ABSTRACTS

Please submit your abstract for oral talks and poster presentations using this Google Form: https://forms.gle/yjtAcGnoxdup5Quu6 

Abstract submission will close on 7/19/2026.

Invited Speaker Abstracts: 

Jeff Lestz — University of California, Irvine

Experimental Evidence of Helicon Wave Heating and Current Drive in DIII-D 

J.B. Lestz, B. Van Compernolle, R.I. Pinsker, S.X. Tang, A. Dupuy, A.M. Garofalo, L. McAllister, C.P. Moeller, C.C. Petty, M. Porkolab, M.P. Ross, G. Rutherford, and A. Torrezan

Helicon current drive is an attractive solution for driving off-axis current to sustain steady state tokamak operation in reactor conditions. Dedicated DIII-D experiments have been conducted with a MW-level helicon system and successfully demonstrated core power deposition and current drive with helicon waves launched via a traveling wave antenna. The profile of the measured electron temperature response to helicon power injection is in good agreement with time-dependent integrated modeling that incorporates ray tracing and the effects of thermal transport simultaneously. The absorption is observed to scale with the normalized electron pressure βe, as theoretically predicted by Landau damping for single pass absorption. When the helicon is injected continuously to drive co-Ip current, the reconstructed safety factor profile flattens significantly faster and sawteeth are triggered earlier than in comparison shots where the helicon is replaced by a similar amount of electron cyclotron heating. Calculation of the non-inductive current profile due to helicon waves yields a peaked profile in the core, consistent with the observed power deposition profile, and in good agreement with ray tracing predictions. Taken together, these experimental results represent strong evidence for the first definitive observation of auxiliary current drive due to helicon waves on any device.

Shreekrishna Tripathi — University of California, Los Angeles

Destabilization of Ion Cyclotron Emission and EMIC Waves by a Proton Beam in a Large Magnetized Plasma Shreekrishna Tripathi — Physics and Astronomy, UCLA

The resonant interaction between energetic ions and plasma waves is a fundamental topic in space and laboratory plasma physics (e.g., the interaction of protons and alpha particles with ion-cyclotron and Alfvén waves in the solar wind, aurora, and magnetic fusion plasmas). Electromagnetic Ion Cyclotron (EMIC) waves propagate into distinct bands based on the number of ion species and relative concentration ratios. In the magnetosphere, these waves are destabilized by energetic protons (10-100 keV) through Doppler-shifted cyclotron resonance. Ion Cyclotron Emission (ICE) is observed at harmonics of the fast-ion gyro-frequency. The role of resonant processes in destabilizing these waves is examined with unprecedented detail in 3D using unique capabilities of the Large Plasma Device (LAPD). In these experiments, a proton beam (15 keV, 10 A) is injected into a large magnetized plasma (n ≈ 10¹⁰–10¹³ cm⁻³, Te ≈ 5.0–15.0 eV, B = 0.6–1.8 kG, He⁺ and H⁺ ions, 19 m long, 0.6 m diameter) for performing fast-ion studies. The beam forms a helical orbit (pitch angle ≈ 7°–55°) and propagates with an Alfvénic speed (beam-speed/Alfvén-speed = 0.2–3.0). The mode structure of waves and relevant plasma parameters are recorded using a variety of diagnostic tools (retarding-field energy analyzer, three-axis magnetic-loop, Dipole, and Langmuir probes). Experimental results demonstrate that the Doppler-shifted cyclotron resonance with energetic protons is efficient in generating broad spectra of Alfvén, EMIC, and ion cyclotron waves. These experiments have identified specific regimes of resonant interactions, in which beam-destabilized waves scatter protons over a wide range of pitch angles, suggesting a fascinating interplay between plasma waves and energetic protons in a laboratory plasma experiment.

Ehab Hassan — Oak Ridge National Laboratory

Integrated Modeling as a Pathway for Designing, Optimizing, and Controlling Next Generation of Tokamaks and Stellarators by Coupling Plasma Physics to Engineering Constraints Ehab Hassan, S. De Pascuale, C.S. Collins, G.M. Staebler, and J.M. Park — Fusion Energy Division, Oak Ridge National Laboratory

Multi‑fidelity Whole Device Modeling (WDM) frameworks integrate physics and engineering tools to design, evaluate, and optimize fusion reactors. These frameworks comprise multiple coupled subsystems that perform coordinated physics and engineering analyses within integrated workflows. WDM is being applied to re‑assess and optimize poloidal‑field (PF) and toroidal‑field (TF) coil designs and to develop non‑inductive, high‑fusion‑gain plasma scenarios in conceptual fusion devices such as the Fusion National Science Facility (FNSF) and the Compact Advanced Tokamak (CAT). The FreeGSNKE MHD free‑boundary equilibrium code has been used to reduce PF‑coil stresses by optimizing coil placement and structural design for FNSF and CAT, and to simulate time‑dependent full‑pulse evolution in tokamaks. In parallel, IPS‑FASTRAN has been used to develop MHD‑stable, non‑inductive operating scenarios with high fusion gain, a large bootstrap‑current fraction, and strong energy confinement. For stellarators, full‑pulse scenario development can be pursued by coupling equilibrium (VMEC), transport (ASTRA/GX), and heating/current‑drive models to evolve plasma profiles self‑consistently. After an optimal tokamak plasma scenario is identified, an additional engineering optimization layer is carried out to reduce thermal loads on plasma facing components. Overall, reactor performance can be maximized through self‑consistent integration and joint optimization of the physics and engineering components. WDM frameworks, combined with advanced actuators, also provide the foundation for digital‑twin capabilities for tokamaks and stellarators, which require real‑time prediction and control of plasma behavior. To enable real‑time applications, machine‑learning and neural‑network surrogate models are being developed to replace computationally expensive high‑fidelity codes, accelerating simulations and supporting real‑time control in fusion devices. These advances are expected to shorten the path to deploying fusion power on the electrical grid.

