Acceleration Mechanism Research Articles

Electron acceleration in the electron dissipation region of asymmetrical magnetic reconnection driven by ultra-intensity lasers

We performed 3D Particle-In-Cell simulations to study electron acceleration in the electron dissipation region of asymmetrical electron magnetic reconnection driven by ultra-intensity lasers, which is similar to the Earth’s magnetosphere reconnection process. Within the electron dissipation region, electrons exhibit a nonthermal distribution, and as the asymmetry increases, the power-law spectrum becomes steeper. Remarkably, the electron spectrum closely resembles a delta distribution, arising from the intense acceleration imparted by the reconnection electric field near the X-line. Both parallel electric field acceleration and the Betatron acceleration mechanism play pivotal roles in this reconnection process. Furthermore, as the magnetic reconnection asymmetry intensifies, the parallel electric acceleration mechanism becomes stronger near the X-point region, whereas the Betatron acceleration mechanism wanes, primarily concentrated in the outflow region.

Acceleration mechanism of riboflavin on Fe0-to-microbe electron transfer in corrosion of EH36 steel by Pseudomonas aeruginosa

Riboflavin (RF), as a common electron mediator that can accelerate extracellular electron transfer (EET), is usually used as a probe to confirm EET-microbiologically influenced corrosion (MIC). However, the acceleration mechanism of RF on EET-MIC is still unclear, especially the effect on gene expression in bacteria. In this study, a 13-mer antimicrobial peptide E6 and tetrakis hydroxymethyl phosphonium sulfate (THPS) were used as new tools to investigate the acceleration mechanism of RF on Fe0-to-microbe EET in corrosion of EH36 steel caused by Pseudomonas aeruginosa. 60 min after 20 ppm (v/v) THPS and 20 ppm THPS & 100 nM E6 were injected into P. aeruginosa 1 and P. aeruginosa 2 (two glass bottles containing P. aeruginosa with different treatments) at the 3-d incubation, respectively, P. aeruginosa 1 and P. aeruginosa 2 had a similar planktonic cell count, whereas the sessile cell count in P. aeruginosa 1 was 1.3 log higher than that in P. aeruginosa 2. After the 3-d pre-growth and subsequent 7-d incubation, the addition of 20 ppm (w/w) RF increased the weight loss and maximum pit depth of EH36 steel in P. aeruginosa 1 by 0.7 mg cm−2 and 4.1 μm, respectively, while only increasing those in P. aeruginosa 2 by 0.4 mg cm−2 and 1.7 μm, respectively. This suggests that RF can be utilized by P. aeruginosa biofilms since the corrosion rate should be elevated by the same value if it only acts on the planktonic cells. Furthermore, the EET capacity of P. aeruginosa biofilm was enhanced by RF because the protein expression of cytochrome c (Cyt c) gene in sessile cells was significantly increased in the presence of RF, which accelerated EET-MIC by P. aeruginosa against EH36 steel.

Experimental study on the combustion and flame propagation characteristics of CH4/O2/N2 premixed turbulent jets

The combustion and flame propagation characteristics of CH4/O2/N2 premixed turbulent jets are investigated experimentally in a constant volume chamber (CVC) under different initial temperature (Tini, 300/400/500/600K) and oxygen fractions (γ, 0.4/0.6/0.8/1.0) conditions using High-speed camera and schlieren system. Four types of jet tip velocity were found: primary vortex motion at the jet top (M-type 1), secondary vortex motion (M-type 2), weaker positive and negative feedback between the flame and the flow field (M-type 3), and stronger positive and negative feedback (N-type 4). With the decrease of γ, the jet acceleration and deceleration mechanism is changed from the top vortex motion mechanism in M-type 1 and M-type 2 to the positive and negative feedback mechanism in M-type 3 and N-type 4. The interaction between the pulsating flow field and the heat release from the pre-chamber transitions to the flow field momentum dissipation. For M-type 1 and M-type 2, there is no significant difference in overpressure dynamics. The N-type 4 exhibits lower peak pressure and pressure rise rates. Moreover, the flame mode was predicted under higher Pini (10 bar ≤ Pini) and lower γ (γ ≤ 0.4) based on empirical equations established by the self-similar analytical model.

