Computation of the Magnetohydrodynamic Spectrum in Axisymmetric Toroidal Confinement Systems

Grimm, R.C.; Greene, J. M.; Johnson, John L.

doi:10.1016/b978-0-12-460816-0.50012-9

Cited by 140 publications

(123 citation statements)

References 35 publications

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“…It was therefore hypothesized that the cause for the reduction in β Nmax was due to the loss of wall stabilization. To verify this effect we have utilized the PEST [21] stability code to calculate the MHD stability of this high elongation discharge.…”

Section: Mhd Analysis High Of Elongation Dischargesmentioning

confidence: 99%

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Gates¹,

Ménard²,

Maingi³

et al. 2007

Nucl. Fusion

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Modifications to the plasma control capabilities and poloidal field coils of the National Spherical Torus Experiment (NSTX) have enabled a significant enhancement in shaping capability which has led to the transient achievement of a record shape factor (S ≡ q 95 (I p /aB t )) of ∼41 (MA m −1 T −1 ) simultaneous with a record plasma elongation of κ ≡ b/a ∼ 3. This result was obtained using isoflux control and real-time equilibrium reconstruction. Achieving high shape factor together with tolerable divertor loading is an important result for future ST burning plasma experiments as exemplified by studies for future ST reactor concepts, as well as neutron producing devices, which rely on achieving high shape factors in order to achieve steady state operation while maintaining MHD stability. Statistical evidence is presented which demonstrates the expected correlation between increased shaping and improved plasma performance. Plasmas with high shape factor have been sustained for pulse lengths which correspond to τ pulse = 1.6s ∼ 50τ E ∼ 5τ CR , where τ CR is the current relaxation time and τ E is the energy confinement time. Plasmas with higher β t ∼ 20% have been sustained for τ pulse = 1.2s ∼ 25τ E ∼ 3τ CR with noninductive current fractions f NI ∼ 50%, with ∼40% pressure driven current and ∼10% neutral beam driven current. An interesting feature of these discharges is the observation that the central value of the safety factor q(0) remains elevated and constant for several current diffusion times without sawteeth, similar to the 'hybrid mode'. Calculations of the profiles of inductive and non-inductive current are compared with measurements of the total current profile and are shown to be in quantitative agreement. Results are shown from experiments which investigate the applicability of high harmonic fast waves (HHFWs) and electron Bernstein waves (EBWs) as current drive and heating sources, and the possibility of LHCD for future ST devices is raised. A calculated scenario which provides 100% non-inductive current drive is described. NSTX operates with peak divertor heat fluxes which are in the same range as those expected for the ITER device, i.e. with P heat max ∼ 10 MW m −2 . High triangularity, high elongation plasmas on NSTX have been demonstrated to have reduced peak heat flux to the divertor plates to <3 MW m −2 .

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Section: Mhd Analysis High Of Elongation Dischargesmentioning

confidence: 99%

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Gates¹,

Ménard²,

Maingi³

et al. 2007

Nucl. Fusion

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“…This issue is recognized by Grimm et al [12] with the first 'mapping code', a code that employs numerical maps to transfer fields from the spatial discretization of an equilibrium code onto the spatial discretization of another code, where the second code typically assesses stability or the evolution of nonlinear perturbations. Despite considerable effort to increase the accuracy of mapping codes, mapping errors are difficult, if not impossible, to completely eliminate.…”

Section: Introductionmentioning

confidence: 99%

Effect of scrape-off-layer current on reconstructed tokamak equilibrium

et al. 2017

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Methods are described that extend fields from reconstructed equilibria to include scrape-off-layer current through extrapolated parametrized and experimental fits. The extrapolation includes both the effects of the toroidal-field and pressure gradients which produce scrape-off-layer current after recomputation of the Grad-Shafranov solution. To quantify the degree that inclusion of scrapeoff-layer current modifies the equilibrium, the χ-squared goodness-of-fit parameter is calculated for cases with and without scrape-off-layer current. The change in χ-squared is found to be minor when scrape-off-layer current is included however flux surfaces are shifted by up to 3 cm. The impact on edge modes of these scrape-off-layer modifications is also found to be small and the importance of these methods to nonlinear computation is discussed. Published version: Phys. Plasmas 24, 012504 (2017) [http://dx

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“…Ideal stability of the JSOLVER equilibria were evaluated using the PEST-1 code [4], which uses a variational method to minimize the Lagrangian for axisymmetric equilibria, yielding eigenvalues and displacement eigenvectors for all unstable modes. Only those equilibria found by PEST to be ideally unstable to n = 1 modes but stable to n = 2, 3 were retained for further analysis.…”

Section: Ideal Stabilitymentioning

confidence: 99%

Onset and saturation of a non-resonant internal mode in NSTX and implications for AT modes in ITER

et al. 2011

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Motivated by experimental observations of apparently triggerless tearing modes, we have performed linear and nonlinear MHD analysis showing that a non-resonant mode with toroidal mode number n = 1 can develop in the National Spherical Torus eXperiment (NSTX) at moderate normalized β N when the shear is low and the central safety factor q 0 is close to but greater than one. This mode, which is related to previously identified 'infernal' modes, will saturate and persist, and can develop poloidal mode number m = 2 magnetic islands in agreement with experiments. We have also extended this analysis by performing a free-boundary transport simulation of an entire discharge and showing that, with reasonable assumptions, we can predict the time of mode onset.

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Computation of the Magnetohydrodynamic Spectrum in Axisymmetric Toroidal Confinement Systems

Cited by 140 publications

References 35 publications

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Effect of scrape-off-layer current on reconstructed tokamak equilibrium

Onset and saturation of a non-resonant internal mode in NSTX and implications for AT modes in ITER

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