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 UP11: Poster Session VIII: In-Person, Hall A (2:00-3:30pm) and Virtual Poster Presentations (3:45-5:00pm)
|
Hide Abstracts |
Room: Exhibit Hall A and Online |
|
UP11.00001: MFE: WHOLE DEVICE MODELING
|
|
UP11.00002: General Atomics Plans for a Tokamak Fusion Pilot Plant Brian A Grierson General Atomics is pursuing integrated fusion pilot plant designs that incorporate plasma physics optimization with practical engineering considerations. In order to contribute to electricity demands expected in a low-carbon energy market, fusion science and technology must be rapidly advanced and demonstrate the capability and attractiveness of fusion power. Key considerations are given to the mission and requirements for a fusion pilot plant, and the pilot plant's role in maturing a first-of-a-kind commercial fusion power plant. A 200 MWe, high power density compact advanced tokamak provides an attractive solution. Benefits and challenges associated with high magnetic field and high confinement, power exhaust solutions, efficient heating and current drive, control and diagnostics, low activation materials, and operational scenarios will be presented. Integrated simulation tools are being deployed for both rapid and comprehensive assessment of pilot plant designs, enabling trade studies and identification of particularly attractive operating scenarios. Power extraction and tritium breeding may benefit from the use of SiC-based materials, which offer advantages for the blanket concept with inherent safety benefits and high-temperature compatibility for high thermal efficiency. |
|
UP11.00003: FUsion Synthesis Engine: a next-generation framework for integrated design of fusion pilot plants (FPPs) Orso Meneghini, Tim Slendebroek, Brendan C Lyons, Kevin McLaughlin, Joseph T McClenaghan, Luke Stagner, David B Weisberg, Tom F Neiser, Jerome Guterl, Nan Shi, Sterling P Smith, Brian A Grierson Leverage of advanced integrated modeling tools is central to General Atomics' strategy towards rapid and confident deployment of fusion power. The newly developed FUSE framework is GA's unique solution to integrate physics, engineering and costing models of varying fidelity into self-consistent simulations. FUSE is the culmination of years of experience in fusion theory and simulations, and it has been built from the ground up to be computationally capable as well as modeler-friendly, while retaining the ability to be highly modular, flexible, and extensible. The ability to perform uncertainty quantification is supported in FUSE, which allows the design process to rigorously treat unknowns in the system as such. These capabilities are enabled by its ability to run a massive number of parallel simulations at scale, on high performance computing clusters. Within FUSE, physicists and engineers alike are able to easily and efficiently perform a broad range of studies, ranging from design of specific components, to the optimization of a power-plant concept as a whole, or even the ability to evaluate tradeoffs for different power-plant concepts. |
|
UP11.00004: Exploring high performance scenarios for a Fusion Pilot Plant by integrated modeling Nan Shi, Tim Slendebroek, Joseph T McClenaghan, Brendan C Lyons, Orso-Maria O Meneghini, David B Weisberg A 1.5-Dimensional (1.5D) core-pedestal integrated modeling workflow has been developed to explore the possible high performance scenarios for a Fusion Pilot Plant (FPP). The workflow starts with a set of 0-Dimensional (0D) parameters calculated by the General Atomics System Code (GASC)[1,2], and explores advanced scenarios with the well-validated OMFIT STEP integrated models[3]. This workflow predicts self-consistent core transport, current profile, particle/heat source and sink, the pedestal structure, as well as the plasma equilibrium. The discrepancies of predicted plasma performance and fusion power between the 0D and 1.5D calculations are substantially reduced by optimizing the heating and current drive strategy, impurity seeding with different species, and plasma fueling via pellet injection. The modeling also shows that impurity seeding can improve the fusion performance in a significant way. The plasma performance benefits more from the increase of the impurities of moderate-Z elements, but the improvement of fusion performance levels off at higher Zeff (>2). |
|
UP11.00005: A Multi-dimensional Risk-based Optimization of a Fusion Pilot Plant David B Weisberg, Brian A Grierson, James Leuer, Orso M Meneghini A multi-dimensional optimization study of a fusion pilot plant (FPP) is conducted to determine the sensitivity of the optimized design point to the risk assessment of each operational constraint. The GA Systems Code, an integrated 1D tokamak power plant optimization tool, is used to explore the design space of net-electric FPP facilities based on the steady-state tokamak magnetic confinement scheme. Plant optimization is driven by minimizing direct capital cost, with a net-electric target of 200MW(e). A comprehensive list of design parameters and operational constraints is identified, with each parameter assigned a range of risk values. These design parameters encompass fusion technology (e.g. superconducting magnets, blanket breeding material), plasma operation (e.g. proximity to ideal-wall MHD stability limits, maximum bootstrap current fraction), and power conversion (e.g. thermal cycle efficiency, balance of plant power requirements). The space of optimized FPP solutions is presented as a function of associated risk, with the finding that certain design parameters have an outsized impact on facility capital cost. A risk-benefit analysis is presented to inform a down-selection of FPP design parameters, and inform future design efforts. |
|
UP11.00006: Physical Properties and Global Modelling of General Fusion's Magnetized Target Fusion Plasma Colin P McNally, Meritt Reynolds, Sandra Barsky, Samuel Jones, Neeraj Kumar, Zahra Seifollahi Moghadam, Leopoldo Carbajal General Fusion's Magnetized Target Fusion (MTF) scheme exists, in parameter space, between magnetic confinement and inertial confinement schemes. We review in this poster the physical parameters of the MTF plasma in relation to static magnetic confinement plasmas and inertial confinement plasmas, noting the similarities and differences that influence the choice of modelling strategies. We discuss the design constraints, operational regime, and goals for plasma performance in relation to other fusion concepts. General Fusion's MTF plasma target is a spherical tokamak configuration, formed into a liquid metal flux conserver. As the converging liquid metal flow compresses the plasma its current, density, and temperature increase. During compression, plasma-wall interactions are important, and simulations suggest that halo currents develop. Tracking development of axial asymmetry during compression requires three dimensional simulations of plasma and liquid metal. Because of these issues, three dimensional global models are useful for understanding device performance. In this poster, we discuss the relevant theory and simulation requirements in General Fusion's MTF regime. We also demonstrate the application of our current modelling tools and progress on our next generation simulation code. |
|
UP11.00007: Steps towards 3D Integrated System Model of Magnetized Target Fusion at General Fusion Ivan Khalzov, Daymon Krotez, Raphael Segas The Integrated System Model (ISM) project carried out at General Fusion (GF) aims at performing comprehensive predictive simulations of magnetized target fusion (MTF) systems, where a rotating liquid metal liner compresses a spherical tokamak plasma to fusion conditions. The role of the ISM is to guide the current design of the Fusion Demonstration Plant (FDP) and the future design of an MTF reactor. The ISM hydrodynamics code predicts the compression trajectory of the rotating liquid metal liner depending on applied pressure pulses and geometrical constraints. Currently the code solves the reduced form of the Navier-Stokes equation for a compressible fluid in either (r,z)-plane axisymmetric setting or (r,θ)-plane non-axisymmetric setting, where (r,θ,z) are the cylindrical coordinates. The code uses a mixed Eulerian-Lagrangian approach, where a numerical mesh follows the fluid elements only in the r direction and is fixed in θ and z directions. The code is coupled with a self-consistent model of driving system, which produces the pressure pulses for liner compression. The main advantage of the code is its speed: a simple case takes several minutes of wall-clock time, allowing for fast optimization of the FDP design. Verification of simulations against other codes and comparison with ongoing GF compression experiments will be presented. |
Author not Attending |
UP11.00008: Improved magnetic diagnostics on General Fusion Plasma Injector 3 Filiberto G Braglia, Curtis Gutjahr, Stephen Bolanos, Mohamed Ahmed General Fusion (GF) recently completed a campaign to improve the accuracy of the Mirnov coils (B-probes) in their largest plasma injector machine, Pi3. This is part of a broader project aimed at reaching the 1% relative uncertainty required for the magnetic diagnostics on GF's Fusion Demonstration Plant (FDP). |
|
UP11.00009: Coupling the TRANSP code to FAR3D for Kinetic Stability Calculations Joshua A Breslau, Donald A Spong, Francesca M Poli, Mario L Podesta A new capability for MHD and kinetic stability analysis is being added to the tokamak transport analysis code TRANSP by coupling it to existing stability codes. To accomplish this, we have established a standard equilibrium interface for communication between the codes. As a proof-of-concept, TRANSP has been coupled to the gyro-Landau fluid kinetic stability code FAR3D using this interface and additional kinetic profile data passed by file exchange. The FAR3D code can be invoked via library call at arbitrary times during a TRANSP run, tracking growth rates, real frequencies, and mode structures of the most unstable Alfvén eigenmodes during the course of the discharge. Validation tests will be presented based on a well-characterized DIII-D discharge with Alfvénic activity. |
|
UP11.00010: Relaxation of energetic particles distribution in NUBEAM due to the multitude of Alfvenic oscillations Marina V Gorelenkova, Alexei Y Pankin, Nikolai N Gorelenkov, Mario L Podesta, Vinicius N Duarte, Joshua A Breslau, Laszlo Glant, Mariya Goliyad, Gopan Perumpilly, Jai Sachdev, Francesca M Poli In this research, the EP relaxation in the presence of multiple Alfvenic |
|
UP11.00011: Control of particle noise in core-edge coupled total-f gyrokinetic simulations Albert V Mollen, Julien Dominski, Robert Hager, Pallavi Trivedi, CS Chang, Jong Choi, Varis Carey The first-principles based Whole Device Model Application (WDMApp) project is an Exascale Computing Project (ECP) with the objective to develop a high-fidelity model of magnetically confined fusion plasmas by coupling gyrokinetic codes that are optimized for different regions of the plasma, the core and the edge region. The total-f particle-in-cell code XGC will perform the simulation of the edge region including the high-confinement-mode pedestal, the magnetic separatrix, and the scrape-off layer. |
|
UP11.00012: Characterization of Core Transport in Compact Tokamak Reactor Scenarios Christopher G Holland, Eric M Bass, Dmitriy M Orlov, Joseph T McClenaghan, Brendan C Lyons, Xiang Jian, Nathan T Howard, Pablo Rodriguez-Fernandez Work previously reported at the 2021 APS-DPP meeting [1] identified self-consistent core transport and equilibrium solutions capable of producing 200 MW or more net electric power in a B0 = 8 T, Rmaj = 4 m device. For both pulsed and steady-state scenarios we find there is significant ion thermal transport through the plasma core, even though alpha heating of electrons is the dominant heating source. Additionally, the low collisionality of these plasmas leads to negligible core neoclassical transport. The combination of these conditions then requires that transport be dominated by microturbulence instabilities capable of driving significant ion to electron thermal transport ratios, i.e. ion temperature gradient and/or kinetic ballooning modes. Finally, it is shown that the transport is sufficiently large for these cases that differences in the stiffness predicted by different TGLF saturation rules leads to significantly different scenario predictions. Ongoing work benchmarking TGLF and CGYRO predictions for these cases will be presented, as well as implications for density peaking and core-edge integration. |
|
UP11.00013: Refactoring GENE for improved parallel scalability on current and upcoming supercomputers Kai Germaschewski, James McClung, John Donaghy, Gabriele Merlo, Bryce Allen, Frank Jenko, Amitava Bhattacharjee GENE is one of the constituent codes of the WDMApp (Whole Device Modeling Application) ECP project, designated to simulate gyrokinetic microturbulence in the core of a fusion device. |
|
UP11.00014: Improving the Performance of a Fusion Neutron Science Facility Luca Guazzotto, Jeffrey P Freidberg Two major modifications to the existing steady state Fusion Neutron Science Facility (FNSF) [1] concept are investigated with the aim of determining whether or not the predicted perfor- mance can be substantially improved. The modifications are high magnetic field and pulsed operation. We find that high field leads to major improvements in a steady state FNSF, although at the expense of lowering the engineering gain. Pulsed operation replaces the problems associ- ated with low current drive efficiency, with hopefully more manageable engineering problems. Here, however, high field is not helpful, and low field is more desirable. Pulsed FNSFs also have a reduced engineering gain. Further modifications lead to FNSF designs satisfying the additional constraint of engineering gain equal to unity. For these designs there is a large cost penalty for the steady state FNSF but only a modest penalty for the pulsed FNSF. All of our modified designs show modest to large potential improvements over the existing design. Over- all, our conclusion is that it may be desirable to carry out a more detailed analysis of one of our improved designs, the choice depending upon which issue in the existing design is most important.
References [1] C. E. Kessel, J. P. Blanchard, A. Davis, L. El-Guebaly, N. Ghoniem, P. W. Humrickhouse, S. Malang, B. J. Merrill, N. B. Morley, G. H. Neilson, M. E. Rensink, T. D. Rognlien, A. F. Rowcliffe, S. Smolentsev, L. L. Snead, M. S. Tillack, P. Titus, L. M. Waganer, A. Ying, K. Young and Y. Zhai, The Fusion Nuclear Science Facility, the Critical Step in the Pathway to Fusion Energy, Fusion Science and Technology, 68:2, 225-236 (2015), DOI: 10.13182/FST14-953 |
|
UP11.00015: Quasi-Spherical Magnetic Confinement of a Fusion Plasma Andrew Egly, Cameron T Chavez, Frank J Wessel The advantages for fusion in a spherical geometry have been recognized for many decades. The design of such systems pose special challenges for magnetic confinement, as magnetic cusps are inherently introduced at the surface boundaries. The (hexahedron) Polywell is a unique case, configured with six-magnetic coils on each face of a cube, biased to produce a null-magnetic field at the polygon's center. Magnetic confinement of a high-power electron-beam, injected through several of the coils, produced a central, negative-potential well for electrostatic ion confinement. Critics dismissed the concept as an implausible-reactor due to its non-thermal particle distribution, even as experiments demonstrated respectable levels of magnetic beta, β ≈ 45%. PIC code simulations configured for the continuous injection of a DD plasma beam, ultimately scaled to near-unity gain for H-B11. Magnetic cusp particle loss remains an identified constraint, that could potentially be addressed through the use of electrostatically-biased reflectors. Our present studies are investigating higher-order magnetic periodicity, in a dodecahedron, which result in substantially reduced particle losses compared to previous work. This paper provides direct comparisons of the loss rates and power balance for several geometries, indicating that even higher magnetic periodicity may be beneficial. Such an approach may eventually provide for a scalable, naturally formed, high-beta, quasi-spherical confinement, suitable for advanced fuels. |
|
UP11.00016: Improvement to Tokamak fusion reactor design using optimized inner TF coil structure and conductor grading: Higher B, lower A, more compact Charles P Swanson Recently, an optimal radial grading of structure and conductor of the inner leg of a Tokamak toroidal field coil was found by applying calculus of variations to an axisymmetric plane strain model. The optimal profile consists of an outer winding pack with just enough structure to support the accumulated radial force (not wedged), and an inner bucking cylinder which has been micro-structured so that its radial compliance assumes a specific profile. This inner bucking cylinder in particular is a significant advance, allowing up to 40% higher magnetic field. This improvement has a complex effect on the optimal Tokamak fusion reactor design point, rippling through plasma physics and engineering constraints such as the beta limit, recirculating power fraction, and neutron wall load. The result is that the fusion reactor can be made more compact and/or higher power than would be otherwise possible. |
|
UP11.00017: MFE: HIGH FIELD TOKAMAKS Session Chairs: |
|
UP11.00018: Overview of the SPARC program -- goals and status Robert T Mumgaard The recent demonstration of a large bore, superconducting magnet has enabled the construction of a new, net energy demonstration facility, SPARC (BT = 12.2, R0 = 1.85m, a = 0.57m, Q ≈ 10, Pfusion ≈ 140MW, at H98 = 1.0), which is fully funded and currently under construction in Devens, MA. SPARC is predicted to demonstrate high gain plasmas and fusion power plant engineering in a compact device while providing a platform to close remaining plasma physics gaps for a fusion pilot plant related to alpha physics, divertor heat exhaust, scenario development, transients, and RF physics. With absolute plasma performance matched only by ITER but significantly sooner, SPARC will be exploited to fast track a fusion energy industry. The physics design is largely closed, the engineering design is in detail stages, building construction is approximately 50% complete, the majority of the auxiliary systems are under procurement agreement, the manufacture of the magnets has begun, and preparations for utilization are being initiated. SPARC’s completion mid-decade will complete the Fusion Pilot Plant Phase 1A mission identified in the National Academies Fusion plan and prepare for first commercial plant, ARC, which incorporates other technologies being developed in parallel needed to close technical gaps. |
|
UP11.00019: Scenario modeling supporting SPARC design activities Devon J Battaglia, M. Brookman, A. J Creely, T. Looby, C. E Myers, M. Reinke, D. T Garnier, R. Granetz, P. Rodriguez-Fernandez, A. Battey, A. O Nelson, I. G Stewart, C. Hansen, J. T Wai A suite of plasma scenario simulation tools has supported the rapid maturation of the SPARC design basis. An important component of the scenario modeling is a time-dependent electromagnetic calculation that includes an axisymmetric description of the toroidally conductive structures suitable for efficient calculations. A framework utilizing modules from the HEAT code was developed to distill 3D Computer-Aided Design (CAD) models into a meshed 2D description that enables rapid evaluation of design options. An accurate 2D description of the conducting structures is especially important for evaluating plasma startup, ramp-down, strike-point sweeping and the vertical position control system in order to refine the power supply requirements. Psi-Tet calculations for the induced 3D currents in the conductive structures inform the calibration of the lower-fidelity 2D axisymmetric model. Coordinated analysis identified the poloidal contour of the outboard limiter based on the size of the vertical excursions and control errors expected during operations and the requirement to achieve good ICRH coupling and shadowing of the antennas. |
|
UP11.00020: Startup scenario development for SPARC Josiah T Wai, Devon J Battaglia, Darren T Garnier, Tom Looby, Andrew O Nelson, Egemen Kolemen Time-dependent vacuum field calculations for the breakdown and burnthrough phase of a SPARC discharge have been completed to support design and procurement plans. Strong toroidal electric field required for robust breakdown and burnthrough (> 1 V/m) is achieved by commutating external resistance into the superconducting solenoid circuit for about 100ms. Scenarios utilizing only the superconducting magnet sets are found that produce the necessary field null quality and passive radial and vertical stability. Including the copper divertor coils in the scenario offers an avenue for achieving the required topology with faster Ip ramp rates. Constraints on the poloidal field null quality is more relaxed than similarly sized machines due to SPARC's increased toroidal field strength, such that the connection length criterion for breakdown is reasonably satisfied. The SPARC plasma initiation scenarios are qualified against existing tokamak databases and reduced models. This framework is used to design startup scenarios for a variety of operational constraints and goals. |
|
