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 NO03: High Field Tokamaks: SPARC, C-Mod, and OthersLive Streamed
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Chair: Ian Hutchinson, Massachusetts Institute of Technology MI Room: Ballroom 100 C |
Wednesday, October 19, 2022 9:30AM - 9:42AM |
NO03.00001: Overview of the high-field path to fusion energy Dan Brunner The SPARC mission is to create and confine a plasma that produces net fusion energy for the first time and the ARC mission is to produce net fusion electricity for the first time. High- temperature, high-field superconductors are the fundamental technology that enables SPARC and ARC to be built at a relatively small scale compared to other proposed net-energy and net-electricity tokamaks; the smaller scale enables them to be completed on a faster timeline. Following the successful completion of the SPARC Toroidal Field Model Coil in summer 2021 and the $1.8B Series B financing for Commonwealth Fusion Systems (CFS) in winter 2021, CFS and its partners are full-steam-ahead on completing the SPARC design and ramping up SPARC construction. The project remains on schedule for first plasma in 2025. In addition, the Series B allows early ARC design and R&D to start in earnest. |
Wednesday, October 19, 2022 9:42AM - 9:54AM |
NO03.00002: The ARC R&D Roadmap Brandon N Sorbom, Cody Dennett, Sara Ferry, Ethan E Peterson, Shiyun Ruan, Michael Short, Caroline Sorensen, Kevin B Woller The most recent developments in the R&D roadmap for an ARC-class fusion power plant are presented in this talk. The original conceptual design for the ARC fusion power plant, a compact, high-field tokamak built using HTS magnets, was presented over two works in Fusion Engineering and Design in 2015 and 2018. Since then, there has been significant advancement in both the physics and technology underlying compact, high-field tokamaks, such as SPARC, as evidenced by the published design basis and hardware demonstrations by CFS, MIT, and collaborators. While SPARC will be risk-retiring many subsystems transferrable to ARC - HTS magnet technology, for example - there are some ARC subsystems which will be risk-retired in parallel to SPARC. Notably, these include the FLiBe molten salt blanket, FLiBe tritium extraction systems, FLiBe-compatible balance-of-plant components, and remote maintenance technology. There are also programs to qualify suitable candidates for fusion power plant structural and functional materials (for both lifetime components and replaceable components like the low activation vacuum vessel) and to demonstrate advanced manufacturing techniques required to optimize performance, cost, and lead times for components. This R&D will be carried out in collaboration with MIT and other research institutions. Performing these R&D efforts in parallel to the construction and operation of SPARC will enable the fastest path to the development, construction, and operation of the first ARC power plant. |
Wednesday, October 19, 2022 9:54AM - 10:06AM |
NO03.00003: Demonstration of Fusion Pilot Plant Physics in SPARC Alexander J Creely, Devon J Battaglia, Michael Brookman, Dan Brunner, Chris Chrobak, Nathan T Howard, Adam Q Kuang, Tom Looby, Robert T Mumgaard, Anders Oberg, Cristina Rea, Matthew L Reinke, Pablo Rodriguez-Fernandez, Steve Scott, Brandon N Sorbom, Ryan M Sweeney, Roy A Tinguely The SPARC tokamak is designed to demonstrate key areas of tokamak physics necessary to design the ARC fusion power plant, and in doing so achieves the Phase 1A goals of a Fusion Pilot Plant as defined in the Bringing Fusion to the U.S. Grid National Academies report [https://doi.org/10.17226/25991]. While early SPARC operations will focus on achieving the Phase 1A Pilot Plant goal of Q>1, later campaigns transition to generating key data to design ARC. High power deuterium operations will extend databases in H-mode confinement, power thresholds, heat flux width, and ELM behavior to high magnetic field (B0 = 12.2T) in a compact (R0 = 1.85m), high density (〈ne〉≈ 3x1020 m-3) tokamak. These campaigns will explore non-ELMing high-confinement regimes such as I-mode (likely accessible given SPARC's field) and possibly others. Fueling at high edge opacity, impurities with RF heating, and disruption prediction and control in SPARC also inform ARC design. Critically, SPARC will operate with power-plant equivalent divertor heat fluxes and tungsten PFCs, allowing ARC-equivalent dissipative divertor solutions to be demonstrated at-scale. High power DT plasmas will closely replicate instantaneous conditions expected in the ARC power plant. |
