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Aerometrics, Inc.'s Rainbow Refractometer was developed through an SBIR (Small Business Innovative Research) contract with Lewis Research Center. The system is a non- intrusive instrument for measuring droplet inside of refraction. It can also derive the temperature and chemical composition of refractive droplets. The technology can be integrated with the Phase Doppler Particle Analyzer systems (featured in Spinoff 1994) or used independently.
Research designed to develop detailed knowledge of the secondary atomization and ignition characteristics of aluminum slurry propellants was started. These processes are studied because they are the controlling factors limiting the combustion efficiency of aluminum slurry propellants in rocket applications. A burner and spray rig system allowing the study of individual slurry droplets having diameters from about 10 to 100 microns was designed and fabricated. The burner generates a near uniform high temperature environment from the merging of 72 small laminar diffusion flames above a honeycomb matrix. This design permits essentially adiabatic operation over a wide range of stoichiometries without danger of flashback. A single particle sizing system and velocimeter also were designed and assembled. Light scattered from a focused laser beam is related to the particle (droplet) size, while the particle velocity is determined by its transit time through the focal volume. Light from the combustion of aluminum is also sensed to determine if ignition was achieved. These size and velocity measurements will allow the determination of disruption and ignition times as functions of drop sizes and ambient conditions.
A planar velocity measurement system (100) is operative to measure all three velocity components of a flowing fluid (106) across an illuminated plane (108) using only a single line of sight. The fluid flow is seeded with small particles which accurately follow the flow field fluctuations. The seeded flow field is illuminated with pulsed laser light source (102) and the positions of the particles in the flow are recorded on CCD cameras (122,124). The in-plane velocities are measured by determining the in-plane particle displacements. The out-of-plane velocity component is determined by measuring the Doppler shift of the light scattered by the particles. Both gas and liquid velocities can be measured, as well as two-phase flows.
Measurements of midrapidity charged-particle multiplicity distributions, dN ch /dη, and midrapidity transverse-energy distributions, dE T /dη, are presented for a variety of collision systems and energies. Included are distributions for Au+Au collisions at √s NN =200, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu+Cu collisions at √s NN =200 and 62.4 GeV, Cu+Au collisions at √s NN =200 GeV, U+U collisions at√s NN =193 GeV, d+Au collisions at √s NN =200 GeV, He3+Au collisions at √s NN =200 GeV, and p+p collisions at √s NN =200 GeV. We present centrality-dependent distributions at midrapidity in terms of the number of nucleon participants, N part , and the number of constituent quark participants, N qp . For all A+A collisions down to √s NN =7.7 GeV, we observed that the midrapidity data are better described by scaling with N qp than scaling with N part . Finally, our estimates of the Bjorken energy density, ε BJ , and the ratio of dE T /dη to dN ch /dη are presented, the latter of which is seen to be constant as a function of centrality for all systems.
Southern Ocean (SO) low-level mixed phase clouds have been a long-standing challenge for Earth system models to accurately represent. While improvements to the Community Earth System Model version 2 (CESM2) resulted in increased supercooled liquid in SO clouds and improved model radiative biases, simulated SO clouds in CESM2 now contain too little ice. Previous observational studies have indicated that marine particles are major contributor to SO low-level cloud heterogeneous ice nucleation, a process that initiates a number of cloud processes that govern cloud radiative properties. In this study, we utilize detailed aerosol and ice nucleating particle (INP) measurements from two recent measurement campaigns to assess simulated aerosol abundance, number size distributions, and composition and INP parameterizations for use in CESM2. Our results indicate that CESM2 has a positive bias in simulated surface-level total aerosol surface area at latitudes north of 58°S. Measured INP populations were dominated by marine INPs and we present evidence of refractory INPs present over the SO assumed here to be mineral dust INPs. Results highlight a critical need to assess simulated mineral dust number and size distributions in CESM2 in order to adequately represent SO INP populations and their response to long-term changes in atmospheric transport patterns and land use change. Furthermore, we also discuss important cautions and limitations in applying a commonly used mineral dust INP parameterization to remote regions like the pristine SO.
