UMD Plasma Seminar

Plasma Physics Seminar

Fall 2024 Schedule

August 28th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 4th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 11th, Wed. 3:30PM ERF 1207, Large Conference Room	Mate Lampert, NSTX Advancing Fusion Energy: The National Spherical Torus Experiment Upgrade The National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory has been crucial in exploring the potential of the spherical tokamak (ST) design for fusion energy. This type of magnetic plasma confinement is now being considered for future fusion pilot plants. Currently, the NSTX is undergoing significant upgrades. Researchers are working to deepen their understanding of how ST plasmas behave to ensure that, once the upgraded device (NSTX-U) is operational, it will provide maximum benefits. This research also aims to improve our confidence in the performance of future fusion devices. Spherical tokamaks (STs) offer several advantages over traditional tokamaks. Their low aspect ratio (the ratio of the torus' minor to major radius) and resulting higher toroidicity contribute to greater stability and enable higher beta (the ratio of plasma pressure to magnetic pressure). Additionally, the higher toroidicity also results in the natural suppression of microinstabilities that lead to particle and energy transport. However, STs also present unique challenges, such as managing high heat flux, starting and sustaining the plasma without room for an induction coil, and dealing with plasma instabilities. Elevated heat fluxes on plasma-facing components (PFCs) are primarily induced by turbulence at the plasma edge and within the scrape-off layer (SOL). The turbulence in the SOL is characterized by its intermittent nature, which gives rise to field-aligned structures known as filaments. These filaments are responsible for transporting significant quantities of plasma density and thermal energy from the confined core to the PFCs, potentially leading to erosion or damage of these components. Consequently, it is imperative to thoroughly investigate this phenomenon to develop effective control and mitigation strategies to reduce the adverse impacts on PFCs to acceptable levels. To this end, a data analysis tool was developed to systematically characterize filaments by estimating key parameters such as their position, velocity, orientation, angular velocity, and morphology. These parameters were subsequently analyzed to establish correlations with one another, as well as with the overall plasma shape and profile characteristics.
September 18th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
September 25th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
October 2nd, Wed. 3:30PM ERF 1207, Large Conference Room	Open
October 9th, Wed. 3:30PM ERF 1207, Large Conference Room	APS DPP Meeting
October 14th, Mon. 3:30PM ERF 1207, Large Conference Room	Plamen Ivanov, EPFL Lausanne When good turns bad: the gyrokinetic field invariant and good-curvature instabilities in fusion plasmas In this talk, we discuss the theory of curvature-driven modes in fusion plasmas and demonstrate that their instability is linked to the conservation law of the so-called gyrokinetic field invariant. The evolution equation of this invariant, whose electrostatic version is well known, implies that electrostatic modes that are driven unstable by the local magnetic curvature, are bound to reside in the regions of bad curvature. More importantly, we deduce that any mode that is driven unstable in good, rather than bad, curvature must be electromagnetic in nature. As an example, we investigate the properties of a novel good-curvature instability and contrast its properties with the well-known electron-temperature-gradient instability.
October 16th, Wed. 3:30PM ERF 1207, Large Conference Room	Arnas Volcokas, EPFL Staircase Safety Factor Profiles in Gyrokinetic Simulations at Low Magnetic Shear In this work, we investigate the impact of electromagnetic effects on plasma turbulence self-organization at low magnetic shear using nonlinear gyrokinetics. Our previous electrostatic studies showed that turbulent eddies extend along magnetic field lines for hundreds of poloidal turns when the magnetic shear s is low or zero. Such ``ultra-long'' eddies have significant consequences on turbulent transport due to parallel self-interaction. At low magnetic shear, parallel self-interaction induces strong corrugations in plasma profiles at low-order rational surfaces, including the formation of stationary current layers. When electromagnetic effects are considered, turbulence-generated currents lead to the development of stationary zonal magnetic potential, locally flattening the safety factor profile to form staircase structures or broaden the safety factor profile minimum. This represents a crucial feedback mechanism between turbulence and the imposed safety factor profile, resulting in a reduction in turbulent transport. We study the corrugated safety factor profiles using both the local flux tube code GENE and the global particle-in-cell code ORB5. To further explore this interaction, we employed a novel extension of the flux tube model, allowing simulations of non-uniform magnetic shear profiles, including minimum-q profiles relevant for Internal Transport Barrier (ITB) formation. Our findings indicate that turbulence-generated current layers can flatten the imposed non-uniformity across the entire domain or substantially widen rational surface regions, consistent with global simulation results. We believe these results are relevant for understanding ITB formation and inform long-standing experimental observations.
