Doppler backscattering systems on the Globus-M2 tokamak

Doppler backscattering (DBS) was successfully previously used on the Globus-M tokamak. The diagnostic was utilised in the form of either a single-frequency or a four-frequency dual homodyne system. It was used primarily for the study of zonal flows, filaments and Alfvén eigenmodes. These phenomena are worth being studied both on the periphery and in the core region of the plasma in a tokamak. For this specific reason two multifrequency DBS systems were installed on the upgraded Globus-M2 tokamak. The first four-frequency system with dual homodyne detection had already been used on the Globus-M tokamak and has lower probing frequencies which provide measurements from the periphery plasma. The second and new six-frequency DBS system was installed with a non-linear transmission line that was adapted to generate probing signals at frequencies 50, 55, 60, 65, 70 and 75 GHz. In general, the range of probing frequencies corresponds to the region of critical plasma densities from 5 × 1018 to 7 × 1019 m−3 at normal incidence. The pyramidal horn antennas are located inside the vacuum vessel with a special cardan-like rotator outside the camera so as to tilt antennas in the toroidal and poloidal directions. A previously developed code was applied to simulate 3D raytracing for all frequency channels. Calculations were carried out for different angles of incidence and for different electron density distributions in order to investigate the possibilities of the implementation of radial and poloidal correlation Doppler reflectometry. Examples of the DBS system application for study of plasma properties in the Globus-M2 tokamak are presented.

Electrochemical trepanning of blades made of Inconel 625

In the aerospace field, difficult-to-machine materials are used widely to improve engine performance. As a nickel-based material that performs well in all aspects, Inconel 625 is used for the blisks of aircraft engines, and electrochemical trepanning (ECTr) is used widely to fabricate such blisks because of its unique advantages regarding ruled surface parts. In this study, to investigate the performance of Inconel 625 in ECTr, measurements were made of the electrochemical characteristics firstly, specifically the anodic polarization curve and the actual volumetric electrochemical equivalent curve. Then, via dynamic electric-field simulations, the processes for forming Inconel 625 blades using ECTr were examined under direct voltage (DV) and pulsed voltage. The contours and current density distributions of formed blades at different times were obtained under different duty cycles. With decreasing duty cycle, the forming accuracy improved gradually and the stray current was reduced. To verify the simulation results, ECTr experiments with Inconel 625 were performed under different voltage conditions. With DV and 90% and 80% duty cycle, the taper angles of the machined blades were 7.784°, 6.278°, and 5.191°, respectively, and the surface roughness ( Ra) values were 0.95, 0.81, and 0.72 μm, respectively. With DV, there were obvious flow marks and gullies on the microscopic surface. With decreasing duty cycle, stray corrosion was reduced effectively and the state of the flow field was improved. Overall, the simulation results were verified effectively.

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Interactions between ions and water at hydrophobic interfaces within ion channels and nanopores are suggested to play a key role in the movement of ions across biological membranes. Previous molecular dynamics (MD) simulations have shown that the affinity of polarizable anions to aqueous/hydrophobic interfaces can be markedly influenced by including polarization effects through an electronic continuum correction (ECC). Here, we designed a model biomimetic nanopore to imitate the polar pore openings and hydrophobic gating regions found in pentameric ligand-gated ion channels. MD simulations were then performed using both a non-polarizable force field and the ECC method to investigate the behavior of water, Na+ and Cl- ions confined within the hydrophobic region of the nanopore. Number density distributions revealed preferential Cl- adsorption to the hydrophobic pore walls, with this interfacial layer largely devoid of Na+. Free energy profiles for Na+ and Cl- permeating the pore also display an energy barrier reduction associated with the localization of Cl- to this hydrophobic interface, and the hydration number profiles reflect a corresponding reduction in the first hydration shell of Cl-. Crucially, these ion effects were only observed through inclusion of effective polarization which therefore suggests that polarizability may be essential for an accurate description for the behavior of ions and water within hydrophobic nanoscale pores, especially those that conduct Cl-.

Cluster decay half-lives using asymmetry dependent densities

Adopting different neutron and proton density distributions the cluster decay half-lives have been investigated using double-folding potentials with constant and nuclear asymmetry dependent sets of the parameters of nuclear densities. Two adopted asymmetry dependent sets of the parameters are fitted based on the microscopic calculations and calculated based on the neutron skin/halo-type nuclei assumption and employing experimental rms charge radii. The bulk agreement between theory and experiment has been obtained for entire sets of parameters using calculated cluster preformation probability. The very little differences between skin and halo-type assumption have been observed. However, the notable role of the asymmetry parameter has been seen in relatively large differences between the skin and skin-type with zero thickness.

