Magnetic reconnection converts magnetic energy into particle energization and heating, yet the kinetic mechanisms responsible for this conversion remain incompletely understood. In particular, the role of micro-instabilities and wave-particle interactions in mediating electron energization near reconnection separatrices is an open question. Controlled laboratory experiments provide a means to directly probe these processes and establish quantitative connections between wave activity and velocity-space dynamics. In this work, we present measurements from the PHAse Space MApping (PHASMA) experiment, where guide-field magnetic reconnection is produced in a reproducible, well-diagnosed plasma environment. Lower-hybrid drift waves (LHDWs) are observed in the separatrix region using a linear Langmuir probe array and multi-tip fluctuation probes, simultaneous measurements of the electron velocity distribution function (EVDF) using incoherence Thomson scattering (TS) show pronounced non-Maxwellian features, including transient bump-on-bulk structures. These features appear at velocities consistent with the parallel phase speed of the measured LHDWs, indicating resonant wave-particle coupling.

We investigate precursor soliton dynamics driven by finite-sized charged sources in a two-dimensional plasma using two-dimensional three-velocity particle-in-cell simulations with OSIRIS. The study examines how source geometry, charge density, vertical alignment, and external magnetic fields influence soliton formation, structure, and coherence. A single finite line source generates forward-propagating solitons with trailing wakes, while the precursors generated by two vertically aligned sources interact nonlinearly in a non-elastic manner, forming bow- or crescent-shaped fronts. An external magnetic field aligned with the dual-source motion suppresses transverse expansion, eliminating bow- or crescent-shaped fronts and producing narrow, axially elongated, field-aligned solitons with enhanced longitudinal coherence. Unequal source-to-plasma charge ratios induce asymmetric precursor solitons with tilted fronts and uneven downstream structures. Increasing source charge enhances soliton amplitude and propagation distance, whereas low electron-to-ion temperature ratios strengthen Landau damping and reduce coherence. Systematic variations in source shape-including triangular and V-shaped profiles-reveal that the number and orientation of leading slopes govern whether solitons appear one-sided, dual-sided, symmetric, or asymmetric. Scalability tests confirm predictable dependence on the ion-acoustic speed, and simulations under low-Earth-orbit conditions reveal stationary ("pinned") solitons. These results provide critical insights into how source configuration, plasma parameters, magnetic effects, and non-elastic interactions collectively shape nonlinear wakefields and debris-plasma interactions in laboratory and space plasmas.

We study the effect of ambient magnetic fields on ion-acoustic precursor solitons generated by a finite-sized charged object moving supersonically through a plasma using 2D3V particle-in-cell simulations. A magnetic field parallel to the source velocity ( B-x) couples with the out-of-plane velocity ( v(z)), producing inward transverse forces that suppress lateral expansion and accelerate forward propagation, forming compact, focused soliton structures. In-plane perpendicular ( B-y) and out-of-plane ( B-z) fields induce longitudinal and transverse suppression, with By opposing the disturbance and B-z generating a clockwise shear that inhibits propagation. Oblique fields tilt soliton structures along the field direction, resulting in asymmetric evolution. Comparison across plasma densities shows that soliton formation is primarily governed by the magnetization parameter, Omega(c)/omega(p), where Omega(c) is the cyclotron frequency and omega p is the plasma frequency for ions and electrons. These effects associated with the magnetic field orientation and strength provide new insights into the dynamics of precursor solitons that can be tested in laboratory experiments and can prove useful in space plasma applications.

The study of plasma dynamics at the kinetic scale (scales smaller than the particle gyroradius) requires detailed measurements of the complete phase space (3D position and 3D velocity) of the plasma constituents. In space plasmas, this goal is readily accomplished with instruments aboard spacecraft whose dimensions are typically smaller than the Debye length and the electron gyroradius. In the laboratory, phase space measurements at the electron gyroradius scale are much more challenging. The PHAse Space MApping (PHASMA) experiment employs non-perturbative, optical diagnostics for multi-dimensional ion velocity distribution function, electron velocity distribution function, magnetic field, and turbulence measurements at the kinetic scale. A primary scientific goal of PHASMA is to explore the processes whereby energy stored in magnetic fields is converted into kinetic energy of the ions and electrons. Over the past few decades, there has been considerable progress in developing theoretical models of magnetic reconnection, the process responsible for the energy conversion. The models are distinguishable by their predictions of electron thermal anisotropy and spatial structure of heating throughout the reconnection region. 3D electron phase space measurements in PHASMA during electron-only reconnection have confirmed theoretical predictions of models in which the primary mechanism for electron heating is the parallel electric field that arises during electron-only reconnection. These measurements along with measurements of suprathermal electron generation during reconnection will be described and discussed.

