Collisional Energy Loss Research Articles

A unified global model accompanied with a voltage and current sensor for low-pressure capacitively coupled RF discharge

A global model (GM) assumes ion energy ( ε ) on the electrode equals the time-averaged sheath voltage ( Vshtt ). However, using particle-in-cell simulation, we found that ε differs from Vshtt. We propose a unified global model (UGM) that calculates ε and collisional energy losses of ions by employing plasma circuit and sheath models, accompanied by a voltage and current sensor. We compared the results of the UGM with the experimental measurements and the results revealed that UGM is closer to the experiment than GM. UGM shows a linear relationship with the experiment, indicating that the UGM is applicable for plasma monitoring.

Energy loss of a heavy fermion in a collisional QED plasma

We compute the energy loss of heavy fermions moving in a plasma, taking into account the modification of the photon collective modes induced by collisions using a Bhatnagar-Gross–Krook collisional kernel. We include contributions from both hard and soft scatterings of the heavy fermion using a collisionally modified hard-thermal-loop resummed propagator. Using this method, one does not need to introduce a separation scale between hard- and soft-momentum exchanges. To place our calculation in context, we review other theoretical approaches to computing the collisional energy loss of fermions and discuss the systematics and results obtained in each approach compared to using a resummed propagator for both hard and soft momentum exchanges. Our final results indicate that self-consistently including the effect of collisions in the self-energies of the resummed propagator results in an increased energy loss compared to using collisionless hard-thermal-loop propagators. The effect becomes larger as the magnitude of the coupling constant and the velocity of the fermion increase. Published by the American Physical Society 2024

Dynamics of heavy flavor in a weakly magnetized hot QCD medium

We obtain the spatial and momentum-diffusion coefficients (Ds and κ) and the collisional energy loss (dE/dx) of a heavy quark (HQ) traversing through a thermal medium of quarks and gluons in a weak magnetic field (B), for the two cases of the HQ moving either parallel or perpendicular to B. For that purpose, we consider Coulomb scatterings (t-channel) of the HQ with the light quarks, obtained from the imaginary part of the HQ self-energy via the cutting rules. Both the normalized (by T3) κ, and dE/dx, for charm quarks are larger than that for bottom quarks due to the larger mass of the latter. Also, the effect of B is more feeble on the bottom quark, compared to the charm quark. Comparatively, the magnitudes of both κ and dE/dx are significantly smaller for the case of v⊥B. For both the cases, our results show that the momentum transfer between the HQ and the medium takes place preferentially along the direction of HQ velocity, thus leading to a significant increase in the momentum-diffusion anisotropy, compared to B=0. We also calculate the (scaled) spatial diffusion coefficient, which we find to be independent of the heavy flavor mass and is almost unaffected by changes in B. Published by the American Physical Society 2024

Research on Two-Phase Flow and Wear of Inlet Pipe Induced by Fluid Prewhirl in a Centrifugal Pump

In deep-sea mining hydraulic lifting systems, centrifugal pumps are very important as power units. In the process of transportation, the fluid prewhirl phenomenon in the impeller inlet will lead to changes in the state of motion of the particles and fluid and cause the wear of the inlet pipe, which can lead to centrifugal pump failure in serious cases. In this paper, a numerical simulation of the centrifugal pump is carried out based on the CFD-DEM coupling method to analyze the influence of the prewhirl on the wear of the inlet pipe. The results show that the velocity streamline near the impeller inlet position changes significantly. The flow field velocity increases along the radial direction of the inlet pipe, and it has a maximum value at r/R = 0.98. The prewhirl flow pulls the particles to change their original motion direction, and the area where the particles are subjected to high fluid force is concentrated between 0.5 d/D and 1 d/D, about 0.015 to 0.018 N, resulting in the uneven distribution of particles. The high-wear area appears in the bottom-left area (specifically, L4, L9, and L13), and this is also the location of the largest cumulative force; the high-wear area shows a triangle. The collision energy loss of particles increases due to the influence of the prewhirl, which leads to an increase in wear.

