Particle Confinement Research Articles

Fast ion confinement in quasi-axisymmetric stellarator equilibria

Abstract This report presents an initial analysis of the fast ion confinement and losses within quasi-axisymmetric stellarator equilibria in consideration by Thea Energy. The equilibria have not yet been explicitly optimized for fast particle confinement and require validation. Modeling with the ASCOT5 code is used to directly examine the fast ion transport. The particle tracking simulations are purely (neo)classical in nature and simply contain the supplied equilibrium and collisions (pitch-angle, energy slowing, and velocity diffusion) from supplied thermal profiles. Uniform marker deposition is used to probe the general confinement properties of the equilibria while a realistic beam-born population is provided from the BEAMS3D code and an alpha particle population is calculated from a fusion source integrator. A first wall is included and defines the loss boundary. Analysis for NBI ions within Thea Energy’s conceptual Eos neutron source are presented along with alpha particles in an enlarged DT-plasma. The fast ions are assessed in regards to their confinement time, pitch, energy, and spatial coordinates. For each population, the impact of collisions and orbit drifts are discussed. It is found that NBI born ions in Eos are strongly confined until slowing-down, owing largely to the tangential injection geometry, while 22% of DT-born alpha energy is lost in the scaled device, indicating that any fusion pilot plant design optimization should include metrics for fast ion confinement.

Semi-Confinement Effect Enhances CH4 and C2H4 Production in CO2 Electrocatalytic Reduction.

Achieving fast conversion and precise regulation of product selectivity in electrochemical CO2 reduction reaction (CO2RR) remains a challenge. The space confinement effect provides a theoretical basis for the design of catalysts of different morphology and sizes and reveals the physical phenomena caused by the confinement of electrons and other particles at the nanoscale. In this work, a semi-confinement concept is introduced and a mesoporous silica nanosphere supported Cu catalyst (Cu-MSN) is prepared as a typical example to realize CO2RR enhancement and product selectivity regulation (methane vs ethylene). The semi-confined structure partially solves the mass transfer problem of classical confined catalysis. Cu-MSN allows flexible controls aggregation form of Cu species by loading amount, which achieves a free switch from methane Faraday efficiency of 71.1% to ethylene Faraday efficiency of 66.4%. Various characterizations confirm that the fast adsorption behavior and local coordination structure transformation of Cu (from Cu─O─Si to Cu─O─Cu), which can stabilize key intermediates *CHO and *CO*COH for generating respective methane and ethylene.

Interaction between MTM and EGAM for energy and particle confinement improvements on HL-3 tokamak

Abstract We report the first observation of microtearing mode (MTM) and its interaction with energetic-particle-induced geodesic acoustic mode (EGAM) in the reduction of ambient turbulence, leading to improvements in energy and particle confinements in electron cyclotron resonance heating (ECRH) plasma on HL-3 tokamak. MTM, observed in the magnetic fluctuation spectrum with a frequency range of 80–120 kHz, is found to be driven by the electron temperature gradient. It has been shown that MTM propagates in the electron diamagnetic drift direction with a poloidal normalized wavenumber 0.05 ≤ k θ ρ s ≤ 0.17 . The n = 0 , m = − 2 magnetic structure of EGAM with a frequency range of 14–20 kHz is observed in the magnetic fluctuation spectrum, where n and m are the toroidal and poloidal mode numbers, respectively. The V E × B oscillation of EGAM has also been observed in the Doppler reflectometry phase derivative perturbation spectrum. The frequency of EGAM corresponds to half that of the conventional GAM. Bispectral analysis during ECRH shows pairwise interactions among EGAM, MTM and ambient turbulence (low frequency). It has been found that the reduction of ambient turbulence due to MTM and EGAM leads to the improvement of particle and energy confinements. Experimental results on HL-3 show that the interaction between MTM and EGAM provides a possible way to the turbulence control for energy and particle confinement improvements in future reactors.

