Observation of thermal effects on the LEP wire scanners

A new wire scanner was installed in LEP for the 1994 run. It incorporates an improved mechanical design for the wire movement and can accept three mechanisms, two horizontal and one for vertical scans. Wires of different materials and of various diameters were fixed to new ceramic forks. Viewing ports were installed opposite each wire to allow the direct observation of the wires with a TV camera during a scan. Recordings of the wire resistance and of the light emitted by the wire were made during scans. These observations have provided the first experimental evidence of the various wire heating mechanisms by the beams. The heating due to coupling to the electro-magnetic field generated by the beam exceeds the heating due to particle collisions. An evaluation is made on the behaviour of carbon and quartz wires. Conclusions are drawn for defining a safe operating regime.