Mechanism of Surface Hydroxylation Acceleration and Laser-Induced Damage Threshold Reduction during Ion Beam Sputtering of Fused Silica

Mechanism of Surface Hydroxylation Acceleration and Laser-Induced Damage Threshold Reduction during Ion Beam Sputtering of Fused Silica

Acceleration mechanisms of Fe and Mn doping on CO2 separation of CaCO3 in calcium looping thermochemical heat storage

The doping strategy with dark metallic oxide has proven effective in improving optical absorptions and heat storage performances of calcium-based materials for the direct solar-driven thermochemical energy storage system, but the microscopic mechanisms of accelerated decomposition of CaCO3 during heat storage process are still unclear. Carbide slag as an industrial waste with low cost and high CaO content is considered as a potential calcium-based precursor for large-scale thermochemical energy storage. Herein, the novel Fe-doped and Mn-doped calcium-based materials were synthesized from carbide slag and their optical absorption properties and heat storage performances were determined in the experiment. The optimum decomposition temperatures of CaCO3 during heat storage process decreased 10.5 °C and 18.6 °C due to Fe doping and Mn doping, respectively. The acceleration mechanisms by Fe doping and Mn doping for enhancing the CO2 separation of CaCO3 in the calcination stage of the heat storage process were investigated by density functional theory (DFT) calculations. The structural parameters, partial density of states, electron differential densities and energy barriers during CO32– dissociation in heat storage process on the doped CaCO3 and undoped CaCO3 surfaces were compared to clarify the effects of Fe doping and Mn doping on the CaCO3 decomposition. The energy barriers of Fe-doped material and Mn-doped material are 1.68 eV and 1.42 eV, respectively, which are 29.4% and 40.3% lower than that of undoped material. This work helps to understand the microscopic mechanisms of accelerated CaCO3 decomposition by Fe and Mn during heat storage process.

Precisely constructing Ce-loaded sulfur resistant catalyst for efficient methane dry reforming

Previous studies have shown that pure cerium dioxide as Lewis acid-base catalyst can effectively resist sulfur poisoning. At a certain H2S concentration, it can effectively promote methane dry reforming reaction, while the selection of a suitable support is of great significance to reduce the dosage of cerium, thus reducing the production cost and improving the reaction efficiency simultaneously. The hydroxyapatite (HAP) chosen as the support in this work has the advantages of low cost, easy preparation and high stability. Meanwhile, it is verified that ion exchange occurred on the surface of HAP contributes to higher amount of Ce3+and oxygen vacancies, when compared with other carriers, as proved by XPS, Raman, EPR, and in situ NH3-DRIFTS, thus forming higher amount of Lewis acid-base active sites and improving the reforming activity. Besides, H2S acceleration mechanism over oxygen vacancy induced catalyst is also proposed in this work.

