MHD equilibrium and stability of tokamaks and RFP systems with 3D helical cores

Bifurcated magnetohydrodynamic (MHD) equilibrium states are computed for ITER hybrid scenario and RFX-mod SHAx configurations with very flat or reversed core magnetic shear conditions. In the ITER studies, the minimum inverse rotational transform qmin is near unity, while for RFX-mod it is 1/8. Two equilibrium states are obtained: one is axisymmetric, the other displays a 3D helical core. In tokamak devices, the structure resembles a saturated ideal MHD internal kink mode. In the reversed-field pinch, the structure is seven-fold toroidally periodic. The equilibrium magnetic field spectrum in the Boozer coordinate frame is calculated in both the ITER and RFX-mod configurations and the implications are discussed. The RFX-mod equilibria are strongly unstable to external ideal MHD kink modes, which become stabilized with a closely fitting conducting shell when the equilibrium state has a weak reversed core shear. It is marginally unstable with a monotonic q-profile. Unstable modes are driven by the Ohmic current, with pressure and Pfirsch–Schl¨uter currents having a very weak effect. The external kink mode spectrum is dominated by coupled $m = 1$, $n = 6$ and $m = 2$, $n = 13$ Fourier components, which revert to $m = 1$, $n = 8$ and $m = 2$, $n = 15$ terms with a conducting wall in proximity to the plasma–vacuum interface.

Dendy, Richard
Published in:
Plasma Physics and Controlled Fusion, 53, 8, 084001
Presented at:
15th Workshop on MHD stability control:
US-Japan Workshop on 3D Magnetic Field Effects in MHD Control, Univ. Wisconsin, Madison, WI, USA, 15-17 November 2010
Bristol, United Kingdom, IOP Publishing

 Record created 2011-05-31, last modified 2018-01-28

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