Vertical drift chambers for the Hall A high-resolution spectrometers at Jefferson Lab

Abstract

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 Group 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 inherent per-plane resolution for 5-cell cosmic-ray tracks of 145 μm FWHM when operated on the bench at −4.8 kV with argon–isobutane gas, and 225 μm FWHM for 5-cell electron tracks when operated in the High-Resolution Spectrometer detector stack at −4.0 kV with argon–ethane gas. The design and construction facilitates wire placement and replacement to 50 μm, very low dark current, and no cross-talk. The detectors have been in almost continuous use since April 1996, providing reliable, high-resolution charged-particle tracking data for the Hall A physics program. A complete overview of this project is presented.