Jalaan Avritte — Auburn University

Analysis of Mixed Modes of Filament Morphologies in the MDPX Device Through a Convolutional Neural Network

To study the magnetic effects on dusty plasmas, magnetic fields, |B| ≥ 1 Tesla are often required. When these fields are applied to the capacitively coupled plasmas that are typically used to these systems, the uniformity of the plasma is disrupted. Past experiments have shown that the plasma will form self-organized, magnetic field aligned structures that are referred to as "filaments". A previous study categorized these filaments as singular "types" and their correlation with the degree of magnetization through the ion-Hall parameter. This talk expands on this previous work by classifying these filaments as azimuthal modes m similar to Archimedean spirals. Under this new classification, filament transformations and mixed modes are permitted to exist. By using a Convolutional Neural Network (CNN) to quantify these modes, the m = 1 mode is shown to be valuable in identifying filament transformations and mixed mode states. Lastly, future applications utilizing these morphologies to gain a deeper understanding of temporal and spatial plasma dynamics like electric field and transport are discussed.

Ben Antognetti — University of Wisconsin–Madison

Interactions between Bursts of High-Frequency Waves and Runaway Electrons in MST Tokamak Plasmas B.R. Antognetti, A.F. Almagri, B.E. Chapman, N.C. Hurst, M. Poulos, J.S. Sarff, M.A. Thomas, C.B. Forest — University of Wisconsin–Madison; M. Poulos — CompX

Non-thermal particle distributions can resonantly exchange energy with waves in magnetospheric, astrophysical, and laboratory plasmas. In tokamak fusion devices, this process may help to passively mitigate the harmful effects of high-energy runaway electrons (RE). We present results from low-density tokamak plasmas in the Madison Symmetric Torus where an internal B-dot probe is used to study waves driven by runaway electrons at high frequencies near and above the electron cyclotron frequency. Periodic bursts of waves are detected primarily in three frequency bands centered on 35 MHz, 1.3 GHz, and 3.2 GHz, and x-rays are simultaneously observed with energy 10–100 keV, likely due to RE striking the wall. The experiments are carried out with toroidal field BT = 0.13 T, average electron density 3×10¹⁷ m⁻³, edge safety factor 1.5–2.5, and background electron temperature Te = 100 eV. The bursts coincide with sawtooth-like MHD behavior which may serve to both accelerate the RE and drive them to the wall. Spatially-separated coils on the B-dot probe are used to measure the toroidal and poloidal wavenumbers. The data show that waves arrive in packets with varying wavenumbers. Ray-tracing simulations from the GENRAY code show that the waves may be confined, allowing them to gain energy from the RE over many orbits. Further properties of the waves and possible resonances inferred by the B-dot data are discussed. These novel results show that resonant wave-particle interactions with RE in tokamaks can be directly studied at high frequencies using internal probes, with applications to space/astrophysics and fusion energy.

Work supported by U.S. DOE award DE-SC0018266 and NSF award PHY 1828159

Krishan Kumar — West Virginia University

Role of Laser Polarization in Quantum Beat Spectroscopy for Magnetic Field Measurements in Plasmas

Magnetic fields exert a strong influence on plasma behavior, highlighting the need for diagnostic techniques that can measure magnetic fields with high accuracy while minimizing plasma perturbation. Quantum Beat Spectroscopy (QBS), recently demonstrated by Gilbert et al. [Plasma Sources Sci. and Technol. 34 025020 (2025)], is a laser-based optical diagnostic that provides Doppler-free, near single-shot measurements of magnetic field strength in laboratory plasmas. In this work, the effect of laser polarization on the QBS signal is investigated using a femtosecond laser in an argon plasma. The experiments are performed in a tabletop six-way cross vacuum chamber. A pair of Helmholtz coils mounted on a rotational stage keeps the chamber centered between the coils, allowing precise control over the orientation of the applied magnetic field. This study evaluates the feasibility of using polarization-resolved QBS measurements to determine both the magnitude and orientation of the magnetic field.

Cameron Kuchta — University of Wisconsin–Madison

Measurement of Electron Pressure Anisotropy during Laboratory Magnetic Reconnection

The Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) studies collisionless magnetic reconnection using a cylindrically symmetric architecture. We have developed a pressure anisotropy probe that can measure plasma flows and temperature anisotropies during reconnection. With a three coil driving system, magnetic reconnection in our machine is in the collisionless kinetic regime in which we expect electron anisotropy effects to dominate the physics of the ion diffusion regime. Embedded jets, seen in laboratory data, are driven into the outflow as expected from spacecraft observation of the magnetosphere, theory, and simulations. Additionally, we have measured pressure anisotropy in the laboratory with the pressure anisotropy probe that validates prior results.

Tommy Steinberger — West Virginia University

Non-Perturbative Mapping of Inverted Sheaths in Low-Temperature Plasmas Using Planar LIF and QBS T.E. Steinberger and J.W. McLaughlin — Department of Physics and Astronomy, West Virginia University, Morgantown, WV

Plasma sheaths are among the most widely studied plasma phenomena because of their central role in regulating particle fluxes and energy deposition at plasma-facing boundaries. Despite this importance, key aspects of sheath formation remain poorly understood, particularly when the boundary emits electrons. In the classical picture, electrons and ions are lost from the plasma bulk to a surface such that the net current to a floating plasma-facing component is zero. This balance is significantly modified when the boundary emits electrons through thermionic emission or secondary electron emission. With increasing electron emission, a classical sheath can transition to a space-charge-limited sheath and, under sufficiently strong emission, to an inverted sheath. In the inverted sheath regime, ion current to the boundary is suppressed, and ions are no longer accelerated through a presheath from the plasma bulk to the sheath edge. Although inverted sheaths have been investigated extensively through computational and theoretical studies, direct experimental confirmation of these potential structures remains limited. In this talk, we describe recent developments of a plasma facility designed to systematically control electron emission from a boundary and access the transition from classical to inverted sheath structures. We also present emerging laser spectroscopic approaches for nonperturbative measurements of ion dynamics and electric potentials from the plasma bulk to the plasma-facing boundary.

