| 1. |
- Creely, A. J., et al.
(författare)
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Overview of the SPARC tokamak
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- The SPARC tokamak is a critical next step towards commercial fusion energy. SPARC is designed as a high-field (B-0 = 12.2 T), compact (R-0 = 1.85 m, a = 0.57 m), superconducting, D-T tokamak with the goal of producing fusion gain Q > 2 from a magnetically confined fusion plasma for the first time. Currently under design, SPARC will continue the high-field path of the Alcator series of tokamaks, utilizing new magnets based on rare earth barium copper oxide high-temperature superconductors to achieve high performance in a compact device. The goal of Q > 2 is achievable with conservative physics assumptions (H-98,H- y2 = 0.7) and, with the nominal assumption of H-98,H- y2 = 1, SPARC is projected to attain Q approximate to 11 and P-fusion approximate to 140 MW. SPARC will therefore constitute a unique platform for burning plasma physics research with high density (< n(e)> approximate to 3 x 10(20) m(-3)), high temperature (< Te > approximate to 7 keV) and high power density (P-fusion/V-plasma approximate to 7 MWm(-3)) relevant to fusion power plants. SPARC's place in the path to commercial fusion energy, its parameters and the current status of SPARC design work are presented. This work also describes the basis for global performance projections and summarizes some of the physics analysis that is presented in greater detail in the companion articles of this collection.
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| 2. |
- Izzo, V. A., et al.
(författare)
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Runaway electron deconfinement in SPARC and DIII-D by a passive 3D coil
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:9
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Tidskriftsartikel (refereegranskat)abstract
- The operation of a 3D coil-passively driven by the current quench (CQ) loop voltage-for the deconfinement of runaway electrons (REs) is modeled for disruption scenarios in the SPARC and DIII-D tokamaks. Nonlinear magnetohydrodynamic (MHD) modeling is carried out with the NIMROD code including time-dependent magnetic field boundary conditions to simulate the effect of the coil. Further modeling in some cases uses the ASCOT5 code to calculate advection and diffusion coefficients for REs based on the NIMROD-calculated fields, and the DREAM code to compute the runaway evolution in the presence of these transport coefficients. Compared with similar modeling in Tinguely et al (2021 Nucl. Fusion 61 124003), considerably more conservative assumptions are made with the ASCOT5 results, zeroing low levels of transport, particularly in regions in which closed flux surfaces have reformed. Of three coil geometries considered in SPARC, only the n = 1 coil is found to have sufficient resonant components to suppress the runaway current growth. Without the new conservative transport assumptions, full suppression of the RE current is maintained when the thermal quench MHD is included in the simulation or when the RE current is limited to 250kA, but when transport in closed flux regions is fully suppressed, these scenarios allow RE beams on the order of 1-2 MA to appear. Additional modeling is performed to consider the effects of the close ideal wall. In DIII-D, the CQ is modeled for both limited and diverted equilibrium shapes. In the limited shape, the onset of stochasticity is found to be insensitive to the coil current amplitude and governed largely by the evolution of the safety-factor profile. In both devices, prediction of the q-profile evolution is seen to be critical to predicting the later time effects of the coil.
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| 3. |
- Sweeney, R., et al.
(författare)
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MHD stability and disruptions in the SPARC tokamak
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- SPARC is being designed to operate with a normalized beta of beta(N) = 1.0, a normalized density of n(G) = 0.37 and a safety factor of q(95) approximate to 3.4, providing a comfortable margin to their respective disruption limits. Further, a low beta poloidal beta(p) = 0.19 at the safety factor q = 2 surface reduces the drive for neoclassical tearing modes, which together with a frozen-in classically stable current profile might allow access to a robustly tearing-free operating space. Although the inherent stability is expected to reduce the frequency of disruptions, the disruption loading is comparable to and in some cases higher than that of ITER. The machine is being designed to withstand the predicted unmitigated axisymmetric halo current forces up to 50 MN and similarly large loads from eddy currents forced to flow poloidally in the vacuum vessel. Runaway electron (RE) simulations using GO+CODE show high flattop-to-RE current conversions in the absence of seed losses, although NIMROD modelling predicts losses of similar to 80 %; self-consistent modelling is ongoing. A passive RE mitigation coil designed to drive stochastic RE losses is being considered and COMSOL modelling predicts peak normalized fields at the plasma of order 10(-2) that rises linearly with a change in the plasma current. Massive material injection is planned to reduce the disruption loading. A data-driven approach to predict an oncoming disruption and trigger mitigation is discussed.
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