633 research outputs found
Equivalence between Poly\'a-Szeg\H{o} and relative capacity inequalities under rearrangement
The transformations of functions acting on sublevel sets that satisfy a
P\'olya-Szeg\H{o} inequality are characterized as those being induced by
transformations of sets that do not increase the associated capacity.Comment: 9 page
Second-order -regularity in nonlinear elliptic problems
A second-order regularity theory is developed for solutions to a class of
quasilinear elliptic equations in divergence form, including the -Laplace
equation, with merely square-integrable right-hand side. Our results amount to
the existence and square integrability of the weak derivatives of the nonlinear
expression of the gradient under the divergence operator. This provides a
nonlinear counterpart of the classical -coercivity theory for linear
problems, which is missing in the existing literature. Both local and global
estimates are established. The latter apply to solutions to either Dirichlet or
Neumann boundary value problems. Minimal regularity on the boundary of the
domain is required. If the domain is convex, no regularity of its boundary is
needed at all
Characterization of self-injected electron beams from LWFA experiments at SPARC_LAB
The plasma-based acceleration is an encouraging technique to overcome the
limits of the accelerating gradient in the conventional RF acceleration. A
plasma accelerator is able to provide accelerating fields up to hundreds of
, paving the way to accelerate particles to several MeV over a short
distance (below the millimetre range). Here the characteristics of preliminary
electron beams obtained with the self-injection mechanism produced with the
FLAME high-power laser at the SPARC_LAB test facility are shown. In detail,
with an energy laser on focus of and a pulse temporal length (FWHM) of
, we obtained an electron plasma density due to laser ionization of
about , electron energy up to and beam
charge in the range .Comment: 6 pages, 11 figures, conference EAAC201
Conceptual design of electron beam diagnostics for high brightness plasma accelerator
A design study of the diagnostics of a high brightness linac, based on X-band
structures, and a plasma accelerator stage, has been delivered in the framework
of the EuPRAXIA@SPARC_LAB project. In this paper, we present a conceptual
design of the proposed diagnostics, using state of the art systems and new and
under development devices. Single shot measurements are preferable for plasma
accelerated beams, including emittance, while m level and fs scale beam
size and bunch length respectively are requested. The needed to separate the
driver pulse (both laser or beam) from the witness accelerated bunch imposes
additional constrains for the diagnostics. We plan to use betatron radiation
for the emittance measurement just at the end of the plasma booster, while
other single-shot methods must be proven before to be implemented. Longitudinal
measurements, being in any case not trivial for the fs level bunch length, seem
to have already a wider range of possibilities
Thermal issues for the optical transition radiation screen for the ELI-NP compton gamma source
A high brightness electron LINAC is being built in the Compton Gamma Source at the ELI Nuclear Physics facility in Romania. To achieve the design luminosity, a train of 32 bunches, 16 ns spaced, with a nominal charge of 250 pC will collide with a laser beam in two interaction points. Electron beam spot size is measured with Optical Transition Radiation (OTR) profile monitors. In order to measure the beam properties, the OTR screens must sustain the thermal and mechanical stress due to the energy deposited by bunches. This paper is an ANSYS study of the issues due to the high energy transferred to the OTR screens. Thermal multicycle analysis will be shown; each analysis will be followed by a structural analysis in order to investigate the performance of the materia
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