Collisions between ions and neutral atoms or molecules regulate the electrical conductivity in Earth's ionosphere and therefore play an important role in closing the magnetospheric current system. Here, we present measurements of the total collision cross-sections of and ions in the energy range from 1 to 7 keV, scattered from mixtures of different species of neutrals (, and ). Cross sections for on the individual target species are well known and were used to validate the experimental process that was then used to measure the cross sections in mixtures of the target species. The measurements were conducted in the Space and Beam Experimental Device (SABER), which includes an ion gun to accelerate selected ion species and a movable Faraday cup that enables two different methods to measure the total cross section. The total scattering cross section of a gas mixture is commonly approximated as a weighted sum of the cross sections of the individual species, based on their respective concentrations. However, our findings indicate that the total scattering cross-section for target gas mixtures is not always equal to the proportional sum of the individual cross-sections of the mixture components.

This study presents the experimental observation of precursor soliton excitation in a flowing plasma. Previous theoretical investigations have predicted that when a charged object moves through a plasma at a velocity exceeding a certain critical threshold, it can induce the periodic generation of ion-acoustic solitons. These solitons form ahead of the object and travel faster than it, effectively serving as early indicators of the object’s presence. A number of experiments have been carried out to excite solitons in a dusty plasma medium. In experiments reported here are performed in the Space Plasma Simulation Chamber (SPSC) at the Naval Research Laboratory (NRL). A series of biased rings placed at the end of the SPSC are used to create a radial electric field along with an applied axial magnetic field resulting in an azimuthal plasma flow. The inferred flow speed (assuming the driven flow is the $\mathrm{E} \times \mathrm{B}$ speed) changes in a wide range by different combinations of radial electric fields and axial magnetic fields. A debris object is placed in the chamber such that plasma flows over it. Under these conditions, we observe the regular generation of precursor solitons propagating upstream, against the direction of the plasma flow as shown in Fig. 1. The ability to detect such solitons in space environments could offer a novel method for identifying and tracking small-scale space debris in the Earth’s ionosphere and lower magnetosphere.

Atomic layer etching (ALE) of SiO2 using fluorocarbon plasmas offers a pathway toward lowdamage, highly controllable dielectric processing, but practical implementation in conventional ICP-RIE tools remains challenging. In fluorocarbon-based ALE, the modification step forms a non-self-limiting fluorocarbon (FC) passivation layer, and the activation step must remove this layer to enable controlled etching. As a result, multiple regimes are expected: FC accumulation (etch suppression), stochastic quasi-ALE (partial FC removal with unstable etch-per-cycle), and FC depletion (ion-driven RIE-like erosion). While these regimes have been proposed theoretically and observed in specialized reactors, their boundaries in standard room-temperature plasma tools are not well established.

From the near-Earth solar wind to the intracluster medium of galaxy clusters, collisionless, high-beta, magnetized plasmas pervade our universe. Energy and momentum transport from large-scale fields and flows to small-scale motions of plasma particles is ubiquitous in these systems, but a full picture of the underlying physical mechanisms remains elusive. The transfer is often mediated by a turbulent cascade of Alfv & eacute;nic fluctuations as well as a variety of kinetic instabilities; these processes tend to be multi-scale and/or multi-dimensional, which makes them difficult to study using spacecraft missions and numerical simulations alone. Meanwhile, existing laboratory devices struggle to produce the collisionless, high ion beta ( $\beta _i \gtrsim 1$ ), magnetized plasmas across the range of scales necessary to address these problems. As envisioned in recent community planning documents, it is therefore important to build a next generation laboratory facility to create a $\beta _i \gtrsim 1$ , collisionless, magnetized plasma in the laboratory for the first time. A working group has been formed and is actively defining the necessary technical requirements to move the facility towards a construction-ready state. Recent progress includes the development of target parameters and diagnostic requirements as well as the identification of a need for source-target device geometry. As the working group is already leading to new synergies across the community, we anticipate a broad community of users funded by a variety of federal agencies (including National Aeronautics and Space Administration, Department of Energy and National Science Foundation) to make copious use of the future facility.

Charged-particle acceleration – a signature of the plasma phenomenon known as magnetic reconnection - has been studied in extensive detail with West Virginia University's PHAse Space MApping (PHASMA) experiment. These studies were conducted with a retarding field energy analyzer (RFEA) built to measure electron energy distribution functions (EEDFs) and to identify localized zones of energetic electron production. The results show a guide-field dependent spatio-temporal distribution of energetic electrons, which consist of field-aligned electron beams at locations with high-energy currents.

