Magnetic helicity transport and the reversed field pinch

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Abstract
The Reversed Field Pinch plasma is described by a model based on magnetic helicity transport. It is shown that the mean correlation between fluctuations in fluid velocity and in magnetic field, , provides non-dissipative transport of helicity that persists whether or not the plasma is fully relaxed, as well as a non-Ohmic energy sink that vanishes when the fully relaxed state is attained. Such energy losses account for the anomaly in loop voltage or resistance seen in experiments, which can be interpreted as a loss of helicity associated with obstruction of parallel current flow and magnetic flux emerging from the plasma because of plasma-wall contact. Loss of magnetic flux through the bounding surface of the plasma enhances the helicity transport, which increases the loop voltage necessary to sustain the toroidal current. The increase, which is shown to be proportional to the flux intercepted and the local electron temperature, compares well with that observed in experiments.