4,118 research outputs found
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
A steerable UV laser system for the calibration of liquid argon time projection chambers
A number of liquid argon time projection chambers (LAr TPC's) are being build
or are proposed for neutrino experiments on long- and short baseline beams. For
these detectors a distortion in the drift field due to geometrical or physics
reasons can affect the reconstruction of the events. Depending on the TPC
geometry and electric drift field intensity this distortion could be of the
same magnitude as the drift field itself. Recently, we presented a method to
calibrate the drift field and correct for these possible distortions. While
straight cosmic ray muon tracks could be used for calibration, multiple coulomb
scattering and momentum uncertainties allow only a limited resolution. A UV
laser instead can create straight ionization tracks in liquid argon, and allows
one to map the drift field along different paths in the TPC inner volume. Here
we present a UV laser feed-through design with a steerable UV mirror immersed
in liquid argon that can point the laser beam at many locations through the
TPC. The straight ionization paths are sensitive to drift field distortions, a
fit of these distortion to the linear optical path allows to extract the drift
field, by using these laser tracks along the whole TPC volume one can obtain a
3D drift field map. The UV laser feed-through assembly is a prototype of the
system that will be used for the MicroBooNE experiment at the Fermi National
Accelerator Laboratory (FNAL)
Resposta de genĂłtipos de batata ao estresse de seca quanto ao inĂcio do perĂodo de tuberização e Ă produção de tubĂ©rculos.
O objetivo do presente trabalho foi avaliar a resposta de 12 genĂłtipos de batata submetidos ao estresse de seca quanto ao inicio do perĂodo de tuberização e a produção de massa fresca de tubĂ©rculos.ENPOS
Relativistic nucleon optical potentials with isospin dependence in Dirac Brueckner Hartree-Fock approach
The relativistic optical model potential (OMP) for nucleon-nucleus scattering
is investigated in the framework of Dirac-Brueckner-Hartree-Fock (DBHF)
approach using the Bonn-B One-Boson- Exchange potential for the bare
nucleon-nucleon interaction. Both real and imaginary parts of isospin-dependent
nucleon self-energies in nuclear medium are derived from the DBHF approach
based on the projection techniques within the subtracted T -matrix
representation. The Dirac potentials as well as the corresponding Schrodinger
equivalent potentials are evaluated. An improved local density approximation is
employed in this analysis, where a range parameter is included to account for a
finite-range correction of the nucleon-nucleon interaction. As an example the
total cross sections, differential elastic scattering cross sections, analyzing
powers for n, p + 27Al at incident energy 100 keV < E < 250 MeV are calculated.
The results derived from this microscopic approach of the OMP are compared to
the experimental data, as well as the results obtained with a phenomenological
OMP. A good agreement between the theoretical results and the measurements can
be achieved for all incident energies using a constant value for the range
parameter.Comment: 10 pages, 16 figure
On the Electric Breakdown in Liquid Argon at Centimeter Scale
We present a study on the dependence of electric breakdown discharge
properties on electrode geometry and the breakdown field in liquid argon near
its boiling point. The measurements were performed with a spherical cathode and
a planar anode at distances ranging from 0.1 mm to 10.0 mm. A detailed study of
the time evolution of the breakdown volt-ampere characteristics was performed
for the first time. It revealed a slow streamer development phase in the
discharge. The results of a spectroscopic study of the visible light emission
of the breakdowns complement the measurements. The light emission from the
initial phase of the discharge is attributed to electro-luminescence of liquid
argon following a current of drifting electrons. These results contribute to
set benchmarks for breakdown-safe design of ionization detectors, such as
Liquid Argon Time Projection Chambers (LAr TPC).Comment: Minor revision according to editor report. 17 pages, 15 figures, 2
tables. Turboencabulato
Silent Springs: Why Are All the Frogs “Croaking”?
Amphibians are a fabulously successful group of animals; however, it is increasingly clear that they are experiencing extinction rates that far exceed those experienced by other classes of vertebrates. A new book examines the various reasons why amphibians are so threatened, and what can be done about it
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