Abstract for JLAB Technical Note 00-016

The High Resolution Spectrometers in Hall A at Jefferson Laboratory have been instrumented with state-of-the-art Vertical Drift Chambers designed and constructed by the Nuclear Interactions Croup at MITLNS in conjunction with the Physics Division at Jefferson Lab. These chambers rely on a unique, high cell-density design made possible by the absence of field-shaping wires. Each chamber has an inert per-plane resolution for S-cell cosmic ray track of 145 mu-m FWHM when operated on the bench at -4.8 kV with argon-isobutane gas, and 225mu-m FWHM for 5-cell electron tracks when operated in the High Resolution Spectrometer detector stack a t -4.0 kV with argon-ethane gas. The design and construction facilitates wire placement and replacement to 50mu-m, very low dark current, and no crosswalk. The detectors have been in almost continuous use since April 1996, providing reliable, high-resolution charged-particles tracking data for the hall A physics program.

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