Lingling Zhao — University of Alabama in Huntsville

Multiscale Interaction Between Solar Wind Turbulence and Shocks

Collisionless shocks in the solar wind are embedded within a turbulent plasma environment where fluctuations spanning a broad range of scales both influence and are modified by the shock transition. Understanding the coupling between shocks, turbulence, waves, and particles is essential for describing energy transfer and dissipation in heliospheric plasmas. We investigate turbulence-shock interactions through a combination of theoretical modeling and in-situ spacecraft observations. We present a theoretical framework in which pre-existing turbulence modifies shock structure, alters energy partition, and enables non-adiabatic energy conversion across scales. We then examine observations from Parker Solar Probe, Solar Orbiter, and Wind to characterize the multiscale plasma processes associated with collisionless shocks in the inner heliosphere. The analysis reveals the generation of ion-scale waves near shocks, systematic evolution of proton temperature anisotropy across shock transitions, and significant changes in turbulence properties and polytropic behavior downstream of shocks. These results support a multiscale picture in which collisionless shocks act not only as sites of energy dissipation but also as sources of waves and turbulence that regulate particle distributions and energy transfer.

Shea Hess-Webber — Stanford University & COFFIES Science Center

Connecting Laboratory Plasmas to the Solar Interior Presenting Author: Shea A. Hess-Webber, Stanford University & COFFIES Science Center Collaborators: Mel Abler, SSI; JT Stefan, NJIT; Nat Mathews, Paris Observatory; Bibhuti Kumar Jha, SwRI; Andrés Muñoz-Jaramillo, SwRI; Sushant Mahajan, Stanford University; Todd Hoeksema, Stanford University

Laboratory plasma experiments have been used extensively to study the necessarily-remote physics of the solar atmosphere and heliosphere in detail for decades. The coupling of these scientific disciplines comes naturally out of the accessible conditions of the plasma environment and the direct observations above the photospheric optical depth (τ=1). While experiments exist to investigate high plasma-beta physical regimes, it is more challenging to replicate solar surface/interior conditions. This is due to both the conditions required within the laboratory setting as well as the lack of directly comparable observations within the opaque solar surface. However, current solar surface and interior techniques — including MHD theory, flux transport models, and helioseismology — can greatly benefit from the measurements and insights that laboratory plasma physics can provide. In this talk, I will discuss some recent work in solar surface/interior, including machine-learning efforts, that would benefit from lab plasma collaborations, some proposed work that we are hoping to do in the near future, and some broader ideas about where our disciplines might be able to cross-pollinate.

Anna Tenerani — University of Texas at Austin

3D Spherically Polarized Alfvén Waves

The solar wind originating from coronal holes is made of Alfvén waves propagating away from the Sun. Despite the large amplitude of these magnetic fluctuations — sometimes producing field reversals known as switchbacks — the total magnetic field magnitude (B) remains remarkably constant. Geometrically, this property corresponds to spherical polarization, which is observed from near-Sun regions out to beyond 1 au, together with negligible density fluctuations. These characteristics motivate the common assumption in turbulence models that compressible effects play a minor role in the nonlinear dynamics of Alfvénic fluctuations. A longstanding question is whether fully three-dimensional, smooth magnetic field configurations can satisfy the constant-B constraint, and how such fields can be constructed analytically or numerically. Here we present a numerical method to construct magnetic field configurations that are exactly spherically polarized, reproducing key features of solar wind fluctuations. Within this framework, we demonstrate that, in three-dimensional geometry, discontinuities must develop where such solutions cease to exist. This result implies that continuous field rotations can preserve the constant-B condition only in limited regions of space, separated by discontinuities where magnetic compressibility cannot be neglected.

Yevgeny Raitses — Princeton Plasma Physics Laboratory

Electron-Beam-Generated E×B Plasmas and Their Applications: User and Host Team Research at the Princeton Collaborative Research Facility (PCRF) Yevgeny Raitses — Princeton Plasma Physics Laboratory, Princeton, NJ

There is growing interest in electron-beam (e-beam) generated low-temperature plasmas for atomic-scale materials processing with applications in microelectronics and quantum technologies. In these systems, the plasma (electron density ~10⁹–10¹² cm⁻³ and electron temperature ~0.1–10 eV) is produced by injecting an energetic electron beam (10²–10⁴ eV) into a low-pressure (10⁻¹–10² mTorr) background gas along an applied magnetic field (10–10³ G). The magnetic field confines the electron beam as it propagates through the plasma source, while an electric field applied perpendicular to the magnetic field enables control of the cross-field ion flux. This crossed electric and magnetic field (E×B) configuration allows selective generation of ions and reactive species while maintaining a spatially uniform flux of low-energy particles to large-area substrates, such as semiconductor wafers, located at the plasma periphery. These unique characteristics make e-beam-generated E×B plasmas highly attractive for low-damage materials processing. This talk will present an overview of theoretical, experimental, and computational studies of e-beam-generated magnetized plasmas conducted at the Princeton Collaborative Research Facility (PCRF). Topics will include electron and ion kinetics in e-beam plasmas, beam–plasma instabilities, plasma chemistry, applications to gentle processing of two-dimensional materials and diamond for quantum technologies, and advanced plasma diagnostics.

Kristopher Klein — University of Arizona

The Oblique Drift Instability: A Route to Ion Heating via Drifts in Magnetically Dominated Plasmas

Weakly collisional magnetized plasmas can store significant free energy in multi-component velocity distributions (VDFs), exhibited as temperature anisotropies and relative drifts between components or species. These instabilities can, in turn, impact the thermodynamics of the system in which they are embedded. Given the abundance of relative drifts in the solar wind, a quintessential collision-poor plasma in which VDFs can be measured in situ, we focus on oblique drift instability (ODI) in magnetically dominated plasmas driven by secondary ion populations. These instabilities convert ion drift energy into electromagnetic fluctuations which is subsequently transformed to heating of the proton core distribution. Motivated by Parker Solar Probe observations of typical plasma conditions, we show that this mechanism can regulate both the minimum attainable proton plasma β through proton heating and the maximum relative drift between alpha particles and core protons. ODI is shown to be able to alter the plasma kinetics at ion timescales — equivalent to MHz in most plasma devices — developing non-linear saturations during the lifetime of the plasma flow in a chamber. These results provide a laboratory-relevant, potentially testable, example of how kinetic instabilities mediate energy exchange, constrain distribution functions, and produce effective relaxation in weakly collisional multi-ion or multi-component plasmas.