October 23rd, Wed. 3:30PM ERF 1207, Large Conference Room	Rahul Gaur, Princeton University A database of omnigenous stellarator equilibria including umbilic-torus-like designs and their applications with DESC Omnigenity is a favorable property of a toroidal magnetic field that ensures trapped particle confinement. Since omnigenity is a superset of quasisymmtry, in theory, the design space of omnigenous configurations will be larger than that of quasi-symmetric configurations. To better understand this design space, we generate a database of 50k omnigenous equilibria generated using the DESC optimizer. In the first part of this talk, we find interesting trends in stability, coil complexity, and degree of omnigenity with respect to the shape parameters of the plasma, such as magnetic axis torsion, number of field periods, elongation, and aspect ratio. We choose equilibria for each type of omnigenity: toroidal, poloidal, and helical. Using DESC, we then perform multiobjective MHD and kinetic stability optimization to find omnigenous equilibria with enhanced Mercier, ballooning, and kinetic ballooning stability. In the second part, we present a small subset of this database comprising omnigenous umbilic-torus-like equilibria; equilibria with a single closed, continuous sharp edge that goes around multiple times toroidally and behaves like an X-point. This causes the iota to be a low order rational number on the boundary, which can be useful for generating resonant divertor concepts.
October 30th, Wed. 3:30PM ERF 1207, Large Conference Room	Jonathan Ng, University of Maryland Reconnection, jets and a few X-rays - kinetic physics at Earth's dayside magnetosphere The interaction of the solar wind and Earth's dipole field creates a wide variety of physical phenomena including turbulence, shocks and magnetic reconnection. The solar wind is shocked as it interacts with Earth's magnetic field, causing the formation of the bow shock and a downstream region known as the magnetosheath. Solar wind plasma is then allowed to enter Earth's magnetosphere through magnetic reconnection. In this talk I will discuss global and local physics at the dayside magnetosphere with a focus on magnetopause reconnection. Using hybrid simulations, I will first discuss the role of high-speed jets -- regions of enhanced dynamic pressure in the magnetosheath -- in triggering magnetopause reconnection, and show how magnetosheath fluctuations can affect the magnetopause reconnection rate. I will also discuss how soft X-rays can be used to image the magnetosphere using the recent May 2024 storm as an example. This can complement the in-situ measurements made by current missions. I will then discuss fully kinetic simulations of the role of lower-hybrid drift waves during asymmetric reconnection based on experiments at the Magnetic Reconnection eXperiment (MRX), and show that kinetic simulations underestimate their amplitudes and effects on momentum balance.
November 6th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
November 13th, Wed. 3:30PM ERF 1207, Large Conference Room	Joel Dahlin, GSFC Decoding Three-Dimensional Reconnection Dynamics in Solar Flare Ribbons & Loops Solar flares are spectacular manifestations of explosive energy release powered by magnetic reconnection. The three-dimensional structure and dynamics of flares are thought to be critical to understanding the nature of this energy release. Of particular interest are coherent magnetic structures known as plasmoids, which are understood to play important roles in facilitating explosive energy release and driving nonthermal particles. Direct measurement of the magnetic fields in the corona where the reconnection occurs is, however, highly challenging. By contrast, `indirect' high-resolution observations of flare loops and ribbons are plentiful and contain critical information regarding the three-dimensional structure. Flare ribbons are chromospheric patches illuminated by particle beams, tracing the footpoints of newly reconnected field lines. Hot and dense plasma evaporated by these beams form `flare loops' that reveal the morphology of the reconnected magnetic field. We present high-resolution, three-dimensional MHD modeling of an eruptive flare and discuss our efforts to understand the reconnection dynamics revealed in these observations. We demonstrate in detail how the evolution of flare ribbon fine structure corresponds to plasmoid birth, propagation, and annihilation. We furthermore show that the geometry (e.g., the tilt) of the flare loops encodes key information about the spatiotemporal evolution of the reconnection guide field. We discuss the implications for understanding reconnection energy release and particle acceleration throughout the universe.
