Non-Resonant n = 1 Helical Core Induced by m/n = 2/1 Neoclassical Tearing Mode in JT-60U

Bando, T.; Inoue, Shizuo; Shinohara, K.; Isayama, A.; Wakatsuki, Takuma; Yoshida, M.; Honda, M.; Matsunaga, G.; Takechi, M.; Oyama, N.; Ide, S.

doi:10.1585/pfr.16.1402030

Cited by 5 publications

(11 citation statements)

References 46 publications

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“…The precursor oscillation of the ST crash is dominated by the 1/1 mode. After the NTM onset, the ST crash event is not observed, consistent with the observations in JT-60U [20][21][22]. The dramatic drop of the stored energy and beta indicates the degradation of the energy confinement by the NTM.…”

Section: Observations Of 3/2 and 2/1 Ntms In High β H-mode Plasmassupporting

confidence: 84%

“…In addition, such HC is also observed simultaneously with the 2/1 NTM in shot 36871. The NTM (both for m/n = 3/2 and m/n = 2/1) and the HC rotate keeping the same frequency, resulting in the phase locking, similar to the observations on JT-60U [21]. Note that the 1/1 HC cannot be distinguished from the Mirnov coils, which might due to the fact that it is too far away from the coils.…”

Section: Observations Of 3/2 and 2/1 Ntms In High β H-mode Plasmassupporting

confidence: 80%

“…The 'hybrid' operation scenario, which is a steady-state, high performance H-mode scenario and can operate near the n = 1 above 1, and has been realized in many devices including DIII-D [4,5], ASDEX-Upgrade [6,7], JET [8,9] and JT-60U [10,11] tokamaks. Magnetic-flux pumping [12][13][14][15][16][17][18][19][20][21][22] produced by MHD modes (especially 1/1 helical structure) is considered to play an important role in the maintaining of q min 1 and the avoidance of sawtooth (ST) crash, which (especially with long period and large amplitude) is the detrimental ingredient to drive large disruptive 2/1 neoclassical tearing mode (NTM).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Coupling among neoclassical tearing modes, edge localized modes and Alfvén eigenmodes in HL-2A high β H-mode plasmas

Jiang¹,

Xu²,

Chen³

et al. 2022

Nucl. Fusion

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In this work, the coupling among several MHD modes across different spatial regions, including the neoclassical tearing mode (NTM) and two branches of Alfvén eigenmode (AE) in the core and the edge localized mode (ELM), has been investigated in the HL-2A high beta H-mode plasmas. The NTMs induce a saturated m/n=1/1 helical core (m and n are the poloidal and toroidal mode numbers, respectively) through the ”magnetic-flux pumping” effect. The ELM crash results in a rapid (< 1 ms) decrease of the NTM island width followed by a much slower recovery. The degree of the island-width drop is proportional to the normalized beta as well as the ELM size, and can be up to 60%. In addition, two branches of AEs, in the toroidal Alfvén eigenmode (TAE) and beta-induced Alfvén eigenmode (BAE) bands, become evident after the 2/1 NTM onset and their magnitudes are modulated by the 2/1 NTM rotation. Besides, the changes of the TAE and BAE amplitudes are closely related to the temporal evolution of the ELM crash event, implying the strong interaction between AEs and the ELM. It is found that the coupling among these MHD modes in the core region during the NTM phase regulates the edge transport, i.e., relaxation of the pressure profiles, mitigation of the peeling-ballooning instability, reduction of the radial electric field shear and enhancement of the turbulent transport in the pedestal region.

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Section: Observations Of 3/2 and 2/1 Ntms In High β H-mode Plasmassupporting

confidence: 84%

Section: Observations Of 3/2 and 2/1 Ntms In High β H-mode Plasmassupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coupling among neoclassical tearing modes, edge localized modes and Alfvén eigenmodes in HL-2A high β H-mode plasmas

Jiang¹,

Xu²,

Chen³

et al. 2022

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…Third, the contribution of the n = 1 helical core (HC) should be considered in the case of JT-60U, which has been reported recently [19,47]. The n = 1 HC is observed with the m/n = 2/1 NTM and the n = 1 HC can induce the non-resonant NTV torque.…”

Section: Discussionmentioning

confidence: 94%

Torque to counter-current direction driving low frequency tearing modes in JT-60U

Bando¹,

Honda²,

Inoue³

et al. 2021

Plasma Phys. Control. Fusion

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In the JT-60U tokamak, low frequency modes (LFMs) have been reported recently when the m/n = 2/1 neoclassical tearing mode grows sufficiently. LFMs show the low mode frequencies (<20 Hz) with the rotation direction to the counter-current direction (ctr-direction) toroidally, even if strong injection power to the co-current direction (co-direction) is applied by tangential neutral beam injections. As a candidate to drive the rotation to the ctr-direction, the neoclassical toroidal viscosity (NTV) torque is investigated in this study. Indeed, when a LFM is observed, the estimated 'offset velocity' of the NTV torque is larger than the observed toroidal velocity around the q = 2 surface and results in the torque to the ctr-direction (ctr-torque). The torque balance between the NTV torque and the torque induced by the eddy current on the resistive wall is investigated. It is found that the rotation to the ctr-direction having the low mode frequency is obtained as the result of the ctr-torque to the offset velocity. Our investigation suggests the requirement to include the NTV torque in the modeling on the mode locking of neoclassical tearing modes in tokamaks.

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“…In DIII-D, flux pumping was observed with n = 1 helical cores (HCs) induced by the n = 1 magnetic perturbation [19], or with neoclassical tearing mode-edge localized mode (NTM-ELM) coupling [21]. JT-60U showed flux pumping through n = 1 HC induced by m/n = 2/1 NTM [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

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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Non-Resonant n = 1 Helical Core Induced by m/n = 2/1 Neoclassical Tearing Mode in JT-60U

Cited by 5 publications

References 46 publications

Coupling among neoclassical tearing modes, edge localized modes and Alfvén eigenmodes in HL-2A high β H-mode plasmas

Coupling among neoclassical tearing modes, edge localized modes and Alfvén eigenmodes in HL-2A high β H-mode plasmas

Torque to counter-current direction driving low frequency tearing modes in JT-60U

Sawtooth suppression by flux pumping on HBT-EP

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