690 research outputs found
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
Multimodal rehabilitation for faecal incontinence: experience of an Italian centre devoted to faecal disorder rehabilitation
Plasma boosted electron beams for driving Free Electron Lasers
In this paper, we report results of simulations, in the framework of both
EuPRAXIA \cite{Walk2017} and EuPRAXIA@SPARC\_LAB \cite{Ferr2017} projects,
aimed at delivering a high brightness electron bunch for driving a Free
Electron Laser (FEL) by employing a plasma post acceleration scheme. The
boosting plasma wave is driven by a tens of \SI{}{\tera\watt} class laser and
doubles the energy of an externally injected beam up to \GeV{1}. The injected
bunch is simulated starting from a photoinjector, matched to plasma, boosted
and finally matched to an undulator, where its ability to produce FEL radiation
is verified to yield O(\num{e11}) photons per shot at \nm{2.7}.Comment: 5 pages, 2 figure
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
Emittance measurements at the TTF photoinjector
The TTF Free Electron Laser requires high current electron bunches with small emittances. The beam is produced by an injector based on a laser driven rf gun. The design aims for a bunch charge of 1 nC, a bunch length in the mm range, and a normalized transverse emittance approaching1mm mrad. Emittance measurements in the photoinjector after preacceleration to 17MeV are presented and compared to simulations
Optical issues for the diagnostic stations 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 the laser beam in the interaction point. Electron beam spot size is measured with optical transition radiation (OTR) profile monitors. In order to measure the beam properties, the optical radiation detecting system must have the necessary accuracy and resolution. This paper deals with the studies of different optic configurations to achieve the magnification, resolution and accuracy in order to measure very small beam (below 30 ÎĽm) or to study the angular distribution of the OTR and therefore the energy of the beam. Several configurations of the optical detection line will be studied both with simulation tools (e.g. Zemax) and experimentally. The paper will deal also with the sensibility of optic system (in terms of depth of field, magnification and resolution) to systematic error
Quadrupole scan emittance measurements for the ELI-NP compton gamma source
The high brightness electron LINAC of the Compton
Gamma Source at the ELI Nuclear Physics facility in Roma-
nia is accelerating a train of 32 bunches with a nominal total
charge of
250 pC
and nominal spacing of
16 ns
. To achieve
the design gamma flux, all the bunches along the train must
have the designed Twiss parameters. Beam sizes are mea-
sured with optical transition radiation monitors, allowing a
quadrupole scan for Twiss parameters measurements. Since
focusing the whole bunch train on the screen may lead to
permanent screen damage, we investigate non-conventional
scans such as scans around a maximum of the beam size
or scans with a controlled minimum spot size. This paper
discusses the implementation issues of such a technique in
the actual machine layou
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