Rayleigh-Taylor instability for immiscible fluids of arbitrary viscosities: Magnetic levitation investigation and theoretical model*

A magnetic field gradient was used to draw down a low density paramagnetic fluid below a more dense fluid in a Hele-Shaw cell. \ On turning off the field a Rayleigh-Taylor instability was observed \textit{in situ}, and the growth of the most unstable wavevector was measured vs. time. \ A theory for the instability that permits different viscosities for two immiscible fluids was developed, and good agreement was found with the experimental results. The technique of magnetic levitation promises to broaden significantly the accessible parameter space of gravitational interfacial instability experiments.