Divertor heat flux challenge and mitigation in SPARC

Kuang, Adam; Ballinger, S.; Brunner, D.; Canik, J.; Creely, A. J.; Gray, Travis; Greenwald, M.; Hughes, J.W.; Irby, J.; LaBombard, B.; Lipschultz, B.; Lore, J.; Reinke, M.L.; Terry, J. L.; Umansky, M.; Whyte, D.G.; Wukitch, S.

doi:10.1017/s0022377820001117

Cited by 61 publications

(55 citation statements)

References 64 publications

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“…This is a consequence of the impurity assumption and radiation model accounting for coronal equilibrium of all charge states used in this work, which predicts that 39 % of the total power is radiated inside the LCFS (13.2 MW). This significant radiated power fraction can be beneficial for divertor power handling (Kuang et al 2020). Line radiation from W contributes to 46 % of the total radiated power, and comes predominantly from the plasma edge.…”

Section: Transport Physicsmentioning

confidence: 99%

Predictions of core plasma performance for the SPARC tokamak

et al. 2020

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SPARC is designed to be a high-field, medium-size tokamak aimed at achieving net energy gain with ion cyclotron range-of-frequencies (ICRF) as its primary auxiliary heating mechanism. Empirical predictions with conservative physics indicate that SPARC baseline plasmas would reach $Q\approx 11$ , which is well above its mission objective of $Q>2$ . To build confidence that SPARC will be successful, physics-based integrated modelling has also been performed. The TRANSP code coupled with the theory-based trapped gyro-Landau fluid (TGLF) turbulence model and EPED predictions for pedestal stability find that $Q\approx 9$ is attainable in standard H-mode operation and confirms $Q > 2$ operation is feasible even with adverse assumptions. In this analysis, ion cyclotron waves are simulated with the full wave TORIC code and alpha heating is modelled with the Monte–Carlo fast ion NUBEAM module. Detailed analysis of expected turbulence regimes with linear and nonlinear CGYRO simulations is also presented, demonstrating that profile predictions with the TGLF reduced model are in reasonable agreement.

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Section: Transport Physicsmentioning

confidence: 99%

Predictions of core plasma performance for the SPARC tokamak

et al. 2020

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“…The vacuum vessel and all internal components are being designed to withstand the highest expected halo and eddy current forces. Where viable passive solutions have not been identified, such as for the thermal quench divertor heat flux (Kuang et al 2020), active disruption mitigation is planned. Disruption prediction is required to trigger active mitigation and a machine learning approach that can be trained on both existing devices and simulation data is under investigation.…”

Section: Introductionmentioning

confidence: 99%

MHD stability and disruptions in the SPARC tokamak

et al. 2020

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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 $q_{95}\approx 3.4$ , 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 ${\sim }80$ %; 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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“…Unmitigated ELMs on SPARC are likely to be at the high end of this range. Using a set of assumptions for the spatial and temporal distribution of this energy, a range of surface heat flux factor can be calculated and compared with the limits of candidate divertor materials (Kuang et al 2020). To increase margin with respect to the ELM loading limits imposed by divertor PFCs, ELM mitigation schemes require consideration in SPARC.…”

Section: Expectations For Edge Transientsmentioning

confidence: 99%

“…The divertor effect remains one of the largest sources of variability in the projection of power threshold. The SPARC divertor is being designed to facilitate parallel heat flux mitigation via small inclination angle and strike point sweeping, and also to have a long outer leg to enable the creation of an X-point target (Kuang et al 2020). This will create a significant variation on X-point and divertor geometry across various scenarios and even within a single discharge, and may influence the entry into H-mode.…”

Section: H-mode Accessmentioning

confidence: 99%

“…The objective of this manuscript is to describe the methods used to make pedestal projections for SPARC, which can inform both the core performance projections and the divertor power handling requirements, as described in detail in separate papers (Kuang et al 2020; Rodriguez-Fernandez et al 2020). The methods described all have a basis in the extensive experience of the tokamak community.…”

Section: Introductionmentioning

confidence: 99%

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Projections of H-mode access and edge pedestal in the SPARC tokamak

et al. 2020

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In order to inform core performance projections and divertor design, the baseline SPARC tokamak plasma discharge is evaluated for its expected H-mode access, pedestal pressure and edge-localized mode (ELM) characteristics. A clear window for H-mode access is predicted for full field DT plasmas, with the available 25 MW of design auxiliary power. Additional alpha heating is likely needed for H-mode sustainment. Pressure pedestal predictions in the developed H-mode are surveyed using the EPED model. The projected SPARC pedestal would be limited dominantly by peeling modes and may achieve pressures in excess of 0.3 MPa at a density of approximately 3 × 1020 m−3. High pedestal pressure is partially enabled by strong equilibrium shaping, which has been increased as part of recent design iterations. Edge-localized modes (ELMs) with >1 MJ of energy are projected, and approaches for reducing the ELM size, and thus the peak energy fluence to divertor surfaces, are under consideration. The high pedestal predicted for SPARC provides ample margin to satisfy its high fusion gain (Q) mission, so that even if ELM mitigation techniques result in a 2× reduction of the pedestal pressure, Q > 2 is still predicted.

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Divertor heat flux challenge and mitigation in SPARC

Cited by 61 publications

References 64 publications

Predictions of core plasma performance for the SPARC tokamak

Predictions of core plasma performance for the SPARC tokamak

MHD stability and disruptions in the SPARC tokamak

Projections of H-mode access and edge pedestal in the SPARC tokamak

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