Multipactor is a surface-driven electron avalanche phenomenon that degrades the performance and reliability of radio-frequency (RF) systems in particle accelerator and vacuum electronics applications. Multipactor behavior in a given device structure is conventionally assessed through susceptibility charts, which provide a parameter-space characterization of the instability. In this work, we assess the capabilities of machine-learning (ML) models to learn and predict such susceptibility charts and analyze the constraints governing their generalization across materials. Using a simulation-derived dataset spanning six distinct secondary-electron-yield material profiles in a canonical two-surface planar geometry, we train supervised regression models and artificial neural networks to predict the time-averaged electron growth rate, δavg, across the relevant parameter space. Model performance is evaluated using metrics that explicitly probe the structure of susceptibility charts, including Intersection over Union, Structural Similarity Index, and correlation analysis. Tree-based ensemble models outperform neural-network models in reconstructing susceptibility regions and in generalizing across material domains. Principal-component analysis reveals disjoint material feature distributions, indicating that the piecewise mode structure of multipactor susceptibility is difficult to represent with a single global model and that generalization is constrained by data coverage rather than by model complexity. An exhaustive reduced-coverage study further shows that sparse material-space coverage can yield mean performance in the same general range but producing large variability in the susceptibility-region overlap. These results clarify the capabilities of ML-based surrogate models for parameter-space characterization of multipactor discharge. They also provide guidance for their appropriate use in RF system design.
The Forward Time-of-Flight system for the large-acceptance CLAS12 spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility is described. The system is positioned at distances in the range from 6.2 m to 7.2 m from the beam–target interaction point and spans laboratory polar angles from 5 deg → 45 deg and nearly the full azimuth. The system consists of 540 individual scintillation counters with double-ended readout that range in length from 17 cm to 426 cm of discrete widths of 6 cm, 15 cm, and 22 cm, and of discrete thicknesses of 5 cm and 6 cm. We see the effective counter time resolution for passing charged particles varies from 50 ps for the shortest counters at small angles to 200 ps for the longest counters at large angles. The detectors are part of the forward-angle particle identification system for CLAS12 during offline event reconstruction and are a component of the online data acquisition trigger to select final state event topologies with forward-going charged particles.
In some tokamak discharges, a number of Alfvén eigenmodes (AEs) have been observed to cause a large-scale collapse of the high energy particle distribution, a phenomenon referred to as an avalanche. We examine the necessary conditions for an avalanche using the available experimental information from NSTX on the equilibrium and mode properties for two cases, one with a measurable but benign AE activity and one with an AE activity leading up to an avalanche. To produce an avalanche, the modes present in the discharge must possess resonances that can overlap with a modest increase in instability magnitude, providing a path to global particle stochastic motion. In this paper, we find that the modes present in the avalanche-free discharge do not provide such a path even at a very large amplitude. During the discharge which subsequently produces an avalanche, the high energy population is growing and the Alfvén frequency is dropping due to increasing density, and we find that both these changes, producing a small increased drive or an increased resonance width for the Alfvén modes, can lead in this case to uncontrolled mode growth and large-scale beam particle loss.
Long-range behavior of effective one-body potential representing particle compound system interaction, using modified effective range theory to extrapolate cross section data to zero energy
This study investigates the theoretical design parameters and thermal performance of a kW-scale continuous oxidation reactor for high temperature (~1000 °C) thermochemical energy storage (TCES) applications. The concept comprises a counter-current particle-based system that includes a reaction zone with a heat exchanger to extract the heat produced from the oxidation reaction. Both above and below the hot reactive volume are sensible heat recuperation zones to enable the feed and removal of particles and oxidizing gas near ambient temperature during steady state operation. Two operation types for the reaction zone are studied, a fluidized bed reactor (FBR) and a moving bed reactor (MBR). The results of the parametric analysis suggest that the MBR requires a smaller volume per kW of heat produced, achieving power densities in excess of 2500 kW/m3 compared to ~ 900 kW/m 3 in the FBR. Additionally, the MBR achieves between 0.71 and 0.99 oxidation conversions compared to between 0.23 and 0.38 conversions in the FBR with the same volumes and flowrates. However, the FBR has the potential to maintain a uniform reactor temperature which can produce heat transfer fluid (HTF) outlet temperatures as high as the reactor temperature, i.e., ~1000 °C, whereas the MBR produces variable reactor temperatures that can create overheating zones and low HTF outlet temperatures (< 800 °C) depending on the operating conditions selected. Future work should aim at understanding the coupled fluid dynamics, heat and mass transfer, and thermochemical reaction for any given combination of reactor volume and contacting patterns. Here, these studies should be complemented by experimental work on particle-gas TCES reactors.
