Beam Velocity Research Articles

Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry

Solar radio U-bursts are generated by electron beams traveling along closed magnetic loops in the solar corona. Low-frequency (<100 MHz) U-bursts serve as powerful diagnostic tools for studying large-sized coronal loops that extend into the middle corona. However, the positive frequency drift component (descending leg) of U-bursts has received less attention in previous studies, as the descending radio flux is weak. In this study, we utilized LOFAR interferometric solar imaging data from a U-burst that has a significant descending leg component, observed between 10 and 90 MHz on 2020 June 5th. By analyzing the radio source centroid positions, we determined the beam velocities and physical parameters of a large coronal magnetic loop that reached just about 1.3 R ⊙ in altitude. At this altitude, we found the plasma temperature to be around 1.1 MK, the plasma pressure around 0.20 mdyn, cm−2, and the minimum magnetic field strength around 0.07 G. The similarity in physical properties determined from the image suggests a symmetric loop. The average electron beam velocity on the ascending leg was found to be 0.21c, while it was 0.14c on the descending leg. This apparent deceleration is attributed to a decrease in the range of electron energies that resonate with Langmuir waves, likely due to the positive background plasma density gradient along the downward loop leg.

Predictive process diagram for parameters selection in laser powder bed fusion to achieve high-density and low-cracking built parts

The laser powder bed fusion process (LPBF) has been widely used in many industrial sectors, including automotive, aerospace, and biomedical devices. With the fast development of new materials designed for critical applications, the conventional design of experiments for determining an optimal LPBF process window is a time and material-consuming activity. This can impose difficulties on small-to-medium industrial businesses where investing resources are limited. To address these challenges, this study draws inspiration from a reliable diagram used in laser welding to construct a similar diagram for the LPBF process. The objective is to enable the "right-first-time" selection of parameters that achieve a minimum of 99% density, regardless of the metallic materials and machine platforms. The diagram is established based on dimensionless beam power and velocity, derived from multiple LPBF process parameters (e.g., laser power, scan speed, hatch spacing) and the thermophysical properties of materials (e.g., melting point, density, thermal diffusivity). Furthermore, hot cracking susceptibility is considered by a strain-rate approach incorporated with the dimensionless thermal strain factor, which benefits when processing hard-to-weld alloys. The diagram shows high reliability in determining parameters corresponding to lack of fusion, keyhole porosity and 99% dense parts when plotting against literature data of LPBF for several metallic materials. Similar results were observed when applying to a novel material ABD-900AM Ni-based alloy, for which no previously published data were available. Moreover, the diagram proved effective in selecting parameters to process the high-cracking susceptible CM247LC Ni-based alloy, resulting in significant mitigation of hot cracking in the as-fabricated parts.

On the dynamics of large-amplitude ion-acoustic waves in a non-Maxwellian plasma with nonthermal electrons and an electron beam

This work investigates the characteristics of nonlinear large-amplitude ion-acoustic waves that occur and propagate in a non-Maxwellian plasma consisting of inertial ions and electrons beam as well as inertialess Cairns-distributed electrons. For this purpose, this inquiry utilizes a two-fluid model with the Sagdeev pseudopotential technique. By utilizing the Sagdeev pseudopotential, a mathematical equation similar to an energy balance equation is derived. The effects of the related physical parameters, including the inertialess electron concentration, the electron beam concentration, and the electron beam velocity, on the existence region of the solitary waves (SWs), and accordingly, the properties of ion-acoustic SWs (IASWs) are examined. Also, the Cairns distribution of electrons can significantly affect the features of large-amplitude IASWs, depending on the parameter that controls the distribution (the inertialess electron nonthermality). Additionally, the distinctive features of the solitary waves and their existence domain in connection with the relevant plasma parameters are also addressed.

Rf and thermal design studies of a 704.4 MHz, β≈0.2 , continuous-wave rf quadrupole accelerator for frequency jump

The radio-frequency quadrupole (RFQ) linac is often used as the first radio-frequency (rf) structure for both bunching and preaccelerating proton or heavy ion beams directly behind an ion source or a low-energy beam transport section. Typically, RFQ linacs operate at frequencies below 450 MHz and beam velocity ranges from β=0.01–0.08. Taking the MYRRHA project as an example, a 704.4 MHz continuous-wave (cw) RFQ linac has been recently proposed to realize an efficient fourfold frequency jump at β≈0.2. Due to its high frequency, small dimensions, and cw operation mode, careful design studies for the RFQ cavity structure including the water-cooling channels have been further performed, integrating the idea of using additive manufacturing technology for future construction. Systematic rf and thermal simulations and analysis demonstrated the reliability of the 704.4 MHz RFQ linac at cw operation and the frequency tuning ability via water-speed adjustments. This investigation shows that it could be a highly promising solution to perform an efficient frequency jump with a high-frequency RFQ accelerator at β≈0.2 for large-scale hadron linacs, which could potentially shorten the low- and medium-β parts of the whole facility. Published by the American Physical Society 2024