Cross-field Diffusion Effects on Particle Transport in a Solar Coronal Flux Rope

Solar energetic particles associated with solar flares and coronal mass ejections (CMEs) are key agents of space weather phenomena, posing severe threats to spacecraft and astronauts. Recent observations by Parker Solar Probe indicate that the magnetic flux ropes of a CME can trap energetic particles and act as barriers, preventing other particles from crossing. In this Letter, we introduce the novel COCONUT+PARADISE model to investigate the confinement of energetic particles within a flux rope and the effects of cross-field diffusion (CFD) on particle transport in the solar corona, particularly in the presence of a CME. Using the global magnetohydrodynamic coronal model COolfluid COroNal UnsTructured (COCONUT), we generate background configurations containing a CME modeled as a Titov–Démoulin flux rope (TDFR). We then utilize the particle transport code PArticle Radiation Asset Directed at Interplanetary Space Exploration (PARADISE) to inject monoenergetic 100 keV protons inside one of the TDFR legs near its footpoint and evolve the particles through the COCONUT backgrounds. To study CFD, we employ two different approaches regarding the perpendicular proton mean free path (MFP): a constant MFP and a Larmor radius-dependent MFP. We contrast these results with those obtained without CFD. While particles remain fully trapped within the TDFR without CFD, we find that even relatively small perpendicular MFP values allow particles on the outer layers to escape. In contrast, the initially interior trapped particles stay largely confined. Finally, we highlight how our model and this Letter's results are relevant for future research on particle acceleration and transport in an extended domain encompassing both the corona and inner heliosphere.

Spherical quantum dot described by a scalar exponential potential under the influence of a linear electric field

We study the confinement of a spinless charged particle to a spherical quantum dot under the influence of a linear electric field. The spherical quantum dot is described by a short-range potential given by the power-exponential potential. Then, by analysing the region near the spherical quantum dot centre, we discuss two cases where the energy levels can be obtained for s-waves and how the linear electric field modifies the spectrum of energy of the spherical quantum dot.

Tuning Intermediate Band Solar Cell Efficiency: The Interplay of Electric Fields, Composition, Impurities, and Confinement.

In this study, we investigated the influence of structural parameters, including active region dimensions, electric field intensity, In-composition, impurity position, and potential profiles, on the energy levels, sub-gap transitions, and photovoltaic characteristics of a p-GaN/i-(In, Ga)N/GaN-n (p-QW-n) structure. The finite element method (FEM) has been used to solve numerically the Schrödinger equation. We found that particle and sub-gap energy levels are susceptible to well width, electric field, and impurity position. Particle energy decreases with increasing well size and electric field intensity, while impurity position affects energy based on proximity to the well center. Potential profile shapes, such as rectangular (RQW) and parabolic (PQW), also play a significant role, with PQW profiles providing stronger particle confinement. IB width increases with electric field intensity and saturates at higher In-content. Voc increases with field strength but decreases with In-content, and the parabolic profile yields higher efficiency than the rectangular one. Photovoltaic efficiency is improved with an appropriately oriented electric field and decreases with higher In-content and field intensity. These findings highlight the critical role of structural parameters in optimizing QW-IBSC performance.

Divertor Tokamak Test: Impact of NBI shine-through and beam-plasma interaction on Divertor Tokamak Test facility

IntroductionIn this work, we aim to explore numerically the behavior of beam energetic particles in the Divertor Tokamak Test (DTT), a superconductive device equipped with a Neutral Beam Injection (NBI) system capable of injecting neutrals up to 510 keV.MethodWe explore beam ionization and beam slowing down for different DTT plasma scenarios. Numerical simulations are performed using the ASCOT suite of codes, including a wide-range scan of plasma density and beam injection energy. For different plasma conditions, we estimate shine-through losses, including the heat fluxes on the first wall thanks to dedicated particle tracing simulations. Orbits of newly-born fast ions are characterized by means of the constant of motion phase space, showing how trapped energetic particles’ population and prompt losses change with plasma density and NBI energy.Results and discussionSlowing down simulations show that NBI injection at 510 keV is well coupled to DTT plasmas. DTT NBI will be one of the sources of auxiliary ion heating, with an absorbed power ratio of up to ∼50% depending on plasma and beam parameters. At low plasma densities, energetic particle confinement is less efficient, and NBI power and/or energy reduction is expected.

