Search results for "INSTABILITIES"
showing 10 items of 61 documents
Kerr Beam Self-Cleaning in Multimode Fibers
2018
We overview recent experimental results of beam self-cleaning observed in various types of multimode fibers. We analyze the output spatial beam shapes and their connection with the refractive index profile of the fibers.
Periodic Beam Current Oscillations Driven by Electron Cyclotron Instabilities in ECRIS Plasmas
2014
Experimental observation of cyclotron instabilities in electron cyclotron resonance ion source plasma operated in cwmode is reported. The instabilities are associated with strong microwave emission and a burst of energetic electrons escaping the plasma, and explain the periodic oscillations of the extracted beam currents. The instabilities are shown to restrict the parameter space available for the optimization of high charge state ion currents. nonPeerReviewed
Ground motion phenomena in Caltanissetta (Italy) investigated by InSAR and geological data integration
2008
Urban areas are frequently affected by ground instabilities of various origins. The location of urban zones affected by ground instability phenomena is crucially important for hazard mitigation policies. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) has demonstrated its remarkable capability to detect and quantify ground and building motion in urban areas, especially since the development of Advanced Differential Interferometric SAR techniques (A-DInSAR). In fact, the high density of re.ectors like buildings and infrastructures in urban areas improves the quality of the InSAR signal, allowing sub-centimetric displacements to be reliably detected. The A-DInSAR techniques a…
Numerical relativity simulations of tilted black hole-torus systems
2016
Las fusiones de objetos compactos se encuentran entre los eventos más interesantes de la astrofísica relativista, siendo, en particular, el principal objetivo de la astronomía de ondas gravitatorias. En esta tesis investigamos los posibles estados finales de la fusión de sistemas binarios formados por agujero negro-estrella de neutrones o por dos estrellas de neutrones: discos gruesos (o toros) de acrecimiento alrededor de agujeros negros en rotación tipo Kerr. Estos sistemas agujero negro-toro se cree que constituyen el motor central de los eventos más luminosos del Universo: los llamados estallidos de rayos gamma. Nuestro conocimiento sobre la evolución y la estabilidad de estos sistemas …
Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma
2022
International audience; Electron Cyclotron Resonance (ECR) ion source plasmas are prone to kinetic instabilities. The onset of the instabilities manifests as emission of microwaves, bursts of electrons expelled from the plasma volume, and the collapse of the extracted highly charged ion (HCI) currents. Consequently, the instabilities limit the HCI performance of ECR ion sources by limiting the parameter space available for ion source optimization. Previous studies have shown that the transition from stable to unstable plasma regime is strongly influenced by the magnetic field structure, especially the minimum field value inside the magnetic trap (Bmin). This work focuses to study the role o…
Controllable morphology of flux avalanches in microstructured superconductors
2014
The morphology of abrupt bursts of magnetic flux into superconducting films with engineered periodic pinning centers (antidots) has been investigated. Guided flux avalanches of thermomagnetic origin develop a tree-like structure, with the main trunk perpendicular to the borders of the sample, while secondary branches follow well-defi ned directions determined by the geometrical details of the underlying periodic pinning landscape. Strikingly, we demonstrate that in a superconductor with relatively weak random pinning, the morphology of such flux avalanches can be fully controlled by proper combinations of lattice symmetry and antidot geometry. Moreover, the resulting flux patterns can be re…
Signal processing in photonic crystals and nanostructures
2006
International audience; Optical devices employing photonic crystals and novel nanostructure materials may exhibit useful properties for applications to all-optical signal processing. In this work we analyze as a first example four-wave mixing of polarized beams in photonic crystal fibers. We show that by properly tuning the pump wavelength and the linear dispersion properties of the fiber one may obtain broadband parametric amplification and frequency conversion. Next we consider the in-line periodic amplification of short optical pulses by means of quantum-dot semiconductor optical amplifiers. We show by numerical simulations that pattern-free amplification of a 40 Gbit/s soliton signal at…
Quasi-periodical kinetic instabilities in minimum-B confined plasma
2022
We present the results of an experimental investigation of quasi-periodical kinetic instabilities exhibited by magnetically confined electron cyclotron resonance heated plasmas. The instabilities were detected by measuring plasma microwave emission, electron losses, and wall bremsstrahlung. The instabilities were found to be grouped into fast sequences of periodic plasma losses, separated by ∼100 µs between the bursts, followed by 1–10 ms quiescent periods before the next event. Increasing the plasma energy content by adjusting the plasma heating parameters, in particular the magnetic field strength, makes the instabilities more chaotic in the time domain. Statistical analysis reveals that …
Numerical and Experimental Study of a Novel Concept for Hydraulically Controlled Negative Loads
2016
This paper presents a numerical and experimental investigation of a novel concept that eliminates oscillations in hydraulic systems containing a counterbalance valve in series with a pressure compensated flow supply. The concept utilizes a secondary circuit where a low-pass filtered value of the load pressure is generated and fed back to the compensator of the flow supply valve. The novel concept has been implemented on a single boom actuated by a cylinder. A nonlinear model of the system has been developed and an experimental verification shows good correspondence between the model and the real system. The model is used for a parameter study on the novel concept. From the study it is found…