The Polarized-Target System for the SpinQuest Experiment at Fermilab

The SpinQuest experiment at Fermilab aims to measure the Sivers asymmetry for the $\bar{u}$ and $\bar{d}$ sea quarks in the range of 0.1 $< x_{B} <$ 0.5 using the Drell-Yan production of dimuon pairs. A nonzero Sivers asymmetry would provide an evidence for nonzero orbital angular momentum of the sea quarks. The proposed beam intensity is 1.5~$\times$~10$^{12}$ of 120 GeV unpolarized proton/sec. The experiment utilizes a target system consisting of a 5T superconducting magnet, transversely polarized NH$_3$ and ND$_3$ targets, a $^4$He evaporation refrigerator, a 140 GHz microwave source and a large pumping system. The expected average target polarization is 80$\%$ for the protons and 32$\%$ for the deuterons. The polarization will be measured with three NMR coils per target cell. A quench analysis and simulation in the superconducting magnet are performed to determine the maximum intensity of the proton beam before the magnet become resistive. A GEANT based simulation is used to calculate the heat deposited in the magnet and the subsequent cooling processes are modeled using the COMSOL Multiphysics.