Magnetic flux penetration into a superconducting double stripline with an edge barrier

An analytical solution to a problem concerning the behavior of a superconducting contour comprising two parallel thin-film strips in a magnetic field of increasing strength. The entrance of vortices into the films, which are free of bulk inhomogeneities, is controlled by an edge barrier (of the Bean-Livingston or geometric type). It is established for the first time that the Meissner state can be realized in two regimes: the classical Meissner state in the interval of magnetic field strengths 0≤H≤H _s (where H _s is field strength corresponding to the entrance of the first vortex) and the state in the interval H _s≤H≤H _c for which vortices formed on the boundaries of the films penetrate into the gap. For H≥H _c, the magnetic flux penetration is accompanied by the appearance of a mixed state in the films. Expressions describing the inductance of the superconducting circuit in the entire range of magnetic fields are also obtained for the first time.     

Liquid helium cooled sample stage for scanning electron microscope

A cryogenic stage is described for use with a Cambridge S4-10 scanning electron microscope. The stage is operated with liquid helium in direct contact with the back of the sample to be irradiated by the electron beam. This bath cryostat principle will work at temperatures between 1.5 K and 4.2 K with good cooling performance. The installation of the stage within the microscope does not require any modification of the microscope chamber or the detector arrangement. A precision adjustment of the sample perpendicular to the electron beam is achieved by micrometric screws.     

High-speed penetration into sand

The series of experiments aimed at the exploring high-speed impact of bullet on non-solid target were carried out at IPE RAS. The electro-discharge launcher (EDL) employed in these experiments can reach the projectile velocities of 4 km/s. The following topics were considered: the phenomena related to the high-speed penetration into non-solid targets, the parameters that influence the penetration depth and the projectile design suitable for the deepest penetration into sand. Experimental equipment allows the measurement of the penetration depth of bullet, its path inside the sand and the shock waves caused by the high-speed bullet impact. Experiments had shown the absence of significant deviation from a straight-line trajectory for the any tested bullet shapes at the impact velocity of 1.5–3.0 km/s. The most interesting result is the existence of a critical velocity for this type of interaction. The full bullet wear due to the friction with sand occurs at this velocity. The critical velocity value depends on bullet material and dimensions. Experiments show that exceeding the critical velocity leads to reduce in penetration depth. The influence of bullet material, shape and velocity on its penetration depth into sand was measured. These data allow a determination of the main characteristics of projectile for deep penetration into sand.     

Energy absorbing passive impact barrier for profiled blastwalls

After the Piper Alpha accident, the Health and Safety Executive (UK) now require safety cases to be submitted for all new and existing installations on offshore topsides. The findings from a recent Joint Industry Project have revealed that peak overpressures developed from typical hydrocarbon explosions can be much higher than previously used in the design of offshore topsides and thus has necessitated strengthening of many existing installations, including blastwalls. This paper presents one such technique where the response of the blastwalls is modified by the inclusion of a passive impact barrier system placed at a certain offset behind the walls. An explicit non-linear finite element model has been validated against two large scale blast tests of shallow profiled blastwalls. This has included modelling the effect of contact, weld tearing, large displacement and plasticity in order to provide a realistic model. The study has been extended to investigate the response of deep profiled blastwalls with various arrangements of the passive impact barrier systems. The increase in the containment pressure and the influence of strain rate, load duration, offset of the impact barriers and its stiffness are discussed.     

Study on multi-peak behavior of pulsed dielectric barrier discharges in atmospheric-pressure helium

In this work the multi-peak behavior of the dielectric barrier discharge excited by repetitive voltage pulses (pulsed DBD) in atmospheric-pressure helium has been systematically investigated, based on a one-dimensional fluid model. The effects of the parameters of the applied voltage pulse and dielectrics on the multi-peak behavior of the pulsed DBD have been analyzed in detail. The parameters of the applied voltage pulse include voltage growth rate, amplitude, pulse-width, and frequency. The parameters of dielectrics refer to relative permittivity and dielectric thickness. Under the given amplitude of the applied voltage pulse, the number of current pulses presents no monotonic decrease with increasing voltage growth rate, and the dependence of the amplitude of each current pulse on voltage growth rate is different. For a given voltage growth rate, the number of current pulses will increase with increasing applied voltage amplitude, but the amplitude of each current pulse does not vary. In addition, the increase of the pulse-width or the frequency can induce not only later appearance of current pulses and smaller amplitude of the last current pulse at the rising edge of the applied voltage pulse but also larger amplitude of the last current pulse at the falling edge of the applied voltage pulse. Also, the decrease of relative permittivity of the dielectric or the increase of dielectric thickness results in smaller discharge current density and shorter time of charging dielectrics, which may increase the number of current pulses.     

Detection of a single electron produced inside bulk superfluid helium

The HERON project is an effort to develop a detector for low-energy solar neutrinos in real time by observing their elastic scattering from electrons using superfluid helium as the target material. By applying appropriate electric fields, the recoil electron can be separated from the positive ion, drifted upward to the liquid–vacuum interface, transmitted through the surface with the aid of a vortex ring, and detected using a calorimeter. By studying the correlation of the 16 eV photon signal produced by scintillation and the single-electron signal, we can locate a neutrino event in a large detector and distinguish it from the background events involving multiple Compton scattering.     

