Dynamo power balance in a reversed‐field pinch

A study of the steady‐state magnetohydrodynamic dynamo power balance in the Extrap T1 reversed‐field pinch [Nucl. Fusion 34, 427 (1994)] is reported. The power transfer between the poloidal and toroidal magnetic fields is discussed in terms of a dynamo efficiency which is degraded with increasing pinch parameter Θ=Bθ(a)/〈Bφ〉 as a consequence of a larger fraction of the input power (up to 50% at high Θ) being dissipated by the fluctuations. It is shown that this anomalous (non‐Spitzer) input power scales specifically with the power in nonlinearly driven dissipative m∈[0,2] modes. This is consistent with numerical results indicating the dynamo arises primarily from the m=1 modes.