Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Plasma Physics
Monday–Friday, October 30–November 3 2023; Denver, Colorado
Session NO05: MFE: SPARC Tokamak and High Magnetic Field Devices |
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Chair: Florian Laggner, North Carolina State University Room: Governor's Square 14 |
Wednesday, November 1, 2023 9:30AM - 9:42AM |
NO05.00001: The high magnetic field path to fusion energy Dan Brunner Commonwealth Fusion Systems (CFS), in collaboration with MIT and other institutions, is building the SPARC tokamak to demonstrate net fusion energy. SPARC is enabled by recent advances in high-field superconducting magnets by CFS and MIT. Construction of SPARC is well underway, with most major buildings complete and the first toroidal field coil being manufactured by CFS. In addition, CFS is beginning R&D for its envisioned fusion pilot plant, ARC. Research and development is focused on critical areas such as: fusion nuclear materials, tritium processing, and molten salt blankets. This talk will give an update on progress CFS and its collaborators have made on the high magnetic field path to fusion energy since this conference last year. |
Wednesday, November 1, 2023 9:42AM - 9:54AM |
NO05.00002: Q > 1 operation space in the first SPARC campaign Devon J Battaglia, Thomas A Body, Michael W Brookman, Alex J Creely, Thomas Eich, Christoph Hasse, Clayton E Myers, Matthew L Reinke, Steve Scott, Ryan M Sweeney, Nathan T Howard, Amanda E Hubbard, Jerry W Hughes, Conor J Perks, Cristina Rea, Pablo Rodriguez-Fernandez, John E Rice, Audrey Saltzman, Alex Tinguely, Theresa M Wilks, Michael Wigram, Andrew O Nelson, Carlos A Paz-Soldan, Nikolas C Logan Q > 1 is predicted to be achieved on SPARC with L-mode confinement scaling assumptions, Ip ~ 8.5 MA, and BT = 12.2T, producing more than 8 MW of D:T fusion power for at least two seconds. L-mode Q > 1 operation space exists at volume average densities in the range of 1 - 3 x 1020 m-3 (fG = 0.12 - 0.36) where the lowest densities are near the expected LOC-SOC confinement transition. Probabilistic analysis of error field sources quantifies a < 1% chance that access to low density will be restricted by locked-modes. Reduced models of the ICRH heating provide fast estimates of the RF coupling and operation limit at low density. The core and boundary impurity species and concentrations are set by the requirements to radiate sufficient power to reach strike point temperatures, ~40 eV, that do not exceed prior empirical demonstrations while also maintaining Zeff < 3 as required by the ohmic flux consumption rate and minimizing the dilution of the main ions. Elevating the L-mode confinement scaling expectation by 20% results in achieving Q > 1 over a wide operational window, while reducing it by 20% makes Q > 1 unlikely in L-mode. Recent L-mode energy and particle transport predictions for SPARC help quantify the likelihood of success for the Q > 1 mission with L-mode scenarios. |
Wednesday, November 1, 2023 9:54AM - 10:06AM |
NO05.00003: Integrating edge exhaust in SPARC L-mode scenario development Thomas A Body, Adam Q Kuang, Matthew L Reinke, Thomas Eich, Tom Looby, Michael W Brookman, Christoph Hasse, Pablo Rodriguez-Fernandez, Nathan T Howard, Michael Wigram, Sean B Ballinger, Leonardo Corsaro, Oak A Nelson High performance L-modes on SPARC operate with high plasma current (∽8.5MA) and poloidal magnetic field (Bpol,omp∽3T), resulting in a narrow heat flux decay length of λq∽0.6mm (Brunner scaling). The Q>1 scenario requires just ∽10MW of heating power, but because of the narrow SOL width the predicted unmitigated heat fluxes in L-mode will be 20MW/m2 perpendicular to the target. To avoid recrystallization or excessive sputtering of the tungsten divertor targets, scenario development in SPARC will target radiative, impurity-seeded regimes. A model for impurity-seeded core and edge radiation has recently been integrated into the CFS-POPCON 0D scoping tool. Here, we use a two-point-model and a Lengyel-model to determine the xenon and neon concentrations required to achieve a given target temperature, and calculate a consistent dilution and effective charge (Zeff). A scenario achieving Q>1 in L-mode was identified with a surface heat flux of 4MW/m2, a 40eV target and a 140eV upstream temperature. This scenario uses 60% core radiation and 80% edge radiation, resulting in a fuel dilution of ∽85% and a Zeff of ~2.5. The scenario is now being studied using higher-fidelity core and edge simulations. |
