709 research outputs found
NIEL Dose Dependence for Solar Cells Irradiated with Electrons and Protons
The investigation of solar cells degradation and the prediction of its
end-of-life performance is of primary importance in the preparation of a space
mission. In the present work, we investigate the reduction of solar-cells'
maximum power resulting from irradiations with electrons and protons. Both GaAs
single junction and GaInP/GaAs/Ge triple junction solar cells were studied. The
results obtained indicate how i) the dominant radiation damaging mechanism is
due to atomic displacements, ii) the relative maximum power degradation is
almost independent of the type of incoming particle, i.e., iii) to a first
approximation, the fitted semi-empirical function expressing the decrease of
maximum power depends only on the absorbed NIEL dose, and iv) the actual
displacement threshold energy value (Ed=21 eV) accounts for annealing
treatments, mostly due to self-annealing induced effects. Thus, for a given
type of solar cell, a unique maximum power degradation curve can be determined
as a function of the absorbed NIEL dose. The latter expression allows one to
predict the performance of those solar cells in space radiation environment.Comment: To appear on the Proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics
Applications, Villa Olmo (Como, Italy), 23--27 October, 2013, to be published
by World Scientific (Singapore
Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction
We implemented a quasi time-dependent 2D stochastic model of solar modulation
describing the transport of cosmic rays (CR) in the heliosphere. Our code can
modulate the Local Interstellar Spectrum (LIS) of a generic charged particle
(light cosmic ions and electrons), calculating the spectrum at 1AU. Several
measurements of CR antiparticles have been performed. Here we focused our
attention on the CR antiproton component and the antiproton over proton ratio.
We show that our model, using the same heliospheric parameters for both
particles, fit the observed anti-p/p ratio. We show a good agreement with
BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment
Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary-Magnetic-Field Polar Correction
The cosmic rays differential intensity inside the heliosphere, for energy
below 30 GeV/nuc, depends on solar activity and interplanetary magnetic field
polarity. This variation, termed solar modulation, is described using a 2-D
(radius and colatitude) Monte Carlo approach for solving the Parker transport
equation that includes diffusion, convection, magnetic drift and adiabatic
energy loss. Since the whole transport is strongly related to the
interplanetary magnetic field (IMF) structure, a better understanding of his
description is needed in order to reproduce the cosmic rays intensity at the
Earth, as well as outside the ecliptic plane. In this work an interplanetary
magnetic field model including the standard description on ecliptic region and
a polar correction is presented. This treatment of the IMF, implemented in the
HelMod Monte Carlo code (version 2.0), was used to determine the effects on the
differential intensity of Proton at 1\,AU and allowed one to investigate how
latitudinal gradients of proton intensities, observed in the inner heliosphere
with the Ulysses spacecraft during 1995, can be affected by the modification of
the IMF in the polar regions.Comment: accepted for publication inAdvances in Astronom
Suprathermal particle addition to solar wind pressure: possible influence on magnetospheric transmissivity of low energy cosmic rays?
Energetic (suprathermal) solar particles, accelerated in the interplanetary
medium, contribute to the solar wind pressure, in particular during high solar
activity periods. We estimated the effect of the increase of solar wind
pressure due to suprathermal particles on magnetospheric transmissivity of
galactic cosmic rays in the case of one recent solar event
HelMod in the works: from direct observations to the local interstellar spectrum of cosmic-ray electrons
The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons for the
energy range 1 MeV to 1 TeV is derived using the most recent experimental
results combined with the state-of-the-art models for CR propagation in the
Galaxy and in the heliosphere. Two propagation packages, GALPROP and HelMod,
are combined to provide a single framework that is run to reproduce direct
measurements of CR species at different modulation levels, and at both
polarities of the solar magnetic field. An iterative maximum-likelihood method
is developed that uses GALPROP-predicted LIS as input to HelMod, which provides
the modulated spectra for specific time periods of the selected experiments for
model-data comparison. The optimized HelMod parameters are then used to adjust
GALPROP parameters to predict a refined LIS with the procedure repeated subject
to a convergence criterion. The parameter optimization uses an extensive data
set of proton spectra from 1997-2015. The proposed CR electron LIS accommodates
both the low-energy interstellar spectra measured by Voyager 1 as well as the
high-energy observations by PAMELA and AMS-02 that are made deep in the
heliosphere; it also accounts for Ulysses counting rate features measured out
of the ecliptic plane. The interstellar and heliospheric propagation parameters
derived in this study agree well with our earlier results for CR protons,
helium nuclei, and anti-protons propagation and LIS obtained in the same
framework.Comment: 11 pages, 14 figures, 4 tables; ApJ, in pres
Deciphering the local Interstellar spectra of primary cosmic ray species with HelMod
Local interstellar spectra (LIS) of primary cosmic ray (CR) nuclei, such as
helium, oxygen, and mostly primary carbon are derived for the rigidity range
from 10 MV to ~200 TV using the most recent experimental results combined with
the state-of-the-art models for CR propagation in the Galaxy and in the
heliosphere. Two propagation packages, GALPROP and HelMod, are combined into a
single framework that is used to reproduce direct measurements of CR species at
different modulation levels, and at both polarities of the solar magnetic
field. The developed iterative maximum-likelihood method uses GALPROP-predicted
LIS as input to HelMod, which provides the modulated spectra for specific time
periods of the selected experiments for model-data comparison. The interstellar
and heliospheric propagation parameters derived in this study are consistent
with our prior analyses using the same methodology for propagation of CR
protons, helium, antiprotons, and electrons. The resulting LIS accommodate a
variety of measurements made in the local interstellar space (Voyager 1) and
deep inside the heliosphere at low (ACE/CRIS, HEAO-3) and high energies
(PAMELA, AMS-02).Comment: 13 pages, 13 figures, 6 tables, ApJ in press. arXiv admin note: text
overlap with arXiv:1704.0633
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