Transport parameters from AMS-02 F/Si data and fluorine source abundance

The AMS-02 collaboration recently released cosmic ray F/Si data with an unprecedented accuracy. Cosmic ray fluorine is predominantly produced by fragmentation of heavier progenitors, while silicon is mostly accelerated at source. This ratio is thus maximally sensitive to cosmic ray propagation. We study the compatibility of the transport parameters derived from the F/Si ratio with those obtained from the lighter Li/C, Be/C, and B/C ratios. We also inspect the cosmic ray source abundance of F, which is one of the few elements that has a high first ionisation potential but is only moderately volatile and is a potentially key element to study the acceleration mechanism of cosmic rays. We used the 1D diffusion model implemented in the code and performed $ analyses accounting for several systematic effects (energy correlations in data, nuclear cross sections, and solar modulation uncertainties). We also took advantage of the nuclear database to update the F production cross sections for its most important progenitors (identified to be 56Fe, 32S, 28Si, 27Al, 24Mg, 22Ne, and 20Ne). The transport parameters obtained from AMS-02 F/Si data are compatible with those obtained from AMS-02 (Li,Be,B)/C data. The combined fit of all of these ratios leads to a $ 1.1$, with $ 10<!PCT!>$ adjustments of the B and F production cross sections (which are based on very few nuclear data points and would strongly benefit from new measurements). The F/Si ratio is compatible with a pure secondary origin of F, with a best-fit relative source abundance F/^ Si) CRS $ and an upper limit of $ $. Unfortunately, this limit is not sufficient to test global acceleration models of cosmic ray nuclei, for which values at the level of $ $ are required. Such levels could be attained with F/Si data with a few percent of accuracy at a few tens of TV, which is possibly within reach for the next generation of cosmic ray experiments.

Rapid Acceleration Bursts in the Van Allen Radiation Belt

AbstractThe fast Van Allen radiation belt electron dynamics during geomagnetic storms have not yet been fully explained, in part due to limitations of standard satellite missions in both orbit and the number of spacecraft. Here we overcome these limitations using measurements from the Global Positioning System (GPS) constellation during an acceleration event on 26 August 2018. We show that the acceleration of relativistic electrons occurs in two distinct bursts, each dominated by a different acceleration mechanism. The first burst enhances the radiation belt electrons by four orders of magnitude in 2 hr and is consistent with ULF‐wave radial diffusion. The second burst is likely caused by the local acceleration and delivers an order‐of‐magnitude increase in 20 min. This work demonstrates how distributed, operational measurements can be used to resolve phenomena not observable with previous capabilities, and that rapid energization of the radiation belt can occur much faster than previously reported.

Supernova Remnants in Gamma Rays

In the 1960s, the remnants of supernova explosions (SNRs) were indicated as a possible source of galactic cosmic rays through the Diffusive Shock Acceleration (DSA) mechanism. Since then, the observation of gamma-ray emission from relativistic ions in these objects has been one of the main goals of high-energy astrophysics. A few dozen SNRs have been detected at GeV and TeV photon energies in the last two decades. However, these observations have shown a complex phenomenology that is not easy to reduce to the standard paradigm based on DSA acceleration. Although the understanding of these objects has greatly increased, and their nature as efficient electron and proton accelerators has been observed, it remains to be clarified whether these objects are the main contributors to galactic cosmic rays. Here, we review the observations of γ-ray emission from SNRs and the perspectives for the future.

The Role of Stochastic Fermi-type Particle Acceleration in the Inner Jets of Active Galactic Nuclei

High-resolution radio observations of nearby active galactic nuclei have revealed extended, limb-brightened structures in their inner jets. This ties in with other multiwavelength observations from radio to X-ray and gamma ray, indicating that a structured jet model is required. While electrons need to be kept energized to account for the observed features, the underlying particle acceleration mechanism is still unclear. We explore the role of stochastic Fermi-type particle acceleration, i.e., classical second-order Fermi and shear acceleration, for understanding the multiwavelength observations of the inner jets of M87. An analytical Fokker–Planck description is adopted to infer characteristic spectral indices and cutoff energies for these two mechanisms. We focus on electron synchrotron radiation as the dominant emission process. We find that the multiwavelength observations of M87 can be satisfactorily accounted for in a framework, where the X-rays are produced at a larger distance from the core than the radio emission region. This provides further support to multizone, broadband emission modeling. We use our findings to also comment on the acceleration of cosmic rays entrained in the sheath.

