Impurity ion heating and drift velocity in the AL'FA experiment

High impurity ion energies (>100 eV) and toroidal drift velocities were reported in the early, ohmically heated experiment, Al'fa (Альфа, ~1960, major radius 1.6 m). These are explained here in terms of charged particle acceleration by the toroidal electric field corresponding to the noisy loop voltage, using data from the experiment, atomic cross section data, and 1-D momentum equations without turbulence, radial fluxes, or microfield anomalies. In general, the impurities are thermally decoupled from the H (bulk) ions and electrons in the transiently runaway discharges.Высокие энергии (>100 эВ) и дрейфы примесных ионов обнаруживались в ранней установке с омическим нагревом "Альфа" (~1960 г., большой радиус 1.6 м). Результаты здесь объясняются ускорением заряженных частиц тороидальным электрическим полем, соответствующим шумному напряжению на оси шнура. Используются измерительные данные, информация об атомных сечениях и одноразмерные уравнения движения, не привлекая турбулентность, радиальные потоки, или аномалии микрополя. Вообще, ионы водорода и примесей (и электроны) термически развязаны в нестационарно убегающих разрядах.Високі енергії (>100 eВ) і дрейфи домішкових іонів виявлялися в ранній установці з омічним нагріванням "Альфа" (~1960 р., великий радіус 1.6 м). Результати тут порозуміваються прискоренням заряджених часток тороїдальним електричним полем, що відповідає шумовій напрузі на осі шнура. Використовуються вимірювальні дані, інформація про атомні перетини і однорозмірні рівняння руху, не залучаючи турбулентність, радіальні потоки, або аномалії мікрополя. Взагалі, іони водню і домішок (і електрони) термічно розв'язані в нестаціонарно втікаючих розрядах

Impurity ion drift and toroidal rotation in tokamaks

This is an analysis of the toroidal drifts of bulk (hydrogenic) and impurity ions, and electrons, in ohmically heated tokamaks. Experimentally observed ion drift is consistently explained by a 1-D model with Ohm's law and the charged particle equations of motion in a quiescent plasma. Calculations show that the drifts are usually decoupled, so the notion of "toroidal rotation" of the plasma as a whole is untenable in this situation.Анализируются тороидальные дрейфы основных (водородных) и примесных ионов и электронов в токамаках с омическим нагревом. Экспериментально обнаруженные дрейфы ионов самосогласованно объясняются одномерной моделью с законом Ома и уравнениями движения заряженных частиц в стационарной плазме. Расчеты показывают, что, как правило, дрейфы разных сортов частиц развязаны, поэтому понятие "тороидальное вращение" плазмы в целом здесь несостоятельно.Аналізуються тороїдальні дрейфи основних (водневих) та домішкових іонів і електронів у токамаках з омічним нагріванням. Експериментально виявлені дрейфи іонів самоузгоджено пояснюються одномірною моделлю з законом Ома і рівняннями руху заряджених часток у стаціонарній плазмі. Розрахунки показують, що, як правило, дрейфи різних сортів часток розв'язані, тому поняття "тороїдальне обертання" плазми в цілому тут неспроможне

Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background

The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society

On the progenitor of binary neutron star merger GW170817

On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ∼40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ∼2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr

Dissociative excitation as the source of neutral atoms in hydrogen discharges

Electron impact dissociative excitation of H/sub 2/ molecules is identified as the origin of the narrow width and structure of Balmer lines observed in various low density hydrogen discharges. On the basis of this data and estimates of the rates of competing processes in plasmas, dissociative excitation, together with other molecular reactions, is proposed as the source of neutral atoms and protons in these discharges

Molecular origin of background light in Thomson scattering measurements

The plasma background light in Thomson scattering measurements is often far higher than expected for a pure hydrogen plasma. The spectral distribution of light from three plasmas (duration: 1 ms to steady state; electron density: below 10/sup 12/ to over 10/sup 14/ cm/sup -3/; temperature: below 20 to over 1000 eV) and signal-to-noise and intensity data from the Thomson scattering systems used on them are compared with analytic estimates to show that in two of these plasmas molecular light dominates the spectrum, while in the other, molecular light is present, but bremsstrahlung is usually more intense. Knowledge of the mechanism for background light can aid in designing detection systems for Thomson scattering and provide information on the neutral species composition and effective charge of the plasma

Power balance in ELMO Bumpy Torus: bulk electrons and ions in a 37 kW discharge

The power balance of the bulk electrons and ions in discharges with 37 kW of applied microwave power in the ELMO Bumpy Torus (EBT) is examined in a zero-dimensional model using data on the intensity and linewidth of the molecular and atomic hydrogen emission. At least 60% of the applied power is ultimately dissipated by processes involving the neutral particles, including dissociation of molecules, ionization of and radiation from atoms, and heating of cold electrons produced during atomic ionization. The molecular influx rate and the density of atoms are used independently to determine the bulk electron particle confinement time, and an upper bound estimate is made of the diffusional power loss from the bulk plasma electrons. Parameters derived from the basic spectroscopic data presented in this paper include the neutral atom density 2 - 5x10/sup 10/ cm/sup -3/, incident molecular flux 3 - 5x10/sup 15/ cm/sup -2/s/sup -1/, bulk ion temperature approx. =3 eV, and particle confinement time <1.1 ms. The bulk electron energy confinement time is 0.7 ms or less in the standard operating regime. Published data on the nonthermal electron and ion populations in the plasma are used to evaluate approximately the overall energy flow in the discharge. 54 refs

Narrow H-alpha emission profiles in tokamaks: molecular origin and observational effects

The narrow hydrogen Balmer alpha profiles observed in tokamaks are explained in terms of the slow (approx. 0.3 eV) and fast (2 to 6 eV) excited atoms formed by dissociation of molecular hydrogen at the plasma edge. Extra widening of the spectrum in the wings can be explaind by Zeeman split H-alpha that is reflected from the vacuum vessel. This interpretation is consistent with available high-resolution data. The use of H-alpha as a diagnostic is discussed briefly