Flow pattern dynamics in convecting liquid helium - art. no. 045301

We present experimental data which correlate, thermal measurements and flow visualization in convecting liquid He-4. For a small range R-C<R<R-1 of th e Rayleigh number R above the convection threshold value R-C a robust stati onary pattern is observed. This pattern exhibits periodic pulsation when R> R-1, generating thermal oscillations as in earlier reports. At higher R val ues the time dependence becomes aperiodic with the surprising appearance of spiral-defect chaos at an aspect ratio smaller than has previously been re ported.