Generation Of Radiation Research Articles

Angular Dispersion of Free-Electron-Light Coupling in an Optical Fiber-Integrated Metagrating.

Free electrons can couple to optical material excitations on nanometer-length and attosecond-time scales, opening-up unique opportunities for both the generation of radiation and the manipulation of the electron wave function. Here, we exploit the Smith-Purcell effect to experimentally study the coherent coupling of free electrons and light in a circular metallo-dielectric metagrating that is fabricated onto the input facet of a multimode optical fiber. Using hyperspectral angle-resolved (HSAR) far-field imaging inside a scanning electron microscope, we probe the angular dispersion of Smith-Purcell radiation (SPR) that is simultaneously generated in free space and inside the fiber by an electron beam that grazes the metagrating at a nanoscale distance. Furthermore, we analyze the spectral distribution of SPR that is emitted into guided optical modes and correlate it with the numerical aperture of the fiber. By varying the electron energy between 5 and 30 keV, we observe the emission of SPR from the ultraviolet to the near-infrared spectral range, and up to the third emission order. In addition, we detect incoherent cathodoluminescence that is generated by electrons penetrating the input facet of the fiber and scattering inelastically. As a result, our HSAR measurements reveal a Fano resonance that is coupled to a Rayleigh anomaly of the metagrating, and that overlaps with the angular dispersion of second-order SPR at 20 keV. Our findings demonstrate the potential of optical fiber-integrated metasurfaces as a versatile platform to implement novel ultrafast light sources and to synthesize complex free-electron quantum states with light.

Review of High Voltage Pulsed Power Supplies and Power Electronics in Pulse Power Generation

Recently, pulse-shaped power supplies have become more popular. Pulsed power is versatile and useful as a supply method since it can take several shapes and has many pulse characteristics. The release of electrons, protons, and neutrons from an atom and the synthesis of molecules to generate ions or other molecules require a lot of immediate energy. Pulsed power is needed for decomposition, molecular fusion and material joining, radiation generation (e.g., electrons, lasers, radar), explosive processes for concrete recycling, wastewater and exhaust gas treatment, and material surface treatments. Industrial and environmental applications require pulsed power, which requires efficient and adaptive pulse modulators. Higher-quality repeating pulses are needed for plasma fusion and laser weapons. Marx Generators, Magnetic Pulse Compressors, Pulse Forming Networks, and Multistage Blumlein Lines have several uses. Pulse modulators use spark gap and hydrogen thyratron gas/magnetic switching technologies for their high voltage tolerance and low-rise times. These creatures are inefficient, unreliable, repetitious, and short-lived. These devices are heavy, bulky, and expensive. Solid-state switching technology can replace conventional devices, improving pulse supply. High-frequency switching repeats the pulsed power supply. These items are compact, efficient, affordable, reliable, and durable. Solid-state transistor applications may not meet switch voltage ratings and rise time constraints. Various power electronics configurations can produce solid-state high-voltage pulses.

A synthetic diagnostics platform for microwave imaging diagnostics in tokamaks

Interpreting experimental diagnostics data in tokamaks, while considering non-ideal effects, is challenging due to the complexity of plasmas. To address this challenge, a general synthetic diagnostics (GSD) platform has been established that facilitates microwave imaging reflectometry and electron cyclotron emission imaging. This platform utilizes plasma profiles as input and incorporates the finite-difference time domain, ray tracing and the radiative transfer equation to calculate the propagation of plasma spontaneous radiation and the external electromagnetic field in plasmas. Benchmark tests for classical cases have been conducted to verify the accuracy of every core module in the GSD platform. Finally, 2D imaging of a typical electron temperature distribution is reproduced by this platform and the results are consistent with the given real experimental data. This platform also has the potential to be extended to 3D electromagnetic field simulations and other microwave diagnostics such as cross-polarization scattering.

