Experimental studies on long-wavelength instability and spiral breakup in a reaction-diffusion system.

We investigate the behavior of spiral waves in a quasi-two-dimensional spatial open reactor using Belousov-Zhabotinsky reaction. The goal of this study is to answer two questions raised recently: Can a system sustain a stable long-wavelength modulated spiral? What causes the transition from spiral to defect-mediated turbulence? Our experimental results show that in a certain range of control parameters, a sustained long-wavelength modulated spiral is stable. The amplitude and the wavelength of modulations increase with the control parameter. As the latter is increased to across a threshold, defects are generated far away from the spiral center as a result of the neighboring two wave fronts being too close.