The three enduring paradoxes of tokamak physics are: 1. Good neoclassical conductivity contradicts the anomalously high transport of particles. 2. Particle density has maximum at the core, while the main particle source is near the edge. 3. Improvement of confinement by plasma current ramp-down and thus weakening of the poloidal magnetic field near the edge. While resolving these paradoxes is imperative for establishing a predictive theory of tokamaks, limited discussions on these complexities exist in the literature. The authors suggest that resolution of the first paradox is a coexistence of regular and chaotic trajectories of particles; resolution of the second paradox is turbulent equipartition of particles and a decrease of the specific poloidal volume to the center; resolution of the third paradox is an increase of the specific poloidal volume near the edge, resulting in the expansion of plasma, lowered density and temperature, consequently reducing the heat flux.
Particle accelerators require energetic positron sources to satisfy next generation requirements. Positrons are currently sourced using solid targets. Here, we consider the collision of an energetic electron beam (≥5 GeV) with an intense laser pulse (2×1022 Wcm−2) as a potential positron beam source. Prolific pair production occurs due to strong field quantum electrodynamic effects in the interaction resulting in a high positron yield. Through the decoupling of initial and final positron energy, positrons converge towards the same average energy regardless of the initial energy they are produced at. Through 1D particle-in-cell simulations we demonstrate that positron beams with 200MeV average energy may be generated through non-linear Breit-Wheeler pair production. By reducing the electron beam energy, the energy spread of resulting positron beam decreases by up to 38% while the final positron energy remains constant. Comparison between the simulations and the analytical model show that the simulated positrons agree with the model within 4%. The low energy spread and low shot-to-shot variation in energy make these beams ideal for injection into particle accelerators.
Research on atmospheric-pressure plasma jets (APPJs) generated using argon (Ar), helium (He), and their oxygen (O₂) mixtures has been widely reported; however, direct comparisons of optical emission characteristics under identical operating conditions remain scarce, particularly for sinusoidal AC excitation. Most previous studies have focused on radio-frequency or pulsed discharges, which do not fully represent excitation modes relevant to stable AC-driven jets. In this work, the optical emission characteristics of APPJs operated in Ar, He, and their O₂ mixtures are systematically investigated using a dielectric barrier discharge configuration driven by a high-frequency sinusoidal power source. The relative intensities of emissive species, including Ar I, He I, O I, OH, and N₂(SPS)/N₂⁺(FNS), were analyzed in the ambient region downstream of the plasma plume using optical emission spectroscopy (OES). Electrical measurements were simultaneously performed to support the interpretation of the optical emission trends. Notable intensity variations were identified for Ar I (650–850 nm), He I (725 nm), O I (777 nm), OH (307 nm, A²Σ⁺→X²Π), and N₂(SPS)/N₂⁺(FNS) bands (335–405 nm), indicating that O₂ addition significantly modifies excited-species populations and plasma chemistry. The addition of O₂ to Ar or He favors the excitation of the N₂(SPS) band. In the Ar plasma, a small amount of O₂ slightly increases the Ar I emission, whereas higher O₂ concentrations progressively suppress Ar I, OH(A–X), and O I emissions. In the He plasma, a small O₂ addition slightly decreases OH emission while enhancing atomic oxygen excitation, resulting in a moderate increase in the O I (777 nm) line at low O₂ flow rates, whereas He I emission remains relatively stable. The results represent time-integrated optical emission from the plasma effluent under ambient conditions and are interpreted in a comparative manner under identical operating parameters.
