We study the rheology of dense granular flows for frictionless spherocylinders by means of 3D numerical simulations. As in the case of spherical particles, the effective friction μ is an increasing function of the inertial number I, and we systematically investigate the dependence of μ on the particle aspect ratio Q, as well as that of the normal stress differences, the volume fraction, and the coordination number. We show in particular that the quasistatic friction coefficient is nonmonotonic with Q: from the spherical case Q=1, it first sharply increases, reaches a maximum around Q≃1.05, and then gently decreases until Q=3, passing its initial value at Q≃2. We provide a microscopic interpretation for this unexpected behavior through the analysis of the distribution of dissipative contacts around the particles: as compared to spheres, slightly elongated grains enhance contacts in their central cylindrical band, whereas at larger aspect ratios particles tend to align and dissipate by preferential contacts at their hemispherical caps.
Diagnosing the density profile at the edge of high temperature fusion plasmas by accelerated Lithium beam is a known technique since decades. By knowledge of the relevant atomic physics rate coefficients the plasma electron density profile can be calculated from the relatively calibrated light profile along the beam. Several additional possibilities have already been demonstrated: CXRS for ion temperature/flow, Zeeman polarimetry for edge plasma current; therefore the Li-beam diagnostic offers a wealth of information at the plasma edge. The weaknesses of the method are the relatively faint light signal, background light and technical difficulties of the beam injector which usually seriously limit the applicability. In this talk we present systematic developments in alkali-beam diagnostics (Li, Na) both for the injector, observation system and detectors which resulted in strongly increased capabilities. Advanced systems have been built and microsecond scale density profile, turbulence and zonal flow measurement demonstrated. A novel edge current measurement technique has also been designed and components tested with potentially microsecond-scale time resolution. Additional possibilities of these advanced systems for spectral measurements (CXRS, various Zeeman schemes) are also discussed.
The rheology of a 3-dimensional granular system consisting of frictional elongated particles was investigated by means of discrete element model (DEM) calculations. A homogenous shear flow of frictional spherocyliders was simulated, and a number of rheological quantities were calculated. In the framework of the µ(I) rheology, the effective friction was found to be a non-monotonic function of the aspect ratio for interparticle friction coefficient µp 0.4, while it was an increasing function for larger µp. We reveal the microscopic origin of this peculiar non-monotonic behavior. We show the non-trivial dependence of the velocity fluctuations on the dissipation regime, and trace back the behavior of the normal stress differences to particle-level quantities.
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