November 20th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
November 27th, Wed. 3:30PM ERF 1207, Large Conference Room	Thanksgiving Week
December 4th, Wed. 3:30PM ERF 1207, Large Conference Room	John Ball and Shon Mackie, MIT Measuring Net Energy Gain Plasmas on SPARC with a Spectrometric Neutron Camera The SPARC tokamak, now under construction in Devens, MA by Commonwealth Fusion Systems, is predicted to robustly enter the burning plasma regime, Q_p > 5. In order to verify the performance of SPARC and probe the novel physics of this regime, a suite of four neutron diagnostics are being designed and built for the device. This includes a poloidal neutron camera, which will be capable of resolving neutron emission from the device in time, space, and energy for both pure deuterium and deuterium-tritium plasmas. These capabilities will allow the camera to measure the fusion power density, ion temperature, and alpha birth profiles. This is accomplished through the use of two modern neutron detection technologies: deuterated liquid scintillators and single-crystal chemical vapor deposition diamonds. The current state of the camera design and supporting prototyping activities are discussed as are predictions for the instrument's performance. A High-Resolution Magnetic Proton Recoil Neutron Spectrometer for Burning Plasma studies at SPARC The neutron emissions from a fusion plasma are rich with information about the kinetic distributions of fuel ions. In particular, the neutron energy spectrum encodes the fuel ion temperature, the ratio of fuel species, the alpha particle birth spectrum, and information about nothermal populations. This talk describes the design of a Magnetic Proton Recoil (MPR) neutron spectrometer that is being developed for detailed study of burning plasmas on SPARC, a high-field, compact tokamak under construction in Devens, MA. The operating principles and design optimizations are discussed before predictions of measurement capabilities are presented.
December 11th, Wed. 3:30PM ERF 1207, Large Conference Room	Open
(Special date) December 17th, Wed. 3:30PM ERF 1207, Large Conference Room	Nobumitsu Yokoi, University of Tokyo Modeling turbulent transports in fluid plasmas based on multiple-scale response-function formulation Turbulence plays an important role in the transports in flows at high Reynolds numbers. However, it is just impossible to numerically solve fully non-linear system of equations for flows at huge Reynolds numbers, which are of practical interest. In order to self-consistently close a system of strongly non-linear equations with large-scale inhomogeneity, anisotropy, and non-equilibrium properties of turbulence, we consider a response-function formulation in combination with multiple-scale analysis. Among several applications of this scheme, I present a few illustrative examples. The first one is the kinetic helicity (velocity-vorticity correlation) effect in hydrodynamic turbulence. In a non-mirror-symmetric system with rotation, the inhomogeneity of turbulent kinetic helicity, as well as the turbulent energy, enters the expression of the Reynolds stress and contributes to the linear- and angular-momentum transport. Large-scale flow generation due to the inhomogeneous helicity effect is argued [1,2]. The second one is the cross-interaction responses in magnetohydrodynamic (MHD) turbulence. In the response-function formulation of the MHD turbulence, we have to consider at least four response functions, which represent the velocity responses to velocity perturbation and to the magnetic perturbation and the magnetic responses to the velocity perturbation and to the magnetic perturbation. With treating the cross-interaction responses, the expressions of the transport coefficients should be altered as compared with the cases with treating self-interaction responses. The conditions of such cross-interaction will be discussed with special reference to possible roles of them [3,4]. The third one is the non-equilibrium turbulence effect on the transport in convection. A deviation from the local-equilibrium of turbulence represented by the time variation of the fluctuation along the large or coherent fluid motions is incorporated into turbulence modelling. Such non-equilibrium properties of turbulence may serve as a prescription for the "convection conundrum" in the angular momentum and heat transport in the stellar convection [5,6]. All these evaluations of turbulence transport are possible in the multiple-scale response function formulation. References [1] Yokoi, N. and Brandenburg, A. (2016) Phys. Rev. E, 93, 033125. [2] Yokoi, N. (2024) "Transports in helical fluid turbulence," in Helicities in Geophysics, Astrophysics, and Beyond. (Eds.) K. Kuzanyan, N. Yokoi, M. Gregolius, and R. Stepanov (Wiley, 2024) pp.25-50. [3] Yokoi, N. (2023) Rev. Mod. Plasma Physics. 7, 33. [4] Miserski, K., Yokoi, N., and Brandenburg, A. (2023), J. Plasma Physics. 89, 905890412. [5] Yokoi, N., Masada, Y., and Takiwaki, T. (2022) Mon. Not. Roy. Astron. Soc. 516, 2718. [6] Yokoi, N. (2023) Atmos. 14, 01013.

Contact Information: Marc Swisdak or Ian Abel