UP11.00021: Investigation of pedestal stability in SPARC Theresa M Wilks, Jerry W Hughes, Philip B Snyder, Amanda E Hubbard, Nathan T Howard, Pablo Rodriguez-Fernandez, Alexander J Creely The SPARC Primary Reference Discharge (PRD) is a proposed scenario capable of achieving performance exceeding the mission of Q > 2. Previous analysis has assessed the impact of varied pedestal pressure on core profiles [Rodriguez-Fernandez JPP 2020], as well as estimated pedestal pressure using EPED indicating a pedestal regime subject to peeling instabilities over a broad range of proposed operating densities [Hughes JPP 2020]. However, SPARC will require a set of staged scenarios leading up to the PRD as well as potential scenarios to be used in lieu of the PRD if certain SPARC parameters cannot be met [Creely APS DPP 2020]. |
|
UP11.00022: Evolution of the SPARC divertor design: engineering and physics trade-offs Adam Q Kuang, Matthew L Reinke, Sean B Ballinger, John Canik, Robert S Granetz, Trey Henderson, Matthew Honickman, Michael Lagieski, Bruce Lipschultz, Jeremy D Lore, Valeria Riccardo, Ryan M Sweeney, Michael Wigram, Dina Yuryez SPARC is a compact, high-field tokamak (B0 = 12.2 T, R0 = 1.85 m) with a close-fitting tungsten first wall. The resulting thermal and structural loads are challenging for the engineering design. Divertor targets will need to survive 10s pulses with unmitigated divertor parallel heat fluxes of ∽10 GW/m2; while disruptions can drive ∽2 kT/s changing magnetic fields, leading to large eddy current structural loads. Nonetheless, it is important that the divertor has sufficient diagnostic access and shaping to ensure that the SPARC divertor mission can be executed – exploration of highly dissipative, low erosion regimes, with neutral pumping for projections to next step devices. The present SPARC divertor is up-down symmetric, with both horizontal and vertical target plate configurations on the inner and outer divertors. In addition, the outer divertors feature highly baffled long legs (Lpol∽0.5 m, Rtarget/Rxpt∽1.2) and can form a X-point target divertor. The trade-offs between the engineering and physics requirements have driven the evolution of the divertor design from a beam-dump to the present SPARC divertor. These driving factors will be presented alongside the details of the SPARC divertor design. |
|
UP11.00023: Automated UEDGE Modeling of the C-Mod Heat Flux Width Database Sean B Ballinger, Dan Brunner, Jerry W Hughes, Adam Q Kuang, Brian LaBombard, James L Terry, Maxim Umansky, Anne E White, Michael Wigram The Alcator C-Mod heat flux width database suggests a strong correlation of λq at the outer divertor target with the inverse square root of the volume-averaged plasma pressure [1], implying that a high-performance core will lead to challenging target heat fluxes. The C-Mod database was augmented with plasma midplane profiles, finding a correlation between λq and the edge plasma pressure but failing to observe a clear Spitzer-Härm scaling of λq = 2/7 λTe [2]. This work evaluates whether the edge plasma fluid model of the UEDGE code can explain the variation of λq in the database. 75 discharges from the database are modeled using an automated process that tunes transport coefficients to match experimental midplane profiles of ne and Te. The UEDGE and experimental values of λq measured in the divertor are found to be correlated, but UEDGE overestimates the heat flux width by an average factor of 1.8. The survey is repeated with UEDGE models of increased and reduced complexity. This UEDGE framework is successful in modeling a wide range of plasma conditions in C-Mod and could be extended to other devices. |
|
UP11.00024: Investigating particle flux-gradient relationships at the edge of high density plasmas through an empirical database and SOLPS-ITER modeling on Alcator C-Mod Marco A Miller, Jerry W Hughes, Aaron M Rosenthal, Francesco Sciortino, Saskia Mordijck, Richard Reksoatmodjo, Tomas Odstrcil, Robert Wilcox Quantifying particle fluxes in the edge and pedestal region is crucial for understanding the formation of transport barriers. High fields (Bt > 5T) on C-Mod allow study of H-mode pedestals with high density, opaque edges. We present particle source and flux profiles spanning a region of ~6cm about the last closed flux surface (LCFS) inferred from line-integrated Ly-α brightness measurements at the outer midplane. This workflow is used to create a database of inferred particle fluxes and electron density gradients throughout the pedestal. Constraining edge neutral modeling with Ly-α presents a unique opportunity to study how deuterium neutrals affect the formation of the edge transport barrier. SOLPS-ITER is run interpretively on two upper single-null H-Mode shots. Changing pumping conditions affects the particle source, which is modeled with the EIRENE Monte Carlo neutral code in SOLPS-ITER. Experimentally, this has a small effect on the ne profile but does increase Te, possibly because of a reduction in heat sinks. A set of particle and heat diffusivities (D,e) is found iteratively to allow matches to experimental ne and Te profiles. Varying core flux boundary conditions constrained by experiment allows a study of the transport required to reproduce experimental profiles. |
|
UP11.00025: Argon impurity pumpout by ICRF waves in C-Mod L- and I-mode plasmas Conor J Perks, John E Rice, Ivan Marshall, Katie Crowley, Yijun Lin, Francesco Sciortino, Matthew L Reinke, Earl S Marmar, Norman M Cao, Stephen J Wukitch, John C Wright, Roberto Bilato, Dmitry Mossev Pumpout of argon ions by ICRF waves has been observed in C-Mod deuterium L- and I-mode plasmas with substantial hydrogen dilution. Previous work on C-Mod analyzed this effect through the observed reduction of core argon x-ray brightness. Up to a 90% reduction on time scales of ~10ms follows injection of ICRF power. Time traces for different lines-of-sight suggests that this effect is stronger at mid-radius than in the plasma center. This motivates the need to invert the brightness data into inferred impurity charge state density profiles to understand where impurities are being pumped out and how many ions are being pumped out. C-Mod x-ray and VUV spectroscopy data are used to constrain ImpRad, a Bayesian optimization framework that samples transport coefficient inputs into the AURORA impurity transport forward model until synthetic brightness profiles from inferred density profiles match the experiment. TORIC and CQL3D simulations are performed to calculate the ICRF power coupled to the argon. We hypothesize that, at an optimal hydrogen-to-deuterium ratio, the ICRF heats the argon increasing the radial excursion of the banana orbits until the ions drift out of the plasma. To confirm this, the ASCOT full-orbit solver is used to track argon ion trajectories during pumpout. |
Author not Attending |
UP11.00026: Finite Element Modeling of the SPARC ICRF System Michael W Brookman, Erik Johnson, Kris Anderson, Peter Matthews, Yijun Lin, John C Wright, Tom Looby, Pablo Rodriguez-Fernandez, steven D scott, Alexander J Creely Radiofrequency heating will raise the SPARC plasma temperature from an initial ~5 keV Ohmic plasma to the ~20 keV sufficient to produce a true burning plasma . As the only auxiliary heating system on SPARC, the ICRF system must reliably provide 25 MW of power through 12 4-strap dipole phased antennas. Finite element modeling has baselined antenna RF coupling, heating, and disruption loading. COMSOL Multiphysics allows the determination of coupled power and electric fields that can drive breakdown, which are themselves a function of coupling. The 8 straps of the antenna are fully 3D, 5 axis CNC machined facet to align with the plasma both poloidally and toroidally. A cold plasma tensor derived from TRANSP profiles is extended into the edge in a 2D equilibrium, and RF is applied to 16 ports to drive a pair of 4 strap antennas to evaluate coupled power. Full 3D electric and magnetic RF fields can be evaluated for their B-field aligned and perpendicular components in a high fidelity 3D CAD model. Fields are compared with established empirical and modeled breakdown thresholds and combined with a tuning plan to establish the coupled power of 2.5MW/4 strap antenna, sufficient to meet the needs of SPARC. |
|
UP11.00027: Design of Vacuum Spectroscopy System for SPARC Inwoo Song, Matthew L Reinke, Thomas Shields, Jessica Ilagan, Jae-Sun Park, John Canik, Jeremy D Lore, Pablo Rodriguez-Fernandez, Nathan T Howard The preliminary design of a vacuum spectroscopy (VCSP) system for SPARC was performed based on the results of spectral simulations. The main objective of VCSP is to operate a real-time impurity monitor for SPARC core and divertor plasma in zones where electron temperatures range from 10's of eV to several keV. Line emission from EUV to VUV are to be measured, typically in the 1 – 200 nm wavelength range, using techniques established on existing tokamaks. The SPARC VCSP instrument consists of two sub-systems: a core and divertor survey spectrometers to cover both regions. Detailed physics design is conducted by a spectral simulation utilizing the Python open-source code, AURORA [1], with additionally developed code modules for synthetic diagnostics, and is supported by ANSYS calculations of electromechanical loads for survival of in-vessel mirrors. SOLPS-ITER simulation results of SPARC's Ne seeding scenario in the lower divertor improved the alignment design of VCSP components. Positioning optimization of mirror and beamline was conducted via calculations of etendue of the system and line brightness of Ne ions. Primary design review will be followed by design of out-vessel parts. |
|
UP11.00028: Overview of the Early Campaign Diagnostics Planned for the SPARC Tokamak Matthew L Reinke, Robert S Granetz, Clayton E Myers, James H Irby, Chris Chrobak, Ana Koller, John E Rice, Inwoo Song, Adam Q Kuang, Roy A Tinguely, Jerry W Hughes, Nathan T Howard, Yijun Lin The SPARC tokamak plans to begin operations in mid-2025 and execute a series of mission-driven campaigns, the first of which is to demonstrate net energy, Qfus > 1, and then move to close tokamak science gaps required to complete the design of ARC. Accomplishing this will require a plasma diagnostic set that can be used for real-time control, inter-shot learning and enable in-depth analysis. Planned tools cover approximately 40 sub-systems including magnetics, interferometry, neutral pressure, x-ray to visible spectroscopy, camera imaging, bolometry, neutron imaging and spectroscopy, Thomson scattering, ECE, reflectometry, Langmuir probes and temperature and strain sensing for in-vessel components. Capabilities and requirements for these diagnostics are outlined at a high level, along with their time-phasing relative to SPARC’s planned operational milestones. Examples of ongoing physics and engineering design activities are presented in order to highlight how diagnostics interface with fixed electrical and optical feedthroughs, a series of replaceable midplane (x9) and off-midplane (x20) port-plugs and transmit neutrons, photons and electrical signals from the Tokamak Hall via 31 configurable penetrations to five dedicated diagnostic laboratory spaces. |
Author not Attending |
UP11.00029: Overview of planned SPARC Neutron Spectroscopic Camera Shon P Mackie, John Ball, Alex Tinguely Neutron diagnostics are a critical tool for verifying that SPARC has achieved its fusion goals. Currently planned are a suite of diagnostics consisting of neutron flux monitors, a foil activation system, and a spectroscopic neutron camera (NCAM). The current NCAM design includes 11 lines of sight (LOS) through the midplane diagnostic port. Each LOS will be equipped with a liquid organic scintillator and CVD diamond detectors to measure DD and DT neutron rates, respectively. During the primary reference discharge (Creely JPP 2020), we expect count rates high enough to be able to use the CVD diamonds to extract spectroscopic information as well. In addition, a magnetic proton recoil spectrometer will be installed on the midplane LOS in order to make detailed measurements of neutron spectra in both DD and DT discharges. From neutron rates, the spatial neutron birth profile and fusion rate can be inferred. Spectral information can used to deduce the fuel temperature, fuel ratio, and to understand certain kinetic phenomena (alpha knock-on, RF fast ion tail, impurity effects). The current state of the SPARC NCAM system and supporting calculations and OpenMC simulations will be presented. |
|
UP11.00030: Neutronics modeling of activation diagnostics in SPARC John L Ball, Shon P Mackie, Roy A Tinguely The SPARC tokamak, now under construction in Devens, Massachusetts, is slated to operate with a |
|
UP11.00031: The Magnetic Diagnostics for SPARC Robert S Granetz, Ryan M Sweeney, Roy A Tinguely, Clayton E Myers, Matthew L Reinke, Chris Chrobak, Devon J Battaglia, Alexander J Creely, Ian G Stewart, Carlos A Paz-Soldan Although SPARC will be groundbreaking in many ways, its magnetic diagnostics (MAGX) are rather conventional, albeit with several key features driven by SPARC’s unique conditions. Nearly all sensors will be located on the interior walls of the vacuum chamber, and therefore baking and D-T operation necessitate the use of mineral-insulated cable for the sensors and leads. The lack of in-vessel maintenance opportunities after initial operation warrants careful attention to redundancy and elimination of failure modes. For this reason MAGX will have electrical joints only at the vacuum feedthroughs, and feedthrough prototyping will include exhaustive testing for reliability. The high heat loads and disruption forces on first wall components require extensive structural supports, severely limiting the spaces in which MAGX sensors and leads can be located. As a consequence, nearly all flux measurements will use saddle flux loops in lieu of full toroidal loops, and there will be no in-vessel plasma current Rogowski sensors. SPARC plasmas will be ~30 s long (10 s flattop), so conventional analog integration of the inductive signals is suitable. Details of sensor layout and prototyping will be discussed. (See also Myers et al in this session.) |
|
UP11.00032: Planning for the fabrication, calibration, and installation of the magnetic diagnostics for SPARC Clayton E Myers, Robert S Granetz, Ryan M Sweeney, Roy A Tinguely, Matthew L Reinke, Devon J Battaglia, Chris Chrobak, Alexander J Creely, Ted Wyeth, Ian G Stewart, Carlos A Paz-Soldan Magnetic diagnostics are the foremost tool for understanding and controlling the magnetohydrodynamic equilibrium and stability of tokamak plasmas. Here we present the status of the plans for fabricating, calibrating, and installing the magnetic diagnostics that are being designed for the SPARC tokamak (see also Granetz et al. in this poster session). The SPARC magnetic diagnostics will include equilibrium magnetic field and flux sensors, plasma current sensors, low-m/n 3D sensor arrays, halo current sensors, and high-frequency Mirnov arrays. To emphasize sensor survivability and reliability given both the high-temperature and high-neutron-flux (but low-neutron-fluence) environment in SPARC and the limited opportunities for maintenance, most sensors will be fabricated from mineral insulated cable and joints in the leads will be minimized or avoided altogether. The status of the engineering design and the fabrication plans for the various SPARC magnetic sensors will be reported, along with the plans for both benchtop and in situ calibrations. Finally, the plans for sensor installation and as-built metrology during SPARC assembly will also be discussed. |
|
UP11.00033: Design concepts for visible, UV and IR imaging and spectroscopy diagnostic systems for SPARC Ana Koller, Matthew L Reinke, Devon J Battaglia, Michael Brookman, Alexander J Creely, Thomas Ernst, Sebastian Fray, Robert S Granetz, Jessica Ilagan, Adam Q Kuang, Cristina Rea, Thomas Shields, steven D scott, Roy A Tinguely Imaging and spectroscopy in the visible, UV, and IR regions of the electromagnetic spectrum are two of SPARC's necessary, early campaign diagnostic systems. Even though imaging and spectroscopic systems rarely vary in design and function when used in different types of tokamaks, they face specific challenges when designed for SPARC. The design is mainly influenced by the environmental constraints, especially on the in-vessel collection optics (such as large disruption loads and neutron and plasma thermal heat fluxes), unique physical and enabling interfaces within the SPARC facility, and the anticipated mission-driven measurement requirements that these diagnostic systems must meet. |
|
UP11.00034: Vertical stability and its implications for the SPARC tokamak Darren T Garnier, Andrew O Nelson, Devon J Battaglia The SPARC tokamak will operate with a highly shaped equilibrium (κa ~ 1.75, δ = 0.54) to achieve its performance goals, and thus be subject to vertical instability. However, the vertical instability growth rate, γ, is slower than comparably sized tokamaks due to the relatively thick vacuum vessel walls needed to withstand disruption forces at high field and current. Using the Toksys suite of tools, a survey of possible accessible shapes near the SPARC primary reference discharge indicates a maximum γ < 100 s-1. Steel vertical stability plates, which are positioned near the diverter shaping coils, have a modest (~25%) effect of reducing the vertical growth rate. Using a "max Z" analysis, we set the required power supply voltage and current to account for a vertical displacement of 10% of the minor radius a, defined as robust vertical control. Requirements for power supply energy and vertical stability coil heating are obtained from the expected spectra of plasma disturbances and diagnostic noise. Furthermore, this work suggests a small modification of the outboard limiter location to allow for an unmitigated vertical disturbance of 5% of the minor radius and subsequent additional vertical motion due to finite control system response without allowing the plasma to become limited. |
|
UP11.00035: Edge scanning reflectometry on SPARC Yijun Lin, Matthew L Reinke Edge scanning reflectometry (ESRL) on SPARC aims at determining the ICRF evanescent layer location to help assess the ICRF antenna loading and also measuring the H-mode pedestal density profiles. ESRL uses the standard frequency sweep technique and has three bands (Ka-band, U-band and E-band) to cover frequencies from 27 to 90 GHz. Both O-mode and left-hand-cutoff (LHC) X-mode are implemented. For B0 ~ 12 T, the cutoff density ranges from ~0.1e20 m-3 at 27 GHz O-mode to ~4e20 m-3 at 90 GHz LHC X-mode. Each band has one launching horn antenna and two receiving horn antennas for O-mode and X-mode respectively. Vacuum windows are carefully designed for the tritium environment. Considering the relatively short distance (~15 m) from the diagnostic hall to the tokamak, overmoded waveguides are adequate to minimize signal loss while allow system flexibility. The mm-wave and IF electronics have been analyzed and optimized based on synthetic reflectometry data. Choosing a fast frequency sweep rate (full-band sweep at 5 microsecond) and 50 MHz digitizer sampling rate, ESRL is expected to have sufficient spatial and temporal resolution. The horn antennas and other critical parts are optimized with COMSOL modeling. The latest status will be presented. |
|
UP11.00036: Evaluating Coil Sets for a High-Field Reactor at Negative Triangularity Nikolai de Boucaud, Alessandro Marinoni, Theodore Golfinopoulos This work investigates the feasibility of a reactor with a cross-sectional shape at negative triangularity (NegT) by evaluating coil set requirements of such a configuration in a high-field reactor. NegT plasmas are attractive for reactors since they have H-mode-grade normalized pressure and confinement levels despite their relaxed pressure profiles near the edge. As such, they are free of ELMs, have low impurity retention and a lower heat flux at the divertor plates. |
|
UP11.00037: MFE: TOKAMAKS Session Chairs: |
|
UP11.00038: HBT-EP Program: MHD Dynamics and Active Control through 3D Fields and Currents Gerald A Navratil, David A Arnold, James M Bialek, Rian N Chandra, Nigel J DaSilva, Jeffrey P Levesque, Boting Li, Michael E Mauel, Alex R Saperstein, Yumou Wei, Christopher J Hansen The HBT-EP active mode control research program aims to: (i) understand the physics of scrape-off layer currents (SOLC) and interactions between the helical plasma edge and conducting boundary structures, (ii) test new methods for measurement and mode control that integrate optical and magnetic detector arrays with both magnetic and SOLC feedback, and (iii) understand fundamental MHD issues associated with disruptions, resonant magnetic perturbations, and SOLC. A two-color multi-energy EUV/SXR tangential array has been used to study internal MHD mode structure. Sawtoothing MHD has been observed correlated with reduced amplitude of 2/1 tearing mode activity. Disruption dynamics and current paths in the SOL and the vacuum vessel have been studied. The scaling of the MHD mode rotation frequency during the current quench phase studied by Myers [NF 58 (2018)016050] has been extended to include HBT-EP data leading to a new drift-frequency based scaling law [Saperstein et al., NF 62 (2022) 026044]. Stable non-disruptive operating space boundaries in HBT-EP have been mapped using a variational autoencoder neural network with a reduced dimensional representation [Wei et al., NF 61 (2021)126063]. A deep-learning-based MHD mode tracking algorithm to process video frames from the upgraded HBT-EP high-speed videography system shows significant improvement over the previous SVD-based method to determine the n=1 mode amplitude and phase. |
|