Contributed Abstracts (Oral Presentations)

Magnetized Plasma Experiment on Inhomogeneous Mixing, Layering and Turbulence Spreading in an Evolving Vortex-Filament Lattice

R. Sydora (University of Alberta), T. Simala-Grant (University of Alberta), F. R. Ramirez (University of California, San Diego), P. H. Diamond (University of California, San Diego), S. Tripathi (University of California, Los Angeles)

In this work, we investigate layering and inhomogeneous mixing using a fluctuating cellular array consisting of magnetized vortex-filaments. This basic experiment addresses some of the key questions in layering and staircase dynamics, such as deviation from marginality and the percolation of density and thermal mixing in magnetized plasmas. A vortex-filament array is created in a large linear magnetized plasma (Large Plasma Device (LAPD) at UCLA) that is designed to model a system of interacting filaments. In order to create the vortex-filament lattice in the LAPD experiment, a smaller lanthanum hexaboride (LaB6) cathode source is placed at the opposite end of the device, relative to the main discharge LaB6 cathode. A carbon mask containing a patterned array of holes is placed in front of this smaller cathode. When this smaller cathode is biased to a mesh anode located in the front of the main discharge cathode, a stream of electrons flows through the lattice of holes in the mask and current channels are created in the pattern of the mask. The experiments were carried out using a patterned mask that consisted of four inner holes and eight outer holes, both arranged in a circular pattern. Through vortex-filament merging and ExB azimuthal flows, a two layered structure formed with a mixing layer interspersed. From an analysis of the results, three main processes have been observed with associated time scales. The first is a rapid mixing of the density and temperature within a vortex-filament with fluctuations driven by the local pressure gradient. The second process is the azimuthal merging of the vortex-filaments, evolving into two layers with spatial gradients in pressure and azimuthal flow velocity. The third, and slower process, is the interlayer cross-field transport where inner vortex-filaments interact with the outer ones and exchange material in a finger-like pattern. In order to further investigate the cross-field transport, a separate mask without the outer eight cells were removed and only the inner four vortex-filaments were present. The setup was used to quantify the observed amount of cross-field, outward turbulent spreading of the annular vortex-filament layer into the stable region that is absent of gradients.

Particle-in-Cell Simulation of the Parametric Decay Instability of Alfven Waves with Absorbing Boundary Conditions

V. Shankar (New Mexico Consortium), F. Li (New Mexico Consortium), S. Dorfman (Space Science Institute; University of California, Los Angeles), X. Fu (New Mexico Consortium; Los Alamos National Laboratory)

The Alfven wave parametric decay instability (PDI) facilitates energy transfer, plasma heating, and turbulence generation in space, astrophysical, and fusion plasmas. Most previous simulation studies of Alfven wave PDI have focused on kinetic ions under periodic boundary conditions. To investigate energy partitioning in a more realistic open system, we perform fully kinetic one-dimensional simulations (k-perp = 0) of low-beta Alfven wave PDI using absorbing wave boundary conditions. For beta = 5x10^-4 and a normalized wave amplitude dB/B0 = 0.01, approximately 92% of the pump-wave energy is transferred to the backward-propagating daughter Alfven wave, while the remainder is partitioned between electrons (~1-2%) and ions (~6-7%). In the parameter regime considered, ion and electron heating become significant only after the PDI reaches the nonlinear stage. The heating rates are approximately twice the linear PDI growth rate, consistent with the quadratic scaling of fluctuation energy with amplitude. Furthermore, numerical growth rates show good agreement with linear theory across a range of plasma and wave parameters. This work provides a foundation for future extension to finite k-perp waves in higher dimensions, where enhanced electron heating may occur.

Laboratory investigation of global oscillations and fast wave excitation in an eruptive arched magnetized plasma

G. Joshi (University of California, Los Angeles), S. Tripathi (University of California, Los Angeles)

The solar atmosphere is threaded by arched magnetic structures that support a wide variety of plasma waves and oscillations that significantly contribute to energy transport from the photosphere to the corona and influence the formation of magnetized plasma structures. Transverse oscillations of coronal loops, first imaged with TRACE, are now understood as standing fast magnetoacoustic (kink) waves. Coronal loops and laboratory-arched plasmas lack spatial uniformity; therefore, broad spectra of fast and torsional Alfven waves can resonantly couple to the global oscillations, leading to efficient energy transfer via continuum damping. This process is hypothesized to play a crucial role in coronal seismology and magnetic fusion plasmas. To gain better insight into this process, well-designed laboratory plasma experiments were conducted on the Solar Plasma Device (SPD) at UCLA. In our experiments, an eruptive arched plasma (beta ~ 10^-3, Lundquist number ~ 10^2-10^5, plasma radius/ion-gyroradius ~ 20, B ~ 1000 G at the footpoints, repetition rate 0.5 Hz) exhibited spontaneous global oscillations and a broad spectrum of fast waves. To gain better insight into this finding, we developed a novel technique to drive the arched plasma current at a fixed frequency (50-400 kHz), producing phase-locked oscillations and higher-resolution measurements of wave-induced fluctuations in the magnetic field, plasma density, and electron temperature in three dimensions. These measurements were complemented by spectral analysis of spontaneously destabilized fast waves. We plan to present results on the dispersion and damping characteristics of these waves.

Acknowledgments: This research is supported by the US Department of Energy under award number DE-SC0022153.

High-amplitude, saturated kink modes in toroidal plasmas with edge safety factor near the Kruskal-Shafranov limit

N. Hurst, A. F. Almagri, B. E. Chapman, D. J. Den Hartog, J. B. Flahavan, C. B. Forest, K. H. Franco, A. K. Keyhani, J. S. Sarff, C. R. Sovinec (University of Wisconsin - Madison)

In the region of edge safety factor 0 < q(a) < 2 between the reversed-field pinch and the tokamak, there exists a class of low-safety-factor toroidal plasmas that is difficult or impossible to access in most devices due to disruptive kink instabilities. In the Madison Symmetric Torus (MST), this regime can be accessed in steady (non-disruptive) conditions due to a thick, conductive, close-fitting wall with resistive wall time 800 ms, and a high-voltage, high-bandwidth, feedback-controlled power supply driving the plasma current. When q(a) is held fixed near unity (the Kruskal-Shafranov limit), very large amplitude, locked, saturated, helical kink modes are observed with edge n=1 amplitude up to 25% of the mean poloidal field. When q(a) is slightly above unity the modes have somewhat lower amplitude and rotate. We show that a strong resonant magnetic perturbation (RMP) with m=1 can be used to phase-lock the modes. Edge magnetic data are complemented by 11-chord interferometer measurements and internal magnetic probe data to reveal a narrow helical core with m/n=1/1 helicity in close proximity to the wall, likely surrounded by a large, diffuse island. Similar modes have been observed recently in RFX-mod and earlier in several other devices with q(a) ~ 1, but not in steady conditions. These results demonstrate steady operation of a toroidal plasma near the Kruskal-Shafranov limit, and show that plasmas with very large-amplitude modes can be sustained and controlled in the presence of a nearly ideal conducting boundary.

