THE α DYNAMO EFFECTS IN LABORATORY PLASMAS

A concise review of observations of the α dynamo eect in laboratory plasmas is given. Unlike many astrophysical systems, the laboratory pinch plasmas are driven magnetically. When the system is overdriven, the resultant instabilities cause magnetic and flow elds to fluctuate, and their correlation induces electromotive forces along the mean magnetic eld. This α-eect drives mean parallel electric current, which, in turn, modies the initial background mean magnetic structure towards the stable regime. This drive-and-relax cycle, or the so-called self-organization process, happens in magnetized plasmas in a time scale much shorter than resistive diusion time, thus it is a fast dynamo process active in a strong magnetic eld. The observed α-eect redistributes magnetic helicity (a measure of twistedness and knottedness of magnetic eld lines) but conserves its total value. It can be shown that fast dynamos are natural consequences of a driven system, where fluctuations are statistically either not stationary in time or not homogeneous in space, or both. Implications to astrophysical phenomena will be discussed. 1. Introduction. Phenomen