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Invited Abstracts
Integrating Recent Innovations in Single-Stage Stellarator Optimization for the Columbia Stellarator eXperiment
Antoine Baillod, Columbia University
The Columbia Stellarator eXperiment (CSX), currently in the design phase at Columbia University, is focused on investigating quasi-axisymmetric plasma with a small aspect ratio, and on validating recent developments in stellarator technology, theory, and optimization techniques. It is designed to test some of the theoretical predictions of quasi-axisymmetric plasmas, in particular plasma flow damping, MHD stability properties, and the study of trapped particle confinement. The magnetic field is generated by a set of two circular and planar poloidal field (PF) coils alongside two shaped interlinked (IL) coils, with the potential consideration of additional coils to enhance shaping or experimental flexibility. While the PF coils and vacuum vessel are repurposed from the former Columbia Non-Neutral Torus (CNT) experiment, the two IL coils will be wound at Columbia University, using non-insulated High-Temperature Superconducting (HTS) tapes. These coils undergo shape and strain optimization to produce the desired plasma configuration while adhering to engineering constraints. Discovering a plasma shape that aligns with the physics objectives and can be produced by such a restricted number of coils poses a significant challenge. Indeed, the constrained coil set's limited capacity to produce varied plasma shapes hinders the application of the traditional two-stage stellarator optimization approach. Instead, novel single-stage optimization techniques are employed, where plasma and coils are optimized concurrently. During this presentation, two single-stage optimization methodologies will be introduced. We will explore their application to the CSX experiment's design, aiming to identify configurations that fulfill engineering constraints and generate a plasma within a desired regime for the experiment's physics objectives.
Characterization of fast magnetosonic waves driven by compact toroid plasma injection along a magnetic field
Feng Chu, Los Alamos National Laboratory
Magnetosonic waves are low-frequency, linearly polarized magnetohydrodynamic (MHD) waves commonly found in space, responsible for many well-known features, such as heating of the solar corona. In this work, we report observations of interesting wave signatures driven by injecting compact toroid (CT) plasmas into a static Helmholtz magnetic field at the Big Red Ball Facility at Wisconsin Plasma Physics Laboratory. By comparing the experimental results with the MHD theory, we identify that these waves are the fast magnetosonic modes propagating perpendicular to the background magnetic field. Additionally, we further investigate how the background field, preapplied poloidal magnetic flux in the CT injector, and the coarse grid placed in the chamber affect the characteristics of the waves. Since this experiment is part of an ongoing effort of creating a target plasma with tangled magnetic fields as a novel fusion fuel for magneto-inertial fusion (MIF), our current results could shed light on future possible paths of forming such a target for MIF.
Investigating the dynamics of fractal-shaped ice grains is a cryogenic RF plasma
André Nicolov, Caltech
Ice grains are formed in a laboratory RF plasma in which neutral gas is cooled to cryogenic temperatures. The ice grains are observed to be highly elongated and have fractal structures, causing them to have small cross-sections and low masses relative to their sizes. The ice grains undergo complex nonlinear dynamics as motion is driven by ion drag, thermophoresis, gravity, and electrostatic confinement, which change as the grains grow over time. In the plasma afterglow, the dynamics simplify to a balance between gravity, neutral drag, and the thermophoretic force. High-speed imaging is used to track the grain trajectories upon RF power shutoff. A laser-induced fluorescence scheme is used to measure the temperature profile of the neutral argon gas, from which the thermophoretic force can be computed. The ratio of ice grain mass to cross-section can then be directly obtained from the measured trajectories. Using microscope imaging of the ice grains and invoking their fractal geometry, grain mass and cross-section are calculated.
Supported by NSF/DOE Partnership in Plasma Science and Engineering via DOE Award DE-SC0020079, and NSF grant #2308558.
Laboratory Investigation of Low Collisional Magnetic Reconnection Using a Drive Cylinder
Paul Gradney, University of Wisconsin Madison
For most laboratory plasma experiments, Coulomb collisions between the particle species are sufficiently frequent that the particle distribution functions are relaxed to a near-Maxwellian form. This hampers the applicability of such experiments to phenomena observed in tenuous and near-collisionless space plasma. The Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory aims to study collisionless reconnection for parameters relevant to the Earth's magnetosphere. To reduce the role of collisional effects, a reconnection Drive Cylinder has been developed, which increases both the effective system size of the TREX configuration and the rate at which reconnection can be driven. These two effects now permit TREX to reach a kinetic reconnection regime where collisional effects are minimized. The Drive Cylinder is comprised of 12 single loop drive-coils connected in parallel to a 10 kV capacitor bank. Insulated sheets of aluminum are applied to smooth the magnetic fields and enhance the drive efficiency. Following is a description of the technical details and performance of the Drive Cylinder.