Wednesday, October 19, 2022 10:06AM - 10:18AM |
NO03.00004: First-principles performance prediction of burning plasmas with self-consistent kinetic profiles Pablo Rodriguez-Fernandez, Nathan T Howard, Jeff Candy Self-consistent, high-fidelity predictions of kinetic profiles are required to accurately scope future experiments and pilot plants. In this presentation, we present a framework that allows for first-principles simulations of core profiles with an accelerated convergence rate [Rodriguez-Fernandez, NF 2022]. The high computational cost of self-consistent, first-principles, multi-channel predictions (which require flux-driven, gyrokinetic frameworks) has long precluded their use to study experiments and to aid the design of new devices. Thanks to the surrogate-based optimization framework presented here, nonlinear simulations of the core of the SPARC tokamak using the CGYRO code have been possible. The predictions of kinetic profiles and performance with full nonlinear turbulence simulations are compared to empirical and TGLF modeling. While all predictive frameworks show the Primary Reference Discharge in SPARC to be above the burning plasma regime (Q>5), clear differences are seen in predicted profiles, in particular in the density peaking. Improvements to the workflow to further reduce the computational cost will also be presented, as well as the potential of the surrogate-modeling techniques to predict variations of the nominal scenario at minimal computational expense. |
Wednesday, October 19, 2022 10:18AM - 10:30AM |
NO03.00005: Equilibrium reconstruction sensitivity studies on SPARC Ian G Stewart, Carlos A Paz-Soldan, Ryan M Sweeney, Darren T Garnier, Robert S Granetz, Alexander J Creely, Clayton E Myers, Devon J Battaglia, Matthew L Reinke Accurate reconstruction of the plasma equilibrium is imperative for the successful operation of the SPARC tokamak. In order to assess the expected reconstruction accuracy throughout the duration of design-point discharges, the EFIT equilibrium reconstruction code was deployed for SPARC. Reconstructions from SPARC baseline scenarios were compared with free-boundary equilibria generated by FreeGS, Toksys, and the Tokamak Simulation Code (TSC). The key geometric areas of interest to focus design tolerances include: the inner and outer gaps, the X-point locations, as well as the strike point locations. The deviation of these and other geometric quantities from their nominal positions in the synthetic equilibria were determined considering the addition of error to synthetic measurements of magnetic flux and magnetic field, contributions from eddy currents in conducting structures, applied resonant magnetic perturbations, and the omission of certain sensor sets. Optimization of the magnetic sensor locations is presented, highlighting a Monte Carlo workflow that balances the engineering constraints of sensor placement with achieving sufficient reconstruction fidelity for science and operations missions. |
Wednesday, October 19, 2022 10:30AM - 10:42AM |
NO03.00006: The SPARC Error Field Strategy Ryan M Sweeney, Nikolas C Logan, Clayton E Myers, Carlos A Paz-Soldan, Alexander J Creely, Robert S Granetz, Cristina Rea, Ruben Tukker, Ted Wyeth, Zimi Zhang SPARC is a high-field DT tokamak experiment with a mission to produce twice the power absorbed by the plasma, but without care, error fields could reduce confinement or even disrupt the plasma. The SPARC error field risk is quantified by considering the probability density functions (PDF) for locking and for the intrinsic error. For the locking PDF, we choose the most sensitive SPARC scenario (i.e. the 12.2 T L-mode) and Monte Carlo sample the ITPA overlap power-law scaling [Logan 2021 PPCF]. Next, the machine intrinsic error PDF is modeled using detailed coil windings and Monte Carlo simulations of the random tilts and shifts. The magnitude of each tilt and shift is represented by a hollow distribution, giving a higher probability of being near the alignment tolerance than below it. The two PDFs are used to derive the probability that the intrinsic error exceeds the correction limit of the error field correction coils, assumed to be twice the locking threshold. Under these assumptions we prescribe the tolerances to reduce the locked mode risk to ≤0.1%, and preliminary tolerancing schemes suggest ~3 mm tolerances on most degrees of freedom. Metrology and direct identification plasma experiments will be used to measure the error field. |
