Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session BP13: Poster Session: Magnetic Confinement: High Field Tokamaks (9:30am - 12:30pm)On Demand
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BP13.00001: SPARC and the High-field Path to Fusion Energy Martin Greenwald, J. Irby, E. Marmar, D. Whyte, D. Brunner, A. Creely, R. Mumgaard, B. Sorbom The SPARC tokamak is under design as a mid-sized, DT burning experiment. By employing novel high-temperature superconducting magnets, it will achieve 12.2 T, 8.7 MA in a device with R = 1.85 m and a = 0.57 m. The SPARC physics mission is to create and confine a plasma that produces net fusion power and retire risks on the high-field path to commercial fusion energy. The performance to satisfy that mission has been defined as Q $>$ 2 and P$_{Fusion}$ $>$ 50 MW which would be comfortably more than the 25 MW of ICRF input power. Achieving this goal, we believe, would be a sufficient demonstration to place fusion firmly into the world’s energy plans. Significant margin against uncertainties in performance assumptions has been built into the design such that well-established physics predicts that SPARC could produce more than 140 MW of fusion power with Q $>$ 10. Successful operation of SPARC would inform and enable the construction of an ARC-class fusion pilot plant – a device with a major radius on the order of 3 m, producing over 500 MW of fusion power. In this development path, a parallel program to develop required fusion technologies is envisioned as a broadly based collaboration. [Preview Abstract] |
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BP13.00002: Conceptual Design for the ICRF Antennas and Transmission Lines for SPARC Yijun Lin, S.J. Wukitch ICRF will be the sole auxiliary heating method on SPARC to provide up to 25 MW heating power. A total of 12 field-aligned 4-strap antennas in 6 ports has been selected as the first option while 3-strap antennas are the backup antenna option. The k$_{\mathrm{\vert \vert }}$ of the launched fast wave peaks at \textasciitilde 17.5 m$^{\mathrm{-1}}$ for both good core wave absorption and edge coupling. The analysis behind the antenna decision will be presented, including physics analysis on the expected core absorption, edge coupling and impurity control and preliminary engineering analysis for power and voltage handling. The transmission lines and the matching network need to operate under a large range of antenna load for different plasma regime. They also need to maintain matching during periods of rapid load variation during L-H transitions and ELMs. Several methods will be analyzed: fixed-length triple-stub, frequency feedback and external conjugate T. By combining these methods, RF power reflection coefficient $\le $ 11{\%} (VSWR $\le $ 2) can be achieved and maintained for all SPARC plasmas. [Preview Abstract] |
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BP13.00003: UEDGE Modeling of the Scrape-Off Layer and Divertor in SPARC Sean Ballinger, Daniel Brunner, Martin Greenwald, Adam Kuang, Brian LaBombard, James Terry, Maxim Umansky, Michael Wigram The SPARC divertor will need to handle unprecedented levels of heat flux, and detachment through impurity seeding could provide significant benefits. In this work, the UEDGE code is used to explore the SPARC divertor and edge plasma parameter space. The simulations are carried out in the lower-half edge plasma domain of an up-down symmetric double-null configuration. The Braginskii fluid equations are used with anomalous cross-field transport coefficients chosen to obtain agreement with expected midplane plasma profiles, target plate heat flux profiles, and inner/outer divertor power sharing, based on existing empirical scalings. Convective effects are included in the anomalous transport model, a fluid model is used for hydrogen neutrals, and carbon and neon impurities are introduced using the fixed-fraction model. We find that at the full projected exhaust power, a 2{\%} carbon fraction can significantly reduce the peak heat flux to the divertor surface, though not enough ensure divertor survivability without sweeping the strike point. Sensitivity studies are carried out to assess the robustness of the results with respect to the assumptions in the model, in particular the choice of boundary conditions at the outer walls. [Preview Abstract] |
