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This study aims to investigate the impact of cavitation states on the stability of cryogenic pumps. Steady and unsteady simulations of the internal flow were conducted based on an SST k–ω turbulence model and a modified Zwart cavitation model considering thermodynamic effects. The modified cavitation model was verified using the hydrofoil model and compared with the Hord test results. The results indicate that the variation in pressure at the pump inlet has a significant influence on the cavitation in the pump. The cavitation states and fluid flow directions vary across the different spans in the impeller channel. The smaller the distance from the front cover of the impeller, the more severe is the cavitation, in addition to the appearance of a vortex. The influence of the formation of a longitudinal vortex at the impeller outlet on the pressure fluctuation in the cavitation state was revealed. The rotation of the impeller has negligible influence on the pressure load distribution at the blade inlet. However, it has a higher influence on that of the second half of the blade, particularly when the blade passes through the volute tongue. Cavitation can exacerbate the instability of pump operation. The research results are significant for accurately predicting cavitation performance and improving the anti-cavitation capability of cryogenic pumps. [ABSTRACT FROM AUTHOR]

Past investigations of thermal counterflow in He II were mostly conducted in pipes/channels of constant cross-sections, which are often unduly influenced by the presence of walls. We devise and carry out an experiment using a spherically symmetric setup to study unbounded counterflow in order to gain better understanding of interactions between quantized vortices and counterflow; the preliminary analysis shows that this method is viable. [ABSTRACT FROM AUTHOR]

We study quantum vortex states consisting of a ring of vortices with alternating sign, in a homogeneous superfluid confined to a circular domain. We find an exact stationary solution of the point vortex model for the neutral vortex necklace. We investigate the stability of the necklace state within both the point-vortex model and the Gross–Pitaevskii equation describing a trapped atomic Bose–Einstein condensate at low temperature. The point-vortex stationary states are found to also be stationary states of the Gross–Pitaevskii equation provided the finite thickness of the outer fluid boundary is accounted for. Under significant perturbation, the Gross–Pitaevskii evolution and point-vortex model exhibit instability as expected for metastable states. The perturbed vortex necklace exhibits sensitivity to the perturbation, suggesting a route to seeding vortex chaos or quantum turbulence. [ABSTRACT FROM AUTHOR]

A micro-electromechanical resonator, consisting of a 125 × 125 μ m 2 center plate suspended 2 μ m above a substrate, was immersed in 4 He along with a quartz tuning fork. The tuning fork was placed 5 mm above the resonator and was used to generate turbulence. The damping of the resonator was investigated in the presence of turbulence generated by the tuning fork. We observe a velocity, v c ≃ 5 mm s - 1 , above which the damping on the resonator is drastically reduced for all tuning fork velocities studied. We attribute this change in damping to the shedding and capture of vortices. [ABSTRACT FROM AUTHOR]

A micro-electromechanical plate resonator suspended 2 μ m above a substrate was immersed in 4 He at 14 mK at saturated vapor pressure. At these temperatures, four vibrational modes of the device are observed. The corresponding motion of these modes is identified by comparing the observed modes with computer simulations. Owing to its large surface area and small mass, the resonator is sensitive to remnant vortices. The behavior of the modes is studied in the presence of remnant vortices and also in the presence of fully developed turbulence generated by a quartz tuning fork. [ABSTRACT FROM AUTHOR]

We investigate the formation of Shannon information entropy in a rotating Bose-Einstein condensates confined in a harmonic potential combined with an optical lattice (OL) using the mean field Gross-Pitaevskii equation. With the increase of OL depth V0, at the same rotational frequency Ω, we show that the information entropy increases in momentum space Sr and total entropy S and it decreases in position space Sk. We also calculate the Landsberg order parameter δ and its dependence on Ω. We find that the critical points between the case of OL and non-OL move along the direction of decreasing Ω with the increase of V0. In particular, the dynamics behaviors indicate that the periodicity of S and Smax loses due to the broken symmetry when OL is added. [ABSTRACT FROM AUTHOR]

We studied the strong-coupling effect upon an isolated vortex in a two-dimensional chiral p-wave superconductor. We solved the Eilenberger equation for the quasiclassical Green's functions and the Éliashberg equation with single-mode Einstein boson self-consistently. We calculated the free energy of each obtained vortex and found that a non-axisymmetric vortex metastably exists in some situation. [ABSTRACT FROM AUTHOR]

Pulsed laser ablation of metal targets immersed in superfluid $$^4\hbox {He}$$ is visualized by time-resolved shadowgraph photography and the products are analyzed by post-experiment atomic force microscopy (AFM) measurements. The expansion dynamics of the gaseous ablation half-bubble on the target surface appears underdamped and follows the predicted behavior for the thermally induced bubble growth mechanism. An inherent instability of the ablation bubble appears near its maximum radius and no tightly focused cavity collapse or rebound events are observed. During the ablation bubble retreat phase, the presence of sharp edges in the target introduces flow patterns that lead to the creation of large classical vortex rings. Furthermore, on the nanometer scale, AFM data reveal that the metal nanoparticles created by laser ablation are trapped in spherical vortex tangles and quantized vortex rings present in the non-equilibrium liquid. [ABSTRACT FROM AUTHOR]

