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DOE OSTI2024

Flat Spectra of Energetic Particles in Interplanetary Shock Precursors

The observed energy spectra of accelerated particles at interplanetary shocks often do not match the diffusive shock acceleration (DSA) theory predictions. In some cases, the particle flux forms a plateau over a wide range of energies, extending upstream of the shock for up to seven flux e-folds before submerging into the background spectrum. Remarkably, at and downstream of the shock we have studied in detail, the flux falls off in energy as ϵ -1 , consistent with the DSA prediction for a strong shock. The upstream plateau suggests a particle transport mechanism different from those traditionally employed in DSA models. We show that a standard (linear) DSA solution based on a widely accepted diffusive particle transport with an underlying resonant wave–particle interaction is inconsistent with the plateau in the particle flux. To resolve this contradiction, we modify the DSA theory in two ways. First, we include a dependence of the particle diffusivity κ on the particle flux F (nonlinear particle transport). Second, we invoke short-scale magnetic perturbations that are self-consistently generated by, but not resonant with, accelerated particles. They lead to the particle diffusivity increasing with the particle energy as ∝ϵ 3/2 that simultaneously decreases with the particle flux as 1/F. The combination of these two trends results in the flat spectrum upstream. We speculate that nonmonotonic spatial variations of the upstream spectrum, apart from being time-dependent, may also result from non-DSA acceleration mechanisms at work upstream, such as stochastic Fermi or magnetic pumping acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1980

Development of test methods for scale model simulation of aerial applications in the NASA Langley Vortex Research Facility

As part of basic research to improve aerial applications technology, methods were developed at the Langley Vortex Research Facility to simulate and measure deposition patterns of aerially-applied sprays and granular materials by means of tests with small-scale models of agricultural aircraft and dynamically-scaled test particles. Interactions between the aircraft wake and the dispersed particles are being studied with the objective of modifying wake characteristics and dispersal techniques to increase swath width, improve deposition pattern uniformity, and minimize drift. The particle scaling analysis, test methods for particle dispersal from the model aircraft, visualization of particle trajectories, and measurement and computer analysis of test deposition patterns are described. An experimental validation of the scaling analysis and test results that indicate improved control of chemical drift by use of winglets are presented to demonstrate test methods.

Jordan, F. L., Jr.↗

NASA NTRS1980

Development of test methods for scale model simulation of aerial applications in the NASA Langley Vortex Facility

Methods have been developed at the Langley Vortex Research Facility to simulate and measure the deposition patterns of aerially applied sprays and granular materials by means of tests with small-scale models of agricultural and dynamically scaled test particles. Interactions between the aircraft wake and the dispersed particles are studied with the aim of modifying wake characteristics and dispersal techniques in order to increase swath width, improve deposition pattern uniformity, and minimize drift. This paper examines the particle sizing analysis, test methods for particle dispersal from the model aircraft, and measurement and computer analysis of test deposition patterns. Results that indicate improved control of chemical drift by winglets are presented to demonstrate test methods.

Jordan, F. L., Jr.↗

NASA NTRS1983

Electrostatic waves and anomalous transport in the solar wind

In situ measurements of fluctuation spectra and particle distribution functions have now been carried out throughout interplanetary space. The link between these observations is established by theories of wave particle interaction. Linear instability analysis for the actual nonMaxwellian particle distribution functions and an examination of the velocity dependence of microscopic diffusion coefficients form the basis of such an investigation. It is described in more detail for the short wavelength, ion acoustic like turbulence which is found by linear instability analysis to correspond to the observed electrostatic fluctuations. Of the transport processes associated with these fluctuations, electron heat conduction and electron ion energy transfer are of particular importance for macroscopic solar wind expansion. These effects are studied with the aid of an anomalous transport theory. This theory (Dum, 1978 a,b) is based on the dominance of elastic scattering of electrons by fluctuations, similar to (enhanced) electron ion collisions. It has a much wider range of applicability than classical transport theory, which assumes dominance of Coulomb collisions for elastic and inelastic scattering.

Dum, C. T.↗

NASA NTRS1984

Nuclear processes in the jets of SS433

The very narrow gamma-ray lines observed at 1.495 and 6.695 MeV from SS433 which are blueshifted 1.369 and 6.129 emissions from deexcitations of (24)Mg* and (16)O* in grains moving with the jets and inelastically excited by interactions with the ambient medium are discussed. Energetic particle interactions in grains produce very narrow gamma ray lines from deexcitation of nuclear levels whose lifetimes are long enough that the excited nuclei stop before deexcitation. The presence of grains in the jets resolves hitherto discussed difficulties of inelastic excitation models for gamma ray production in SS433, the very narrow widths of the observed lines and the absence of other strong lines, expected from abundant elements. A model is proposed which could be distinguished from a previously proposed fusion model by gamma ray line observations.