Disinfection and sterilization are essential processes in healthcare determined by the level of contact between medical devices and the human body. While disinfection eliminates most pathogenic microorganisms, sterilization ensures the complete destruction of all microbial life, including spores. Conventional sterilization techniques such as steam autoclaving and ethylene oxide (EtO) gas sterilization are widely used; however, they present limitations when applied to temperature-sensitive medical devices such as catheters and fiber-optic instruments. Additionally, EtO sterilization involves long cycle times and raises environmental and safety concerns.Low-temperature plasma sterilization has emerged as a promising alternative, but existing systems typically rely on radio-frequency (RF) power sources, which are costly, complex, and often imported, making maintenance challenging. To address these limitations, this study presents the design and development of an indigenously built pulsed plasma sterilizer. The system incorporates a variable high-voltage pulsed power supply (PHVPS) integrated with a controlled vacuum environment to generate effective plasma for sterilization.The performance of the developed system was evaluated using chemical indicators in accordance with the ANSI/AAMI/ISO 11140-1:2014 standard. Both simulation and experimental analyses were conducted to validate system functionality and sterilization efficacy.The results demonstrate stable plasma generation at 200–400 Pa and 300–400 V using a pulsed high-voltage power supply operating at 10–30 kHz. A base pressure of 3.6 Pa was achieved within 4–5 min, and chemical indicator testing confirmed repeatable sterilization performance. The developed system satisfies the functional requirements for low-temperature sterilization while providing a cost-effective and scalable alternative to RF-based plasma sterilizers. The key novelty lies in replacing conventional RF plasma generation and impedance matching networks with a simplified indigenous pulsed architecture.
Laser-produced plasma expansion into vacuum involves a dynamic transition from collisional hydrodynamics to nonlocal transport as microscopic relaxation scales approach macroscopic density gradients. We employ a fully three-dimensional hybrid kinetic–fluid model to resolve this transition self-consistently under near-solid initial density conditions on nanosecond timescales. A time-dependent expansion–collisionality parameter, χ(t), is introduced to quantify scale separation. The condition χ ≈ 1 marks the onset of nonlocal electron transport and coincides with a change in electron cooling rate and the formation of a localized electrostatic double layer at the plume front. This structure drives cumulative ambipolar ion acceleration, producing a suprathermal tail extending to ∼120 eV. Three-dimensional expansion enhances adiabatic cooling by 20–30% relative to one-dimensional predictions and advances the transport transition in time, demonstrating the fundamental role of geometry. Quantitative comparison with interferometry and time-of-flight diagnostics shows agreement within experimental uncertainty (normalized RMSE < 10%). These results provide a unified kinetic–fluid description linking thermodynamic evolution, transport ordering, and double-layer–mediated ion acceleration in expanding laser plasmas.
We revisit radiative transfer in purely absorbing binary stochastic mixtures. To this end, benchmark results of the ensemble-averaged specific radiation intensity for one-dimensional (1D) arbitrary mixtures are presented based on the renewal theory, which can quantitatively reproduce high-accuracy numerical simulation data. We are for the first time to derive the analytical solutions for periodic statistics, which precisely follow the benchmarks in cases considered. Furthermore, we propose a delta-function expansion method to approximate the statistical distributions for non-Markovian mixtures, which successfully explains the remarkable transition of oscillating structures from periodic to block statistics. The accuracy of present approximate method is compared to the Markov-based correction approach and benchmark solutions in several typical cases. Our results provide new understanding on absorption-dominated radiative transfer in binary stochastic mixtures.
We verify a recently-developed nonperturbative guiding center formalism to charged particle dynamics in fields with two-parameter continuous symmetry groups. This entails finding exact constants of motion, valid in the nonperturbative regime, that agree with Kruskal’s adiabatic invariant series to all orders in the perturbative regime, when the field scale length is large compared with a typical gyroradius. We demonstrate that the nonperturbative guiding center model makes exact predictions in these cases, even though it eliminates the cyclotron timescale, thereby establishing a theoretical baseline for performance of the nonperturbative formalism.
This study examines how photoemission affects the differential charging of satellite structures during the transition between eclipse and sunlit phases under a turbulent plasma environment. The absence and presence of solar flux during an eclipse and during sunlight conditions induce a positive potential leading to differential charging between sunlit and shaded areas. Despite this, spacecraft can still achieve a significant negative potential in sunlight conditions. The presented investigation focuses on the primary photoemission effect of surface reflective properties through analytical methods and numerical simulations. The disparity in charging generates an electric field on shaded surfaces that extends to sunlit sides, forming a potential barrier that curtails photoemission. This paper is focused on the effect of direct consequences of photoemission on satellite charging in both normal and worst-case GEO environmental conditions. The obtained results will be helpful in satellite design and operation under challenging space conditions.