Wednesday, October 19, 2022 10:42AM - 10:54AM |
NO03.00007: Disruption Research for SPARC Cristina Rea, Ryan M Sweeney, Roy A Tinguely, Robert S Granetz, Darren T Garnier, Benjamin Stein-Lubrano, Jinxiang Zhu, Andrew Maris, Matthew L Reinke, Valeria Riccardo, Carlos A Paz-Soldan, Alexander F Battey, Christopher J Hansen, Nathaniel M Ferraro SPARC Disruption Research will deliver first-principle and machine learning-based solutions for disruption prevention strategies ensuring that SPARC will accomplish its mission goals. We present critical research advancements addressing disruption prediction, avoidance, and mitigation strategies on SPARC. First, we will discuss progress made in developing a potential candidate algorithm for the Disruption Mitigation System (DMS) trigger based on deep learning. The algorithm leverages a recently developed complex architecture, showing state-of-the-art performances on several existing tokamaks, with domain adaptation capabilities across devices. Several Massive Gas Injection valves will be installed as SPARC DMS, and a study of their effectiveness for thermal mitigation is required. Results on fueling efficiency investigations, prediction of required quantities, as well as their layout and performance optimization via 3D MHD modeling will be presented. Finally, initial results on the development of the Runaway Electron Mitigation Coil (REMC) research plan will be given: scenario dependent analyses will be presented to evaluate optimal threshold voltages for the REMC switch and added coil resistances to optimize current and effectively suppress runaway electron formation in SPARC. |
Wednesday, October 19, 2022 10:54AM - 11:06AM |
NO03.00008: 3D Electromagnetic Physics-Based Modeling to Support Tokamak Design Alexander F Battey, Christopher J Hansen, Alexander J Creely, Carlos A Paz-Soldan, Darren T Garnier, Devon J Battaglia, Ryan M Sweeney, David B Weisberg Three dimensional electromagnetic capabilities have been developed using the new Psi-Tet finite-element model in support of design work for both the SPARC and DIII-D tokamaks. A 3D model of the SPARC tokamak was used to assess the effect of possible non-axisymmetric eddy currents on future SPARC start-up scenarios such as the ability to produce a large null in the poloidal magnetic field. The connection length during the plasma breakdown phase was also assessed using 3D field line tracing as well as studies in the eigenvalue-domain to determine the modification of 3D-effects on the characteristic vertical instability time-scale. A model of the DIII-D device was also created to study the effects of eddy currents on the performance of a passive runaway electron mitigation coil (REMC) currently being developed which is designed to passively drive large non-axisymmetric fields during the plasma. This coil design has been evaluated using electromagnetic analysis, linear MHD modeling, relativistic drift orbit tracing, and 3D finite-element modeling. This presentation will highlight modeling carried out in support of the design which studied the effect of induced eddy currents on the coils ability to apply a strong n=1 radial field at the plasma magnetic axis. It was determined that these currents had a significant effect on the response-time of the coil and similar studies were completed for the SPARC PREMC which is currently under development. |
Wednesday, October 19, 2022 11:06AM - 11:18AM |
NO03.00009: ICRF Heating Scenarios for SPARC John C Wright, Michael Brookman, Yijun Lin, Pablo Rodriguez-Fernandez, Andrew Seltzman In this talk we will present an overview of the most recent analysis of the ion cyclotron radio frequency (ICRF) heating performance in SPARC H and L-mode scenarios. This includes discussion of the absorbed power fractions that are predicted during both high and low field operation and the status of analysis of RF sheath formation and the potential ICRF coupling during plasma formation. |
