The spin physics program is an important part of the LHE JINR scientific program. An intensive study of polarization phenomena was carried out at the Dubna 4.5 Gev/nucl. synchrophasotron, using cryogenic source of polarized deuterons (↑D+) POLARIS. There is a proposal to make a polarized deuteron beam in the new accelerator Nuclotron to continue the spin physics experiments. The Nuclotron has a short one‐turn injection (8 μs) of positive ions at present. To increase the intensity of the accelerated polarized beam up to 0.7–1*1010↑d/pulse a multyturn charge exchange injection of negative ions (20–30 turns) should be applied. It is realized by injection into the accelerator of ↑D− ions and stripping them inside the ring. The source POLARIS is reconstructed into the ↑D− source now. The existing ↑D+ cryogenic charge exchange ionizer modified into the ↑D− ionizer. The 10 mA H− plasma beam have been measured at a test bench. The tests of the ionizer are in progress.