Inter-comparison study of wind measurement between the three-lidar-based virtual tower and four lidars using VAD techniques

ABSTRACT The accurate three-dimensional wind field obtained from a Doppler lidar not only helps to comprehend the refined structure of complex airflow but also provides important and valuable solutions for many fields. However, the underlying homogeneity assumption of the typical wind retrieval methods, such as Doppler Beam Swinging (DBS) and Velocity Azimuth Display (VAD) based on a single-lidar, will introduce the measurement uncertainty in complex terrain. In this paper, a new design of a wind measurement campaign involving seven lidars was carried out, which contained the three-lidar-based Virtual Tower (VT) using a time-space synchronization technique and four single-lidars with different elevation angles. This study investigates the performance of VT and VAD measurements under various conditions and evaluates the sensitivity of wind measurement uncertainty of VAD to the horizontal spatial- and probe volume-average effects associated with elevation angles of the laser beam. The inter-comparison results between VT and four VADs show consistent trends with small relative errors under neutral atmospheric conditions with weak wind velocity. Under convective or high Turbulence Intensity (TI) conditions, the relative errors between VT and VAD become larger and more fluctuant. Moreover, it is found that the measurement uncertainty of VAD increases at a given elevation angle with the increasing measurement heights, which is caused by the horizontal homogeneity associated with the conical scanning area. Additionally, the simulated and measured results of four VADs indicate that a larger elevation angle corresponds to a lower measurement uncertainty for a given height.

Particle-In-Cell simulation of electrostatic waves in the ionosphere

In the upper atmosphere (ionosphere), plasma with two electron populations is very common. The cold electrons (Te∼1 eV) usually originate in the ionosphere, while the hot electrons (Te∼100 eV) come from the magnetosphere. In addition to these two electron populations, there may be a beam of electrons streaming along the magnetic field lines. These electrons are responsible for exciting various electrostatic wave modes. In this article, we provide a systematic insight in the evolution of the system, based on the beam energy. With an increase in beam velocity, the beam temporarily recovers a portion of its initial energy as well as a higher saturation energy. The wave energy is lost significantly before saturation and after linear growth at a relatively modest beam velocity. In addition, the low beam velocity generates BGK electron holes in the phase space, which are missing at higher beam velocities. We also present the analysis of the condition of sustained electron holes in the phasespace.

High-harmonic Plasma Emission Induced by Electron Beams in Weakly Magnetized Plasmas

Electromagnetic radiation at higher harmonics of the plasma frequency (ω ∼ n ω pe, n > 2) has been occasionally observed in type II and type III solar radio bursts, yet the underlying mechanism remains undetermined. Here we present two-dimensional fully kinetic electromagnetic particle-in-cell simulations with high spectral resolution to investigate the beam-driven plasma emission process in weakly magnetized plasmas of typical coronal conditions. We focused on the generation mechanisms of high-harmonic emission. We found that a larger beam velocity (u d ) favors the generation of the higher-harmonic emission. The emissions grow later for higher harmonics and decrease in intensity by ∼2 orders of magnitude for each jump of the harmonic number. The second and third harmonic (H2 and H3) emissions get closer in intensity with larger u d . We also show that (1) the H3 emission is mainly generated via the coalescence of the H2 emission with the Langmuir waves, i.e., H2 + L → H3, wherein the coalescence with the forward-propagating beam-Langmuir wave leads to the forward-propagating H3, and coalescence with the backward-propagating Langmuir wave leads to the backward-propagating H3; and (2) the H4 emission mainly arises from the coalescence of the H3 emission with the forward- (backward-)propagating Langmuir wave, in terms of H3 + L → H4.

