Session KP01 - Poster Session III.
POSTER session, Tuesday afternoon, March 23
Exhibit Hall, GWCC
This work unveils new features of the single helicity (SH) ohmic states of the cylindrical RFP in the framework of resistive MHD at zero pressure, and of their connection with the multiple helicity (MH) states. It is shown that since \mu = \fracj_\parallelB reverses in RFP SH states, the Grad-Shafranov equation in helical coordinates generally yields solutions with a minimum of \mu in the center of the plasma. The finite radial magnetic field associated with these helical equilibria turns out to be necessary to satisfy Ohm's law, as required by Cowling theorem. It is shown that there is no need for a dynamo acting at field reversal, in agreement with the dynamo velocity pattern found in SH resistive MHD simulations. The diagram of the bifurcation between MH and quasi SH (QSH) states controlled by the Prandtl number is revisited, and the importance of the Lundquist number is emphasized. The role of these QSH states in improving the transport properties of the RFP is analyzed by comparing the level of stochasticity of the magnetic field in the MH and QSH cases computed by numerical simulation.