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Results for “PARTICLE COLLISION”

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 OSTI2011

Heavy Particle Collision Data for Fusion and Astrophysics

A wide range of applications, for example, diagnostics and modeling of fusion plasmas, interpretation of astronomical observations and modeling of astrophysical environments, and simulation of material processing plasmas, require large, accurate, and complete collections of data for electron, photon, heavy particle, and surface interactions. Consequently, over several decades, experimental and theoretical efforts have been developed in order to measure or to calculate such data, and to synergistically explore the fundamental physical mechanisms that underlie interactions at the atomic scale. The present report illustrates some of the recent progress in development of techniques and their use in describing heavy particle collisions, in particular, those involving ions interacting with atoms and simple molecules, with specific applications of the resulting data in fusion energy research and astrophysics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Unlike-particle collision operator for gyrokinetic particle simulations

Plasmas in modern tokamak experiments contain a significant fraction of impurity ion species in addition to main deuterium background. A new unlike-particle collision operator for {delta}f particle simulation has been developed to self-consistently study the non-local effects of impurities on neoclassical transport in toroidal plasmas. A new algorithm for simulation of cross-collisions between different ion species includes test-particle and conserving field-particle operators. The field-particle operator is designed to enforce conservation of number, momentum and energy. It was shown that the new operator correctly simulates the thermal equilibration of different plasma components. It was verified that the ambipolar radial electric field reaches steady state when the total radial guiding center particle current vanishes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

A higher-order finite-element implementation of the nonlinear Fokker–Planck collision operator for charged particle collisions in a low density plasma

Collisions between particles in a low density plasma are described by the Fokker–Planck collision operator. In applications, this nonlinear integro-differential operator is often approximated by linearised or ad-hoc model operators due to computational cost and complexity. In this work, we present an implementation of the nonlinear Fokker–Planck collision operator written in terms of Rosenbluth potentials in the Rosenbluth–MacDonald–Judd (RMJ) form. The Rosenbluth potentials may be obtained either by direct integration or by solving partial differential equations (PDEs) similar to Poisson's equation: we optimise for performance and scalability by using sparse matrices to solve the relevant PDEs. We represent the distribution function using a tensor-product continuous-Galerkin finite-element representation and we derive and describe the implementation of the weak form of the collision operator. We present tests demonstrating a successful implementation using an explicit time integrator and we comment on the speed and accuracy of the operator. Finally, we speculate on the potential for applications in the current and next generation of kinetic plasma models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Predicting the impact of particle-particle collisions on turbophoresis with a reduced number of computational particles

A common feature of wall-bounded turbulent particle-laden flows is enhanced particle concentrations in a thin layer near the wall due to a phenomenon known as turbophoresis. Even at relatively low bulk volume fractions, particle-particle collisions regulate turbophoresis in a critical way, making simulations sensitive to collisional effects. Lagrangian tracking of every particle in the flow can become computationally expensive when the physical number of particles in the system is large. Artificially reducing the number of particles in the simulation can mitigate the computational cost. When particle-particle collisions are an important aspect determining the simulation outcome, as in the case when turbophoresis plays an active role, simply reducing the number of particles in the simulation significantly alters the computed particle statistics. This paper introduces a computational particle treatment for particle-particle collisions which reproduces the results of a full simulation with a reduced number of particles. This is accomplished by artificially enhancing the particle collision radius based on scaling laws for the collision rates. The proposed method retains the use of deterministic collision models and is applicable for both low and high Stokes number regimes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1968

Heavy particle collisions

Diatomic heavy particle collisions and elastic scattering and inelastic processes involving electronic excitation, ionization, and charge transfer or electronic energy

Smith, F. T.↗
NASA NTRS1969

Heavy particle collisions.

Diatomic heavy particle collisions with emphasis on epithermal energy range, discussing elastic scattering and inelastic processes

Smith, F. T.↗
NASA NTRS1985

New theory of transport due to like-particle collisions

Cross-magnetic-field transport due to like-particle collisions is discussed for the parameter regime lambda sub D much greater than r sub L, where lambda sub D is the Debye length and r sub L is the characteristic Larmor radius of the colliding particles. A new theory based on collisionally produced E x B drifts predicts a particle flux which exceeds the flux predicted previously, by the factor (lambda sub D/r sub L)-squared much greater than 1.