We establish the temporal analogue of transition radiation, when space boundary effects are ignored, and only temporal transitions are considered. We study the radiation spectrum emitted by a bunch of charged particles when they move in a medium where the refractive index abruptly changes in time. We apply it to the case of vacuum-plasma transitions due, for instance, to the sudden ionization of a neutral gas, and determine the spectral range of expected radiation. The case of Rydberg ultracold plasmas is also considered, where the spectral range of emitted radiation is considerably enhanced.
Estimation of the time scale of differential charging between adjacent metal–dielectric surfaces on a Geosynchronous Earth Orbit (GEO) satellite is crucial due to its potential to trigger Electrostatic Discharge (ESD) events. Since the capacitance between spacecraft surfaces strongly influences the dynamics of differential charging, this work investigates the transient variation of spacecraft body potential by developing a capacitance-based circuit model. The spacecraft is represented by a simplified geometric structure consisting of a metallic cuboid with two co-planar metallic plates, while a thin dielectric layer placed over the plates is used to emulate the cover glass of a solar array. The coupling capacitance between the metallic cuboid and the dielectric layer is evaluated using a Method of Moments (MoM) formulation derived from the electrostatic boundary conditions on conductor and dielectric interfaces. Using the computed capacitance values, the temporal evolution of the spacecraft body potential is analyzed under Maxwellian plasma environments representative of GEO conditions. The study further investigates the influence of induced electron emission processes on the enhancement of differential charging between the solar array cover glass and the spacecraft body. To capture realistic operational conditions, the spacecraft material is modeled as aluminium (Al) in two representative surface states: oxidized Al corresponding to the Beginning of Life (BOL) condition and Al with a thin carbon-rich contamination layer representing the End of Life (EOL) condition. The analysis provides insight into how surface conditions, secondary electron emission characteristics, and electrostatic coupling between dielectric and conducting surfaces affect the magnitude and time scale of differential charging, thereby contributing to improved prediction of ESD risks for spacecraft operating in GEO plasma environments.
If fusion energy is commercialized and deployed by 2040 and then scaled up quickly, it has the potential to significantly mitigate the effects of climate change and meet the growing global energy demand. One of the key factors in the speed of deployment is the licensing and regulatory framework, which can accelerate or impede deployment. Fortunately, this is a factor that can be addressed well in advance, but the time to do so is now. In fact, the United States, Germany, Japan, and the United Kingdom have realized this and are planning to regulate fusion power plants differently from fission power plants, outside of nuclear law. As is the case in other areas of licensing and regulation, this process will begin with national frameworks and progress through a phase of harmonization, potentially culminating in a global framework. However, if the destination is clear, why take the long way around? This paper argues for starting with a global licensing and regulation framework for fusion energy now. It shows examples from other fields that demonstrate the feasibility of this approach and develops a seven-step plan for such a framework.
Motivated by evidence for core-edge coupling in the form of double-peaked fishbone-like low-frequency modes (≲20kHz) in KSTAR, which exhibit synchronized Alfvénic activity both in the central core and near the plasma edge Lee et al. (2023) , we study the nonlocal response of a tokamak plasma in a visco-resistive full MHD simulation model using the code MEGA. The waves are driven by an internal “antenna” that is localized both radially and azimuthally in the poloidal (R,z) plane and has a sinusoidal form exp(inζ−iωt) with Fourier mode number n=±1 in the toroidal angle ζ and fixed angular frequency ω in time t. By flattening the safety factor profile q(r) at suitable locations in the minor radius r, we created plateaus in the low-frequency Alfvén continua that act as wave “receivers”. First, we confirm that such continuum plateaus respond with a coherent quasi-mode even when the driving antenna is located at a distant radius. Second, by varying the antenna location, we confirm the expectation of inward drive being more efficient than outward drive, which we attribute to volumetric focusing. Third, we find that the central core also responds well at frequencies below the central Alfvénic continuum plateau, which could facilitate chirping. Our results show that a core-localized low-frequency response does not necessarily require core-localized drive nor an exactly matching continuum, but may be driven from the edge and sub-resonantly. It remains to be seen to what extent the examined effects play a role in double-peaked fishbone-like activity. Other possible contributing mechanisms are discussed to motivate further study. Our analyses also elucidate the mode structure formation process, from transients to quasi- or eigenmodes, here in the realm of MHD, and to be followed by a verification study against kinetic models.
