Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

Levesque, J.P.; Hughes, Paul E.; Bialek, J.; Byrne, P.J.; Mauel, M. E.; Navratil, G.A.; Peng, Qian; Rhodes, Dov; Stoafer, C.C.

doi:10.1063/1.4918360

Cited by 10 publications

(9 citation statements)

References 34 publications

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“…In the RWM theory, usually ferromagnetic effects are disregarded, which is justified by analytical and numerical analysis [84, 85] for slow modes. The situation is different for fast modes (at ) [86], which can be expected in future experiments in the JT-60SA tokamak [26] and, possibly in experiments with a movable ferromagnetic wall in the HBT-EP tokamak [87]. However, more often the results obtained with are good enough and can be easily extended to the area with [86].…”

Section: Boundary Conditionsmentioning

confidence: 99%

Plasma stability theory including the resistive wall effects

Pustovitov

2015

J. Plasma Phys.

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Plasma stabilization due to a nearby conducting wall can provide access to better performance in some scenarios in tokamaks. This was proved by experiments with an essential gain in${\it\beta}$and demonstrated as a long-lasting effect at sufficiently fast plasma rotation in the DIII-D tokamak (see, for example, Straitet al.,Nucl. Fusion, vol. 43, 2003, pp. 430–440). The rotational stabilization is the central topic of this review, though eventually the mode rotation gains significance. The analysis is based on the first-principle equations describing the energy balance with dissipation in the resistive wall. The method emphasizes derivation of the dispersion relations for the modes which are faster than the conventional resistive wall modes, but slower than the ideal magnetohydrodynamics modes. Both the standard thin wall and ideal-wall approximations are not valid in this range. Here, these are replaced by an approach incorporating the skin effect in the wall. This new element in the stability theory makes the energy sink a nonlinear function of the complex growth rate. An important consequence is that a mode rotating above a critical level can provide a damping effect sufficient for instability suppression. Estimates are given and applications are discussed.

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Section: Boundary Conditionsmentioning

confidence: 99%

Plasma stability theory including the resistive wall effects

Pustovitov

2015

J. Plasma Phys.

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“…Given that the edge safety factor q is below 3 after 2.5 ms as shown in figure 7(a), and the mode has an m/n = 3/1 structureas shown by the SVD analysis of the PA array data during 3-5 ms in figure 7(c), this mode is categorized as a 3/1 XK. This kink mode saturates and persists without immediately disrupting the plasma, as is often seen in HBT-EP plasmas [33,34]. As shown in figure 8(a), the observed phase inversions in the temperature contour plots indicate the existence of a TM.…”

Section: Mode Analysis Of Sawtooth-suppressed Phenomenamentioning

confidence: 60%

Sawtooth suppression by flux pumping on HBT-EP

Li,

Levesque,

Navratil

et al. 2024

Nucl. Fusion

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This study examines the mechanisms underlying sawtooth suppression in the High Beta Tokamak-Extended Pulse (HBT-EP) device. It is observed that strong-intensity sawtooth activities correlate with reduced-amplitude MHD edge modes which are identified as m/n=3/1 external kink modes (XK), while sawtooth suppression correlates with larger and saturated edge mode amplitudes. To further investigate these correlations, the plasma-wall coupling was manipulated by adjusting the positions of the conducting walls in HBT-EP. It was found that strong sawtooth events occur when the normalized wall radius b/a is within a critical value. This implies that the plasma-wall distance must be sufficiently small to ensure effective stabilization of the edge mode. Even slight differences in major radius result in significantly different discharge styles, categorized as "sawtoothing discharges" and "sawtooth-suppressed discharges" respectively. Through a series of mode structure analyses, we confirm the coexsitence and coupling of the m/n=1/1 helical core (HC), m/n=2/1 tearing mode (TM), and m/n=3/1 XK during sawtooth-suppression, and that this coupling induces anomalous current broadening. Based on these findings, we conclude that sawtooth suppression in the HBT-EP tokamak is consistent with the process of magnetic flux pumping.

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“…Although FRWM effects have been observed in a linetied pinch [5], early ferromagnetic wall research in tokamak geometry demonstrated that breakdown performance was not impaired [6], and showed success in reducing the toroidal field (TF) ripple [7,8] with no observable reduction of the beta limit even in the presence of a complete ferritic first wall [7,9]. However, preliminary results on the High Beta Tokamak-Extended Pulse (HBT-EP) suggested accelerated mode growth and an enhanced rate of resonant magnetic perturbation (RMP)-induced disruption [10,11]. It was also found that a ferromagnetic wall increased demands on the MHD feedback control system [12].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of MHD instabilities near a ferromagnetic wall

Hughes¹,

Levesque²,

Navratil³

2018

Nucl. Fusion

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Prospective fusion component testing and DEMO power reactor concepts are expected to employ low-activation ferritic steels because of their ability to withstand the high neutron flux of the reactor environment. However, theory suggests that ferromagnetic material may amplify certain external MHD instabilities. Using its ferromagnetic-resistive wall mode (FRWM) upgrade, the High Beta Tokamak-Extended Pulse (HBT-EP) experiment has observed approximately doubled growth rates when operating with a close-fitting ferromagnetic first wall, compared to operation with a stainless steel first wall. The presence of a ferromagnetic wall correlates with earlier disruptions, and FRWM growth rates increase with decreasing mode rotation, as expected due to the increased skin depth allowing greater mode interaction with the bulk ferromagnetic material. It is also seen that introducing low-n asymmetries into the toroidal distribution of ferromagnetic material, similar to the ITER test blanket module toroidal asymmetry, changes the phase preference of rotating modes; meanwhile, a similar change in purely conducting material does not significantly change the mode’s phase preference.

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Active and passive kink mode studies in a tokamak with a movable ferromagnetic walla)

Cited by 10 publications

References 34 publications

Plasma stability theory including the resistive wall effects

Plasma stability theory including the resistive wall effects

Sawtooth suppression by flux pumping on HBT-EP

Dynamics of MHD instabilities near a ferromagnetic wall

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