Nonequilibrium Attractor in High-Temperature QCD Plasmas
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70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
SEARCH · Engineering Papers
Results for “High Temperature Plasma”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Detachment in Fusion Plasmas with Symmetry Breaking Magnetic Perturbation Fields
Power exhaust from the bulk plasma is significantly altered by symmetry breaking magnetic perturbation fields, because these create direct connections (perturbed field lines) from the confined high temperature plasma to solid surfaces. Additionally, the same amount of power is distributed among those new exhaust channels as for a symmetric magnetic configuration, which reduces the local upstream heat flux flowing down the perturbed field lines, thereby making access to detachment easier (i.e., at lower upstream density) for the divertor plasma near the location corresponding to the symmetric magnetic separatrix. However, the divertor plasma regions with connection to the bulk plasma are extended nonaxisymmetrically further outside, where significant heat loads occur, unlike in the symmetric configuration. The temperature remains high at those locations, which reduces the divertor plasma dissipation capacity, making the mitigation of heat loads more difficult to achieve.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
High-n Rydberg transition spectroscopy for heavy impurity transport studies in W7-X (invited)
Here, we present a novel spectroscopy approach to investigate impurity transport by analyzing line-radiation following high-n Rydberg transitions. While high-n Rydberg states of impurity ions are unlikely to be populated via impact excitation, they can be accessed by charge exchange (CX) reactions along the neutral beams in high-temperature plasmas. Hence, localized radiation of highly ionized impurities, free of passive contributions, can be observed at multiple wavelengths in the visible range. For the analysis and modeling of the observed Rydberg transitions, a technique for calculating effective emission coefficients is presented that can well reproduce the energy dependence seen in datasets available on the OPEN-ADAS database. By using the rate coefficients and comparing modeling results with the new high-n Rydberg CX measurements, impurity transport coefficients are determined with well-documented 2σ confidence intervals for the first time. This demonstrates that high-n Rydberg spectroscopy provides important constraints on the determination of impurity transport coefficients. By additionally considering Bolometer measurements, which provide constraints on the overall impurity emissivity and, therefore, impurity densities, error bars can be reduced even further.
Instruments & Instrumentation↗
Coupled radiation transport and plasma physics for ICF simulations [Slides]
Describing high-temperature plasmas requires inclusion of several nonlinear coupled physics, including ion kinetics - for each isotope species present in the plasma, electron kinetics, thermal radiative transfer (TRT), electromagnetic description, and nuclear reactions (fusion burn). Simulating plasmas in ICF hohlraums aims to solve kinetic ions (particles), fluid electrons, energetic electrons, electromagnetics, kinetic radiation (MG DP solver), and laser-plasma interactions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Final CRADA Report – NFE-21-08693
TAE Technologies is developing a magnetic fusion energy concept known as the beam-driven field-reversed configuration (FRC) with the ultimate goal of developing a reactor for commercial electricity production capable of burning aneutronic pB11 fuel. To achieve the high plasma temperatures this requires, auxiliary radiofrequency (RF) heating will likely be needed. High Harmonic Fast Wave (HHFW) heating has been identified as a candidate RF heating scheme to overcome the unique challenges posed to RF heating by the FRC, including the large distance from the plasma edge to the last closed flux surface and a magnetic field profile with strength decreasing from edge to core and reversing sign at a null point inside the plasma. The purpose of this project was to develop the experimental capabilities to test HHFW on TAE’s C-2W device through the design of a phased array antenna and accompanying matching network. The design was performed by ORNL and informed by experiments with a prototype four-strap phased antenna-array that was manufactured and installed on the LArge Plasma Device (LAPD) at UCLA and simulations conducted with the Petra-M code under the purview of a previous INFUSE grant. The ORNL team completed the conceptual design of the antenna and matching network which was then handed off to the TAE Mechanical Design team. The design was then iterated on to ensure changes to the mechanical design did not interfere with the RF performance. This process is now complete, and, with mechanical design in hand, TAE is proceeding with plans for final integration.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Kinetic modeling of hot tail runaway electron generation during plasma disruptions using the JOREK code
