Speaker
Raul Sanchez
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1051.pdf
Application of the free-boundary SIESTA MHD equilibrium code to
bootstrap control scenarios in the W7-X stellarator
R. Sanchez1 , H. Peraza-Rodriguez1 , J.M. Reynolds-Barredo1 , V. Tribaldos1 , J. Geiger2
1 Universidad Carlos III de Madrid, SPAIN
2 Max-Planck-Institut für Plasmapyhsik, Greifswald, GERMANY
SIESTA [1] is an MHD equilibrium code designed to perform fast and accurate calculations
of ideal MHD equilibria for three-dimensional magnetic configurations. SIESTA is an iterative
code that uses the solution previously obtained by the VMEC code [2] for the same problem
to provide an Eulerian background coordinate system and an initial guess of the equilibrium
solution. In contrast to VMEC, SIESTA does not assume closed magnetic surfaces. Thus, the
final equilibrium solution can include magnetic islands and stochastic regions.
In its original implementation, the SIESTA code addressed only fixed-boundary problems.
That is, the shape of the plasma edge, assumed to be a magnetic surface, was the same obtained
by the VMEC code and it was kept fixed as the solution iteratively converges to equilibrium.
This fixed boundary condition has somewhat restricted the possible applications of SIESTA
in the past, limiting it to problems in which a possible variation of the plasma boundary was
not of interest. To circumvent these limitations, SIESTA has been recently extended [3] being
now able to deal with free-plasma-boundary problems, opening up the possibility of addressing
situations in which the plasma boundary is perturbed either externally or internally. The compu-
tational domain of the new version of SIESTA can now be extended all the way to the vacuum
vessel if desired. This is made possible by several techniques that extend the background coor-
dinate system and provide suitable initial guess for the equilibrium solution over the extended
volume. As an illustration of its new capabilities, SIESTA is applied in this contribution to
the study of bootstrap control scenarios to avoid undesired distortions of the island chain that
insulates the plasma edge from the divertor of the W7-X stellarator [4].
References
[1] S.P. Hirshman, R. Sanchez and C.R. Cook, Phys. Plasmas 18 062504 (2011)
[2] S.P. Hirshman and JC Whitson, Phys. Fluids 26 3553 (1983)
[3] H. Peraza-Rodriguez, J.M. Reynolds-Barredo, R. Sanchez, V. Tribaldos, J. Geiger, S.P. Hirshman and M.
Cianciosa, Phys. Plasmas 24 082516 2017)
[4] H. Peraza-Rodriguez, J.M. Reynolds-Barredo, R. Sanchez, V. Tribaldos and J. Geiger, Plasma Phys. Contr.
Fus. 60, 2018 (2018)