Electromagnetic emission from plasma with counter-streaming electron beams in the regime of oblique instability dominance

In this study, we investigate the generation of electromagnetic emission near the second harmonic of the plasma frequency induced by pairs of counter-propagating electron beams. Such systems can naturally occur in cosmic plasmas when particle acceleration regions are closely spaced, and they can also be implemented in a laboratory device. We specifically focus on the regime where the oblique beam–plasma instability dominates. The emission mechanism relies on the coalescence of counter-propagating plasma waves with different transverse structures. It has been demonstrated that the parameters of the system necessary for efficient radiation generation can be determined using the exact linear theory of beam–plasma instability. Through particle-in-cell numerical simulations, we show that a high beam-to-radiation conversion efficiency can be achieved when the beams excite small-scale oblique plasma oscillations. Importantly, we find that the efficiency and spectral characteristics of the radiation are not dependent on the thickness of the beams. We explore two scenarios involving pairs of symmetric beams: one with relativistic beams having a directed velocity of vb=0.9c and another with sub-relativistic beams at vb=0.7c. Additionally, we consider the injection of two beams with different velocities. In all cases considered, the beam-to-radiation power conversion efficiency reaches a level of a few percent, a sufficiently high value for beam–plasma systems.

THz radiation generation from plasma wakefield driven by skew-cosh-Gaussian laser beam under an undulator magnetic field

The paper examines theoretically the generation of terahertz (THz) radiation as a result of wakefields generated by skew-cosh-Gaussian (skew-chG) laser beam propagating in collisional plasma under an undulator magnetic field. Analytical and non-linear equations have been derived to describe the generation of THz radiation by skew-chG laser beam. Using equations of motion, continuity equations, and perturbation technique, the transverse and longitudinal wakefield has also been derived in the presence of an undulator magnetic field. It is shown that the collisional plasma carries a higher longitudinal wakefield amplitude while the undulator amplitudes are lower. In addition, it is found that smaller collision frequencies make larger wakefield amplitudes that generate terahertz radiation. However, when the collision frequency becomes equal to the plasma frequency, the wakefield amplitude is greatly reduced. Moreover, it is observed that the THz field decreases with the increase of the beam waist of the skew-chG laser beam. It is also shown that the THz field exhibits an increasing behavior with increasing s parameter and undulator amplitudes despite the presence of significant collisions.

Entropy Generation and Thermal Radiation Impact on Magneto-Convective Flow of Heat-Generating Hybrid Nano-Liquid in a Non-Darcy Porous Medium with Non-Uniform Heat Flux

The principal objective of the study is to examine the impact of thermal radiation and entropy generation on the magnetohydrodynamic hybrid nano-fluid, Al2O3/H2O, flow in a Darcy–Forchheimer porous medium with variable heat flux when subjected to an electric field. Investigating the impact of thermal radiation and non-uniform heat flux on the hybrid nano-liquid magnetohydrodynamic flow in a non-Darcy porous environment produces novel and insightful findings. Thus, the goal of the current study is to investigate this. The non-linear governing equation can be viewed as a set of ordinary differential equations by applying the proper transformations. The resultant dimensionless model is numerically solved in Matlab using the bvp4c command. We obtain numerical results for the temperature and velocity distributions, skin friction, and local Nusselt number across a broad range of controlling parameters. We found a significant degree of agreement with other research that has been compared with the literature. The results show that an increase in the Reynolds and Brinckmann numbers corresponds to an increase in entropy production. Furthermore, a high electric field accelerates fluid velocity, whereas the unsteadiness parameter and the presence of a magnetic field slow it down. This study is beneficial to other researchers as well as technical applications in thermal science because it discusses the factors that lead to the working hybrid nano-liquid thermal enhancement.