Helical Electron Beam Status Online Evaluation for Magnetron Injection Gun

The magnetron injection gun (MIG) is an essential component of the gyrotron traveling wave tube (gyro-TWT). Although the electron beam status influences the performance of the device, it cannot be measured directly in the experiment. An online evaluation module (OEM) for the experiment is developed to calculate the instant beam parameters of MIG. The OEM, by reconstructing the geometry of the MIG and related magnetic field distribution, can obtain the electron beam status under the operating parameters through the online simulation. The beam velocity spread of thermal emission with instant temperature and surface roughness are also considered. The validation is done in a W-band gyro-TWT, and the beam performance is evaluated in the experiment. With a pitch factor of 1.06 electron beam, the velocity spread affected by the electric-magnetic mismatch, thermal emission, and roughness is 1.00%, 0.56%, and 0.43%, respectively. The other beam parameters are also presented in the developed module. The OEM could guide and accelerate the testing process and ensure the safe and stable operation of the device.

Effect of self-healing behavior and self-healing technologies on the structural characteristics of cracked RC/ECC composite beams

The improving potential of self-healing behavior and self-healing technology to degradation of structural characteristics of cracked reinforced concrete structures was explored at the member level. Reinforced concrete/engineered cementitious composite (RC/ECC) composite beams were prepared by three self-healing technologies, including crystalline additives (CA), two types of superabsorbent polymers (SAP), and beam without self-healing technology was used as reference specimens. The self-healing properties of structural characteristics of beams were studied by four-point bending tests, including bear capacity, stiffness, ductility index, energy absorption capacity (EAC), and failure mode. The self-healing behavior of damage was evaluated by ultrasonic wave test and damage identification test based on natural frequency. Self-healing behavior of four types of RC/ECC composite beams improved the structural characteristics after cracking to varying degrees. The stiffness of CB-0, CB-S, CB-C, and CB-SH after self-healing increased by 10.80%, 22.88%, 36.71%, and 28.80% compared to that without self-healing, respectively. Recovery ability of structural characteristics of RC/ECC composite beam is enhanced by self-healing technologies. Moreover, CA exhibits a superior improvement in the recovery ability of the structural characteristics compared with two types of SAP. Moreover, the natural frequency and ultrasonic velocity of pre-cracked beams after self-healing were higher than those without self-healing, especially when self-healing technologies were applied. There is a positive correlation between the recovery ability of ultrasonic velocity and self-healing behavior of the structural characteristics of RC/ECC composite beams. This also explains why the structural characteristics of pre-cracked beams have been improved to varying degrees due to different self-healing techniques.

Enhanced Total Vibrational Excitation Yield in a Slow Narrow-Pulsed Hydrogen Molecular Beam.

High-efficiency excitation of a molecular beam is critical for investigating state-selected chemistry. However, achieving vibrational excitation of the entire beam for Raman-active molecules such as H2 proves extremely challenging, primarily because laser pulses are much shorter than the molecular beam. In this study, we achieve a total excitation efficiency of over 20% by employing stimulated Raman pumping (SRP) in a slow, narrow-pulsed molecular beam. Through optimizing the intensity and spot shape of the SRP lasers, we attain saturated excitation within the laser crossing region. Furthermore, by reducing the beam velocity and narrowing the beam pulse using a cold valve and a fast chopper, we significantly enhance the total excitation yield. COMSOL simulation and a newly developed model reveal that a critical velocity allows the chopper to block unexcited molecules and reserve most of the excited ones from the beam, resulting in the highest overall excitation yield. This innovative setup opens new possibilities for state-selected experiments in surface science and ion-molecule reaction dynamics, particularly involving weak transitions and pulsed lasers.

Enhancement of fusion reactivity under non-Maxwellian distributions: effects of drift-ring-beam, slowing-down, and kappa super-thermal distributions

Non-Maxwellian distributions of particles are commonly observed in fusion studies, especially for magnetic confinement fusion plasmas. The particle distribution has a direct effect on fusion reactivity, which is the focus of this study. We investigate the effects of three types of non-Maxwellian distributions, namely drift-ring-beam, slowing-down, and kappa super-thermal distributions, on the fusion reactivities of D-T (Deuterium-Trillium) and p-B11 (proton-Boron) using a newly developed program, where the enhancement of fusion reactivity relative to the Maxwellian distribution is computed while keeping the total kinetic energy constant. The calculation results show that for the temperature ranges of interest to us, namely 5–50 keV for D-T and 100–500 keV for p-B11, these non-Maxwellian distributions can enhance the fusion reactivities. In the case of the drift-ring-beam distribution, the perpendicular ring beam velocity leads to decreased enhancement in low temperature range and increased enhancement in high temperature range. This effect is favorable for p-B11 fusion reaction and unfavorable for D-T fusion reaction. This is because the important temperature range for fusion reaction significantly overlaps with the high temperature enhancement range, while the important temperature range for fusion significantly overlaps with the low temperature reduction range. In the slowing-down distribution, the birth speed plays a crucial role in both reactions, and increasing birth speed leads to a shift in the enhancement ranges towards lower temperatures, which is beneficial for both reactions. Finally, the kappa super-thermal distribution results in a relatively large enhancement in the low temperature range with a small high energy power-law index . Overall, this study provides insight into the effects of non-Maxwellian distributions on fusion reactivity and highlights potential opportunities for enhancing fusion efficiency.