Work supported by the Wisconsin Plasma Physics Laboratory under US DOE grant DE-SC0018266 with major research instrumentation support from NSF grant PHY 1828159.

Driven Fermi Acceleration in a Ring of Reconnection X-Lines: Scaling to D-D and p-11B Energies

J. B. Worth (Independent Researcher), Madrid, Spain

Magnetic reconnection accelerates ions, but laboratory configurations that produce and sustain Fermi-type acceleration remain limited. We present a ring configuration in which eight simultaneous reconnection X-lines are driven around a closed loop with a central convergence region. Two-dimensional hybrid particle-in-cell simulations resolve the formation of the eight current sheets from an in-plane flux topology, the plasmoid coalescence cascade, and the ion energization. Energy-stratified tracking gives a discrete-step (“staircase”) signature consistent with a Fermi mechanism, with a measured per-encounter energy gain and an injection threshold near five Alfvénic energy units; undriven, the cascade self-terminates after roughly two encounters per particle. Periodically re-energizing the configuration at the natural period of its central compression cycle multiplies the accumulated per-particle acceleration by extending the active merger window rather than strengthening individual encounters, identifying encounter count as the controlling design variable; a stability limit

appears at high drive amplitude, where re-driving fuels asymmetric coalescence. Because the Alfvénic energy unit scales as B2/n, the energization maps to laboratory conditions: near 85 T the driven population reaches order 100 keV, low on the D-D cross section; near 150 T, 200 to 300 keV; at 300 T, where the unit is approximately 89 keV, the population approaches the 675 keV p-11B resonance within a few pulses. These are scaling estimates from collisionless 2D simulations; no rates or yields are claimed. Within that limitation, driven ring reconnection may offer an alternative route to fusion-relevant ion populations, generated and sustained by reconnection rather than by bulk heating or beam injection.

Measurement of the Alfven wave Parametric Decay Instability Growth Rate in the Laboratory

S. Dorfman (Space Science Institute; University of California, Los Angeles), F. Li (New Mexico Consortium), X. Fu (Los Alamos National Laboratory; New Mexico Consortium), S. Vincena (University of California, Los Angeles), P. Pribyl (University of California, Los Angeles), T. A. Carter (University of California, Los Angeles; Oak Ridge National Laboratory)

Alfven waves, a fundamental mode of magnetized plasmas, are ubiquitous in space and laboratory plasmas. The nonlinear behavior of these modes is thought to play a key role in important problems in space plasma, such as the heating of the solar corona and solar wind turbulence. In particular, theoretical predictions show that these Alfven waves may be unstable to various parametric instabilities, but space observations of these processes are limited. We demonstrate the first measurement of the Alfven wave parametric decay instability (PDI) growth rate. Experiments are conducted on the Large Plasma Device at UCLA in which a high amplitude dB/B0 ~ 0.7% pump Alfven wave is launched from one end of the device and a smaller seed Alfven wave is launched from the other side. When the frequency of the seed wave is chosen to match the backward wave expected from PDI, damping of the seed wave is reduced. We compare this reduction in damping to the theoretically expected PDI growth rate while accounting for acoustic mode damping. Results show excellent agreement between measurements, theoretical predictions, and hybrid simulations. This not only provides critical validation for PDI theories and simulations that could help interpret future space observations but also suggests a new way of studying similar nonlinear wave phenomena.

Experiments on Thermal Diffusion Waves: Transition from Ballistic to Diffusive Regime

T. Simala-Grant (University of Alberta), R. Sydora (University of Alberta), S. Karbashewski (TAE Technologies, Inc.), S. Tripathi (University of California, Los Angeles)

In this work, we investigate the transition from ballistic to diffusive thermal transport in a magnetized plasma pressure filament. Experiments were conducted at the Large Plasma Device (LAPD), UCLA where the filament is created using a cerium hexaboride (CeB6) crystal cathode source (3mm diameter) inserted into the plasma and is positioned to face the main discharge cathode. The small cathode source is heated and biased with respect to a mesh anode in front of the main cathode, which results in thermionic emission of electrons. This causes the formation of a filamentary structure with elevated temperature, which propagates along the magnetic field. The experiments are performed in the afterglow phase of the discharge when the small cathode source is activated. Previous studies have examined these filamentary structures in the cross-field plane, approximately 2 meters from the source, once the thermionically emitted electrons have thermalized. In this work, we use a probe which can translate along the axis of the magnetic field to within 15-20 centimeters of the crystal cathode (within the mean free path of a thermal electron) to observe the near-field regime before the thermionically emitted electrons have significantly thermalized. This allows for direct measurement of the transition from ballistic to diffusive electron thermal transport. Additionally, an AC bias voltage was added to the crystal cathode to drive thermal diffusion waves, which is studied in the near-field regime. The phase shift of the diffusion wave gives a direct measure of the thermal wave propagation which can be used to determine the electron thermal diffusivity. Preliminary results of the Langmuir probe analysis reveals the presence of an electron beam population that thermalizes beyond the estimated mean free path distance from the source. Results on the parallel electron thermal diffusivity in the transition region from ballistic to diffusive using the oscillating emissive source will be presented.