The static and dynamic properties of vortices in a nanosized superconducting strip with one central weak link (weakly superconducting region or normal metal) are investigated in the presence of external magnetic and electric fields. The time-dependent Ginzburg-Landau equations are used to describe the electronic transport and have been solved numerically by a finite element analysis. Anisotropy is included through the spatially dependent anisotropy coefficient $$\zeta $$ in different layers of the sample. Our results show that the energy barrier for vortices to enter a weak link is smaller than that for vortices to enter the superconducting layers. The magnetization shows periodic oscillations. With the introduction of the weak link, the period of oscillations decreases. [ABSTRACT FROM AUTHOR]

Insulating columnar inclusions in a type II chiral $$p_x \pm i p_y$$ superconductor are shown to affect essentially the electronic structure of pinned vortices, and, as a consequence, the scanning tunneling microscopy (STM) patterns and the microwave response in the vortex phase. The structure of the anomalous spectral branch analyzed within the Bogolubov-de Gennes theory is found to depend strongly on the mutual orientation of the angular momenta of the center of mass and the relative motion of two electrons in the Cooper pair. This dependence reveals itself in the nontrivial behavior of the Hall part of the microwave response and difference of the STM patterns for opposite magnetic field orientations. [ABSTRACT FROM AUTHOR]

We calculate the relaxation of Brinkman-Smith mode via Leggett-Takagi relaxation in the presence of an isolated vortex in superfluid $$^{3}$$ He-B. The calculation is based on an analytical solution of the order parameter far from the vortex axis. We obtain an expression for the dissipated power per vortex length as a function of the tipping angle of the magnetization and the orientation of the static magnetic field with respect to the vortex. [ABSTRACT FROM AUTHOR]

Motivated by recent experiments carried out by Spielman's group at NIST, we study the vortex formation in a rotating Bose-Einstein condensate in synthetic magnetic field confined in a harmonic potential combined with an optical lattice. We obtain numerical solutions of the two-dimensional Gross-Pitaevskii equation and compare the vortex formation by synthetic magnetic field method with those by rotating frame method. We conclude that a large angular momentum indeed can be created in the presence of the optical lattice. However, it is still more difficult to rotate the condensate by the synthetic magnetic field than by the rotating frame even if the optical lattice is added, and the chemical potential and energy remain almost unchanged by increasing rotational frequency. [ABSTRACT FROM AUTHOR]

We examine the effects of stationary vortices in superfluid $$^6$$ Li atoms at zero temperature in the frame of the recently developed fluiddynamical scheme, that includes the pair density and its associated pair current and pair kinetic energy in addition to the fields appearing in the hydrodynamical description of normal fluids. In this frame, the presence of any particle velocity field gives rise to the appearance of a pair current. As an illustration, we consider a stationary vortex with cylindrical geometry in an unpolarized fluid, and examine the effects of the rotational velocity field on the spatial structure of the equilibrium gap and the profiles of the pair current. We show that the latter is intrinsically complex and its imaginary part is the source of a radial drift for the velocity field. We discuss the consequences on the stationary regime. [ABSTRACT FROM AUTHOR]

We study the effects of non-magnetic impurity scattering on the Andreev bound states (ABS) in an isolated vortex in two-dimensional chiral p-wave superconductors numerically. We incorporate the impurity scattering effects into the quasiclassical Eilenberger formulation through the self-consistent t-matrix approximation. Within this scheme, we calculate the local density of states (LDOS) around two types of vortices: 'parallel' ('anti-parallel') vortex where the phase winding of the pair-potential coming from the vorticity and that coming from the chirality have the same (opposite) sign. When the scattering phase-shift δ of each impurity is small, we find that the impurities affect differently the spectra of quasiparticles localized around the two types of vortices in a way similar to that in the Born limit ( δ→0). For a larger δ(≲ π/2), ABS in the vortex is strongly suppressed by the impurities for both types of vortices. We find that there are some correlations between the suppression of ABS near vortex cores and the low energy density of states due to the impurity bands in the bulk. [ABSTRACT FROM AUTHOR]

We study dynamics of a two-dimensional $$s$$ -wave superconductor in the presence of a moving single vortex on the basis of the quasiclassical theory generalized by Kita (Phys Rev B 64:054503, ). We numerically calculate the linear response of a moving single vortex driven by a dc external current in a self-consistent way, in the sense that the gap equation, Maxwell equations and generalized quasiclassical equation with the impurity self-energy (self-consistent Born approximation) are solved simultaneously. We obtain Hall conductivity induced by vortex motion using the generalized quasiclassical equation, while we confirm that it vanishes in the conventional quasiclassical equation. [ABSTRACT FROM AUTHOR]

One of the important performance parameters of superconducting nanowire single photon detectors (SNSPD) is the dark count rate. Dark counts are related to thermally-activated hopping of magnetic vortices across the nanowire. We present an experimental analysis of how the thermal coupling of the NbN SNSPD to the heat sink affects the dark count rate. It was found that the rate decreases with the increase in coupling strength while the detection efficiency remains almost constant. [ABSTRACT FROM AUTHOR]

Recently, it was shown that giant vortices with arbitrarily large quantum numbers can possibly created in dilute Bose-Einstein condensates by cyclically pumping vorticity into the condensate. However, multiply quantized vortices are typically dynamically unstable in harmonically trapped nonrotated condensates, which poses a serious challenge to the vortex pump procedure. In this theoretical study, we investigate how the giant vortices can be stabilized by the application of a Gaussian potential peak along the vortex core. We find that achieving dynamical stability is feasible up to high quantum numbers. To demonstrate the efficiency of the stabilization method, we simulate the adiabatic creation of an unsplit 20-quantum vortex with the vortex pump. [ABSTRACT FROM AUTHOR]