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BP13.00004: Predictive modeling of SPARC divertor conditions using SOLPS-ITER Jeremy Lore, J.M. Canik, A.Q. Kuang, B. LaBombard, B. Lipschultz, M.L. Reinke The SOLPS-ITER code [1] is used to predict divertor conditions and study particle balance and impurity seeding for the SPARC tokamak [2,3]. The simulations use the V2 plasma facing component geometry with a double null magnetic topology biased towards the lower divertor along with 29 MW of boundary input power and a separatrix electron density of 1x1020 m-3. Cross-field diffusivities are selected to approximately reproduce the design guideline heat flux width of \textasciitilde 0.18 mm at the outboard midplane. Under these conditions the flux to the outer target, with peak heat flux density of \textasciitilde 180MW/m2, necessitates mitigation from strike point sweeping or dissipation from impurity species. In the case of tungsten divertor material extrinsic neon seeding is considered, with additional intrinsic sputtering included in the case of carbon divertors. The simulations are used to inform requirements on fuel ion and impurity flow rate, optimal puff locations, and pumping requirements. [1] Bonnin, X., et al Plasma Fusion Res. 11, 1403102 (2016). [2] Creely, A., et al, Submitted to J. Plasma Phys. [3] Kuang, A.Q. Submitted to J. Plasma Phys [Preview Abstract] |
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BP13.00005: SOLPS-ITER study of the relative roles of fueling and plasma transport on setting the density pedestal in high SOL opacity H-modes on Alcator C-Mod Richard Reksoatmodjo, Saskia Mordijck, Jerry Hughes, Jeremy Lore, Xavier Bonnin The formation of the density pedestal is found to be unaffected by high scrape-off layer neutral opacity in experiments performed on Alcator C-Mod, in H-mode regimes approaching ITER-like edge opacities[1]. To assess the roles of fueling vs transport, we use the SOLPS-ITER code to compute neutral density profiles for a high current (1.3MA) and reduced current (1.0MA) discharge. Simulated n_e and T_e profiles are matched to upstream empirical data by varying radial transport coefficient profiles, revealing midplane separatrix neutral densities an order-of-magnitude lower in the high current (~10^15 m^-3) vs lower current (~10^16 m^-3) discharge, in line with measurements of edge neutral densities (~10^17 m^-3) in slightly lower current (0.9MA) C-Mod discharges[1]. A ballooning transport model is implemented to approximate expected poloidal asymmetries[2], resulting in an order-of-magnitude difference between LFS and HFS neutral densities. Fitted neutral density e-folding lengths in the edge are found to saturate with increased plasma density, supporting empirical observations that the pedestal is not sensitive to neutral opacity, and is primarily set by plasma transport. [1] J. W. Hughes et al 2006 Physics of Plasmas 13 056103 [2] B. LaBombard et al 2004 Nucl. Fusion 44 1047 [Preview Abstract] |
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BP13.00006: Current Drive is Tough - Time to Revisit Pulsed Tokamak Reactors Jeffrey Freidberg, Daniel Segal, Antoine Cerfon The work presented here re-examines the long held consensus in the US fusion community that a tokamak reactor must operate as a steady state, rather than pulsed device. There are two basic reasons motivating this re-examination. First, current drive has proven to be more difficult to achieve than originally believed. Second, the recent development of REBCO high field (23 T) superconductors offers the possibility of substantially reducing the size and cost of pulsed reactors. Our analysis presents a side-by-side design comparison of steady state vs. pulsed tokamak reactors, both subject to standard tokamak physics and engineering constraints. A summary of our main conclusions are as follows. (a) Pulsed reactors are competitive with steady state reactors. (b) Our analysis is focused on a 250 MWe reactor rather than the usual larger 1000 MWe reactors. Lower power reactors are desirable from an industrial competitiveness point of view. (c) 250 MWe steady state and pulsed reactors both require an enhanced value of H above the empirical value H$=$1, in order to achieve power balance. (d) High field (23 T) is a potential game changer for steady state reactors, improving performance on virtually all fronts. (e) High field helps pulsed reactors, but not as much as steady state reactors. In fact there is an optimum value of the maximum toroidal magnetic field on the coil (about 16 T) that is below the maximum value achievable technologically. [Preview Abstract] |
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