UP11.00039: Asymmetric halo current rotation scalings on HBT-EP and Alcator C-MOD Alex R Saperstein, Roy A Tinguely, Robert S Granetz, Jeffrey P Levesque, Michael E Mauel, Gerald A Navratil Halo current (HC) rotation during disruptions can be potentially dangerous if resonant with the structures surrounding a tokamak plasma. A poloidal ExB drift-frequency-based scaling law has been proposed [1] for the rotation frequency of the asymmetric component of the HC as a function of toroidal field strength and plasma minor radius (frot ∝ 1/(BT a2 )). This scaling law is consistent with results reported for many tokamaks and is motivated by the faster HC rotation observed in the HBT-EP tokamak. It accurately describes the HC rotation as it evolves dynamically throughout the disruption in simple circular-limited plasmas like those on HBT-EP, and is seen to describe the average HC rotation in other plasmas like those on Alcator C-Mod. The 1/a2 dependence of this scaling law, as well as a dependence on the edge safety factor (qedge), suggest that the plasma predominantly rotates poloidally. Projections of the rotation frequency to ITER and SPARC parameters suggest the asymmetric HC rotation will be on the order of 10 Hz and 60 Hz, respectively, as opposed to the order of 2 kHz and 40 kHz observed on C-Mod and HBT-EP. |
|
UP11.00040: Real-time capable MHD mode tracking using deep learning algorithm and high-speed video cameras on HBT-EP Yumou Wei, David A Arnold, Rian N Chandra, Nigel J DaSilva, Jeffrey P Levesque, Boting Li, Alex R Saperstein, Michael E Mauel, Gerald A Navratil, Christopher J Hansen We present recent developments on deep-learning-based MHD mode tracking using the newly upgraded high-speed videography system on HBT-EP. This algorithm uses the convolutional neural network architecture to process video frames recorded during plasma discharges by one or multiple cameras and predict the n=1 mode amplitude and phase over time. Training and testing datasets were assembled from multiple run campaigns conducted on HBT-EP, during which two Phantom S710 cameras operating at 250 kfps, 128×64 pixels resolution were set to measure Dα emissions on the plasma’s poloidal cross-sections at different toroidal positions. The target mode information was obtained through least-squares fitting using the in-vessel magnetic sensors. The resulting model is able to track the n=1 external kink mode consistently over the testing shots, with the amplitude and phase errors bounded by ±2 G (over 0-20 G amplitude range) and ±20 degrees during the mode-active period of a discharge. This indicates a significant improvement over the previous SVD-based method [1]. Variations of the model’s architecture as well as the inference latency and robustness of different models are also investigated. |
|
UP11.00041: Observation of sawtooth dynamics using tangential EUV/SXR diagnostic system on HBT-EP tokamak Boting Li, Jeffrey P Levesque, Yumou Wei, Alex R Saperstein, Rian N Chandra, Gerald A Navratil, Michael E Mauel, Christopher J Hansen Measurements and analyses of the signals from the extreme ultraviolet (EUV) and soft x-ray (SXR) detectors are used to study the internal characteristics of MHD mode structures, including the time-evolution of local electron temperature and temperature profiles. We present the initial results from the two-color multi-energy EUV/SXR diagnostic system in the HBT-EP tokamak. This system includes a filter wheel with five different groups of dual-filter structures and two AXUV16ELG 16-channel diode arrays. The ratio between the amplitudes of the signals from a 100 nm Aluminum filter and a 200 nm Titanium filter with identical tangential plasma views provides temperature profile information versus time. A two-stage single-channel signal amplifying system is built to improve the frequency response and advance the ability to study fast rotating modes. It has a bandwidth up to 200 kHz and gains varying from 1 MOhm to 60 MOhm corresponding to different channels of the diode arrays to optimize the signal amplitudes. Internal MHD modes are studied using this system. Sawtooth activity accompanying low-amplitude 2/1 tearing mode has been detected and analyzed. Weaker or non-existent sawteeth are correlated with larger and saturated 2/1 mode amplitudes. |
|
UP11.00042: Exploration of Mode Frequency Control and Observation of Multiple Independent Modes on HBT-EP Rian N Chandra, Jeffrey P Levesque, Boting Li, Alex R Saperstein, Yumou Wei, David A Arnold, Nigel J DaSilva, Michael E Mauel, Gerald A Navratil, Christopher J Hansen This poster explores internal mode structures with a poloidal array of 64 Extreme Ultraviolet (EUV) diodes (15 ≤ Eγ ≲ 104 eV) on the HBT-EP tokamak. A combined-diagnostic Singular Value Decomposition is used to identify coherent signatures across optical and magnetic signals. One application of this study is the identification and frequency control of an internal emissive 2/1 mode structure locked to an edge magnetic 3/1 mode structure. A non-iterative tomographic scheme and projection matrix is employed to extract the phase of this feature, on an NVIDIA GPU in an 8μs cycle. HBT-EP’s 4×10 poloidal and toroidal control coils are actuated with a pre-defined surface ψ3/1 to control the rotation frequency. Compared to phase tracking with Mirnov probes, similar ∆fmhd of roughly ±30% is observed. A second application is the observation of multiple independent modes. The combined diagnostics show 2D profiles associated with the progression of a sawtooth event: an internal 1/1-like mode precedes the β-collapse, which in turn destabilize an edge mode. Separately, a high frequency 3/2 mode is observed independent of the dominant 3/1 mode. The correlation in time of these mode amplitudes is discussed. |
|
UP11.00043: Modeling the effect of wall asymmetry on MHD instabilities and scrape-off-layer currents in HBT-EP David A Arnold, Rian N Chandra, Jeffrey P Levesque, Boting Li, Alex R Saperstein, Christopher J Hansen The NIMROD [1] and PSI-Tet [2] codes are used to validate multiphysics models for the prediction of resistive MHD mode structures and Scrape-Off-Layer (SOL) currents in tokamaks using high-resolution current, magnetic, and optical diagnostic data from the HBT-EP tokamak [3]. Available signals are used to constrain equilibrium profiles using linear calculations. With added limiters, efforts to reproduce non-disruptive, saturated, nonlinear mode activity as observed in HBT-EP is underway. Comparison of simulated signals to experimental measurements, including poloidal and tangential EUV arrays, will be shown. Applications to creating a self-consistent picture of internal MHD instability structures and sawtoothing activity will be discussed. Effects of 3D wall resistivity are investigated within NIMROD and compared to results from PSI-Tet, which captures the 3D wall geometry. Plans to validate numerical models for wall-connected currents within the SOL using the diverse, high-resolution diagnostics on HBT-EP will also be presented, with applications for improving models of predicted current dynamics between the plasma and the first wall in ITER and next step devices. |
|
UP11.00044: Core temperature evolution in HBT-EP during L- to biased H-mode transitions Nigel J DaSilva, Jeffrey P Levesque, Yumou Wei, Boting Li, Alex R Saperstein, Rian N Chandra, Michael E Mauel, Gerald A Navratil A robust method of accessing the biased H-mode on HBT-EP was recently demonstrated [1]. From these studies it is known that while the pedestal temperature increases, the core temperature does not upon entering the biased H-mode [1], and this observation is consistent with other small tokamaks. This poster extends this analysis by exploring core temperature evolution during L- to biased H-mode (and the reverse) transitions using a tangential extreme ultraviolet (EUV) sensor array. Transitions into and out of the biased H-mode are controlled by varying the strength of a bias probe’s voltage as well as when it is tuned on/off during a plasma cycle. Comparisons of the temporal core temperature measurements and other plasma parameters between the H- and L-mode cases as well as during transitions are discussed. A survey of measurements of profile evolution and evolution time-scales will also be presented. |
|
UP11.00045: Scrape-off-layer currents during disruptions in HBT-EP Jeffrey P Levesque, David A Arnold, James Bialek, Rian N Chandra, Nigel J DaSilva, Boting Li, Michael E Mauel, Gerald A Navratil, Alex R Saperstein, Yumou Wei, Christopher J Hansen Non-axisymmetric halo currents that occur during tokamak disruptions can result in significant asymmetric forces on the vessel, potentially causing damage to components. Understanding the generation and rotation of these currents is important for establishing design requirements for devices to tolerate disruptions. A new set of halo current diagnostic and control tiles has been installed on the high-field-side (HFS) of the HBT-EP tokamak, in regions where there is strong plasma-wall contact during disruptions. The tiles can be switched between having passive low resistance connections to the vessel, or active biasing with respect to the vessel or other tiles. Driving current during active biasing is expected to be severely constrained due to the low density of the plasma edge and scrape-off layer; possible methods to increase the current limit for control purposes are discussed. This first stage of HFS implementation uses tiles at 2 toroidal locations separated by Δφ=90°, integrating over 6 poloidal regions with Δθ∼13° resolution. We present initial measurements from these tiles during disruptions and non-disruptive mode activity. Plans to expand the system to a set of four equally-spaced poloidal arrays are described. |
|
UP11.00046: Science Opportunties for HBT-EP Enhanced by REBCO Superconducting TF Coils Michael E Mauel, Jeffrey P Levesque, Gerald A Navratil, Carlos A Paz-Soldan, Elizabeth J Paul With the success of the CFS/TFMC (MIT News, Sept 8, 2021), magnetic fusion research has entered a new age: moving from copper to high temperature superconductor. In this poster, we illustrate the advantages that would result if the HBT-EP pulsed copper TF coils are replaced by steady-state REBCO coils. The superconducting TF coils would greatly enlarge the experimental toroidal volume. Scientists and students would benefit from an easily configurable toroidal plasma with improved control capabilities. Increased scientific productivity results from repetitively pulsed, long plasma discharges. Unlike the very high-field CFS/TFMC, superconducting TF coils in HBT-EP would operate at lower field, lower stress, very high quench margin, but retain high current density. Non-insulated REBCO tapes would be co-wound with SS strip (as was proposed for the LDX upgrade), and each of twenty TF coils would be supported in individual SS cryostats and dewars like used in the CLEO device (from which HBT-EP was built.) With a steady TF, we show how HBT-EP's pulse-power systems could be replaced by solid-state equilibrium control amplifiers, illustrate several plasma shape scenarios, including those with large vacuum transforms, and describe frontier science questions that can be answered using a configurable superconducting research facility. |
|
UP11.00047: Randomized-SVD produces accurate characterizations of tokamak discharges from multiple data-streams James Anderson, Alvin Pan, Jeffrey P Levesque, Michael E Mauel Modern magnetic fusion research involves high-resolution temporal and spatial diagnostics from multiple sensor arrays that generate large data streams well-suited to advanced scalable numerical linear algebra methods. This presentation introduces the first results of applying randomized numerical linear algebra (rNLA) techniques to the analysis of fusion data obtained from The Columbia University High Beta Tokamak-Extended Pulse (HBT-EP). rNLA techniques allow us to make use of distributing computing architectures and hence harness the power of GPU computing and massive parallelization for computing large matrix factorizations. Such factorizations provide the foundations of large-scale data analysis. To make use of rNLA methods we must trade off solution accuracy against computation time. In this work we show that a randomized singular value decomposition applied to data obtained from HBT-EP’s magnetic field sensors (poloidal, toroidal, and feedback arrays) produces results that are comparable to those obtained via exact direct (and thus not scalable) methods. The long term aims of this project are to integrate rNLA methods into pipelines involving highspeed video images of the plasma and push towards real-time control. |
|
UP11.00048: Comparative study between flowing two-fluid and single-fluid equilibria of spherical torus plasmas Takashi Kanki, Masayoshi Nagata A two-fluid equilibrium with small but non-zero two-fluid parameter ε is regarded as a singular perturbation of a single-fluid (MHD) equilibrium. The reduction from the two-fluid equilibrium to the MHD one was an open problem for several years, but was recently solved by Hameiri1 and Guazzotto2. We have solved the problem by clarifying the relationship between electrostatic potential and total enthalpy. The relationship is derived from the appropriate selection of reference physical quantities for normalization that electrostatic potential (electric field) become relatively large, and the nearby-fluid model is required to eliminate the 1/ε singularities appearing in the Ampere’s equation and the combined Bernoulli equation. The flowing two-fluid equilibria observed in the HIST experiment have been reconstructed, and have the diamagnetic toroidal field in the central open flux column and the poloidal flow velocity with zonal flow like structure. In the toroidal ion flow velocity, the parallel flow along the magnetic field and the Hall effect are dominant. These can be almost cancelled, because their radial profiles are similar, and their signs are different each other. Therefore, the radial profile of the toroidal ion flow velocity is similar to that of the ExB drift velocity. |
|
UP11.00049: Energetic ion experiments with three-ion ICRF scenarios in non-active plasmas at JET Yevgen Kazakov, Massimo Nocente, Jeronimo Garcia, Vasili Kiptily, Jozef Ongena, Rui Coelho, Teddy Craciunescu, Andrea Dal Molin, Ephrem Delabie, Elena De La Luna, Mykola Dreval, Remi Dumont, Giu Marcer, Davide Rigamonti, Sergei Sharapov, Mireille Schneider, Paula Siren, Ziga Stancar, Hongjuan Sun, Marco Tardocchi, Henri Weisen, . JET Contributors Significant progress with the development of three-ion ICRF scenarios [1,2] in support of the ITER Research Plan has been recently achieved [3]. We report the results of energetic ion experiments at JET, where the three-ion 4He-(3He)-H scheme was applied for heating non-active H-4He plasmas, both on-axis and off-axis [4]. The spatial profile of energetic 3He ions was controlled by varying the ICRF antenna phasing, resulting in significant differences in MHD behaviour and sawtooth dynamics. Our results confirm that the three-ion ICRF scenario can be applied to control the radial profile of the safety factor and sustain plasmas with an inverted q-profile at JET, complementing earlier observations of its application in D-3He plasmas [5]. Another important highlight of the JET experiments in H-4He plasmas reported here is the demonstration of the capability to measure simultaneously both He isotopes, n(4He)/ne ≈ 5-15% and n(3He)/ne ≈ 0.2%, using the highresolution sub-divertor gas spectroscopy [6]. |
|
UP11.00050: The isotope effect on core heat transport in JET-ILW ohmic plasmas in H, D and T Ephrem Delabie, F.F.M. Nave, Pablo Rodriguez-Fernandez, Bartosz Lomanowski, Matteo Baruzzo, Theodore M Biewer, Jeronimo Garcia, Jon C Hillesheim, Damian B King, Morten Lennholm, Costanza F Maggi The development of main ion charge exchange spectroscopy has enabled studies of the ion heat |
|
UP11.00051: Fluctuation-induced particle transport during sawtooth reconnections in H-mode plasmas on HL-2A tokamak Weixing Ding, Jie Wu, Tao Lan, Ge Zhuang, J.R. Wu, Min Xu, W Chen, L Nie The inward particle flux has been observed in many fusion devices[1, 2] and has attracted attention through its involvement in suppressing turbulence and forming the transport barrier in fusion research[3]. The fluctuation-induced inward particle flux after the sawtooth reconnection has been measured in H-mode plasmas by using the probes. Sawtooth reconnections generally exist near the q = 1 magnetic surface of the tokamak, and sawtooth reconnection periodically causes outward particles and heat transport from the core. During recovery of plasmas, an inward flux peak can be observed after a sawtooth reconnection, meanwhile, the edge transport barrier begins to form. Low-frequency fluctuations (<50 kHz) contribute to most of the inward flux. The magnetic turbulence increases two orders of magnitude after crash, where Maxwell stress induced particle flux can play an important role in inward particle flux. |
Author not Attending |
UP11.00052: Improved Confinement Due to Boron Powder Injection in WEST L-Mode Plasmas Grant M Bodner, Clarisse Bourdelle, Pierre Manas, Laure Vermare Alternative operating scenarios to H-mode are desired for future fusion pilot plants in order to avoid the need to suppress/mitigate ELMs. A promising scenario is to use impurity injection to achieve a discharge with improved confinement and a high radiative fraction without the creation of a pressure pedestal. This has been done successfully on a number of tokamaks using gaseous impurity injection. Experiments with impurity powder droppers, installed worldwide for active conditioning, have reported improvements in plasma confinement during particulate injection. On WEST, L-mode plasmas with dominant electron heating and no core torque source observed such improvements in confinement with B powder injection. These results are reminiscent of previous gaseous N2 injection experiments on WEST. During powder injection, WMHD and the neutron rate increased up to 25% and 200%, respectively, depending upon the powder drop rate. The improvements in confinement are thought to be the result of stabilized ▽T TEM turbulence through increases in Zeff and/or collisionality leading to core density peaking at zero particle flux. The increase in density peaking stabilizes ITG-driven turbulence allowing for the achievement of increased Ti. To identify the dominant mechanisms and the causality chain behind these improvements in confinement, we employ interpretative modelling using METIS, predictive integrated modelling using a HFPS and QuaLiKiz, and stand-alone gyrokinetic simulations using GKW and QuaLiKiz. |
|
UP11.00053: Developing tools to accelerate divertor design and full-power operation Benjamin Dudson, Maxim Umansky, Thomas D Rognlien, Filippo Scotti, Xiao Chen, Ruipeng Li, Alex Friedman We aim to address the design and operation challenges of future tokamak fusion reactors by developing tools which combine data and simulations with automation and uncertainty quantification techniques . We will present recent progress towards this goal in model development, workflow automation, and plans to develop and validate these tools in collaboration with current and near-term experimental facilities including the DIII-D national fusion facility. The divertor is a critical part of any high-power tokamak device and an integral part of the overall design, strongly impacting the plasma operating space and choice of poloidal field coil configuration. The time required to identify and refine performant divertor designs has the potential to delay the whole design process. Once a tokamak is constructed, ramp-up to full power operation is dependent on managing risks of damage to the divertor and other plasma facing components. As with design, the time required to assess the safe operating space of the divertor with confidence could delay the start of full power operation. We aim to accelerate these timelines by automating the assimilation of data and simulations and their uncertainties. The physics basis of our tools is provided by two open-source codes: The well-established UEDGE (https://github.com/LLNL/UEDGE) and a new code, Hermes-3 (https://github.com/bendudson/hermes-3/). The Hermes-3 code has been developed based on BOUT++ and is capable of multi-fluid transport and turbulence calculations in tokamak single and double-null geometries. We will present these tools, their advantages and disadvantages, and their potential role as part of a larger multi-fidelity suite of modelling tools to accelerate the design and operation of tokamak fusion reactors. |
|
UP11.00054: Investigating Divertor-safe Burning-Plasma Regimes in ITER using a Core-edge Model with SOLPS Scalings Vincent R Graber, Eugenio Schuster To maximize fusion power, ITER will need to access burn regimes that push against operational limits. These limits include saturation of actuators such as neutral beam injectors and pellet injectors. Furthermore, the heat load on the divertor target should remain below 10 MW/m2 to avoid melting. Using Plasma Operation Contour (POPCON) plots based on a model coupling the plasma’s core with the scrape- off-layer and divertor regions, the temperature-density space of ITER plasmas is investigated in this work to determine which operational limits are most restrictive towards achieving higher fusion powers. In this core-edge model, the core-plasma region is governed by nonlinear density and energy response models, while the edge-plasma regions are modeled with scalings. These scalings were generated from SOLPS4.3 simulation results [1] and depend on the core-plasma's power and particle outflows, the separatrix impurity concentration, and the gas injection rate. Outputs of the scalings such as the neutral influx, the separatrix temperatures, and the separatrix densities enter into the core-plasma response models. In addition, the scalings yield the target's heat load which is crucial to identify the high-fusion-power regimes compatible with safe divertor operation.
