Fermilab electron cooling project: field measurements in the cooling section solenoid

To provide the maximum possible cooling rate for the Recycler Electron Cooling (REC), the cooling section has to be immersed into a high-quality longitudinal magnetic field. Namely, the solenoidal field of 50-150 G should have an integral of the transverse component below 1 G-cm over the whole 20-m cooling section. The transverse field components are measured by a dedicated compass-based sensor, which has been designed and manufactured at Budker INP, Novosibirsk. The paper describes results of the field measurements performed on the cooling section solenoid prototypes as well as the design and the calibration procedure of the sensor.