OSCILLATORY INSTABILITY, LIMIT-CYCLE, AND TRANSITION TO DOUBLETS IN DIRECTIONAL SOLIDIFICATION

An oscillatory instability is experimentally evidenced in directional solidification of nominally pure succinonitrile in a unity Peclet numb er regime. It involves long-time oscillations of both cell width and c ell tip position in a nearly phase quadrature and at a wavelength equa l to twice the cell spacing. The instability displays subcritical feat ures and two instability domains, one at large cell spacing and the ot her at small cell spacing. Close to its upper stability boundaries, it succeeds in saturating onto a limit cycle; farther inside the unstabl e domains, it mediates a transition from cells to a different branch o f solution, the doublets.