Fractional Brownian motion in confining potentials: non-equilibrium distribution tails and optimal fluctuations

Abstract At long times, a fractional Brownian particle in a confining external potential reaches a non-equilibrium (non-Boltzmann)
steady state. Here we consider scale-invariant power-law potentials $V(x)\sim |x|^m$, where $m>0$, and employ the optimal fluctuation method (OFM) to determine the large-$|x|$ tails of the steady-state probability distribution $\mathcal{P}(x)$ of the particle position. The calculations involve finding the optimal (that is, the most likely) path of the particle, which determines these tails, via a minimization of the exact action functional for this system, which has recently become available. Exploiting dynamical scale invariance of the model in conjunction with the OFM ansatz, we establish the large-$|x|$ tails of $\ln \mathcal{P}(x)$ up to a dimensionless factor $\alpha(H,m)$, where $0<H<1$ is the Hurst exponent. We determine $\alpha(H,m)$ analytically (i) in the limits of $H\to 0$ and $H\to 1$, and (ii) for $m=2$ and arbitrary $H$, corresponding to the fractional Ornstein-Uhlenbeck (fOU) process. Our results for the fOU process are in agreement with the previously known exact $\mathcal{P}(x)$ and autocovariance. The form of the tails of $\mathcal{P}(x)$ yields exact conditions, in terms of $H$ and $m$, for the particle confinement in the potential.
For $H\neq 1/2$, the tails encode the non-equilibrium character of the steady state distribution, and we observe violation of time reversibility of the system except for $m=2$. To compute the optimal paths and the factor $\alpha(H,m)$ for arbitrary permissible $H$ and $m$, one needs to solve an (in general nonlinear) integro-differential equation. To this end we develop a specialized numerical iteration algorithm which
accounts analytically for an intrinsic cusp singularity of the optimal paths for $H<1/2$.


I-mode plasma confinement improvement by real-time lithium injection and its classification on EAST tokamak

Abstract I-mode is a promising regime for future fusion reactors due to the high energy confinement and the moderate particle confinement. However, the effect of lithium, which has been widely applied for particle recycling and impurity control, on I-mode plasma is still unclear. Recently, experiments of real-time lithium powder injection on I-mode plasma have been carried out in EAST Tokamak. It was found that the confinement performance of the I-mode can be improved by the lithium powder injection, which can strongly reduce electron turbulence (ET) and then trigger ion turbulence (IT). And it was observed that the ET intensity is inversely proportional to the velocity shear, which suggests that the injection of lithium powder leads to a gradual enhancement of the shear flow, whereby the turbulence is reduced and consequently the confinement is improved. Four different regimes of I-mode have been identified in EAST. The Type I I-mode plasma is characterized by the weakly coherent mode (WCM) and the geodesic-acoustic mode (GAM). The Type II I-mode is featured as the WCM and the edge temperature ring oscillation (ETRO). The Type III I-mode corresponds to the plasma with the co-existence of ETRO, GAM, and WCM. The Type IV I-mode denotes the plasma with only WCM but without ETRO and GAM. It was observed that the WCM intensity is increased with lithium powder injection by the confinement improvement/pedestal temperature increase. EAST experiments demonstrate that lithium powder injection is an effective tool for real-time control and confinement improvement of I-mode plasma.

MightyLev: An acoustic levitator for high-temperature containerless processing of medium- to high-density materials.

"MightyLev," a new multi-emitter ultrasonic acoustic levitation device capable of extremely stable levitation of materials of density up to at least 11.3g cm-3, is described. The exceptional stability of medium- to high-density samples levitated in MightyLev makes the device highly suitable for chemical and structural analysis using micro-focused spectroscopic and x-ray scattering techniques. In combination with mid-infrared laser heating, MightyLev is capable of levitating metallic and oxide materials during high-temperature cycling and melting above 1500K. Instabilities in particle confinement during heating were investigated by directly visualizing the acoustic field using schlieren imaging. The results reveal jets of hot-air directed along the anti-nodes of the acoustic field. The reaction force on the sample from the jet, coupled with the restoring force of the acoustic trap, generates a parametric lateral oscillation of the sample. This result provides valuable insight for future optimization and wider application of acoustic levitation for high-temperature containerless material processing.