Into the Fire: Plasma Physics of the Turbulent Solar Corona
Steven R. Cranmer, University of Colorado Boulder
The solar corona is the hot and ionized outer atmosphere of the Sun. It traces out the complex solar magnetic field and expands into interplanetary space as the supersonic solar wind. In 1958, Eugene Parker theorized that the presence of a million-degree corona necessarily requires the outward acceleration of a wind. However, despite many years of exploration of both phenomena, we still do not have a complete understanding of the processes that heat the coronal plasma to its bizarrely high temperatures. In this talk, I will discuss some new observations and theoretical concepts that are helping us get closer to an answer to this infamous coronal heating problem. We will begin by examining super-high-resolution images of the Sun's surface from the Daniel K. Inouye Solar Telescope (DKIST), zoom out to ultraviolet and X-ray images that illustrate how magnetic field lines thread their way through the corona, and then follow the Parker Solar Probe (PSP) spacecraft through its repeated dives into the innermost zones of the solar wind. We will also confront these new pieces of observational data with theoretical models of magnetohydrodynamic turbulence. Such models are now being used as the basis for global simulations of the corona and solar wind, but there are still some major missing pieces. Lastly, I will do my best to make useful connections between this massive plasma laboratory (that sits about 150 million kilometers away) and the many other (smaller, but controllable!) laboratory plasma experiments that will be discussed at MagNetUS.
Experimental method to produce true two-dimensional dust clouds and clusters in complex plasmas
Ravi Kumar, The University of Memphis
Two-dimensional (2D) dust monolayers are ideal systems for developing and testing thermodynamic models and studying the statistical behavior of complex/dusty plasmas. However, creating a perfect 2D dust monolayer or eliminating unwanted off-plane micron-sized dust grains inside an active laboratory complex plasma experiment is extremely challenging. There are some methods to manipulate and control the charged dust grains via electromagnetic fields, varying discharge parameters, controlling confinement boundary conditions, UV irradiation, etc.; however, these techniques affect the plasma parameters and disturb the dynamic equilibrium of dust grains. We present a method to precisely manipulate and control the density and dimensionality of dust clouds levitated above the powered electrode in complex plasmas. The developed technique is independent of any discharge parameters and does not alter the dust dynamic equilibrium. It can produce perfect 2D dust layers by eliminating off-plane particles via lowered confinement potential induced by the electrode control arms located outside the plasma chamber. The method is stable and precise enough to eliminate dust grains by N = 1, creating the desired N-clusters, which were only possible by trial-n-error till now.
This research is supported by the US Department of Energy FY2020 Early Career Award DE-SC0021106 and Facilities Award DE-SC0023416 from the Office of Fusion Energy Science.
Spatio-temporal dynamics of confined filaments in magnetized plasmas in the MDPX device
Elon Price, Auburn University
The Magnetized Dusty Plasma eXperiment (MDPX) is a unique apparatus capable of generating steady-state, magnetic fields up to 3.5 T within a experimental volume of 50 cm in diameter and over 20 cm in length. At magnetic fields exceeding 1 T, radio frequency (rf)-generated, capacitively-coupled plasmas can form coherent, field-aligned structures known as ""filaments"". These structures, which can be either stable or mobile, disrupt the uniform plasma background and can significantly perturb dusty plasma experiments. Understanding the spatio-temporal dynamics of these filaments in a dust-free environment has become an important aspect of MDPX studies. Investigations into confining single or multiple filaments involve introducing copper rings on the bottom electrode to restrict motion. Previous work [1] correlated the trends of spatial morphology with the ion Hall parameter. A series of confinement experiments have been conducted over the last year resulting in a controlled ion Hall parameter scan to classify various types of spatio-temporal filament dynamics, including translation, rotation, mode transformation, splitting, and recombination. Preliminary analysis of these spatio-temporal phenomena will be reported. A robust tracking and characterization algorithm using Python and OpenCV library has been developed in our lab to analyze the rich and complex dynamics.