Unraveling the collisional energy loss of a heavy quark in a quark-gluon plasma

At leading order in the QCD coupling constant, we compute the energy loss per traveling distance of a heavy quark dE/dz from elastic scattering off thermal quarks and gluons at a temperature T, including the thermal perturbative description of soft scatterings (−t<−t*) and a perturbative QCD-based calculation for hard collisions (−t>−t*). Within this soft-hard factorization model, we find that the full results of dE/dz behaves a mild sensitivity to the intermediate cutoff t*, supporting the validity of the soft-hard approach within the temperature region of interest. We rederive the analytic formula for dE/dz in the high-energy approximation, E1≫m12/T, where E1 is the injected heavy quark energy and m1 is its mass. It is realized that the soft logarithmic contribution, dE/dz∝ln(−t*/mD2), arises from the t-channel scattering off thermal partons, while the hard logarithmic term, dE/dz∝ln[E1T/(−t*)], stems from the t-channel scattering off thermal partons, and the one dE/dz∝ln(E1T/m12) comes from the s- and u-channel scattering off gluons. The sum of these contributions cancels the t*-dependence as observed in the full result. The mass hierarchy is observed dE/dz(charm)>dE/dz(bottom). Our full results are crucial for a better description of heavy quark transport in QCD medium, in particular at low and moderate energy. We also calculate the energy loss by imposing the Einstein’s relationship. The related results appear to be systematically larger than that without imposing the Einstein’s relationship. Published by the American Physical Society 2024

Quenching and flow of charm and bottom quarks via semi-leptonic decay of D and B mesons in Pb+Pb collisions at the LHC* *Supported in part by the National Natural Science Foundation of China (12225503, 11935007, 11890710, 11890711, 12175122, 2021-867). W.-J. X. is supported in part by China Postdoctoral Science Foundation (2023M742099). Some of the calculations were performed in the Nuclear

Heavy flavor particles provide important probes of the microscopic structure and thermodynamic properties of the quark-gluon plasma (QGP) produced in high-energy nucleus-nucleus collisions. We studied the energy loss and flow of charm and bottom quarks inside the QGP via the nuclear modification factor ( ) and elliptic flow coefficient ( ) of their decayed leptons in heavy-ion collisions at the LHC. The dynamical evolution of the QGP was performed using the CLVisc (3+1)-dimensional viscous hydrodynamics model; the evolution of heavy quarks inside the QGP was simulated with our improved Langevin model that considers both collisional and radiative energy loss of heavy quarks; the hadronization of heavy quarks was simulated via our hybrid coalescence-fragmentation model; and the semi-leptonic decay of D and B mesons was simulated via PYTHIA. Using the same spatial diffusion coefficient for charm and bottom quarks, we obtained smaller and larger of charm decayed leptons than bottom decayed leptons, indicating stronger energy loss of charm quarks than bottom quarks inside the QGP within our current model setup.

Collision characteristics of coal particles in arc-shaped plug elbow for pneumatic conveying

Particle collisions are one of the main causes of elbow wear. In this study, an arc-shaped plug elbow was proposed. Combined with the pneumatic conveying experiment of coal particles and the computational fluid dynamics and discrete element method (CFD–DEM) simulation of Euler–Lagrangian bilateral coupling, the variation rules of particle distribution, elbow wear, particle velocity, and collision energy loss were analyzed, the weakening characteristics of the arc-shaped plug on particle collision and elbow wear were revealed, and the criterion of the optimal structure was deduced. The results show that the arc angle is the main factor influencing particle collision and elbow wear in arc-shaped plugs, which determines the reasonable range of the dimensionless height. The average particle velocity of the arc-shaped plug elbow decreased rapidly during the plug-filling stage and was much lower than that of an ordinary elbow during the stable conveying stage. The growth rate of the collision energy loss tends to stabilize after stable particle accumulation. This is an important criterion for the optimal structure, in which the arc angle satisfies the condition that the plug completely contains the radiation area of the wear center, and the dimensionless height satisfies the condition that stable particle accumulation is formed in the plug.