Escape from a rotating barred galaxy

We study the dynamics in the outer regions of a rotating barred galaxy and in particular, we observe the escape of a test particle from the gravitational potential of the galaxy. The acceleration mechanism of the test particle is a close encounter with one of the ends of the bar with the right relative phase of the position of the bar. This is a possible mechanism for the creation of high-velocity stars, i.e. stars with an energy sufficient to escape from the galaxy. Our results suggest that good candidates for high-velocity stars accelerated by this mechanism are the old low-mass high-velocity stars moving close to the disc. We will encounter the asymptotic dynamics which leads naturally to the study of a type of Poincaré map which can be reinterpreted as a scattering map. Thereby an iterated scattering map enters the picture in a quite natural form. The present work is a supplement to previous work on the dynamics in the inner region of the same model.

A Study of Particle Acceleration in Blazar Jets

The particle acceleration of blazar jets is crucial to high-energy astrophysics, yet the acceleration mechanism division in blazar subclasses and the underlying nature of these mechanisms remain elusive. In this work, we utilized the synchrotron spectral information (synchrotron peak frequency, logνsy , and corresponding curvature, b sy) of 2705 blazars from the literature and studied the subject of particle acceleration in blazar jets by analyzing the correlation between logνsy and 1/b sy. Our results suggested that the entire sample follows an energy-dependent probability acceleration (EDPA). Specifically, the low inverse Compton peak sources (LCPs) follow the mechanism of fluctuations of fractional gain acceleration (FFGA), while the high inverse Compton peak sources (HCPs) follow an acceleration mechanism of EDPA. Our results indicated that the separation between LCPs and HCPs results from the electron peak Lorentz factor (γ p), and the differentiation should originate from different acceleration mechanisms. Moreover, our study revealed a transition in the acceleration mechanism from FFGA to EDPA around logνsy∼15 through a detailed analysis of binned- logνsy . The mechanism of FFGA dominates the particle acceleration in LCP jets because of stronger jets and the EDPA dominates the particle energy gain in the HCPs due to a more efficient acceleration process.

Quantitative Analysis of Electron Heating and Acceleration in Coalescing Magnetic Flux Ropes at Earth's Magnetopause

AbstractCoalescence of magnetic flux ropes (MFRs) is suggested as a crucial mechanism for electron acceleration in various astrophysical plasma systems. However, how electrons are being accelerated/heated via MFR coalescence is not fully understood. In this paper, we quantitatively analyze electron heating and acceleration during the coalescence of three MFRs at Earth's magnetopause using in‐situ Magnetospheric Multiscale (MMS) observations. We find that suprathermal electrons are enhanced in the coalescing MFRs than those in the ambient magnetosheath and non‐coalescing MFRs. Both first‐order Fermi and E|| acceleration were responsible for this electron acceleration, while the overall effect of betatron process cooled the electrons. The most intense Fermi acceleration was observed in the trailing part of the middle MFR, while E|| acceleration occurred primarily at the reconnection sites between the coalescing MFRs. For non‐coalescing MFRs, the dominant mechanism for energizing electrons is the E|| acceleration. Our results further consolidate the important role of MFR coalescence in electron heating/acceleration in space plasma.

Dearomatization drives complexity generation in freshwater organic matter

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain1–3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle4,5. Here we use complementary multiplicity-edited 13C nuclear magnetic resonance (NMR) spectra to quantify key substructures assembling the carbon skeletons of DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We find that one type of reaction mechanism, oxidative dearomatization (ODA), widely used in organic synthetic chemistry to create natural product scaffolds6–10, is probably a key driver for generating structural diversity during processing of DOM that are rich in suitable polyphenolic precursor molecules. Our data suggest a high abundance of tetrahedral quaternary carbons bound to one oxygen and three carbon atoms (OCqC3 units). These units are rare in common biomolecules but could be readily produced by ODA of lignin-derived and tannin-derived polyphenols. Tautomerization of (poly)phenols by ODA creates non-planar cyclohexadienones, which are subject to immediate and parallel cycloadditions. This combination leads to a proliferation of structural diversity of DOM compounds from early stages of DOM processing, with an increase in oxygenated aliphatic structures. Overall, we propose that ODA is a key reaction mechanism for complexity acceleration in the processing of DOM molecules, creation of new oxygenated aliphatic molecules and that it could be prevalent in nature.

