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The ultra-low mass cylindrical drift chamber designed for the MEG IIexperiment is a challenging apparatus made of 1728 phi = 20 micron gold platedtungsten sense wires, 7680 phi = 40 micron and 2496 phi = 50 micron silverplated aluminum field wires. Because of electrostatic stability requirementsall the wires have to be stretched at mechanical tensions of about 25, 19 and29 g respectively which must be controlled at a level better than 0.5 g. Thischamber is presently in acquisition, but during its construction about 100field wires broke, because of chemical corrosion induced by the atmospherichumidity. On the basis of the experience gained with this chamber we decided tobuild a new one, equipped with a different type of wires less sensitive tocorrosion. The choice of the new wire required a deep inspection of itscharacteristics and one of the main tools for doing this is a system formeasuring the wire tension by means of the resonant frequency technique, whichis described in this paper. The system forces the wires to oscillate byapplying a sinusoidal signal at a known frequency, and then measures thevariation of the capacitance between a wire and a common ground plane as afunction of the external signal frequency. We present the details of themeasuring system and the results obtained by scanning the mechanical tensionsof two samples of MEG II cylindrical drift chamber wires and discuss thepossible improvements of the experimental apparatus and of the measuringtechnique.

The measuring systems of the wire tension for the MEG II Drift Chamber by means of the resonant frequency technique