High-pT suppression in small systems

We present first results for leading hadron suppression in small collision systems, from a convolved radiative and collisional pQCD energy loss model which receives a short path length correction to the radiative energy loss. We find that the short path length correction is exceptionally large for light flavor final states at high-pT , for all system sizes. We numerically investigate the self-consistency of various assumptions underlying the radiative energy loss model, in an effort to understand the size of the short path length correction. This calculation shows that the large formation time assumption, which is utilized by most contemporary energy loss models, is invalid for a large portion of the phenomenologically relevant parameter space.

Initial-state and final-state effects on hadron production in small collision systems

Heavy meson production in reactions with nuclei is an active new frontier to understand QCD dynamics and the process of hadronization in nuclear matter. Measurements in various colliding systems at RHIC and LHC, including Pb-Pb, Xe-Xe, O-O, p-Pb, and p-O, enable precision tests of the medium-size, temperature, and mass dependencies of the in-medium parton propagation and shower formation. We employ a coupled DGLAP evolution framework that takes advantage of splitting functions recently obtained in softcollinear effective theory with Glauber gluons (SCETG) and hard thermal loop (HTL) motivated collisional energy loss effects. With jet quenching effects constrained to the nuclear modification factor of charged hadrons in Pb-Pb collisions at 5.02 TeV, we present predictions for light and heavy-meson in Xe-Xe, O-O and p-Pb collisions at the LHC.We find that the nuclear modification scales non-trivially with the quark mass and medium properties. In particular, there can be sizeable collision-induced attenuation of heavy mesons in small systems such as oxygen-oxygen and high-multiplicity p-Pb events. Finally, we analyze the impact of different models of initial-state parton dynamics on the search for QGP signatures in small colliding systems.

Driving intention prediction algorithm based on TPA-LSTM for autonomous vehicles

To avoid the potential risk triggered by the failure of the conflict arbitration of autonomous vehicles, a driving intention prediction method based on the Long Short-Term Memory (LSTM) neural network involving Temporal Pattern Attention (TPA) is proposed. To be more specific, the TPA is embedded into the LSTM network to improve predictive accuracy. Furthermore, for evaluating the risk of the candidate trajectory, a risk assessment based on the velocity obstacle method which considers influence factors such as time to collision and collision energy loss is proposed. Finally, the proposed trajectory prediction algorithm is verified with the Next Generation Simulation data set and actual vehicle experiment. The results demonstrate the effectiveness of the proposed Method.

Modeling of electron refluxing and TNSA fields in laser–target interactions based on analysis of K α emission

We analyze and model fast-electron-induced Kα emission from an experiment in which a high-intensity ultra-short laser irradiated foil and bulk titanium targets. The motion of electrons inside the targets is calculated allowing for multiple scattering and collisional energy loss, while outside the target, electric fields of arbitrary configurations are assumed. It is shown that both the radial Kα-intensity distributions and the somewhat non-intuitive dependence of the absolute Kα emission on the target thickness can be reproduced by taking into account the fast-electron refluxing with an electric field configuration based on the target normal sheath acceleration model. We infer the presence of a sheath electric field on the order of TV/m, extending to about 100μm in the radial direction. In addition, we obtain a temporal profile of the Kα radiation.

Pressure drop prediction in a pneumatic conveying system with different curvature radius pipes for conveying particles

To investigate the system pressure drop distribution when conveying particle using different curvature radius pipes for the pneumatic conveying system, this paper measured the particle velocity distribution, particle-particle collision characteristics, collision energy loss, minimum pressure drop gas velocity, system pressure drop distribution, and power dissipation for R/D = 3.75, R/D = 5, and R/D = 6.25 pipes. Subsequently, the artificial neural network technique is used to predict the pressure drop of the pneumatic conveying system. It is found that the pressure drop of the system is lower when using the pipe with R/D = 6.25 for conveying particles. Compared to the pipe with R/D = 3.75, the reduction in power dissipation is 3.18 and 5.27% for conveying pellets when using R/D = 5 and R/D = 6.25 pipes, respectively. In addition, the energy loss of the system can be effectively reduced when using the pipe with R/D = 6.25 for conveying particles, which is more beneficial for the particles move in the pipe. The pressure drop model built with artificial neural network can predict the pressure drop value of the system more accurately within ±1.5%.