Investigating the Properties of the Relativistic Jet and Hot Corona in AGN with X-ray Polarimetry

X-ray polarimetry has been suggested as a prominent tool for investigating the geometrical and physical properties of the emissions from active galactic nuclei (AGN). The successful launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 9 December 2021 has expanded the previously restricted scope of polarimetry into the X-ray domain, enabling X-ray polarimetric studies of AGN. Over a span of two years, IXPE has observed various AGN populations, including blazars and radio-quiet AGN. In this paper, we summarize the remarkable discoveries achieved thanks to the opening of the new window of X-ray polarimetry of AGN through IXPE observations. We will delve into two primary areas of interest: first, the magnetic field geometry and particle acceleration mechanisms in the jets of radio-loud AGN, such as blazars, where the relativistic acceleration process dominates the spectral energy distribution; and second, the geometry of the hot corona in radio-quiet AGN. Thus far, the IXPE results from blazars favor the energy-stratified shock acceleration model, and they provide evidence of helical magnetic fields inside the jet. Concerning the corona geometry, the IXPE results are consistent with a disk-originated slab-like or wedge-like shape, as could result from Comptonization around the accretion disk.

Acceleration mechanisms of energetic ion debris in laser-driven tin plasma EUV sources

Laser-driven tin plasmas are driving new-generation nanolithography as sources of extreme ultraviolet (EUV) radiation centered at 13.5 nm. A major challenge facing industrial EUV source development is predicting energetic ion debris produced during the plasma expansion that may damage the sensitive EUV channeling multilayer optics. Gaining a detailed understanding of the plasma dynamics and ion acceleration mechanisms in these sources could provide critical insights for designing debris mitigation strategies in future high-power EUV sources. We develop a fully kinetic model of tin-EUV sources using one-dimensional particle-in-cell simulations to study ion debris acceleration, which will be valuable for cross-validation of radiation-hydrodynamic simulations. An inverse-bremsstrahlung heating operator is used to model the interaction of a tin target with an Nd:YAG laser, and thermal conduction is included through a Monte Carlo Coulomb collision operator. While the large-scale evolution is in reasonable agreement with analogous hydrodynamic simulations, the significant timescale for collisional equilibration between electrons and ions allows for the development of prominent two-temperature features. A collimated flow of energetic ions is produced with a spectrum that is significantly enhanced at high energies compared to fluid simulations. The dominant acceleration mechanism is found to be a large-scale electric field supported mainly by the electron pressure gradient, which is enhanced in the kinetic simulations due to the increased electron temperature. We discuss the implications of these results for future modeling of tin-EUV sources and the development of debris mitigation schemes.

Velocity match between plasma and flame in microwave-assisted spark ignition

As a prospective ignition technique, microwave-assisted spark ignition (MAI) can accelerate flame and thus satisfy the demand for effective ignition. However, its acceleration mechanism on flame velocity is still unclear, which hinders its application and optimizations. Therefore, this research focuses on understanding the flame acceleration mechanism behind MAI. In this paper, MAI is achieved through radiating a microwave pulse after spark ignition. The flame velocity and the precise absorbed energy under different combustion conditions are investigated with flame kernel's Schlieren images and microwave energy diagnostics, respectively. The results show that MAI accelerates flame primarily by the interaction between microwave plasma and flame front, rather than the free electrons within the flame. Specifically, microwave accelerating flame takes two processes: energy absorption, and velocity match. Energy absorption refers to the microwave energy absorbed by residual electrons after ignition to generate and sustain microwave plasma, while velocity match involves the outward plasma with faster velocity propelling the slower flame front. Moreover, the plasma velocity shows a positive relationship with absorbed microwave energy. The velocity match between microwave plasma and flame is important to successful flame acceleration. Besides, the efficiency of energy absorption and flame acceleration varies with plasma type (glow or incandescent). Glow plasma is characterized by effective flame acceleration but relatively low absorption efficiency, and incandescent plasma is in reverse. The maximum absorption efficiency can be elevated to 70 % with incandescent plasma occurring. Ultimately, the plasma velocity declines with its traveled distance, which might impair the flame acceleration.

