Vibrating Wire Field-Measuring Technique

The vibrating wire field-measuring technique presented here is dedicated to the problem of alignment of quadrupole magnets and is based on the following principle. The stretched wire has vibrational modes consisting of the fundamental mode and higher harmonics. The half wave length of the fundamental mode is equal to the length of the wire. Suppose there is a transverse magnetic field surrounding wire. If the frequency of the current in the wire is an eigenmode frequency of wire vibration, it will excite a corresponding harmonic. The strength and phase of excitation will depend on the field distribution along the wire. Using various frequencies and measuring amplitudes and phases of the resulting vibrations, one can extract information about the field distribution in order to reconstruct it. The field in turn shows the misalignment of quadrupoles. In comparison with the pulsed-wire method, the vibrating wire technique does not require the wire length to be longer than the length of the test region, and due to its extraordinary sensitivity it does not require the higher voltage for the long wire scheme. Therefore, it may be more appropriate for some projects.