Pulse Length Monitor for Breakdown Diagnostics in THz and Mm-Wave Accelerators

The development of novel high-gradient accelerating structures operating at THz frequencies is critical for future free-electron lasers and TeV scale linear colliders. To reach high energies with reasonable length requires high accelerating gradients of ~100 MV/m. The main limitation to reaching these high-energy gradients is the vacuum RF breakdown phenomenon, which disrupts normal accelerator operations. For stable operations and to understand the breakdown microscopic dynamics, a new device capable of detecting the breakdown occurrences is required. In this paper, we provide the design of a pulse length monitor based on an analog to digital converter for fast signal digitization without the need to use high-speed digitizers to be used in a commercial mm-wave heterodyne spectrometer.

Centrifugal Waves in Tornado-like Vortices: Kelvin’s solutions and their Applications to Multiple-Vortex Development and Vortex Breakdown

About 140 years ago, Lord Kelvin derived the equations describing waves that travel along the axis of concentrated vortices such as tornadoes. Although Kelvin’s vortex waves, also known as centrifugal waves, feature prominently in the engineering and uid dynamics literature, they have not attracted as much attention in the field of atmospheric science. To remedy this circumstance, Kelvin’s elegant derivation is retraced, and slightly generalized, to obtain solutions for a hierarchy of vortex ows that model basic features of tornado-like vortices. This treatment seeks to draw attention to the important work that Lord Kelvin did in this field, and reveal the remarkably rich structure and dynamics of these waves. Kelvin’s solutions help explain the vortex breakdown phenomenon routinely observed in modeled tornado-like vortices, and it is shown that his work is compatible with the widely used criticality condition put forth by Benjamin in 1962. Moreover, it is demonstrated that Kelvin’s treatment, with the slight generalization, includes unstable wave solutions that have been invoked to explain some aspects of the formation of multiple-vortex tornadoes. The analysis of the unstable solutions also forms the basis for determining whether e.g., an axisymmetric or a spiral vortex breakdown occurs. Kelvin’s work thus helps understand some of the visible features of tornado-like vortices.

Space Charge Accumulation Phenomena in PI under Various Practicable Environment

Polyimide is widely used insulation materials, such as power equipment, motor windings, multi layer insulated, and so on. As the operation environment is high temperature, high humidity, radiation, the dielectric insulation characteristic is decreased compared with pristine one. Especially, the space charge characteristics are obtained big different. Furthermore, the breakdown phenomenon is frequently produced. In this chapter, we discuss the dielectric phenomena through the viewpoints of charge accumulation under the following environment. High temperature, High humidity, DC application, PWM application, Radio-active rays (electron, proton).

Flow patterns of non-Newtonian nanofluid flow in cylindrical enclosure with rotating endwall: Effects of nanoparticles concentration

In this paper, a numerical study on the flow structure of non-Newtonian nanofluid in cylindrical enclosure with rotating end wall. The considered nanofluid, MWCNT-water, exhibits a strong power-law shear-thinning behavior with the increase in nanoparticles loading. The main focus in this study is the effect of nanoparticles concentration on the vortex breakdown phenomenon. The simulation results showed that adding a small amount of nanoparticle eliminate the vortex breakdown which is considered as a positive in mixing process. However, the increase in nanoparticles concentration as well as the enclosure aspect ratio promotes the apparition of secondary recirculation zone and stagnation zone.