High power target systems are crucial elements in enabling future neutrino and other rare particle beams. These systems transform intense source of protons into secondary particles of interest to enable new scientific discoveries. As primary beam intensities increase in next-generation multi-megawatt accelerator facilities, high power target systems face key challenges. Thermal shock and radiation damage effects in beam-intercepting devices were identified as the leading cross-cutting challenges of high-power target facilities. Target materials R&D to address these challenges are therefore essential to enable and ensure reliable operation of future accelerator target facilities. This paper provides an overview of the R&D activities underway to help support high power target systems development for next-generation multi-MW facilities.
The cost of space plasma sensors is high for several reasons: (1) Most are one-of-a-kind and state-of-the-art, (2) the cost of launch to orbit is high, (3) ruggedness and reliability requirements lead to costly development and test programs, and (4) overhead is added by overly elaborate or generalized spacecraft interface requirements. Possible approaches to reducing costs include development of small 'sensors' (defined as including all necessary optics, detectors, and related electronics) that will ultimately lead to cheaper missions by reducing (2), improving (3), and, through work with spacecraft designers, reducing (4). Despite this logical approach, there is no guarantee that smaller sensors are necessarily either better or cheaper. We have previously advocated applying analytical 'quality factors' to plasma sensors (and spacecraft) and have begun to develop miniaturized particle optical systems by applying quantitative optimization criteria. We are currently designing a Miniaturized Optimized Smart Sensor (MOSS) in which miniaturized electronics (e.g., employing new power supply topology and extensive us of gate arrays and hybrid circuits) are fully integrated with newly developed particle optics to give significant savings in volume and mass. The goal of the SwRI MOSS program is development of a fully self-contained and functional plasma sensor weighing 1 lb and requiring 1 W. MOSS will require only a typical spacecraft DC power source (e.g., 30 V) and command/data interfaces in order to be fully functional, and will provide measurement capabilities comparable in most ways to current sensors.
The goal of this research is to examine the causes of field-aligned plasma acceleration in the auroral zone using satellite data and numerical simulations. A primary question to be addressed is what causes the field-aligned acceleration of electrons (leading to precipitation) and ions (leading to upwelling ions) in the auroral zone. Data from the Fast Auroral SnapshoT (FAST) and Polar satellites is used when the two satellites are in approximate magnetic conjunction and are in the auroral region. FAST is at relatively low altitudes and samples plasma in the midst of the auroral acceleration region while Polar is at much higher altitudes and can measure plasmas and waves propagating towards the Earth. Polar can determine the sources of energy streaming earthward from the magnetotail, either in the form of field-aligned currents, electromagnetic waves or kinetic particle energy, that ultimately leads to the acceleration of plasma in the auroral zone. After identifying and examining several events, numerical simulations are run that bridges the spatial region between the two satellites. The code is a one-dimensional, long system length particle in cell simulation that has been developed to model the auroral region. A main goal of this research project is to include Alfven waves in the simulation to examine how these waves can accelerate plasma in the auroral zone.
A field theory and the associated structure-preserving geometric particle-in-cell (PIC) algorithm are developed to study low frequency electrostatic perturbations with fully kinetic ions and adiabatic electrons in magnetized plasmas. The algorithm is constructed by geometrically discretizing the field theory using discrete exterior calculus, high-order Whitney interpolation forms, and non-canonical Hamiltonian splitting method. The discretization preserves the non-canonical symplectic structure of the particle-field system, as well as the electromagnetic gauge symmetry. As a result, the algorithm is charge-conserving and possesses long-term conservation properties. Because drift wave turbulence and anomalous transport intrinsically involve multi time-scales, simulation studies using fully kinetic particles demand algorithms with long-term accuracy and fidelity. The structure-preserving geometric PIC algorithm developed adequately serves this purpose. The algorithm has been implemented in the code, tested and benchmarked using the examples of ion Bernstein waves and drift waves. We apply the algorithm to study the ion temperature gradient (ITG) instability and turbulence in a 2D slab geometry. Simulation results show that at the early stage of the turbulence, the energy diffusion is between the Bohm scaling and gyro-Bohm scaling. Finally, at later time, the observed diffusion is closer to the gyro-Bohm scaling, and density blobs generated by the rupture of unstable modes are the prominent structures of the fully developed ITG turbulence.
