| 1. |
- Hao, G. Z, et al.
(författare)
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Stabilization of the Resistive Wall Mode Instability by Trapped Energetic Particles
- 2011
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 18, s. 032513-
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model for investigating the effect of the trapped energetic particles (EPs) on the resistive wall mode (RWM) instability is proposed. The results demonstrate that the trapped EPs have a dramatic stabilizing effect on the RWM because of resonant interaction between the mode and the magnetic precession drift motion of the trapped EPs. The results also show that the effect of the trapped EPs depends on the wall position. In addition, the stabilizing effect becomes stronger when the plasma rotation is taken into account. For sufficiently fast plasma rotation, the trapped EPs can lead to the complete stabilization of the RWM. Furthermore, the trapped EPs can induce a finite real frequency of the RWM in the absence of plasma rotation.
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| 2. |
- He, Y., et al.
(författare)
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Combined effects of trapped energetic ions and resistive layer damping on the stability of the resistive wall mode
- 2016
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- A dispersion relation is derived for the stability of the resistive wall mode (RWM), which includes both the resistive layer damping physics and the toroidal precession drift resonance damping from energetic ions in tokamak plasmas. The dispersion relation is numerically solved for a model plasma, for the purpose of systematic investigation of the RWM stability in multi-dimensional plasma parameter space including the plasma resistivity, the radial location of the resistive wall, as well as the toroidal flow velocity. It is found that the toroidal favorable average curvature in the resistive layer contributes a significant stabilization of the RWM. This stabilization is further enhanced by adding the drift kinetic contribution from energetic ions. Furthermore, two traditionally assumed inner layer models are considered and compared in the dispersion relation, resulting in different predictions for the stability of the RWM.
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| 3. |
- Lanctot, M.J., et al.
(författare)
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Measurement and modeling of three-dimensional equilibriua in DIII-D
- 2011
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 18, s. 056121-
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Tidskriftsartikel (refereegranskat)abstract
- A detailed experiment-theory comparison reveals that linear ideal MHD theory is in quantitative agreement with external magnetic and internal soft x-ray measurements of the plasma response to externally applied non-axisymmetric fields over a broad range of beta and rotation. This result represents a significant step toward the goal of advancing the understanding of three-dimensional tokamak equilibria. Both the magnetic and soft x-ray measurements show the driven plasma perturbation increases linearly with the applied perturbation, suggesting the relevance of linear plasma response models. The magnetic and soft x-ray measurements are made at multiple toroidal and poloidal locations, allowing well resolved measurements of the global structure. The comparison also highlights the need to include kinetic effects in the MHD model once beta exceeds 80% of the kink mode limit without a conducting wall. Two distinct types of response fields are identified by the linear ideal MHD model: one that consists of localized currents at the rational surfaces that cancel the applied resonant field and another that is excited by the components of the external field that couple to the kink mode. Numerical simulations show these two fields have similar amplitudes in ITER-shaped DIII-D discharges where n = 3 fields are used to suppress edge localized modes.
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| 4. |
- Lanctot, M. J., et al.
(författare)
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Validation of the linear ideal magnetohydrodynamic model of three-dimensional tokamak equilibria
- 2010
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 17:3, s. 030701-
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Tidskriftsartikel (refereegranskat)abstract
- The first quantitative comparison of linear ideal magnetohydrodynamic (MHD) theory with external magnetic measurements of the nonaxisymmetric plasma perturbation driven by external long-wavelength magnetic fields in high-temperature tokamak plasmas is presented. The comparison yields good (within 20%) agreement for plasma pressures up to ∼ 75% of the ideal stability limit calculated without a conducting wall. For higher plasma pressures, the ideal MHD model tends to overestimate the perturbed field indicating the increasing importance of stabilizing nonideal effects.
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| 5. |
- Li, L., et al.
