Detection of a Flow Induced Magnetic Field Eigenmode in the Riga Dynamo Facility

In a closed volume of molten sodium an intense single-vortex-like helical flow has been produced by an outside powered propeller. At a flow rate of $0.67{\mathrm{m}}^3/\mathrm{s}$ a slowly growing magnetic field eigenmode was detected. For a slightly lower flow, additional measurements showed a slow decay of this mode. The measured results correspond satisfactorily with numerical predictions for the growth rates and frequencies.