Equilibrium and magnetic properties of a rotating plasma annulus

Local linear analysis shows that magneto-rotational instability can be excited in laboratory rotating plasmas with a density of ^{1019 m-3}, a temperature on the order of 10 eV, and a magnetic field on the order of 100 G. A laboratory plasma annulus experiment with a dimension of ∼1 m, and rotation at ∼0.5 sound speed is described. Correspondingly, magnetic Reynolds number of these plasmas is ∼1000, and magnetic Prandtl number ranges from about one to a few hundred. A radial equilibrium, ρ Uθ2 r=d (p+ Bz2 2 _μ0) dr= _K0, with _K0 being a nonzero constant, is proposed for the experimental data. Plasma rotation is observed to drive a quasisteady diamagnetic electrical current (rotational current drive) in a high- Β plasma annulus. The rotational energy depends on the direction and the magnitude of the externally applied magnetic field. Radial current (_Jr) is produced through biasing the center rod at a negative electric potential relative to the outer wall. _Jr × _Bz torque generates and sustains the plasma rotation. Rotational current drive can reverse the direction of vacuum magnetic field, satisfying a necessary condition for self-generated closed magnetic flux surfaces inside plasmas. The Hall term is found to be substantial and therefore needs to be included in the Ohm's law for the plasmas. Azimuthal magnetic field ( _Bθ) is found to be comparable with the externally applied vacuum magnetic field _Bz, and mainly caused by the electric current flowing in the center cylinder; thus, _Bθ ^r-1. Magnetic fluctuations are anisotropic, radial-dependent, and contain many Fourier modes below the ion cyclotron frequency. Further theoretical analysis reflecting these observations is needed to interpret the magnetic fluctuations.