Significance of heat generation in MHD channel flow of a maxwell fluid with heat suction and blowing effects

This investigation aims to provide numerical analyses for a complex problem involving magnetohydrodynamics (MHD), radiation and heat generation of a Maxwell fluid within a porous medium on the channel. The governing equations for momentum, concentration, and energy are converted from nonlinear partial differential equations (NLPDEs) into nonlinear ordinary differential equations (NLODEs) for concentrated analysis using a similarity transformation. Dimensionless velocity, temperature and concentration fields corresponding to steady motions of Maxwell fluid over a channel are numerically recognized using the bvp4c scheme in MATLAB. We verified our findings by comparing them with existing work, achieving an outstanding agreement. The impact of physical parameters on fluid motion is plotted and debated. The results indicate that as the Deborah number increases, the temperature profile decreases, but the velocity and concentration contours increase for the suction effect. However, the opposite trend is detected for the injection parameter. Heat generation amplifies the temperature contour for suction and injection effects.

Dual solutions of Darcy-Forchheimer radiative-convective magneto-nanofluid flow over an exponentially stretching/shrinking surface: Stability and entropy generation analysis

A numerical investigation was conducted to examine the existence of dual solutions over exponentially stretching or shrinking permeable surfaces. The study aimed to analyze the impact of thermal and second-order velocity slip on magnetohydrodynamic (MHD) mixed convective radiative nanofluid flow within a Darcy-Forchheimer porous medium while considering heat generation. Two distinct types of nanofluids, namely Cu-water and TiO 2/water, were employed in the investigation. To address the nonlinear partial differential equations (PDEs), similarity transformations were utilized to transform them into a system of ordinary differential equations (ODEs). The resulting coupled higher-order nonlinear ODEs were then solved using a MATLAB-based boundary value algorithm known as bvp4c. Two distinct solutions are observed within a restricted range of the stretching/shrinking parameter ξ ( ξ > ξ c ) and suction parameter S ( S > S c ), terminating respectively at ξ = ξ c or S = S c . The critical values are identified as ξ c = − 1.1952 ( Cu − water ) , − 0.9304 ( Ti O 2 − water ) and S c = 1.6437 ( Cu − water ) , 1.8900 ( Ti O 2 − water ) , maintaining the fixed values of the remaining physical parameters. Notably, the critical value for Cu-water is lower than that of TiO 2-water. Moreover, in both solution branches, the range of skin-friction coefficient and local Nusselt number for Cu-water surpasses that of TiO 2-water. An evaluation of the temporal stability of these solutions reveals that only the first solution remains stable. This is supported by the positivity of the smallest eigenvalues ( γ 1 > 0 ), indicating stability. Conversely, for the second solution, the smallest eigenvalues ( γ 1 < 0 ) are negative, signifying its instability. Also, Cu-water nanofluid exhibits higher fluid velocity and lower fluid temperature than TiO 2-water nanofluid for stable solutions and the opposite behavior for unstable solution branches. Significantly, within the initial solution branch, there is an escalation in velocity profiles attributed to the magnetic parameter, Grashof number, porous parameter, and first- and second-order velocity slip parameter. Conversely, a decrease is observed for the Forchheimer number, while the opposite holds true for the second solution branch. For both solution branches, the temperature profiles experience a reduction due to thermal slip and stretching/shrinking parameters, whereas enhancements are noted for thermal radiation and heat generation parameters. Furthermore, an increase in the suction parameter leads to elevated skin friction coefficient and local Nusselt number in the first stable solution, thereby promptly improving heat transfer efficiency. Moreover, improvements in entropy generation arise from factors such as thermal radiation, magnetic field, and nanoparticle solid volume fraction, presenting opportunities to optimize heat transmission in cooling and heating systems.

Generation of THz radiation through molecular modulation in hydrogen-filled hybrid anti-resonant fibers.

We study the generation of narrowband terahertz (THz) pulses by stimulated Raman scattering and molecular modulation in hydrogen-filled hybrid hollow-core fibers. Using a judicious combination of materials and transverse structures, this waveguide design enables simultaneous confinement of optical and THz signals with reasonably low attenuation, as well as high nonlinear overlap. The THz pulses are then generated as the second Stokes band of a ns-long near-infrared pump pulse, aided by Raman coherence waves excited in the gaseous core by the beat-note created by the pump and its first Stokes band. Optimization of the fiber characteristics facilitates phase matching between the corresponding transitions and coherence waves while avoiding coherent gain suppression, resulting in potential optical-to-THz conversion efficiencies up to 60%, as confirmed by rigorous numerical modelling under ideal zero-loss conditions. When the current optical material constraints are considered, however, the attainable efficiencies relax to 0.2%, a still competitive value compared to other systems. The approach is in principle power and energy scalable, as well as tunable in the 1-10 THz range without any spectral gaps, thereby opening new pathways to the development of fiber-based THz sources complementary to other mature technologies such as quantum cascade lasers.

