Production Of Energetic Particles Research Articles

Investigation on flash boiling of superheated acetone spray under low vacuum conditions

Spray Flash Evaporation has recently demonstrated promising results in various fields of application and has more recently shown potential in the elaboration of nanoenergetic materials. This technique offers advantages in terms of morphology, size, and reactivity of the produced materials. However, specific thermodynamic conditions are required to produce these materials using acetone as a solvent: high injection temperature (typically between 80 and 160 °C) and low pressure (generally between 10 and 100 mbar) in the chamber are needed, i.e., superheat level. The study on the formation of acetone droplets in the far-field and under such conditions is lacking. Consequently, we propose here to further understand the relationship between injection temperature and back pressure in the chamber with nucleation and droplets characteristics (velocity, average size, size distribution, and concentration) in order to find optimal conditions for generating theoretically smaller particles through droplet evaporation. The tests were conducted in an unusual range of injection temperatures and pressures for flash boiling but commonly used for the production of energetic particles, from 80 to 200 °C and from 12 to 300 mbar, respectively. By using such conditions, it has been found that increasing the injection temperature and decreasing the back pressure are beneficial for generating a large concentration (up to 27.0 x 106droplets.cm−3) of smaller droplets with a narrow size distribution (down to 2.13 ± 0.13 µm) and high velocity (up to 204.2 m·s−1). It was also shown that there is an injection temperature threshold above 160 °C, beyond which the size distribution widens again by 12 % at 200 °C, and the number of droplets decreases by 64 %. This phenomenon can be observed only if we use a very high superheat level. This study demonstrates that these conditions are likely to promote and ultimately lead to the production of particles that are as fine and uniform in size as possible. Nevertheless, operating at very high injection temperatures (>160 °C) could hinder the nucleation and the formation of uniform droplets due to the high competition between the superheat level (Rp > 1188) and the surface tension of the liquid approaching near-zero values. By introducing the use of criteria related to mechanic and thermodynamics, along with droplet size and velocity, it was also observed that the droplet size is primarily influenced by the nucleation rate, while droplet velocity is influenced by both driving forces (mechanical and thermodynamic). The temperature and pressure in the chamber must therefore be carefully chosen to improve droplet formation and potentially produce smaller, homogeneous particles in size as they evaporate.

Spectroscopy in the Middle Corona: Probing the Kinetic Processes in the Nascent Solar Wind and Solar Energetic Particle Production

Spectroscopy in the Middle Corona: Probing the Kinetic Processes in the Nascent Solar Wind and Solar Energetic Particle Production

Abstracts from the 131st Meeting of the Tennessee Academy of Science November 2021

Adam Holley grew up in Raleigh, North Carolina, but attended college in Pennsylvania, where he earned a B.S. in physics and mathematics from Haverford College. Uncertain about whether theoretical or experimental physics was right for him, he temporized by teaching high school physics in New York City, where he had the good fortune to collaborate on the development and teaching of a three-year research course for high school students. That experience ultimately helped him decide to become an experimentalist. This he did at North Carolina State University, joining a group of scientists developing the United States' first ultracold neutron (UCN) source at Los Alamos National Lab. He earned his Ph.D. as part of the associated UCNA experiment that for the first time used UCN to measure the neutron beta decay asymmetry. During his subsequent postdoc at Indiana University, Dr. Holley got involved in another beta decay experiment called UCNτ. He continued his involvement with that effort when he joined the faculty at Tennessee Tech, where he leverages unique aspects of UCN physics to involve undergraduates in the work. The Tortoise and the Hare: A Race for Answers to Big Questions about the Universe The production of energetic exotic particles has long been a primary method for discovering the rules that underlie what we observe about the universe. There are, however, a number of gaps in this understanding, which the study of more familiar systems, such as neutrons, atoms, or molecules, can help elucidate. As the overall precision of these experimental efforts increases, there are a growing number of tantalizing anomalies, any of which could point the way to a shift in our understanding of how the universe formed, what makes it up, and whether ours is the only universe or is one of many universes. The race to discover new fundamental physical behavior currently features a diverse array of high-precision approaches, spanning an enormous range of energies. “Ultracold” neutrons (UCN), with twenty orders of magnitude smaller energies than particles produced at the Large Hadron Collider, provide one example of how low-energy measurements can facilitate the requirement for high precision. A classic example of a UCN-based experiment is determination of the free neutron lifetime, an empirical observable involved in a number of potentially interesting anomalies. An experiment called UCNτ that operates at Los Alamos National Laboratory has set the standard for precise determinations of this quantity. Using UCNτ as an example of the physics, engineering, and computational challenges high-precision work entails, this talk will describe the ongoing race to answer some long-standing questions about the universe.

