  We present a concept for control of the ion polarization, called a
transparent spin method. The spin transparency is achieved by designing such a
synchrotron structure that the net spin rotation angle in one particle turn is
zero. The polarization direction of any ions including deuterons can be
efficiently controlled using weak quasi-static fields. These fields allow for
dynamic adjustment of the polarization direction during an experiment. The main
features of the Transparent Spin method are illustrated in a figure-8 collider.
The results are relevant to the Electron-Ion Collider considered in the US, the
ion-ion collider NICA constructed in Russia, and a polarized Electron-ion
collider planned in China.