The generation of runaway electrons (REs) during disruptions poses a significant challenge for the operation of tokamaks. The production of these high-energy electrons can cause substantial damage, particularly when the plasma current is high, making it a critical concern for ITER. For the high-temperature plasmas anticipated in ITER, the primary generation of REs may be dominated by the hot tail mechanism, which consists of the acceleration of hot electrons from the pre-disruption population which have not yet thermalized with the bulk following the rapid cooling of the plasma. To account for the significant 3D effects on RE production, a hot tail modeling framework has been developed within the non-linear 3D extended MHD code JOREK. This paper presents the structure of this framework, which is based on test electrons evolving in MHD fields. The verification of the method shows good agreement with the reference DREAM code for 0D test cases, as well as for axisymmetric simulations of 15 MA ITER H-mode disruption scenarios. Furthermore, a proof-of-principle application to a DIII-D case demonstrates the framework’s capability to capture for the first time the hot tail generation in 3D MHD simulations in realistic geometry. Preliminary results suggest that the production of REs is significantly reduced by stochastic losses.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Polarimetry-Interferometry Diagnostic for Magnetic Field and Magnetic Fluctuation Measurements in High-Performance and Long-Pulse Tokamaks (Final Report)
In this grant, we executed a multi-year plan to develop an advanced Faraday-effect polarimeter-interferometer system to address both fluctuation and equilibrium diagnostic needs by providing a measurement of the plasma internal magnetic field fluctuations (including non-axisymmetric 3-D perturbations) and plasma vertical position. This diagnostic included both fast time response and low phase noise so that both the temporal dynamics of equilibrium quantities as well as high-frequency electromagnetic fluctuations could be measured simultaneously, adding new and unique measurement capabilities for the core of high-temperature plasmas. The combined polarimeter-interferometer diagnostic development was applied primarily to the tokamak magnetic configuration, focusing on high-performance regimes including H-mode, reversed shear advanced tokamak scenarios, and non-inductive current drive.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A study of velocity, temperature, and density in the plasma generated by laser-induced breakdowns
The paper presents velocity measurements of shock-induced flow field, leading to vortex generation and plasma deformation in air. Femtosecond-laser electronic excitation tagging (FLEET) velocimetry was performed at the times Δt = 3, 20, 50, and 100 µs post laser-induced breakdown. Emissions over Δt = 3–10 µs showed the propagations of the initially elliptic shock, transitioning into a spherical front. The shock emanated along the laser axis causes the flow outward, and then the pressure gradient generated by the rarefaction wave drives the inward flow at later moments, with the velocity magnitude approaching a steady-state value of 40 m s -1 . Temporal velocity evolution was compared with non-self-similar solutions behind the propagating shock, which are sensitive to the size of the energy deposition, and the use of the measured initial plasma diameter reproduced the experiment. There establishes a region of uniform velocity around 35 m s -1 in the air-flow running through the plasma, which triggers the roll-up of the plasma surface by a large-scale vortex, providing the detail of flow field evolution from the shock propagation to the plasma deformation. A collective Thomson scattering and hybrid fs/ps pure rotational coherent anti-Stokes Raman scattering (CARS) were also performed to gain insight into the high-temperature plasma. An effective electron–ion recombination rate of 2 x 10 -12 cm 3 s -1 was measured at Δt = 0.5–10 µs, during a dynamic plasma expansion and compression. When the shock resides close to the plasma at Δt = 0.5–1 µs, the temperature distributions were found to follow the similarity law.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Breaking Beams: A Kinetic Treatment of the Filamentation and Forward Scatter of Laser Beams in Plasma (Abbreviated Final Report)
Precise and predictable propagation and deposition of laser energy in high energy density (HED) plasma is threatened by the breakup of the beam into filaments. Such filaments can be deflected and sprayed but also locally intensify the light, increasing the likelihood of other problematic interactions with the plasma. Adequately modeling, anticipating, and avoiding such processes in HED experiments requires a thorough understanding of the thresholds and nonlinear saturation mechanisms, particularly for the weakly collisional, high temperature plasmas achieved at the National Ignition Facility (NIF).
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Breaking Beams: A Kinetic Treatment of the Filamentation and Forward Scatter of Laser Beams in Plasma
Precise and predictable propagation and deposition of laser energy in high energy density (HED) plasma is threatened by the breakup of the beam into filaments. Such filaments can be deflected and sprayed but also locally intensify the light, increasing the likelihood of other problematic interactions with the plasma. Adequately modeling, anticipating, and avoiding such processes in HED experiments requires a thorough understanding of the thresholds and nonlinear saturation mechanisms, particularly for the weakly collisional, high temperature plasmas achieved at the National Ignition Facility (NIF).