Accurate measurement of magnetic field strengths is critical in many plasma environments, ranging from astrophysical systems to fusion energy research. In this work, a non-perturbative laser-based optical diagnostic known as quantum beat spectroscopy is demonstrated to be good alternative for measuring the magnetic field strength in low-pressure laboratory plasmas. The technique is investigated using both ns and fs pulsed lasers in an argon plasma. Preliminary results for a helium plasma are also given. Zeeman-split J = 1 electron states with transitions from metastable states were identified and tested for neutral argon (2P1/2o)4p 2[1/2] and neutral helium 1s3p 1P1o. Magnetic fields are measured with sub-Gauss precision at near single laser pulse acquisition rates.

Excitation of precursor solitons in a flowing plasma is reported. Theoretical studies have suggested that when a charged object moves through a plasma at a speed higher than a threshold, it triggers the periodic formation of ion acoustic solitons. These solitons emerge ahead of the object and propagate faster than the object, thereby giving early warning of the object's approach. In experiments reported here, an E × B flow is created in a plasma that passes over an object to which a surface charge is applied with a square wave voltage pulse. We observe the periodic excitation of precursor solitons that propagate in the upstream direction of the flow. Detection of these solitons in space may enable the tracking of small-scale space debris in the Earth's ionosphere and lower magnetosphere.

This study employs a fast camera with frame rates up to 900,000 fps to measure the transfer of energy across spatial scales in helicon source plasmas and during flux rope mergers and the measurement of azimuthal mode structures in helicon plasmas. By extracting pixel-scale dispersion relations and power spectral density (PSD) measurements, we measure the details of turbulent wave modes and energy distribution across a broad range of spatial scales within the plasma. We confirm the presence of drift waves in helicon plasmas, as well as the existence of strong dissipation regions in the PSD at electron skin depth scales for both helicon and flux rope merger experiments. This approach overcomes many limitations of conventional probes, providing high spatial and temporal resolution, without perturbing the plasma.

Orbital debris, defined as any anthropogenic space object orbiting Earth that no longer serves any useful purpose, poses a risk to all space missions. Due to the dynamic nature of the near-Earth space environment, predicting the trajectory of the debris is extremely difficult, necessitating persistent monitoring. While debris larger than 10 cm can be detected and tracked, smaller debris cannot be tracked using current capabilities. Debris that is too small to track, often termed “lethal non-trackable debris” (LNT), can create significant damage to spacecraft and jeopardize space missions. The detection, tracking, and characterization of LNT space debris would support the safe operation of valuable space assets worldwide.

Following the First Helicon Plasma Physics and Applications (HPPA) Workshop, which was held in 2021 remotely due to COVID-19, this Second HPPA Workshop aimed to establish a regular onsite meeting for the specific field of helicon plasma. It was held on 11–14 April 2024 in Chongqing, China, and organized by Chongqing University and co-organized by Southwestern Institute of Physics. This workshop attracted 160 registrations, 140 onsite participants, and 27,000 number of views through the live streaming online. The 48 presentations covered most topics about helicon plasma, e.g., from fundamental physics to various applications. This paper summarizes the important findings of fundamental physics research, progresses on source and diagnostic developments, and new explorations of laboratory and industrial applications, together with enlightening comments and perspectives regarding future research for this field. It serves as a valuable reference for the helicon research community and other relevant fields.

Over the past decade, theoretical studies by Sen et al. [1] have proposed that when charged object moves through a plasma at a speed larger than the ion acoustic speed, it generates ion acoustic solitons. The solitons are excited in front of the moving object and propagate faster than the object. This novel effect has possible application in tracking small sized space debris in the Earth’s ionosphere. To explore this application, Truitt and Hartzell [2] investigated the excitation of precursor soliton for the plasma conditions expected in low Earth orbit (LEO), i.e. 200-1000 Km. The first experimental demonstration of the generation of a precursor soliton in a flowing dusty plasma over a charged object was reported by Jaiswal et al. [3]. Recently, Kumar et al. [4] demonstrated the excitation of two and three-dimensional precursor solitons in a flowing dusty plasma. In this work, we report experimental studies looking for precursor solitons in a flowing plasma. The experiments are performed in the Space Plasma Simulation Chamber (SPSC) at the Naval Research Laboratory (NRL). A series of biased rings placed at the end of the SPSC are used to create a radial electric field along with an applied axial magnetic field resulting in an azimuthal plasma flow. The inferred flow speed (based assuming the driven flow is the E x B speed) changes from a subsonic to a supersonic value by different combinations of radial electric fields and axial magnetic fields. A debris object is placed in the chamber such that plasma flows past over it. The debris is biased with a square voltage pulse.