Full-f gyrokinetic simulations of hydrogen isotope mixing in tokamak plasmas

Hydrogen isotope mixing phenomena in tokamak plasmas are analyzed using global full-f gyrokinetic simulations. Model plasma parameters are chosen based on hydrogen isotope pellet experiments on JET, in which fast hydrogen isotope mixing in the timescale of the energy confinement time τE occurred after injecting deuterium (D) pellets into hydrogen (H) plasmas. Two numerical experiments are conducted using plasma profiles before and after the pellet injection. In both cases, turbulent fluctuations in the plasma core are characterized by ion temperature gradient driven turbulence. In the former case, the density profile of bulk H ions is kept in a quasi-steady state, and the particle confinement time of bulk H ions τH is an order of magnitude longer than τE. In the latter case, the density profiles of bulk H ions and pellet D ions show transient relaxation in the timescale of τE, and both τH and the timescale of particle pinch τD become comparable to τE, indicating the fast hydrogen isotope mixing. In the toroidal angular momentum balance, it is found that the enhanced ion particle transport leading to the fast hydrogen isotope mixing is driven by the toroidal field stress.

Encapsulation of Ru nanoparticles within NaY zeolite for ammonia decomposition

Uniform and minuscule Ru particles confined in NaY zeolite (Ru@NaY) are prepared via a simple in situ synthesis technique. Transmission electron microscopy studies indicate that the Ru particles are encapsulated within the micropores of NaY zeolite and form a uniform size of 1.5–3.5 nm. Thanks to the effective confinement of Ru particles within the NaY zeolite, as well as the high concentration of B-5 sites and basic sites, the prepared Ru@NaY catalysts show excellent NH3 decomposition activity and highly efficient H2 formation. Notably, the 0.1Ru@NaY catalyst achieves a 92.7% NH3 conversion and a H2 formation rate of 690 mmol min−1·gRu−1 at 500 °C and GHSV = 9000 mLNH3·gcat−1·h−1 and shows outstanding stability throughout a 95-h lifetime test. The encapsulation synthesis of Ru clusters in zeolites endows the catalysts with exceptional catalytic activities and excellent stability, thus providing new prospects for the production of H2 from NH3 decomposition.

Overview of results from the 2023 DIII-D negative triangularity campaign

Abstract Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV and DIII-D tokamaks motivated the installation of graphite-tile armor on the low-field-side lower outer wall of DIII-D. A dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During the DIII-D NT campaign, high confinement ( H 98 y , 2 ≳ 1), high current ( q 95 < 3), and high normalized pressure plasmas ( β N > 2.5) were simultaneously attained in strongly NT-shaped discharges with average triangularity δ avg = −0.5 that were stably controlled. Experiments covered a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) and did not trigger an ELM in a single discharge as long as sufficiently strong NT was maintained; in contrast, to other high-performance ELM-suppression scenarios that have narrower operating windows. These strong NT plasmas had a lower outer divertor X-point shape and maintained a non-ELMing edge with an electron temperature pedestal, exceeding that of typical L-mode plasmas. Also, the following was achieved during the campaign: high normalized density ( n e / n GW of at least 1.7), particle confinement comparable to energy confinement with Z eff ∼ 2 , a detached divertor without impurity seeding, and a mantle radiation scenario using extrinsic impurities. These results are promising for a NT fusion pilot plant but further questions on confinement extrapolation and core-edge integration remain, which motivate future NT studies on DIII-D and beyond.

Thrust Generation Through a Collimated Electron Beam in a Magnetic Mirror and its Possible Applications in Plasma Thrusters

In this article, we apply some basic concepts of electric thrusters, using Monte Carlo simulations. One such concept is the thrust, which we calculate for the simulated case of a simple thruster, consisting of two stages. The goal is to study the thrust in a magnetic bottle as a function of the collimation of an assembly of particles. In the first stage, a voltage applied between a pair of electrodes accelerates the particles. We perform simulations of the behavior of the assembly of charged particles. A normal distribution is used for the initial velocities of the assembly, with a given standard deviation. The resulting velocity distribution and its dependence on the applied voltage are analyzed. Further, the set of particles, whose pitch angles follow a normal distribution with a given standard deviation, enters a magnetic bottle where it is collimated to reduce its dispersion upon the exit of the thruster. In this second stage, we study the conditions for which the collimation produced, by the magnetic bottle, leads to the least thrust reduction. For the simulations, we assume electrons; However, the concepts apply to any charged particle species. The simulations show that the standard deviation of the pitch angle distribution has an important influence on the confinement of charged particles and on the thrust that can be generated when collimating the particle beam in a magnetic bottle.