Magnetic Topology, Electron Acceleration, and the Emergence of Non-Maxwellian Electron Distributions in Laboratory and Space Plasmas

E. Kostadinova (Auburn University), S. Battles (Auburn University), J. Eskew (Auburn University), D. Orlov (University of California, San Diego)

Magnetic reconnection, turbulence, and magnetic island dynamics produce profound changes in magnetic topology that fundamentally alter electron diffusion and acceleration across laboratory and space plasmas. These processes drive plasmas away from thermodynamic equilibrium, resulting in anisotropic and non-Maxwellian distributions that cannot be adequately described by classical diffusion theory. Understanding how specific topological changes influence electron energization and the resulting distribution functions is therefore essential for predicting plasma behavior in fusion devices, planetary magnetospheres, and astrophysical environments. This presentation explores several complementary mechanisms of topology-driven electron acceleration across multiple plasma environments. In magnetically confined fusion plasmas, magnetic island bifurcation and island overlap cause electron acceleration through island contraction and stochastic processes. In Earth's magnetosphere, observations from the Magnetospheric Multiscale (MMS) mission demonstrate how contracting magnetic islands in both the turbulent magnetosheath and the magnetotail produce electron energization through different Fermi acceleration mechanisms. Specifically, dynamics of coherent structures in the magnetosheath cause bulk electrons to increase energy by an order of magnitude, while larger, longer-lived islands in the magnetotail preferentially interact with suprathermal electrons and accelerate them to relativistic energies. For both lab and space, we discuss how distinct magnetic configurations result in characteristic departures from Maxwellian equilibrium, including anisotropic, suprathermal, and power-law electron distributions.

Work supported by NSF-PHY-2440328, EPSCoR FTPP OIA-2148653, DE-SC0023061, DE-FG02-05ER54809.

Mapping Mirror Trapped Energetic Electron Activity with Injected Tungsten Pellets

J. Han (University of California, Los Angeles)

Energetic electrons produced by Electron Cyclotron Resonance Heating (ECRH) in a magnetic-mirror configuration on the Large Plasma Device (LAPD) can excite whistler waves and provide a controlled laboratory platform for studying energetic particle transport and wave-particle interactions. We present a minimally perturbative diagnostic that uses freely falling 2 mm tungsten pellets as transient, localized bremsstrahlung targets. X-ray pulses are measured with a NaI(Tl) scintillator detector, while fast-camera measurements are used to reconstruct and extrapolate the pellet trajectory through the energetic electron cloud. By varying the pellet's release time across highly reproducible discharges, localized x-ray measurements from separate shots are assembled into a spatial-temporal map of the energetic electron population. Results at different axial locations reveal a time dependent vertical asymmetry in detected x-ray signal. Separate magnetic measurements show no resolved pellet related suppression, enhancement, or shifts of the whistler-band activity, indicating that the pellet does not produce a detectable scale perturbation to the energetic electron population. The diagnostic provides a new approach for studying energetic electron dynamics in laboratory plasmas.

Phase-Space Resolved Measurements of Resonant Energy Transfer by Alfven Eigenmodes

J. Rueda-Rueda (UC Irvine), X. D. Du (General Atomics), W. W. Heidbrink (UC Irvine), G. G. Howes (University of Iowa), P. Oyola (PPPL), T. Barberis (PPPL), D. Liu (General Atomics), M. Van Zeeland (General Atomics), F. O. Khabanov (UW-Madison), K. J. Callahan (UC Irvine)

Resonant energy exchange between waves and particles is a fundamental concept in plasma physics. It was previously measured in satellite and basic laboratory experiments but has never been measured in the core of a magnetic fusion device. Now, thanks to DIII-D's diagnostic suite, resonant energy exchange between energetic particles and Alfven waves has been measured. The DIII-D imaging neutral particle analyzer (INPA) systems were upgraded with a new set of 16 channels with 350 kHz temporal resolution and good resolution in phase space (7 keV in energy and 10 cm in radius). These new capabilities capture the fluctuations of the confined population of energetic particles (EPs) both in the Alfvenic frequency range (~100 kHz usually for DIII-D) and the tearing- and fishbone-mode frequency range (~15 kHz usually for DIII-D). In both frequency ranges, fluctuations of a few percent over baseline signals are observed. The measured fluctuation of the confined EPs, together with the electric fields extracted from the density and temperature fluctuations, allows for the characterization of the energy exchanged between the EPs and the waves for the Toroidal Alfven Eigenmodes (TAEs). The secular energy exchange is mostly carried by the interaction of EP drift velocities with the perpendicular (poloidal) electric field; parallel and radial components are negligible. Comparison with ASCOT simulations using a mode structure predicted by the NOVA code agree with the observed energy exchange within the approximation of the calculation. ASCOT scans show that a magnetic fluctuation amplitude of dB/B ~ 2x10^-6 (corresponding to ~O(1 eV) temperature fluctuation) produces non-overlapping phase-space islands, which is compatible with coherent INPA signals; a mere ~3x increase causes island overlap and likely diffusive transport, explaining why large-amplitude TAEs observed in the ramp-up and other scenarios are invisible to the INPA fast channel.

Work supported by US DOE under DE-FC02-04ER54698, DE-SC0020337, DE-AC02-09CH11466, DE-SC0014664 and DE-SC0026430.

Machine learning-based surrogate models for energetic particle transport in tokamaks

Y. Ghai (ORNL), D. Spong (ORNL), J. Varela (UT, Austin), L. Garcia (U. Madrid, Spain)

We have developed machine learning-based surrogate models for energetic particle (EP) transport in ITER that are significantly faster and reasonably accurate compared to existing high-fidelity nonlinear simulation codes. Such reduced-order models are essential for optimizing ITER plasma scenarios, particularly for steady-state burning plasma operation, where confinement of fusion-born alpha particles is critical for sustained self-heating. Energetic alpha particles produced in D-T fusion reactions can resonantly interact with and destabilize Alfven eigenmodes (AEs), leading to enhanced EP transport and potential alpha losses. These losses reduce plasma self-heating efficiency and may increase heat loads on plasma-facing components. Accurately quantifying the impact of EP-driven transport on burning plasma performance remains a key challenge for reactor-scale devices such as ITER. Our approach begins with the generation of a comprehensive nonlinear simulation database using the FAR3d code for two ITER steady-state scenarios. These simulations capture EP-driven transport under varying equilibrium and profile conditions. The resulting dataset is used to train surrogate models of alpha particle flux using neural networks (NNs) and Gaussian Process (GP) regression. We assess and compare these models in terms of prediction accuracy, generalization capability, and associated confidence bounds. The development of this surrogate framework provides a computationally efficient tool for EP transport prediction in ITER and establishes a pathway toward constructing more general surrogate models applicable to reactor-level fusion devices beyond ITER. Such models can be incorporated into integrated modeling platforms, including the IPS-FASTRAN framework, to enable self-consistent evaluations of burn performance in next-generation burning plasma scenarios.

