Analysis of parameters affecting beam gauge performance

Beam gauges have been used in the last decade or so far measuring the inter nal azimuthal compressive coil stresses in superconducting magnets, In earl y model Large Hadron Collider Interaction Region (LHC IR) quadrupoles teste d at Fermilab, the beam gauges indicated excessively high amounts of inner and outer coil prestress during the collaring process, inconsistent with th e coil size and modulus data. In response to these measurements, a simple m echanics based quantitative understanding of different factors affecting be am gauges has been developed. A finite element model with contact elements and non-linear material behavior, confirmed with experimental results, was developed. The results indicate that a small plastic deformation of either the beam or the backing plate can cause significant errors in the measured stress values. The effect of variations in coil modulus and support boundar y conditions on beam gauge performance are also discussed.