This work is supported with funding from the NSF EPSCoR program and the U.S. Department of Energy – Office of Fusion Energy Sciences.
[1] S. Williams et al, Phys Plasmas 29, 012110 (2022)
Effects of neutral transport and negative triangularity on plasma scrape-off layer turbulence in gyrokinetic simulations
Tess Bernard, General Atomics
The paper describes a direct pathway toward high-fidelity, first-principles simulations with predictive capabilities for plasma particle fuelling and detachment, which are top physics priorities for ITER, SPARC, and other fusion reactor operations. It presents the coupling of a continuum full-f gyrokinetic turbulence model with a 6D continuum model for kinetic neutrals, carried out using the Gkeyll code, which has been extended to include general geometry capabilities. A successful exhaust design will rely on both neutral interactions and plasma shaping in order to reduce the flux of heat and particles to the divertor without degrading core plasma conditions. In gyrokinetic simulations of inner-wall-limited (IWL) plasmas with DIII-D parameters, the effect of neutral interactions and triangularity on coherent turbulent structures, called plasma blobs, is explored due to the effect they can have in setting the scrape-off layer (SOL) width or introducing impurities through interactions with plasma-facing components. Seeded blob simulations with neutrals in shaped SOL scenarios demonstrate that increasing elongation and triangularity decreases radial blob velocities but neutral interactions had a minor effect. Fully turbulent simulations of DIII-D IWL plasmas include both open- and closed-field-line regions. They show similarities to experimental profiles. Qualitative differences in turbulent structures are observed, with increased power at high k_y modes of density fluctuations for the negative triangularity case. A blob analysis shows that the negative triangularity case has over twice as many blobs with a greater average size and lifetime than the positive triangularity case.
Acknowledgements: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, Theory Program, under Award No. DE-FG02-95ER54309 and DOE Contract No. DE-AC02-09CH11466 (PPPL Field Work Proposal Number 3219).
3D Dynamics of Reconnecting Non-Parallel Flux Ropes in Simulations of the PHASMA Experiment
Regis John, West Virginia University
Magnetic flux ropes are columns of plasma with axial and azimuthal magnetic fields and are commonly observed in the solar corona, magnetotail reconnection, planetary magnetospheres and various other astrophysical contexts. The PHAse Space MApping (PHASMA) experiment at West Virginia University generates two flux ropes in the lab using pulsed plasma guns in a strong background magnetic field, to investigate their dynamics and reconnection process. These flux ropes are fixed in space at one end (the plasma gun end), and their other end terminates on a conical anode, which introduces a small degree of tilt between the two flux ropes. In the experiment, the flux ropes rotate around each other and move towards and away from each other throughout the discharge, with reconnection happening between them during their relative “pull” and “push” motions. Here, we present 3D electron-magnetohydrodynamics (EMHD) simulations of the PHASMA device with experimental parameters. We use the F3D code with reconnecting flux ropes tilted at an angle, just like in the experiment, and find that reconnection spreads in a zipper-like fashion. The dynamics depend on the axial magnetic field strength and the ropes fully merge if the axial magnetic field is less than ten times the reconnecting field. We perform a parametric study as a function of the axial magnetic field and compare it to the laboratory observations.
Generation of laboratory nanoflares from multiple braided plasma loops
Yang Zhang, Caltech
Solar flares are intense bursts of electromagnetic radiation accompanied by energetic particles and hard X-rays. They occur when magnetic flux loops erupt in the solar atmosphere. Solar observations detect energetic particles and hard X-rays but cannot reveal the generating mechanism because the particle acceleration happens at a scale smaller than the observation resolution. Thus, details of the cross-scale physics that explain the generation of energetic particles and hard X-rays remain a mystery. In this talk, I will present observations from a laboratory experiment that simulates solar coronal loop physics. Transient, localized 7.6-keV X-ray bursts and a several-kilovolt voltage spike are observed in braided magnetic flux ropes of a 2-eV plasma when the braid strand radius is choked down to be at the kinetic scale by either magnetohydrodynamic (MHD) kink or magnetic Rayleigh–Taylor instabilities. This sequence of observations reveals a cross-scale coupling from MHD to non-MHD physics that is likely responsible for generating solar energetic particles and X-ray bursts. All the essential components of this mechanism have been separately observed in the solar corona.
