Three Dimensional Disortations Of The Tkamak Plasma Boundary: II Boundary Displacements In The Presence Of Resonant Magnetic Perturbations
Authors: IT Chapman, S. Lazerson, et.al.
Abstract:
The three dimensional plasma boundary displacements induced by applied nonaxisymmetric
magnetic perturbations have been measured in ASDEX Upgrade,
DIII-D, JET, MAST and NSTX. The displacements arising from applied resonant
magnetic perturbations (RMPs) are measured up to +_ 5% of the minor radius in
present day machines. Good agreement can be found between different experimental
measurements and a range of models - be it vacuum field line tracing, ideal three
dimensional MHD equilibrium modelling, or nonlinear plasma amplification. The
agreement of the various experimental measurements with the different predictions
from these models is presented, and the regions of applicability of each discussed. The
measured displacement of the outboard boundary from various machines is found to
correlate approximately linearly with the applied resonant field predicted by vacuum
modelling (though it should be emphasised that one should not infer that vacuum
modelling accurately predicts the displacement inside the plasma). The RMP-induced
displacements foreseen in ITER are expected to lie within the range of those predicted
by the different models, meaning less than +_ 1.75% (+_ 3.5cm) of the minor radius
in the H-mode baseline and less than +_ 2.5% (+_ 5cm) in a 9MA plasma. Whilst a
displacement of 7cm peak-to-peak in the baseline scenario is marginally acceptable
from both a plasma control and heat loading perspective, it is important that ITER
adopts a plasma control system which can account for a three dimensional boundary
corrugation to avoid an n = 0 correction which would otherwise locally exacerbate the
displacement caused by the applied fields.
Submitted to: Nuclear Fusion (November 2013)
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