Speaker
Andrew Ware
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1040.pdf
Computational modeling of quasi-single helicity states in an RFP
A.S. Ware and C. Miele
University of Montana, Missoula, Montana, USA
This work explores the impact of boundary shaping on access into and out of quasi-single
helicity states in reverse-field-pinch (RFP) plasmas. Experiments have shown that RFP plasmas
can self-organize to a quasi-single helicity (QSH) equilibrium with a helical axis [1, 2]. These
states have improved confinement and lower magnetic turbulence levels compared to a standard
RFP plasma which has multiple helicities in the magnetic spectrum. The VMEC code can obtain
similar equilibria with a helical axis and a symmetric boundary [3]. These equilibria all have
circular, or nearly-circular cross-sections. In this work we analyze the VMEC input parameters
that control access to QSH states and test the impact of 2D-shaping of the boundary on RFP
equilibria. Particular attention is paid to the impact that shaping has on access to quasi-single
helicity states. The effect of increasing elongation and triangularity are tested systematically.
Increased elongation results in lower plasma current for the same safety factor profile a nd a
larger radial excursion of the helical axis in a QHS state. Optimization of the boundary coeffi-
cients targeting an increased radial excursion of the helical axis is undertaken. Results will be
presented.
References
[1] D.F. Escande, et al., Phys. Rev. Lett. 85, 1662 (2000)
[2] L. Marrelli, L., et al. Phys. Plasmas 9, 2868 (2002)
[3] J.D. Hanson, et al., Nucl. Fusion 53, 083016 (2013)
