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Particle Detection Wire (Drift Wire) General Information "Drift chambers are comprised primarily of a gas volume through which fine wires are stretched. Drift chambers are used to track charged particles emanating from nuclear interactions. Charged particles leave trails of ions in the gas volume as they strip electrons from the gas molecules. The charge from the ionized gas is amplified by an avalanche as freed electrons are accelerated by a strong electric field toward wires which collect the charge. Signals produced by the collected charges are further amplified by exterior electronics and processed by a data acquisition system which maps the track of the particle by registering which wires fired by recording the time it took the electrons to ‘drift’ to the read-out wires. In addition to tracking charged particles, drift chambers can be also used to determine the amount of energy deposited in the drift chamber gas. This information helps to identify the type of particle passing through. The proper operation of the drift chamber depends strongly on the quality and diameter of the fine wires stretched across the gas volume" - CEBAF The wires used are classified as "sense wires" (anode wires) and "field wires" (cathode wires). The sense wires are the read-out wires for the chamber. The field wires provide the electrical potential to achieve satisfactory operation of the drift chamber. The electric field is set high enough to cause the electrons from the gas to "avalanche" as they near the surface of the sense wires. Because of the relatively high electric field on the surface of the cathode, it is important that the wire be smooth and free of defects that would cause electrons to be sputtered off the wire and to create false signals. Cathode wires are normally larger in diameter than the anode wires. The choice of the diameter of the wires varies by research facility. The requirements placed on the production of the wires presents an interesting demand on the manufacturer. Because of the relative small diameter required, normally less than 200µ, the manufacturing process requires complete control. Even the smallest defect in the starting raw material appears to be magnified at the finished size. The process, drawing, annealing (if required), plating (if required), and final spooling must be constantly monitored. California Fine Wire Company has developed these controls in its’ "Ultra Finish" process. General Characteristics Ultra Finish: Special process used to manufacture wire with extremely smooth surface, free of defects and uniform wire diameter. Diameter tolerance - .000025" Out of roundness tolerance - .000025" Low Creep Ratio: Special process used to manufacture wire with minimal creep ratio. Thus eliminating wire sagging and enhances the life of the chamber. General Materials for Particle Detection Wire (Drift Wire)
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