[1] H.D. Pacher, et. al., J. Nucl. Mater. 463 (2015) 591–595.
|
|
UP11.00055: Preventing H-mode with Negative Triangularity to Improve Exhaust Handling at High Core Plasma Performance Andrew O Nelson, Carlos A Paz-Soldan, Haley S Wilson, Samuli Saarelma Negative triangularity (NT) plasmas are typically characterized by high core plasma performance while simultaneously maintaining an L-mode edge. In this work, we explore the potential to establish this regime in reactor-like conditions through two studies. First, we explore the potential for robust NT L-mode reactor operation by modeling infinite-n ballooning stability as a function of internal profiles and equilibrium shape using a combination of the CHEASE and BALOO codes. These modes prevent the growth of pedestal gradients while still allowing for strong core performance, and are found to be essential to edge behavior in the simulated NT plasmas. Second, the gradient-limiting mechanism of the infinite-n ballooning modes is expanded to 1D modeling of NT reactor scenarios using the STEP code. Self-consistent reactor operating scenarios are established by comparing converged STEP simulations with POPCON-style regime descriptions, demonstrating a wide range of conditions accessible for an NT reactor. Comments on the integration of these high performance core scenarios with a reactor-friendly exhaust scheme are presented, highlighting the potential benefits of an L-mode edge in the reactor environment. |
|
UP11.00056: Impact of High Heat Fluxes from an Electrothermal Arc Plasma Source on Ultra-high Temperature Ceramics for Fusion Reactor Limiter Applications Lauren Nuckols, Trey E Gebhart, Chad M Parish, Juergen Rapp, Cami S Collins Sacrificial limiters are a physical mitigation method that will likely be employed in a Fusion Pilot Plant (FPP) to protect the breeding blanket first wall from catastrophic damage caused by plasma transients. Ideal limiters would withstand heat and particle fluxes from both nominal operation and from unplanned plasma transients, be radiation resistant and chemically inert (avoiding tritium retention), and be composed of low- or mid-Z elements to prevent plasma contamination. Such requirements lead to the appeal of ultra-high temperature ceramics (UHTCs) which have favorable properties of both ceramics (high hardness and melting temperature) and metals (high electrical and thermal conductivity). In this work, initial testing of two UHTC compositions, ZrB2 and TiB2, is completed by analyzing the impact of several plasma discharges from a pulsed capillary plasma source on ZrB2 and TiB2 targets. Each plasma discharge lasts ~1 ms and generates 1 – 2 GW/m2 heat fluxes due to impacts of ions, electrons, and neutrals onto the target material, simulating potential energy loadings of long ELMs from a future fusion device. This work aims to find an ELM magnitude threshold for UHTCs in an FPP and to compare UHTC surface evolution and failure response to other candidate materials. |
|
UP11.00057: Building database of 2D UEDGE simulations for the development of a surrogate model of divertor detachment control Menglong Zhao, Thomas D Rognlien, Ben Zhu, William H Meyer, Xueqiao Xu, Harsh Bhatia, Nami Li, Peer-Timo Bremer A large set of 2D UEDGE simulations with currents and cross-field drifts based on a generic medium-size tokamak geometry are obtained for the development of machine learning surrogate models for detachment control. For the current 2D data set, three control parameters are varied: gas puff rate, power input and impurity fraction. In addition, the values of the perpendicular anomalous transport coefficients are scanned because they are the most important uncertainty input of UEDGE or other 2D transport codes. The range of the parameters covers the normal experimental control range. A spatial constant concentration of impurities (fixed-fraction) is assumed, and currents for solving electric potential and cross-field drifts are included since they are important in determining divertor plasma states. Compared to our previous work of building a large data set of 1D UEDGE simulations [1] that already captures the main SOL physics by solving plasma parallel transport equations in a flux tube with recycled atom neutrals, these 2D simulations have higher fidelity by including cross-field drifts and the uncertainty of perpendicular transport coefficients, which provides 2D plasma states toward both inner and outer target plates. The data set shows that for a certain power input and impurity fraction, the target plate ion saturation current roll-over appears as the puff rate increases, recovering the trend of experimental data. However, the roll-over appears earlier (at a smaller upstream density) than the results of our previous 1D simulations due to higher radiation. A surrogate model is under development using the 2D UEDGE simulations for detachment control [2]. Possible extensions of including geometry effects: varying divertor leg lengths and divertor target tilt angles, will also be discussed. |
|
UP11.00058: MFE: DIII-D Session Chairs: |
|
UP11.00059: DIII-D: Closing the Gaps to Future Fusion Reactors Charles M Greenfield The DIII-D program is pursuing an ambitious plan to close critical design gaps to a Fusion Pilot Plant (FPP), including integrating performance and exhaust solutions, addressing plasma interacting material and technology issues, and resolving the path to ITER and a high fusion gain pulsed FPP. Increasing ECH power to 10 gyrotrons, with extension to 20 by FY28, will provide low-torque electron heating and profile control, while new reactor-relevant solutions for efficient off-axis current drive will be pioneered by high-field-side LHCD, helicon waves and top launch ECCD to enable FPP steady-state scenarios. A series of closed, modular divertors will allow exploration of innovative plasma solutions for combined core and plasma exhaust in high opacity/low collisionality regimes made possible by stronger shaping to maximize the pedestal pressure and density along with a BT rise to 2.5 T. A dedicated material interaction test station will help close gaps in compatible fusion materials. The control and mitigation of plasma transients will be addressed through a passive runaway electron dissipation coil and exploration of novel disruption mitigation techniques (EM launch, hyper-velocity W pellets,…). An exciting option for a negative triangularity path is being assessed. |
|
UP11.00060: A Reference Governor for Vertical Control near Stability Limits Andres Pajares, Anders Welander, David A Humphreys A reference governor has been designed to calculate target shapes that ensure safe tokamak operation at high vertical-instability growth rates. Due to their inherent vertical instability, the elongated plasmas envisioned for ITER and beyond are usually attained in present devices by means of feedback (FB). This FB control pursues elongated target shapes usually pre-defined before a discharge and rejects a certain range of disturbances in parameters such as Ip, li, or βp. However, machine-condition changes and off-normal disturbances may make pre-defined shapes unattainable, sometimes resulting in disruptions. Advanced-control strategies that go beyond traditional FB loops can help minimize disruptions in ITER and fusion power plants. In this work, a reference-governor algorithm has been designed to update, in real time, the target shapes that keep the plasma below a safe growth-rate limit during the whole discharge. The algorithm adapts the target shapes in response to machine-condition changes as well as disturbance variations estimated from magnetic measurements. The algorithm uses gspert [1], which solves a perturbed Grad-Shafranov equation to model the plasma response. Initial DIII-D simulations show the advantages of this algorithm to ensure FB control near stability limits. |
|
UP11.00061: Robust Control of the Electron Temperature Profile in DIII-D Shira Morosohk, Sai Tej Paruchuri, Zibo Wang, Tariq Rafiq, Eugenio Schuster Control of kinetic profiles is crucial to achieving a high level of plasma performance in tokamak plasmas. This requires feedback algorithms that use measurements of the plasma state in real time to determine the necessary actuator trajectories to reach the target profile. To that end, a robust control scheme has been developed for the electron temperature (Te) profile on DIII-D. A linearized model of the dynamics of the electron temperature is derived from the heat transport equation, and the electron density profile is modeled as an uncertainty. The mixed-sensitivity H-infinity technique results in a controller that is capable of tracking a target profile near the linearization point for an expected range of uncertainty. The controller is then tested in closed-loop nonlinear simulations by using the Control Oriented Transport SIMulator (COTSIM). Preliminary predictive simulation results show that this controller is indeed capable of regulating the electron temperature profile with expected dynamic performance and robustness. |
|
UP11.00062: Synthetic camera diagnostic for plasma boundary measurement Wilkie Choi, David Humphreys Fusion pilot plant and reactor devices will likely operate in long-pulse, steady-state scenarios. For Mirnov coils, flux loops, and other integrated magnetic diagnostics, noise and offsets in the dB/dt measurements coupled with long integration time would result in integration drifts that dominate over the actual signal. Since real-time control of the plasma boundary presently relies on equilibria reconstructed from magnetic signals, a new type of diagnostic is needed for boundary identification on future devices. In this work, filtered line-emissions from partially ionized impurities in the edge are proposed to aid in identifying the last-closed flux surface. A synthetic camera diagnostic has been developed, which calculates the expected image based on an equilibrium reconstruction and electron temperature and density profiles near the edge. Some useful capabilities include impurity selection, wavelength filtering, and flexible camera settings. Comparisons are made between synthetic images and actual experimental measurements on DIII-D and EAST. |
|
UP11.00063: Vessel current compensation for improved equilibrium reconstruction and control just after plasma formation in DIII-D* Yanzheng Jiang, Edward J Strait, John R Ferron High fidelity equilibrium reconstructions are essential for accurate plasma control and equilibrium-based analysis. Equilibrium reconstruction and plasma control usually suffer from reduced equilibrium accuracy at the starting phase of plasma operation for tokamaks, because of massive eddy currents induced in the vessel wall from large variation of ohmic heating coil flux and control coil field. A magnetic response function model [Y. Jiang, RSI 2017] provides a set of time-dependent Green’s functions, which contain a group of 3 parameters calibrated by fitting magnetic measurement with individual coils energized at varying frequencies. The present result shows that high \chi^2, indicating poorer quality of a fit to data in equilibrium reconstruction, corresponds well with the eddy current response level in the magnetic signals used in equilibrium calculation. Instead of the DC Green’s function that EFIT [L.L. Lao, NF 1985] now uses, the AC Green’s functions provide the vessel current compensation for the magnetic sensors to optimize the equilibrium reconstructions in the presence of large induced currents. This new technique will improve the accuracy of equilibrium reconstructions during plasma startup and other transient events. |
|
UP11.00064: Model-based Safety-Factor-Profile Slope Control at Predefined Rational Surfaces in DIII‑D Sai Tej Paruchuri, Eugenio Schuster Magnetohydrodynamic instabilities like neoclassical tearing modes appearing at rational safety-factor surfaces can degrade and even disrupt plasma confinement. It has been proposed that active regulation of the safety-factor-profile slope at these rational surfaces may mitigate the onset of such instabilities [1]. Recently proposed algorithms for local control of the safety-factor profile rely on indirectly regulating the slope of the poloidal-flux-gradient profile to achieve the desired control objective [2]. However, due to the nonlinear relation between the safety factor and the gradient of the poloidal flux, regulating only the slope of the poloidal-flux-gradient profile may not always achieve the desired safety-factor-profile slope. A novel algorithm is proposed in this work based on a model that governs the evolution of the safety-factor-profile gradient, which enables control synthesis for direct regulation of the safety-factor-profile slope. The effectiveness of the proposed model and the associated model-based controller are demonstrated using nonlinear COTSIM simulations for a DIII‑D scenario. |
|
UP11.00065: Proximity Control and Robust VDE Protection on DIII-D and KSTAR Jayson L Barr, David A Humphreys, Nicholas W Eidietis, Brian Sammuli, David Orozco, Erik Olofsson, Himank Anand, Zichuan A Xing, Francesca Turco, Sang-hee Hahn, Cristina Rea, Mark D Boyer, Dennis Mueller ITER will require exceptionally low disruptivity while pushing performance limits. This will require a comprehensive strategy, including continuous regulation of the proximity to stability and control limits (Proximity Control). DIII-D has been developing a real-time Proximity Control architecture which modifies control targets and actuator constraints based on stability metrics. Robust Vertical Displacement Event (VDE) avoidance has been demonstrated using real-time adjustment in shaping to regulate the VDE growth-rate at 800 rad/s for >3s, intervening only beyond thresholds in acceptable growth-rates. H-L back-transition protection has been demonstrated with real-time modification of minimum input power based on radiated power, and a machine learning predictor for the likelihood of H-/L-mode. Limited controllability of edge gradients in J|| in the ITER Baseline Scenario using adjustments in plasma triangularity and squareness has been demonstrated, providing a potential tool for tearing mode avoidance. |
|
UP11.00066: Minimum divertor leg length for detached divertor operation compatible with a high performance core plasma Anthony Leonard, John Canik, Aaro Jarvinen, Adam McLean, Morgan W Shafer, Filippo Scotti Poloidal gradients in the outer leg of DIII-D detached divertor discharges are characterized for minimum leg length for high divertor dissipation without perturbative cooling of the X-point region. Measurements from the divertor Thomson scattering (DTS) diagnostic indicate poloidal electron temperature gradients of up to 200 eV/m through the dissipative region of a detached divertor leg. The gradients are consistent with convective-dominated transport and dissipation due to intrinsic and seeded low-Z impurities. The Te poloidal scale length is estimated as LTe≈vpolqeTe/Lzfzne where vpol is the effective plasma poloidal velocity from parallel convection and E×B poloidal flow, Lz is the radiative loss parameter, and fz is the radiating impurity fraction. For DIII-D high performance scenarios with ≥ 10 MW of injected power and a goal of high divertor dissipation while maintaining the X-point region at Te ≥ 80 eV, a minimum divertor leg length of ≥ 40 cm is indicated. This is a factor of 2-3 longer than the typical DIII-D configuration and would present a target for future divertor designs. For future tokamaks the scaling appears to be favorable with larger size, higher field and higher density, but will also depend on the scaling of radial transport and plasma drifts. |
|
UP11.00067: Floating Potential Fluctuation Measurements with Langmuir Probes in the DIII-D Divertor During Wide Pedestal QH-Mode Dinh D Truong, Jonathan G Watkins, Huiqian Wang, Alessandro Bortolon, Xi Chen, Darin R Ernst Recent experiments show considerable negative floating potential (Vf) and increased fluctuation levels peaking near the strike point in the first such measurements during wide pedestal quiescent H-mode (WPQH-mode) in DIII-D. The fluctuation amplitude decay profile in the scrape-off layer (SOL) indicates that upstream pedestal turbulence, near the separatrix, is driving fluctuations in the divertor. WPQH-mode is an ELM-free operating regime with significantly improved core confinement and a pedestal limited by broadband turbulence. Previous measurements of the divertor heat flux width (λq) suggest that λq increases with pedestal density fluctuations, exceeding the Eich scaling. These results motivated Vf fluctuation measurements in the divertor during WPQH-mode. One of the DIII-D fixed Langmuir probes was used to continuously measure Vf (DC-500kHz) as the strike point was swept past the probe. The effects of Vf fluctuations on λq will be analyzed. The Langmuir probe Vf fluctuations will be correlated with Beam Emission Spectroscopy (BES) density fluctuation measurements in WPQH-mode experiments during the 2022 DIII-D experimental campaign. |
|
UP11.00068: Evaluating the influence of particle sources and drifts on SOL flow and stagnation point in DIII-D L-mode discharges using Coherence Imaging Spectroscopy and UEDGE modeling Marcus G Burke, Filippo Scotti, Steven L Allen, Max E Fenstermacher, Adam McLean, William H Meyer, Morgan W Shafer, Huiqian Wang, Robert S Wilcox, Menglong Zhao In lower-single-null (LSN) DIII-D discharges, regardless of the ∇B drift direction or the degree of detachment, the C2+ flow is found to stagnate at a single point near the crown of the main plasma, away from the divertor X-point. In contrast, in upper-single-null, the C2+ flow stagnates near the low-field-side X-point. Coherence imaging spectroscopy (CIS) is used to study main-chamber scrape-off-layer (SOL) carbon flows under a variety of divertor configurations in L-mode discharges on DIII-D. CIS on DIII-D utilizes an in-situ velocity calibration technique to absolutely calibrate the zero-velocity phase shift. This allows for accurate estimation of the location of the C2+ flow stagnation point in the SOL. The degree of divertor closure and background neutral pressure slightly modifies the stagnation point with flow near the divertor region being generally decreased with higher background neutrals. These experimental measurements are compared to UEDGE fluid simulations with drifts. In detached conditions, UEDGE roughly agrees with the measured C2+stagnation point. In contrast, in attached conditions, UEDGE underpredicts the C2+ flow in the main SOL when compared to measurements, and does not show a clear stagnation point. |
|
UP11.00069: Predictive Modeling of a Dissipative Divertor in DIII-D using SOLPS-ITER Jonathan H Yu, Roberto Maurizio, Anthony Leonard, Adam McLean, Morgan W Shafer, Dan M Thomas A new dissipative divertor installation is planned in DIII-D to inform power exhaust physics issues in regimes pushed toward the conditions expected in a fusion pilot plant. SOLPS-ITER [1] simulations of a long leg divertor concept demonstrate impurity seeding requirements for achieving deep detachment and trade-offs due to reduced dissipation with divertor pumping for density control. Increasing the outer divertor leg length up to ~50 cm reveals benefits of enhanced dissipation due to longer connection lengths and increased stability of the radiation front between the X-point and target, avoiding a MARFE condition. Simulations are run with upstream separatrix electron density scanned around ~2x1019 m-3 and input powers up to 30 MW, which represents the potential of future electron cyclotron heating upgrades along with existing neutral beam injection. |
Author not Attending |
UP11.00070: Relating upstream SOL temperature and density profiles to downstream ion flux profiles and pumping efficiency Morgan W Shafer, Adam McLean, Anthony Leonard, Huiqian Wang, Robert S Wilcox Experiments on DIII-D over a range of plasma current and densities are used to examine two-point model estimates for downstream ion flux profiles used in estimating cryopump coupling. Density control via cryo-pumping in present-day machines requires coupling a portion of the recycled neutrals into a plenum entrance to be exhausted that would otherwise re-fuel the plasma. In attached conditions, this requires creating baffling geometry to accept large fraction of the ion flux. The ion flux width, ??Γ, can be related to the heat flux width, ??q through the ITPA scaling by assuming fixed or a range of values for ??n/??T, representing the temperature and density fall-off lengths through the two-point model assuming equipartition. In low recycling attached conditions, ??n/??T~1-1.5, but this ratio can increase as overall density increases to high recycling and detached conditions. In the limit recycled neutrals do not ionize prior to entering the plenum, the characteristic factor of ??Γ entering the divertor plenum can be estimated for the best particle exhaust. We use a range of plasma conditions varying plasma current and density governing the width of the SOL quantities to examine these relations. |
|
UP11.00071: First power exhaust experiments in DIII-D's new V-shaped Small Angle Slot divertor Roberto Maurizio, Dan M Thomas, Jonathan H Yu, Tyler Abrams, Alan Hyatt, Jeffrey L Herfindal, Anthony Leonard, Xinxing Ma, Adam McLean, Jun Ren, Morgan W Shafer, Gregory Sinclair, Huiqian Wang, Jonathan G Watkins Initial DIII-D experiments in the new V-shaped SAS-VW slot divertor reveal a more abrupt cliff-like transition to dissipative conditions compared to the legacy flat-end SAS slot divertor, for ion B×B drift into the slot, whereas the dependence of dissipation on strike point position in the slot is similar to SAS. DIII-D modified its original Small Angle Slot (SAS) divertor into a V-shaped slot (SAS-VW). Recent H-mode experiments studied its basic power exhaust properties. Outer strike point (OSP) sweeps at fixed plasma density reveal that, for ion B×B drift into the slot, the OSP Te is ~50% lower if the OSP is on the inner compared to the outer slant. In contrast, for ion B×B drift out of the slot, the OSP Te is ~50% lower if the OSP is on the outer compared to the inner slant. Such geometric dependence is consistent with SAS data and SOLPS-ITER drift modeling. Plasma density ramps at fixed OSP, for ion B×B drift into the slot, show that, at low density, the near-SOL Te is higher in SAS-VW compared to SAS but, for increasing density, it drops at a faster rate in SAS-VW, causing an abrupt cliff-like transition to dissipative conditions (~5-10 eV) at densities similar to SAS. Advanced data analysis and SOLPS-ITER drift modeling are carried out to interpret these results. |
|