Tunneling from electron bubbles beneath the surface of liquid helium

Schoepe and Rayfield have measured the lifetime for escape of electrons from bubbles beneath a liquid He surface. We compute using the tunneling Hamiltonian method of Bardeen. If accepted bubble parameters are assumed, is found to be approximately two orders of magnitude smaller than the measured value. Agreement with experiment can be obtained if the radius is taken to be 50% larger than currently believed. We consider the effects of diffuseness of the bubble boundary, diffuseness of the liquid-vapor interface, and polarizability of the bubble. A discrepancy remains which may be explicable in terms of surface deformation when the bubble is very close to the surface.     

High-speed jet group penetration into brittle materials

The group impact of space charge jets (SCJs) on a composite target consisting of corundum and fiber glass-reinforced plastic layers has been studied. It is established that, under certain spatial and temporal conditions, the collective action of SCJs enhances the efficiency of brittle material resistance to high-speed jet penetration. These features are manifested for a subsonic character of penetration and confirm the proposed mechanism of the radial action of a crater formed in a high-strength brittle material on the SCJ propagation.     

Kinetics of cumulative jet penetration into glass

Assumption concerning violation of the regime of continuous hydrodynamic penetration is justified using experimental data on the cumulative jet (CJ) penetration into a glass obstacle. It is established that the CJ penetration into glass has a jumplike character and consists of a primary hydrodynamic penetration stage, cavity collapse, and secondary penetration into the collapsed material. In the case of continuous CJ supply, this process is repeated over the penetration depth. Necessary conditions for the secondary penetration are (i) a high strength of the glass target and (ii) a high rate of fracture, which ensure spalling of the material and collapse of the cavity walls. The jumplike penetration ceases when a pressure release wave arrives at the primary penetration zone.     

Simulation of penetration into porous geologic media

We present a computational study on the penetration of steel projectiles into porous geologic materials. The purpose of the study is to extend the range of applicability of a recently developed constitutive model to simulations involving projectile penetration into geologic media. The constitutive model is nonlinear, thermodynamically consistent, and properly invariant under superposed rigid body motions. The equations are valid for large deformations and they are hyperelastic in the sense that the stress tensor is related to a derivative of the Helmholtz free energy. The model uses the mathematical structure of plasticity theory to capture the basic features of the mechanical response of geological materials including the effects of bulking, yielding, damage, porous compaction and loading rate on the material response. The new constitutive model has been successfully used to simulate static laboratory tests under a wide range of triaxial loading conditions, and dynamic spherical wave propagation tests in both dry and saturated geologic media.     

Time-resolved penetration into pre-damaged hot-pressed silicon carbide

We have conducted a series of experiments to examine projectile penetration of cylindrical hot-pressed silicon carbide (SiC) ceramic targets that are pre-damaged to varying degrees under controlled laboratory conditions prior to ballistic testing. SiC was thermally shocked to introduce non-contiguous cracks. Another set of targets was thermally shocked and then additional damage was induced by load–unload cycling in an MTS machine while the ceramic specimen was confined in a 7075-T6 aluminum sleeve. Finally, targets were made by compacting SiC powder into a 7075-T6 aluminum sleeve. For each of these target types, long gold rod penetration was measured as a function of impact velocity v_p over the approximate range of 1–3 km/s, with most data between 1.5 and 3 km/s. Penetration as a function of time was measured using multiple independently timed flash X-rays. Results are compared with previous results for non-damaged (intact) SiC targets. Key results from these experiments include the following: (1) penetration is nominally steady state for v_p>1.5 km/s; (2) for all target types, the penetration velocity u is a linear function of v_p (except for the lowest impact velocities); and (3) it is found that u_intact<u_pre-damaged<u_{in-situ comminuted}<u_powder<u_hydrodynamic.     

Anomalous electron transport in the narrow conducting channels over liquid helium

No Heading The carrier transport in a quasi-one-dimensional (Q1D) electron system on liquid helium have been investigated. It has been shown that the unusual behavior of the electron transport take place at high densities of charges. The anomalous behavior of the electron transport in the low-temperature region can be explained by polaron effects in confined conducting channels.PACS numbers: 67.40.Jd, 73.20.–r     

Heat pulse transmission from sodium fluoride into helium I

Heat pulse transmission across a NaF-He I interface reveals behavior not observed at a He II interface. Longitudinal and transverse crystal modes are resolved at the detector with the longitudinal pulse exhibiting a unique characteristic structure. The detected longitudinal pulse appears with an initial overshoot lasting about 100 nsec and a reduced rear portion lasting the duration of the input pulse. The initial overshoot component echoes repeatedly between opposite surfaces of the crystal, and is indicative of the small transmission predicted by the acoustic mismatch theory. No echoing of the rear portion has been observed, and apparently the rear portion has a different coupling process at the interface. For the transverse pulse, a change in shape and a delay in arrival time are noted upon transmission into liquid, suggesting that certain portions of the pulse are not transmitted. Measurements of the amplitude dependence of the various pulses are made, and compared with a model having a frequency-selective coupling at the interface.     

Time-resolved penetration of long rods into steel targets

The penetration behavior of tungsten alloy, long-rod penetrators into high-hard steel is investigated at two impact velocities; 1.25 km/s and 1.70 km/s. The positions of the nose and tail of the projectile were measured by means of a 600 kV flash X-ray system at different times during penetration. The wavecode CTH was used to numerically simulate the experiments. The computational results are in very good agreement with the experimental position-time data. Additionally, the computational model reproduces the qualitative behavior for impact conditions near the ballistic limit.