CAPACITIVE FORCE SENSORS FOR PRESTRESS IN ACCELERATOR MAGNET COILS

摘要

The capacitive force sensors are set up to determine the compressive stress in the collared coil assemblies of superconducting quadrupole magnets throughout assembly and cold testing. The sensors are designed as printed circuits, consisting of an alternated stack of dielectric and electrodes. The dielectric is a polyimide film without adhesives, and the electrodes are made of copper. Compressive stresses bring about a variation in the thickness of the dielectric and thus, capacitance. The calibration curves determine the force as a function of the capacitance and the temperature. The first results are encouraging as the sensors exhibit near linear capacitance-force curves, a low hysteresis and a good accuracy. The sensors are insensitive to magnetic field. The paper describes the design of the sensors, reviews the results of characterization and shows an application.