Field Quality Measurements at High Ramp Rates in a Prototype Dipole for the FAIR Project

Brookhaven National Laboratory (BNL) has built a prototype superconducting dipole for the Facility for Antiproton and Ion Research (FAIR) at GSI that can be ramped at a high rate (1–4 T/s). To characterize the field quality at such high ramp rates, a measurement system consisting of 16 printed circuit windings was developed. In this system, the signals induced in all the windings as the magnet is ramped are analyzed to obtain the field harmonics. Initial measurements with this system suffered from somewhat poor resolution of the ADCs used for data acquisition. Also, only a few low order harmonics could be obtained with the 16 signals. These drawbacks have been addressed by replacing the ADCs with HP3458A voltmeters and by combining data taken with two different orientations of the probe. This has allowed us to measure very precisely ($\sim$10 ppm of the dipole field) all the harmonics up to the 26-pole at ramp rates up to 4.3 T/s. The data analysis and results with this improved system are presented.