Wednesday, November 1, 2023 10:06AM - 10:18AM |
NO05.00004: Predictions of Reactor Performance Utilizing Nonlinear Gyrokinetic Simulations: SPARC, ITER, and ARC-class reactors Nathan T Howard, Pablo Rodriguez-Fernandez, Christopher G Holland, Alexander J Creely, Jeff Candy |
Wednesday, November 1, 2023 10:18AM - 10:30AM |
NO05.00005: Neutron based measurements planned in SPARC early campaigns Prasoon Raj, Russell Gocht, Ian Holmes, Matthew L Reinke, Roy A Tinguely, John L Ball, Shon P Mackie, Xinyan Wang, Enrico Panontin The SPARC mission of demonstrating Q > 1 in its first year of operations requires accurate neutron yield measurements, and multiple instruments are being designed for use in early campaigns. A set of 15 flux monitors at various locations in the tokamak hall will deliver yield data on fast (dt~10 ms) timescales for real-time control. They use 235U and 238U fission chambers and 10B based proportional counters and compensated ion chambers. A neutron activation system, with foil irradiation locations re-entrant into the vacuum vessel and pneumatic retrieval tools, will monitor the neutron yield per pulse. A radial neutron camera with ≥ 7 collimated lines of sight, served with spectrometric detectors (diamond and liquid organic scintillator), will provide emissivity profiles with spatial resolutions of a/8 (~7 cm), and support in reconstruction of Ti and ni profiles and potentially also the confined fusion product distribution functions. Finally, a magnetic proton recoil spectrometer providing dE/E~1% at DT/DD peak, is planned for a radial, midplane line of sight. Detectors' optimization for over 4-5 decades wide dynamic range is discussed here, and engineering design for the port components and the neutron laboratory (part of SPARC diagnostics hall) are also highlighted. |
Wednesday, November 1, 2023 10:30AM - 10:42AM |
NO05.00006: Measuring fusion gain Q > 1 in SPARC Roy A Tinguely, Matthew L Reinke, Carlos A Paz-Soldan, John L Ball, Robert S Granetz, Nathan T Howard, Shon Mackie, Enrico Panontin, Conor J Perks, John E Rice, Pablo Rodriguez-Fernandez, Xinyan Wang, Devon J Battaglia, Alexander J Creely, Russell Gocht, Ian Holmes, Clayton E Myers, Prasoon Raj, Didier Vezinet, Alexandra Lachmann, Nils Leuthold, Ian G Stewart An early-operations mission of the SPARC tokamak [Creely 2020 JPP] is to achieve a fusion plasma gain Q > 1, a measurement which will be fairly scrutinized. In this talk, we present an approach to make this claim with confidence and transparency. The numerator of Q will be the total fusion power (Pfus) from a majority DT plasma with He3 as a minority species. A suite of neutron diagnostics will make complementary and redundant (primarily DT) fusion neutron measurements. Kinetic profile information (density, temperature, and dilution) will also be used to assess Pfus, with a minimum viable subset of measurements and chords down-selected by exploring a range of physical synthetic profiles. The denominator of Q will be the sum of ohmic power (measured by standard magnetics) and radio frequency (RF) heating less the stored energy’s rate of change (dW/dt). The RF contribution will be the power launched from the antennas, not necessarily absorbed by the plasma, which is both conservative and easier to measure. A relative contribution of |dW/dt| <10% is targeted to define a "quasi-stationary" scenario. Lastly, statistical methods are explored to evaluate confidence in Q > 1 based on these diagnostics’ data and expectations for their random and systematic uncertainties. |
Wednesday, November 1, 2023 10:42AM - 10:54AM |
