Mode Conversion and Period Doubling at Plasma-$\beta$ Unity in an Alfv\'en-Wave Experiment with Liquid Rubidium

Abstract

We report Alfv\'en-wave experiments with liquid rubidium at the Dresden High Magnetic Field Laboratory (HLD). Reaching up to 63 T, the pulsed magnetic field exceeds the critical value of 54 T at which the Alfv\'en speed becomes equal to the sound speed (plasma-$\beta$ unity). At this threshold we observe a period doubling of an applied 8 kHz CW excitation, a clear footprint for a parametric resonance between magnetosonic waves and Alfv\'en waves.Comment: 5 pages, 4 figure