The COMPASS polarized target

The spin structure of the nucleons has been investigated by studying spin dependent process of deep inelastic scattering of a polarized muon beam and a polarized nucleon target in the COMPASS experiment since 2001. In order to achieve high luminosities it is necessary to use a large solid polarized target. The target consists of two independent and oppositely longitudinal polarized cells. The cells are filled with irradiated 6LiD granulated material. One of the characteristics of the polarized target is the spin reversal by magnetic field rotation in order to cancel the systematic error. The polarized target apparatus consists of a large refrigerator providing a low temperature of below 100 mK and a high cooling power with 200-300 mK, a superconducting magnet producing 2.5 T with good field homogeneity, two high power of a few watts microwave systems producing 70 GHz for Dynamic Nuclear Polarization (DNP) and 10 NMR signals detection system for the polarization measurement. (author)