Double-peaked fishbone events across multiple KSTAR discharges are investigated. The normalized beta βN and the edge safety factor q95 under which the fishbones appear vary depending on the presence and form of external magnetic perturbations. The fishbone strength is closely related to βN and q95: as βN increases and q95 decreases, the fishbone strength increases. Measured fishbone-relevant signals are decomposed into amplitude envelope and phase components in the temporal domain, which are analyzed separately. In terms of the amplitude envelope component, the edge electron temperature fluctuation T̃eEdge becomes more correlated with the poloidal magnetic fluctuation Ḃθ compared to the core electron temperature fluctuation T̃eCore as fishbone strength increases. In terms of the phase component, the phase of T̃eEdge precedes the phase of T̃eCore except in the case of very weak fishbones where the phase relations are inconclusive due to weak fishbone activity at the edge plasma, which is comparable to background fluctuations. The investigation suggests the possibility that the edge activity is not a mere side effect of the core activity, but could play an active role.
The generalized (2+1)-dimensional Caudrey–Dodd–Gibbon–Kotera–Sawada (CDGKS) model is investigated to understand nonlinear coherent structures and their intricate interactions. By employing Hirota’s bilinear scheme in combination with symbolic computation, we derive a spectrum of exact multi-wave solutions, encompassing two-, three-, and four-soliton configurations along with their extended forms. Particular attention is devoted to localized–periodic hybrid behaviors, highlighting the interactions between lump solutions, stripe solitons, periodic waves, and Jacobi elliptic structures. The study uncovers rich dynamical phenomena, including lump–soliton collisions, lump–periodic fusion–fission events, and the emergence of Kuznetsov–Ma breathers and rogue-wave patterns. Sensitivity analysis reveals a pronounced dependence of solution dynamics on initial conditions, whereas multistability confirms the coexistence of multiple attractors under identical parameter regimes. These contributions broaden the known solution space of the generalized CDGKS model and deepen the understanding of higher-dimensional integrable systems. Beyond theoretical insights, the results have potential relevance to applications in plasma physics, fluid dynamics, and other nonlinear physical contexts.
Turbulent flow in neutral fluids and fusion plasmas is known to have many commonalities, one example being the application of energy and enstrophy cascades. In this review, we discuss a cyclic process which may also be common to both fluids and plasmas: this includes exact coherent states (or magnetic islands), Reynolds stress-driven (zonal) flows and internal interface layers (or internal transport barriers). We connect this picture to the broader literature on layered “staircase” states in both magnetized plasmas and stratified/rotating fluids, where sharp interfaces separate well-mixed regions. We briefly review the current understanding of internal interface layers in fluids, summarize a minimal set of driving/damping relations for mean flows and transport suppression, and discuss open questions and possible research directions. The main objective is to create awareness of shared mechanisms to motivate further interdisciplinary research in this field, by both the fluid mechanics and plasma physics communities.
We investigate the underexplored multiphoton ionization regime of resonantly enhanced harmonic generation in gallium laser-ablation plumes. Resonant harmonics generate quasi-monochromatic extreme ultraviolet radiation with a pronounced coherent intensity enhancement. In this experimental study, we systematically examine high-order harmonic generation yield by independently varying the energies of the pre-pulse, which forms the laser-ablation plume, and the main pulse, which drives the harmonic emission. This approach enables precise evaluation of how each pulse contributes to the overall efficiency of resonant harmonic generation. Throughout this study, we identify the optimal conditions for maximizing the generation efficiency of gallium resonant harmonics driven by a 400 nm laser. Our results demonstrate an effective method for generating intense, quasi-monochromatic femtosecond extreme ultraviolet radiation and offer valuable insight into the role of autoionizing resonances within the multiphoton ionization regime.
