(TH/P2-08) Two-Fluid and Nonlinear Effects of Tearing and Pressure-Driven Resistive Modes in Reversed Field Pinches

**Abstract.** Large-scale tearing instabilities have long been considered to
underlie transport and dynamo processes in the reversed field pinch
(RFP). The vast majority of theoretical and computational RFP work has
focused on pressureless, single-fluid MHD in cylindrical plasmas driven
solely by a toroidal electric field. We report results of five
investigations covering two-fluid dynamos, toroidal nonlinear MHD
computation, nonlinear computation of Oscillating Field Current Drive
(OFCD), the effect of shear flow on tearing instability, and the effect of
pressure on resistive instability. The key findings are: (1) two-fluid
dynamo arising from the Hall term is much larger than the standard MHD
dynamo present in a single-fluid treatment, (2) geometric coupling from
toroidicity precludes the occurrence of laminar single helicity states,
except for nonreversed plasmas, (3)OFCD, a form of AC helicity injection,
can sustain the RFP plasma current, although magnetic fluctuations are
enhanced, (4) edge shear flow can destabilize the edge resonant m = 0 modes,
which occur as spikes in experiment, and (5) pressure driven modes are
resistive at low beta, only becoming ideal at extremely high beta.

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*IAEA 2003*