Wednesday, October 19, 2022 11:18AM - 11:30AM |
NO03.00010: Surface power density on SPARC PFCs due to lost alphas steven D scott, Gerrit J Kramer, Roy A Tinguely, Thomas Looby, Dina Yuryev, Matthew L Reinke, Nathaniel Shields, Anson Braun, Pablo Rodriguez-Fernandez, Elizabeth A Tolman Alpha-particle simulations using the ASCOT and SPIRAL codes have been performed on candidate SPARC PFC CAD models that include misalignments of the vacuum vessel and limiter surfaces. The computed surface power density is large (~MW/m2), substantially larger than reported previously for SPARC with a simplified wall model (S. Scott et al., J. Plasma Phys 2020). Although the total ripple-induced alpha power loss is small (~100 kW), the loss is highly spatially concentrated on the outer x18 ~130mm wide poloidal rail limiters (peak/mean < 20). Tungsten-based PFCs allow localized fast-ion heat fluxes to be conducted away sufficiently fast to keep surface temperatures well below the melt limit, but at risk of exceeding the recrystallization limit. Banana-trapped alphas experience small radial excursions at the midplane due to ripple, yielding a mm-scale scrape off distance which may be a design driver in long-pulse reactors. The surface power density due to the lost alphas can be spread out by appropriate PFC shaping in the toroidal and poloidal directions, but these adjustments may not be compatible with the need to minimize heat loads from filaments and small ELMs. Additional loss of alpha particles due to 3/2 and 2/1 neoclassical tearing modes is found to increase the surface heating up to ~50%. |
Wednesday, October 19, 2022 11:30AM - 11:42AM |
NO03.00011: 3D PFC Power Exhaust Predictions for the SPARC Tokamak Tom Looby, Matthew L Reinke, Alexander J Creely, Adam Q Kuang, Devon J Battaglia, Dina Yuryev, Steve Scott, Michael Brookman, Valeria Riccardo, Matthew Honickman, Trey Henderson, Kris Anderson Designing PFCs to handle the heat loads that will be present in SPARC involves simultaneous optimization of the tokamak operational scenario and the PFC geometry. A code developed for such analysis, HEAT, is being used to couple these domains of physics and engineering. HEAT uses computer aided design (CAD) models and MHD equilibria to calculate heat fluxes and temperatures using empirical plasma models derived from experimental databases. HEAT can predict heat fluxes that arise as a result of power transported along the magnetic field lines, as well as power transported along the helical trajectories of ions with finite Larmor radii. Recent HEAT development has yielded a deterministic module capable of predicting the radiated power transported by photons from the plasma, as well as inter-PFC photon reflections. This talk will provide a synopsis of the HEAT power exhaust calculations that have been completed to date for SPARC. The heat flux profiles that arise from 3D PFC protection schemes will be highlighted. Time-varying 3D discharge simulations that incorporate strike point sweeping will demonstrate how integrating PFC engineering design with physics operations enables the PFCs to remain within their thermal limits despite peak parallel heat fluxes of up to 10 GW/m2. |
Wednesday, October 19, 2022 11:42AM - 11:54AM |
NO03.00012: Intermittent scrape-off layer plasma fluctuations in Alcator C-Mod at high Greenwald fractions Sajidah Ahmed, Odd Erik Garcia, Adam Q Kuang, Brian LaBombard, James L Terry, Audun Theodorsen Turbulence in the far scrape-off layer (SOL) on the low-field side of tokamak plasmas is defined by intermittent transport events that transfer particles and heat radially outwards. A stochastic model called the filtered Poisson process (FPP) describes fluctuations at a single point in the far SOL as a superposition of uncorrelated events [1]. In this contribution, fluctuation data from gas-puff imaging and mirror-Langmuir probes were analyzed to study the effects of varying the line-averaged density and plasma current (in low-confinement mode and lower-single null configurations) and relate them to the FPP parameters (mean amplitudes, average duration time and intermittency). A variant of the Richardson-Lucy deconvolution algorithm was used to recover more event amplitudes and arrival times from these time series, as opposed to the conditional averaging method. Both diagnostics show that the average duration times of the events are independent of these plasma parameters. Increasing the line-averaged density (increasing Greenwald fraction) leads to strongly enhanced levels of intermittency and is found to increase the probability of large-amplitude events. However, decreasing plasma current (increasing Greenwald fraction) had the opposite result. |