Simultaneous Sensing of Velocity and Position of a Moving Light Source Using Metal-Insulator-Semiconductor Structures.

Photodetectors based on semiconductor devices have been widely used to sense light position, intensity, and wavelength. However, monitoring the motion velocity of a light beam generally requires complex integration of device arrays. Here, we report a single device of a simple metal-insulator-semiconductor structure for self-powered sensing not only position but also velocity of a light beam or shadow. A velocity-dependent voltage output between two terminals of the metal is observed. It is attributed to light illumination-induced local surface potential change in semiconductors and the following movement of local charges accumulated in the metal due to capacitive coupling. The amplitude of the velocity-dependent voltage can be facilely modulated by applying a gate voltage. These results shed light on compact devices with multiple sensing functions.

Enhanced Measurement of Vortex Beam Rotation Using Polarization-Assisted Particle Swarm Optimization for Phase Retrieval

In detecting the rotation velocity of an object employing the rotational Doppler effect of vortex beams, atmospheric turbulence can easily cause phase distortion and spiral spectrum dispersion, consequently reducing velocity measurement accuracy. This study combines adaptive optical intelligence algorithms with polarization compensation information to propose a novel approach, the Stokes–Particle swarm optimization Gerchberg–Saxton (Stokes-PSO GS) algorithm, which integrates Stokes polarization information assistance and PSO for GS phase retrieval. The algorithm adjusts the phase and amplitude of the pre-compensated phase screen of the GS algorithm utilizing Stokes information of polarized vortex beam (with lL = 5 and lR = −5) before and after distortion. The PSO is then employed to optimize the pre-compensated phase screen and perform compensations. Simulation results at zS-T = 200 m and Cn2 = 1 × 10−14 m−2/3, demonstrate that the Stokes-PSO GS algorithm exhibits strong stability (small angular spectrum purity deviation, σp, Stokes-PSO GS = 0.005675% &lt; σp, GS = 11.62%), superior optical field recovery (well-recovered Stokes optical field, up to 33.76% improvement in angular spectrum purity), and high-velocity measurement accuracy (25.93% improvement) compared to the GS algorithm. This approach enables precise measurement of the rotation velocity of the vortex beam, demonstrating its potential in practical applications.

On the Existence of Subsonic Solitary Waves Associated with Reconnection Jets in Earth’s Magnetotail

The Magnetospheric Multiscale Spacecraft (MMS) has detected the signature of electrostatic solitary waves (ESWs) occurring in the reconnection jet site of the Earth’s magnetotail (Liu et al.). These observations have motivated us to explore the mechanism underlying the formation of fast- and slow-mode ion-acoustic solitary waves in the magnetotail region. To this end, we have formulated a three-component magnetized plasma model consisting of nonthermal electrons and two cold ion beams streaming parallel and antiparallel to the magnetic field, respectively. In this work, we have examined the existence conditions for ion-acoustic subsonic waves in a suprathermal space plasma comprising two counterstreaming (drifting) ion beams interacting with a suprathermal electron background. An exact (nonperturbative) nonlinear technique has been adopted to examine the role of the beam velocity and the spectral index on the evolution of subsonic waves. Linear analysis reveals that subsonic waves are unstable when the beam velocity is lower than a threshold value; hence in this regime, only conventional supersonic (fast) waves are formed. On the other hand, when the beam velocity exceeds the threshold, either supersonic or subsonic waves may exist. The combined impact of the beam velocity and electron superthermality on the characteristics of subsonic solitary waves has been analyzed. Our results are shown to be in good agreement with observations of slow ESWs by the MMS spacecraft. Our findings will help to unfold the so-far unexplored dynamical characteristics of subsonic waves that may occur in the reconnection site of Earth’s magnetotail.