Interaction between Multiple Current Sheets and a Shock Wave: 2D Hybrid Kinetic Simulations

Abstract Particle acceleration behind a shock wave due to interactions between magnetic islands in the heliosphere has attracted attention in recent years. The downstream acceleration may yield a continuous increase of particle flux downstream of the shock wave. Although it is not obvious how the downstream magnetic islands are produced, it has been suggested that current sheets are involved in the generation of magnetic islands due to their interaction with a shock wave. We perform 2D hybrid kinetic simulations to investigate the interaction between multiple current sheets and a shock wave. In the simulation, current sheets are compressed by the shock wave and a tearing instability develops at the compressed current sheets downstream of the shock. As the result of this instability, the electromagnetic fields become turbulent and magnetic islands form well downstream of the shock wave. We find a “post-cursor” region in which the downstream flow speed normal to the shock wave in the downstream rest frame is decelerated to ∼ 1V A immediately behind the shock wave, where V A is the upstream Alfvén speed. The flow speed then gradually decelerates to 0 accompanied by the development of the tearing instability. We also observe an efficient production of energetic particles above 100 E 0 during the development of the instability some distance downstream of the shock wave, where E 0 = m p V A 2 and m p is the proton mass. This feature corresponds to Voyager observations showing that the anomalous cosmic-ray intensity increase begins some distance downstream of the heliospheric termination shock.

Magnetic Reconnection during the Post-impulsive Phase of a Long-duration Solar Flare: Bidirectional Outflows as a Cause of Microwave and X-Ray Bursts

Abstract Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bidirectional plasma outflows located within a large-scale plasma sheet observed in extreme-ultraviolet emission and scattered white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each of the bidirectional outflows originates in the plasma sheet from a discrete site, identified as a magnetic reconnection site. These reconnection sites reside at very low altitudes (<180 Mm, or 0.26 R ⊙) above the top of the flare arcade, a distance only <3% of the total length of a plasma sheet that extends to at least 10 R ⊙. Each arrival of sunward outflows at the loop-top region appears to coincide with an impulsive microwave and X-ray burst dominated by a hot source (10–20 MK) at the loop top and a nonthermal microwave burst located in the loop-leg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directed energy flux induces particle acceleration and plasma heating in the post-flare arcades, observed as the hot and nonthermal flare emissions.

The Coronal Volume of Energetic Particles in Solar Flares as Revealed by Microwave Imaging

Abstract The spectrum of gyrosynchrotron emission from solar flares generally peaks in the microwave range. Its optically thin, high-frequency component, above the spectral peak, is often used for diagnostics of the nonthermal electrons and the magnetic field in the radio source. Under favorable conditions, its low-frequency counterpart brings additional, complementary information about these parameters as well as thermal plasma diagnostics, either through gyrosynchrotron self-absorption, free–free absorption by the thermal plasma, or the suppression of emission through the so-called Razin effect. However, their effect on the low-frequency spectrum is often masked by spatial nonuniformity. To disentangle the various contributions to low-frequency gyrosynchrotron emission, a combination of spectral and imaging data is needed. To this end, we have investigated Owens Valley Solar Array (OVSA) multi-frequency images for 26 solar bursts observed jointly with RHESSI during the first half of 2002. For each, we examined dynamic spectra, time- and frequency-synthesis maps, RHESSI images with overlaid OVSA contours, and a few representative single-frequency snapshot OVSA images. We focus on the frequency dependence of microwave source sizes derived from the OVSA images and their effect on the low-frequency microwave spectral slope. We succeed in categorizing 18 analyzed events into several groups. Four events demonstrate clear evidence of being dominated by gyrosynchrotron self-absorption, with an inferred brightness temperature of ≥108 K. The low-frequency spectra in the remaining events are affected to varying degrees by Razin suppression. We find that many radio sources are rather large at low frequencies, which can have important implications for solar energetic particle production and escape.