UP11.00072: DIII-D upper-divertor baffle optimization for pumping high-triangularity discharges Thomas D Rognlien, Menglong Zhao, Maxim Umansky, Robert Wilcox, Mogen Shafer, Gary Porter, Marv Rensink, Tom Osborne, Tony Leonard, Mathias Groth, Max Fenstermacher, Steve Allen Magnetic equilibria with high divertor triangularity provide a potential path to stable high-beta discharges in DIII-D at higher pedestal density. Core plasma density control utilizing a cryo pump adjacent to the upper/outer divertor of DIII-D is a key component for this scenario.1 The present study focuses on the impact of self-consistent plasma+neutral 2D profiles in the full scrape-off layer using UEDGE solutions with cross-field plasma drifts in a double-null magnetic geometry. The results provide local plasma fluxes for an analytic pumping-rate model benchmarked with Monte Carlo neutral simulations1 and in turn, pumping is shown to modify the plasma. The highest pumping rates are obtained for the ion B´B drift directed away from the upper divertor region, which leads to a densification of the outer target. Optimization of the baffle and pump-duct locations and shapes are obtained via iteration between the plasma and pumping models. |
|
UP11.00073: 3D Modeling of RMP Erosion and Impurity Transport in L-Mode Discharges in the DIII-D Open Divertor using the ERO2.0 Code Marcos X Navarro, Juri Romazanov, Andreas Kirschner, Edward T Hinson, Tyler Abrams, Oliver Schmitz The 3D kinetic Monte Carlo ERO2.0 code is used to model PWI and impurity transport for three L-mode discharges in the DIIID tokamak reconstructed with EMC3-EIRENE: (1) a no RMP reference, (2) 0-degree phasing, and (3) 60-degree phasing for n = 3. The discharges correspond to an open divertor configuration and (a) a fully carbon (C) target and (b) a tungsten (W) metal ring. A parameter scan for anomalous diffusion and starting carbon background concentrations show higher toroidally averaged net erosion for the no-RMP reference cases across all parameters, whereas the 60-degree RMP phasing performs best. Divertor surface maps show that particle re-erosion contributes to significant C deposition between the lobe structures, and their perimeter on the low-field side. Location tracing for C show radially outward particle trajectories along lobe structures. No full buildup of C is observed along the W ring cases for low concentrations of C in the background (<1%), with it occupying a maximum of ~15% of the ring surface concentration increasing the integrated C erosion as the mixing layer composition changes. This analysis can be used for H-Mode scenarios, experimental validation of tungsten erosion, and divertor studies considering the impact of RMP induced impurity transport. |
|
UP11.00074: Feasibility Study of Pedestal Plasma Current Measurements in DIII-D Colin Chrystal, Keith H Burrell, Richard J Groebner, Lang L Lao, Anthony Leonard, Thomas H Osborne, Dan M Thomas, Francesca Turco, Brian S Victor, Marcus G Burke, Theresa M Wilks, Philip B Snyder, Elijah H Martin, Shaun R Haskey, Florian M. Laggner, Jie Chen, Ryan Albosta, Benedikt Geiger, Thomas P Crowley, Diane R Demers, Peter J Fimognari At the DIII-D tokamak, a working group recently made a concerted effort to evaluate the feasibility of measuring the plasma current in and around the H-mode pedestal, and the findings of this working group are presented. The plasma current in this region is key to pedestal transport and stability, so measurements of this quantity are highly desirable as they would improve the physics understanding of issues that are key for tokamak performance. The working group first determed what physics questions stood to benefit from these measurements and then determined the associated measurement requirements (spatial and temporal resolution, accuracy, etc.). Diagnostic experts then submitted proposals for making the required measurements with multiple techniques (microwave polarimetry, spectroscopy, etc.). The content and evaluation of all these proposals are presented. No proposal was found to be superior overall, but lithium beam spectroscopy, deuterium beam spectroscopy (multiple techniques), and Doppler-free saturation spectroscopy are the most promising techniques. |
|
UP11.00075: Density Shoulder Formation in DIII-D Jose A Boedo, Adam McLean, Dmitry L Rudakov, Xinxing Ma, Huiqian Wang, Morgan W Shafer, Thomas H Osborne Midplane density profiles in DIII-D plasmas develop a long decay length in the SOL as discharge average density increases and divertor detachment progresses. Length increase is accompanied by enhanced radial transport, decreased parallel transport and increased local neutral pressure, the latter dependent on divertor ExB direction. As line averaged density increases from 1 to 4E13 cm-3, the near scrape-off layer (SOL) decay length stays constant at ~1.6 cm while the far SOL increases from 1.8 to 3.5 cm. Measured radial turbulent particle and heat transport at the midplane increase by factors of 10 with average discharge density, as expected from a filamentary transport model due to the collisionality changes along flux tubes. The measured radial transport at the midplane increases strongly as collisionality at the divertor region varies from 0.05 and surpasses 1. New findings are that the density shoulder is correlated with the active divertor's ExB drift direction pushing particles to the outer strike point, which also can increase the chamber neutral pressure by a factor of 3. These results indicate that the shoulder formation is a combination of increased radial transport and ionization source coupled with a reduction in parallel transport. |
|
UP11.00076: Impact Of The Plasma Configuration On H-mode Pedestal Ionization Source And ELM Dynamics In DIII-D Florian M. Laggner, Alessandro Bortolon, Florian Effenberg, Shaun R Haskey, Aaron M Rosenthal, Jerry W Hughes, Theresa M Wilks, Tomas Odstrcil, Thomas H Osborne, Huiqian Wang, Marcus G Burke, Filippo Scotti, Brian Victor, Ryan A Chaban, Saskia Mordijck, Dinh D Truong, Mathias Groth We present a study of the H-mode pedestal profile structure, edge localized mode (ELM) behavior and ionization source for varied plasma configurations (single null with open and more closed divertor as well as double null (DN)) and both directions of the ion B×∇B drift. The ELM behavior and the poloidal ionization source distribution show strong variations with changes in the divertor configuration. In DN shapes, the pedestal structure is most stable to peeling-ballooning modes due to plasma shaping and it exhibits the lowest ELM repetition frequency. When the ion B × ∇B drift direction is pointing away from the X-point, the ELM frequency is at least by a factor of two higher than for cases with ion B × ∇B drift direction pointing towards the X-point. The pedestal ionization source in the main chamber can exhibit significant poloidal asymmetries with one order of magnitude larger ionization source on high field side in comparison to the low field side. Our observations point towards modifications of the edge profile peeling-ballooning stability and dynamics through variations of the edge density, which are related to the variation in pedestal particle fueling. |
|
UP11.00077: Poloidal dependence of pellet ELM triggering in low-collisionality discharges Andreas Wingen, Robert S Wilcox, Brendan C Lyons, Larry R BAYLOR Previous linear M3D-C1 simulations found a strong poloidal dependence of the critical pellet size threshold for ELM triggering in low-collisionality discharges in DIII-D. However, such linear simulations do not include pellet ablation physics or time evolution of density and temperature. A new scheme of 2D nonlinear simulations, coupled with linear stability analysis at various steps throughout the nonlinear time evolution, was developed to include such physics and improve on the previous linear results. These new nonlinear-to-linear simulations confirm previous findings. Especially, contrary to experimental observations in JET for higher collisionality pedestals, the simulations find the outboard midplane to be the location with by far the lowest threshold and therefore most effective triggering in these DIII-D discharges. |
|
UP11.00078: Planned modification of DIII-D upper divertor to produce more reactor relevant H-mode pedestal conditions Tom Osborne, Livia Casali, Aaro Jarvinen, Morgan W Shafer, Philip B Snyder DIII-D plans to modify the upper divertor baffle design to increase plasma elongation and triangularity while maintaining density control to expand access to high pedestal pressure. Good overall performance in H-mode based reactors requires high H-mode pedestal pressure, pPED, at high density, nePED. These pedestals will be in a regime of high opacity to neutrals entering from the scrape off layer but low collisionality. These conditions are difficult to achieve simultaneously in present experiments but are expected to impact achievable pPED through effects on pedestal transport and stability. These conditions can be more closely approached in DIII-D at high plasma current in high triangularity, high elongation, large minor radius discharges in the super-H-mode regime where pPED increases with nePED. Entering and maintaining super-H-mode requires control of nePED as a function of temperature during the ramp-up to avoid reaching the ballooning mode limit where pPED is reduced and decreases with nePED. The density control requirement creates a tension between the achievable elongation and triangularity, the requirements to accommodate a range of scrape off layer widths, and sufficient divertor leg length to maintain midplane to divertor temperature difference. A proposed modular divertor design to maximize flexibility in these competing parameters will be presented. |
|
UP11.00079: Simulation of H-mode Edge Turbulence and Comparison to Phase Contrast Imaging Measurements on DIII–D Jon C Rost, Alessandro Marinoni, Miklos Porkolab Initial comparisons have been made between H-mode edge turbulence observed with Phase Contrast Imaging and simulations of the edge region with CGYRO. The PCI[1] diagnostic on DIII–D observes high-frequency ion-scale turbulence in Quiescent H-mode localized to the center of the Er well, providing an absolutely calibrated, wavenumber-resolved measurement in a stationary plasma. Simulations using CGYRO[2], a gyrokinetic solver for collisional plasmas, find broadband turbulence to be unstable in the bottom of the Er well, causing transport that matches the experimental particle and energy fluxes in both the electron and ion channels. Post processisng with a synthetic PCI diagnostic model shows the peak spectral amplitude approaches the experimental value, though the spectral width is much narrower. Study of these discrepancies and identification of the instability are ongoing, along with expanding the simulated region deeper into the pedestal. |
|
UP11.00080: Changes in pedestal ballooning stability with 3D magnetic perturbation on DIII-D Tyler B Cote, Matthias Willensdorfer, Nils Leuthold, Carlos A Paz-Soldan, Alessandro Bortolon, Matthias Knolker There is a significant need for understanding the physics of resonant magnetic perturbation (MP) ELM mitigation and suppression in order to understand how ELM control scenarios extrapolate to ITER. The 3D magnetic geometry associated with the kink response to MPs can change the local MHD stability boundary, with destabilized toroidally localized ballooning modes observed in AUG[1]. Evidence suggests that this mechanism also causes the ELM births to localize to the same toroidal position as the ballooning instabilities[2]. |
|
UP11.00081: Refining a finite difference-based approach to helium transport analysis Edward T Hinson, Tyler Abrams, Igor Bykov, Colin Chrystal, Cami S Collins, Brian A Grierson, Carlos A Paz-Soldan, Oliver Schmitz, Ezekial A Unterberg A He transport model based on spatial finite differences has been developed to quantify increases in helium transport observed in an ITER-like tokamak plasma during RMP-ELM suppression*. Due to coarse spatial sampling in this data, in contrast to conventional methods that compare trial solutions of the continuity PDE to data, a discrete finite-difference approximation to this PDE is used. |
|
UP11.00082: Validation of Density Pump-out by Magnetic Island Formation in KSTAR and DIII-D Tokamaks Qiming Hu, Jong-Kyu Park, Nikolas C Logan, SeongMoo Yang, SangKyeun Kim, Raffi Nazikian, J.S. Kang, Carlos A Paz-Soldan, Yongkyoon In, W.H. Ko, GunYoung Park Nonlinear TM1 simulations reveal characteristics of density pump-out by pedestal-foot island formation when applying n=1 RMPs, including: 1) bifurcation in pump-out with low RMP coil current threshold, 2) sensitivity of pump-out magnitude on q95, and 3) the magnitude of pump-out scales linearly with the island width. Dedicated experiments are carried out in KSTAR and DIII-D to validate these features and we find that: 1) staircase bifurcation in density pump-out is observed when slowly ramping up the n=1 RMP current, and the current threshold is ~1kAt when using one single row coils; 2) the magnitude of density pump-out becomes weaker when decreasing q95 from 5.5 to 4.5, and the density recovery is observed when q95 is ramped down to lower than 4.9; 3) analysis of DIII-D database of n=3 RMP experiment finds that the magnitude of density pump-out is proportional to the square root of RMP coil current Δne/ne∝IRMP0.5. These experimental observations are all consistent with TM1 simulations. The validated model also predicts that n=2-4 RMP in the baseline scenario of ITER plasma will cause 5-20% density pump-out, and high-n RMP leads to weaker pump-out. This indicates high-n RMPs are favorable for minimizing confinement degradation in RMP ELM control. |
|
UP11.00083: Evidence of turbulence spreading in the inner shear layer of wide-pedestal QH-mode discharges of DIII-D* Kshitish Kumar Barada, Terry L Rhodes, Tanmay Macwan, Lei Zeng, Max Austin, Richard J Groebner Trapped Electron Mode (TEM)-scale density turbulence (ñ) has been found to be first excited near the bottom of the Er well and then seemingly propagates towards the pedestal top of wide-pedestal [1] QH-mode discharges. This radially inward propagation is evidenced by a delay in the limit cycle oscillation (LCO) [2] modulated ñ amplitude evolution. This ñ amplitude evolution correlates with a radially inward propagation of an increased electron temperature (Te) gradient front. The turbulence front is found to be followed by a correlated decrease in local Te (and its gradient). This phenomenon of local cooling in Te resembles that of an inward cold pulse propagation and maybe related to the turbulence driven local transport. As these processes evolve (i.e., increase in local Te gradient leads to increase in ñ amplitude followed by a cold pulse propagation) at LCO timescale, the pedestal structure (height and width) is also found to be modulated [2] at LCO timescales indicating role of turbulence spreading and related local transport on pedestal structure. |
|
UP11.00084: Estimates of carbon sputtering from fast-ion losses on DIII-D QH-mode plasmas Alessandro Bortolon, Filippo Scotti, Jon T Drobny, Gerrit J Kramer, Davide Curreli Modeling of carbon sputtering by fast ion losses in quiescent H-mode mode plasmas indicates minimal impact toward high Zeff conditions, counter to previous expectations. This indicates the divertor sources the majority of the carbon leading to Zeff>3 in these scenarios. The 3D spatial distribution of fast-ion flux to the DIII-D wall is computed with Monte-Carlo simulations with the full-orbit code SPIRAL, retaining local distributions of energy and impact angle and using a realistic 3D wall, including features as bumper limiters, beam ducts and diagnostic ports. The RustBCA code is used to compute the distribution of the C physical sputtering source, finding contributions at bumper limiters and inner wall from prompt losses and at outer target from partially thermalized ions. Under conservative assumptions on impurity assimilation probability and confinement time, a contribution to Zeff of the order of 0.1 is inferred. The results suggest a dominant role for the divertor C source, exacerbated by the high electron temperature temperature and C dilution at the divertor targets in this scenario. |
|
UP11.00085: Real-time confinement mode classification and ELM onset prediction with the BES diagnostic system at DIII-D Semin Joung, David R Smith, Benedikt Geiger, Kevin Gill, George McKee, Zheng Yan, Jeffrey Zimmerman, Mark D Boyer, Ryan Coffee, Azarakhsh Jalalvand, Egemen Kolemen, Finn H O'Shea The 2D Beam Emission Spectroscopy (BES) system at DIII-D can measure the localized pedestal dynamics of edge-localized mode (ELM) events and the edge turbulence dynamics associated with confinement regimes (L-mode, H-mode, QH-mode, and wide pedestal QH-mode). Here, we report on machine learning (ML) models for the real-time prediction of ELM onset and the real-time classification of the confinement regime using the 2D BES real-time data stream. The models will be deployed on a high-throughput FPGA accelerator for integration in the real-time plasma control system (PCS). To facilitate the avoidance or mitigation of impending ELM events by the real-time PCS, the BES ML models will generate a real-time output signal that corresponds to ELM onset likelihood. Similarly, to facilitate the access and sustainment of enhanced confinement regimes, the BES ML models will generate real-time output signals that correspond to confinement regime indicators. In addition, we report on a flexible feature space to support multiple simultaneous real-time tasks such as ELM onset prediction, confinement mode classification, and disruption prediction. Finally, we explore the feasibility to monitor in real-time the radial electric field (Er) shear and turbulent Reynolds stress in the pedestal. |
|
UP11.00086: Investigation of pedestal parameters and divertor heat fluxes in small ELM regimes on DIII-D Peter J Traverso, Matthias Knolker, Tom Osborne, Charles J Lasnier, Huiqian Wang, Anthony Leonard, Max Austin Small ELM regimes offer a potential solution for core-edge integration as a means to avoid high transient heat loads from type-I ELMs, without large reduction in plasma performance and stored energy. An important physics question to answer remains, how these currently observed small ELM regimes scale to a future fusion reactor. An investigation into the divertor heat flux and its dependencies on pedestal parameters has been performed on DIII-D. DIII-D's flexible plasma-shaping and pressure control provide the capability to study a wide-range of naturally occurring small ELM regimes including high beta poloidal, type-II/grassy, and ELMs in negative triangularity H-modes. Using high-time resolution infrared thermography, the parallel heat flux and total heat loads to the divertor are determined and compared to the observed losses in stored energy. Additionally, the pedestal parameters are obtained from the self-consistent kinetic equilibrium reconstructions using the profile measurements conditionally averaged over the ELM cycle. The pedestal parameters are presented as a function of normalized ELM energy loss across the various small ELM regimes and compared to the type-I ELM energy density scalings. |
|
UP11.00087: 2D characterization and boundary model validation of radiative divertor regimes with impurity seeding in the DIII-D divertor Filippo Scotti, Adam McLean, Anthony Leonard, Steven L Allen, Max E Fenstermacher, Mathias Groth, Robert S Wilcox, Colin Chrystal, Charles J Lasnier, Menglong Zhao Radiative divertor regimes are characterized and modeled in DIII-D H-mode discharges via measurement of divertor radiated power constituents and concentrations of intrinsic and seeded impurities in the divertor and confined plasma. In lower single null H-mode discharges (PNBI=3-10 MW, Ip=1.3 MA), carbon concentrations fC in the outer divertor were reduced with density in attached conditions (from ~5 to 2%). In fully detached condition, fC at the radiation front was further reduced to below 1%. In nitrogen-seeded radiative divertors, no reduction in divertor fC was observed, with the reduced carbon contribution to radiation driven by a drop in ne and the total Prad sustained by a higher total impurity concentration fZ=fC+fN. In fully detached conditions, fZ scaled with SOL power and inversely with ne at the radiation front. Multi-fluid UEDGE simulations with inclusion of cross field drifts and charge state resolved C and N impurity species can match measured line-integrated emission and radiated power share while local emissivities and fZ are higher than those derived experimentally. Recent experiments extended seeded divertor characterization to plasma currents of 0.9-1.5 MA to explore dependence on SOL heat channel width and seeded impurity species N, and Ne. |
|
UP11.00088: Study on Divertor Detachment and H-mode Pedestal Characteristics in DIII-D with Upper Closed Divertor Huiqian Wang, Dan M Thomas, Anthony Leonard, Xinxing Ma, Houyang Y Guo, Auna L Moser, Jonathan G Watkins, Filippo Scotti, Charles J Lasnier, Max E Fenstermacher, Adam McLean, Morgan W Shafer, Brian A Grierson, Jun Ren, Tom Osborne, Richard J Groebner, Florian M. Laggner, Saskia Mordijck, Livia Casali Experiments performed in DIII-D demonstrate that higher plasma current and heating power combining with impurity seeding facilitate the achievement of divertor detachment with a higher pedestal pressure and higher plasma performance in the H-mode plasmas with a closed divertor. With 3x variation in heating power or 2x in plasmas current and with only D2 puffing, no significant difference in the separatrix density at detachment onset is found, which is inconsistent with theoretical predictions. Higher heating power requires higher N2 puffing rate to achieve the same degree of detachment, while higher N2 puffing leads to lower detachment onset separatrix density, both of which agree with 1-D detachment scaling theory. In contrast to the narrower and steeper pedestal in the open divertor approaching detachment, the pedestal density width in the closed divertor increases with separatrix density, while the peak gradient remains unchanged. At higher power the pedestal density gradient is much weaker, while the SOL density is significantly higher and wider. With different plasma current and heating power, the normalized pressure gradient remains identical. Hence, divertor detachment with a higher pedestal pressure and higher performance can be achieved with higher current and power. |
|