Scalar propagator in a background gluon field beyond the eikonal approximation

We investigate the path integral representation of the scalar propagator in a background gluon field, extending beyond the eikonal approximation by considering all gauge field components and incorporating its x− dependence. Utilizing the worldline formalism, we integrate the Schwinger proper time to express the scalar propagator in light-cone coordinates, facilitating a direct comparison with known results in the literature. The derived propagator captures the change of longitudinal momentum of the projectile within the medium. In the high-energy limit, our result simplifies to the effective gluon propagator employed in the BDMPS-Z formalism. Hence, we propose that our outcome serves as a foundational point for investigating corrections to the BDMPS-Z spectrum arising from the longitudinal momentum transfer of the radiated gluon with the medium, as well as for studying collisional energy loss phenomena. Lastly, by employing an expansion around the classical saddle point solution, we systematically derive an eikonal expansion in inverse powers of the boost parameter, encompassing corrections related to longitudinal momentum transfer and interactions of the projectile with the transverse component of the field.

Search for heavy, long-lived, charged particles with large ionisation energy loss in pp collisions at sqrt{s} = 13 TeV using the ATLAS experiment and the full Run 2 dataset

This paper presents a search for hypothetical massive, charged, long-lived particles with the ATLAS detector at the LHC using an integrated luminosity of 139 fb−1 of proton–proton collisions at sqrt{s} = 13 TeV. These particles are expected to move significantly slower than the speed of light and should be identifiable by their high transverse momenta and anomalously large specific ionisation losses, dE/dx. Trajectories reconstructed solely by the inner tracking system and a dE/dx measurement in the pixel detector layers provide sensitivity to particles with lifetimes down to mathcal{O} (1) ns with a mass, measured using the Bethe–Bloch relation, ranging from 100 GeV to 3 TeV. Interpretations for pair-production of R-hadrons, charginos and staus in scenarios of supersymmetry compatible with these particles being long-lived are presented, with mass limits extending considerably beyond those from previous searches in broad ranges of lifetime.

Searching for QGP droplets with high- pT hadrons and heavy flavor

The search for the smallest quark-gluon plasma (QGP) droplets in nature has motivated recent small collisions system programs at RHIC and LHC. Unambiguous identification of jet quenching due to final-state interactions is key to confirming QGP formation in these reactions. We compute the nuclear modification factors $R_{AA}$ and $R_{p(d)A}$ of charged hadrons and heavy flavor mesons in large (Au-Au, Xe-Xe, Pb-Pb) and small ($d$-Au, $p$-Pb, O-O) colliding systems, respectively. Our results include the Cronin effect and initial-state parton energy loss in cold nuclear matter. In the final state, hard partons undergo collisional energy loss and branching that was recently derived using Soft-Collinear-Effective-Theory with Glauber Gluon (SCET$_{\rm G}$). In large colliding systems, medium-modified QCD evolution of the fragmentation functions dominates the nuclear correction. As the system size decreases, we find that cold nuclear matter effects, collisional energy loss, and QGP-induced radiations can become equally important. A systematic scan over the medium size and mass/flavor dependence of $R_{AA}$ provides the opportunity to separate these individual contributions and identify QGP signatures in small systems. Predictions for $R_{AA}^{h}$, $R_{AA}^{D}$, $R_{AA}^{B}$ in O-O collisions at $\sqrt{s}=7$ TeV are presented with and without the formation of a QGP and contrasted with the corresponding $R_{p(d)A}$ calculations. Upcoming single-hadron measurements at the LHC will not only test the O-O predictions for both light and heavy flavor production, but will shed light on the possibly very different dynamics of $p$-A and A-A reactions at similar soft particle production multiplicities.

Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sqrt{s_{_text {NN}}}=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 text {pb}^{-1} of pp collisions collected in 2017 and 1.4 text {nb}^{-1} of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-k_{t} algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R= 0.2 and R= 0.4, and only R= 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R= 0.2 jets are also measured using 1.7 text {nb}^{-1} of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, R_text {AA}, is calculated for both b-jets and inclusive jets with R= 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet R_text {AA} to inclusive jet R_text {AA} is also presented and suggests that the R_text {AA} for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.

