Extensions to the HELIUM code to handle intense X-ray light

The X-ray free electron lasers currently being built promise light of sufficient intensity to cause direct double photoionization of the inner K-shells of Ne and Ar atoms. The Ne and Ar K-shell electrons experience a binding energy that is almost the same in the neutral atom as in the corresponding two-electron ion, Ne8+ or Ar16+. We report on new numerical methods we have implemented for calculating double ionization rates for these two-electron positive ions interacting with an intense X-ray free electron laser pulse. The numerical method builds upon an existing code (HELIUM) for solving the full-dimensional time-dependent Schrodinger equation that, operating within the electric dipole approximation, has found successful application in the optical to XUV wavelength range. The primary extensions to HELIUM are the inclusion of magnetic dipole and electric quadrupole interaction terms appropriate to extreme laser intensities and wavelengths approaching atomic dimensions.