Scaling of spontaneous rotation with temperature and plasma current in tokamaks

Using theoretical arguments, a simple scaling law for the size of the intrinsic rotation observed in tokamaks in the absence of momentum injection is found: the velocity generated in the core of a tokamak must be proportional to the ion temperature difference in the core divided by the plasma current, independent of the size of the device. The constant of proportionality is of the order of $10\,\mathrm{km \cdot s^{-1} \cdot MA \cdot keV^{-1}}$. When the intrinsic rotation profile is hollow, i.e. it is counter-current in the core of the tokamak and co-current in the edge, the scaling law presented in this Letter fits the data remarkably well for several tokamaks of vastly different size and heated by different mechanisms.Comment: 5 pages, 3 figure

Geosynthetic landfill cap stability: comparison of limit equilibrium, computational limit analysis and finite-element analyses

The stability of the veneer cover soil (landfill cap) is an important issue in landfill design. Incorrect design of the landfill cap can lead to failure, which may result in the veneer cover soil sliding on an underlying geosynthetic layer, or in tension failure of the geosynthetic itself. Previous limit equilibrium (LE) analyses of veneer cover layer stability presented in the literature have generally considered whole-slope failure. In this paper, modified LE equations are proposed that (a) encompass more critical cases of localised slope failure for specific cases, and (b) are calibrated against two other methods: 2-D computational limit analysis (CLA) using LimitState:GEO and 2-D elasto-plastic finite-element (FE) analysis using PLAXIS. The scenarios examined encompass a cover of uniform thickness, a buttressed cover, a cover of tapered thickness, the effects of seepage forces, and the effects of construction equipment. It is shown that the LE method provides a reasonable estimate of veneer cover layer stability for most cases examined, although it is in general non-conservative, relative to the CLA and FE analyses. Local failure was found to be critical in the case of the construction equipment, buttress and horizontal seepage scenarios. In the latter case the LE equations previously presented in the literature significantly overestimate stability compared with the LE, CLA and FE analyses considered in this paper

Superconducting crossed correlations in ferromagnets: implications for thermodynamics and quantum transport

It is demonstrated that non local Cooper pairs can propagate in ferromagnetic electrodes having an opposite spin orientation. In the presence of such crossed correlations, the superconducting gap is found to depend explicitly on the relative orientation of the ferromagnetic electrodes. Non local Cooper pairs can in principle be probed with dc-transport. With two ferromagnetic electrodes, we propose a ``quantum switch'' that can be used to detect correlated pairs of electrons. With three or more ferromagnetic electrodes, the Cooper pair-like state is a linear superposition of Cooper pairs which could be detected in dc-transport. The effect also induces an enhancement of the ferromagnetic proximity effect on the basis of crossed superconducting correlations propagating along domain walls.Comment: 4 pages, RevTe

Mesoscopic Ferromagnet/Superconductor Junctions and the Proximity Effect

We have measured the electrical transport of submicron ferromagnets (Ni) in contact with a mesoscopic superconductor (Al) for a range of interface resistances. In the geometry measured, the interface and the ferromagnet are measured separately. The ferromagnet itself shows no appreciable superconducting proximity effect, but the ferromagnet/superconductor interface exhibits strong temperature, field and current bias dependences. These effects are dependent on the local magnetic field distribution near the interface arising from the ferromagnet. We find that the temperature dependences may be fit to a modified version of the Blonder-Tinkham-Klapwijk theory for normal-superconductor transport.Comment: 4 eps fig

Frictional behaviour of three critical geosynthetic interfaces

This paper’s scope is the shear interaction mechanisms of three critical geosynthetic interfaces (geotextile/geomembrane; drainage geocomposite/geomembrane and soil/geomembrane) typically used for lined containment facilities such as landfills. A large direct shear machine was used to carry out 159 geosynthetic interface tests. The results showed strain softening behaviour, a very small dilatancy, 0.1–1 mm, and non-linear failure envelopes at normal stress range of 25–500 kPa. The three types of interfaces present the same main interaction mechanisms: interlocking and friction. For geotextile/geomembrane and drainage geocomposite/geomembrane interfaces, the higher the asperity height, the higher the interface shear strength.Whereas for soil/geomembrane interfaces, the higher the soil shear strength, the higher the interface shear strength. The drainage geocomposite/geomembrane interface showed the lowest friction angles, followed by the geotextile/geomembrane and the soil/geomembrane interfaces

Spin accumulation induced resistance in mesoscopic ferromagnet/ superconductor junctions

We present a description of spin-polarized transport in mesoscopic ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and the interfaces are transparent. It is shown that the spin reversal associated with Andreev reflection generates an excess spin density close to the F/S interface, which leads to a spin contact resistance. Expressions for the contact resistance are given for two terminal and four terminal geometries. In the latter the sign depends on the relative magnetization of the ferromagnetic electrodes.Comment: RevTeX 10 pages, 4 figures, submitted to Phys.Rev. Let

Laboratory Measurements of GCL Shrinkage under Cyclic Changes

ABSTRACT: Recently, several geomembrane/geotextile-encased geosynthetic clay liner (GCL) composite liner systems have been exhumed where separation of GCL panel overlaps has been observed due to GCL shrinkage. All of the documented cases involved installations where the GCL was overlain by an HDPE geomembrane, which was exposed for a duration ranging from two months to five years with no soil cover. This paper presents the results of an original laboratory study of GCL shrinkage. The mechanism used in the laboratory testing program to induce shrinkage consists of cyclic changes in GCL water content and temperature. These cyclic changes are intended to simulate the conditions in the field, where bentonite hydration-drying cycles are related to day-night cycles. Samples of reinforced GCLs were tested with various types of cap and carrier geotextiles, various water contents, and various densities of needlepunch reinforcement. The results show that the test provides values of GCL shrinkage within the range of values observed in the field. The experimental data also quantify differences in the potential GCL shrinkage between different reinforced GCLs

Effect of toroidal field ripple on plasma rotation in JET

Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect