A mole for warm magnetic and optical measurements of LHC dipoles

A new rotating coil probe (a mole) has been developed for the simultaneous measurement of the magnetic field and magnetic axis of warm superconducting LHC dipoles and associated corrector windings. The mole houses a radial ro tating coil and travels inside the magnet aperture by means of an externall y driven two-way traction belt. The coil is rotated by an on-board piezo mo tor, being tested in view of future devices for cold measurements as the on ly type of motor compatible with strong magnetic fields. A virtual light sp ot is generated in the coil center by a LED source. The position of this li ght spot is measured from the outside by a system including a telescope, a CCD camera and a DSP. Jigs on reference granite tables are used to transfer the optical measurements to the magnet fiducials. We describe here the mai n characteristics and performance of the mole.