The Aerodyne Aerosol Chemical Speciation Monitor (ACSM) measures particle mass loading and chemical composition in real time for non-refractory sub-micron aerosol particles. The ACSM is designed for long-term unattended deployment and routine monitoring applications.
The V-shaped potential structures formed by the injection of a non-neutral electron current into a cold background plasma were simulated numerically. The injection disturbs the initial quasi-neutral plasma, leading to the excitation of strong turbulences which heat the plasma. This leads to expulsion of the plasma from the simulation region. Due to ambipolar electric fields the current injection is interrupted and the initial background plasma is extracted from the system. A particle composition with the characteristics of the two plasma reservoirs now represents the plasma in the simulation region. The interaction of the electron beam with this plasma excites turbulences of smaller amplitudes. A nearly constant time averaged potential drop with nonstationary distribution develops across the system. Single and multiple double layers may form for the duration of one ion plasma period.
Formation of ice particles in the atmosphere strongly affects cloud properties and Earth’s climate. While mineral dust has been known as an effective ice nucleating particle, the role of aerosols from anthropogenic pollution in ice nucleation is still under debate. Here we probe the ice nucleation ability of different aerosol types by combining 11-year observations from multiple satellites and cloud-resolving model simulations. We find that, for strong convective systems, ice particle effective radius near the cloud top decreases with increasing loading of polluted continental aerosols, because the ice formation is dominated by homogeneous freezing of cloud droplets that are smaller under more polluted conditions. In contrast, an increase in ice particle effective radius with polluted continental aerosols is found under moderate convection. Our simulations suggest that enhanced heterogeneous ice nucleation and prolonged ice particle growth are key to explaining the positive correlation. The results indicate that polluted continental aerosols contain a significant fraction of ice nucleating particles triggering heterogeneous nucleation. Similar aerosol-ice relationships are observed for dust aerosols, further corroborating the ice nucleation ability of polluted continental aerosols. By catalyzing ice formation, aerosols from anthropogenic pollution can have profound impacts on cloud lifetime and radiative effect as well as precipitation efficiency.
A polar nephelometer has been developed at NCAR to measure the angular variation of the intensity of light scattered by air molecules and particles. The system has been designed for airborne measurements using outside air ducted through a 5-cm diameter airflow tube; the sample volume is that which is common to the intersection of a collimated source beam and the detector field of view within the airflow tube. The source is a linearly polarized helium-neon laser beam. The optical system defines a collimated field-of-view (0.5deg half-angle) through a series of diaphragms located behind a I72-mm focal length objective lens. A photomultiplier tube is located immediately behind an aperture in the focal plane of the objective lens. The laser beam is mechanically chopped (on-off) at a rate of 5 Hz; a two-channel pulse counter, synchronized to the laser output, measures the photomultiplier pulse rate with the light beam both on and off. The difference in these measured pulse rates is directly proportional to the intensity of the scattered light from the volume common to the intersection of the laser beam and the detector field-of-view. Measurements can be made at scattering angles from 15deg to 165deg with reference to the direction of propagation of the light beam. Intermediate angles are obtained by selecting the angular increments desired between these extreme angles (any multiple of 0.1deg can be selected for the angular increment; 5deg is used in normal operation). Pulses provided by digital circuits control a stepping motor which sequentially rotates the detector by pre-selected angular increments. The synchronous photon-counting system automatically begins measurement of the scattered-light intensity immediately after the rotation to a new angle has been completed. The instrument has been flown on the NASA Convair 990 airborne laboratory to obtain data on the complex index of refraction of atmospheric aerosols. A particle impaction device is operated simultaneously to collect particles from the same airflow tube used to make the scattered-light measurements. A size distribution function is obtained by analysis of the particles collected by the impaction device. Calculated values of the angular variation of the scattered-light intensity are obtained by applying Mie scattering theory to the observed size distribution function and assuming different values of the complex index of refraction of the particles. The calculated values are then compared with data on the actual variation of the scattered-light intensity obtained with the polar nephelometer. The most probable value of the complex refractive index is that which provides the best fit between the experimental light scattering data and the parameters calculated from the observed size distribution function.