Toward a Quantitative Model for Simulation and Forecast of Solar Energetic Particle Production during Gradual Events. I. Magnetohydrodynamic Background Coupled to the SEP Model

Abstract Solar energetic particles (SEPs) are an important aspect of space weather. SEP events possess a high destructive potential, since they may cause disruptions of communication systems on Earth and be fatal to crew members on board spacecraft and, in extreme cases, harmful to people on board high-altitude flights. However, currently the research community lacks efficient tools to predict such a hazardous threat and its potential impacts. Such a tool is a first step for mankind to improve its preparedness for SEP events and ultimately to be able to mitigate their effects. The main goal of the presented research effort is to develop a computational tool that will have the forecasting capability and can serve as an operational system that will provide live information on the current potential threats posed by SEP based on the observations of the Sun. In the present paper we discuss the fundamentals of magnetohydrodynamical simulations to be employed as a critical part of the desired forecasting system.

Observations of a Coronal Shock Wave and the Production of Solar Energetic Particles

Abstract We present a study that clarifies the acceleration source/mechanism of the solar energetic particle (SEP) event on 2011 August 9. Based on the assumption of scatter-free propagation of charged particles along the interplanetary magnetic field, the solar particle release times of the electrons and protons are derived and both found to be in the decay phase of the flare emission. Furthermore, we compare the peak-flux spectra of the in situ particles and the remote-sensing hard X-ray photons and find a weak correlation between them. In particular, we note that an extreme ultraviolet shock wave, presumed to be a signature of coronal mass ejection (CME) shock front on the solar surface, and an associated type II radio burst were observed alongside this event. Under the framework of diffusive shock acceleration, the derived shock compression ratio can accelerate particles with a theoretical spectral index , which is comparable to the observational index of ∼2.0. Our results appear to support the notion that the coronal shock wave was most likely responsible for the SEP event. Specifically, we find that the electrons were released in a low coronal site at ∼0.58 solar radii, and protons were released when the CME-driven shock propagated to ∼1.38 solar radii. The multi-spacecraft observations, in addition, reveal the connection between the acceleration of shock waves and the release of SEPs.

Cosmic rays: the spectrum and chemical composition from 1010 to 1020 eV

The production of energetic particles in the universe remains one of the great mysteries of modern science. The mechanisms of acceleration in astrophysical sources and the details about the propagation through the galactic and extragalactic media are still to be defined. In recent years, the cosmic ray flux has been measured with high precision in the energy range from 1010 to 1020.5 eV by several experiments using different techniques. In some energy ranges, it has been possible to determine the flux of individual elements (hydrogen to iron nuclei). This paper explores an astrophysical scenario in which only our Galaxy and the radio galaxy Cen A produce all particles measured on Earth in the energy range from 1010 to 1020.5 eV . Data from AMS-02, CREAM, KASCADE, KASCADE-Grande and the Pierre Auger Observatories are considered. The model developed here is compared to the total and if available to the individual particle flux of the experiments considered.The flux of each element as determined by AMS-02, CREAM, KASCADE and KASCADE-Grande and the mass sensitivity parameter Xmax measured by the Pierre Auger Observatory above 10^ eV are also explored within the framework of the model. The transition from 1016 to 1018 eV is carefully analyzed. It is shown that the flux measured in this energy range suggest the existence of an extra component of cosmic rays yet to be understood.

