Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session TM10: Mini-Conference: The Integrated Tokamak Exhaust and Performance Gap IILive Streamed
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Chair: Robert Wilcox, ORNL Room: 206 CD |
Thursday, October 20, 2022 9:30AM - 9:35AM |
TM10.00001: Introductory Remarks
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Thursday, October 20, 2022 9:35AM - 9:55AM |
TM10.00002: Improvements in wall conditioning and performance throughout the phase I of WEST operations Alberto Gallo, David Douai, Nicolas Fedorczak, Thierry Alarcon, Vivien Anzallo, Clarisse Bourdelle, Sebastijan Brezinsek, Jerome Bucalossi, Eric Caprin, Matthieu De Combarieu, Corinne Desgranges, Pascal Devynck, Annika Ekedahl, Jonathan Gaspar, Christophe Guillemaut, Remy Guirlet, James Paul Gunn, Julien Hillairet, Thierry Loarer, Patrick Maget, Pierre Manas, Philippe Moreau, Francis-Pierre Pellissier, Emmanuelle Tsitrone The tungsten (W) Environment in Steady-state Tokamak (WEST) is the only superconducting EU device with metallic plasma-facing components (PFC). The main goal of WEST is to test actively cooled, ITER-like, W diverter PFC under a steady state heat load of qdiv~10 MWm-2. In campaigns 1 and 2 no glow discharge boronization (GDB) was performed, to study W PFC all installed at once. After a challenging commissioning, frequent deuterium (D2) glow discharge cleaning (GDC) led to pulses up to ~10 s, lower hybrid power up to PLH~2.4 MW, and central density up to n~1.5e19 m-2, but with high impurity content, radiated fraction frad>0.8, and qdiv~0 MWm-2. During campaign 3, besides D2 and helium GDC, diborane (B2D6) GDB was first deployed, significantly opening the operational space: improved startup conditions and lower oxygen content allowed for long pulses (>30 s) at more than twice the density ( n~3.5e19 m-2), with higher injected power (PLH~5 MW), lower frad~0.6, and qdiv~2.5 MWm-2. Large use of GDC and GDB in campaign 4, with a renewed GD system in campaign 5, pushed performance further: WEST achieved minute-long pulses with better LH coupling and qdiv~6 MWm-2. W content remains high and the spectral brightness of light impurities sputtering W (mainly oxygen and carbon) rises back to pre-GDB levels after a few long pulses. |
Thursday, October 20, 2022 9:55AM - 10:15AM |
TM10.00003: Impact of the separatrix plasma on core L mode performances in the WEST full W environment Clarisse Bourdelle, Jorge Morales, Jean-François Artaud, Ondrej Grover, Tenessee Radenac WEST database analysis shows a correlation of the recycled neutral source around the separatrix with core performances. This observation questions the causality chain between particle source and turbulent transport up to the core in L mode, high recycling plasmas, an unavoidable phase of all scenarios. |
Thursday, October 20, 2022 10:15AM - 10:35AM |
TM10.00004: A systems engineering approach to integrated design of a steady-state fusion pilot plant David B Weisberg, Brian A Grierson, James Leuer, Orso M Meneghini, David Humphreys, Tsuyoshi Akiyama, Wayne M Solomon, Paul Beharrell, Dariusz Appelt, Ross MacDonald, Kurt Zeller, Mark Tillack, Kevin McLaughlin, Jonathan H Yu, Jerome Guterl, Zichuan A Xing, Jayson L Barr, Joseph T McClenaghan An integrated design study of a fusion pilot plant (FPP) is conducted, with an emphasis on accelerating the development cycle via mature design tools and an iterative workflow. This workflow is based on the systems engineering approach to product development, which prioritizes the strategic and technical requirements of such a facility from both the stakeholder and developer perspectives. Starting with the FPP requirements proposed in the NASEM 2021 report "Bringing Fusion to the U.S. Grid", this design study first outlines the necessary aspects of each major subsystem in the FPP via functional decomposition. A cost-based systems code optimization then narrows the reactor operating space, with a steady-state advanced tokamak (AT) solution shown to be the lowest cost path to a 200MW(e) pilot plant. Each FPP subsystem is modeled with high-fidelity physics and engineering computational tools to validate the integrated system performance, and functional conflicts between subsystems are resolved via iterative design evolution. A set of trade studies are conducted to down-select among critical design choices, and the sensitivity of the final FPP conceptual design parameters is discussed. |
Thursday, October 20, 2022 10:35AM - 10:55AM |