Coupled global and PIC modelling of the REGULUS cathode-less plasma thrusters operating on xenon, iodine and krypton

In recent years, the increasing demand for simple and low-cost propulsion for small satellites has given rise to a growing interest in low-power cathode-less plasma thrusters. Plasma is produced within a source tube using radiofrequency (RF) ionisation, enhanced by a magnetic field which also accelerates the discharge via the magnetic nozzle effect. A key advantage of cathode-less thrusters is that they can operate on a wider range of propellants, more easily stored, and often inexpensive (e.g., iodine) compared to traditional xenon. Despite simple hardware, plasma dynamics in this kind of device are highly complex. This work presents a numerical suite developed for cathode-less plasma thruster design and analysis. First, a 0D Global Source Model provides the plasma production in the source. A fully kinetic Particle-in-Cell model (2D and 3D) then handles plasma expansion in the magnetic nozzle. The capabilities of the suite are presented by-way-of investigation into the behaviour of alternative propellants iodine and krypton within the 50 and 150 W class REGULUS thrusters. The performance of each propellant is assessed in terms of plasma source and magnetic nozzle efficiencies. The results are then benchmarked against experimental measurements, obtaining agreement of <30%. At absorbed powers <20 W, iodine exhibits comparable performance to xenon but produces about 50% less thrust as the power is increased above 40 W. This occurs because of the molecular reaction processes seen by iodine, and associated inelastic energy thresholds which result in higher collisional energy losses. The high ionisation energy of krypton results in a low source efficiency. Instead, in the magnetic nozzle, krypton was found to perform best, facilitating the most thermal-to-kinetic conversion. But, the final thrust is <20% of xenon; instead iodine performs within 43% of the thrust provided by xenon. Finally, iodine contamination of spacecraft surfaces is found to be comparable to estimates found in other electric propulsion devices.

Energy loss in oblique collisions

The decrease in kinetic energy of a ball incident vertically on a rigid horizontal surface depends on the normal coefficient of restitution, [Formula: see text]. It is shown in the present paper that if the ball is incident obliquely on the surface then the total decrease in kinetic energy has two independent contributions, one depending on [Formula: see text], the other depending on the tangential coefficient of restitution, [Formula: see text].

Understanding mass hierarchy in different energy loss mechanisms through heavy flavor data

The theoretical analysis of experimental observations, such as the mass hierarchy effect, often neglects some ingredients, which may have a significant impact. The forthcoming measurements at RHIC and LHC will generate heavy flavor data with unprecedented precision, providing an opportunity to utilize high-p⊥ heavy flavor data to analyze the interaction mechanisms in QGP. To this end, we use our recently developed DREENA framework based on the dynamical energy loss formalism. We present: i) How to disentangle the signature of different interaction mechanisms (radiative and collisional energy losses) at the same dataset. ii) Novel observables susceptible to these different mechanisms to be tested by future high-precision measurements. iii) Analytical and numerical extraction of the mass hierarchy effect in energy losses through this observable.

Development and validation of an iodine plasma model for gridded ion thrusters

Iodine is emerging as an attractive alternative propellant to xenon for several electric propulsion technologies due to its significantly lower cost and its ability to be stored unpressurized as a solid. Because of the more complex reaction processes and energy-loss channels in iodine plasmas however, as well as the historical lack of reliable collision cross-section data, the development of accurate theoretical and numerical models has been hindered. Using recently calculated theoretical cross-sections, we present an iodine plasma model and perform a comparison with experimental data obtained from an iodine-fuelled gridded ion thruster. The model is in reasonable agreement with experimental measurements of the ion beam current, propellant mass utilization efficiency, and ion beam composition, and is able to quantitatively and qualitatively reproduce system behaviour as the input mass flow rate and RF power are varied. In addition, both the model and experiment show that the use of iodine can lead to a performance enhancement when compared with xenon. This occurs because of the combination of different iodine reaction processes, collision cross-section values, and inelastic energy thresholds which result in lower collisional energy losses, as well as an increased antenna-plasma power transfer efficiency for thrusters using a radio-frequency inductive coil.