Ramaty, R.↗

NASA NTRS1984

Nuclear processes in the jets of SS 433

The very narrow gamma-ray lines observed at 1.495 and 6.695 MeV from SS 433 which are blueshifted 1.369 and 6.129 emissions from deexcitations of (24)Mg-asterisk and (16)O-asterisk in grains moving with the jets and inelastically excited by interactions with the ambient medium are discussed. Energetic particle interactions in grains produce very narrow gamma ray lines from deexcitation of nuclear levels whose lifetimes are long enough that the excited nuclei stop before deexcitation. The presence of grains in the jets resolves hitherto discussed difficulties of inelastic excitation models for gamma ray production in SS 433, the very narrow widths of the observed lines and the absence of other strong lines, expected from abundant elements. A model is proposed which could be distinguished from a previously proposed fusion model by gamma ray line observations.

Ramaty, R.↗

NASA NTRS1995

Heat flux and viscosity of ions in the collisionless solar wind

Between 1 and 2 solar radii, the Coulomb-collision mean free path for thermal ions exceeds the scale height of the solar atmosphere. The expanding solar plasma becomes collisionless and the kinetics of the solar wind are no longer dominated by thermalizing collisions. The usual Braginskii-type expressions for solar wind ion heat flux and viscosity are no longer valid. However, another microscale still exists in the solar wind, dictated by the gyro-radius of ions in the turbulent embedded solar wind magnetic field. Wave-particle interactions will act to isotropize (but not thermalize) particle distributions, and the relevant microscale for this process is the ion gyro-radius. The ion distribution can be modelled as undergoing isotropizing 'collisions,' with the relevant mean free path scaling with gyro-radius. Here, the author presents the heat flux and viscosity expected for solar wind protons which are relaxing to isotropy on a microscale that scales with gyro-radius. The collisionless viscosity and heat flux have a functional dependence different than their collisional analogs. The collisional expressions for ion viscosity and heat flux drastically overestimate the efficiency of diffusive energy and momentum transport actually operative in the solar wind.

Williams, L. L.↗

NASA NTRS2003

The ATIC Long Duration Balloon Project

Long Duration Balloon (LDB) scientific experiments, launched to circumnavigate the south pole over Antarctica, have particular advantages compared to Shuttle or other Low Earth Orbit (LEO) missions in terms of cost, weight, scientific 'duty factor' and work force development. The Advanced Thin Ionization Calorimeter (ATIC) cosmic ray astrophysics experiment is a good example of a university-based project that takes full advantage of current LDB capability. The ATIC experiment is currently being prepared for its first LDB science flight that will investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10(exp 10) to 10(exp 14) eV. The instrument is built around a fully active, Bismuth Germanate (BGO) ionization calorimeter to measure the energy deposited by the cascades formed by particles interacting in a thick carbon target. A highly segmented silicon matrix, located above the target, provides good incident charge resolution plus rejection of the 'backscattered' particles from the interaction. Trajectory reconstruction is based on the cascade profile in the BGO calorimeter, plus information from the three pairs of scintillator hodoscope layers in the target section above it. A full evaluation of the experiment was performed during a test flight occurring between 28 December 2000 and 13 January 2001 where ATIC was carried to an altitude of approx. 37 km above Antarctica by an approx. 850,000 cu m helium filled balloon for one circumnavigation of the continent. All systems behaved well, the detectors performed as expected, more than 43 gigabytes of engineering and cosmic ray event data was returned and these data are now undergoing preliminary data analysis. During the coming 2002-2003 Antarctica summer season, we are preparing for a ATIC science flight with approx. 15 to 30 days of continuous data collection in the near-space environment of LDB float altitudes.

Guzik, T. G.↗

DOE OSTI2024

The three-pion K -matrix at NLO in ChPT

The three-particle K-matrix, Κ df,3 , is a scheme-dependent quantity that parametrizes short-range three-particle interactions in the relativistic-field-theory three-particle finite-volume formalism. In this work, we compute its value for systems of three pions in all isospin channels through next-to-leading order in Chiral Perturbation Theory, generalizing previous work done at maximum isospin. We obtain analytic expressions through quadratic order (or cubic order, in the case of zero isospin) in the expansion about the three-pion threshold.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

The isospin-3 three-particle K -matrix at NLO in ChPT

The three-particle K-matrix, K df,3 , is a scheme-dependent quantity that parametrizes short-range three-particle interactions in the relativistic-field-theory three-particle finite-volume formalism. In this work, we compute its value for systems of three pions at maximal isospin through next-to-leading order (NLO) in Chiral Perturbation Theory (ChPT). We compare the values to existing lattice QCD results and find that the agreement between lattice QCD data and ChPT in the first two coefficients of the threshold expansion of K df,3 is significantly improved with respect to leading order once NLO effects are incorporated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Short-wavelength plasma turbulence and temperature anisotropy instabilities: Recent computational progress

Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. In addition, temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave–particle interactions which transfer particle kinetic energy to field fluctuation energy; the resulting enhanced fluctuations are typically narrowband in wavevector magnitude and direction. Whatever their sources, short-wavelength fluctuations are those at which charged particle kinetic, that is, velocity-space, properties are important; these are generally wavelengths of the order of or shorter than the ion inertial length or the thermal ion gyroradius. The purpose of this review is to summarize and interpret recent computational results concerning short-wavelength plasma turbulence, short-wavelength temperature anisotropy instabilities and relationships between the two phenomena.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1992

Interaction of photons in a canopy of finite-dimensional leaves

Neutral particle interaction for photons traveling in media consisting of finite-dimensional scattering centers is investigated. A leaf canopy, a typical example of such media, is idealized as a binary medium consisting of gaps (voids) and regions with phytoelements (turbid phytomedium). The leaf canopy is represented by a combination of all possible open oriented spheres. The extinction coefficient at any phase-space location in a leaf canopy is the product of the extinction coefficient in the turbid phytomedium and the probability of absence gaps at that location. An expression for the differential scattering coefficient is derived using the same approach. The effect of canopy parameters and direction of photon travel on the extinction coefficient is illustrated by numerical examples.

