3,499 research outputs found
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
Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources
Laser-driven plasma accelerators can generate accelerating gradients three
orders of magnitude larger than radio-frequency accelerators and have achieved
beam energies above 1 GeV in centimetre long stages. However, the pulse
repetition rate and wall-plug efficiency of plasma accelerators is limited by
the driving laser to less than approximately 1 Hz and 0.1% respectively. Here
we investigate the prospects for exciting the plasma wave with trains of
low-energy laser pulses rather than a single high-energy pulse. Resonantly
exciting the wakefield in this way would enable the use of different
technologies, such as fibre or thin-disc lasers, which are able to operate at
multi-kilohertz pulse repetition rates and with wall-plug efficiencies two
orders of magnitude higher than current laser systems. We outline the
parameters of efficient, GeV-scale, 10-kHz plasma accelerators and show that
they could drive compact X-ray sources with average photon fluxes comparable to
those of third-generation light source but with significantly improved temporal
resolution. Likewise FEL operation could be driven with comparable peak power
but with significantly larger repetition rates than extant FELs
PLATO: A Program Library for the Analysis of 4D Nonlinear Transverse Motion
The PLATO (Perturbative Lattice Analysis and Tracking tOols) program, a program library for analyzing four-dimensional betatronic motion in circular particle accelerators is presented. The routines included in this library provide both the resonant and the nonresonant perturbative series that approximate nonlinear motion (normal forms); standard numerical tools such as the Lyapunov exponent, frequency analysis and evaluation of the dynamic aperture are also available. To ensure the highest flexibility, the code is fully compatible with standard tracking programs commonly used in the accelerator physics community
- …