Characteristics of Alfvén eigenmodes, burst modes and chirping modes in the Alfvén frequency range driven by negative ion based neutral beam injection in JT-60U

Kusama, Y.; Kramer, G. J.; Kimura, Hiroyuki; Saigusa, M.; Ozeki, T.; Tobita, K.; Oikawa, T.; Shinohara, K.; Kondoh, T.; Moriyama, Makoto; Tchernychev, F V; Nemoto, M.; Morioka, A.; Iwase, M.; Isei, N.; Fujita, T.; Takeji, S.; Kuriyama, M.; Nazikian, R.; Fu, G. Y.; Hill, K. W.; Cheng, C. Z.

doi:10.1088/0029-5515/39/11y/324

Cited by 80 publications

(84 citation statements)

References 18 publications

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“…In addition to the slowing down effect of the density discussed here, recent analysis with the Nova code [28] indicates that the Alfvén continuum in the core of these plasmas during the high density phase is relatively closed, which may also contribute to the reduced AE activity and resulting fast ion transport. These results are similar to the observations in [29,30] that AE modes are stable in negative shear discharges with large density gradient at the ITB, although the regime under consideration here is significantly different, with a q-profile that is flatter in the core and overall significantly higher [see figure 3(c)]. …”

Section: Mhd Stability Limits and Fast Ion Lossessupporting

confidence: 88%

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Garofalo¹,

Gong²,

Grierson³

et al. 2015

Nucl. Fusion

117

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Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by ⩾30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled by improved understanding of the 'relaxation oscillations', previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the 'relaxation oscillations' are coupled core-edge modes amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced to classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ⩾80%, β ⩽ 4 N , β ⩾ 3 P , and β ⩾ % 2 T . These results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor.

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Section: Mhd Stability Limits and Fast Ion Lossessupporting

confidence: 88%

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Garofalo¹,

Gong²,

Grierson³

et al. 2015

Nucl. Fusion

117

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“…The basic properties of these chirping modes are the same as the DIII-D 'chirping modes' reported in [33]: f 1 2 f TAE , δf/f ∼ 50%, burst duration of ∼1 ms, toroidal mode numbers of n = 1, 2, and 3. (Similar instabilities are observed in other conventional [34] and spherical [35] tokamaks.) A major difference, however, is that these modes are rare in DIII-D, occurring in 1% of the discharges with beam-driven instabilities.…”

Section: Discussionsupporting

confidence: 74%

The effect of electric fields and pitch-angle scattering on the radial neutral flux

Heidbrink

Beitzel

Burrell

et al. 2001

Plasma Phys. Control. Fusion

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The radial flux of 10 keV neutrals from the Asdex-Upgrade tokamak has been interpreted as a diagnostic of the radial electric field E r near the plasma edge (Herrmann W and Asdex-Upgrade Team 1995 Phys. Rev. Lett. 75 4401), with the conclusion that E r changes gradually at a transition from the L-mode confinement regime to the H-mode regime. In contrast to the Asdex-Upgrade results, a similar installation on the DIII-D tokamak finds no measurable signal in H-mode plasmas with deep E r wells. Measurable signals only occur in plasmas with relatively large pitch-angle scattering rates at the plasma edge (or with anomalous beam-ion confinement). Large scattering rates require a large electron temperature and are invariably accompanied by deep ripple wells. The results suggest an alternative explanation for the gradual evolution of the neutral-particle signal from Asdex-Upgrade: as the H-mode pedestal develops, more beam ions are pitch-angle scattered into the phase space measured by the detector.

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“…The effect of the energetic ions on the MHD fluid is taken into account in the MHD momentum equation [Eq. (2)] through the energetic-ion current. The MHD equations are solved using a finite difference scheme of fourth-order accuracy in space and time.…”

Section: Simulation Modelmentioning

confidence: 99%

“…1) plasmas heated with negative ion based neutral beam (NNB) injection. [2][3][4][5] Frequencies of the three instabilities are in the range of shear Alfvén eigenmodes. Frequency sweeping of slow FS mode has a good correlation with equilibrium parameter evolution with time scale Ӎ200 ms. On the other hand, time scales of the fast FS mode and the ALE are, respectively 1 -5 ms and 200-400 s, much shorter than the equilibrium time scale.…”

Section: Introductionmentioning

confidence: 99%

Nonlocal energetic particle mode in a JT-60U plasma

Todo

Shinohara²,

Takechi³

et al. 2004

Physics of Plasmas

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Energetic-ion driven instability in a Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [S. Ishida et al., Phys. Plasmas 11, 2532(2004] plasma was investigated using a simulation code for magnetohydrodynamics and energetic particles. The spatial profile of the unstable mode peaks near the plasma center where the safety factor profile is flat. The unstable mode is not a toroidal Alfvén eigenmode (TAE) because the spatial profile deviates from the expected location of TAE and the spatial profile consists of a single primary harmonic m / n =2/1 where m and n are poloidal and toroidal mode numbers. The real frequency of the unstable mode is close to the experimental starting frequency of the fast frequency sweeping mode. Simulation results demonstrate that energetic-ion orbit width and energetic-ion pressure significantly broaden radial profile of the unstable mode. For the smallest value among the investigated energetic-ion orbit width, the unstable mode is localized within 20% of the minor radius. This gives an upper limit of the spatial profile width of the unstable mode which the magnetohydrodynamic effects alone can induce. For the experimental condition of the JT-60U plasma, energetic ions broaden the radial width of the unstable mode spatial profile by a factor of 3. The unstable mode is primarily induced by the energetic particles.

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Characteristics of Alfvén eigenmodes, burst modes and chirping modes in the Alfvén frequency range driven by negative ion based neutral beam injection in JT-60U

Cited by 80 publications

References 18 publications

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

The effect of electric fields and pitch-angle scattering on the radial neutral flux

Nonlocal energetic particle mode in a JT-60U plasma

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