Modelling of ICRH slow wave propagation and absorption in Wendelstein 7-X stellarator

Abstract The propagation and absorption of the slow waves in the three-ion plasma of the Wendelstein 7-X stellarator have been investigated by ray tracing. The aim of the study is to obtain a qualitative notion of the penetration into the plasma and absorption of the wave excited by the potential difference between the antenna conductors and the antenna box. It has been discovered that the rays propagate along the magnetic field lines over a significant distance, up to 6 m, from the antenna. They weakly, to a depth of 0.1 m, penetrate into the plasma. Absorption of the slow waves by electrons does not lead to the generation of the currents capable of affecting the plasma equilibrium. Most of the slow waves are absorbed beyond the region of ion-ion hybrid resonance in the zone of cyclotron resonance of He3 ions at the periphery of the plasma. The ICRH of the three-ion W 7-X plasma will be used to heat He3 ions to high energies and simulate the confinement of alpha particles in an optimized stellarator configuration. The presence of a source of hot He3 ions, which are poorly confined, at the periphery of the plasma can affect the experimental results.

Alpha particle loss measurements and analysis in JET DT plasmas

Burning reactor plasmas will be self-heated by fusion born alpha particles from deuterium-tritium reactions. Consequently, a thorough understanding of the confinement and transport of DT-born alpha particles is necessary to maintain the plasma self-heating. Measurements of fast ion losses provide a direct means to monitor alpha particle confinement. JET’s 2021–2022 second experimental DT-campaign offers burning plasma scenarios with advanced fast ion loss diagnostics for the first time in nearly 25 years. Coherent and non-coherent alpha losses were observed due to a variety of low frequency MHD activity. This manuscript will present the loss mechanisms, spatial and pitch dependencies, scalings with plasma parameters, correlations with wall impurities, and magnitude of DT-alpha born losses.

Metal‐Decorated Porous Organic Polymers: Bridged the Gap between Organic and Inorganic Scaffolds†

Comprehensive SummaryAdvanced functionalization‐decorated porous organic polymers (POPs) are emerging as a prominent research focus, spanning from their construction to applications in gas storage and separation, catalysis, energy storage, electrochemistry, and other areas. Furthermore, the inherent organic nature, tailored pore structures, and adjustable chemical components of POPs offer a versatile platform for the incorporation of various metal active sites. Meticulously designed molecular building blocks can serve as organic ligands uniformly distributed throughout POPs, leading to the effective isolation of inorganic metal active sites at the molecular level. In this manner, POPs containing active metal centers bridge the gap between organic and inorganic scaffolds. This review aims to provide an overview of recent research progress on metal‐decorated POPs, focusing on strategies for incorporating metal active sites into POPs and their applications in adsorption, separation, catalysis, and photoelectrochemistry. Finally, current challenges and future prospects are discussed for further research. Key ScientistsAdvanced functionalized porous organic polymers have become a new research hotspot, ranging from their construction to their use in gas storage and separation, catalysis, energy storage, electrochemistry, and other applications. In 2002, the McKeown group was the first to report phthalocyanine‐based MPOPs with permanent porosity and a moderate surface area. In 2010, the Yu group prepared nanoporous polyporphyrin materials P(Fe‐TTPP) from the metallated porphyrin with functionalized thiophenyl groups by the FeCl3 catalyzed oxidation couple reaction showing the surface area of 1522 m2·g–1. Subsequently, in 2013, the Deng group was the first to use metalated salens as the original building blocks for preparing MPOPs. The Morin group was the first to produce a series of ferrocene‐based nanoporous frameworks via radical polymerization, with surface areas ranging from 385 to 899 m2·g–1. In 2016, the Han group synthesized two N‐pyridinylphenylcarbazole (PPC) ligands to produce a series of metalized polycarbazole networks. Recently, the Tan group reported a solvent‐knitting hyper‐cross‐linking reaction to produce HUST‐1, which contains a porphyrin unit. The porphyrin moiety provides a centered square‐planar metal post‐coordination site, resulting in the metalated HUST‐1‐Co, which exhibits high efficiency in the catalytic conversion of CO2. Additionally, the Kegnæs group combined the decomposition of the palladium complex with an in situ catalyzed polymerization reaction, enabling the confinement of nascent Pd particles in the developing polymer network. This review focuses on recent research progress in metal‐decorated POPs, emphasizing strategies for incorporating metal active sites into POPs and their applications.

