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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Continuation of full-scale three-dimensional numerical experiments on high-intensity particle and laser beam-matter interactions

We present results from the grant entitled, Continuation of full-scale three-dimensional numerical experiments on high-intensity particle and laser beam-matter interactions. The research significantly advanced the understanding of basic high-energy density science (HEDS) on ultra intense laser and particle beam plasma interactions. This advancement in understanding was then used to to aid in the quest to make 1 GeV to 500 GeV plasma based accelerator stages. The work blended basic research with three-dimensions fully nonlinear and fully kinetic simulations including full-scale modeling of ongoing or planned experiments. The primary tool was three-dimensional particle-in-cell simulations. The simulations provided a test bed for theoretical ideas and models as well as a method to guide experiments. The research also included careful benchmarking of codes against experiment. High-fidelity full-scale modeling provided a means to extrapolate parameters into regimes that were not accessible to current or near term experiments, thereby allowing concepts to be tested with confidence before tens to hundreds of millions of dollars were spent building facilities. The research allowed the development of a hierarchy of PIC codes and diagnostics that is one of the most advanced in the world.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

EFFECT OF COHERENT STRUCTURES ON ENERGETIC PARTICLE INTENSITY IN THE SOLAR WIND AT 1 AU

We present results from an analysis of Advanced Composition Explorer (ACE) observations of energetic particles in the 0.047–4.78 MeV range associated with shocks and discontinuities in the solar wind. Previous work found a strong correlation between coherent structures and energetic particles measured by ACE/EPAM. Coherent structures are identified using the Partial Variance of Increments (PVI) method, which is essentially a normalized vector increment. The correlation was based on a superposed epoch analysis using over 12 years of data. Here, we examine many individual high-PVI events to better understand this association emphasizing intervals selected from data with shock neighborhoods removed. We find that in many cases the local maximum in PVI is in a region of rising or falling energetic particle intensity, which suggests that magnetic discontinuities may act as barriers inhibiting the motion of energetic particles across them.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

AN INTERPRETATION OF GLE71 CONCURRENT CME-DRIVEN SHOCK WAVE

Particle accelerations in solar flares and CME-driven shocks can sometimes result in very high-energy particle events (≥1 GeV) that are known as ground level enhancements (GLEs). Recent studies on the first GLE event (GLE71 2012 May 17 01:50 UT) of solar cycle 24 suggested that CME-driven shock played a leading role in causing the event. To verify this claim, we have made an effort to interpret the GLE71 concurrent shock wave. For this, we have deduced the possible speed and height of the shock wave in terms of the frequency (MHz) of the solar radio type II burst and its drift rate (MHz min{sup –1}), and studied the temporal evolution of the particle intensity profiles at different heights of the solar corona. For a better perception of the particle acceleration in the shock, we have studied the solar radio type II burst with concurrent solar radio and electron fluxes. When the particle intensity profiles are necessarily shifted in time at ∼1 AU, it is found that the growth phases of the electron and cosmic ray intensity fluxes are strongly correlated (>0.91; ≥0.87) with the frequency drift rate of the type II burst, which is also consistent with the intensive particle accelerations at upper coronal heights (∼≥0.80 R {sub S} < 1.10 R {sub S}). Thus, we conclude that the CME-driven shock was possibly capable of producing the high-energy particle event. However, since the peaks of some flare components are found to be strongly associated with the fundamental phase of the type II burst, the preceding flare is supposed to contribute to the shock acceleration process.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Dependence of energetic ion and electron intensities on proximity to the magnetically sectored heliosheath: Voyager 1 and 2 observations

Taken together, the Voyager 1 and 2 (V1 and V2) spacecraft have collected over 11 yr of data in the heliosheath. Despite extensive study, energetic particles and magnetic fields measured in the heliosheath have not been reconciled by existing models. In particular, the differences between the energetic particle intensity variations at V1 and V2 are unexplained. While energetic particle intensities at V1 change gradually over 7 yr in the heliosheath, those at V2 vary by a factor ∼10 in 1 yr. Energetic particle intensities at V2 show temporally coherent variations over a broad range of species and energies: from suprathermal ions (10s of keV) to galactic cosmic rays (>1 GeV), as well as electrons from 10s of keV to >100 MeV, corresponding to a range ∼10{sup 4} in particle gyroradii. Here we suggest that many of the intensity variations of energetic particle populations in the heliosheath are organized by their proximity to two fundamentally different regions—the unipolar heliosheath (UHS) and the sectored heliosheath (SHS). The SHS is a region of enhanced particle intensities, wherein particle transport, acceleration, and magnetic connectivity differ from those in the UHS. The SHS may serve as either a reservoir of energetic particles or as a region of enhanced transport, depending on the particle species and energy. Comparatively, particle intensities in the UHS are greatly reduced. We propose that the boundary between the SHS and UHS plays as important a role in the physics of heliosheath particles and fields as do the termination shock and heliopause.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Diffusive shock acceleration and reconnection acceleration processes

Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination of diffusive shock acceleration (DSA) and downstream magnetic-island-reconnection-related processes as an energization mechanism for charged particles. Observations of electron and ion distributions downstream of interplanetary shocks and the heliospheric termination shock (HTS) are frequently inconsistent with the predictions of classical DSA. We utilize a recently developed transport theory for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets. Particle energization associated with the anti-reconnection electric field, a consequence of magnetic island merging, and magnetic island contraction, are considered. For the former only, we find that (i) the spectrum is a hard power law in particle speed, and (ii) the downstream solution is constant. For downstream plasmoid contraction only, (i) the accelerated spectrum is a hard power law in particle speed; (ii) the particle intensity for a given energy peaks downstream of the shock, and the distance to the peak location increases with increasing particle energy, and (iii) the particle intensity amplification for a particular particle energy, f(x,c/c{sub 0})/f(0,c/c{sub 0}), is not 1, as predicted by DSA, but increases with increasing particle energy. The general solution combines both the reconnection-induced electric field and plasmoid contraction. The observed energetic particle intensity profile observed by Voyager 2 downstream of the HTS appears to support a particle acceleration mechanism that combines both DSA and magnetic-island-reconnection-related processes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Study of Nonlinear Dynamics of Intense Charged Particle Beams in the Paul Trap Simulator Experiment

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory device that simulates the nonlinear dynamics of intense charged particle beams propagating over a large distance in an alternating-gradient magnetic transport system. The radial quadrupole electric eld forces on the charged particles in the Paul Trap are analogous to the radial forces on the charged particles in the quadrupole magnetic transport system. The amplitude of oscillating voltage applied to the cylindrical electrodes in PTSX is equivalent to the quadrupole magnetic eld gradient in accelerators. The temporal periodicity in PTSX corresponds to the spatial periodicity in magnetic transport system. This thesis focuses on investigations of envelope instabilities and collective mode excitations, properties of high-intensity beams with significant space-charge effects, random noise-induced beam degradation and a laser-induced-fluorescence diagnostic. To better understand the nonlinear dynamics of the charged particle beams, it is critical to understand the collective processes of the charged particles. Charged particle beams support a variety of collective modes, among which the quadrupole mode and the dipole mode are of the greatest interest. We used quadrupole and dipole perturbations to excite the quadrupole and dipole mode respectively and study the effects of those collective modes on the charge bunch. The experimental and particle-in-cell (PIC) simulation results both show that when the frequency and the spatial structure of the external perturbation are matched with the corresponding collective mode, that mode will be excited to a large amplitude and resonates strongly with the external perturbation, usually causing expansion of the charge bunch and loss of particles. Machine imperfections are inevitable for accelerator systems, and we use random noise to simulate the effects of machine imperfection on the charged particle beams. The random noise can be Fourier decomposed into various frequency components and experimental results show that when the random noise has a large frequency component that matches a certain collective mode, the mode will also be excited and cause heating of the charge bunch. It is also noted that by rearranging the order of the random noise, the adverse effects of the random noise may be eliminated. As a non-destructive diagnostic method, a laser-induced- fluorescence (LIF) diagnostic is developed to study the transverse dynamics of the charged particle beams. The accompanying barium ion source and dye laser system are developed and tested.

LIF↗
DOE OSTI2018

Properties of Intense Field-Aligned Lower-Band Chorus Waves: Implications for Nonlinear Wave-Particle Interactions: INTENSE FIELD-ALIGNED CHORUS WAVE-PACKETS

Resonant interactions between electrons and chorus waves are responsible for a wide range of phenomena in near-Earth space (e.g., diffuse aurora and acceleration of > 1 MeV electrons). Although quasi-linear diffusion is believed to be the primary paradigm for describing such interactions, an increasing number of investigations suggest that nonlinear effects are also important in controlling the rapid dynamics of electrons. However, present models of nonlinear wave-particle interactions, which have been successfully used to describe individual short-term events, are not directly applicable for a statistical evaluation of nonlinear effects and the long-term dynamics of the outer radiation belt, because they lack information on the properties of intense (nonlinearly resonating with electrons) chorus waves. In this paper, we use the Time History of Events and Macroscale Interactions during Substorms and Van Allen Probes data sets of field-aligned chorus waveforms to study two key characteristics of these waves: effective amplitude Β w (nonlinear interaction can occur when Β w >2) and wave packet length β (the number of wave periods within it). While as many as 10–15% of chorus wave packets are sufficiently intense (Β w >2–3) to interact nonlinearly with relativistic electrons, most of them are short (β < 10) reducing the efficacy of such interactions. Revised models of nonlinear interactions are thus needed to account for the long-term effects of these common, intense but short chorus wave packets. We also discuss the dependence of Β w , β on location (MLT and L-shell) and on the properties of the suprathermal electron population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