Nonlinear spectral back transfer limits the temporal coherency of zonal modes

R. Singh (UC San Diego), P. H. Diamond (UC San Diego)

Zonal modes are central to magnetic confinement because their radial shears regulate turbulence and transport. The effectiveness of turbulent regulation depends on the product of the shearing rate and its persistence time, quantified by the shearing Kubo number Ku. While the generation of these flows via the modulational instability of drift wave turbulence is well understood, the mechanisms limiting their persistence in collisionless regimes remain unresolved. In this paper, we demonstrate that nonlinear spectral back-transfer of free energy from zonal modes to turbulence sets the fundamental limit on the temporal coherency of the shearing field. Back-transfer events induce stochastic phase and amplitude scattering of zonal shear that limits its auto-coherence time. Using local gyrokinetic GENE simulations, we show that back-transfer is highly intermittent and occurs in bursts. This process defines a dynamic, saturated state where the birth of zonal flows (via forward transfer) and their death (via back-transfer of free energy to turbulence) coexist. As a result, zonal flows are not steady structures but are subject to a continuous, nonlinear birth-and-death cycle with a finite lifetime set by the back-transfer process. The probability distribution of the zonal free energy transfer is strongly non-Gaussian. Positive triangularity (PT) exhibits substantially higher kurtosis than negative triangularity (NT), reflecting the markedly more intermittent and heavy-tailed character of back-transfer bursts in PT. We find that NT plasmas exhibit significantly reduced back-transfer compared to PT. This suppression reduces the zonal shear phase decoherence, thereby increasing the shear auto-coherence time and the shearing Kubo number. Consequently, NT sustains more coherent and resilient shear layers that regulate turbulence more effectively despite possessing lower absolute zonal kinetic energy. Beyond providing a first-principles explanation for the NT advantage, these results identify back-transfer as a key nonlinear damping mechanism and suggest that it must be explicitly treated in reduced models of drift-wave zonal-flow turbulence.

This research was supported by U.S. DOE under Award No. DE-FG02-04ER54738.

Poster Presentations — Abstracts

Overview of FLARE Initial Operations

P. Shi (Princeton Plasma Physics Laboratory), J. Yoo, H. Ji, S. Avrutsky, S. Bose, E. Jung, K. Maheshwari, Y. Ren, A. Robbins, M. Yamada, Y. Zhang

The newly commissioned FLARE (Facility of LAboratory Reconnection Experiments) device is designed to primarily investigate multiple X-line reconnection regimes relevant to space and astrophysics plasmas. The first FLARE plasmas have been achieved in April 2025. We will introduce the main facility capability of its subsystems including capacitor banks, coils, vacuum, control and data acquisition systems, and key diagnostics including magnetic probe arrays, interferometer, ion tomography spectroscopy and Langmuir probes. The physical results obtained during initial operations regarding the achievable operation regimes and ongoing multiple X-line reconnection campaigns will be highlighted. Lastly, we will present future plans to operate FLARE as one DOE collaborative research user facility.

3D-Printed Magnetic Probe Array for High-Resolution Magnetic Reconnection Measurements in PHASMA

M. Pantor (West Virginia University), S. Yadav (West Virginia University), T. Rood (West Virginia University), E. Scime (West Virginia University)

Here we present a discussion of the design and calibration of the B-dot array in the PHAse Space MApping (PHASMA) experiment. The coils are wound on 3D printed, 4 x 4 x 4 mm alumina cube forms to reduce manufacturing time and improve mechanical strength over previously used materials. This more compact form factor facilitates high-frequency response of up to 20 MHz while providing higher spatial resolution for consistent detection of fine-scale magnetic field variations. Each probe coil consists of 60 turns of 40-AWG copper wire around a 2 mm inner core diameter. Two orthogonal windings enable independent B-dot measurements in the x and y directions. Calibration of the 18 sense coils is accomplished with a pulsed copper rod to determine voltage response for known B-dot values, with a final cross-talk correction performed to account for mutual inductance in the orthogonally wound pickup coils. Calibrated sense coils are installed in a motorized probe that traverses the radius of the PHASMA machine. Measurements confirm magnetic reconnection occurring between adjacent flux ropes of PHASMA, validating the performance of the improved diagnostic.

Laboratory characterization of two nonlinear Alfven wave processes relevant to imbalanced turbulence

M. Abler (Space Science Institute), S. Dorfman (Space Science Institute), C. H. K. Chen (Queen Mary University of London)

Imbalanced plasma turbulence (turbulence with a much higher flux of waves in one direction than another) is a fundamental process which occurs throughout the universe, including many regions of the solar wind. The ubiquity of imbalanced plasma turbulence makes understanding the underlying nonlinear interactions critical to our understanding of energy transport across scales throughout the heliosphere. We compare laboratory measurements of a novel Hall-driven interaction between co-propagating Alfven waves to theoretical predictions; we then further compare these measurements to a Hall-driven wave steepening process across a variety of plasma conditions to study the relative importance of each process for energy transfer at ion scales in a highly imbalanced regime.

Supported by DE-SC0023326, NSF SHINE 2401219.

Stereoscopic 3D Reconstruction of Debris and Dust Transport in DIII-D

J. Burzachiello (UC San Diego), C. Marini (UC San Diego), C. Lasnier (Lawrence Livermore National Laboratory), R. Smirnov (UC San Diego), D. Orlov (UC San Diego)

Macroscopic debris generated from plasma-facing components is routinely observed in magnetic confinement fusion devices. These Unidentified Fast Objects (UFOs) provide important information on plasma-material interactions but also pose potential threats to plasma performance and reliable reactor operation. This highlights the need for automated UFO detection, tracking, and classification capabilities in future fusion pilot plants. The DIII-D facility uses camera diagnostics extensively but currently lacks automated surveillance pipelines for three-dimensional reconstruction of UFO trajectories. Implementation of these tools would significantly improve analysis of macroscopic particle transport. We thus present a computer vision framework for automated detection of UFOs and three-dimensional trajectory reconstruction from multiple DIII-D cameras via stereoscopic triangulation. This currently leverages two fast framing visible light cameras in DIII-D but future work will incorporate data from additional sensors, such as infrared cameras. The reconstructed trajectories quantify particulate motion following release from plasma-facing components, facilitating statistical characterization of particle transport and validation of transport simulation codes (e.g., UEDGE-DUSTT). Our work provides new diagnostic capabilities for studying macroscopic particle transport in DIII-D.