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Final Technical Report for DoE award DE‐SC0023367 “Energetic Electron Transport in Magnetized Plasma with Magnetic Islands”
This project investigated how plasmas interact with energetic particles and solid materials under extreme conditions relevant to fusion energy, space plasmas, and planetary environments. Using experiments on the DIII-D National Fusion Facility, the research first examined how high-energy electrons move, become trapped, and are released in plasmas containing magnetic islands—structures commonly found in fusion reactors and Earth’s magnetosphere—providing new insight into particle transport and acceleration processes. The project also explored plasma-driven chemical reactions that can occur during meteoroid entry into planetary atmospheres, demonstrating that simple molecules such as ammonia can be produced and survive in high-temperature plasma conditions. Together, these results improve understanding of plasma behavior across laboratory, space, and planetary systems while informing fusion plasma control and plasma–material interaction studies. The project additionally contributed to workforce development by training graduate students, undergraduates, and early-career researchers and by disseminating results through peer-reviewed publications and international scientific conferences.
Orlov, Dmitri Mikhailovich [UC San Diego] (ORCID:0↗
Model for the electrical conductivity in dense plasma mixtures
A new density functional theory, average atom based model for the electrical conductivity of dense plasmas with a mixture of ion species, containing no adjustable parameters, is presented herein. The model takes the temperature, mass density and relative abundances of the species as input. It takes into account partial ionization, ionic structure, and core-valence orthogonality, and uses quantum mechanical calculations of cross sections. Comparison to an existing high fidelity but computationally expensive method reveals good agreement. The new model is computationally efficient and can reach high temperatures. A new mixing rule is also presented that gives reasonably accurate conductivities for high temperature plasma mixtures.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Studies of Autoionizing States relevant to Dielectronic Recombinaton
Doubly excited autoionizing states of alkaline earth atoms are explored by multistep laser spectroscopy, which is precisely the inverse process to dielectronic recombination, the recombination of hot electron with ions via an autoionizing state. Dielectronic recombination is an important mechanism leading to power loss in high temperature plasmas. Measurements included the autoionization rates of atoms in zero field and in the presence of electric and magnetic fields, as might be encountered in a plasma. To mimic the effects of the rapidly varying fields of electron collisions measurements were made in the presence of microwave electric fields. These experiments are analogous to experiments conducted with combined high intensity infrared and vuv laser fields, In laser/microwave experiments the effects of laser pulse envelope timing relative to the microwave phase were explored extensively.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
X-ray spectroscopy of multi-temperature plasmas using the differential emission measure formalism
We present a theoretical construct that nominally underlies spectroscopic data analysis of multi-temperature plasmas, known as the differential emission measure (DEM). From a data analytic perspective, the DEM formalism is used to derive temperature distributions from line spectra that are formed in the presence of temperature gradients and by time integrations of evolving plasmas. From a modeling perspective, DEMs are convenient intermediaries between radiation hydrodynamics simulations and spectroscopic measurements acquired in the laboratory. The DEM concept and its associated methodologies were originally developed by spectroscopists working with astrophysical data. We borrow from these earlier investigations. In this manuscript, intended primarily as a tutorial, we discuss the basic concepts, but also augment various aspects of the theory by the way of extension and example, including a detailed treatment of various weighting and averaging schemes, intended to mitigate ambiguities that often arise when reporting temperature information. We focus on high-temperature plasmas that are not in local thermodynamic equilibrium and the x-ray spectra that they produce, although the core ideas presented here are applicable to spectroscopy in other energy bands. A few examples involving the derivation and manipulation of model DEMs in simple geometries are provided.