Effect of Beam Velocity Spread With Spatial Variation on Mode Excitation in Gyrotrons

Effect of Beam Velocity Spread With Spatial Variation on Mode Excitation in Gyrotrons

Threshold for ionization-induced defect annealing in silicon carbide

Ion track formation in SiC has never been observed, but this material is well-known for easily achieving ionization-induced defect annealing. Therefore, the aim of this work is to study the threshold for ionization-induced defect annealing in silicon carbide using Rutherford backscattering spectrometry in channeling mode. It was established that 3 MeV O beam can activate the ionization-induced defect annealing in SiC, but 12 MeV O cannot, despite the same electronic stopping values. We attribute this finding to the velocity effect and propose systematic investigations of ionization-induced defect annealing with respect to the velocity of the ion beams used.

Optimal Exposure Parameters for Microsurgery of Embryo Zona Pellucida Using Femtosecond Laser Pulses

We applied femtosecond laser pulses for microsurgery of the zona pellucida (ZP) of mouse embryos in terms of assisted reproductive technologies. The embryos were subjected to a series of laser pulses (wavelength of 514 nm, pulse duration of 280 fs, repetition rate of 2.5 kHz). Optical microscopy was used to study the dependence of the ZP cut width on the pulse energy E and velocity v of the laser beam. It is shown that the same value of the cut width can be obtained for different combinations of these parameters. The boundaries of admissible values were found to be E = (19–52) nJ, v = (0.001–0.03) mm/s; recommendations on their proper choice are given. An analytical expression of the cut width of the ZP for a given combination of laser-pulse energy, beam velocity, and pulse repetition rate is proposed. This simple and easy-to-use equation allows for quick prediction of ZP cut width in embryo microsurgery procedures of laser-assisted hatching and embryo laser tagging using femtosecond laser pulses.

Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel.

This paper proposes a robust symbol timing synchronization scheme for return link initial access based on the Digital Video Broadcasting-Return Channel via Satellite 2nd generation (DVB-RCS2) system for the Low Earth Orbit (LEO) satellite channel. In most cases, the feedforward estimator structure is considered for implementing Time Division Multiple Access (TDMA) packet demodulators such as the DVB-RCS2 system. More specifically, the Non-Data-Aided (NDA) approach, without using any kind of preamble, pilot, and postamble symbols, is applicable for fine symbol timing synchronization. However, it hinders the improvement in estimation accuracy, especially when dealing with short packet lengths during the initial access from the User Terminal (UT) to the Gateway (GW). Moreover, when a UT sends a short random access packet for initial access or resource request to the LEO satellite channel, the conventional schemes suffer from a large Doppler error depending on UT's location in a beam and satellite velocity. To ameliorate these problems, we propose a novel symbol timing synchronization algorithm for GW, and its advantage is confirmed through computer simulation.

Effect of Beam Velocity on Firehose Instability in Earth’s Magneto-plasma with General Loss-Cone Distribution Function

The dynamics of firehose instability (FHI) in the presence of beams is investigated by applying kinetic theory and general loss cone distribution (GLCD) function. It is explained how ion/electron beams affect the growth rate and length of the FHI in low beta homogeneous plasma. The energy of the transversely heated ions is found to be reduced by the ion beam, whereas the temperature anisotropy arranges free energy, to begin with, and accelerates the growth rate of the instability. It has been discovered that the firehose instability results from the extraction of energy from ions heated perpendicularly in the presence of upflowing ion beams in the asymmetrical magneto-plasma. In the auroral acceleration region, the findings are expressed in terms of the firehose instability. The findings may be checked and then may be applied in dusty and multi-component space plasma also.

A novel damage detection technique for laminated composite beams under the action of a moving load

The present paper investigates damage detection in laminated composite beams under the action of a moving load. A novel approach is introduced to present damage indices by utilizing the dynamic response of the beam. The equations of motion for the beam have been derived by considering in-plane and out-of-plane deformations, rotary inertia, and shear effects. To obtain the solution, the finite element method, in conjunction with the Newmark algorithm, has been employed. Three damage indices, namely the Displacement Variation Index (DVI), Velocity Variation Index (VVI), and Acceleration Variation Index (AVI) have been introduced. These indices are utilized to detect the location of damage based on the beam's displacement, velocity, and acceleration, respectively. Furthermore, the proposed approach enables to detect single and multiple damages at different severities, locations, and boundary conditions. Likewise, it is applicable to various velocities of moving forces and can effectively operate in both normal and noisy conditions. The results of this investigation demonstrate that the proposed damage indices are able to accurately detect damage along the entire length of the beam without prior knowledge of its healthy state. It is noteworthy that the acceleration-based index, among the indices proposed in this study, exhibits the highest efficiency in determining the precise location of the damage under operational conditions.