Double-to-single photoionization ratio of plasma-embedded helium atom at X-ray energies

The double photoionization of helium by absorption of a high-frequency photon have gained considerable interest in theoretical [1-2] and experimental [3] studies during the last decades. In this work, we have investigated the asymptotic ratios of double-to-single photoionization of plasmas-embedded helium atom at very high photon but non-relativistic energies in the framework of the Debye model for weakly coupled plasmas [4]. The ratio of double-to-single photoionization for free atom is determined as 1.644{\%}, in good agreement with the synchrotron measurements [3] and other theoretical predictions [1, 2]. The asymptotic ratio of double-to-single photoionization cross-sections for different screening parameters along with the single, the double, and the total photoionization asymptotic cross sections will be presented at the meeting. [1] R. C. Forrey, et al., Phys. Rev. A \textbf{51}, 2112 (1995). [2] R. Krivec, M. Ya. Amusia, and V. B. Mandelzweig, Phys. Rev. A \textbf{62}, 064701 (2000). [3] J. C. Levin \textit{et al.}, Phys. Rev. Lett. \textbf{67}, 968 (1991); \textbf{76}, 1220 (1996). [4] S. Kar and Y. K. Ho, Phys. Rev. A, to be published (2008).