Knyazikhin, Yuri V.↗

DOE OSTI2018

A Mechanical Model of Brownian Motion for One Massive Particle Including Slow Light Particles

We provide a connection between Brownian motion and a classical mechanical system. Precisely, we consider a system of one massive particle interacting with an ideal gas, evolved according to non-random mechanical principles, via interaction potentials, without any assumption requiring that the initial velocities of the environmental particles should be restricted to be “fast enough”. We prove the convergence of the (position, velocity)-process of the massive particle under a certain scaling limit, such that the mass of the environmental particles converges to 0 while the density and the velocities of them go to infinity, and give the precise expression of the limiting process, a diffusion process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Graph neural network for neutrino physics event reconstruction

Liquid argon time projection chamber (LArTPC) detector technology offers a wealth of high-resolution information on particle interactions, and leveraging that information to its full potential requires sophisticated automated reconstruction techniques. Here, this article describes NUGRAPH 2, a graph neural network for low-level reconstruction of simulated neutrino interactions in a LArTPC detector. Simulated neutrino interactions in the MicroBooNE detector geometry are described as heterogeneous graphs, with energy depositions on each detector plane forming nodes on planar subgraphs. The network utilizes a multihead attention message-passing mechanism to perform background filtering and semantic labeling on these graph nodes, identifying those associated with the primary physics interaction with 98.0% efficiency and labeling them according to particle type with 94.9% efficiency. The network operates directly on detector observables across multiple two-dimensional representations but utilizes a three-dimensional-context-aware mechanism to encourage consistency between these representations. Model inference takes 0.12 s / event on a CPU and 0.005 s / event batched on a GPU. This architecture is designed to be a general-purpose solution for particle reconstruction in neutrino physics, with the potential for deployment across a broad range of detector technologies, and offers a core convolution engine that can be leveraged for a variety of tasks beyond the two described in this paper.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for leptophobic bosons decaying into µµ, b jets, and MET with the CMS experiment

The standard model (SM) lacks a description for dark matter, which is implied by astrophysical observations to exist but has not yet been detected directly. An extension of the SM to include a leptophobic Z’ boson allows for the production of stable weakly interacting particles that offer dark matter candidates. Signatures of this interaction that can be detected by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider are mumu, b jets, and MET. As part of a sensitivity study, an examination of Z’ boson kinematics in the low Z’ mass range is presented along with event reconstruction methods and comparisons to ttbar and Drell-Yan backgrounds.

Kong, Livia↗

NASA NTRS1981

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time-varying magnetic field and their pitch angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, is used to predict the consequences of the process for cases that are not tractable by analytical means. The model is applied to the outer Jovian magnetosphere for two purposes; to find magnetospheric regions in which the mechanism may energize trapped particles, and to generate distribution functions involving pitch angle diffusion caused by wave-particle interactions. Beyond 20 Jupiter radii in the outer magnetosphere particles may be magnetically pumped to energies of the order of 1-2 MeV and two-temperature distribution functions with 'break points' at 1-4 keV for electrons and 8-35 keV for ions are predicted.

Borovsky, J. E.↗

NASA NTRS1988

An exact solution to the relativistic equation of motion of a charged particle driven by a linearly polarized electromagnetic wave

An exact analytic solution is found for a basic electromagnetic wave-charged particle interaction by solving the nonlinear equations of motion. The particle position, velocity, and corresponding time are found to be explicit functions of the total phase of the wave. Particle position and velocity are thus implicit functions of time. Applications include describing the motion of a free electron driven by an intense laser beam..

Shebalin, John V.↗

NASA NTRS1988

Simulation and non-linear stage of the electrostatic waves observed during the AMPTE lithium release in the solar wind

During the AMPTE lithium releases in the solar wind intense electrostatic waves with frequencies between a few tens of Hz to several kHz were observed outside the diamagnetic cavity. The results of linear Vlasov theory have suggested that these waves may be generated through two types of instabilities. One is the ion-ion instability associated with the relative drift between the lithium ions and the solar wind protons, and the other is the ion-acoustic instability due to the relative drift between the electrons and the ions. In order to look at the non-linear behavior of the wave-particle interactions, and discern the effect of waves on the particles, full particle electrostatic simulations have been performed, and the results are presented here. It is shown that the ion-ion instability whose phase velocity is oblique to the solar wind velocity can cause considerable anisotropic 'heating' of both the lithium ions and the solar wind protons.

Omidi, N.↗