Kelvin–Helmholtz instability (KHI) is a shear flow-driven instability that imposes important changes in the macroscopic dynamics of some space and laboratory magnetized plasmas, such as the solar corona and astrophysical jets. Earth’s magnetopause and Tokamak devices. Using two-dimensional resistive magnetohydrodynamic (MHD) simulations, the effect of uniform resistivity on the amplification of magnetic energy during KHI with a uniform magnetic field is studied. Dimensionless resistivity value varies by four orders of magnitude, with the minimum value of 1.0×10−7. Irrespective of the resistivity value, the results indicate that, up to a specific time, amplification of magnetic energy, in particular in the linear and early nonlinear phases of KHI, happens by the flow’s work on the magnetic field. This work is mainly efficient on the boundaries of growing vortices of KHI, where, consequently, the magnetic field is amplified significantly. As the KHI proceeds into the fully nonlinear regime, magnetic energy dissipation via Ohmic heating balances the flow’s work, so the magnetic energy becomes saturated. We found that the sporadic magnetic reconnection initiated by KHI in the turbulent regime plays an important role in dissipating and converting magnetic energy within strong current sheets. We also show that increasing the plasma resistivity weakens the mechanism of generating magnetic energy. The amplification of the magnetic energy is completely suppressed in a highly collisional plasma.
Institute for Plasma Research (IPR), a premier national institute working in the field of plasma physics and nuclear fusion has designed a 500 kV/2 A DC High Voltage Power Supply (HVPS) System. This power supply is best suited for High Power (≥ 1 MW) and High Energy (≥100 keV) Neutral Beam Injector (NBI), an important Heating & Current Drive System used in magnetic confinement reactor TOKAMAK. The HVPS design emphasizes on its tight performance requirements viz. wider output voltage control range (20 % - 100%), stability (≤ 1%), ripple (≤ 5%), fast turn ON & OFF time (few tens of µsec), repeated breakdown withstand capability together with lower input harmonics and near unity power factor. The design also takes into account the modularity, scalability, reliability, availability and maintainability aspects. The power supply comprises of a thyristor controlled rectifier forming common DC-Link powering the five stages of Inverter coupled High Voltage Transformer Rectifiers Units (HV-TRU). The output of each HV-TRUs are connected in series to produce 500 kV DC output. This paper elaborates the design of HVPS for NBI system including component sizing, selection, and topology of all the key elements of the power supply system supported by the simulation analysis carried out in ®MATLAB/Simulink/SimPowerSys validating the functional and performance requirements mentioned above.
The derivation of the oscillation-center quasilinear theory in an unmagnetized plasma by Dewar (1973) is rederived by Lie-transform perturbation method. New results not included in Dewar’s original paper are rigorously derived and the conservation laws of energy and momentum, which combine the contributions of the resonant and non-resonant particles, are presented in both particle phase space and oscillation-center phase space.
The light emitted spectra of air and air/argon plasmas at ambient pressure in a dielectric barrier discharge (DBD) operating at power supply frequency, 50 Hz, were recorded using an optical emission spectrometer (OES). The spectra cover the full wavelength range from 2000 A0 to 11,000 A0. It was found that air/argon plasma displays the radical composed of OH (A²Σ⁺(v′=0) → X²Π(v″=0)) at 3090 A0, a feature not observed in air plasma. The LIFBASE software suite was utilized to obtain the best fit between simulated and experimental spectra. At a voltage amplitude of 11.6 kV and a discharge gap of 0.3 cm, the plasma gas temperature, determined from the OH (3090 A0) line, was found to be 420 ± 10 K. Additionally, the intensity of the OH radical (3090A0) in air/argon plasma was studied in relation to the argon gas flow rate, applied voltage, and discharge gap. The results showed that, at a constant discharge gap, the OH intensity increases with higher argon flow and applied voltage. However, as the discharge gap increases, the OH intensity first rises and then decreases. The maximum OH intensity for a given applied voltage occurs at a discharge gap of 0.3 cm. Furthermore, the electrical diagnostics of air/argon plasma were done. Using the current density method, the electron concentration was found to be around 1017 m-3. Analysis of the current and voltage waveforms, along with the Lissajous figure approach, indicated that the reactor's power consumption was 6.2 watts. These findings contribute to a better understanding of DBD plasma's physical and chemical properties, and its potential applications in fields such as plasma agriculture, plasma chemistry and plasma medicine.