Alfvénic Turbulence in Multiple Regimes: Results from Prior LAPD Experiments and Plans for the Near-Future
Samuel Greess, Queen Mary University of London
TBA
Saving Data that Endures: Using xarray and hdf5 to Store Scientific Data in a Standard, Sharable, and Flexible File Format
Erik Tejero, US Naval Research Laboratory
In this talk, we will present a data writer Python module that we have developed at the Naval Research Laboratory to store, self-document, and archive experimental data. This has solved a long-standing issue of how to standardize our file structures that collect various measurements comprising an individual dataset, including metadata required to understand and use the data many years in the future, while maintaining the flexibility needed for each new, unique type of experiment. The new module builds off of the Python xarray package, organizing the data into datasets and saving it as HDF files with appropriate descriptive data attributes to store large, diverse data sets. The data writer leverages the power of the xarray package, which excels at handling multi-dimensional scientific data, offering intuitive indexing and powerful data visualization tools. As a case study for using the module, we will present some recent experimental results from an investigation of soliton generation by orbital debris. We have found that our data writer module works well for the majority of our needs, and we are interested in getting more people using it to see how it can be improved and help others that have run in to similar data archiving issues.
Crossover of space exploration and fusion research: spacecraft heat shields and meteoroids in the DIII-D tokamak.
Dmitri Orlov, UC San Diego
The development of materials that can withstand extreme heat flux environments is crucial for both the realization of fusion energy and the exploration of the solar system. Testing heat shield materials is challenging due to the lack of adequate ground testing facilities. Here, we present a study of carbon ablation in high-heat plasma relevant to hypervelocity spacecraft entries that was conducted in the DIII-D tokamak. We showed that conditions in the DIII-D L-mode edge plasma can reproduce the flow velocity and high heat flux experienced during the Galileo probe's entry into the atmosphere of Jupiter.
In this study, three types of experiments were conducted using stationary graphite rods, porous carbon spherical pellets, and glassy carbon spherical pellets. In each case, the mass loss rates as a function of heat flux was determined from an extensive array of spectroscopic measurements and compared against several semi-empirical ablation models obtained from spacecraft flight data. Additionally, the experimental results for the pellet trajectories and mass loss rates of the porous and glassy carbon pellets were confirmed using the UEDGE-DUSTT simulations. The coefficients learned from the experiment and the semi-empirical models were used in simulations to investigate the ablation of different carbonaceous objects as they enter Jupiter's atmosphere. The results of this study demonstrate that scaling between DIII-D experiments, available flight data, and numerical models can be used to optimize heat shields for future planetary missions.
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-SC0022554, DE-SC0021338, DE-SC0023375, and DE-FC02-04ER54698.
Eruption of Dynamic Jets from an Arched Magnetized Laboratory Plasma
Shreekrishna Tripathi, UCLA
Solar photosphere and chromosphere are composed of partially ionized plasma, where interactions among neutrals and charged particles play important role in structure formation and dissipation of energy. A laboratory plasma experiment at UCLA has explored formation of jets from an eruptive arched magnetized plasma with dimensionless parameters relevant to the Sun's photosphere (β ≈0.001, Lundquist number ≈ 10000, plasma radius/ion gyroradius ≈ 20, ion-neutral collision frequency » ion cyclotron frequency). The arched plasma was kink- and torus-stable, therefore eruption leading to formation of a dynamic jet is not intuitive. Detailed measurements of plasma density, flow, temperature, and three-dimensional magnetic-field were performed. Development of a strong magnetic-shear in the arched plasma was identified to be the primary driver of the jet. Strong magnetic and thermal pressure gradients were recorded near the birthplace of jets prior to its formation. The jet evolves impulsively with supersonic speeds in the beginning (Mach 1.5). The plasma flow persists up to the resistive-diffusion time in the arched plasma. Highly-twisted magnetic structure of the jet, as a consequence of diamagnetic-currents, was observed. Ion-neutral charge-exchange collisions were identified to be efficient in producing the cross-field current that plays an important role in controlling the dynamics and aspect-ratio (ratio of length and width) of the jet.
References: Sklodowski, Tripathi, & Carter, “Dynamic Formation of a Transient Jet from Arched Magnetized Laboratory Plasma”, Astrophys. J., 953(1), 2023, 5
Acknowledgment: This research was primarily supported by the US Department of Energy under award number DE-SC0022153.