Isentropic compression of solid CO$_2$ at megabar pressures

Experiments on the dynamic isentropic compression of solid CO$_2$ samples by the megabar pressure induced by the superstrong magnetic field of an explosive magnetic generator have been performed with the X-ray diffraction detection of the state of the compressed samples. The generator operation is based on the fast compression of the initial magnetic flux in the cavity of the generator by a conducting cylindrical liner accelerated by the products of the explosion of a cylindrical explosive charge. Two points at pressures of 349 and 459 GPa on the compressibility diagram of CO$_2$ have been determined in the experiments, where the degree of compression $\rho/\rho_0$ of CO$_2$ has reached currently highest values of 3.90 and 4.02, respectively. Comparison has shown that theoretically calculated equations of states for crystal phases of CO$_2$ almost completely reproduce the experimental results, which confirms a high accuracy of theoretical predictions and the identity of the experimental and theoretical equations of states of CO$_2$ modifications stable at high pressures.