Experimental verification of the MHD dynamo in the axisymmetric linear machine

We report the first experimental verification of the magnetohydrodynamic (M HD) dynamo in the axisymmetric linear machine. The dynamo phenomenon, in wh ich the magnetic-field-aligned electric current is self-generated by plasma dynamics, has been a puzzle not only in astrophysical plasmas, but also in magnetically confined laboratory plasmas for many decades. The mirror trap axisymmetric plasma, in which the unstable differential rotation of plasma column in crossed ExB fields excites the helical MHD turbulence, is a new and particularly vivid example arf the dynamo effect. By manipulating the trap's magnetic and plasma conditions, we have obtained both the parallel and the antiparallel to the magnetic field electric curr ent with density to the order of 100 A/cm(2) (total current up to 6 kA) in the plasma. The measured mean electromotive force F-em has linear dependenc e from the turbulent diffusion coefficient D-T (r,t) and reachs up to 50 V/ m. By measuring each term of F-em, the parallel MHD mean-field Ohm's law ha s been observed to hold within experimental error bars during plasma flow:p ulse. A comprehensive physical picture of the dynamo phenomenon has been ob tained.