Predicting Accessibility to the High-Beta-p Regime in Negative Triangularity Plasmas

F. Munguia-Wulftange (UC San Diego), T. Slendebroek (UC San Diego), J. McClenaghan (General Atomics), T. Neiser (General Atomics), S. Ding (General Atomics), J. M. Park (Oak Ridge National Laboratory), K. Kim (Oak Ridge National Laboratory), A. Garofalo (General Atomics), A. Marinoni (UC San Diego)

Predictive transport simulations indicate that access to the high-beta-p regime in negative triangularity (NT) plasmas on DIII-D is limited to low plasma current (Ip <= 0.9 MA), requires off-axis current drive provided by ECCD with auxiliary power in the range of 1.5-3.0 MW, and is achieved at a Greenwald fraction of fGW >~ 0.6. We study accessibility to the high-beta-p regime using NT plasmas on DIII-D to maximize core fusion performance while keeping power exhaust below damage thresholds. High-beta-p scenarios maximize energy confinement using internal transport barriers (ITBs) reaching H98,y2 ~ 1.5 at Greenwald fraction exceeding unity, while NT configurations reduce power exhaust constraints while maintaining H-mode confinement via weakening of turbulence. This computational study uses FUSE and its neural network transport surrogate TGLF-NN for rapid parameter exploration. A diverted NT DIII-D discharge serves as the base case for the scans, with variations in Zeff, auxiliary power, power deposition radius, plasma current, line-averaged density, core rotation, and confining magnetic field. Code improvements to FUSE supported this work, including changes to the plasma equilibrium and a direct reader for pyD3D outputs. A positive-triangularity high-beta-p discharge was reproduced with good accuracy at several times along the discharge trajectory (stored thermal energy within 9% on average), demonstrating the validity of the workflow. This work indicates that combining high-beta-p with NT plasmas can achieve high fusion performance with benign, ELM-free edges, going beyond the standard NT configuration.

Strong Nonlinear Alfven Wave Interactions in a Laboratory Plasma

C. Chen (Queen Mary University of London), S. Dorfman, S. Boldyrev, L. Franci, A. Mallet, M. Abler, S. Vincena, S. Greess, T. A. Carter

Alfven waves and their nonlinear interactions are ubiquitous in space and astrophysical plasmas, and are thought to play important roles in the dynamics of these systems, yet their nature remains to be fully understood. We describe experiments performed on the Large Plasma Device to study the nature of counter- and co-propagating wave interactions relevant to strong Alfvenic turbulence. Both interactions were found to produce a broad spectrum of nonlinear modes as a result of a dominant quadratic nonlinearity. The standard reduced MHD nonlinearity allows only counter-propagating interactions, however, a recently-proposed model shows that nonlinear Hall MHD terms that dominate at large imbalance and scale with the ion inertial length are present in both cases, which can explain the co-propagating interaction. The predictions of this model were tested in both the experiment and in 3D hybrid simulations, where the nonlinear mode growth rate and ion inertial scale dependence were found to be consistent. Finally, at the obtained interaction strengths, energy was seen to be transferred to progressively smaller perpendicular scales, consistent with a local cascade, although not a state of fully-developed turbulence. These results reveal and verify the mechanisms occurring in balanced and imbalanced turbulence (as well as other Alfvenic nonlinear processes), and represent an important step towards the generation of controlled Alfvenic turbulence in the laboratory.

Characterization of D thermal release, retention, and erosion of Cr in PISCES-RF

Z. Yu (UC San Diego), F. O'Neill (UC San Diego), M. I. Patino (UC San Diego), D. Nishijima (UC San Diego), G. Dose (General Atomics), Z. Popovic (General Atomics), J. Guterl (General Atomics), A. Marinoni (UC San Diego), G. R. Tynan (UC San Diego), M. J. Baldwin (UC San Diego)

Bulk chromium (Cr) is presented as a potential plasma-facing material (PFM) for next-generation magnetic fusion devices due to a moderately high melting point and thermal conductivity, low neutron activation, and favorable radiative properties. However, experimental data on chromium plasma-material interactions is limited. In this work, bulk Cr was exposed to high-flux deuterium (D) plasma in the PISCES-RF linear plasma device to investigate plasma-induced erosion and D retention. Because retained hydrogen isotopes contribute to fuel inventory buildup and negatively impact reactor operation, post-exposure thermal desorption spectroscopy (TDS) was used to characterize D retention and release behavior over a range of exposure temperatures and fluences, while erosion measurements quantified material loss under sustained plasma bombardment. The results demonstrate temperature- and fluence-dependent D retention behavior together with manageable erosion rates, providing new experimental insight into chromium plasma-material interactions and supporting its evaluation as a candidate plasma-facing material for future fusion reactors.

Collaborative research in the Magnetized Plasma Research Laboratory: Levitated particles to laser ablated plasmas

S. Chakraborty Thakur (Auburn University), E. Thomas Jr. (Auburn University), C. Royer (Auburn University), and the MPRL Team; B. Ramkorun (The University of the South, Sewanee); R. Kumar, R. Gopalakrishnan (University of Memphis); P. Ekanayaka, C. Wang (Mississippi State University); Z. White, G. Xu (University of Alabama in Huntsville)

The Magnetized Plasma Research Laboratory (MPRL) at Auburn University is a fundamental plasma science Collaborative Research Facility (CRF) to study low temperature plasmas and dusty plasmas influenced by strong magnetic fields and with unique capabilities to study the physics of magnetized dusty plasmas. In this presentation, we shall go over the existing facilities at MPRL that future users can have access to, as well as some examples of graduate student led collaborative projects which led to four PhD theses last year.