Using a New Phenomenon of Electronic Oscillations Near the Positive Electrode to Generate Powerful Microwave Radiation

A novel microwaves generator scheme is introduced, where electrons perform oscillations within the electric field of a positively charged electrode. This phenomenon is based on a recently developed theory of the interaction of electrons with electric fields, which predicts the presence of a repulsive force acting on an electron near strongly positively charged bodies. Along with the usual attractive force acting at a distance, this newly discovered repulsive force causes specific oscillations of electrons in the vicinity of a positively charged electrode, leading to the generation of electromagnetic radiation. The proposed generator represents a new variant of a vircator, wherein a virtual cathode is formed in front of, rather than behind, a positively charged anode.

On mean free path of X-ray transition radiation generation in radiator

An algorithm for the space distribution of X-ray transition radiation generated by a relativistic charged particle in regular radiators is discussed in the framework of the Geant4simulation toolkit. The model predictions are compared with experimental data.

Highlighting the NIAID Radiation and Nuclear Countermeasures Program's Commitment to Training and Diversifying the Radiation Workforce.

Developing and maintaining a robust and diverse scientific workforce is crucial to advance knowledge, drive innovation, and tackle societal issues that impact the economy and human health. The shortage of trained professionals in radiation and nuclear sciences derives from many factors, such as scarcity of specialized coursework, programming, professional development, and experiential learning at educational institutions, which significantly disrupt the training pipeline. Other challenges include small numbers of faculty and educators with specialized radiation/nuclear expertise that are continually overextended professionally and scientifically, with the burden of training falling on this subset of individuals. Even more alarming is the recent loss of radiobiologists due to increased retirements and deaths, leaving the radiobiology community with a void of mentors and knowledge. Lastly, inconsistency in acquiring stable grant funding to recruit and retain scientists is a major hurdle to training the next generation of radiation and nuclear scientists. Recommendations from the scientific community and the National Academies of Sciences, Engineering, and Medicine describe the need to bolster educational resources and provide more hands-on training experiences. Of equal importance was the suggestion that funding agencies provide more opportunities for training and tracking the radiation workforce. The Radiation and Nuclear Countermeasures Program (RNCP), and the Office of Research Training and Special Programs (ORTSP), both within the National Institute of Allergy and Infectious Diseases (NIAID) are committed to helping to develop and sustain the radiation research workforce. This commentary illustrates the importance of addressing radiation workforce development and outlines steps that the RNCP is taking to help mitigate the issue. In addition, the role for Diversity, Equity, Inclusion, and Accessibility (DEIA) in helping to increase the number of students trained in the radiation sciences is discussed, and the NIH's DEIA priorities and RNCP efforts to improve DEIA in the research community are highlighted. One of the main goals of this commentary is to provide awareness of available educational (i.e., development of a radiation biologist eBook) and funding resources. A summary of available awards targeting early- to mid-stage investigators and diversity candidates is given, and it is hoped that this list, although not exhaustive and not specific for all focus areas in radiation (e.g., cancer research), will encourage more radiation biologists to explore and apply to these under-utilized opportunities.