Oneil, T. M.↗
DOE OSTI2011

Emergent flux from particle collisions near a Kerr black hole

The escape fraction at infinity is evaluated for massless particles produced in collisions of weakly interacting particles accreted into a density spike near the particle horizon of an extremal Kerr black hole, for the case of equatorial orbits. We compare with the Schwarzschild case, and argue that in the case of extremal black holes, redshifted signatures can be produced that could potentially explore the physics of particle collisions at center of mass energies that extend beyond those of any feasible terrestrial accelerator.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Imaging particle collision data for event classification using machine learning

We propose a method to organize experimental data from particle collision experiments in a general format which can enable a simple visualisation and effective classification of collision data using machine learning techniques. The method is based on sparse fixed-size matrices with single- and two-particle variables containing information on identified particles and jets. As a result, we illustrate this method using an example of searches for new physics at the LHC experiments.

47 OTHER INSTRUMENTATION↗
NASA NTRS1989

The role of particle collisions in pneumatic transport

A model of dilute gas-solid flow in vertical risers is developed in which the particle phase is treated as a granular material, the balance equations for rapid granular flow are modified to incorporate the drag force from the gas, and boundary conditions, based on collisional exchanges of momentum and energy at the wall, are employed. In this model, it is assumed that the particle fluctuations are determined by inter-particle collisions only and that the turbulence of the gas is unaffected by the presence of the particles. The model is developed in the context of, but not limited to, steady, fully developed flow. A numerical solution of the resulting governing equations provides concentration profiles generally observed in dilute pneumatic flow, velocity profiles in good agreement with the measurements of Tsuji, et al. (1984), and an explanation for the enhancement of turbulence that they observed.

Mastorakos, E.↗
DOE OSTI2010

Destruction of a metastable string by particle collisions

We calculate the probability of destruction of a metastable string by collisions of the Goldstone bosons, corresponding to the transverse waves on the string. We find a general formula that allows to determine the probability of the string breakup by a collision of arbitrary number of the bosons. We find that the destruction of a metastable string takes place only in collisions of even number of the bosons, and we explicitly calculate the energy dependence of such process in a two-particle collision for an arbitrary relation between the energy and the largest infrared scale in the problem, the length of the critical gap in the string.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Explainable machine learning of the underlying physics of high-energy particle collisions

We present an implementation of an explainable and physics-aware machine learning model capable of inferring the underlying physics of high-energy particle collisions using the information encoded in the energy-momentum four-vectors of the final state particles. We demonstrate the proof-of-concept of our White Box AI approach using a Generative Adversarial Network (GAN) which learns from a DGLAP-based parton shower Monte Carlo event generator. The constrained generator network architecture mimics the structure of a parton shower exhibiting similarities with Recurrent Neural Networks (RNNs). We show, for the first time, that our approach leads to a network that is able to learn not only the final distribution of particles, but also the underlying parton branching mechanism, i.e. the Altarelli-Parisi splitting function, the ordering variable of the shower, and the scaling behavior. While the current work is focused on perturbative physics of the parton shower, we foresee a broad range of applications of our framework to areas that are currently difficult to address from first principles in QCD. Examples include nonperturbative and collective effects, factorization breaking and the modification of the parton shower in heavy-ion, and electron-nucleus collisions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

FERROMAGNETISM AND PARTICLE COLLISIONS: APPLICATIONS TO PROTOPLANETARY DISKS AND THE METEORITICAL RECORD

The meteoritical record shows both iron partitioning and tungsten isotopic partitioning between the matrix and chondrules. Tungsten is not abundant enough to have driven its own isotopic partitioning, but if tungsten were correlated with iron then ferromagnetic interaction grains could help explain both observations. We derive a practical parameterization for the increase in particle–particle collision rates caused by mutually attracting particle magnetic dipole moments. While the appropriate magnetic parameters remain uncertain, we show that ambient magnetic fields in protoplanetary disks are expected to be strong enough to magnetize iron metal bearing dust grains sufficiently to drive large increases in their collision rates. Such increased collision rates between iron-metal-rich grains could help preserve primordial iron and W isotopic inhomogeneities, and would help explain why the meteoritical record shows their partitioning in the solar nebula. The importance of magnetic interactions for larger grains whose growth is balanced by fragmentation is less clear and will require future laboratory or numerical studies.

79 ASTRONOMY AND ASTROPHYSICS↗