Acoustic, thermal and flow processes in a water filled nanoporous glasses by time-resolved optical spectroscopy

We present heterodyne detected transient grating measurements on water filled Vycor 7930 in the range of temperature 20 - 90 degrees C. This experimental investigation enables to measure the acoustic propagation, the average density variation due the liquid flow and the thermal diffusion in this water filled nano-porous material. The data have been analyzed with the model of Pecker and Deresiewicz which is an extension of Biot model to account for the thermal effects. In the whole temperature range the data are qualitatively described by this hydrodynamic model that enables a meaningful insight of the different dynamic phenomena. The data analysis proves that the signal in the intermediate and long time-scale can be mainly addressed to the water dynamics inside the pores. We proved the existence of a peculiar interplay between the mass and the heat transport that produces a flow and back-flow process inside the nano-pores. During this process the solid and liquid dynamics have opposite phase as predicted by the Biot theory for the slow diffusive wave. Nevertheless, our experimental results confirm that transport of elastic energy (i.e. acoustic propagation), heat (i.e. thermal diffusion) and mass (i.e. liquid flow) in a liquid filled porous glass can be described according to hydrodynamic laws in spite of nanometric dimension of the pores. The data fitting, based on the hydrodynamic model, enables the extraction of several parameters of the water-Vycor system, even if some discrepancies appear when they are compared with values reported in the literature.Comment: 32 pages, 11 figure

Evaluation of non-linear phase space distortions via frequency analysis

Several methods have been developed recently to measure the frequencies of a time series to much higher precision than ordinary FFT. The decomposition of tracking or experimental data into a Fourier transform can therefore also be done with largely enhanced precision. On the one hand this allows to free these data from complicated phase space distortions. On the other hand, these high precision spectrum lines can be interpreted as being the result of the excitation of certain resonances. In this report we study how this information can be used to tackle resonances. It has to be stresses that this techniques requires no knowledge concerning the simulation model or the accelerator being studied. the only input needed is a series of tracking data or, in the case of the experiment, a set of turn-by-turn data after kicking the beam

Sorting Strategies for the LHC Dipoles

Sorting strategies are investigated in view of improving the dynamic aperture of the CERN-LHC. Dynamical quantities, computed with perturbative tools of non-linear maps (normal forms), are used as quality factors. They provide a fast estimate of beam stability well-correlated with the results of element-by-element tracking simulations. The most effective quality factor is retained and maximised by an appropriate permutation of the position of the dipoles along the LHC azimuth. The search is made faster by magnet pairing based on local compensation of the random field-shape imperfections. The robustness of the proposed solution is finally checked through extensive tracking of realistic models of the LHC lattice

Normal form via tracking or beam data

Normal Form is a powerful tool to analyse the nonlinear content of a complicated system like an accelerator with its many thousands of high order multipolar errors. This technique needs as input a mapping from the initial to the final coordinates. Unfortunately, a map of an accelerator is not known beforehand but has to be determined for a complete lattice of the accelerator including all calculated and/or measured error tables of the guiding and focussing magnet elements. It is however possible to obtain turn-by-turn position data of a kicked beam for many turns. In various experiments at existing accelerators it has been shown that these data are equivalent to tracking data produced by simulation programs. In this report we will demonstrate how tracking data can be used to determine, with excellent precision, the coefficients of the generating function. The well tested Normal Form tools can then be used to construct the underlying Hamiltonian and the map. The essential tool is the recently developed frequency analysis which allows for a very precise determination of the tunes using beam or tracking data