Experimental study of quasiperiodicity in a hydrodynamical system

In this paper we present an experimental study of quasiperiodicity in a hydrodynamical system. Partial results have already been reported. We present them now in more detail as well as the experiment itself. The system studied is Rayleigh-B\'enard convection in mercury in a time-dependent state with one limit cycle. An external oscillation is coupled to this limit cycle by passing an ac electrical current through the mercury and embedding the system in a horizonal magnetic field. We have measured the fractal dimension of the complement of all locked states on the critical line. Local properties of this line, such as scaling indices, were also measured for two different irrational routes followed. The results are in good agreement with quantitative predictions of the circle map.