Characterization of Supersonic Compressible Fluid Flow Using High-Speed Interferometry

This paper presents a very effective interference technique for the sensing and researching of compressible fluid flow in a wind tunnel facility. The developed technique is very sensitive and accurate, yet easy to use under conditions typical for aerodynamic labs, and will be used for the nonintrusive investigation of flutter in blade cascades. The interferometer employs a high-speed camera, fiber optics, and available “of-the-shelf” optics and optomechanics. The construction of the interferometer together with the fiber optics ensures the high compactness and portability of the system. Moreover, single-shot quantitative data processing based on introducing a spatial carrier frequency and Fourier analysis allows for almost real-time quantitative processing. As a validation case, the interferometric system was successfully applied in the research of supersonic compressible fluid discharge from a narrow channel in a wind tunnel. Density distributions were quantitatively analyzed with the spatial resolution of about 50 μm. The results of the measurement revealed important features of the flow pattern. Moreover, the measurement results were compared with Computational Fluid Dynamics (CFD) simulations with a good agreement.

Analyzing Oxygen Ionization in the Circumgalactic Medium

Galaxies are surrounded by low-density, highly-ionized clouds of gas, called the Circumgalactic Medium (CGM), which provides insight into galaxy evolution. CGM observations are sensitive to ionization levels, which requires studying ionization types: photoionization (PI), more density-dependent and associated with cooler gas, and collisional ionization (CI), more temperature-dependent and associated with hotter gas. We analyzed PI and CI components for oxygen ionization states using cosmological galaxy simulations. For each ion, we plotted mass distributions into PI and CI phases and created 2D covering-fraction projections of column density at different thresholds. We analyzed changes for different mass-bin galaxies. Our results are: O vii and O ix are the only predominantly-CI ion states. O vi is a local minimum in both PI and CI gas. Column density distributions greatly emphasize higher ion states. Shapes of covering-fraction plots at higher thresholds resemble the 3D-plots. CI gas dominates more in higher mass galaxy simulations.

Hydrodynamic Response of the Intergalactic Medium to Reionization. II. Physical Characteristics and Dynamics of Ionizing Photon Sinks

Becker et al. measured the mean free path of Lyman-limit photons in the intergalactic medium (IGM) at z = 6. The short value suggests that absorptions may have played a prominent role in reionization. Here we study physical properties of ionizing photon sinks in the wake of ionization fronts (I-fronts) using radiative hydrodynamic simulations. We quantify the contributions of gaseous structures to the Lyman-limit opacity by tracking the column-density distributions in our simulations. Within Δt = 10 Myr of I-front passage, we find that self-shielding systems (N H I > 1017.2 cm−2) are comprised of two distinct populations: (1) overdensity Δ ∼ 50 structures in photoionization equilibrium with the ionizing background, and (2) Δ ≳ 100 density peaks with fully neutral cores. The self-shielding systems contribute more than half of the opacity at these times, but the IGM evolves considerably in Δt ∼ 100 Myr as structures are flattened by pressure smoothing and photoevaporation. By Δt = 300 Myr, they contribute ≲10% to the opacity in an average 1 Mpc3 patch of the universe. The percentage can be a factor of a few larger in overdense patches, where more self-shielding systems survive. We quantify the characteristic masses and sizes of self-shielding structures. Shortly after I-front passage, we find M = 104–108 M ⊙ and effective diameters d eff = 1–20 ckpc h −1. These scales increase as the gas relaxes. The picture herein presented may be different in dark matter models with suppressed small-scale power.

Study of the matter density distributions of halo nuclei 6He and 16C using the binary cluster model

The harmonic oscillator (HO) and Gaussian (GS) wave functions within the binary cluster model (BCM) have been employ to investigate the ground state neutron, proton and matter densities as well as the elastic form factors of two-neutron 6He and 16C halo nuclei. The long tail is a property that is clearly revealed in the density of the neutrons since it is found in halo orbits. The existence of a long tail in the neutron density distributions of 6He and 16C indicating that these nuclei have a neutron halo structure. Moreover, the matter rms radii and the reaction cross section (σr) of these nuclei have been calculated using the Glauber model.