Liedahl, Duane A. [Lawrence Livermore National Lab↗
Perspectives and challenges of ultra-high temperature ceramics for fusion plasma-facing applications
Ultra-high temperature ceramics (UHTCs) offer several potential advantages as plasma-facing components (PFCs) in fusion reactors due to their extreme melting points, tailorable thermal conductivity, and attractive unirradiated mechanical properties including fracture toughness comparable or superior to tungsten. Here, recent developments and material properties of UHTCs are briefly reviewed, along with an overview of limited studies on their responses to neutron irradiation and an evaluation of plasma-surface interactions. Five key research pathways, primarily focused on irradiation effects, for advancing UHTCs in PFC applications are discussed: (1) assessing irradiation effects on the coupled thermal–mechanical performance (2) addressing the lack of studies on irradiation, plasma-surface interactions, and their synergistic effects; (3) investigating high-temperature (>1000 °C) neutron irradiation effects critical for PFC performance; (4) optimizing multi-component UHTC compositions or composites to improve thermal or mechanical properties; (5) enhancing radiation resistance to mitigate microcracking and void swelling through strategies such as increasing sink strength by reducing grain size, introducing fine particles, and leveraging complex concentrated alloy concepts.
36 MATERIALS SCIENCE↗
Non-Equilibrium in a Dust-Forming Low-Temperature Plasma: A CARS Study
Dust-forming low-temperature plasmas are versatile systems for the production of nanoparticles with tunable functionalities. While attractive from a materials processing point of view, these systems are inherently complex, with several plasma-induced phenomena determining the properties of the produced materials. Here, we characterize a carbon nanoparticle-forming plasma using coherent anti-Stokes Raman spectroscopy (CARS), with the primary goal of measuring gas temperature. While gas temperature is typically assumed to be at or slightly above room temperature in these reactors, we measure gas temperatures exceeding 1000 K under typical process conditions. We find a correlation between the gas temperature and the nanoparticle yield, suggesting that the particle nucleation and growth process releases energy within the reaction volume, leading to significant gas heating. In addition, we find that the relaxation of vibrationally excited species at the particle surfaces is a major contributor to their heating. In conclusion, these results underscore the complexity of these systems and the need for their more in-depth characterization using advanced techniques such as CARS.
Basic Plasma Phenomena and Gas Discharges↗
Modelling of nanometer scale dust grains in tokamak
Dust poses a serious threat to tokamak operation and safety. It is important to study the behaviour of dust grains under tokamak's discharge conditions, which depends heavily on their size and charge. Existing simulations mainly address issues on dust grains with radii larger than 1 μm, in which case, the drift effect due to electromagnetic fields can be safely ignored. For nanometer scale dust grains, however, the drift effect becomes significant and a new model based on guiding-centre system needs to be established. In this work, the NDS has been done under BOUT++ framework. The simulation contains two parts. Part one, NDS evaluates the charging and ablation processes of the dust grains. In the second part, the guiding-centre orbits of dust particles are tracked in tokamak plasmas, whose parameters are obtained from BOUT++, a highly desirable C++ code package for performing parallel plasma fluid simulations with an arbitrary number of equations in 3D curvilinear coordinates. The orbit of nanodust dynamics is described by guiding centre equations for simplicity, and these equations are numerically solved by conventional fourth-order Runge Kutta method. Simulations provide results such as trajectories and evolutions of dust particles with different sizes and velocities for different tokamak geometries. Results show tungsten dust grains with a radius of a few nanometers launched from outer midplane will oscillate before totally ablated in C-Mod. The oscillation in this case is driven by the ion drag force. Larger Nanodust with a radius of 100 nm, on the contrary, cannot be completely constrained by the electromagnetic field. In conclusion, the high plasma temperature and density in the seperatrix region causes severe dust ablation, resulting in total ablation within several ms.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Tokamak ITG-KBM transition benchmarking with the mixed variables/pullback transformation electromagnetic gyrokinetic scheme
Electromagnetic gyrokinetic simulation of high temperature plasma is required to predict confinement in magnetic fusion devices and has posed challenges for existing codes. In this paper, we demonstrate successful global gyrokinetic simulation of the ion temperature gradient-driven mode-kinetic ballooning mode transition in a toroidal fusion plasma test case using the mixed variables/pullback transformation (MV/PT) scheme with the particle-in-cell codes XGC and ORB5, and compare to results from a conventional continuum code from the literature. Furthermore, the MV/PT scheme combines explicit time integration with mitigation of the well-known electromagnetic gyrokinetic “cancelation problem.” We calculate eigenmodes in the electrostatic and parallel vector potentials, and find good agreement in growth rate, real frequency, and the normalized plasma pressure of mode transition.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