An array of compact, high-bandwidth (>200 MHz) and low-cost optical photodiodes has been developed and implemented on the PHASe MApping (PHASMA) experiment. Using purpose-built electronics, an array of 16 photodetectors was constructed and used to monitor broadband (1–5 MHz) fluctuations in light intensity emitted by flux ropes undergoing electron-only magnetic reconnection. These measurements reveal a swath of oscillatory behavior, including wave propagation inward toward the diffusion region at approximately the local electron Alfvén speed. Custom 3D-printed collection optics and mounting hardware allow quick reconfiguration of the array for radial or axial measurements. The electronics design is flexible enough to be used with other current-sourcing transducers, such as avalanche photodiodes; silicon photomultipliers; and infrared, x-ray, and UV photodiodes. A noise-rejecting electrical layout allows for low-noise operation close to pulsed plasma discharges. A 16-channel, 64-pixel tomographic array was constructed and initial reconstructions are presented.

Experiments in helicon sources have shown that more efficient wave-plasma coupling (and therefore higher temperatures and densities) occurs when the antenna excites the m = +1 (i.e., right-hand polarized) helicon wave. Here we present ion and electron temperature measurements, and electron density measurements, on both sides of a helical antenna in a helicon source as a function of antenna frequency and magnetic field strength. These measurements were obtained for two different background magnetic field directions. For both field directions, significant ion heating at frequencies near the lower hybrid frequency was observed. A remarkable and unexpected density difference (~ 2 orders of magnitude) was observed in the downstream region when the magnetic field direction was reversed. Radial wave field profiles and phase measurements were measured to identify the polarization of the helicon waves for both background magnetic field directions, on both sides of the antenna. It was confirmed that the region of hotter ion temperature and higher plasma density were on the m = +1 side of the antenna.

A multi-dimensional incoherent Thomson scattering diagnostic system capable of measuring electron temperature anisotropies at the level of the electron velocity distribution function (EVDF) is implemented on the PHAse Space MApping facility to investigate electron energization mechanisms during magnetic reconnection. This system incorporates two injection paths (perpendicular and parallel to the axial magnetic field) and two collection paths, providing four independent EVDF measurements along four velocity space directions. For strongly magnetized electrons, a 3D EVDF comprised of two characteristic electron temperatures perpendicular and parallel to the local magnetic field line is reconstructed from the four measured EVDFs. Validation of isotropic electrons in a single magnetic flux rope and a steady-state helicon plasma is presented.

Remotely situated diagnostics are desirable for fusion devices since electromagnetic interference (EMI) and radiation are becoming more of an issue as the field moves into an era of burning plasmas. Specifically, diagnostics capable of measuring absolute neutral densities are critical to controlling fueling rates and maintaining transport barriers in the plasma edge. Two-photon absorption laser induced fluorescence (TALIF) non-perturbatively measures spatially resolved neutral velocity distribution functions (NVDF) to determine absolute, ground state neutral densities of hydrogenic species if the measurements are calibrated with a noble gas, commonly krypton or xenon. However, TALIF injects deep ultraviolet light (~205 nm) that is easily absorbed in air and difficult to couple into vacuum chambers. These limitations restrict the location of the TALIF systems to regions of potentially high EMI and eliminate use of fibers and common optical materials. A three-photon laser induced fluorescence (3pLIF) technique has the potential to provide similar measurements, while injecting a more near-visible wavelength, 300–308 nm, alleviating the requirements for special optics, allowing the use of high-power fibers, and allows the laser system to be situated further from the intense EMI environment. In this work, a Quantel Qscan pulsed dye laser produces ~300 nm light over ~7 ns at a repetition of 10 Hz to excite ground state krypton through three-photon excitation. Fluorescence is fiber coupled to detecting electronics. Here krypton spectral lineshapes measured using 3pLIF are presented. The measured lineshapes are unexpectedly broad and blue-shifted. Possible mechanisms responsible for these spectral features are discussed.

Laser-induced fluorescence diagnostics are used routinely for measurements of ion velocity distribution functions (IVDFs) for a wide variety of gases used in processing plasmas. This work explores the viability of a related technique known as two photon absorption laser-induced fluorescence (TALIF) for ions produced in a 1-Torr chlorine reference cell placed in an Evenson microwave cavity driven at 2.45 GHz. Common diagnostic techniques for processing plasmas lack spatial localization (e.g., passive optical emission spectroscopy) or are perturbative to the system (e.g., Langmuir probes). TALIF is a spatially localized, non-perturbative diagnostic suitable for diagnosing a range of plasmas but is rarely implemented on processing plasma systems due to their low ion density production and limited optical access. When performed with a confocal approach, TALIF requires only a single point of optical access making it ideal for probing processing plasma reactors. Initial passive spectroscopy measurements of the chlorine discharge used in this work show sufficient ion production inside the microwave cavity region. This work provides a brief introduction to the TALIF technique and explores its applicability on chlorine ions used for processing-relevant plasmas.