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Author: Samuel Lazerson
Requested Type: Poster
Submitted: 2016-02-05 07:50:23

Co-authors: P. Xanthopoulos, H. Mynick, D. Gates

Contact Info:
Princeton Plasma Physics Laboratory
P.O. Box 451
Princeton, New Jersey   08543
United States

Abstract Text:
The large flexibility of the QUASAR facility is leveraged in order to explore the effect of magnetic shear on electrostatic ITG turbulence. Recent work using fixed boundary optimisation of the LI383 equilibrium (upon which QUASAR is based) has suggested possible improvements to ITG turbulence [Mynick et al., Plasma Phys. Control. Fusion 56 (2014)]. Initial attempts to reproduce such modified equilibria using the coil set of QUASAR did not achieve the desired shaping or reduction in ITG turbulence. In this work, a different approach is taken wherein a series of self-consistent free boundary VMEC equilibria are developed for QUASAR. These equilibria assume temperature and density profiles consistent with a 2% beta configuration with ohmic current profile. In each configuration the toroidal field coils are energised to different values and the STELLOPT code is used to vary the modular coil current and net toroidal current. In each case the edge value of rotational transform is targeted as a fixed value, producing a magnetic shear scan. These configurations all share similar neoclassical transport levels while non-linear GENE flux tube simulations show up to a factor of four change in electrostatic ITG turbulence at all radii. Comparisons to proxy functions and linear flux tube runs are also made. This work highlights the capability of the QUASAR experiment as a tool to explore transport in 3D magnetic fields and the possibility of the further improvements to stellarators through optimisation.