(författare)
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Effect of large magnetic islands on screening of external magnetic perturbation fields at slow plasma flow
- 2017
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:2
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Tidskriftsartikel (refereegranskat)abstract
- A toroidal resistive magneto-hydrodynamic plasma response model, involving large magnetic islands, is proposed and numerically investigated, based on local flattening of the equilibrium pressure profile near a rational surface. It is assumed that such islands can be generated near the edge of the tokamak plasma, due to the penetration of the resonant magnetic perturbations, used for the purpose of controlling the edge localized mode. Within this model, it is found that the local flattening of the equilibrium pressure helps to mitigate the toroidal curvature induced screening effect [Glasser et al., Phys. Fluids 7, 875 (1975)]-the so called Glasser-Greene-Johnson screening, when the local toroidal flow near the mode rational surface is very slow (for example, as a result of mode locking associated with the field penetration). The saturation level of the plasma response amplitude is computed, as the plasma rotation frequency approaches zero. The local modification of the plasma resistivity inside the magnetic island is found to also affect the saturation level of the plasma response at vanishing flow.
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| 6. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields
- 2017
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 24:5
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Tidskriftsartikel (refereegranskat)abstract
- Extensive modelling efforts of the plasma response to the resonant magnetic perturbation fields, utilized for controlling the edge localized mode (ELM), help to identify the edge-peeling response as a key factor, which correlates to the observed ELM mitigation in several tokamak devices, including MAST, ASDEX Upgrade, EAST, and HL-2A. The recently observed edge safety factor window for ELM mitigation in HL-2A experiments is explained in terms of the edge-peeling response. The computed plasma response, based on toroidal single fluid resistive plasma model with different assumption of toroidal flows, is found generally larger in ELM suppressed cases as compared to that of the ELM mitigated cases, in ASDEX Upgrade and DIII-D. The plasma shaping, in particular, the plasma triangularity, contributes to the enhanced plasma response. But the shaping does not appear to be the sole factor-other factors such as the (higher) pedestal pressure and/or current can also lead to increased edge-peeling response.
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| 7. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Full toroidal plasma response to externally applied non-axisymmetric magnetic fields
- 2010
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 17:12, s. 122502-
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Tidskriftsartikel (refereegranskat)abstract
- The plasma response to resonant magnetic perturbation (RMP) and nonresonant perturbation fields is computed within a linear, full toroidal, single-fluid resistive magnetohydrodynamic framework. The response of resonant harmonics depends sensitively on the plasma resistivity and on the toroidal rotation. The response of nonresonant harmonics is not sensitive to most of the plasma parameters, except the equilibrium pressure. Both midplane and the off midplane odd parity RMP coils trigger a similar field response from the plasma. The RMP fields with different toroidal mode numbers trigger qualitatively similar plasma response. A simple model of the electron diamagnetic flow suggests significant effects both in the pedestal region and beyond.
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| 8. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Modeling of resistive wall mode and its control in experiments and ITER
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut, Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.
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| 9. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Modelling current driven resistive wall modes in DIII-D
- 2010
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Ingår i: Physics of Plasmas. - 1089-7674 .- 1070-664X. ; 17, s. 072510-
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Tidskriftsartikel (refereegranskat)abstract
- The stability and resonant field response of current driven resistive wall modes are numerically studied for DIII-D [ J. L. Luxon, Nucl. Fusion 42, 614 (2002) ] low pressure plasmas. The resonant field response of the feedback-stabilized resistive wall mode is investigated both analytically and numerically, and compared with the response from intrinsically stable or marginally stable modes. The modeling qualitatively reproduces the experimental results. Furthermore, based on some recent results and on the indirect numerical evidence in this work, it is suggested that the mode stability behavior observed in DIII-D experiments is due to the kink-peeling mode stabilization by the separatrix geometry. The phase inversion radius of the computed plasma displacement does not generally coincide with the radial locations of rational surfaces, also supporting experimental observations.
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| 10. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Modification of ∆′ by magnetic feedback and kinetic effects
- 2012
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 19, s. 092510-
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Tidskriftsartikel (refereegranskat)abstract
- Two possible ways of modifying the linear tearing mode index, by active magnetic feed- back and by drift kinetic effects of deeply trapped particles, are analytically investigated. Mag- netic feedback schemes, studied in this work, are found generally stabilizing for ∆′ . The drift kinetic effects from both thermal particles and hot ions tend to reduce the power of the large solution from the outer region. This generally leads to a destabilization of ∆′ for the toroidal analytic equilibria considered here.
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