HOME PROGRAM REGISTRATION HOTEL TRANSPORTATION SUBMIT ABSTRACT ABSTRACT LIST PROGRAM COMMITTEE MORE ON MADISON	Single Helicity and Quasi-Single Helicity States in RFPs Author: Finn J. M. Coauthor: R. A. Nebel, C. G. Bathke Institution : Los Alamos National Laboratory Abstract text: Previous studies have shown that both single helicity1 (SH) and quasi-single helicity2 (QSH) states can emerge from 3-D RFP dynamics. However, both states have previously been observed to exist only at very low Hartmann numbers and thus have been of limited relevance to present-day and future experimental devices. In this paper we demonstrate that these states can also be achieved at high Hartmann number if external helical radial magnetic perturbations are applied to the dominant helical mode. For large enough helical perturbation, there may be hysteresis between the QSH states and MH (multiple helicity) states. However, radial magnetic perturbations cause a large class of field lines to intersect the wall. Another type of helical perturbation has been studied. In these, the perturbation consists of a radial electric field (radial current density) at the wall, applied in a manner such that the radial magnetic field vanishes at the boundary, so that no flux surfaces intersect the wall. Using this technique, QSH RFP states have been achieved when a toroidal loop voltage is applied. The observed QSH sidebands are ~ 4 toroidal mode numbers away from the dominant mode. The dominant mode appears to flatten the q profile near the dominant resonance and stabilizes the adjacent modes. When the toroidal loop voltage is removed, the plasma goes into a single helicity state. The applied helical electrostatic field drives both net toroidal current and poloidal current in the device. Although toroidal field reversal is lost, good flux surfaces are maintained everywhere in the device in steady-state. Thus, this system simultaneously maintains good flux surfaces and drives a net steady-state current. 1. J. M. Finn, R. A. Nebel, C. G. Bathke, Phys. Fluids B 4, 1262 (1992). 2. S. Cappello, D. F. Escande, Physical Review Letters 85, 3838 (2000).