Magnetic system for controlling the spin of polarized neutrons

A spin control magnetic system was developed and assembled at the JINR Laboratory of Neutron Physics (Dubna, Russia) and was tested with a beam of polarized neutrons at the POLI instrument of the FRM II reactor in Garching (Germany). This paper presents the principle of operation and a method for compensating the influence of external magnetic fields on polarization using this device. The system consists of three precession coils in a magnetic screen. The first coil allows, by changing the current in it, to ensure the rotation of the neutron spin by an arbitrary angle relative to the magnetic field inside the coil. The remaining two coils are designed to compensate for the effect of scattered magnetic fields on the beam polarization, and to preserve the polarization vector direction.