THREE-DIMENSIONAL SIMULATIONS OF THE NON-THERMAL BROADBAND EMISSION FROM YOUNG SUPERNOVA REMNANTS INCLUDING EFFICIENT PARTICLE ACCELERATION

Supernova remnants are believed to be the major contributors to Galactic cosmic rays. In this paper, we explore how the non-thermal emission from young remnants can be used to probe the production of energetic particles at the shock (both protons and electrons). Our model couples hydrodynamic simulations of a supernova remnant with a kinetic treatment of particle acceleration. We include two important back-reaction loops upstream of the shock: energetic particles can (i) modify the flow structure and (ii) amplify the magnetic field. As the latter process is not fully understood, we use different limit cases that encompass a wide range of possibilities. We follow the history of the shock dynamics and of the particle transport downstream of the shock, which allows us to compute the non-thermal emission from the remnant at any given age. We do this in 3D, in order to generate projected maps that can be compared with observations. We observe that completely different recipes for the magnetic field can lead to similar modifications of the shock structure, although to very different configurations of the field and particles. We show how this affects the emission patterns in different energy bands, from radio to X-rays and $\gamma$-rays. High magnetic fields ($>100 \mu$G) directly impact the synchrotron emission from electrons, by restricting their emission to thin rims, and indirectly impact the inverse Compton emission from electrons and also the pion decay emission from protons, mostly by shifting their cut-off energies to respectively lower and higher energies.

Hot carbon corona in Mars’ upper thermosphere and exosphere: 1. Mechanisms and structure of the hot corona for low solar activity at equinox

Two important source reactions for hot atomic carbon on Mars are photodissociation of CO and dissociative recombination of CO+; both reactions are highly sensitive to solar activity and occur mostly deep in the dayside thermosphere. The production of energetic particles results in the formation of hot coronae that are made up of neutral atoms including hot carbon. Some of these atoms are on ballistic trajectories and return to the thermosphere, and others escape. Understanding the physics in this region requires modeling that captures the complicated dynamics of hot atoms in 3-D. This study evaluates the carbon atom inventory by investigating the production and distribution of energetic carbon atoms using the full 3-D atmospheric input. The methodology and details of the hot atomic carbon model calculation are given, and the calculated total global escape of hot carbon from the assumed dominant photochemical processes at a fixed condition, equinox (Ls = 180°), and low solar activity (F10.7 = 70 at Earth) are presented. To investigate the dynamics of these energetic neutral atoms, we have coupled a self-consistent 3-D global kinetic model, the Adaptive Mesh Particle Simulator, with a 3-D thermosphere/ionosphere model, the Mars Thermosphere General Circulation Model to provide a self-consistent global description of the hot carbon corona in the upper thermosphere and exosphere. The spatial distributions of density and temperature and atmospheric loss are simulated for the case considered.

Production of energetic neutral particles and low energy electrons from four anode rods ion source

The factors affecting the energetic neutral current, the low energy electron current, and the positive ion current emerging from a four-anode-rods ion source have been studied using argon gas. The neutral and electron current were measured using a simple, new technique. It was found that the energetic neutral current and the electron current depend on the positive ion current and the gas pressure. The ratio of the neutral and electron current to the positive ion current increases by increasing the gas pressure. Also it was found that at a pressure equal to 9 × 10(-4) mmHg, the ratio of the neutral to the positive ion current reaches 2.34 while the ratio of the electron current to the positive ion current reaches 1.7.

SMALL-SCALE MICROWAVE BURSTS IN LONG-DURATION SOLAR FLARES

Solar small scale microwave bursts (SMBs), including microwave dot, spike, and narrow band type III bursts, are characterized with very short timescales, narrow frequency bandwidth, and very high brightness temperatures. Based on observations of the Chinese Solar Broadband Radio Spectrometer at Huairou with superhigh cadence and frequency resolution, this work presents an intensive investigation of SMBs in several flares occurred in active region NOAA 10720 during 2005 Jan 14-21. Especially long-duration flares, SMBs occurred not only in early rising and impulsive phase, but also in the flare decay phase, and even in time of after the flare ending. These SMBs are strong bursts with inferred brightness temperature at least 8.18*10^11 - 1.92*10^13 K, very short lifetime of 5-18 ms, relative frequency bandwidths of 0.7-3.5%, and superhigh frequency drifting rates. Together with their obviously different polarizations from the background emission (the quiet Sun, and the underlying flaring broadband continuum), such SMBs should be individual independent strong coherent bursts which is related to some non-thermal energy releasing and production of energetic particles in small scale source region. These facts show the existence of small scale strong non-thermal energy releasing activities after the flare maxima, which is meaningful to the prediction of space weather. Physical analysis indicates that plasma mechanism may be the most favorable candidate for the formation of SMBs. From plasma mechanism, the velocities and kinetic energy of fast electrons can be deduced, and the region of electron acceleration can also be tracke.

