Numerically derived parametrisation of optimal RMP coil phase as a guide to experiments on ASDEX Upgrade

Ryan, D. A.; Liu, Y Q; Li, L; Kirk, A.; Dunne, M.; Dudson, B.; Piovesan, P.; Suttrop, W.; Willensdorfer, M.

doi:10.1088/1361-6587/59/2/024005

Cited by 13 publications

(29 citation statements)

References 54 publications

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“…The most likely explanation for these points is that at they have fallen within narrow regions in which there are large resonant field amplification peaks, caused by nq a being immediately below an integer. This phenomenon is more apparent in the results of [22], which uses a finer grid resolution. In this work as before, these points do not significantly modify the 2D quadratic fit, which is dominated by points outside the resonant peaks.…”

Section: Parametrisation Of Iter Coil Phasementioning

confidence: 97%

“…'Cycle averaged' denotes an (angular) average taken over all studied cycles for a given discharge. It is not claimed that the above definition is statistically robust: the primary use of these RMSE definitions is for a self consistent comparison with the benchmark between the quadratic and MARS-F reported in [22], and do not take account of the uncertainties of the experimental measurement. The RMSEs are calculated for n = 1 and n = 2 separately.…”

Section: To Quantify the Comparison Between Prediction And Measuremenmentioning

confidence: 99%

“…This report and others [22,18] focus primarily on optimisation of |b 1 res | by tuning the coil phase difference ∆Φ ul . The optimum coil phase may take any arbitrary value depending on equilibrium parameters, and therefore precise alignment requires a sinusoidal toroidal waveform which can take any arbitrary phase.…”

Section: Choice Of Toroidal Waveformmentioning

confidence: 99%

“…In this study the rotation profile is modified to be finite at the edge, in order to avoid a rotation zero crossing being co-located with the outermost resonant surfaces, which would not be the general case and merely obstruct the purpose of this study. In a previous study [22], the optimal coil phase was computed with MARS-F while the rotation profile was scaled by factors ranging from 0.1 to 10. The optimal coil phase was found to be robust to this rotation profile scaling to within 10 degrees.…”

Section: Iter Reference Equilibrium and Scaled Equilibrium Setmentioning

confidence: 99%

“…Coefficients of the 2D quadratic parametrisation of ∆Φ opt (equation 1), for the cases which are experimentally validated in this work: n = 1, 2 applied fields, including plasma response (ie, the total field). The parametrisation and coefficients were produced in [22], where the n = 3, 4 and vacuum cases are also listed.…”

Section: Introductionmentioning

confidence: 99%

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Experimental validation of coil phase parametrisation on ASDEX Upgrade, and extension to ITER

Ryan

Liu

Kirk

et al. 2018

Plasma Phys. Control. Fusion

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It has been previously demonstrated in (Li et al 2016 Nuclear Fusion 56 126007) that the optimum upper/lower coil phase shift ∆Φ opt for alignment of RMP coils for ELM mitigation depends sensitively on q 95 , and other equilibrium plasma parameters. Therefore, ∆Φ opt is expected to vary widely during the current ramp of ITER plasmas, with negative implications for ELM mitigation during this period. A previously derived and numerically benchmarked parametrisation of the coil phase for optimal ELM mitigation on ASDEX Upgrade (Ryan et al 2017 Plas. Phys. Cont. Fus. 59 024005) is validated against experimental measurements of ∆Φ opt , made by observing the changes to the ELM frequency as the coil phase is scanned. It is shown that the parametrisation may predict the optimal coil phase to within 32 degrees of the experimental measurement for n = 2 applied perturbations. It is explained that this agreement is sufficient to ensure that the ELM mitigation is not compromised by poor coil alignment. It is also found that the phase which maximises ELM mitigation is shifted from the phase which maximizes density pump-out, in contrast to theoretical expectations that ELM mitigation and density pump out have the same ∆Φ ul dependence. A time lag between the ELM frequency response and density response to the RMP is suggested as the cause. The method for numerically deriving the parametrisation is repeated for the ITER coil set, using the baseline scenario as a reference equilibrium, and the parametrisation coefficients given for future use in a feedback coil alignment system. The relative merits of square or sinusoidal toroidal current waveforms for ELM mitigation are briefly discussed.

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Section: Parametrisation Of Iter Coil Phasementioning

confidence: 97%

Section: To Quantify the Comparison Between Prediction And Measuremenmentioning

confidence: 99%

Section: Choice Of Toroidal Waveformmentioning

confidence: 99%

Section: Iter Reference Equilibrium and Scaled Equilibrium Setmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Experimental validation of coil phase parametrisation on ASDEX Upgrade, and extension to ITER

Ryan

Liu

Kirk

et al. 2018

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields

Liu

Kirk

et al. 2017

Physics of Plasmas

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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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Predicting operational windows of ELMs suppression by resonant magnetic perturbations in the DIII-D and KSTAR tokamaks

Nazikian

Logan

et al. 2021

Physics of Plasmas

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A newly developed plasma response model, combining the nonlinear two-fluid MHD code TM1 and toroidal MHD code GPEC run in ideal mode, quantitatively predicts the narrow isolated q95 windows (Δq95 ∼ 0.1) of edge-localized mode (ELM) suppression by n = 1, 2, and 3 resonant magnetic perturbations (RMPs) in both DIII-D and KSTAR tokamaks across a wide range of plasma parameters. The key physics that unites both experimental observations and our simulations is the close alignment of essential resonant q-surfaces and the location of the top of the pedestal prior to an ELM. This alignment permits an applied RMP to produce field penetration due to the lower E × B rotation at the pedestal top rather than being screened. The model successfully predicts that narrow magnetic islands form when resonant field penetration occurs at the top of pedestal, and these islands are easily screened when q95 moves off resonance, leading to very narrow windows of ELM suppression (typically Δq95 ∼ 0.1). Furthermore, the observed reduction in the pedestal height is also well captured by the calculated classical collisional transport across the island. We recover observed q95, βN and plasma shape dependence of ELM suppression due to the effect of magnetic islands on pedestal transport and peeling-ballooning-mode stability. Importantly, experiments do occasionally observe wide windows of ELM suppression (Δq95 > 0.5). Our model reveals that at low pedestal-top density multiple islands open, leading to wide operational windows of ELM suppression consistent with experiment. The model indicates that wide q95 windows of ELM suppression can be achieved at substantially higher pedestal pressure with less confinement degradation in DIII-D by operating at higher toroidal mode number (n = 4) RMPs. This can have significant implications for the operation of the ITER ELM control coils for maintaining high confinement together with ELM suppression.

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Numerically derived parametrisation of optimal RMP coil phase as a guide to experiments on ASDEX Upgrade

Abstract: the ASDEX Upgrade team 4 and the EUROfusion MST1 team [1]

Cited by 13 publications

References 54 publications

Experimental validation of coil phase parametrisation on ASDEX Upgrade, and extension to ITER

Experimental validation of coil phase parametrisation on ASDEX Upgrade, and extension to ITER

Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields

Predicting operational windows of ELMs suppression by resonant magnetic perturbations in the DIII-D and KSTAR tokamaks

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