NO05.00007: Error Field Physics Constraints on SPARC Assembly Tolerances Nikolas C Logan, Ryan M Sweeney, Clayton E Myers, Carlos A Paz-Soldan, Alexander J Creely, Nils Leuthold, Ruben Tukker, Zimi Zhang, Ted Wyeth, Brad Gallant, Guy Sandford A statistical likelihood model of SPARC construction asymmetries provides error field expectations that, together with a model of the mode locking threshold, constrain tolerances for device construction and assembly. The combination of high field and compact geometry in SPARC means slight asymmetries in the coils can potentially produce deleterious 3D error fields (EFs) that lead to mode locking. To ensure that the EFs do not compromise the SPARC mission, a model including the intrinsic asymmetries of the primary coil windings as well as a statistical model of the shaping (construction) and location (installation) tolerances for each coil is used to produce an EF probability density function (PDF) for the fully assembled machine. This, together with a PDF of mode locking taken from the empirical ITPA EF threshold scaling, provides the risk of locking for any set of given coil designs and tolerances. The full device model enables fast iterative assessment of interconnected coil geometries and assembly plans, examples of which will be shown in this presentation. The EF and locking PDFs it provides also enable efficient mapping of the EF risk across scenarios, providing maps of safe operating regimes for SPARC. |
Wednesday, November 1, 2023 10:54AM - 11:06AM |
NO05.00008: Retiring risk for ion cyclotron range of frequency heating in SPARC through modeling Gregory M Wallace, Christina Migliore, John C Wright, Michael W Brookman, Michael Garrett The SPARC tokamak will primarily rely on ion cyclotron range of frequency (ICRF) heating to reach the high temperatures necessary for fusion breakeven. This talk will cover modeling activities at MIT and CFS leading to the final design of the SPARC Ion Cyclotron Antenna (ICAN). Installing a pair of 4 strap toridally aligned antennas into each of 7 ports should allow for >25 MW coupled power. Two-dimensional modeling efforts of far-field sheath rectification during ICRF heating is underway using the STIX code developed at MIT. The results from scans for various absorption scenarios will be reported, including implications for high-Z impurity generation. Modifications to the TORIC code allow for multiple antennas at specified poloidal locations corresponding to the SPARC ICAN geometry. Simulations show that RF waves from antennas located above and below the plasma mid-plane damp somewhat off-axis (rho ~ 0.2-0.3) as compared with a single antenna at the mid-plane (rho ~ 0-0.1) due to intersection of the launched waves with the cyclotron resonance layer at finite vertical displacement from the mid-plane. |
Wednesday, November 1, 2023 11:06AM - 11:18AM |
NO05.00009: Time-domain modeling of RF sheath potentials for impurity production estimates in SPARC Thomas G Jenkins, David N Smithe, Andy Yue, Davide Curreli, Mikhail Rezazadeh, Michael W Brookman, Michael Garrett We discuss ongoing efforts to estimate impurity production from sputtering during ICRF heating on SPARC, arising from RF-rectified sheaths in the near field of the ICRF antennas. Tech-X’s VSim time-domain plasma-and-sheath software model provides detailed RF sheath information, for use by UIUC’s plasma-material interaction codes [hPIC2/F-TriDYN/RustBCA/GITR], to provide local estimates of impurity yields. This talk focuses on the first part of this process, i.e. the calculation of the ICRF antenna near-fields and sheath voltages. Accurate CAD-derived 3D geometry of the vessel, ICRF antenna, and limiters is used, together with plasma profiles and confining magnetic fields based on previous SPARC operational studies in TRANSP. Of primary concern are sheaths on the limiters immediately adjacent to the antenna, and on the Faraday shields. Preliminary results indicate that SPARC’s high magnetic field and thin dense SOL yield sheath conditions that can result in sputtering when the RF antennas, as presently designed, are run at full power. The nature of RF sheaths on the Faraday shields, in parallel alignment to the magnetic field, may also be more significant in this regime. |