Cosmic Gamma-Ray Spectroscopy

Penetrating gamma- rays require complex instrumentation for astronomical spectroscopy measurements of gamma-rays from cosmic sources. A combination of multiple-interaction detectors in space and post-processing of detector events on ground have lead to a spectroscopy performance which is now capable to provide new astrophysical insights. Spectral signatures in the MeV regime originate from transitions in atomic nuclei, stimulated by either radioactive decays or high-energy nuclear collisions such as with cosmic rays. Lines have been detected from radioactive isotopes produced in stellar and supernova nuclear burning, and from energetic-particle interactions in solar flares. Radioactive-decay gamma-rays from 56Ni directly reflect the power source of supernova light. 44Ti is produced in core-collapse supernova interiors and the largely unknown and dynamical conditions herein. From 26Al and 60Fe which are distributed in interstellar space from massive-star nucleosynthesis over millions of years. Additionally, nuclear de-excitation lines have been measured in solar-flare events, and convey information a b out energetic particle production in these outbursts, and t heir interaction in the solar atmosphere. Annihilating posit rons add another very special astrophysical source, which has been puzzling so far, with its characteristic gamma-rays at 511 keV; it has been measured both in such solar flares, and throughout the interstellar medium of our Milky Way galaxy. - We discuss instrumentation and data processing for cosmic gamma-ray spectroscopy, and the astrophysical issues and insights from these measurements.

From the Naught Orbit to the 4He Excited State

An electron pair (lochon) in a deep hydrogen ‘naught’ orbit (n = 0) has similarities to muonic hydrogen in that it has a small orbital radius that allows the protons in molecular hydrogen to be very much closer together than is possible in a normal molecule. There are also significant differences between lochon- and muon-catalyzed fusion (e.g., one leads to ‘cold’ fusion and the other the ‘hot’ fusion). However, since muon-catalyzed fusion is an accepted phenomenon and Lattice-assisted Nuclear Reaction (LANR) or Low-energy Nuclear Reaction ( LENR) is not, we will examine the similarities and differences in various mechanisms with the fusion of deuterons in mind. We start with the assumption that both solutions of the Klein–Gordon equation are actually real and the one that has here-to-for been rejected correctly identifies a single deep orbit below the n = 1 ground state. (It is generally accepted that, at least for spinless bosons such as the lochon, this solution of the Klein–Gordon equation holds.) We then compare the creation model and characteristics of these two naught orbits with those of the muonic orbits (both atomic and molecular). The similarities lead both naught-orbit and muonic-orbit molecules to fusion. The differences lead the non-relativistic (but >100 MeV excess energy) muon-induced fusion of deuterons to the fragmentation of excited helium nuclei and the relativistic (but <10 eV excess energy) lochon-induced D–D fusion to an excited helium 4He* state that is below these fragmentation levels. The reason for this different response to the respective “tight” orbits is described along with some of the consequences, e.g., electron capture. In addition, internal conversion, a known physical process involving nucleon interaction with atomic electrons, is compared with the Extended Lochon Model to provide a means of de-exciting 4He* without production of energetic particles or radiation.

Curvature oscillations in modified gravity and high energy cosmic rays

It is shown that F(R)-modified gravitational theories lead to curvature oscillations in astrophysical systems with rising energy density. The frequency and the amplitude of such oscillations could be very high and would lead to noticeable production of energetic cosmic ray particles.