UP11.00089: Coupled core, edge pedestal and SOL modeling for DIII-D Kyungjin Kim, J.M. Park, John Canik, Morgan W Shafer, Robert S Wilcox, Jeremy D Lore, Philip B Snyder A theory-based integrated modeling of Core, Edge pedestal, and Scrape-Off-Layer (CESOL) has been tested against existing DIII-D discharges with various divertor closure geometries to study effects of divertor closure on detachment and core performance. Detached divertor operation is necessary to exhaust large particle and energy heat fluxes to the Plasma Facing Components (PFCs) for the future fusion reactors. Combining the detached divertor with the Advanced Tokamak (AT) core is a well-recognized challenge, where edge pedestal plays a crucial role in the tradeoff. In certain conditions and in line with what observed in other tokamaks worldwide, DIII-D experiments showed that higher plasma density required for detachment can degrade confinement in the core plasma due to the lower pedestal pressure and profile stiffness. CESOL can reproduce the experimental measured profiles reasonably well across the regions from the magnetic axis to the divertor by integrating three independent, compound IPS workflows of IPS-FASTRAN, IPS-EPED1, and IPS-C2. The response of the pedestal pressure to increasing density is reproduced by the EPED model and the core transport and confinement depending significantly on this pedestal condition are reproduced by the CESOL simulation. |
|
UP11.00090: Resonant magnetic perturbation (RMP) induced ELM suppression in the DIII-D SAS-VW tungsten slot divertor Tyler Abrams, Dmitry L Rudakov, Gregory Sinclair, David B Weisberg, Robert S Wilcox, Shawn A Zamperini, Alec Cacheris, Jeffrey L Herfindal, Alan W Hyatt, Matthias Knolker, Anthony Leonard, Seth H Messer, Tomas Odstrcil, Jun Ren, Dan M Thomas, Kathreen E Thome, Huiqian Wang Suppression of edge-localized modes (ELMs) was achieved for the first time in the DIII-D tungsten-coated slot divertor (SAS-VW). Robust ELM suppression was sustained for periods >1500 ms with application RMPs of toroidal mode number n=3 at an edge safety factor, q95, of 3.7-3.8 and an edge pedestal electron collisionality, ν*, of ~0.15. A gradual build-up of spectroscopically measured W core content, attributed partially to an increased W source from the divertor, occurred throughout this period. Intermittent periods of ELM suppression (100-150 ms) were also observed during application of n=2 RMPs at a q95 value of 4.0. Increased divertor electron temperatures during the ELM-suppressed phase likely causes the additional W sputtering, but 0.5-1 MW of electron cyclotron heating was applied near the magnetic axis (ρ~0.2-0.3) to inhibit W accumulation. Measurements of W levels deposited on collector probes in the far scrape-off-layer will also be presented. Demonstration of a scenario without damaging edge transients and power exhausted into a slot-like, tungsten divertor represents notable progress towards an integrated core-edge solution for future devices. |
|
UP11.00091: Study of tungsten transport and redeposition during the DIII-D Metal Rings Campaign using the impurity tracing code GITRm Zachary J Bergstrom, Aritra De, Mark S Shephard, Dhyanjyoti Nath, Onkar Sahni, Shawn A Zamperini, Jerome Guterl, Tyler Abrams Experiments have been conducted at DIII-D to understand W impurity transport using toroidally symmetric metal rings located in the lower divertor region of the tokamak. Experimental measurements of W gross erosion and redeposition in the outboard lower divertor and mid-plane collector probes indicate that the long-range transport of W impurities depends significantly on 3D effects induced by poloidal and radial E x B drifts [1]. Here we develop and apply the unstructured mesh-based, and accelerator/GPU-enabled, Global Impurity Tracing code, GITRm [2], to track particles through the entire DIII-D vessel, within the trace-impurity assumption. GITRm has been used to study the erosion, long-range transport, and redeposition of W in the lower divertor and mid-plane collector probes, and benchmarked to previous studies. Background plasmas were extended to the wall and have been previously used to match radial profiles of tungsten deposition with far-SOL collector probes. These benchmarked results demonstrate the utility of GITRm compared to other impurity tracing codes, and highlight the need for 3-dimensional modeling of impurity transport in the scrape-off-layer. |
|
UP11.00092: Characterizing the effect of various D2 pellets and gas insertion frequencies on W divertor erosion in DIII-D Alec Cacheris, Tyler Abrams, Daisuke Shiraki, Robert S Wilcox, David C Donovan Inter- and intra-ELM tungsten erosion during D2 pellet injection has been assessed from the DIII-D Metal Rings Campaign, where toroidally symmetric W-coated tiles were installed in the lower open divertor. Injecting D2 pellets triggers smaller, more frequent ELMs, while the addition of neutrals increases the ion flux to the divertor but decreases the average ion impact energy. Results show a 32% increase in the total gross intra-ELM W erosion rate with 20-40 Hz pellet injection frequencies relative to both the no-pellet case and to a nominal injection frequency of 60 Hz. An inverse correlation between inter-ELM density and W erosion during D2 pellet injection is also observed. Simulations predicted by the ‘free-streaming plus recycling model’ (FSRM) under and over-predict the average W erosion per ELM by approximately 25% when incorporating and excluding a C/W mixed material model, respectively. Experiments are planned to inject D2 pellets and puff D2 gas at the same rate into the W-coated Small Angle Slot (SAS) tightly baffled closed upper divertor to distinguish the effect that adding cold neutrals and triggering smaller, more frequent ELMs has on W erosion. This study presents the use of collector probes and ultraviolet (UV) spectroscopy to investigate net W erosion as well. |
|
UP11.00093: An update on atomic data for the low charge states of W for use in Plasma Facing Component erosion diagnostics Stuart D Loch, Andrew White, Connor P Ballance, Michael McCann, David A Ennis, Tomie Gonda, Curtis Johnson, Ulises Losada, Noah Kim A review is given of recent atomic calculations for tungsten erosion and redeposition diagnostics. This includes electron-impact excitation of W[1] and W+, and the results of new R-matrix calculations for W2+ for excitation and ionization. Spectral measurements close to plasma facing components are used to diagnose the gross and net erosion, requiring high quality atomic. The major uncertainty in the W charge states is the excited state ionization rate coefficients. This issue is explored via a comparison of existing W I S/XB measurements with a range of ionization datasets, allowing some bounds to be put on the ionization rate coefficients. Comparisons of W-I and W-II synthetic spectra with DIII-D spectral measurements were taken using a new high-resolution high-throughput UV spectrometer. In addition, given recent interest in tantalum as a plasma facing component [2], some initial calculations are shown for the ionization of neutral Ta. The results likely indicate that a large fraction of sputtered Ta is promptly redeposited. |
|
UP11.00094: Interpretive analysis of scrape-off layer carbon transport using DIVIMP and impurity collector probes on DIII-D Jeremy D Mateja, Jonah D Duran, Jacob H Nichols, Shawn A Zamperini, Ezekial A Unterberg, Dmitry L Rudakov, David C Donovan DIVIMP simulations based on measurements made using a stable isotopic mixing model (SIMM) were able to quantitively explain the deposition of 13C from isotopically enriched methane puffing and background sources on collector probes (CP) in the far scrape-off layer (SOL) of DIII-D. Impurity CPs at the outboard midplane and crown regions were installed to sample impurities in the far-SOL, with resulting 13C deposition patterns used to infer near-SOL impurity distributions through the use of the 3DLIM synthetic diagnostic toolset. Experimental measurements and DIVIMP modelling suggest that the OSP launch alone cannot fully explain CP deposition measurements. Measurements made using SIMM suggest at least 40% of 13C CP deposition is from a buildup of 13C on the plasma facing components. DIVIMP simulations of 13C sourcing from the walls and inner divertor must be included along with the OSP injection to create the near-SOL sourcing profiles consistent with CP 13C deposition patterns. These findings highlight how a buildup of impurities on plasma facing components can result in migration of the impurity source and impact SOL impurity distributions. |
|
UP11.00095: Effect of Main Ion Density on High-Z Impurity Transport in the Scrape-off Layer of DIII-D Using Collector Probes Seth H Messer, Jake H Nichols, Jonah D Duran, Shawn A Zamperini, Gregory Sinclair, David C Donovan, Tyler Abrams, Tomas Odstrcil, Ezekial A Unterberg, Dmitry L Rudakov, Peter C Stangeby, David Elder, Jun Ren, Jonathan G Watkins An interpretive modeling workflow is presented for assessing impurity leakage and scrape-off layer (SOL) transport of tungsten (W) sputtered from the DIII-D Small Angle Slot (SAS-VW) divertor for a range of main ion densities. SAS-VW is a tightly baffled, closed divertor with W-coated plasma-facing components that is intended to reduce impurity leakage while lowering the target density threshold required to induce detachment. Experiments have been designed to perform a series of L-mode discharges in the case where the B X ∇B drift direction is out of the divertor with increasing main ion density in order to approach and slightly exceed the detachment threshold at the target. Impurity collector probes at the outer midplane (OMP) and crown are used to assess the far-SOL impurity content with the aid of the 3DLIM interpretive model. The near-SOL impurity distribution is developed using DIVIMP, which is constrained using W source spectroscopy. The SOL impurity distribution simulations for SAS-VW will be compared to those from the 2016 DIII-D Metal Rings Campaign used to assess impurity leakage and transport from an open divertor, which suggested the existence of an impurity accumulation zone between the OMP and crown for the equivalent magnetic field direction. |
|
UP11.00096: Evaluation of advanced tungsten alloys under high particle flux and intense transients in the DIII-D tokamak Zana Popovic, Tyler Abrams, Stefan A Bringuier, Jonathan D Coburn, Jan W Coenen, Curtis A Johnson, Robert D Kolasinski, Andrey Litnovsky, Yiran Mao, Carlos Monton, Rudolf Neu, Lauren Nuckols, Johann Riesch, Dmitry L Rudakov, Alexis Terra, Dinh D Truong, Jonathan G Watkins, Marius Wirtz Experiments are planned to test several advanced tungsten alloys under reactor-relevant conditions using the Divertor Material Evaluation System (DiMES) in the DIII-D tokamak. These materials are promising candidates for plasma-facing components in future fusion devices in terms of reduced intrinsic brittleness, hydrogenic retention and surface degradation compared to ITER-grade tungsten (IGW). The effects of high heat and particle fluxes on DiMES samples of tungsten fiber reinforced tungsten (Wf/W) composites [1], micro-structured tungsten, recrystallized and dispersoid-strengthened tungsten alloys (W/ZrC dispersoids [2] and W/SiC [3]) are studied against the performance of IGW. A large disk of Wf/W composite will be exposed to repetitive thermal loading in a tokamak divertor for the first time to examine long range (~3.5 cm) crack formation and mechanical behavior of the material. The post-characterization of the material surfaces will focus on gross erosion, hydrogenic retention, and surface changes such as crack formation, recrystallization, chemical composition and surface bonding of redeposited material. |
Author not Attending |
UP11.00097: Improved atomic calculations of Si+ and W2+ for erosion experiments in DIII-D Andrew P White, Stuart D Loch, David A Ennis, Ulises Losada, Michael McCann, Connor P Ballance, Dmitry L Rudakov A new calculation of electron-impact data for Si+ using the R-matrix with pseudo-states (RMPS) method has yielded ionization and excitation cross sections for both ground and excited states. The ground state ionization cross section is compared to experimental measurements and is in good agreement; thus, we also expect the calculated excited state cross sections (for which no experimental measurements exist) to have high accuracy. The new calculation uses a basis set that is three times the size of previous R-matrix calculations, allowing cross sections to be extended to higher energies, and provides the first excited state ionization cross sections for Si+. The atomic data is used to generate S/XB coefficients, which can be combined with spectroscopic measurements to infer time-resolved erosion and re-deposition rates. A new ionization calculation for W2+, needed to determine W re-deposition rates, is currently underway using the RMPS method. The new Si+ and W ionization calculations will be benchmarked over a range of plasma conditions during upcoming experiments in DIII-D using the DiMES probe and new UV spectroscopy capabilities. |
|
UP11.00098: Pumping optimization for a very high triangularity divertor in DIII-D Robert S Wilcox, Morgan W Shafer, Christopher Murphy, Tom Osborne, Tyler Elsey, Max E Fenstermacher, Brian A Grierson, Christopher T Holcomb, Jeremy D Lore, Adam McLean, Jonathan H Yu Applying first-flight neutral modelling to a new high triangularity divertor configuration (δ=0.9) finds that by optimizing the pump duct and plenum design, ~90% of the current outer leg pumping efficiency is maintained. DIII-D is planning to remove its upper inner cryogenic pump in order to accommodate plasma shapes with increased triangularity and volume. In the first phase of the iterative divertor installations, core confinement and efficient particle removal will be prioritized over divertor dissipation. Removal of the inner pump and relocation of the outer divertor target inboard away from the remaining cryopump plenum necessarily results in a reduction in pumping efficiency. However, estimates with first-flight neutral modelling find that with proper design, the pumping efficiency reduction at the outer leg can be minimized to ~10%. The model balances fast atomic influx from the target into the pump with molecular flow escaping back out of the plenum. Baffling structures for the outer divertor leg are designed to capture magnetic flux equivalent to four times the predicted heat flux width, with flexibility to move the strike point to maximize pumping. |
|
UP11.00099: Helicon generated plasma fluctuations and low-frequency turbulence and flows in the DIII-D tokamak Satyajit Chowdhury, Neal A Crocker, William A Peebles, Lei Zeng, Bart v Compernolle, Michael W Brookman, Robert I Pinsker, Cornwall H Lau, Terry L Rhodes Localized internal DIII-D plasma measurements are presented from broadband plasma fluctuations around 476 MHz (driven by an external helicon wave antenna), turbulence, Alfvén eigenmodes (AE’s) and low harmonic ion cyclotron emission (ICE; f ~ 2fci, 3fci) from a unique E-band DBS system. The observation of broadband fluctuations around 476 MHz is conjectured to be due to interaction of the injected helicon with local plasma turbulence. These observations demonstrate the capabilities of a new system which extends application of DBS to a high-frequency spectral domain (using adjustable frequency down conversion of a selectable frequency range <~1GHz) while allowing simultaneous measurement of turbulence (f < 10 MHz) and poloidal turbulence flow velocity. The new system has good temporal resolution (sub-millisecond) and excellent wavenumber coverage (kθ ~ 1-20 cm-1 and kr ~ 20-30 cm-1) along with selectable O- or X-mode polarization launch. The DBS helicon measurements will be used to validate modeling tools (e.g., GENRAY and AORSA) that predict helicon wave propagation, absorption and current drive location for the newly installed helicon current drive system on DIII-D. |
|
UP11.00100: Progress in Integration of Critical Gradient Fast Ion Transport Modeling Cami S Collins, Eric M Bass, Kyungjin Kim, Jin Myung Park, Brian Victor A major challenge for the core plasma of a sustained, high power density advanced tokamak reactor is the self-consistent ability to reach both high self-generated "bootstrap" current (to reduce auxiliary or inductive current drive needs) and high pressure (to produce enough fusion power). In past DIII-D 'high qmin' experiments, Alfvén Eigenmode (AE) induced fast-ion transport has limited performance. In this work, we build upon recent success with using the TGLF-EP+Alpha fast-ion transport model to calculate AE-induced changes to neutral beam power fluxes, leading to more accurate TGYRO/TGLF thermal profile predictions. The TGLF-EP+Alpha model is implemented in time-dependent modeling workflows to better predict electron, ion temperature profiles and current evolution. The model is applied to high qmin scenario experiment planning to determine the effects of increased density and non-neutral beam heating and current drive, such as DIII-D's new microwave and RF sources. This approach is expected to reduce fast-ion stored energy fraction and reduce AE instability in order to move towards more classical fast-ion transport conditions to reach high performance and high bootstrap fraction. |
|
UP11.00101: Investigations of time-resolved tungsten erosion and re-deposition using UV spectroscopy Ulises Losada, David A Ennis, Stuart D Loch, Curtis Johnson, Tyler Abrams, Douglas Taussig, Adam McLean, Dmitry L Rudakov A new high-resolution, high-throughput spectroscopic system optimized for UV wavelengths has been installed on the DIII-D tokamak for tungsten (W) erosion and re-deposition studies. It is composed of a CCD camera with high sensitivity in the UV range and a spectrometer with a spectral resolution of 0.16 Å around 250 nm. The spectrometer allows simultaneous observation of multiple emission lines from different lower W charge states within the UV wavelength range, required for W re-deposition measurements. Preliminary observations have been made in DIII-D plasmas. The total number of W atoms eroded from a surface (gross-erosion) can be determined from spectroscopy of neutral W emission using the S/XB method. The fraction of re-deposited W requires observing emission from higher charge states. Thus, at least W I and W II emission are needed to estimate W net erosion rates. Measurements of multiple spectral lines can reduce uncertainties and quantify the effect of metastable levels on the radiated spectrum. Spectroscopic measurements of time resolved W erosion and re-deposition rates are benchmarked by cumulative gross and net erosion from a DiMES probe. Further, experiments to quantify tungsten erosion and re-deposition rates during intra- and inter-ELM periods will be presented. |
|
UP11.00102: Differential Rotation Control for the DIII-D Tokamak via Model-Based Reinforcement Learning Ian Char, Joe Abbate, Viraj Mehta, Youngseog Chung, Rory Conlin, Keith Erickson, Mark D Boyer, Nathan J Richner, Laszlo Bardoczi, Nikolas C Logan, Jayson L Barr, Egemen Kolemen, Jeff Schneider Differential Rotation Control for the DIII-D Tokamak via Model-Based Reinforcement Learning |
|
UP11.00103: FUND: RECONNECTION, TURBULENCE
|
|
UP11.00104: Time and Space Resolved Optical Measurements of Reconnection in PHASMA Tom Rood, Peiyun Shi, Gabriela Himmele, Earl Scime In previous studies, the complex dynamical behavior of kinking 3D flux |
|
UP11.00105: Image-Based Turbulence Measurements in the PHAse Space MApping (PHASMA) Experiment Earl Scime, Chloelle M Fitz, Gustavo Bartolo, Matthew J Lazo The PHAse Space MApping (PHASMA) experiment employs non-perturbative, optical diagnostics for ion velocity distribution, electron velocity distribution, magnetic field, and turbulence measurements. Here we review the design and implementation of an imaging system optimized for measurements of plasma turbulence. A Photron NOVA S9 camera provides measurements of spontaneously plasma emission at acquisition rates up to 900,000 frames per second. We describe the optical configuration used to acquire the images and the image analysis routines used to extract high contrast images that emphasize large mode number spatial structures (small scale) in the helicon source region of PHASMA. The high-contrast images are then spatially Fourier analyzed to determine the azimuthal and radial mode structure of the plasma when viewed along the background magnetic field. We report on the structure of high order azimuthal modes as a function of radial location in the plasma and as a function of background magnetic field strength. We also report on application of the same methods to reconnecting flux rope plasmas. |
|
UP11.00106: Evolution of two flux ropes during magnetic reconnection in PHASMA Sonu Yadav, Peiyun Shi, Prabhakar Shrivastav, Regis John, Earl Scime Magnetic reconnection converts magnetic energy into plasma kinetic and thermal energy through change of magnetic topology. PHASMA (PHAse Space MApping) is a linear plasma facility capable of investigating magnetic reconnection phenomena in the laboratory through the merger of parallel flux ropes created with pulsed plasma guns. As the system of two flux ropes evolves, push and pull phases of magnetic reconnection are observed. An array of nine triple Langmuir probes (TLP) is used to measure the temporal evolution of flux ropes. The TLP array enables two dimensional (2D) measurement of plasma density and electron temperature in the reconnection region. The focus of the work here is to understand the nature of measured electric field topology and fluctuations during reconnection events. A linear magnetic probe array is used to map the 2D magnetic topology of reconnecting field lines. Based on the present observations, the dissipation mechanisms and reconnection rate will be discussed. |
|
UP11.00107: Designing an Energy Analyzer for the PHAse Space MApping (PHASMA) Experiment Ripudaman S Nirwan, Earl Scime The PHAse Space MApping experiment is designed to investigate distribution functions in magnetic reconnection events arising from the merger of two flux ropes generated by two pulsed plasma guns. PHASMA is also employed for helicon plasma studies which require measurements of particle velocity and energy distribution functions. To that end, a compact retarding field energy analyzer (RFEA) is constructed with four wire-mesh grids of Debye-scale resolution (0.125mm per grid hole) to measure electron energy distribution functions. Electric potential gradients within the RFEA are set to reject ion collection and minimize secondary electron generation (via photoelectric and electron impact effects) with the use of a suppressor grid. All currents are collected with a circuit designed to minimize perturbations to the energies of incoming particles while providing fast amplification for non-pulsed experiments where the discriminator potential can be swept with a programmable power supply. Here we describe the development of the diagnostic along with the related electronics. |
