Doorway state expansion approach to coupled channels problems and application to heavy ions

The doorway expansion method is extended to coupled channels problems in low energy heavy ion collisions. As a test, it is applied to an exactly soluble model and the convergence problem is discussed. The method is then applied to heavy ion elastic scattering due to the optical potential and to a simple coupled channels problem. In both cases very good convergence is reached with six doorway states. The calculation with a single doorway is shown to be much better than the DWBA. 9 refs., 8 figs., 1 tab