Wednesday, November 1, 2023 11:18AM - 11:30AM |
NO05.00010: Argon pumpout by ICRF waves in C-Mod L- and I-mode plasmas Conor J Perks, Ivan Marshall, John E Rice, Yijun Lin, Francesco Sciortino, Matthew L Reinke Pumpout of argon ions by ICRF waves has been observed in C-Mod deuterium L- and I-mode plasmas with substantial hydrogen dilution [1]. Time traces for different spectrometer lines-of-sight suggests that this effect is stronger at mid-radius than in the plasma center. X-ray and VUV data is therefore inverted to infer impurity charge state density profiles to understand where in the plasma impurities are being pumped out and how many ions are removed. This is done using ImpRad, a Bayesian optimization framework that samples transport coefficient inputs into the AURORA impurity transport forward model until synthetic brightness profiles match the experiment [2, 3]. We hypothesize that, at an optimal hydrogen-to-deuterium ratio, the ICRF directly heats the argon increasing the radial excursion of the banana orbits until the ions drift out of the plasma, causing pumpout. To confirm this, the ASCOT4-RFOF full-orbit solver is used to track argon ion trajectories during RF heating [4]. We will present analysis comparing experimentally inferred argon density profiles against predicted density and brightness profiles from turbulent, neoclassical, and orbit loss transport calculations. We then extrapolate these results to envisage an optimized scheme to actively pumpout tungsten in SPARC. |
Wednesday, November 1, 2023 11:30AM - 11:42AM |
NO05.00011: Comparison of high-Z triggered disruptions in metal-walled tokamaks Robert S Granetz, Eric Nardon, Emmanuelle Tsitrone, Arne Kallenbach, Dalong Chen, Benjamin Stein-Lubrano, Adam Q Kuang, Philippe Moreau, Yann Corre, Jonathan Gaspar, J Gerardin, R Mitteau More than 25% of disruptions on Alcator C-Mod were triggered by injections from molybdenum tiles in the divertor. These so-called 'UFO' events triggered thermal quenches in just 2-5 ms, which precluded the possibility of successfully initiating any avoidance or mitigation actions. An ongoing ITPA joint study of other tokamaks with high-Z plasma-facing surfaces seems to show that C-Mod was unique in this regard. Some high-Z tokamaks do not experience UFO injections in significant numbers, while others have high-Z injections, followed by MHD leading to disruptions, but the disruptions occur hundreds of milliseconds after the injection, and therefore mitigation actions are potentially possible. Possible reasons for the observed differences include the precision of pre-campaign tile alignment, the ability to maintain tile alignment throughout campaigns, the prevalence of open diagnostic ports, and perhaps differences between molybdenum and tungsten, but a definitive explanation has not been determined yet. The source of high-Z injections is usually overheated tiles, but recent long-pulse operation on WEST has shown that build-up of loosely bound layers of redeposited tungsten can also be a significant source. These observations clearly have important implications for ITER, SPARC, and future tokamaks with high-Z plasma-facing components and high power densities. |
Wednesday, November 1, 2023 11:42AM - 11:54AM |
NO05.00012: 3D Disruption Radiation Modeling and Considerations for SPARC Bolometry Design Benjamin Stein-Lubrano, Ryan M Sweeney, Rebecca Li, Jacob Rabinowitz, Nathaniel M Ferraro, Robert S Granetz, Valerie Izzo, Andreas Kleiner, Jack J Lovell, Earl Marmar, Matthew L Reinke, John E Rice At peak performance, SPARC plasmas will reach higher thermal stored energy density than previous tokamaks, over 1MJ/m3. The release of this energy on thermal quench timescales of a millisecond or less risks melt damage. Disruptions on SPARC will be mitigated through Massive Gas Injection (MGI). MGI performance will be evaluated using a dedicated set of 60○ toroidally spaced bolometer arrays deployed to measure disruption radiation. Bolometer designs are tested