A Massive, Position-Resolving, High-Energy-Resolution Detector for Non-Accelerator Cosmic and Intensity Frontier Particle Physics

We proposed to take the first steps in the development of a detector that promises energy resolution of tens of eV FWHM combined with robust nuclear-recoil discrimination and high fidelity, mm-precision position reconstruction for applications in non-accelerator particle physics at the Cosmic and Intensity Frontiers. The detector would obtain these excellent resolutions by sensing athermal phonons produced by particle interactions in crystalline, dielectric targets using a sensitive, highly multiplexable superconducting phonon sensor, the kinetic inductance detector (KID). This detector would be applicable to: the search for low-mass particle dark matter candidates with masses below 5~GeV via direct detection of scattering of dark matter particles with terrestrial nuclei; detection of coherent elastic neutrino-nucleus scattering to test for new physics such as a non-standard value of the weak nuclear charge, non-standard neutrino interactions (perhaps driven by a neutrino magnetic moment), or the existence of sterile neutrinos; and, searches for neutrinoless double-beta decay. During the funding period, we demonstrated scaling up of the detector concept from a 22-mm by 22-mm by 1-mm, 1-g prototype with 0.9~keV FWHM energy resolution to a 75-mm diameter by 1-mm, 9-g prototype while improving the inferred energy resolution to 0.7~keV~FWHM. In the process, we solved many problems associated with scaling device fabrication to large wafers and vastly reduced the fraction of the surface occupied by inactive but energy-absorbing metal. We also demonstrated a new technique that substantially simplifies the process of characterizing a new detector. These results provide a good foundation for future work scaling up the design to 4-mm thickness substrates and improving the resolution to reach 0.035~keV~FWHM, yielding a detector with compelling potential for the above applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

LONGITUDINAL AND RADIAL DEPENDENCE OF SOLAR ENERGETIC PARTICLE PEAK INTENSITIES: STEREO, ACE, SOHO, GOES, AND MESSENGER OBSERVATIONS

Simultaneous measurements of solar energetic particle (SEP) events by two or more of the spacecraft located near 1 AU during the rising phase of solar cycle 24 (i.e., STEREO-A, STEREO-B, and near-Earth spacecraft such as ACE, SOHO, and GOES) are used to determine the longitudinal dependence of 71-112 keV electron, 0.7-3 MeV electron, 15-40 MeV proton, and 25-53 MeV proton peak intensities measured in the prompt component of SEP events. Distributions of the peak intensities for the selected 35 events with identifiable solar origin are approximated by the form exp [ - ({phi} - {phi}{sub 0}){sup 2}/2{sigma}{sup 2}], where {phi} is the longitudinal separation between the parent active region and the footpoint of the nominal interplanetary magnetic field (IMF) line connecting each spacecraft with the Sun, {phi}{sub 0} is the distribution centroid, and {sigma} determines the longitudinal gradient. The MESSENGER spacecraft, at helioradii R < 1 AU, allows us to determine a lower limit to the radial dependence of the 71-112 keV electron peak intensities measured along IMF lines. We find five events for which the nominal magnetic footpoint of MESSENGER was less than 20 Degree-Sign apart from the nominal footpoint of a spacecraft near 1 AU. Although the expected theoretical radial dependence for the peak intensity of the events observed along the same field line can be approximated by a functional form R {sup -{alpha}} with {alpha} < 3, we find two events for which {alpha} > 3. These two cases correspond to SEP events occurring in a complex interplanetary medium that favored the enhancement of peak intensities near Mercury but hindered the SEP transport to 1 AU.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Interactions of cosmic rays in the atmosphere: growth curves revisited

Measurements of cosmic-ray abundances on balloons are affected by interactions in the residual atmosphere above the balloon. Corrections for such interactions are particularly important for observations of rare secondary particles such as boron, antiprotons, and positrons. These corrections either can be calculated if the relevant cross sections in the atmosphere are known or may be empirically determined by extrapolation of the 'growth curves', i.e., the individual particle intensities as functions of atmospheric depth. The growth-curve technique is particularly attractive for long-duration balloon flights where the periodic daily altitude variations permit rather precise determinations of the corresponding particle intensity variations. We determine growth curves for nuclei from boron (Z = 5) to iron (Z = 26) using data from the 2006 Arctic balloon flight of the TRACER detector for cosmic-ray nuclei, and we compare the growth curves with predictions from published cross section values. In general, good agreement is observed. We then study the boron/carbon abundance ratio and derive a simple and energy-independent correction term for this ratio. We emphasize that the growth-curve technique can be developed further to provide highly accurate tests of published interaction cross section values.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ENERGETIC PARTICLE PRESSURE AT INTERPLANETARY SHOCKS: STEREO-A OBSERVATIONS