Current and future cosmological impact of microwave background temperature measurements

The redshift dependence of the cosmic microwave background temperature, T(z)=T0(1+z), is a key prediction of standard cosmology, but this relation is violated in many extensions thereof. Current astrophysical facilities can probe it in the redshift range 0≤z≤6.34. We extend recent work by Gelo et al. (2022) showing that for several classes of models (all of which aim to provide alternative mechanisms for the recent acceleration of the universe) the constraining power of these measurements is comparable to that of other background cosmology probes. Specifically, we discuss constraints on two classes of models not considered in the earlier work: a model with torsion and a recently proposed phenomenological dynamical dark energy model which can be thought of as a varying speed of light model. Moreover, for both these models and also for those in the earlier work, we discuss how current constraints may be improved by next-generation ground and space astrophysical facilities. Overall, we conclude that these measurements have a significant cosmological impact, mainly because they often constrain combinations of model parameters that are orthogonal, in the relevant parameter space, to those of other probes.

Deciphering the Microdroplet Acceleration Factors of Aza-Michael Addition Reactions.

Microdroplet chemistry is emerging as a great tool for accelerating reactions by several orders of magnitude. Several unique properties such as extreme pHs, interfacial electric fields (IEFs), and partial solvation have been reported to be responsible for the acceleration; however, which factor plays the key role remains elusive. Here, we performed quantum chemical calculations to explore the underlying mechanisms of an aza-Michael addition reaction between methylamine and acrylamide. We showed that the acceleration in methanol microdroplets results from the cumulative effects of several factors. The acidic surface of the microdroplet plays a dominating role, leading to a decrease of ∼9 kcal/mol in the activation barrier. We speculated that the dissociation of both methanol and trace water contributes to the surface acidity. An IEF of 0.1 V/Å can further decrease the barrier by ∼2 kcal/mol. Partial solvation has a negligible effect on lowering the activation barrier in microdroplets but can increase the collision frequency between reactants. With acidity revealed to be the major accelerating factor for methanol droplets, reactions on water microdroplets should have even higher rates because water is more acidic. Both theoretically and experimentally, we confirmed that water microdroplets significantly accelerate the aza-Michael reaction, achieving an acceleration factor that exceeds 107. This work elucidates the multifactorial influences on the microdroplet acceleration mechanism, and with such detailed mechanistic investigations, we anticipate that microdroplet chemistry will be an avenue rich in opportunities in the realm of green synthesis.

Proton acceleration from optically tailored high-density gas jet targets

Laser-driven ion acceleration is well established using solid targets mainly in the target normal sheath acceleration regime. To follow the increasing repetition rate available on high-intensity lasers, the use of high-density gas targets has been explored in the past decade. When interacting with targets reaching densities close to the critical one, the laser pulse can trigger different acceleration mechanisms such as Collisionless Shock Acceleration (CSA) or hole boring. Particle-in-cell simulations using ideal target profiles show that CSA can accelerate a collimated, narrow energy spread and few hundreds of megaelectronvolts ion beam on the laser axis. Nevertheless, in real experiments, the laser will not only interact with an overcritical, thin plasma slab with sharp density gradients, but also with lower density regions surrounding the core of the gas jet, extending to several hundreds of micrometres. The interaction of the laser with these lower density wings will lead to nonlinear effects that will reduce the available energy to drive the shock in the high-density region of the target. Optically tailoring this target could mitigate that issue. Recent experiments conducted on different laser facilities aimed at testing several tailoring configurations. We first tested a scheme with a copropagating picosecond prepulse to create a lower density plasma channel to facilitate the propagation of the main pulse, while the second one was a transverse tailoring driven by nanosecond laser pulses to generate blast waves and form a high-density plasma slab. The main results will be presented here and the methods compared.