Melting and dissipative effects about entropy induced Darcy-Forchheimer flow involving ternary-hybrid nanofluids

Here we examine melting heat in flow of ternary-hybrid nanoliquid bounded by stretching surface. Alumina (Al2O3), Silica (SiO2) and Copper Oxide (CuO) are three utilized nanoparticles. Conventional liquid employed here is water. Heat generation, dissipation and radiation comprise energy equation. Analysis of entropy generation rate is carried out. Implementation of adequate variables converts nonlinear partial differential system to ODEs. ND-solve approach is implemented to achieve solution. Quantities of interest are deliberated. It is noticed that an opposite trend of temperature for radiation and heat generation is found. Augmentation against melting heat and radiation for thermal transport rate is observed. Velocity decays for higher Forchheimer number. Reduction for velocity against melting and porosity is noticed. Temperature enhancement through Forchheimer number is witnessed. Rise in entropy production for Brinkman and Eckert numbers is noticed. Skin friction for Forchheimer number and melting variable has opposite trends.

Terahertz and far infrared radiation generation in air plasma created by bichromatic subpicosecond laser pulses

Here, we report on terahertz (THz) radiation generation in air driven by the fundamental and second harmonic of Yb:KGW laser pulses with durations of a few hundred femtoseconds. It was found that the spectrum of generated THz pulses surprisingly spans up to 50 THz, which is comparable to that usually obtained using much shorter Ti:sapphire laser pulses. The broad bandwidth is attributed to a strong spatiotemporal reshaping of the pump pulses in a filament. The achieved energy conversion efficiency is comparable to the one usually obtained from much shorter pump pulses and could be further improved by an optimized experimental setup. The obtained results indicate that compact Yb-based sources provide an attractive alternative to much larger and expensive laser systems.

Future changes in North Atlantic winter cyclones in CESM-LE – Part 2: A Lagrangian analysis

Abstract. Future changes in extratropical cyclone structure and dynamics may lead to important impacts but are not yet fully understood. In the first part of this study, we have applied a composite approach together with potential vorticity (PV) inversion to study such changes in the dynamics of North Atlantic cyclones. Here, this is complemented with the help of a Lagrangian perspective, making use of air parcel trajectories to investigate the causes of altered PV anomalies as well as the role that cyclone airstreams play in shaping these changes. Intense cyclones in the extended winter seasons of two periods, 1990–2000 and 2091–2100, are studied in Community Earth System Model Large Ensemble (CESM-LE) simulations, and backward trajectories are calculated from the cyclone area as a basis to construct cyclone-centered composites of Lagrangian tendencies and their projected future changes. Our results show that diabatic processes on a timescale of 24 h shape the cyclones' low-level PV distribution and corroborate that the increasing moisture content along with enhanced ascent in warm conveyor belts leads to amplified latent heat release and larger low- and mid-level PV anomalies near the cyclone center in a warmer climate. In contrast, projected upper-level PV changes are due to a combination of several processes. These processes include cloud diabatic PV changes, anomalous PV advection, and likely also radiative PV generation in the lower stratosphere above the cyclone center. For instance, enhanced poleward advection is the primary reason for a projected decrease in upper-level PV anomalies south of the cyclone center. Warm conveyor belt outflow regions are projected to shift upward, but there is not robust change in the associated upper-level PV anomalies due to compensation between enhanced low-level PV generation and upper-level PV destruction. In summary, our two-part study points to future changes in the relative importance of different processes for the dynamics of intense North Atlantic cyclones in a warming climate, with important consequences for the near-surface wind pattern. In particular, a larger role of cloud diabatic processes is projected, affecting the cyclones through PV production in the lower troposphere. The role of other mechanisms, in particular radiative changes near the tropopause, should be investigated in more detail in future studies.

Procedure to Solve the One-Dimensional Radiative Transfer Equation (1D-RTE) of an Ionized Medium Using Spatial Discretization and an Iterative Process

A new solution procedure for the one-dimensional radiation transfer equation, which describes the radiation propagation in semi-transparent media, is proposed. The resolution proposed, in this work for the first time, is based on spatial discretization and an iterative method. The emitter medium is subdivided into several layers and each layer is considered homogeneous and at the local thermodynamic equilibrium. The emission intensity of each layer is deduced from that of the previous layer. Comparisons are made between our method and other methods described in the literature. This solution is then used to model the line profiles of the Balmer Hα line emitted by a plasma created by the breakdown of a pulsed laser in water.