Wednesday, October 19, 2022 11:54AM - 12:06PM |
NO03.00013: Filament structures and average radial scrape-off layer profiles in Alcator C-Mod Gregor Decristoforo, Woonghee Han, James L Terry, Odd Erik Garcia Time-averaged radial profiles of electron temperature and density and their fluctuations are suspected to be set by plasma filaments moving through the scrape-off layer (SOL) [1; 2; 3]. The statistical properties of the plasma filaments (their sizes, velocities, amplitudes and frequency of occurrence) determine both the magnitude and the scale length of the average radial profile. |
Wednesday, October 19, 2022 12:06PM - 12:18PM Author not Attending |
NO03.00014: Non-Thermal ``Cool'' Fusion Considered for the Ignitor Program Piero Ferraris, Bruno Coppi, Gilberto Faelli, Edoardo Boggio-Sella, Renato Spigler, Ignitor Program Members The Ignitor Program [1] has produced the first complete design of a machine capable of approaching ignition regimes with normally known conditions and acceptable safety factors. The ability of high field compact experiments of this kind, that include TRIAM-1 the first high field superconducting machine, to produce well confined plasmas with a wide range of collisionalities, is shown to be suitable also at accessing a variety of interesting physical regimes. These can involve “cool fusion” processes that have been identified theoretically and would allow approaching ignition under milder conditions than those based on the properties of thermonuclear plasmas. A special case is that where the excitation of radially “captive” ballooning modes can provide an efficient energy transfer from reaction products to the tails of the distributions in phase space of the fusing nuclei. The superconducting MgB2 technology that Ignitor has pioneered for the equilibrium coils remains adopted with recent advances. A collaboration with CNR laboratories on near term high field superconducting magnets is undertaken and connects to relevant European research and industrial institutions. |
Wednesday, October 19, 2022 12:18PM - 12:42PM |
NO03.00015: Edge Fueling and Neutral Density Studies of the Alcator C-Mod Tokamak Using the SOLPS-ITER Code Richard M Reksoatmodjo, Saskia Mordijck, Jerry W Hughes, Jeremy D Lore, Francesco Sciortino, Xavier Bonnin, Matthew L Reinke Understanding edge neutral dynamics in high-field tokamaks has strong consequences for both fueling and plasma profile predictions. We validate the ability of SOLPS-ITER, a 2D fluid plasma/kinetic Monte Carlo neutral code, to accurately model upstream neutral density profiles of L-mode, I-mode, and H-mode discharges in the Alcator C-Mod tokamak. Via iterative tuning of perpendicular transport coefficient profiles alone, we achieve modeled Lyman-alpha emission, neutral density, and plasma profiles within empirical measurement uncertainties for all discharges, providing confidence in the baseline SOLPS model to accurately simulate neutrals in the upstream plasma edge. SOLPS is then used to assess the relative role of edge fueling versus transport in high density Alcator C-Mod discharges approaching fusion-relevant opaqueness conditions. We model a set of high density H-mode discharges with gas puffs of varying magnitude applied to probe the response of the density pedestal to increased edge fueling. Analysis of the simulated radial neutral e-folding length reveals that in high opacity conditions, neutrals tend to get trapped in the PFR, suggesting that upstream fueling dominates x-point fueling, an important consideration for future fusion devices operating in high opacity regimes. |
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