Different Parts Of Phase Space Research Articles

The phase-space dependence of fast-ion interaction with tearing modesaaIAEA Technical Meeting paper for submission to Nuclear Fusion

Modulation of various neutral beam sources probes the interaction of fast ions with tearing modes (TM) in the DIII-D tokamak. As measured by electron cyclotron emission, the tearing modes have an island width of ∼8 cm and change phase at the q = 2 surface. (Here, m is the poloidal mode number and n is the toroidal mode number.) Deuterium neutral beam injection by six sources with differing injection geometries produces the fast ions. To study the interaction in different parts of phase space, on successive discharges, one of the six sources is modulated at 20 Hz to populate different fast-ion orbits. The modulation only changes the island width by a few millimeters, implying that any fast-ion effect on mode stability is below detection limits. When compared to the expected signals in the absence of TM-induced transport, both the average and modulated neutron signals deviate, implying that fast-ion transport occurs in much of phase space. Fast-ion Dα (FIDA) measurements detect reductions in signal at wavelengths that are sensitive to counter-passing ions. Neutral particle analyzer data imply poor confinement of trapped fast ions. Calculations of the expected fast-ion transport that use measured TM properties successfully reproduce the data.

A Dynamic Laplacian for Identifying Lagrangian Coherent Structures on Weighted Riemannian Manifolds

Transport and mixing in dynamical systems are important properties for many physical, chemical, biological, and engineering processes. The detection of transport barriers for dynamics with general time dependence is a difficult, but important problem, because such barriers control how rapidly different parts of phase space (which might correspond to different chemical or biological agents) interact. The key factor is the growth of interfaces that partition phase space into separate regions. The paper [Froyland, Nonlinearity 2015] introduced the notion of \textit{dynamic isoperimetry}: the study of sets with persistently small boundary size (the interface) relative to enclosed volume, when evolved by the dynamics. Sets with this minimal boundary size to volume ratio were identified as level sets of dominant eigenfunctions of a \textit{dynamic Laplace operator}. In this present work we extend the results of [Froyland, Nonlinearity 2015] to the situation where the dynamics (i) is not necessarily volume-preserving, (ii) acts on initial agent concentrations different from uniform concentrations, and (iii) occurs on a possibly curved phase space. Our main results include generalised versions of the dynamic isoperimetric problem, the dynamic Laplacian, Cheeger's inequality, and the Federer-Fleming theorem. We illustrate the computational approach with some simple numerical examples.

Improving the iterative Linear Interaction Energy approach using automated recognition of configurational transitions

Recently an iterative method was proposed to enhance the accuracy and efficiency of ligand-protein binding affinity prediction through linear interaction energy (LIE) theory. For ligand binding to flexible Cytochrome P450s (CYPs), this method was shown to decrease the root-mean-square error and standard deviation of error prediction by combining interaction energies of simulations starting from different conformations. Thereby, different parts of protein-ligand conformational space are sampled in parallel simulations. The iterative LIE framework relies on the assumption that separate simulations explore different local parts of phase space, and do not show transitions to other parts of configurational space that are already covered in parallel simulations. In this work, a method is proposed to (automatically) detect such transitions during the simulations that are performed to construct LIE models and to predict binding affinities. Using noise-canceling techniques and splines to fit time series of the raw data for the interaction energies, transitions during simulation between different parts of phase space are identified. Boolean selection criteria are then applied to determine which parts of the interaction energy trajectories are to be used as input for the LIE calculations. Here we show that this filtering approach benefits the predictive quality of our previous CYP 2D6-aryloxypropanolamine LIE model. In addition, an analysis is performed of the gain in computational efficiency that can be obtained from monitoring simulations using the proposed filtering method and by prematurely terminating simulations accordingly.Electronic supplementary materialThe online version of this article (doi:10.1007/s00894-015-2883-y) contains supplementary material, which is available to authorized users.

Consequences of temperature fluctuations in observables measured in high-energy collisions

We review the consequences of intrinsic, nonstatistical temperature fluctuations as seen in observables measured in high energy collisions. We do this from the point of view of nonextensive statistics and Tsallis distributions. Particular attention is paid to multiplicity fluctuations as a first consequence of temperature fluctuations, to the equivalence of temperature and volume fluctuations, to the generalized thermodynamic fluctuations relations allowing us to compare fluctuations observed in different parts of phase space, and to the problem of the relation between Tsallis entropy and Tsallis distributions. We also discuss the possible influence of conservation laws on these distributions and provide some examples of how one can get them without considering temperature fluctuations.

Velocity-space studies of fast-ion transport at a sawtooth crash in neutral-beam heated plasmas

In tokamaks the crash phase of the sawtooth instability causes fast-ion transport. The DIII-D tokamak is equipped with a suite of core fast-ion diagnostics that can probe different parts of phase space. Over a variety of operating conditions, energetic passing ions are observed to undergo larger redistribution than their trapped counterparts. Passing ions of all energies are redistributed, but only low-energy (≲40 keV) trapped ions suffer redistribution. The transport process is modeled using a numerical approach to the drift-kinetic equation. The simulation reproduces the characteristic that circulating energetic ions experience the greatest levels of internal transport. An analytic treatment of particle drifts suggests that the difference in observed transport depends on the magnitude of toroidal drift.

A systematic study of two particle correlations from NA49 at CERN SPS

A systematic study of two particle correlations measured by the NA49 experiment is summarized. Radii from Bose Einstein interferometry have been determined separately in different parts of phase space, for different collision systems and at different incident beam energies. Moreover, first results of a new method of accessing space-time asymmetries in the emission of particles by means of non identical particle correlations are presented.

A systematic study of two particle correlations from NA49 at CERN SPS

A systematic study of two particle correlations measured by the NA49 experiment is summarized. Radii from Bose Einstein interferometry have been determined separately in different parts of phase space, for different collision systems and at different incident beam energies. Moreover, first results of a new method of accessing space-time asymmetries in the emission of particles by means of non identical particle correlations are presented.

Electromagnetic probes of quark-gluon plasma in relativistic heavy-ion collisions

Production rates of real and virtual photons from a hot quark-gluon plasma are reviewed with emphasis on recent advances in the perturbative analysis of rate calculations for photons and low-mass lepton pairs. Momentum distributions in central A+A collisions are calculated by convoluting the rates at fixed temperature with hydrodynamic expansion of produced matter. The possibilities to observed thermal electromagnetic signals from plasma are considered in different parts of phase space by comparing the thermal rates with the dominant backgrounds.

The energy independence of proton-emulsion collisions

The density of shower particles in pseudorapidity space from proton-emulsion collisions at 200, 300 and 400 GeV/ c is essentially energy independent but exhibits a linear growth with N h (the number of heavy prongs), different in different parts of phase space. Deviations occur for the largest values of N h and comparisons to the 67 GeV/ c data show a rise in the density of particles in the central region between Serpukhov and FNAL energies. Special attention is given to the new 400 GeV/ c data and some correlations between different parts of phase space are discussed.

The energy independence of proton-emulsion collisions

The density of shower particles in pseudorapidity space from proton-emulsion collisions at 200, 300 and 400 GeV/c is essentially energy independent but exhibits a linear growth with Nh (the number of heavy prongs), different in different parts of phase space. Deviations occur for the largest values of Nh and comparisons to the 67 GeV/c data show a rise in the density of particles in the central region between Serpukhov and FNAL energies. Special attention is given to the new 400 GeV/c data and some correlations between different parts of phase space are discussed.