PPPL-5385
Non-axisymmetric ideal equilibrium and stability of ITER plasmas
with rotating RMPs
Author: S.A. Lazerson
Abstract: The magnetic perturbations produced by the
resonant magnetic perturbation (RMP) coils will be rotated in ITER
so that the spiral patterns due to strike point splitting which are
locked to the RMP also rotate. This is to ensure even power
deposition on the divertor plates. VMEC equilibria are calculated
for different phases of the RMP rotation. It is demonstrated that
the off harmonics rotate in the opposite direction to the main
harmonic. This is an important topic for future research to control
and optimize ITER appropriately. High confinement mode (H-mode) is
favourable for the economics of a potential fusion power plant and
its use is planned in ITER. However, the high pressure gradient at
the edge of the plasma can trigger periodic eruptions called edge
localized modes (ELMs). ELMs have the potential to shorten the life
of the divertor in ITER [Loarte et al. Plasma Phys. Control.
Fusion (2003) 45 1549] and so methods for mitigating or
suppressing ELMs in ITER will be important. Non-axisymmetric RMP
coils will be installed in ITER for ELM control. Sampling theory is
used to show that there will be significant a ncoils−nrmp harmonic sideband. There are
nine coils toroidally in ITER so ncoils =
9. This results in a significant n = 6 component to the nrmp = 3 applied field and a
significant n = 5 component to the nrmp = 4 applied field. Although
the vacuum field has similar amplitudes of these harmonics the
plasma response to the various harmonics dictates the final
equilibrium. Magnetic perturbations with toroidal mode number n = 3
and n = 4 are applied to a 15MA,
q95
≈ 3 burning ITER plasma. We use a three-dimensional ideal
magnetohydrodynamic model (VMEC) to calculate ITER
equilibria with applied RMPs and to determine growth rates of
infinite n ballooning modes (COBRA). The nrmp
= 4 case shows little change in ballooning mode growth rate as the
RMP is rotated, however there is a change with rotation for the nrmp
= 3 case.
Submitted to: Physics of Plasmas
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