We study periods of elevated energetic particle intensities observed by STEREO-A when the partial pressure exerted by energetic (≥83 keV) protons (P{sub EP}) is larger than the pressure exerted by the interplanetary magnetic field (P{sub B}). In the majority of cases, these periods are associated with the passage of interplanetary shocks. Periods when P{sub EP} exceeds P{sub B} by more than one order of magnitude are observed in the upstream region of fast interplanetary shocks where depressed magnetic field regions coincide with increases of energetic particle intensities. When solar wind parameters are available, P{sub EP} also exceeds the pressure exerted by the solar wind thermal population (P{sub TH}). Prolonged periods (>12 hr) with both P{sub EP} > P{sub B} and P{sub EP} > P{sub TH} may also occur when energetic particles accelerated by an approaching shock encounter a region well upstream of the shock characterized by low magnetic field magnitude and tenuous solar wind density. Quasi-exponential increases of the sum P{sub SUM} = P{sub B} + P{sub TH} + P{sub EP} are observed in the immediate upstream region of the shocks regardless of individual changes in P{sub EP}, P{sub B}, and P{sub TH}, indicating a coupling between P{sub EP} and the pressure of the background medium characterized by P{sub B} and P{sub TH}. The quasi-exponential increase of P{sub SUM} implies a radial gradient ∂P{sub SUM}/∂r > 0 that is quasi-stationary in the shock frame and results in an outward force applied to the plasma upstream of the shock. This force can be maintained by the mobile energetic particles streaming upstream of the shocks that, in the most intense events, drive electric currents able to generate diamagnetic cavities and depressed solar wind density regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

COMBINING DIFFUSIVE SHOCK ACCELERATION WITH ACCELERATION BY CONTRACTING AND RECONNECTING SMALL-SCALE FLUX ROPES AT HELIOSPHERIC SHOCKS

Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes and filaments. This led Zank et al. to investigate a new paradigm whereby energetic particle acceleration near shocks is a combination of diffusive shock acceleration (DSA) with downstream acceleration by many small-scale contracting and reconnecting (merging) flux ropes. Using a model where flux-rope acceleration involves a first-order Fermi mechanism due to the mean compression of numerous contracting flux ropes, Zank et al. provide theoretical support for observations that power-law spectra of energetic particles downstream of heliospheric shocks can be harder than predicted by DSA theory and that energetic particle intensities should peak behind shocks instead of at shocks as predicted by DSA theory. In this paper, a more extended formalism of kinetic transport theory developed by le Roux et al. is used to further explore this paradigm. We describe how second-order Fermi acceleration, related to the variance in the electromagnetic fields produced by downstream small-scale flux-rope dynamics, modifies the standard DSA model. The results show that (i) this approach can qualitatively reproduce observations of particle intensities peaking behind the shock, thus providing further support for the new paradigm, and (ii) stochastic acceleration by compressible flux ropes tends to be more efficient than incompressible flux ropes behind shocks in modifying the DSA spectrum of energetic particles.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Particle Accelerators at the Intensity Frontier for Elementary Particle Physics Research

In 1897, Prof. J. J. Thomson used a cathode ray tube that operated at a few kiloelectron volts (keV) to discover the electron and measured its charge-to-mass ratio. In this case, the electrons were not created, but ejected from hot filament. This experiment is considered to be one of the earliest uses of particle accelerators in elementary particle physics research. Imparting a few keV of energy to a beam of electrons was considered as high energy at that time. The meaning of the phrase High Energy Physics (HEP) has changed significantly over the last century.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Traverse Focusing of Intense Charged Particle Beams with Chromatic Effects for Heavy Ion Fusion

A fi nal focusing scheme designed to minimize chromatic effects is discussed. The Neutralized Drift Compression Experiment-II (NDCX-II) will apply a velocity tilt for longitudinal bunch compression, and a fi nal focusing solenoid (FFS) for transverse bunch compression. In the beam frame, neutralized drift compression causes a suffi ciently large spread in axial momentum, pz , resulting in chromatic effects to the fi nal focal spot during transverse bunch compression. Placing a weaker solenoid upstream of a stronger fi nal focusing solenoid (FFS) mitigates chromatic effects and improves transverse focusing by a factor of approximately 2-4 for appropriate NDCX-II parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