Magnetohydrodynamics stability of compact stellarators

Fu, G. Y.; Ku, L. P.; Cooper, W. A.; Hirshman, Steven; Monticello, D.; Redi, M. H.; Reiman, A.; Sánchez, Raúl; Spong, D. A.

doi:10.1063/1.874002

Cited by 18 publications

(18 citation statements)

References 20 publications

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“…The development of a second kink stabilization scheme-a three-dimensional corrugation of the plasma boundary with little associated shear-to augment externally generated shear is therefore key to generating attractive kink-stable configurations for NCSX. 5,14 The stabilizing corrugation is illustrated in Fig. 3, which shows the cross section of the reference configuration at several values of the toroidal angle, as well as the cross section of a closely related kink-unstable configuration.…”

Section: A Quasi-axisymmetric Plasma Configurationsmentioning

confidence: 99%

Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments

et al. 2000

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High-beta, low-aspect-ratio (“compact”) stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2–4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A β=4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at β=4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described.

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Section: A Quasi-axisymmetric Plasma Configurationsmentioning

confidence: 99%

Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments

et al. 2000

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“…We asked, moreover, that the rotational transform supplied by rippling the boundary alone be of certain shape and magnitude (for the baseline, monotonically increasing and of magnitude 0.45), that the transform increases as radius increases, and that there exists a magnetic well in the absence of the plasma pressure. Although recent results from W7AS and LHD showed that the linear, ideal MHD theories have limited applicability in predicting the stability limit in stellarators, we still included the stability to the infinite-n ballooning and ideal external kink modes calculated based on such theories as constraints in the optimization since in the NCSX studies we found that including, for instance, the external kinks as a constraint the structure of local shears would respond in such a way that the resulting configuration would generally have more favorable MHD stability characteristics [23]. However, we did not strictly enforce such constraints and in some advanced configurations these constraints were relaxed considerably, as suggested by the nonlinear theory [24].…”

Section: Physics Design and Optimizationmentioning

confidence: 99%

Physics Design for ARIES-CS

2007

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Novel stellarator configurations have been developed for ARIES-CS. These configurations are optimized to provide good plasma confinement and flux surface integrity at high beta. Modular coils have been designed for them in which the space needed for the breeding blanket and radiation shielding was specifically targeted such that reactors generating GW electrical powers would require only moderate major radii (<10 m). These configurations are quasi-axially symmetric in the magnetic field topology and have small number of field periods (≤3) and low aspect ratios (≤6). The baseline design chosen for detailed systems and power plant studies has 3 field periods, aspect ratio 4.5 and major radius 7.5 m operating at β~6.5% to yield 1 GW electric power. The shaping of the plasma accounts for ≥75% of the rotational transform. The effective 2 helical ripples are very small (< 0.6% everywhere) and the energy loss of alpha particles is calculated to be ≤5% when operating in high density regimes. An interesting feature in this configuration is that instead of minimizing all residues in the magnetic spectrum, we preferentially retained a small amount of the non-axisymmetric mirror field. The presence of this mirror and its associated helical field alters the ripple distribution, resulting in the reduced ripple-trapped loss of alpha particles despite the long connection length in a tokamak-like field structure. Additionally, we discuss two other potentially attractive classes of configurations, both quasi-axisymmetric: one with only two field periods, very low aspect ratios (~2.5), and less complex coils, and the other with the plasma shaping designed to produce low shear rotational transform so as to assure the robustness and integrity of flux surfaces when operating at high β.3

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“…All of the configurations explored have large axisymmetric (or toroidal average) elongation and triangularity, to enable good stability to ballooning and kink modes. The vertical mode (n=0) is calculated to be robustly stable [22], allowing consideration of average elongations up to 3.…”

Section: Configuration Design and Stabilitymentioning

confidence: 99%

Physics of Compact Advanced Stellarators

Zarnstorff¹,

Berry²,

Brooks³

et al. 2001

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Abstract. Compact optimized stellarators offer novel solutions for confining high-beta plasmas and developing magnetic confinement fusion. The 3D plasma shape can be designed to enhance the MHD stability without feedback or nearby conducting structures and provide drift-orbit confinement similar to tokamaks. These configurations offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio 4 -4.4 and average elongation ~1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for β > 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at β=4% (the rest is from the coils), thus the equilibrium is much less non-linear and is more controllable than similar advanced tokamaks. The enhanced stability is a result of 'reversed' global shear, the spatial distribution of local shear, and the large fraction of externally generated transform. Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties.3

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Magnetohydrodynamics stability of compact stellarators

Cited by 18 publications

References 20 publications

Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments

Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments

Physics Design for ARIES-CS

Physics of Compact Advanced Stellarators

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