The feedback phase instability in the HBT-EP tokamak

Nadle, D.; Cates, C.; Dahi, H.; Mauel, M. E.; Maurer, D.A.; Mukherjee, S.; Navratil, G.A.; Shilov, M.; Taylor, E.

doi:10.1088/0029-5515/40/10/309

Cited by 8 publications

(8 citation statements)

References 6 publications

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“…A similar phase instability has long been known in the context of the control of magnetic islands with external resonant magnetic perturbations. 20,21,24,25 Here, for the first time, we show why, from essential physics and mathematics, the same occurs in the case of ECCD control; we believe our arguments can help interpreting and understanding the failed attempts of ECCD control, alongside with the successful ones.…”

Section: -3mentioning

confidence: 66%

Nonlinear response of magnetic islands to localized electron cyclotron current injection

et al. 2014

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The magnetic island evolution under the action of a current generated externally by electron cyclotron wave beams is studied using a reduced resistive magnetohydrodynamics plasma model. The use of a two-dimensional reconnection model shows novel features of the actual nonlinear evolution as compared to the zero-dimensional model of the generalized Rutherford equation. When the radio frequency control is applied to a small magnetic island, the complete annihilation of the island width is followed by a spatial phase shift of the island, referred as “flip” instability. On the other hand, a current-drive injection in a large nonlinear island can be accompanied by the occurrence of a Kelvin-Helmholtz instability. These effects need to be taken into account in designing tearing mode control systems based on radio frequency current-drive.

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Section: -3mentioning

confidence: 66%

Nonlinear response of magnetic islands to localized electron cyclotron current injection

et al. 2014

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“…In deriving Eqs. (17) and (18), we have practically assumed a δ-function in pitch angle, δ(Λ − Λ max ), for the particle equilibrium distribution function. To somewhat relax this assumption, we introduce a fraction coefficient f kinetic in Eq.…”

Section: Deeply Trapped Limitmentioning

confidence: 99%

“…To somewhat relax this assumption, we introduce a fraction coefficient f kinetic in Eq. (18). This coefficient roughly represents the fraction of deeply trapped particles among the total trapped particles, with f kinetic = 1 corresponds to the δ-function distribution in particle pitch angle for deeply trapped particles.…”

Section: Deeply Trapped Limitmentioning

confidence: 99%

“…This is a non-magnetic control scheme. Magnetic control of the tearing mode, by directly controlling the magnetic islands with external fields seems to encounter a difficulty of the so-called phase instability [16,17,18], in which the island chain naturally locks to the external resonant field in such a helical phase, that the islands are destabilized. This process is non-linear and is beyond the scope of the present work.…”

Section: Introductionmentioning

confidence: 99%

“…We vary the kinetic fraction parameter f kinetic from Eq. (18), in order trace the change in ∆ ′ , as shown in Fig. 5.…”

mentioning

confidence: 99%

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Modification of Δ′ by magnetic feedback and kinetic effects

2012

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Two possible ways of modifying the linear tearing mode index, by active magnetic feedback and by drift kinetic effects of deeply trapped particles, are analytically investigated. Magnetic 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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A Kalman filter for feedback control of rotating external kink instabilities in the presence of noise

et al. 2009

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The simulation and experimental optimization of a Kalman filter feedback control algorithm for n=1 tokamak external kink modes are reported. In order to achieve the highest plasma pressure limits in ITER, resistive wall mode stabilization is required [T. C. Hender et al., Nucl. Fusion 47, S128 (2007)] and feedback algorithms will need to distinguish the mode from noise due to other magnetohydrodynamic activity. The Kalman filter contains an internal model that captures the dynamics of a rotating, growing n=1 mode. This model is actively compared with real-time measurements to produce an optimal estimate for the mode’s amplitude and phase. On the High Beta Tokamak-Extended Pulse experiment [T. H. Ivers et al., Phys. Plasmas 3, 1926 (1996)], the Kalman filter algorithm is implemented using a set of digital, field-programmable gate array controllers with 10 μs latencies. Signals from an array of 20 poloidal sensor coils are used to measure the n=1 mode, and the feedback control is applied using 40 poloidally and toroidally localized control coils. The feedback system with the Kalman filter is able to suppress the external kink mode over a broad range of phase angles between the sensed mode and applied control field. Scans of filter parameters show good agreement between simulation and experiment, and feedback suppression and excitation of the kink mode are enhanced in experiments when a filter made using optimal parameters from the scans is used.

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The feedback phase instability in the HBT-EP tokamak

Cited by 8 publications

References 6 publications

Nonlinear response of magnetic islands to localized electron cyclotron current injection

Nonlinear response of magnetic islands to localized electron cyclotron current injection

Modification of Δ′ by magnetic feedback and kinetic effects

A Kalman filter for feedback control of rotating external kink instabilities in the presence of noise

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