against virtual disruption radiation from M3D-C1 and NIMROD MGI simulations. Virtual radiation is observed in the Cherab synthetic diagnostic framework to produce synthetic bolometry measurements, as well as local radiation intensities on plasma facing components. Radiation structure reconstruction is conducted through Emis3D to ensure that disruption radiated power and peaking factors can be accurately determined from planned bolometer sightlines. The addition of toroidal bolometer sightlines is found to improve toroidal peaking factor measurement accuracy during the pre-thermal quench in single-injector MGI mitigation. |
Wednesday, November 1, 2023 11:54AM - 12:06PM |
NO05.00013: First results of Magnetic Field Decomposition of SPARC simulations using Gauss' Separation Algorithm Gregorio Luigi Trevisan, Ryan M Sweeney, Robert S Granetz Gauss' Separation Algorithm (GSA), first introduced by Gauss in 1839 while tackling terrestrial magnetism and later exploited in many fields including planetary sciences, has been revisited in recent years and applied to plasma physics and tokamak experiments. |
Wednesday, November 1, 2023 12:06PM - 12:18PM |
NO05.00014: Physics basis for the Divertor Tokamak Test (DTT) facility Piero MARTIN, Roberto Ambrosino, Flavio Crisanti, Lori Gabellieri, Gerardo Giruzzi, Gustavo Granucci, Paolo Innocente, Paola Mantica, Andrea Murari, Giuseppe Ramogida, Gregorio Vlad This paper summarizes the physics basis of the Divertor Tokamak Test facility (DTT) under construction in Frascati,Italy, the target core plasma scenarios of the device and the current status of the research plan. DTT is a superconducting tokamak with 6 T on-axis maximum toroidal magnetic field, carrying plasma current up to 5.5 MA in pulses with total length up to 100 s. DTT has major radius R=2.19 m, minor radius a=0.70. The auxiliary heatingpower coupled to the plasma at maximum performance is 45 MW, provided by a mixture of ECRH, ICRH and by a 510 keV NIB. This allows matching the PSEP/R values (where PSEP is the power crossing the separatrix) with those of ITER and DEMO. The primary mission of DTT is to accelerate reaching the goal of fusion electricity with the study of plasma exhaust and of tokamak divertor in conditions relevant to ITER and DEMO and in regimes where highperformance plasma core and large Scrape Off Layer energy (SOL) flux will have to coexist. In addition, DTT willprovide a facility for fusion relevant tokamak physics and to address core confinement and stability issues in a varietyof plasma configurations, including negative triangularity scenarios, and the management of transient events like disruptions and ELM. |
Wednesday, November 1, 2023 12:18PM - 12:30PM |
NO05.00015: Non-Thermal Fusion Processes and Innovations Considered for the Ignitor Program* Pier 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 based on normally known conditions and adopting well tested structural and current conducting materials. The design, referred to as Ignitor EVO, is being updated consistently in order to take the results of new and significant experiments into account and to benefit from developments of technology and materials science that become known. Given the proven ability of high field compact machines to produce well confined plasmas with a wide range of collisionalities, Non-thermal (“Cool”) Fusion processes can be fruitfully investigated with them. Another important possibility is that of inducing high currents in low and high density plasmas in order to adopt the most appropriate current drive procedures and means. Given the pressing need to investigate meaningful burning plasmas, Ignitor has pioneered the development of large MgB2 superconducting magnets of the kind adopted for the largest poloidal field coils. Collaborations on near term high field superconducting magnets will be maintained with U.S. and European research and industrial institutions in order to identify the most suitable materials for the innermost machine magnets. *Sponsored in part by C.N.R. of Italy. |
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