglass in order to eliminate eddy-current forces during possible magnet quenches. The non-conducting endplate allowed the use of compact wire connecting and signal transfer hardware, thus minimizing the loss of acceptance of the Region 2 chambers. Wires were positioned by flared trumpet-shaped metal feedthroughs that were glued directly into precision holes drilled into the endplates. ort test results from two prototype chambers. A single-cell prototype proved general functionality of the endplate/feedthrough design and showed that the active area of the chamber starts approximately 10 mm from the end of the sense wire. A 36-cell prototype achieved a tracking resolution of better than 150 μm with various gas mixtures.