Thermodynamic properties of a nonideal helium plasma at quasi-isentropic compression by a factor of 575 at a pressure of 3000 GPa

The quasi-isentropic compressibility of a nonideal helium plasma has been measured in a two-cascade spherical chamber with separated cavities with the use of an explosive charge with the mass of ≈55 kg. The experiment has been performed on an X-ray diffraction complex consisting of three betatrons and a multichannel optoelectronic system for recording X-ray images. The density of the compressed helium plasma measured at the initial pressures of the gas in the outer and inner cavities P 1 = 36.4 MPa and P 2 = 5.1 MPa, respectively, is ρ = 4.6 g/cm 3 , which corresponds to the degree of compression σ = 575 at pressure P ≈3000 GPa under the condition of strong nonideality (γ ∼ 7) and noticeable degeneracy of electrons ( n λ 3 ∼ 5). The pressure of compressed helium has been determined from the results of the gas-dynamics calculation.