UBC Theses and Dissertations

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UBC Theses and Dissertations

Development of a high magnetic field drift chamber for the chaos spectrometer Hofman, Gertjan J.


Design considerations for the Canadian High Acceptance Orbit Spectrometer (CHAOS) led to a set of apparently mutually inconsistent requirements for the inner (WC3) drift chamber. This detector chamber has to be cylindrical, of low mass, have excellent spatial resolution (<200 µm) and operate in a variable magnetic field of up to 1.6 T. This thesis describes the investigations which culminated in the testing of a unique new drift chamber which satisfies all the requirements for the CHAOS WC3. An overview is given of present drift chamber technology and its application in high magnetic fields. Methods to obtain the space-time relationship are reviewed. In particular, the integral, displacement and trackfitting methods have been applied to prototype chambers. A trackfitting algorithm developed to calibrate a set of wire chambers and correct systematic wire position offsets is presented. Three types of prototype chambers were designed and constructed. Tests were carried out in beams at TRIUMF to measure the spatial resolution of these chambers in a 1 T magnetic field. The results indicate that a resolution of as σx ≈ µm can be achieved. A simplified model of electron transport through gasses is used to explain electron drift properties in high magnetic field chambers. A method to resolve the usual left-right ambiguity, proposed within the framework of this model, involves the comparison of the charge induced on diagonally opposed cathode strips mounted parallel to the potential wires. After extensive simulations using the Garfield drift chamber program, a final, unique prototype was designed on which the WC3 chamber to be built for CHAOS is now based. A final beam test in a 1.6 T magnetic field showed that the left-right problem is resolved for track angles between -45° and +45°.

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