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 PM10: Mini-Conference: The Integrated Tokamak Exhaust and Performance Gap ILive Streamed
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Chair: Nathan Howard, MIT; Brian Grierson, General Atomics; Livia Casali, University of Tennessee Knoxville Room: 206 CD |
Wednesday, October 19, 2022 2:00PM - 2:05PM |
PM10.00001: Introductory Remarks Livia Casali . |
Wednesday, October 19, 2022 2:05PM - 2:34PM |
PM10.00002: Strategic Input Developed by the Boundary/PMI and High Heat Flux Expert Groups during the Community Planning Process Tyler Abrams, Aaro Jarvinen, Ane Lasa Esquisabel, Matthew L Reinke, George R Tynan A review of strategic roadmaps towards construction and operation of a Fusion Pilot Plant (FPP), as developed by the Boundary/PMI and High Heat Flux expert groups during the 2019-2020 APS Community Planning Process, will be presented. Five critical physics gaps (CPGs) were identified in the areas of (1) divertor detachment control; (2) heat flux widths; (3) damaging edge transients; (4) material migration; and (5) core-edge integration. Additionally, five key engineering design issues (EDIs) were identified regarding (a) heat flux limits; (b) tritium retention probability; (c) synergistic irradiation effects, (d) first wall lifetime, and (e) manufacturability, waste, and licensing. A set of coordinated program elements (based on community white paper submissions) comprising each of these roadmaps will be discussed and the level of outstanding risk for FPP assessed within the context of these CPGs and EDIs. Roadmaps range from "major risk," where bold steps towards fusion energy in the near term are almost completely missing, to "reduced risk" where all CPGs and EDIs are addressed before FPP operation at the expense of significantly increased cost and/or development time. |
Wednesday, October 19, 2022 2:34PM - 3:03PM |
PM10.00003: Implications of net erosion and redeposition of solid-surface plasma facing material in long-pulse fusion devices E.A. Unterberg, Peter C Stangeby, J.W. Davis, Alessandro Bortolon, Igor Bykov It is estimated that long-pulse fusion devices may experience rates of net erosion and deposition of solid PFC (Plasma Facing Component) material of 103 – 105 kg/year, whatever the material used. Even if the net erosion (wear) problem can be solved, the redeposition of so much material has the potential for major interference with operation. The potential implications appear to be no less serious than for plasma contact with the divertor target, i.e., a dust explosion or major UFO-disruption could be as damaging as target failure for an actively-cooled device. It will therefore be necessary to manage material deposits to prevent fouling operation. This situation appears to require a fundamental paradigm shift regarding meeting the challenge of taming the plasma-material interface; in that any acceptable solid PFC material will in effect be flow-through, like liquid-metal PFCs, although at far lower mass flow rates. Therefore, the solid PFC material will have to be treated as a consumable like brake pads in cars. A critical open issue is the formation of large/thick redeposited material in the divertor region, colloquially called slag. Unfortunately, understanding and predictive capability for the formation and stability of these thick layers is almost completely lacking, but new developments, like powder dropping into discharges, provide a unique opportunity to carry out controlled studies on the management of low-Z slag in all current magnetic confinement devices. The implications for such a paradigm shift and near-term research needs will be discussed. |
Wednesday, October 19, 2022 3:03PM - 3:32PM |
PM10.00004: Resolving the ITEP Divertor Exhaust Physics GAP with DIII-D Anthony Leonard Since dimensionless demonstrations of atomic physics-dominated regimes are not possible, DIII-D is proposing hardware upgrades to validate the underlying physics of models used to design and project exhaust solutions for a fusion pilot plant (FPP). To achieve this, DIII-D divertor plasmas must reach parameter regimes where the appropriate processes are significant in determining the boundary layer plasma conditions. With field, current, shape and power upgrades, the characteristic scale lengths of atomic physics processes of ionization, recombination, neutral interactions and radiation opacity are projected to be smaller than both the radial and poloidal lengths of the divertor. This will make possible the study of these processes in a regime similar to that for a FPP. Recent data has shown that increased radial transport can be driven at high power density, allowing for dissipative divertor operation at lower core electron and impurity density than predicted by empirical heat flux width scaling. Finally, DIII-D’s proposal for a modular divertor will provide a test of the minimum divertor leg length needed for maintaining a hot X-point and robust H-mode pedestal plasma. Working alongside other high-performance facilities, this will close a critical part of the ITEP gap for an FPP. |
