The current strategy to achieve high luminosity for high energy physics experiments as well as high brilliance in synchrotron radiation sources is to store huge currents distributed in many bunches in circular machines. This approach has the disadvantage that the performance of these machines is most likely to be limited by coupled bunch instabilities. To circumvent this problem strong feedback...

Stable operation of both axial and radial compressors is constrained by the occurence of aerodynamic flow instabilities: rotating stall and surge. Developments in the understanding of the physics behind these instabilities and ideas of how t o stabilize the compressor system, have opened the door t o a new era in the field of compressor control. This study gives an overview of the current state...

The initiation and growth of instabilities in granular materials loaded by air shock waves are investigated via shock-tube experiments and numerical calculations. Three types of granular media, dry sand, water-saturated sand and a granular solid comprising PTFE spheres were experimentally investigated by air shock loading slugs of these materials in a transparent shock tube. Under all shock pre...

Three-dimensional (3D) transport within geophysical vortices (e.g. ocean eddies) is important in understanding processes at a variety of scales, ranging from plankton production to climate variability. 3D transport can be affected by hydrodynamic instabilities of geophysical vortices; however, how the insta-bilities affecting 3D transport is not clear. Focusing on barotropic, inertial and 3D in...

A theory is developed from which it follows that energetic-ion-driven instabilities can, first, channel the energy of the energetic ions outside the region where these ions are located and, second, considerably affect the electron heat flux across the magnetic field. A new mechanism of the frequency chirping is revealed. Namely, it is shown that instabilities caused by the energetic ions can in...

The fluid flow between a pair of coaxial circular cylinders generated by the uniform rotation of the inner cylinder and an azimuthal pressure gradient is susceptible to both Taylor and Dean type instabilities. The flow can be characterised by two parameters: a measure of the relative magnitude of the rotation and pressure effects and a non-dimensional Taylor number. Neutral curves associated wi...

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite acoustic modes in the test masses in the frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical cavity parameters with fused silica test masses, parametric instability excites 7 acoustic modes in each test mass, with parametric gain R up to 7. For the alternati...

The transition from a regime dominated by drift instabilities to a regime dominated by pure interchange instabilities is investigated and characterized in the simple magnetized toroidal device TORPEX TORoidal Plasma EXperiment, A. Fasoli et al., Phys. of Plasmas 13, 055906 2006 . The magnetic field lines are helical, with a dominant toroidal component and a smaller vertical component. Instabili...

We study the time evolution of the quantum fluctuations of the axion field for both the QCD axion as well as axions arising in the context of supergravity and string theories. We explicitly keep track not only of the coherently oscillating zero momentum mode of the axion but also of the higher non-zero momentum modes using the full axion potential. The full axion potential makes possible two ki...