Solar flares and energetic particles

Solar flares are now observed at all wavelengths from γ-rays to decametre radio waves. They are commonly associated with efficient production of energetic particles at all energies. These particles play a major role in the active Sun because they contain a large amount of the energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X-rays and γ-rays. Energetic particles can also escape to the corona and interplanetary medium, produce radio emissions (electrons) and may eventually reach the Earth's orbit. I shall review here the available information on energetic particles provided by X-ray/γ-ray observations, with particular emphasis on the results obtained recently by the mission Reuven Ramaty High-Energy Solar Spectroscopic Imager. I shall also illustrate how radio observations contribute to our understanding of the electron acceleration sites and to our knowledge on the origin and propagation of energetic particles in the interplanetary medium. I shall finally briefly review some recent progress in the theories of particle acceleration in solar flares and comment on the still challenging issue of connecting particle acceleration processes to the topology of the complex magnetic structures present in the corona.

Collective behaviour of partons could be a source of energetic hadrons

We discuss the idea that collective behaviour of the quarks/partons, which has been intensely discussed for the last 40 years in relativistic hadron-nuclear and nuclear-nuclear interactions and confirmed by new data coming from the ultrarelativistic heavy ion collisions, can lead to energetic particle production. Created from hadronization of the quark/parton (or quarks/partons), energetic particles could get the energy of grouped partons from coherent interactions. Therefore, we think that in the centre of some massive stars, a medium with high density, close to Quantum Chromodynamic one could be a source of the super high-energy cosmic rays.

Production and diagnosis of energetic particles in FAST

The Fusion Advanced Study Torus (FAST) has been proposed as a possible European satellite facility to study fast-ion physics in deuterium plasmas under conditions relevant to a burning plasma. Energetic minority ions (H or 3He) accelerated by ion cyclotron resonance heating (ICRH), with dimensionless parameters close to those of fusion-born alphas in ITER, can be produced in FAST via 30 MW power ICRH minority heating. This work provides a first assessment of the extent to which the 3He fast-ion population can be diagnosed in FAST with a set of dedicated diagnostics for confined fast particles. Neutron emission spectroscopy (NES), gamma-ray spectroscopy (GRS) and collective Thomson scattering (CTS) diagnostics have been reviewed with a description of the state-of-the-art hardware and a preliminary analysis of the required lines of sight. The results of the analysis, based on numerical simulations of the spatial and energetic particle distribution function of the ICRH-accelerated ions for the standard FAST H-mode scenario, suggest that NES and GRS measurements can provide information on the fast 3He population effective tail temperature, with time resolutions in the range 20–100 ms. The proposed CTS diagnostic can measure the fast-ion parallel and perpendicular temperature with a spatial resolution of 5–10 cm and a time resolution of 10 ms. The paper provides a scientific basis for the prediction of the production and diagnosis of energetic ions in FAST.

OFF-LIMB SOLAR CORONAL WAVEFRONTS FROM SDO /AIA EXTREME-ULTRAVIOLET OBSERVATIONS—IMPLICATIONS FOR PARTICLE PRODUCTION

We derive kinematic properties for two recent solar coronal transient waves observed off the western solar limb with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) mission. The two waves occurred over $\sim10$-min intervals on consecutive days - June 12 and 13, 2010. For the first time, off-limb waves are imaged with a high 12-sec cadence, making possible detailed analysis of these transients in the low corona between $\sim1.1$-2.0 solar radii ($R_{s}$). We use observations in the 193 and 211 {\AA} AIA channels to constrain the kinematics of both waves. We obtain initial velocities for the two fronts of $\sim1287$ and $\sim736$ km s$^{-1}$, and accelerations of $-1170$ and $-800$ m s$^{-2}$, respectively. Additionally, differential emission measure analysis shows the June 13 wave is consistent with a weak shock. EUV wave positions are correlated with positions from simultaneous type II radio burst observations. We find good temporal and height association between the two, suggesting that the waves may be the EUV signatures of coronal shocks. Furthermore, the events are associated with significant increases in proton fluxes at 1 AU, possibly related to how waves propagate through the coronal magnetic field. Characterizing these coronal transients will be key to connecting their properties with energetic particle production close to the Sun.