|
UP11.00108: Detecting Energetic Electrons during Magnetic Reconnection in the PHAse Space MApping (PHASMA) Experiment Ripudaman S Nirwan, Earl Scime The Phase Space Mapping experiment is designed to investigate distribution functions in magnetic reconnection events arising from the merger of two flux ropes generated by two pulsed plasma guns. A compact retarding field energy analyzer (RFEA) is constructed with four wire-mesh grids of Debye-scale resolution (0.125mm per grid hole) to measure electron energy distribution functions perpendicular to the plane of reconnection. Electric potential gradients within the RFEA are set to reject ion collection and minimize secondary electron generation (via photoelectric and electron impact effects) with the use of a suppressor grid. Any long tails in the measured energy distributions are interpreted as being non-Maxwellian features. Here we describe the development of the diagnostic and first results from magnetic reconnection experiments. |
|
UP11.00109: Magnetic Nozzle Studies on the Bryn Mawr Experiment Joshua M Carlson, David A Schaffner, Carlos A Cartagena-Sanchez The Bryn Mawr Experiment (BMX) investigates the magnetic turbulence of toroidal plasma structures formed within a flux conserving cylindrical chamber. The BMX generates these compact tori via an internal coaxial plasma gun source. An internal coil creates a stuffing flux within the gun source, and two outer coils are implemented in a magnetic nozzle configuration. Modeling of the nozzle in COMSOL Multiphysics is presented, and the responses of the plasma structures’ bulk speed to parametric sweeps on BMX – energy injection, nozzle field strength, stuffing flux strength, and density – are presented and explored. |
|
UP11.00110: Turbulent plasma wind tunnel studies on the Bryn Mawr Experiment (BMX) David A Schaffner, Joshua M Carlson, Carlos A Cartagena-Sanchez An overview and recent progress of activities at the Bryn Mawr Plasma Laboratory (BMPL) is presented. The main experiment at the facility, the Bryn Mawr Experiment (BMX), consists of a 4mF pulse-forming network that generates ~180us of stationary broadband fluctuations of magnetic field and plasma using a magnetized coaxial plasma gun source. A measurement of a dissipation scale, the Taylor microscale, has recently been made with values found on the order of 10-20% of the chamber radius. Wind tunnel velocity parameter space has also been explored through variations of stuffing magnetic field strength of the plasma gun, voltage of the gun discharge, and most recently through an addition of a magnetic nozzle. Measurement of velocity using a two-point time delay correlation technique show that use of the nozzle can increase velocities from approximately 10% the local Alfven speed up to about 50% Alfven speed. Updates on spectral studies are also given. |
|
UP11.00111: Phase space approach to inhomogenous incompressible 2-D MHD turbulence Suying Jin, Ilya Y Dodin Magnetohydrodynamic (MHD) turbulence can be understood as an effective plasma of Alfven waves serving as quasi-particles called alfvenons. Then, coherent structures in this turbulence can be understood as mean fields through which the alfvenons interact. Their formation can be described by kinetic theory, but classical kinetic theory does not suffice. Instead, one must account for the fact that alfvenons have polarization (``spin''), and the alfvenon wavelengths are generally nonnegligible compared to the scales of coherent structures. This means that quantum-like kinetic theory is needed to describe MHD turbulence as alfvenon plasma. We report the corresponding (Wigner-Moyal) formalism and its application to calculating quasilinear modulational instabilities in two-dimensional MHD turbulence. Comparison of this theory with numerical simulations, both quasilinear and nonlinear, will also be presented. |
|
UP11.00112: The feasibility of viscosity-driven hot ion mode Tal Rubin, Elijah J Kolmes, Ian E Ochs, Mikhail Mlodik, Nathaniel Fisch A radial fuel ion current into the core of a cylindrical plasma, and a quick removal of ash ions, can set up plasma flows leading naturally to a “hot-ion mode” [1]. The heating is the result of the viscous dissipation of the ion fluid. Solutions to the flow profile are obtained using the MITNS code [2], and nontrivial limitations are found: The centrifugal force caused by the rotation empties out the density at the core. The quadratic dependence of the viscosity on the density makes it such that large angular velocity gradients are required in order to produce the viscous shear needed to balance the torque produced by the radial current and the magnetic field. The viscous heating itself, which increases the plasma temperature, further reduces the viscosity coefficient. These effects lead to a runaway behavior when the density at the center approaches 0. The “natural hot-ion mode” is limited at large magnetizations. At small magnetizations, the collisional energy transfer between species and the viscous heating are of similar magnitude. |
|
UP11.00113: Amplification of Turbulence by Multiple Planar Shocks Michael F Zhang, Seth Davidovits, Nathaniel Fisch We study the amplification of isotropic, incompressible turbulence through multiple planar shocks, using results from Linear Interaction Analysis (Ribner 1953). There are two limiting cases we explore. The first assumes shocks occur rapidly in time such that the turbulence does not evolve between shocks. Whereas the second case allows enough time for turbulence to isotropize between each shock. For the latter case, through a quasi-EOS, we show that the weak multi-shock limit is agnostic to the distinction between thermal and vortical turbulent pressures, like an isotropic volumetric compression. When turbulence does not return to isotropy between shocks, we find that amplification is sensitive to the shock ordering. We map how choices of shock strength can impact these amplification differences due to ordering, finding, for example, shock pairs which lead to identical mean post-shock fields (density, temperature, pressure) but maximally distinct turbulent amplification. |
|
UP11.00114: Momentum Transport and Blob Generation in the Large Plasma Device Thomas Look, Gurleen Bal, Stephen T Vincena, Troy Carter Intermittent turbulence and turbulent transport via blob-filaments are widely observed in the edges of magnetized plasma experiments and shear flow suppression of turbulent transport has previously been studied in the Large Plasma Device (LAPD) [1]. Recent simulations have explored how the parallel variation of flows can significantly contribute to the reduction of blob-filament radial velocity [2]. Recent LAPD experiments with the new LaB6 cathode produce plasmas with steep edge density gradients, reduced radially-propagating blob activity, and azimuthal rotation of the plasma column without the use of a limiter or biasing. We will present recent experiments exploring the interplay between plasma flows and currents with the momentum transport and generation of blobs in the LAPD. |
|
UP11.00115: Laboratory Study of Arched Plasma Eruptions in a Sheared Magnetic Field Kamil D Sklodowski, Shreekrishna Tripathi, Troy Carter Solar atmosphere is carpeted with arched magnetic structures that confine millions degree hot plasma and drive energetic eruptions. We present results from a laboratory plasma experiment on spatio-temporal evolution of an arched magnetized plasma (β ≈ 10-3, Lundquist number ≈ 104, plasma radius/ion gyroradius ≈ 20) in a sheared magnetic configuration. The arched plasma is produced using a hot-cathode lanthanum hexaboride (LaB6) source and it evolves in an ambient magnetized plasma produced by another LaB6 source [1]. The experiment is designed to model conditions relevant to the formation and destabilization of similar structures in the solar atmosphere. In this experiment, magnitude of a nearly horizontal overlying magnetic field was varied to study its role in producing a sheared magnetic configuration and destabilizing the arched plasma [2]. Under eruptive conditions, large-scale ejections appear resembling characteristics of solar jets produced from emerging magnetic flux in a large-scale coronal field [3]. Nature and evolution of eruptive structures were investigated in the experiment using three-dimensional measurements of relevant plasma parameters. |
|
UP11.00116: Stochastic heating and entropy cascade in a solvable model of collisionless plasma turbulence Michael L Nastac, Robert J Ewart, Wrick Sengupta, Alexander A Schekochihin, Michael Barnes, William D Dorland A (1+1)-D nearly collisionless plasma stirred by a stochastic external turbulent electric field, analogous to the Kraichnan model of passive advection, is considered. The mean effect on the particle distribution function is turbulent diffusion in velocity space—so-called stochastic heating. Associated with this heating is the generation of fine structure in the distribution function, which can be characterized by the collisionless (Casimir) invariant C2 = ∫ dx dv δf2—a proxy for minus the entropy of the perturbed distribution function. C2 is found to be transferred from large to small scales in position and velocity space via a phase-space `entropy' cascade driven by particle streaming and nonlinear field-particle interactions. The flux of C2 in wavenumber space is dominated by the ‘critical balance’ region in phase space where the linear and nonlinear time scales are comparable. Integrating over velocity wavenumbers, the k-space flux of C2 is constant down until a ‘Kolmogorov’ length scale that tends to zero as the collision frequency does. These results reveal that stochastic heating is in fact an entropy-cascade process and that phase mixing can be suppressed in the inertial range of a turbulent collisionless plasma while simultaneously being an effective means of dissipation. |
|
UP11.00117: Intermittency and the Fourth Order Cumulant of Toroidal Ion Temperature Gradient Driven Turbulence Augustus Azelis, Paul W Terry Intermittency in the turbulent fluctuations associated with the Dimits regime of toroidal ion temperature gradient (ITG) driven turbulence is investigated via weak turbulence closure. The fourth order cumulant is calculated perturbatively and employed as a primitive metric to quantify both the strength of a system's departure from Gaussianity as well as the timescales associated with this behavior. Intermittency is of interest as it is observed that the turbulent fluctuation probability distribution features a significant non-Gaussian tail in the Dimits regime, where there exists a discrepancy between instability growth rate and heat flux both as a function of temperature gradient. In a phenomenon known as the Dimits shift, the heat flux is considerably suppressed at and above the linear critical gradient until sufficiently large values of temperature gradient are imposed upon the system. This increase in the critical gradient above the threshold predicted by linear theory has recently been attributed to resonance in mode coupling, but the intermittent behavior of fluctuations was not included in that analysis. The weak turbulence closure calculates fourth order cumulants which express non-Gaussian behavior due to the presence of correlation and resonant interactions amongst tetrads of fluctuations. The intermittency arising from consideration of said cumulants is evaluated numerically and compared with preexisting theory and simulation to assess the approximate influence of non-Gaussian statistics on features of toroidal ITG driven turbulence. |
|
UP11.00118: The effect of compressibility on magnetic island dynamics Maria Stefany Cancino, François L Waelbroeck, Julio J Martinell Magnetic islands are commonly generated in fusion plasmas with toroidal geometry. Their study is important because they affect the global dynamics of the plasma but there are several aspects that are still poorly understood, in particular the role of compressibility. The present work develops the analytical and numerical solution of the nonlinear tearing mode for magnetic islands with a width less than the sonic Larmor radius, w « ρs, taking into account the compressibility of the plasma. A cold ion fluid model is used in the semi-collisional regime for the slab geometry approximation. The differences in plasma profiles between the incompressible and compressible cases are shown, as well as the corresponding effect on the natural velocity of the islands through the plasma. The effect that plasma compressibility has on the evolution of the width of the magnetic islands and, consequently, on the stability of the tearing mode is studied. |
|
UP11.00119: Generation of a strong parallel electric field and embedded electron jet in the exhaust of moderate guide field reconnection Blake A Wetherton, Jan Egedal, Ari Le, William S Daughton MMS observed an extended current layer concurrent with a strong parallel electric field. The current |
|
UP11.00120: Multiscale Magnetic Reconnection, Phase Transition, Particle Heating and Acceleration, and the FLARE Project Hantao Ji, Andrew D Alt, Kendra A Bergstedt, Abraham Chien, Eric G Blackman, Sayak Bose, William S Daughton, William R Fox, Lan Gao, Aaron Goodman, Ari Le, Stephen P Majeski, Adam J Stanier, Masaaki Yamada, Jongsoo Yoo, Shu Zhang Magnetic reconnection is widely recognized as a fundamental plasma process underlying many explosive and energetic phenomena observed throughout the Universe and laboratory fusion plasmas (Ji & Daughton 2011, Ji+ 2022). Here we summarize our recent progress. A thermodynamic phase transition from collisional Sweet-Parker reconnection to collisionless Hall reconnection has been identified (Jara-Almonte & Ji 2021). The phase transition occurs when the reconnection electric field reaches Dreicer electric field reduced by the square root of the ion-to-electron mass ratio including pair plasmas. Statistical properties of multiscale magnetotail reconnection have been studied by using MMS data and machine learning techniques are being developed (Bergstedt+2020, this meeting). Guide field effects on MHD plasmoids distributions and particle acceleration by large plasmoids are studied (Majeski+2021, this meeting). In MRX, ion heating and flow generation have been measured during guide field reconnection (Goodman+2021,2022). Electron acceleration, ion and electron acoustic bursts during low-beta reconnection by laser-powered capacitor coils have been detected (Chien+2022, Zhang+2022). The upcoming FLARE (Ji+2018) will study multiscale physics, reconnection onset and particle acceleration. |
|
UP11.00121: Positive potential-side global ion heating during high guide field reconnection in the TS-6 merging spherical tokamak formation experiment Hiroshi Tanabe, Haruaki Tanaka, Yunhan Cai, Ryo Someya, Chio Z Cheng, Michiaki Inomoto, Yasushi Ono Here we report our new finding of positive potential-side global ion heating during high guide field reconnection in the TS-6 merging spherical tokamak formation experiment. Particle accleration and heating during guide field reconnection is one of the major topic of reconnection studies and the contribution of the quadrapole potential structure and inplane electric field are investigated in many laboratory experiments and numerical simulations. Previously most of studies reported that ions are heated at the lower potential-side of the quadrapole potential region by in-plane electric field Ep and it was proposed that the increment of ion temperature Ti is proportional to the potential drop: △Ti ∝ △Φ. However, our full-2D global ion Doppler tomography imaging of Ti profile revealed that Ti is actually higher in the positive potential side and the structure gets flipped when toroidal field (Bt) polarity is changed. In the sufficiently high guide field condition (Bt ~ 5Bp), inductive/reconnection electric field Et made a major contribution to ion acceleration as well as electron ones. Around the quadrapole potential region, ions just pass through by E×B drift and △Φ ~ 0 on the orbit. Then, the major contribution comes from parallel electric field E// = E·B/|B|. The combination of Et and Bt forms large negative parallel electric field and ions are accelerated to the positive potential-side. After the end of merging, in-plane heat transport process equilibrated the characteristic structure and finally globally hollow ion temperature profile is formed. It is sustained by better plasma confinement by guide field (κi///κi⊥ ~ 2(ωciτii)2 >> 1) in the quasi-steady phase after merging and successfully bridging the double-peak heating characteristics reported in many merging experiments such as MAST and TS-3. |
|
UP11.00122: Influence of In-plane Electrostatic Potential on the Ion Heating Characteristic during ST Merging Haruaki Tanaka, Shinjiro Takeda, Ryo Someya, Hiroshi Tanabe, Tara Ahmadi, Yunhan Cai, Yasushi Ono The characteristic quadrupole electrostatic potential structure has been confirmed in the guide field magnetic reconnection during ST merging experiment in TS-6. The key question is how this electrostatic potential structure is formed and to what extent potential well accelerates particles. During ST merging startup, the reconnection electric field is aligned with the magnetic field, significantly accelerating electrons which are detected as energetic electrons around X-point and in the inboard-side downstream by a soft x-ray fast imaging system. The electrostatic potential profile develops synchronized with the increase of reconnection electric field and soft x-ray, indicating that the accelerated electrons have a crucial role in potential structure formation. Furthermore, we have first demonstrated that the amplitude of potential linearly increases both with reconnecting magnetic field Brec and guide field Bg . We will discuss this electrostatic potential dependence on magnetic field and derive the ion outflow, which mainly consists of E×B flow where in-plane electrostatic field is stronger than reconnection electric field, scales mainly with reconnecting magnetic field. This result ultimately explains the ion heating scaling during ST merging startup, that is, △Ti ∝ B2rec. |
|
UP11.00123: Experimental Research of Reconnection Heating / Acceleration by Ion Flow and Temperature Profile Measurement Probe Array Ryo Someya, Itsuki Nakau, Yunhan Cai, Hiroshi Tanabe, Yasushi Ono We developed a 1D spatial profile measurement of ion flow and temperature by a parallel glass-tube-pair type Doppler spectroscopy probe array. This diagnostic can measure ion flow and temperature at 7 points on a straight line at 2.5 cm intervals by a single shot. Using the system, we measured the time evolution of the radial profile of ion flow and temperature around the diffusion region of two merging tokamak plasmas. We found that the maximum heating point where the local temperature increment ≃ 40 eV agrees with the point where the outflow(the maximum local outflow speed ≃ 8 km/s) damps to < 1 km/s. We observed for the first time that the direction of ion outflow rotated 90 degrees to that of the quadrupole poloidal electric field by the Hall effect after the completion of guide field reconnection. We are measuring the spatial profile of ion density and poloidal field to examine the Rankine-Hugoniot relations for fast shock. We are now upgrading 1D spatial profile measurement to 2D spatial profile measurement by increasing the number of parallel glass tube pairs for the purpose of validating the ion acceleration by the quadrupole poloidal electric field. |
|
UP11.00124: Electron-only reconnection in 3D kinetic-scale plasma turbulence in a low electron beta environment Cristian S Vega, Vadim S Roytershteyn, Gian Luca Delzanno, Stanislav A Boldyrev Magnetic reconnection has long been considered as one of the fundamental mechanisms of plasma heating and particle acceleration in astrophysical and space plasmas. Recent observations by the MMS mission have hinted at the existence of reconnection events with no ion coupling [1]. In our previous numerical study of 2.5D kinetic scale turbulence, these electron-only reconnection events were seen to be produced naturally in the turbulent environment [2]. In this presentation, we discuss the results of our more recent 3D numerical simulation, run with spectral code SPS. We identify and characterize potential quasi-2D electron-only reconnection sites looking for signatures like electron outflows and particle heating. |
|
UP11.00125: Using Magnetohydrodynamics With Adaptively Embedded Particle-In-Cell (MHD-AEPIC) to Simulate Magnetic Island Coalescence Dion Li, Chuanfei Dong, Yuxi Chen, Liang Wang Simulating collisionless magnetic reconnection usually requires kinetic models that are computationally expensive in comparison with fluid approaches. In the present work, we study the magnetic island coalescence problem using the magnetohydrodynamics with adaptively embedded particle-in-cell (MHD-AEPIC) model, an innovative approach that embeds one or more adaptive particle-in-cell regions into a global MHD simulation domain such that the kinetic treatment is applied only in regions where kinetic physics is significant. We provide comparisons of simulation results among three different approaches: MHD with adaptively embedded PIC regions, MHD with statically embedded PIC regions, and a full PIC simulation. We analyze reconnection rates, magnetic island O-point separations, and the structures of the out-of-plane current densities, ion pressure tensor elements, and ion agyrotropy, yielding excellent agreement among all three approaches. |
|
UP11.00126: Studying reconnection heating in the solar corona via gyrokinetic simulations Shu-Wei Tsao, M.J. Pueschel, Anna Tenerani, David R Hatch Reconnection turbulence, which here refers to turbulence generated by reconnecting current sheets, is a promising candidate for explaining the solar corona heating rate. Commonly, gyrokinetic simulations employ artificial mass ratio and β values to reduce numerical expense. Here, nonlinear 2D corona simulations are performed with the gyrokinetic code GENE at realistic β and hydrogen mass ratio to verify that the heating rate of the reconnection turbulence matches the observed solar corona heating rate, confirming extrapolations made in earlier studies. [Pueschel et al., ApJS 213, 30 (2014)] |
|