Wednesday, October 19, 2022 3:32PM - 4:01PM |
PM10.00005: Design and Utilization of SPARC To Address ITEP Gaps for ARC Matthew L Reinke, Adam Q Kuang, Jerry W Hughes, Nathan T Howard, Pablo Rodriguez-Fernandez, Carlos A Paz-Soldan, Ryan M Sweeney, Jeremy D Lore, John Canik, Bruce Lipschultz, Dennis G Whyte, Alexander J Creely, Dan Brunner, Robert T Mumgaard, Valeria Riccardo, Ana Koller, Chris Chrobak The SPARC tokamak is expected to begin operation in mid-2025 and be used to inform the design of an ARC pilot plant that can begin operation in the early 2030’s. This will require using SPARC to close known exhaust physics gaps faster than any anticipated timeline for a DOE-led EXCITE facility. SPARC physics and engineering details relevant for addressing ITEP gaps are outlined. The divertor and diagnostic set are designed to test access to and control of detached divertor solutions at pilot-plant relevant unmitigated SOL heat fluxes, q|| ~10 GW/m2, in a variety of magnetic geometries. The high-field operating space allows investigation of ELM-less scenarios like I-mode, and pellet-pacing and external coils to produce n=3 RMPs allow for exploration of ELM mitigation and suppression in H-mode. SPARC’s PFCs will use tungsten, and while its total plasma operational life limits understanding of long-term material migration, gaps related to main-chamber erosion mechanisms (C-X, filaments) at pilot-plant relevant pedestal conditions can be closed. The study of burning plasma physics in a fully integrated reactor scenario will be possible if H98 ~ 0.9-1.0 can be sustained in detached, D-T plasmas. No technology barrier is expected to preclude SPARC from achieving this goal. |
Wednesday, October 19, 2022 4:01PM - 4:30PM |
PM10.00006: A Performance Upgrade to Resolve the Physics of the ITEP Gap with DIII-D Richard J Buttery The critical challenge for a viable concept for a fusion pilot plant is to resolve a highly dissipative divertor and its compatibility with a high-performance core. An upgrade to DIII-D is proposed to close gaps on reactor physics regimes in divertor, SOL, pedestal and core, to test critical physics, pioneer solutions and resolve their mutual compatibility. The key is to raise pressure. This enables high density to be sustained at low collisionality to marry a high dissipation divertor with a high-performance core. This is achieved through a rise in shaping, field, current and RF power, exploiting the natural properties of improved pedestals at high shape to close gaps and push limits. The increased parallel heat flux and density raise opacity and shorten mean free paths to access reactor relevant physics in the divertor. This also shortens neutral penetration depths into the core to study relevant particle and impurity transport with unique access into low collisionality, thermalized, peeling limited reactor-like regimes. A modular divertor, high Z wall coatings and DIII-D’s flexible plasma configurations then provide the range to test physics, solutions and their materials compatibility in divertor and core in order to resolve and project the approach for the pilot. |
Wednesday, October 19, 2022 4:30PM - 4:59PM |
PM10.00007: Physics and engineering drivers for the mission and design of an EXCITE facility Jonathan E Menard, Brian A Grierson, Tom Brown, Chirag Rana, Yuhu Zhai, Francesca M Poli, Rajesh Maingi, Walter Guttenfelder Compact tokamaks have been proposed as a means of potentially reducing the capital cost of a fusion pilot plant (FPP). However, compact tokamak FPPs with higher magnetic field and reduced major radius and surface area face the challenge of integrating high core confinement, plasma pressure, and high divertor parallel heat flux and wall loading. This integration is sufficiently challenging that construction and operation of an EXhaust and Confinement Integration Tokamak Experiment (EXCITE) has been proposed by the U.S. community to close this integration gap. This presentation will review EXCITE in the context of present and planned facilities and describe recent systems studies and design activities for superconducting steady-state EXCITE facilities. Specific core-edge integration challenges including edge density operating windows and choice of impurities for detached divertor operation, the potential to access turbulence-driven broadening of the scrape-off-layer heat fluxes, and H-mode access and sustainment with high core radiation fraction will be described as a function of facility size and aspect ratio [1]. |
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