Second-grade fluid with carbon nanotubes flowing over an elongated curve surface possessing thermal radiation and internal heat generation effects

Second-grade fluid with carbon nanotubes flowing over an elongated curve surface possessing thermal radiation and internal heat generation effects

Analyzing the Effect of Magnetic Drag Force on Carbon Nanotubes Suspended in Casson Fluid Within Parallel Surfaces with Heat Diffusion and Rate of Molar Reaction: An Analytical Approach

The study of hydromagnetic CNTs of Casson fluids in Poiseuille flow has significant implications for various industries and can provide valuable insights into the fundamental properties, such as viscosity and conductivity of these fluids. They can improve the heat transfer properties of fluids and enhance the overall efficiency of thermal systems and the presence of CNTs can induce a magnetic field in the fluid. The main goal of using carbon nanotubes (CNTs) in Poiseuille flow is to enhance the fluid flow properties, such as viscosity, thermal conductivity, and heat transfer and the novelty of CNTs in Poiseuille flow lies in their ability to modify the fluid flow properties by altering the structure of the fluid at the nanoscale level. The use of CNTs in Poiseuille flow has gained attention due to their unique mechanical, electrical, and thermal properties. An analytical approach to the investigation of heat transmission in hydro-magnetic forces of natural convective flow of Casson-fluid in a Poiseuille flow implanted by Darcian regime on Carbon Nanotubes with the impacts of magnetic field, heat generation, diffusion thermo, porosity, radiation and first order chemical reaction is presented. In this research, dual solutions are introduced for single-wall and multiple-wall carbon nanotubes over velocity and temperature of nanofluid by the application of various physical and they are elaborated via plane curves. The base fluid is considered for the CNTs as Engine oil. Validity of this model has established by comparing with the available previous literature and is found acceptable agreement with it. In the present study, it is found that the fluctuation in radiation and heat generation plays a significant role in CNTs. It is known that a rise in the Casson parameter and nanoparticle volume fraction enhances the fluid velocity. It is concluded that, the volume fraction of nanoparticles in Poiseuille flow can have a significant impact on the flow behaviour and properties of the fluid. This study has tremendous feasible applications in the areas related to biomedical sciences, water purification process, technology of fibers, nano-materials technology, storage of energy and various applications.

Investigation of terahertz radiation generation from laser-wakefield acceleration

We investigate the generation of terahertz (THz) radiation from laser-wakefield acceleration (LWFA) in a helium gas jet. We consider a three-dimensional setup incorporating a realistic gas density distribution and use particle-in-cell simulations to study the interaction of a femtosecond intense laser pulse with the gas medium. Our results show that LWFA can efficiently produce THz radiation. In the simulations, we use multiple probes to record the electric and magnetic fields arising from the interaction. In addition, we compare the results of fixed and moving window simulation boxes used to capture electromagnetic fields in the THz range. We demonstrate that a moving window with a 600 μm width can be significantly useful for THz studies. We further analyze the spectrum of spatially and temporally resolved electromagnetic radiation and its emission angle. Our results are consistent with experimental data. Our findings provide valuable insights into the potential of LWFA as a strong source of THz radiation.

THz transition radiation of electron bunches laser-accelerated in long-scale near-critical-density plasmas

Direct laser electron acceleration in near-critical density plasma produces collimated electron beams with high charge Q (up to µC). This regime could be of interest for high-energy THz radiation generation, as many of the mechanisms have a scaling ∝Q2 . In this work, we focus specifically on the challenges that arise during numerical investigations of transition radiation in such interactions. Detailed analytical calculations that include both the diffraction and decoherence effects of the characteristics of transition radiation in the THz range were conducted with the input parameters obtained from 3D particle-in-cell and hydrodynamic simulations. The calculated characteristics of THz radiation are in good agreement with the experimentally measured ones. Therefore, this approach can be used both to optimize the properties of THz radiation and to distinguish the transition radiation contribution if several mechanisms of THz radiation generation are considered.