The disk accretion rate for dynamo-generated turbulence

Dynamo-generated turbulence is simulated in a modified shearing box approximation that removes scale invariance and allows finite accretion rates for a given distance from the central object. The effective Shakura-Sunyaev viscosity parameter, alpha(ss), is estimated in three different ways using the resulting mass accretion rate, the heating rate, and the horizontal components of the Maxwell and Reynolds stress tensors. The results are still resolution dependent: doubling the resolution leads to 1.4-1.6 times larger values for the viscosity parameter. For 63 x 127 x 64 meshpoints we find that alpha(ss) = 0.007.