UP11.00127: Laboratory Study of Extended Electron Jets during Reconnection on TREX Cameron Kuchta, Jan Egedal, Joseph R Olson, Alexander Millet-Ayala, Paul Gradney, Rene Flores Garcia, Samuel Greess, Adam J Stanier The Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) studies collisionless magnetic reconnection. Pairing experimental results with results from Vector Particle In Cell (VPIC) simulations we identify electron jets that extend into the outflow in highly collisionless regimes. We examine the regimes in which these electron jets show up and measure the anisotropic pressure effects using a newly development electron pressure anisotropy probe. Using a newly developed drive cylinder that drastically increases the Lundquist Number, we explore new physics that may be present in the collisionless regime. |
|
UP11.00128: Reconnection Drive Cylinder for the Terrestrial Reconnection EXperiment Paul Gradney The Terrestrial Reconnection EXperiment (TREX) at Wisconsin Plasma Physics Laboratory (WiPPL) [1] aims to explore the kinetic regime by driving an induced electric field through a cylindrical coil geometry. The enhanced drive will reduce the effective collisionality of the experiment, such that electron pressure anisotropy can develop unimpeded by Coulomb collisions providing a more accurate model of Earth’s magnetospheric plasma dynamics. The drive cylinder is composed of aluminum and Teflon, has a radius of 60cm, and is surrounded by 13 copper coils. Compared to TREX’s previous four drive coil configuration [2], we estimate that the drive cylinder reconnection current layer will be up to a factor of 2 longer, achieving an absolute maximum system size of L/di = 20, increase the absolute reconnection rate to Erec ≈ 1kV/m, and reaching a maximum Lundquist number of S = 105, which will be the largest Lundquist number ever reached in a dedicated reconnection experiment. These effects will allow us to reliably access the regime of kinetic reconnection where electron pressure anisotropy is known to strongly impact the reconnection dynamics. |
|
UP11.00129: Role of 3D plasmoid dynamics on the transition from collisional to kinetic reconnection Adam J Stanier, William S Daughton, Ari Le, Hantao Ji, Jonathan M Jara-Almonte Laboratory and solar reconnection events are often simulated with a resistive-MHD collisional fluid model, or a collisionless particle in cell (PIC) model. However, for these applications, the current sheet collisionality can vary with time and lead to a transition between these two regimes. Here we study this transition process by 3D PIC simulations with Fokker-Planck collision operator in both Cartesian slab geometry [1] and a geometry relevant to the upcoming FLARE experiment [2]. This approach is able to self-consistently model the plasma heating and transport during this transition from collisional to kinetic reconnection. |
|
UP11.00130: Unified theory of Alfven resonances and forced reconnection Daniel E Urbanski, Jau-Uei Chen, Anna Tenerani, Tan Bui-Thanh, Francois Waelbroeck Most of the plasmas encountered in space and laboratory are weakly collisional or collisonless, in the sense that diffusion time scales at macroscopic spatial scales are too long to explain the fast energy release as well as heating observed during explosive events, such as flares, geomagnetic storms and disruptions in magnetic confinement devices. For this reason, understanding the dynamical formation of quasi-singular boundary layers is fundamental to understanding explosive energy release as well as plasma heating and control. Alfven wave resonance and forced reconnection are two processes by which such boundary layers can be generated in inhomogeneous plasmas. In this project, we investigate these two processes in a unified theoretical and numerical framework. In particular, we investigate the transition from the Alfven wave resonance to forced reconnection by introducing a forcing that is parameterized through a main driving frequency, by considering both a monochromatic and a non-monochromatic spectrum. We determine the properties of the boundary layer and of the timescale required to form such a layer as a function of the forcing spectrum and of the Lundquist number. In future work we will extend our results to the fully nonlinear regime to investigate the stability of these boundary layers. |
|
UP11.00131: Experimental Studies of Magnetic Reconnection in 3D Geometries Including Magnetic Nulls. Xinyu Yu, Jan Egedal Magnetic reconnection is typically studied in nominal 2D magnetic geometries where the magnetic field remains finite through the domain. However, in natural occurring reconnection the magnetic field geometry can be much more complex including 3D magnetic structures known as magnetic nulls. To elucidate the importance of magnetic nulls for magnetic reconnection we are proposing a new experimental setup in the Big Red Ball (BRB) at the Wisconsin Plasma Physics Laboratory. Plasma guns will be applied to create a back-ground plasma in a uniform magnetic field, where biasing can be applied to drive field aligned currents. A single magnetic coil will encircle the plasma column creating a physical-dipole field opposite to the back-ground field. As the coil-current is increased two double null are created and the 3D magnetic geometry is expected to interrupt the plasma column in a 3D magnetic reconnection burst. At oblique angles of the coil the complexity of the magnetic field geometry increases dramatically, and will be characterized by the arrays of magnetic diagnostics available on (BRB). |
|
UP11.00132: Overview of Wisconsin Plasma Physics Laboratory research Karsten J McCollam, Jan Egedal, Noah C Hurst, Joseph R Olson, John S Sarff, Cary B Forest The Wisconsin Plasma Physics Laboratory (WiPPL) is a multi-device collaborative research facility supporting experiments in basic, astrophysical, and fusion plasma science. WiPPL is a founding member of the MagNetUS experimental plasma network, and outside collaborator run time is allocated via MagNetUS proposal review. We present an overview of WiPPL capabilities, recent and ongoing projects, and key WiPPL-led results. In the BRB device, collisionless reconnection is examined with unprecedented spatiotemporal resolution, and a drive system upgrade is expected to reach well into the kinetic regime. New capabilities will include a planar spheromak injector to mimic a galactic jet and a rotating magnetic dipole to emulate a pulsar wind. In the MST device, tokamak plasmas are produced for a variety of studies: the structure and dynamics of runaway electron generation in disruptions, whistler-range wave correlation with runaway electrons, and the self-organization of low-q tokamaks. RFP plasmas in MST are used for studies of plasma self-organization, with programmable power supplies expanding the Lundquist-number overlap with nonlinear MHD simulations. MST's high-temperature plasmas and high availability make it a useful source for the development of advanced x-ray diagnostics. |
|
UP11.00133: Filamentation Morphology in Capacitively Coupled Highly Magnetized Plasmas Stephen Williams, Saikat C Thakur, Mohamad Menati, Edward Thomas Due to the small charge-to-mass ratio of dust particles, it is often necessary to use large magnetic fields of B ≥ 1 T, in order to observe the influence of magnetic forces in laboratory dusty plasmas. However, when experiments are performed at high magnetic fields in capacitively coupled, radio frequency discharges used for these dusty plasma experiments, the plasma is often observed to form filamentary structures between the electrodes that are aligned to the external magnetic field which disrupt the uniformity of the plasma and adversely impact some of our dusty plasma experiments. Recent experiments performed in the Magnetized Dusty Plasma Experiment (MDPX) device seek to identify and characterize these filamentary structures. This presentation discusses the morphology of several distinct filamentary modes that are formed in low temperature plasmas with different neutral gases. There is strong evidence that each spatial mode has a threshold condition that is dependent on the ion Hall parameter – which is a function of magnetic field, neutral pressure, and ion mass. The criteria for the formation of the filaments are shown to be consistent with predictions of recent numerical simulations. |
|
UP11.00134: Study of the collisional effects and increasing transverse magnetic field on the expansion of a laser produced plasma. Zachary K White, Gabe Xu, Saikat Chakraborty Thakur, Edward Thomas The interactions of laser produced plasmas (LPP) with externally applied magnetic fields provides insights into many physical phenomena such as kinetic energy to thermal energy conversion, instabilities on the surface of highly transient plasmas, and particle acceleration and deceleration in magnetic fields. Our study focused on the effects of increasing magnetic fields and varying ambient pressure on the expansion of the LPP. The experiment was conducted using the Magnetic Dusty Plasma Experiment (MDPX) highly uniform superconducting magnet at Auburn University. The LPP was produced by a 10 GW/cm2 laser beam produced by a Nd:Yag pulsed laser operating at the second harmonic (532 nm) and 280 mJ. A carbon rod was used as the target and the plasma plume expanded transverse to the applied magnetic fields. Time evolution images of the plasma expansion were obtained using an iStar ICCD camera. The magnetic field and pressure were varied incrementally from 0.125 to 3 T and 50 mTorr to 300 mTorr, respectively. The main findings were that the critical radius of the plume perpendicular to the applied field was independent of the magnetic field above 1 T, and the primary pressure pushing the plasma past the applied field was kinetic. |
|
UP11.00135: Measuring the evolution of ion canonical vorticity during RFP relaxation with stencils of polyhedral Mach probe clusters Jason Sears, Jens Von Der Linden, Karsten J McCollam, Abdulgader F Almagri, Allyson M Sellner, Mikhail Reyfman, John S Sarff, Haruhiko Himura, Setthivoine You Conversions between twisted magnetic flux tubes and ion flow vorticity flux tubes provide an alternative viewpoint of self-organized processes in plasmas. In the MST RFP, tearing instabilities drive a reorganization of current and momentum. Recent two-fluid simulations indicate that there can be a change in cross helicity, interlinking of magnetic and flow vorticity flux tubes, during sawtooth events. We are developing a canonical vorticity probe to measure the magnetic and ion flow vorticity fluxes simultaneously during sawtooth relaxation in MST. The probe will consist of polyhedral clusters of B-dot and Mach probes. The 3D Mach vector is determined from the geometric addition of the logarithms of ion saturation currents collected at the vertices of a polyhedron, not necessarily 180 degrees apart. The clusters will be arranged in a finite difference stencil so that the curl of these vectors can be determined. Two prototypes of a single cluster have been constructed [1] and fielded on the MST to examine self-organization and sawtooth relaxation. This work will help to generalize our understanding of plasma relaxation to a canonical-helicity-constrained relaxation explaining multi-scale dynamics. |
|
UP11.00136: Drift-Rossby waves past the breaking point in zonally-dominated turbulence Norman M Cao The spontaneous emergence of structure is a ubiquitous process observed in fluid and plasma turbulence. These structures typically manifest as flows which remain coherent over a range of spatial and temporal scales, which resist statistically homogeneous description. This work considers the stochastically forced barotropic β-plane quasigeostrophic equations, a prototypical two-dimensional model for turbulent flows in Jovian atmospheres and a special case of the Charney-Hasegawa-Mima equations. First, analysis of direct numerical simulations demonstrate that a significant fraction of the flow energy is organized into coherent large-scale Rossby wave eigenmodes, comparable to the total energy in the zonal flows. A characterization is given for Rossby wave eigenmodes as nearly-integrable perturbations to Lagrangian flow trajectories, linking finite-dimensional deterministic Hamiltonian chaos in the plane to a laminar-to-turbulent flow transition. Poincaré section analysis of the wave-induced Lagrangian flow demonstrates that the observed large-scale Rossby waves combined with zonal flows induce flows with localized chaotic regions bounded by invariant tori, manifesting as Rossby wave breaking in the absence of critical layers. The resulting inhomogeneous mixing suggests a paradigm for the self-organization of large-scale flows beyond a zonally-averaged sense that accounts for the resilience of the observed Rossby waves. Possible extensions of the method to other plasma systems are also given. |
|
UP11.00137: Three-dimensional Particle-In-Cell Simulations to Study the Stability of Two-Dimensional Bernstein-Greene-Kruskal Modes Matthew Franciscovich, James McClung, Kai Germaschewski, Chung-Sang Ng We will report three-dimensional (3D) Particle-In-Cell (PIC) simulations to study the stability of two-dimensional (2D) Bernstein-Greene-Kruskal (BGK) modes [Ng, Phys. Plasmas, 27, 022301 (2020)] in a magnetized plasma with a finite background uniform magnetic field. The simulations were performed using the Plasma Simulation Code (PSC) [Germaschewski et al., J. Comp. Phys., 318, 305 (2016)]. These modes are exact nonlinear solutions of the steady-state Vlasov equation with an electric potential localized in both spatial dimensions perpendicular to the axial magnetic field that satisfies the Poisson equation self-consistently. These solutions have cylindrical symmetry and are invariant along the axial direction, with distribution functions depending on the particle energy, the axial component of the canonical angular momentum, and the axial component of the canonical momentum. We will present latest 3D simulations to compare with our previous 2D runs to show how the stability changes with dimensionality. |
|
UP11.00138: Three-Dimensional Bernstein-Greene-Kruskal Modes with Finite Field Magnitude Chung-Sang Ng Previously we presented analytic forms of three-dimensional (3D) Bernstein-Greene-Kruskal (BGK) modes in a magnetized plasma with a finite background uniform magnetic field. The existence of solutions was shown analytically and by numerical solutions in the limit of small field magnitude of the modes. We have now developed an iteration scheme that can solve for converged solutions with moderately large field magnitudes. These modes are exact nonlinear solutions of the steady-state Vlasov equation with an electric potential localized in all three spatial dimensions that satisfies the Poisson equation self-consistently, as well as a localized self-consistent magnetic field perturbation satisfying the Ampère Law. Dynamics of both ions and electrons are included in the formulation. These solutions have cylindrical symmetry with distribution functions of ion and electron depending on particle energy, and a disk species with distribution depending also on the axial component of the canonical angular momentum. Example solutions will be presented, showing that the magnetic field of the mode is strong enough to perturb the background magnetic field significantly. |
|
UP11.00139: Stability of Two-Dimensional Bernstein-Greene-Kruskal Modes: Latest Two-Dimensional Particle-In-Cell Simulations James McClung, Matthew Franciscovich, Kai Germaschewski, Chung-Sang Ng We will report latest two-dimensional (2D) Particle-In-Cell (PIC) simulations to study the stability of 2D Bernstein-Greene-Kruskal (BGK) modes [Ng, Phys. Plasmas, 27, 022301 (2020)] in a magnetized plasma with a finite background uniform magnetic field. The simulations were performed using the Plasma Simulation Code (PSC) [Germaschewski et al., J. Comp. Phys., 318, 305 (2016)]. These modes are exact nonlinear solutions of the steady-state Vlasov equation with an electric potential localized in both spatial dimensions perpendicular to the axial magnetic field that satisfies the Poisson equation self-consistently. These solutions have cylindrical symmetry and are invariant along the axial direction, with distribution functions depending on the particle energy, the axial component of the canonical angular momentum, and the axial component of the canonical momentum. Cases with different strength of the background magnetic field will be presented to show the changes in the stability. We will present simulations using higher resolutions to compare with our previous runs. We will also present simulations using ions of realistic mass ratio and with an initial Boltzmann distribution, to contrast with simulations using a background of uniform ion density. |
|
UP11.00140: Relaxation dynamics of plasma bubbles propagating into a background magnetized plasma Shakiba HajiSadeghi, Robert H Dwyer, Mark A Gilmore, Lucas G Webster The interaction of the hot dense magnetized plasma with background plasma is of great interest in space plasma physics, for example in the propagation of coronal mass ejections in background solar winds at solar scales, and in expansion of the radio jets/lobes into the extragalactic medium at astrophysical scales. To investigate the relaxation dynamics of such interactions a compact coaxial magnetized plasma gun is used to launch a hot dense plasma into a background low density plasma generated in a linear device. Bubble plasmas are formed by a coaxial plasma gun, and with the appropriate operating parameters these bubbles form with spheromak-like equilibrium. It is observed that when the bubble plasma is injected into the background magnetized plasma rather than a vacuum, the bubble is deformed asymmetrically due to the magnetic tension force instead of smoothly relaxing to the minimum energy state of a spheromak-like configuration. At one edge of the bubble the growth of Magneto-Raleigh Taylor instability is observed. In order to characterize the density, temperature, and magnetic field configuration of the plasma bubble relaxation we have used the triple Langmuir probe and B-dot magnetic probe array. A visible spectrometer and a fast-framing camera are used to observe the evolution dynamics of the plasma bubble into the background plasma. |
|
UP11.00141: Extended Magnetohydrodynamic simulations of the Plasma Bubble Expansion Experiment Lucas G Webster, Shakiba HajiSadeghi, Mark A Gilmore We study the dynamics of propagating and expanding plasma "jets" and "bubbles" into a lower density, weakly magnetized background plasma. To this end we use the extended magnetohydrodynamic (XMHD) simulation code PERSEUS, in which the Hall and electron inertial terms are included in the generalized Ohm's law (GOL). The simulations mimic the geometry and parameters of the Plasma Bubble Expansion Experiment (PBEX) at the University of New Mexico, and enable experiment-model comparisons in order to validate the numerical model and gain detailed understanding of the underlying physics. The results aid in determining possible conditions that could lead to shock formation and instabilities in future PBEX experiments, as well as in finding the validity regime of the ideal MHD model for the PBEX plasma and the relative importance the Hall term. |
|
UP11.00142: Relaxation to nonthermal equilibria in a Lynden-Bell plasma Robert J Ewart, Andrew Brown, Toby Adkins, Alexander A Schekochihin A plasma whose Coulomb-collision rate is very small may relax on a shorter time scale to non-Maxwellian quasi-equilibria, which, nevertheless, have a universal form, with dependence on initial conditions retained only via an infinite set of Casimir invariants enforcing phase-volume conservation. These are distributions derived by Lynden-Bell (1967) via a statistical-mechanical entropy-maximisation procedure, assuming perfect mixing of phase-space elements. A collision integral that reaches these steady states dynamically is derived and it is further shown that a large class of these distribution functions display power law tails with a power law index that depends on the Casimir invariants. Far from these equilibria, it is shown that the friction between species is anomalous and gives rise to strange relaxation effects in the presence of anisotropies. |
|
UP11.00143: The Efficiency of Nonthermal Particle Acceleration in Relativistic Magnetic Reconnection Omar J French, Fan Guo, Qile Zhang, Dmitri A Uzdensky One of the major questions under investigation in relativistic magnetic reconnection is the heating and acceleration of particles and the energy partition between them. Using fully-kinetic PIC simulations, we evaluate the contributions of three important particle injection mechanisms (parallel electric field, Fermi, and pickup processes) across a parameter scan of varying guide field strength and domain size. Our analysis is based on injection energies, which we systematically derive from a power-law spectrum fitting procedure. From this analysis, we find that for weak guide fields, Fermi reflections account for about half of the injected particles, while pickup acceleration and parallel electric fields are subdominant. For a strong guide field (bg~1), parallel electric fields inject most of the nonthermal particles. In terms of the acceleration efficiency, we find that for weak guide fields, injected particles comprise ~40% of all downstream particles and possess ~90% of the downstream particle energy. For a strong guide field, injected particles comprise ~15% of all downstream particles and possess ~60% of the downstream particle energy. These results highlight the crucial role of guide field strength in controlling the efficiency of particle acceleration from magnetic reconnection. We also show convergence of acceleration efficiency and related key parameters with increasing domain size, which will help explain the nonthermal acceleration and emissions in high-energy astrophysics. |
|
UP11.00144: Magnetized Target Fusion Using Mechanically-Driven Liquid Metal Liner Alexander D Mossman, Michel Laberge, Meritt Reynolds, Stephen J Howard, Colin P McNally, Leopoldo Carbajal, Ivan Khalzov, Aaron Froese, Celso Ribeiro General Fusion (GF) is pursuing a mechanically-driven liquid metal path to Magnetized Target Fusion. A cylindrical cavity is formed in liquid metal through rotation. A plasma target is formed into this cavity by coaxial helicity injection (CHI). The cavity is rapidly collapsed by mechanical drivers. A practical power plant is achieved by cyclically repeating this process. The liquid metal serves as first wall, neutron blanket, compression system, working fluid, and toroidal field return circuit. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700