Heavy ion beam probe for Wendelstein 7-X measurement capabilities as projected through its design.

A heavy ion beam probe (HIBP) diagnostic is being developed for studies of plasma equilibrium and turbulence in the optimized Wendelstein 7-X (W7-X) stellarator. Operation of W7-X has experimentally demonstrated that its optimized magnetic field results in improved neoclassical particle confinement and, as a result, turbulence is the predominant cause of energy transport. The HIBP will have the unique ability to provide experimental data needed to complement models of both neoclassical and turbulent transport. It will acquire direct measurements in the W7-X plasma interior of the electric potential (needed for understanding ambipolar particle flux) and fluctuations of electron density and potential (needed for understanding turbulence). The HIBP for W7-X will inject singly charged ion beams with energies of up to 2MeV and is designed to access the upper cross section of the W7-X plasma. We use trajectory simulations to illustrate the plasma coverage that the diagnostic can achieve in the reference magnetic configurations of W7-X. We calculate beam signal levels, discuss anticipated measurement sensitivity of broadband fluctuations of electron density and plasma potential, and show how they depend on plasma density. We also discuss the diagnostic sensitivity to equilibrium plasma potential.

Influence of support polarity on the selective hydrogenation of nitrostyrene over Pt-based heterogenous catalysts

Enhancing the selectivity of noble metal containing heterogeneous catalysts in the nitro group hydrogenation of functionalized nitroarenes is challenging due to high dependence of selectivity on the catalyst structure. Most reports focus on the influence of metal nanoparticles (NPs) size, confinement, and support-metal interactions, while the effect of support polarity remains unclear. Herein we investigate, for the first time, the influence of support polarity on the selective hydrogenation of NO2 in 3-nitrostyrene over Pt-based heterogeneous catalysts and compare it to the effects of Pt NPs size and location. To achieve this, we confined Pt NPs in the channels of the nonpolar Silicalite-1 (S-1) and benchmarked against catalysts with NPs of various sizes supported on polar SiO2 and nonpolar S-1.We demonstrate that support polarity is the key factor determining selectivity, surpassing the roles of Pt particle size and confinement. Catalysts with the nonpolar Silicalite-1 support exhibit higher NO2 selectivity compared to SiO2-based ones, with a threefold increase observed for Pt@S–S-1 compared to a commercial Pt/SiO2. DRIFT spectroscopy-monitored adsorption experiments and hydrogenation experiments of nitrobenzene and styrene model molecules show that the S-1 support favors the adsorption of –NO2 and the –NH2 formed during the reaction, impeding C=C hydrogenation. To a lower extent, the size of Pt NPs contributed to the obtained results with decreased C=C hydrogenation observed over smaller Pt NPs. Finally, confining Pt in the zeolite restricts the NPs growth during catalyst activation, resulting in a further decrease of particles size and C=C hydrogenation activity.

Spin-dependent linear confinement in a magnetic medium

The linear confinement in two-dimensions can yield an analogue of a triangular well or a quantum bouncer. We discuss a way of achieving a linear confinement of a neutral particle with a permanent magnetic dipole moment in a magnetic medium by dealing with a two-dimensional system with cylindrical symmetry. This linear confinement is characterized by being spin-dependent. Then, by including the Aharonov–Casher geometric quantum phase, we show that bound states analogous to those of the quantum bouncer can be achieved, where the energy levels are infinitely degenerated with regard to the ℓ-waves. Further, we obtain the revival time of the system.