A homopolar disc dynamo experiment with liquid metal contacts

摘要

We present experimental results of a homopolar disc dynamo constructed atCICATA-Quer'etaro in Mexico. The device consists of a flat, multi-arm spiralcoil which is placed above a fast-spinning metal disc and connected to thelatter by sliding liquid-metal electrical contacts. Theoretically,self-excitation of the magnetic field is expected at the critical magneticReynolds number Rm~45, which corresponds to a critical rotation rate of about10 Hz. We measured the magnetic field above the disc and the voltage drop onthe coil for the rotation rate up to 14 Hz, at which the liquid metal startedto leak from the outer sliding contact. Instead of the steady magnetic fieldpredicted by the theory we detected a strongly fluctuating magnetic field witha strength comparable to that of Earth's magnetic field which was accompaniedby similar voltage fluctuations in the coil. These fluctuations seem to becaused by the intermittent electrical contact through the liquid metal. Theexperimental results suggest that the dynamo with the actual electricalresistance of liquid metal contacts could be excited at the rotation rate ofaround 21 Hz provided that the leakage of liquid metal is prevented.