TM10.00005: Characterization of Turbulence and Transport in a Tokamak Power Plant Christopher G Holland Starting from some general considerations, a simple model of transport in a tokamak power plant is proposed. The most important conclusion is that the plasma must be sufficiently well-coupled that there is significant ion thermal transport across the plasma core, even though alpha heating of the electrons will dominate over other heating processes. In addition, the lower collisionality of a future reactor relative to current devices means that neoclassical transport will be inherently weaker relative to turbulent processes in a reactor. When combined with the “fingerprint” paradigm [1], it then follows that tokamak reactor transport must be dominated by ion temperature gradient and/or kinetic ballooning mode turbulence across most of the confined plasma volume. In the context of core-edge integration, the key open questions are whether these instabilities will control transport across the entire confined plasma volume, and if not, how close to the edge does the transition to a different dominant transport process happen for reactor-relevant conditions? Implications for topics including density peaking and model validation in current facilities will be discussed. |
Thursday, October 20, 2022 10:55AM - 11:15AM |
TM10.00006: Leveraging Peeling Pedestal Physics in the Super H-Mode as a Platform for Integrated Core-Edge Studies Theresa M Wilks, Philip B Snyder, Matthias Knolker, David Eldon, Florian M. Laggner, Carlos A Paz-Soldan, Tom Osborne, Alessandro Bortolon, Florian Effenberg, Charles J Lasnier, Adam McLean, Filippo Scotti, Colin Chrystal, Jonathan G Watkins, Alan W Hyatt, Huiqian Wang, Livia Casali, Max E Fenstermacher, Brian A Grierson, Jerry W Hughes DIII-D experiments assess compatibility of Super H-mode (SH) pedestals with high divertor radiation using advanced feedback algorithms for density and radiated power control with impurity seeding. The SH regime, with a current-limited pedestal, allows co-optimization of important parameters for future devices such as pedestal pressure, collisionality and separatrix density. Four optimization avenues for core edge integration have been developed: 1) divertor-focused solution with N2 seeded partially detached plasmas in an open divertor with ~25% degradation to core performance; 2) high recycling open divertor at the onset of detachment with modest penalties (<5%) to core performance, 80% radiated power fraction, 3) closed divertor SH plasmas at detachment onset, and 4) core-focused solution with a modestly cooled, attached open divertor. The high recycling divertor at detachment onset maximizes confinement on closed flux surfaces while providing a target plasma for testing high heat flux scenarios on various divertor configurations. The SH pedestal in the closed divertor is more resilient to D2 puffing than the open divertor, showing less degradation with increased gas. EPED predictions are consistent with experimental pedestal stability, but work is needed to extend stationarity. |
Thursday, October 20, 2022 11:15AM - 11:35AM |
TM10.00007: Real-time wall conditioning in lower and upper divertor configurations at DIII-D Florian Effenberg, Alessandro Bortolon, Tyler Abrams, Darin R Ernst, Florian M. Laggner, Robert A Lunsford, Rajesh Maingi, Alexander Nagy, Jun Ren, Dmitry L Rudakov, Morgan W Shafer, Theresa M Wilks Real-time injection of low recycling powders in cumulative amounts of >100 mg has improved wall conditions and reduced carbon and oxygen influxes at DIII-D in upper, lower, single, and double null configurations. Pure boron and boron nitride powders have been injected in L-mode and H-mode plasmas at several tens of mg/s for durations up to 3 s into the plasma crown or the divertor. Post-mortem analysis of witness samples confirmed the growth of B layers at rates of 1 nm/s, sufficient to re-instate conditions similar to glow-discharge boronization. Real-time powder injection has also been successfully applied at AUG, EAST, KSTAR, NSTX, WEST, LHD, and W7-X for wall conditioning, reduction of C and W sputtering and enhanced plasma performance. Modeling shows that 1-10 µm particles ablate fully in the scrape-off layer (SOL) while >100 µm particles may introduce additional impurity sources in the core. Far SOL ion flows mostly determine boron deposition patterns on the plasma-facing components. The results suggest real-time surface conditioning can extend the operational window for long-pulse and low-collisionality scenarios and help replenish eroded walls in next-step devices. |
Thursday, October 20, 2022 11:35AM - 12:30PM |
TM10.00008: Panel Discussions
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