2,433 research outputs found
Two-surface wave decay: improved analytical theory and effects on electron acceleration
Two-surface wave decay (TSWD), i.e. the parametric excitation of electron
surface waves, was recently proposed as an absorption mechanism in the
interaction of ultrashort, intense laser pulses with solid targets. We present
an extension of the fluid theory of TSWD to a warm plasma which treats boundary
effects consistently. We also present test-particle simulations showing
localized enhancement of electron acceleration by TSWD fields; this effect
leads to a modulation of the current density entering into the target and may
seed current filamentation instabilities.Comment: 4 figures, submitted to Appl.Phys.B (special issue from HFSW X
conference, Biarritz, France, Oct 12-15 2003); slightly revised tex
Two-Surface Wave Decay
Using an analytical model we discuss the parametric excitation of pairs of
electron surface waves (ESW) in the interaction of an ultrashort, intense laser
pulse with an overdense plasma which has a step-like density profile. The ESWs
can be excited either by the electric or by the magnetic part of the Lorentz
force exerted by the laser and, correspondingly, have frequencies around
or , where is the laser frequency.Comment: 4 EPS figures, Revte
Laser ion acceleration using a solid target coupled with a low density layer
We investigate by particle-in-cell simulations in two and three dimensions
the laser-plasma interaction and the proton acceleration in multilayer targets
where a low density "near-critical" layer of a few micron thickness is added on
the illuminated side of a thin, high density layer. This target design can be
obtained by depositing a "foam" layer on a thin metallic foil. The presence of
the near-critical plasma strongly increases both the conversion efficiency and
the energy of electrons and leads to enhanced acceleration of proton from a
rear side layer via the Target Normal Sheath Acceleration mechanism. The
electrons of the foam are strongly accelerated in the forward direction and
propagate on the rear side of the target building up a high electric field with
a relatively flat longitudinal profile. In these conditions the maximum proton
energy is up to three times higher than in the case of the bare solid target.Comment: 9 pages, 11 figures. Submitted to Physical Review
Electric field dynamics and ion acceleration in the self-channeling of a superintense laser pulse
The dynamics of electric field generation and radial acceleration of ions by
a laser pulse of relativistic intensity propagating in an underdense plasma has
been investigated using an one-dimensional electrostatic, ponderomotive model
developed to interpret experimental measurements of electric fields [S. Kar et
al, New J. Phys. *9*, 402 (2007)]. Ions are spatially focused at the edge of
the charge-displacement channel, leading to hydrodynamical breaking, which in
turns causes the heating of electrons and an "echo" effect in the electric
field. The onset of complete electron depletion in the central region of the
channel leads to a smooth transition to a "Coulomb explosion" regime and a
saturation of ion acceleration.Comment: 9 pages, 7 figures, final revised version, to appear on Plasma Phys.
Contr. Fus., special issue on "Laser and Plasma Accelerators", scheduled for
February, 200
A value-driven method for the design of performance-based services for manufacturing equipment
Industrial services are increasingly becoming more relational and customer-oriented, due to manufacturers' adoption of servitisation approaches and product service system offerings. Challenges remain regarding the effective design and delivery of these new offerings, and the understanding of their actual value for both providers and customers. This work focuses on one specific type of product service systems in the context of manufacturing equipment: result-oriented or performance-based services, which aim at delivering an outcome rather than selling the equipment to the customer. A proposal of a value-driven method for their design that engages the customer in the process is presented. This new method has been applied to a real industrial life setting through an application case, involving the service provider and its customer, and targeting manufacturing equipment within customers' plant. Results indicate the effectiveness of this prescriptive approach. Reported benefits from participants refer to its flexibility, adaptability and applicability for different types of equipment, as well as its potential to help providing a modular service portfolio adequate to equipment specific context and requirements
Particle acceleration and radiation friction effects in the filamentation instability of pair plasmas
The evolution of the filamentation instability produced by two
counter-streaming pair plasmas is studied with particle-in-cell (PIC)
simulations in both one (1D) and two (2D) spatial dimensions. Radiation
friction effects on particles are taken into account. After an exponential
growth of both the magnetic field and the current density, a nonlinear
quasi-stationary phase sets up characterized by filaments of opposite currents.
During the nonlinear stage, a strong broadening of the particle energy spectrum
occurs accompanied by the formation of a peak at twice their initial energy. A
simple theory of the peak formation is presented. The presence of radiative
losses does not change the dynamics of the instability but affects the
structure of the particle spectra.Comment: 8 pages, 8 figures, submitted to MNRA
THERMODYNAMIC ORC CYCLE DESIGN OPTIMIZATION FOR MEDIUM-LOW TEMPERATURE ENERGY SOURCES
In the large spectrum of organic fluids suitable for Rankine cycles, a fluid that is already wellknown
and available on industrial scale but currently excluded from this kind of application
has been selected.
This choice is due to the remarkable characteristics of the fluid, such as its high molecular
weight, good thermal stability, non-flammability, and atoxicity.
Compared to those fluids nowadays common in the ORC market, its thermodynamic
properties and fluid dynamic behavior lead to a peculiar configuration of the cycle:
• Supercritical cycle, when heat input is at medium-high temperature;
• Massive regeneration, to obtain higher efficiency;
• Low specific work of the turbine;
• Relatively high volumetric expansion ratio and relatively low absolute inlet volumetric
flow;
Accordingly, an innovative cycle design has been developed, including a once-through
Hairpin primary heat exchanger and a multi-stage radial outflow expander.
This last innovative component has been designed to get the best performance with the chosen
fluid:
• The high inlet/outlet volumetric flow ratio is well combined with the change in cross
section across the radius;
• Compared to an axial turbine, the lower inlet volumetric flow is compensated by
higher blades at the first stage. It is feasible thanks to the change in section available
along the radius, so that there is no need for partial admission;
• The prismatic blade leads to constant velocity diagrams across the blade span;
• It minimizes tip leakages and disk friction losses, due to the single disk / multi-stage
configuration;
• The intrinsical limit of a radial outflow expander to develop high enthalpy drop is not
relevant for this cycle, presenting itself a very low enthalpy drop. Moreover the tip
speed is limited by the low speed of sound and consequently this kind of expander
suits well with this cycle arrangement.
The results of this study, conducted through thermodynamic simulations, CFD, stress analysis
and economic optimization show an ORC system that reaches high efficiencies, comparable
to those typical of existing system
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